Physics of Plasmas Current Issue
https://pubs.aip.org/pop
en-usFri, 29 Sep 2023 00:00:00 GMTFri, 29 Sep 2023 22:46:09 GMTSilverchaireditor@pubs.aip.org/popwebmaster@pubs.aip.org/popA three-band frequency hopping high power microwave oscillator based on magnetic field tuning
https://pubs.aip.org/aip/pop/article/30/9/093108/2913883/A-three-band-frequency-hopping-high-power
Fri, 29 Sep 2023 00:00:00 GMT<span class="paragraphSection">The frequency hopping technology is one of the most significant research directions for high-power microwave (HPM) devices. This paper presented a novel HPM oscillator with frequency hopping across C, X, and Ku bands based on magnetic field tuning. A coaxial transit time oscillator (TTO) is nested onto the outer conductor of the hollow relativistic Cherenkov microwave oscillator, which forms a dual electromagnetic structure with a single-annular cathode. When the electron beam is guided by gradient magnetic fields, it interacts with TTO to produce Ku-band HPMs. If the gradient magnetic field changes into the uniform magnetic field, the electron beam would enter the relativistic Cherenkov microwave oscillator, and the frequency of generated microwaves decreases, which are decided by the strength of the magnetic fields according to the cyclotron resonance absorption theory. In the particle-in-cell simulation, when the diode voltage and gradient magnetic field are 580 kV and 0.5 T, respectively, a Ku-band HPM output with a frequency of 13.9 GHz and a power of 2.09 GW is obtained, corresponding to power efficiency of 42%. When the magnetic field transforms into uniform, the device produces an X-band HPM output with a frequency of 9 GHz and a power of 2.4 GW at a diode voltage of 683 kV and a magnetic field of 0.7 T. When the voltage and magnetic field strength are increased to 699 kV and 1.5 T, respectively, the device generates a C-band HPM output with a frequency of 4.5 GHz and a power of 2.1 GW. The corresponding conversion efficiency of the X-band and C-band Cherenkov microwave oscillators is 35% and 30.7%, respectively.</span>30909310810.1063/5.0163592https://pubs.aip.org/aip/pop/article/30/9/093108/2913883/A-three-band-frequency-hopping-high-powerEnergy transfer and scale dynamics in 2D and 3D laser-driven jets
https://pubs.aip.org/aip/pop/article/30/9/092309/2913879/Energy-transfer-and-scale-dynamics-in-2D-and-3D
Fri, 29 Sep 2023 00:00:00 GMT<span class="paragraphSection">We demonstrate a methodology for diagnosing the multiscale dynamics and energy transfer in complex HED flows with realistic driving and boundary conditions. The approach separates incompressible, compressible, and baropycnal contributions to energy scale-transfer and quantifies the direction of these transfers in (generalized) wavenumber space. We use this to compare the kinetic energy (KE) transfer across scales in simulations of 2D axisymmetric vs fully 3D laser-driven plasma jets. Using the FLASH code, we model a turbulent jet ablated from an aluminum cone target in the configuration outlined by Liao <span style="font-style:italic;">et al.</span> [Phys. Plasmas, <strong>26</strong> 032306 (2019)]. We show that, in addition to its well known bias for underestimating hydrodynamic instability growth, 2D modeling suffers from significant spurious energization of the bulk flow by a turbulent upscale cascade. In 2D, this arises as vorticity and strain from instabilities near the jet's leading edge transfer KE upscale, sustaining a coherent circulation that helps propel the axisymmetric jet farther ( ≈ 25 % by 3.5 ns) and helps keep it collimated. In 3D, the coherent circulation and upscale KE transfer are absent. The methodology presented here may also help with inter-model comparison and validation, including future modeling efforts to alleviate some of the 2D hydrodynamic artifacts highlighted in this study.</span>30909230910.1063/5.0161028https://pubs.aip.org/aip/pop/article/30/9/092309/2913879/Energy-transfer-and-scale-dynamics-in-2D-and-3DThe academic research ecosystem required to support the development of fusion energy
https://pubs.aip.org/aip/pop/article/30/9/090604/2913878/The-academic-research-ecosystem-required-to
Fri, 29 Sep 2023 00:00:00 GMT<span class="paragraphSection">The advent of a fusion energy industry is being strongly supported by academics and universities, with the majority of fusion companies launching out of universities. Universities also play critical roles in technical innovation, workforce development, and independent arbiters of science and technology. The ability of the US academic landscape to support and grow the fusion energy sector is analyzed via a numerical distribution of full time faculty engaged in fusion and plasma. This data is compared to university support in two existing technology-driven industries: nuclear and aeronautics. This comparison clearly shows that the university system requires not only significant absolute growth but also a wider distribution of faculty at universities and across the required disciplines.</span>30909060410.1063/5.0167369https://pubs.aip.org/aip/pop/article/30/9/090604/2913878/The-academic-research-ecosystem-required-toGeneration of the high power by a coaxial dielectric barrier discharge with a perforated electrode in atmospheric pressure air
https://pubs.aip.org/aip/pop/article/30/9/093508/2913876/Generation-of-the-high-power-by-a-coaxial
Fri, 29 Sep 2023 00:00:00 GMT<span class="paragraphSection">The power is believed to play an important role in the treatment effects in both direct and indirect plasma applications. Generation of the high power has been realized by using a perforated inner electrode for a coaxial dielectric barrier discharge (DBD) in atmospheric pressure air. Compared with a non-perforated inner electrode, the perforated electrode has a 10%–20% and 10%–30% increase in the applied power and the discharge power, respectively. The strengthened local electric field of the perforated electrode in the coaxial DBD provides favorable conditions for the generation of the micro-discharge, thus increasing the power. To shed light on the reasons for the increase in the power, an extensive analysis of the optical and electrical characteristics of the DBD with the perforated electrode and the non-perforated one was carried out, including transferred charge, total current, number of discharge pulses, dielectric capacitance, gap capacitance, vibrational and rotational temperatures, and electron temperature trend.</span>30909350810.1063/5.0160137https://pubs.aip.org/aip/pop/article/30/9/093508/2913876/Generation-of-the-high-power-by-a-coaxialNew exact plasma equilibria with axial and helical symmetry
https://pubs.aip.org/aip/pop/article/30/9/092308/2913658/New-exact-plasma-equilibria-with-axial-and-helical
Thu, 28 Sep 2023 00:00:00 GMT<span class="paragraphSection">We derive new exact closed-form solutions of magnetohydrodynamics equations, with and without dynamics, which model astrophysical jets and other prolonged plasma configurations. The solutions are obtained in static and dynamic incompressible equilibrium settings, in axial and helical symmetry assumptions, and are given in terms of Whittaker, Coulomb, and Heun special functions. For each symmetry, two distinct families of physical solutions arise, corresponding to two distinct pressure profiles. One pressure profile models plasmas supported by an external pressure and is suitable for the description of plasma configurations in a medium, such as atmosphere. The second profile features higher pressure inside the plasma domain and can model plasmas residing in a vacuum. Examples of static and dynamic solutions in axially and helically symmetric settings, including solutions with boundary current sheets, are presented and discussed.</span>30909230810.1063/5.0165963https://pubs.aip.org/aip/pop/article/30/9/092308/2913658/New-exact-plasma-equilibria-with-axial-and-helicalFirst large capsule implosions in a frustum-shaped hohlraum
https://pubs.aip.org/aip/pop/article/30/9/092708/2913649/First-large-capsule-implosions-in-a-frustum-shaped
Thu, 28 Sep 2023 00:00:00 GMT<span class="paragraphSection">We report on the first indirect-drive implosions driven by a dual conical frustum-shaped <span style="font-style:italic;">hohlraum</span> denoted “frustraum” and the experimental tuning campaigns leading up to two layered implosions. The campaign used 1.2 and 1.4 mm inner radius high density carbon (HDC) capsules and represented the largest HDC capsules to be imploded on the National Ignition Facility via indirect drive. Several techniques were successfully implemented to control the Legendre mode 2 capsule symmetry of the implosions, including changing the wall angle of the frustraum, which is not possible with cylindrical <span style="font-style:italic;">hohlraums</span>. A mode 4 feature was observed and its implications for hotspot mix discussed. Two layered implosions were conducted with 1.2 mm inner radius capsules, the latter of which achieved the highest layered capsule absorbed energy on the National Ignition Facility using only 1.74 MJ of laser energy. The layered implosion results, along with generalized Lawson parameters, suggest that increasing the energy absorbed by the capsule at the expense of long coast times makes it more challenging to achieve ignition and that further reducing coast time (time between end of laser pulse and bang time) closer to the 1 ns level is warranted to improve the areal density and make it easier to achieve the hotspot temperature, alpha heating, and yield amplification required for ignition.</span>30909270810.1063/5.0163396https://pubs.aip.org/aip/pop/article/30/9/092708/2913649/First-large-capsule-implosions-in-a-frustum-shapedEnhancement of NO x production in water by combining an air bubble plasma jet and an external magnetic field
https://pubs.aip.org/aip/pop/article/30/9/093507/2913648/Enhancement-of-NOx-production-in-water-by
Thu, 28 Sep 2023 00:00:00 GMT<span class="paragraphSection">Production of N O x ( NO 2 − + NO 3 −) in water with an air bubble discharge plasma jet under the influence of an external axial steady magnetic field was investigated experimentally. The gas phase plasma parameters, rotational ( T r), vibrational ( T v) and electronic excitation ( T x) temperatures, and electron density ( n e), as well as the liquid phase pH and the concentrations of nitrite ( NO 2 −) and nitrate ( NO 3 −), were measured as a function of treatment time and magnetic field strength. It was found that T r, T v, T x, and n e slightly increased as a function of magnetic field strength in the gas phase plasma. The pH decreased both with treatment time and magnetic field strength. In the maximum field strength of 290 mT, the concentrations of NO 2 − and NO 3 − were ∼ 82 % and ∼ 74 %, respectively, greater than with B = 0. With B = 290 mT, the energy cost for producing N O x was ∼ 78 % lower than with B = 0. The energy cost may likely be reduced due to decreasing radial diffusion loss of charged species in the discharge with increasing magnetic field strength.</span>30909350710.1063/5.0161173https://pubs.aip.org/aip/pop/article/30/9/093507/2913648/Enhancement-of-NOx-production-in-water-bySuppression of high order mode oscillation in a C-band long pulse high efficiency relativistic backward wave oscillator
https://pubs.aip.org/aip/pop/article/30/9/093303/2913110/Suppression-of-high-order-mode-oscillation-in-a-C
Wed, 27 Sep 2023 00:00:00 GMT<span class="paragraphSection">In order to realize mode control and long pulse operation of the proposed C-band high efficiency relativistic backward wave oscillator, the asymmetric high order mode oscillation and its influences on the working mode operation are investigated in the 3D particle-in-cell simulation. The simulation shows that the quasi-TM<sub>21</sub> mode is the dominant competing mode, which is mainly located in the two-period extraction cavity of the device. Accordingly, a simplified model of a two-period extraction cavity is established to investigate the mechanism of the high order mode excitation. It is indicated that the distance between two gaps of the two-period extraction cavity has great impact on the startup time of the competing mode. By optimizing the gap distance to delay the startup of the competing mode, as well as shortening the rising time of the input pulsed power pulse, the competing quasi-TM<sub>21</sub> mode can be suppressed sufficiently.</span>30909330310.1063/5.0159268https://pubs.aip.org/aip/pop/article/30/9/093303/2913110/Suppression-of-high-order-mode-oscillation-in-a-CThe role of electron current in high- β plasma equilibria
https://pubs.aip.org/aip/pop/article/30/9/092513/2913109/The-role-of-electron-current-in-high-plasma
Wed, 27 Sep 2023 00:00:00 GMT<span class="paragraphSection">This paper is aimed at investigating the role of electrons in creation of currents in plasma equilibria with high plasma pressure ( β ≈ 1). Despite the long history of studies of these equilibria, there is still no consensus on what kind of particle species is responsible for the creation of the diamagnetic current and what characteristic size the current layer should have. For example, simulations of isothermal plasma injection into a multi-cusp magnetic trap [J. Park <span style="font-style:italic;">et al.</span>, Front. Astron. Space Sci. <strong>6</strong>, 74 (2019)] demonstrate the formation of a transition layer with a thickness comparable to the electron Larmor radius, where the equilibrium current is carried by electrons. At the same time, studies of a diamagnetic bubble created by a hot-ion plasma in a mirror trap [I. Kotelnikov, Plasma Phys. Control Fusion <strong>62</strong>, 075002 (2020)] assume ion dominance and completely ignore electron currents. In this paper, we show that the equilibrium initially governed by the ion diamagnetic current is unstable against perturbations at the ion-cyclotron frequency harmonics, and this instability forces the plasma to come to a new equilibrium state in which the current is mainly created by the E × B-drift of electrons. The same type of equilibrium is also found to form in a more realistic problem setup when plasma is continuously injected into the uniform vacuum magnetic field.</span>30909251310.1063/5.0153855https://pubs.aip.org/aip/pop/article/30/9/092513/2913109/The-role-of-electron-current-in-high-plasmaRadiation-dominated injection of positrons generated by the nonlinear Breit–Wheeler process into a plasma channel
https://pubs.aip.org/aip/pop/article/30/9/093107/2913099/Radiation-dominated-injection-of-positrons
Wed, 27 Sep 2023 00:00:00 GMT<span class="paragraphSection">Plasma acceleration is considered a prospective technology for building a compact multi-TeV electron–positron collider in the future. The challenge of this endeavor is greater for positrons than for the electrons because usually the self-generated fields from laser–plasma interaction are not well-suited for positron focusing and on-axis guiding. In addition, an external positron source is required, while electrons are naturally available in the plasma. Here, we study electron–positron pair generation by an orthogonal collision of a multi-PW laser pulse and a GeV electron beam by the nonlinear Breit–Wheeler process. We studied conditions favorable for positron deflection in the direction of the laser pulse propagation, which favors injection into the plasma for further acceleration. We demonstrate using the OSIRIS particle-in-cell framework that the radiation reaction triggered by ultra-high laser intensity plays a crucial role in the positron injection. It provides a suppression of the initial transverse momentum gained by the positrons from the Breit-Wheeler process. For the parameters used in this work, the intensity of at least 2.2 × 10 23 W / cm 2 is needed in order to inject more than 1% of positrons created. Above this threshold, the percentage of injected positrons rapidly increases with intensity. Moreover, subsequent direct laser acceleration of positrons in a plasma channel, using the same laser pulse that created them, can ensure a boost of the final positron energy by a factor of two. The positron focusing and guiding on the axis is provided by significant electron beam loading that changes the internal structure of the channel fields.</span>30909310710.1063/5.0160121https://pubs.aip.org/aip/pop/article/30/9/093107/2913099/Radiation-dominated-injection-of-positronsHamiltonian description for magnetic field lines in fusion plasmas: A tutorial
https://pubs.aip.org/aip/pop/article/30/9/090901/2913098/Hamiltonian-description-for-magnetic-field-lines
Wed, 27 Sep 2023 00:00:00 GMT<span class="paragraphSection">Under certain circumstances, the equations for the magnetic field lines can be recast in a canonical form after defining a suitable field line Hamiltonian. This analogy is extremely useful for dealing with a variety of problems involving magnetically confined plasmas, like in tokamaks and other toroidal devices, where there is usually one symmetric coordinate that plays the role of time in the canonical equations. In this tutorial paper, we review the basics of the Hamiltonian description for magnetic field lines, emphasizing the role of a variational principle and gauge invariance. We present representative applications of the formalism using cylindrical and magnetic flux coordinates in tokamak plasmas.</span>30909090110.1063/5.0170345https://pubs.aip.org/aip/pop/article/30/9/090901/2913098/Hamiltonian-description-for-magnetic-field-linesThe ion acoustic instability during collisionless two-ion-species plasma expansion
https://pubs.aip.org/aip/pop/article/30/9/092113/2912712/The-ion-acoustic-instability-during-collisionless
Tue, 26 Sep 2023 00:00:00 GMT<span class="paragraphSection">A hypothesis of the electrostatic field for the expansion of a plasma composed of two ion species into a vacuum is proposed. The solution for expansion is derived analytically and verified by numerical simulations. The expansion region is predicted to exhibit a constant velocity difference between the two ion components, which could result in ion beam instability and, thus, an increase in ion temperature. The instability, which occurs in CH plasma, is also verified theoretically and examined by particle-in-cell simulations.</span>30909211310.1063/5.0155674https://pubs.aip.org/aip/pop/article/30/9/092113/2912712/The-ion-acoustic-instability-during-collisionlessPower flow in magnetically insulated transmission lines with ion backscatter effects
https://pubs.aip.org/aip/pop/article/30/9/093506/2912711/Power-flow-in-magnetically-insulated-transmission
Tue, 26 Sep 2023 00:00:00 GMT<span class="paragraphSection">Ion backscattering off of surfaces in magnetically insulated transmission lines (MITLs) is often ignored in kinetic simulations of MITL power flow. Backscattering reduces ion current losses and the surface impact heating, which dictates the rate at which surface-adsorbed contaminants are liberated into the anode–cathode gap. Backscatter probabilities are difficult to implement in a kinetic code because there are limited data for incident ion energies less than a few keV. This paper presents an analytic model based on the Rutherford scattering formula that reproduces the measured backscatter probabilities at high incident energies and transitions to the highly reflective behavior expected at low incident energies. The backscatter model is implemented in power flow simulations, which are validated with current loss experiments conducted on the 0.4 TW Mykonos accelerator at Sandia National Laboratories. This simulation setup is then used in a high-current Z-machine shot. Backscatter effects are found to be unimportant in the low-current Mykonos regime but significantly reduce current losses at the Z-machine scale.</span>30909350610.1063/5.0159544https://pubs.aip.org/aip/pop/article/30/9/093506/2912711/Power-flow-in-magnetically-insulated-transmissionCollisional-radiative modeling and radiative emission of tungsten in tokamak plasmas in the temperature range (800–5000) eV
https://pubs.aip.org/aip/pop/article/30/9/093302/2912710/Collisional-radiative-modeling-and-radiative
Tue, 26 Sep 2023 00:00:00 GMT<span class="paragraphSection">We present new collisional-modeling calculations of tungsten plasmas at electron density of about 5 × 10<sup>13</sup> cm<sup>−3</sup> and for electron temperatures in the range 0.8–5 keV. These conditions are relevant to current tokamaks. In this temperature range, the modeling of the ionization balance and of spectra is a long-standing problem. Addressing this problem is also useful for plasmas that will be produced in the future tokamak ITER. In particular, we discuss the problem of ensuring completeness of the list of configurations included in the calculations. We also discuss comparisons of experimental measurements in the EUV range performed in the WEST tokamak with synthetized spectra based on the use of the unresolved transition array and of the spin–orbit split array formalisms. While this work does not rely on a precise identification of detailed lines, modeled spectra display emission features that looks quite similar to the experimental spectra. A conclusion is that standard calculation methods used for the evaluation of the configuration average collisional and radiative rates, are fine provided that a convenient list of configurations is used in the calculations.</span>30909330210.1063/5.0160913https://pubs.aip.org/aip/pop/article/30/9/093302/2912710/Collisional-radiative-modeling-and-radiativeOptimization of target compression for high-gain fast ignition via machine learning
https://pubs.aip.org/aip/pop/article/30/9/092707/2912709/Optimization-of-target-compression-for-high-gain
Tue, 26 Sep 2023 00:00:00 GMT<span class="paragraphSection">The hydrodynamic scaling relations are of great importance for the design and optimization of target compression in laser-driven fusion. In this paper, we propose an artificially intelligent method to construct the scaling relations of the implosion velocity and areal density for direct-drive fast ignition by combining one-dimensional hydrodynamic simulations and machine learning methods. It is found that a large fuel mass and a high areal density required for high-gain fusion can be obtained simultaneously by optimizing the implosion velocity with less compression laser energy, taking full advantage of the separation of the compression and ignition processes in the fast ignition scheme. The obtained scaling relations are applied to the implosion design for the double-cone ignition scheme [Zhang <span style="font-style:italic;">et al.</span>, “Double-cone ignition scheme for inertial confinement fusion,” Philos. Trans. R. Soc., A <strong>378</strong>(2184), 20200015 (2020)]. An optimized implosion is proposed with an areal density of 1.30 g/cm<sup>2</sup> and a fuel mass of 215.7 <span style="font-style:italic;">μ</span>g with a compression laser energy of 168 kJ. Two-dimensional hydrodynamic simulations are further employed to validate the results. Our methods and results may be useful for the optimization of fusion experiments toward high-gain fusion.</span>30909270710.1063/5.0159764https://pubs.aip.org/aip/pop/article/30/9/092707/2912709/Optimization-of-target-compression-for-high-gainNearly integrable flows and chaotic tangles in the Dimits shift regime of plasma edge turbulence
https://pubs.aip.org/aip/pop/article/30/9/092307/2912708/Nearly-integrable-flows-and-chaotic-tangles-in-the
Tue, 26 Sep 2023 00:00:00 GMT<span class="paragraphSection">Transitionally turbulent flows frequently exhibit spatiotemporal intermittency, reflecting a complex interplay between driving forces, dissipation, and transport present in these systems. When this intermittency manifests as observable structures and patterns in the flow, the characterization of turbulence in these systems becomes challenging due to the nontrivial correlations introduced into the statistics of the turbulence by these structures. In this work, we use tools from dynamical systems theory to study intermittency in the Dimits shift regime of the flux-balanced Hasegawa–Wakatani (BHW) equations, which models a transitional regime of resistive drift-wave turbulence relevant to magnetically confined fusion plasmas. First, we show in direct numerical simulations that turbulence in this regime is dominated by strong zonal flows and coherent drift-wave vortex structures, which maintain a strong linear character despite their large amplitude. Using the framework of generalized Liouville integrability, we develop a theory of integrable Lagrangian flows in generic fluid and plasma systems and discuss how the observed zonal flows plus drift waves in the BHW system exhibit a form of “near-integrability” originating from a fluid element relabeling symmetry. We further demonstrate that the BHW flows transition from integrability to chaos via the formation of chaotic tangles in the aperiodic Lagrangian flow, and establish a direct link between the “lobes” associated with these tangles and intermittency in the observed turbulent dissipation. This illustrates how utilizing tools from deterministic dynamical systems theory to study convective nonlinearities can explain aspects of the intermittent spatiotemporal structure exhibited by the statistics of turbulent fields.</span>30909230710.1063/5.0158013https://pubs.aip.org/aip/pop/article/30/9/092307/2912708/Nearly-integrable-flows-and-chaotic-tangles-in-theDevelopment and numerical investigation of Mach probe model in a hypersonic, low-temperature flowing plasma
https://pubs.aip.org/aip/pop/article/30/9/093904/2912707/Development-and-numerical-investigation-of-Mach
Tue, 26 Sep 2023 00:00:00 GMT<span class="paragraphSection">This study conducted a numerical simulation around a Mach probe under hypersonic low-temperature plasma. The Mach probe has three ion collection planes: front, side, and back. Under a hypersonic flowing plasma, the front and side planes are practical ion collection areas, and the backplane collects no ion flux. The collected ion current density on the front plane is almost identical to that of the mainstream ion flux. By contrast, the ion current collected on the side plane is affected by the concentration of the electric field at the probe edge. As this edge effect has a different influence on the front and side planes, the ion current density ratio of the side to the front planes is dominated by a non-dimensional parameter—the ratio of electrostatic to kinetic flow energy. Based on this non-dimensional parameter, the calculated ion current density ratio can be fitted using a simple mathematical formula. Therefore, the proposed Mach probe model with non-dimensional parameters extends the conventional Mach probe model validated in sub-to-supersonic high-temperature plasma to hypersonic low-temperature flowing plasma, which is commonly observed in electric propulsions.</span>30909390410.1063/5.0160945https://pubs.aip.org/aip/pop/article/30/9/093904/2912707/Development-and-numerical-investigation-of-MachEffects of magnetic field configurations on the minimized ECR ion thrusters for micro-Newton and wide-range operations
https://pubs.aip.org/aip/pop/article/30/9/090702/2912706/Effects-of-magnetic-field-configurations-on-the
Tue, 26 Sep 2023 00:00:00 GMT<span class="paragraphSection">Space-based gravitational wave detection missions require precise thrusts over a wide-range of 1–100 <span style="font-style:italic;">μ</span>N. In this study, the axial ring-cusp magnetic field configuration is used to design a miniature electron cyclotron resonance ion thruster with a radius of 5 mm. Two typical configurations, i.e., open-type and closed-type, are compared in terms of electron density, electron temperature, and thrust for micro-Newton and wide-range operations. The results show that the open-type achieves high performances owing to the high efficiency of absorption of input microwave power. The lower limit of the mass flow rate in the electron cyclotron resonance (ECR) discharge is expanded to a very low value of 3 × 10<sup>−2</sup> sccm to achieve 1 <span style="font-style:italic;">μ</span>N in the open-type. The thrust in the open-type could be tuned in a wide-range of 1–119 <span style="font-style:italic;">μ</span>N, meeting the requirement.</span>30909070210.1063/5.0159442https://pubs.aip.org/aip/pop/article/30/9/090702/2912706/Effects-of-magnetic-field-configurations-on-thePlasma modes in QED super-strong magnetic fields of magnetars and laser plasmas
https://pubs.aip.org/aip/pop/article/30/9/092112/2912702/Plasma-modes-in-QED-super-strong-magnetic-fields
Tue, 26 Sep 2023 00:00:00 GMT<span class="paragraphSection">Ultra-magnetized plasmas, where the magnetic field strength exceeds the Schwinger field of about B Q ≈ 4 × 10 13 G, become of great scientific interest, thanks to the current advances in laser-plasma experiments and astrophysical observations of magnetar emission. These advances demand better understanding of how quantum electrodynamics (QED) effects influence collective plasma phenomena. In particular, Maxwell's equations become nonlinear in the strong-QED regime. Here we present the “QED plasma framework,” which will allow one to systematically explore collective phenomena in a QED-plasma with arbitrary strong magnetic field. Further, we illustrate the framework by exploring low-frequency modes in the ultra-magnetized, cold, electron-positron plasmas. We demonstrate that the classical picture of five branches holds in the QED regime; no new eigenmodes appear. The dispersion curves of all the modes are modified. The QED effects include the overall modification to the plasma frequency, which becomes field-dependent. They also modify resonances and cutoffs of the modes, which become both field- and angle-dependent. The strongest effects are (i) the field-induced transparency of plasma for the O-mode via the dramatic reduction of the low-frequency cutoff well below the plasma frequency, (ii) the Alfvén mode suppression in the large-<span style="font-style:italic;">k</span> regime via the reduction of the Alfvén mode resonance, and (iii) the O-mode slowdown via strong angle-dependent increase in the index of refraction. These results should be important for understanding of a magnetospheric pair plasma of a magnetar and for laboratory laser-plasma experiments in the QED regime.</span>30909211210.1063/5.0160628https://pubs.aip.org/aip/pop/article/30/9/092112/2912702/Plasma-modes-in-QED-super-strong-magnetic-fieldsDesigning a large area field emitter for uniform electron emission
https://pubs.aip.org/aip/pop/article/30/9/093106/2912589/Designing-a-large-area-field-emitter-for-uniform
Mon, 25 Sep 2023 00:00:00 GMT<span class="paragraphSection">Obtaining uniform emission from a large area field emitter (LAFE) is a challenge that has proved difficult to overcome, both theoretically and experimentally. We use an approximate analytical formula for the apex field enhancement factor (AFEF) of individual emitters to design a LAFE with uniform electron emission, either by optimizing the location of identical emitters or by optimizing the height of individual emitters placed at fixed locations. The optimized parameters (the location or height) are then fed into COMSOL to check for uniformity in the AFEF, a quantity that determines the emitted current. The AFEFs obtained from COMSOL are found to be nearly identical, thereby validating the semi-analytical design technique. For larger LAFEs containing thousands of emitters, the semi-analytical method can be used for designing the LAFE and estimating the current in the optimized configuration.</span>30909310610.1063/5.0164637https://pubs.aip.org/aip/pop/article/30/9/093106/2912589/Designing-a-large-area-field-emitter-for-uniformCentrifugal-electrostatic confinement fusion
https://pubs.aip.org/aip/pop/article/30/9/092111/2912588/Centrifugal-electrostatic-confinement-fusion
Mon, 25 Sep 2023 00:00:00 GMT<span class="paragraphSection">A model for plasma confinement is developed and applied for describing an electrically confined thermonuclear plasma. The plasma confinement model includes both an analytical approach that excludes space charge effects and a classical trajectory Monte Carlo simulation that accounts for space charge. The plasma consists of reactant ions that form a non-neutral plasma without electrons. The plasma drifts around a negatively charged electrode. Conditions are predicted for confining a deuterium–tritium plasma using a 460 kV applied electric potential difference. The ion plasma would have a 20 keV temperature, a 10<sup>20</sup> m<sup>−3</sup> peak density, and a 110 keV average kinetic energy per ion (including drift and thermal portions at a certain point in the plasma). The fusion energy production rate is predicted to be 10 times larger than the energy loss rate, including contributions associated with both plasma loss to electrodes and secondary electron emission. However, an approach for enhancing the fusion power density may have to be employed to realize a practical use for centrifugal-electrostatic confinement fusion.</span>30909211110.1063/5.0161536https://pubs.aip.org/aip/pop/article/30/9/092111/2912588/Centrifugal-electrostatic-confinement-fusionDischarge characteristics of a low-pressure geometrically asymmetric cylindrical capacitively coupled plasma with an axisymmetric magnetic field
https://pubs.aip.org/aip/pop/article/30/9/093505/2912587/Discharge-characteristics-of-a-low-pressure
Mon, 25 Sep 2023 00:00:00 GMT<span class="paragraphSection">We investigate the discharge characteristics of a low-pressure geometrically asymmetric cylindrical capacitively coupled plasma discharge with an axisymmetric magnetic field generating an <span style="font-style:italic;">E × B</span> drift in the azimuthal direction. Vital discharge parameters, including electron density, electron temperature, DC self-bias, and electron energy probability function (EEPF), are studied experimentally for different magnetic field strength (<span style="font-style:italic;">B</span>) values. A transition in the plasma parameters is observed for a specific range of magnetic fields where the discharge is highly efficient with lower electron temperature. Outside this range of magnetic field, the plasma density drops, followed by an increase in the electron temperature. The observed behavior is attributed to the transition from geometrical asymmetry to magnetic field-associated symmetry due to reduced radial losses and plasma confinement in the peripheral region. The DC self-bias increases almost linearly from a large negative value to nearly zero, i.e., it turns into a symmetric discharge. The EEPF undergoes a transition from bi-Maxwellian for unmagnetized to Maxwellian at intermediate <span style="font-style:italic;">B</span> and finally becomes a weakly bi-Maxwellian at higher values of <span style="font-style:italic;">B</span>. The above transitions present a novel way to independently control the ion energy and ion flux in a cylindrical capacitively coupled plasma system using an axisymmetric magnetic field with an enhanced plasma density and lower electron temperature that is beneficial for plasma processing applications.</span>30909350510.1063/5.0160506https://pubs.aip.org/aip/pop/article/30/9/093505/2912587/Discharge-characteristics-of-a-low-pressureSmall-sized bright point-like source of picosecond soft x-ray pulses based on a high-voltage vacuum discharge
https://pubs.aip.org/aip/pop/article/30/9/094501/2911973/Small-sized-bright-point-like-source-of-picosecond
Wed, 20 Sep 2023 00:00:00 GMT<span class="paragraphSection">A small-sized soft x-ray (energy ≤ 1 keV) source based on a high-voltage vacuum discharge with a current of 20 kA and an ultrashort pulse duration of about 10 ps has been developed. It was shown that the radiation was emitted by a micropinch, which was formed in the discharge plasma and had a size of the order of a micrometer. In a single shot, an image of the test object was obtained with a resolution of several micrometers.</span>30909450110.1063/5.0151441https://pubs.aip.org/aip/pop/article/30/9/094501/2911973/Small-sized-bright-point-like-source-of-picosecondSimulated impact of fill tube geometry on recent high-yield implosions at the National Ignition Facility
https://pubs.aip.org/aip/pop/article/30/9/092706/2911972/Simulated-impact-of-fill-tube-geometry-on-recent
Wed, 20 Sep 2023 00:00:00 GMT<span class="paragraphSection">Inertial confinement fusion capsules fielded at the National Ignition Facility are filled with deuterium and tritium fuel by means of a fill tube. The fill tube introduces a low-density pathway into the fuel region of the capsule that allows high Z contaminant to invade the hot spot during the course of the implosion. A recent series of nominally identical high-yield implosions on the NIF has exhibited significant variability in performance. We evaluate the impact of the fill tube in these implosions computationally to determine whether variations in fill tube geometry could have contributed to this variability. The main contrast between the fill tube geometry in the six shots was the outer diameter of the capsule bore hole, a conical hole into which the fill tube is inserted. In our simulations, the geometry of the bore hole can play a significant role in the development of nonlinear flows seeded by the fill tube. We find that the amount of space between the bore hole and the fill tube is the primary factor that determines the amount of contaminant jetted into the hot spot by the fill tube and, in turn, the level of yield reduction due to the fill tube in our simulations. As a consequence, some capsules with 5 <span style="font-style:italic;">μ</span>m fill tubes are predicted to outperform capsules with 2 <span style="font-style:italic;">μ</span>m fill tubes. We also find that micrometer-scale changes to bore hole size can impact fusion yields by up to four times near the ignition threshold. Nevertheless, simulation trends do not reproduce experimental yield trends, suggesting that the fill tube geometry was not the primary factor contributing to the observed variability in performance and that the fill tube could be masking sensitivity to other asymmetries such as other micrometer-scale capsule defects like voids that were not included in our simulations.</span>30909270610.1063/5.0156346https://pubs.aip.org/aip/pop/article/30/9/092706/2911972/Simulated-impact-of-fill-tube-geometry-on-recentUltrafast relativistic electron probing of extreme magnetic fields
https://pubs.aip.org/aip/pop/article/30/9/093105/2911971/Ultrafast-relativistic-electron-probing-of-extreme
Wed, 20 Sep 2023 00:00:00 GMT<span class="paragraphSection">We investigate the suitability of using GeV laser wakefield accelerated electron beams to measure strong, <span style="font-style:italic;">B</span> > 0.1 MT, magnetic fields. This method is explored as an alternative to proton deflectometry, which cannot be used for quantitative measurement using conventional analysis techniques at these extreme field strengths. Using such energetic electrons as a probe brings about several additional aspects for consideration, including beam divergence, detectors, and radiation reaction, which are considered here. Quantum radiation reaction on the probe is found to provide an additional measurement of the strength and length of fields, extending the standard deflectometry measurement that can only measure the path integrated fields. An experimental setup is proposed and measurement error is considered under near-term experimental conditions.</span>30909310510.1063/5.0163392https://pubs.aip.org/aip/pop/article/30/9/093105/2911971/Ultrafast-relativistic-electron-probing-of-extremeOn the Child–Langmuir law in one, two, and three dimensions
https://pubs.aip.org/aip/pop/article/30/9/093104/2911970/On-the-Child-Langmuir-law-in-one-two-and-three
Wed, 20 Sep 2023 00:00:00 GMT<span class="paragraphSection">We consider the limiting current from an emitting patch whose size is much smaller than the anode–cathode spacing. The limiting current is formulated in terms of an integral equation. It is solved iteratively, first to numerically recover the classical one-dimensional Child–Langmuir law, including Jaffe's extension to a constant, nonzero electron emission velocity. We extend to two-dimensions in which electron emission is restricted to an infinitely long stripe with infinitesimally narrow stripe width so that the emitted electrons form an electron sheet. We next extend to three-dimensions in which electron emission is restricted to a square tile (or a circular patch) with an infinitesimally small tile size (or patch radius) so that the emitted electrons form a needlelike line charge. Surprisingly, for the electron needle problem, we only find the null solution for the total line charge current, regardless of the assumed initial electron velocity. For the electron sheet problem, we also find only the null solution for the total sheet current if the electron emission velocity is assumed to be zero, and the total maximum sheet current becomes a finite, nonzero value if the electron emission velocity is assumed to be nonzero. These seemingly paradoxical results are shown to be consistent with the earlier works of the Child–Langmuir law of higher dimensions. They are also consistent with, or perhaps even anticipated by, the more recent theories and simulations on thermionic cathodes that used realistic work function distributions to account for patchy, non-uniform electron emission. The mathematical subtleties are discussed.</span>30909310410.1063/5.0169276https://pubs.aip.org/aip/pop/article/30/9/093104/2911970/On-the-Child-Langmuir-law-in-one-two-and-threeSpontaneous plasma formation via electrical explosion of nanostructured metal surface layers in plasma–surface interactions
https://pubs.aip.org/aip/pop/article/30/9/092511/2911821/Spontaneous-plasma-formation-via-electrical
Wed, 20 Sep 2023 00:00:00 GMT<span class="paragraphSection">The article is aimed at studying the issue of spontaneous, i.e., triggerless ignition of arcing plasma splashes due to explosive-electron-emission pulses at fiber-form nanostructured (W-fuzz) surface during plasma–surface interaction. There has been proposed an equivalent sputtering yield for arcing <span style="font-style:italic;">Yeff</span> = 4.8 <span style="font-style:italic;">γ</span> C/mg, where <span style="font-style:italic;">γ</span> is the rate of plasma production (mass per charge) from a cathode by vacuum arc discharge. The ratio of the released-to-incident atoms <span style="font-style:italic;">Yeff</span> can reach the value of about 10 for the plasma production rate of 2 mg/C. The increase in the plasma production rate <span style="font-style:italic;">γ</span> has been estimated as (i) an increase in mass due to mechanical destruction of neighboring nanofragments and (ii) a decrease in ions average charge. The resulting twentyfold increase in <span style="font-style:italic;">γ</span> at few-<span style="font-style:italic;">μ</span>m layers agrees with the experimental observations. The critical temperature <span style="font-style:italic;">Tcr</span> (and corresponding cohesive energy <span style="font-style:italic;">Ecoh</span> = 5 <span style="font-style:italic;">Tcr</span>) for the W-fuzz nanostructure has been estimated as <span style="font-style:italic;">Tcr</span> = 2 <span style="font-style:italic;">n</span>/<span style="font-style:italic;">n</span><sub>0</sub> eV, where <span style="font-style:italic;">n</span>/<span style="font-style:italic;">n</span><sub>0</sub> is the relative density of the W-fuzz nanostructure. It falls below 1 eV for typical fuzz layer thickness larger than few tenths of <span style="font-style:italic;">μ</span>m. This results in the experimentally observed reduction of the average W-ions charge in vacuum arc plasma.</span>30909251110.1063/5.0158993https://pubs.aip.org/aip/pop/article/30/9/092511/2911821/Spontaneous-plasma-formation-via-electricalNondiffusive particle transport in the stellarator experiment TJ-K
https://pubs.aip.org/aip/pop/article/30/9/092306/2911820/Nondiffusive-particle-transport-in-the-stellarator
Tue, 19 Sep 2023 00:00:00 GMT<span class="paragraphSection">Current transport modeling follows a local, diffusive paradigm to describe the dynamics in the edge of magnetically confined plasmas. In the presence of steep gradients, the applicability of local transport theory can break down. In the low-temperature plasmas of the TJ-K stellarator, the extent and characteristics of nonlocal transport contributions are investigated experimentally. In this context, the convection–diffusion equation, which obeys a conventional diffusive formalism, is chosen. However, the predicted linear flux-gradient relationship differs significantly from the behavior observed in most discharges. A second method, which requires no previous assumptions on the diffusivity of particle transport, is applied. This model confirms the presence of significant nondiffusive contributions in the turbulent particle transport of TJ-K. Furthermore, three different regimes were identified at large, intermediate, and small scales. These could be governed by conventional, superdiffusive, and subdiffusive processes, respectively. All three regions persist across discharges at different gases and pressures.</span>30909230610.1063/5.0156125https://pubs.aip.org/aip/pop/article/30/9/092306/2911820/Nondiffusive-particle-transport-in-the-stellaratorLarge-incidence-angle multiple-beam two-plasmon decay instability in inertial confinement fusion
https://pubs.aip.org/aip/pop/article/30/9/092702/2911819/Large-incidence-angle-multiple-beam-two-plasmon
Tue, 19 Sep 2023 00:00:00 GMT<span class="paragraphSection">A multi-dimensional code <span style="font-style:italic;">FLAME-MD</span> solving fluid-like laser-plasma instabilities' (LPIs) equations has been developed and is used to study multiple-beam two-plasmon decay (TPD) instability relevant to a laser-entrance-hole window burn-off scenario in inertial confinement fusion (ICF) experiments. It is found that TPD can be collectively driven by multiple beams incident at large incidence angles with respect to the electron density gradient at a very low threshold. The polarization configuration of the laser beams is a key factor determining the way of sharing common daughter electron plasma waves (EPWs). The <span style="font-style:italic;">p</span>-polarized beams arranged on the same incidence cone can collectively drive common EPWs along the cone axis. The common-wave sharing mechanisms among the <span style="font-style:italic;">s</span>-polarized beams are largely dependent on the geometry of the beams and are less robust. The simulation results also show that the <span style="font-style:italic;">p</span>-polarized beams are dominating the multiple-beam TPD processes. The common EPWs along the cone axis can accelerate energetic electrons toward the capsule inside the hohlraum and, therefore, pose a fuel-preheat risk to ICF implosions.</span>30909270210.1063/5.0162495https://pubs.aip.org/aip/pop/article/30/9/092702/2911819/Large-incidence-angle-multiple-beam-two-plasmonError-field penetration thresholds in ohmically heated ITER and SPARC plasmas
https://pubs.aip.org/aip/pop/article/30/9/092512/2911818/Error-field-penetration-thresholds-in-ohmically
Tue, 19 Sep 2023 00:00:00 GMT<span class="paragraphSection">The critical <span style="font-style:italic;">n</span> = 1, <span style="font-style:italic;">n</span> = 2, and <span style="font-style:italic;">n</span> = 3 error-field amplitudes needed to trigger error-field penetration in ITER and SPARC, steady-state, ohmically heated plasmas are calculated using a standard asymptotic matching approach. The calculation incorporates plasma impurities, trapped particles, the bootstrap current, and neoclassical poloidal flow-damping. The energy confinement time is specified by the neo-Alcator scaling law in the low-density linear Ohmic confinement (LOC) regime and by the ITER-89P L-mode scaling law in the high-density saturated Ohmic confinement (SOC) regime. The response of the plasma in the inner region is calculated using a linearized version of the four-field model. At the normal operating electron number density, diamagnetic levels of rotation are found to be sufficient to protect ITER and SPARC ohmically heated plasmas from m = 2 / n = 1 error-field penetration. On the other hand, SPARC, and especially ITER, ohmically heated plasmas may be vulnerable to <span style="font-style:italic;">n</span> > 1 error-field penetration. ITER and SPARC ohmically heated plasmas are also slightly more susceptible to error-field penetration when the electron fluid at the rational surface rotates in the ion diamagnetic direction, rather than the electron diamagnetic direction. At electron number densities that are sufficiently low that the plasma lies in the LOC confinement regime, the error-field penetration threshold increases with increasing density. However, as soon as the electron number density becomes large enough that the plasma enters the SOC regime, the increase in the error-field penetration threshold with increasing density levels off.</span>30909251210.1063/5.0161860https://pubs.aip.org/aip/pop/article/30/9/092512/2911818/Error-field-penetration-thresholds-in-ohmicallyEffect of non-Planckian spectrum on shock velocities and subsonic to transonic transition in mid-Z witness plate elements
https://pubs.aip.org/aip/pop/article/30/9/092703/2911817/Effect-of-non-Planckian-spectrum-on-shock
Tue, 19 Sep 2023 00:00:00 GMT<span class="paragraphSection">In this work, we obtain the shock velocities in mid-Z elements, namely, Al, Ti, and Cu by performing radiation hydrodynamic simulations using constant radiation drives consisting of equilibrium Planckian distribution along with high-energy Gaussian profiles. The drive temperatures have been varied from 80 to 270 eV, and the fraction of total energy density due to Gaussian distribution (<span style="font-style:italic;">α</span>) changes from 0 to 0.4. Though the shock velocity in all the three elements rise with the strength of the drive temperature, its variation with <span style="font-style:italic;">α</span> is quite complicated. Using simulations, we have shown that rear surface expansion is not responsible for the observed variation in shock velocity with the fraction of hard x rays at various temperatures and explained it in terms of distribution of total extinction coefficient over the spectral form of incident drive source leading to change in albedos. The percentage variations in shock velocities are found to be commensurate with those in albedos as expected for x-ray driven ablation process. Accurate scaling laws relating the drive temperatures with the shock velocities and <span style="font-style:italic;">α</span> have also been obtained. In Al, subsonic to transonic transition temperature is found to increase with <span style="font-style:italic;">α</span>, whereas in Ti it is found to decrease. We have explained the variation in transition temperature in terms of Mach number. As this transition temperature in Cu is anticipated to be high due to its higher atomic number and density, we did not observe any transition up to the temperature (500 eV) considered in this paper.</span>30909270310.1063/5.0160839https://pubs.aip.org/aip/pop/article/30/9/092703/2911817/Effect-of-non-Planckian-spectrum-on-shockCorrelations between asymmetric compression, burn amplification, and hot-spot velocities in inertial confinement fusion implosions
https://pubs.aip.org/aip/pop/article/30/9/092705/2911816/Correlations-between-asymmetric-compression-burn
Tue, 19 Sep 2023 00:00:00 GMT<span class="paragraphSection">This manuscript examines the correlations between the hot-spot velocity (an observable signature of residual kinetic energy), low-mode implosion asymmetries, and burn amplification in inertial confinement fusion implosions on the National Ignition Facility (NIF). Using a combination of two-dimensional axis-symmetric and three-dimensional radiation-hydrodynamic simulations coupled to neutronics, we find that for typical NIF implosions, the stagnation asymmetry multiplies the observed hot-spot velocity anywhere from 80% to 120%, while burn amplification always increases it. Additionally, we find stagnation asymmetry typically deflects the observed hot-spot flow. The two mechanisms (low-mode implosion asymmetries and burn amplification) can be decoupled, and application of a simple model to a database of cryogenic implosions on the NIF infers the total hot-spot velocity amplification. This finding modifies the interpretation of data collected from inertial confinement fusion experiments and impacts the magnitude and origin of low-mode asymmetries.</span>30909270510.1063/5.0153421https://pubs.aip.org/aip/pop/article/30/9/092705/2911816/Correlations-between-asymmetric-compression-burnEvolution of coupled weakly driven waves in a dissipative plasma
https://pubs.aip.org/aip/pop/article/30/9/092110/2911815/Evolution-of-coupled-weakly-driven-waves-in-a
Tue, 19 Sep 2023 00:00:00 GMT<span class="paragraphSection">The nonlinear collisional dynamics of coupled driven plasma waves in the presence of background dissipation is studied analytically within kinetic theory. Sufficiently near marginal stability, phase space correlations are poorly preserved and time delays become unimportant. The system is then shown to be governed by two first-order coupled autonomous differential equations of cubic order for the wave amplitudes and two complementary first-order equations for the evolution of their phases. That system of equations can be decoupled and further simplified to a single second-order differential equation of Liénard's type for each amplitude. Numerical solutions for this equation are obtained in the general case, while analytic solutions are obtained for special cases in terms of parameters related to the spacing of the resonances of the two waves in frequency space, e.g., wave lengths and oscillation frequencies. These parameters are further analyzed to find classes of quasi-steady saturation and pulsating scenarios. To classify equilibrium points, local stability analysis is applied, and bifurcation conditions are determined. When the two waves saturate at similar amplitude levels, their combined signal is shown to invariably exhibit amplitude beating and phase jumps of nearly <span style="font-style:italic;">π</span>. The obtained analytical results can be used to benchmark simulations and to interpret eigenmode amplitude measurements in fusion experiments.</span>30909211010.1063/5.0159284https://pubs.aip.org/aip/pop/article/30/9/092110/2911815/Evolution-of-coupled-weakly-driven-waves-in-aFlexible, integrated modeling of tokamak stability, transport, equilibrium, and pedestal physics
https://pubs.aip.org/aip/pop/article/30/9/092510/2911814/Flexible-integrated-modeling-of-tokamak-stability
Tue, 19 Sep 2023 00:00:00 GMT<span class="paragraphSection">The STEP (Stability, Transport, Equilibrium, and Pedestal) integrated-modeling tool has been developed in OMFIT to predict stable, tokamak equilibria self-consistently with core-transport and pedestal calculations. STEP couples theory-based codes to integrate a variety of physics, including magnetohydrodynamic stability, transport, equilibrium, pedestal formation, and current-drive, heating, and fueling. The input/output of each code is interfaced with a centralized ITER-Integrated Modelling & Analysis Suite data structure, allowing codes to be run in any order and enabling open-loop, feedback, and optimization workflows. This paradigm simplifies the integration of new codes, making STEP highly extensible. STEP has been verified against a published benchmark of six different integrated models. Core-pedestal calculations with STEP have been successfully validated against individual DIII-D H-mode discharges and across more than 500 discharges of the H 98 , y 2 database, with a mean error in confinement time from experiment less than 19%. STEP has also reproduced results in less conventional DIII-D scenarios, including negative-central-shear and negative-triangularity plasmas. Predictive STEP modeling has been used to assess performance in several tokamak reactors. Simulations of a high-field, large-aspect-ratio reactor show significantly lower fusion power than predicted by a zero-dimensional study, demonstrating the limitations of scaling-law extrapolations. STEP predictions have found promising scenarios for an EXhaust and Confinement Integration Tokamak Experiment, including a high-pressure, 80%-bootstrap-fraction plasma. ITER modeling with STEP has shown that pellet fueling enhances fusion gain in both the baseline and advanced-inductive scenarios. Finally, STEP predictions for the SPARC baseline scenario are in good agreement with published results from the physics basis.</span>30909251010.1063/5.0156877https://pubs.aip.org/aip/pop/article/30/9/092510/2911814/Flexible-integrated-modeling-of-tokamak-stabilitySimulations of laser-driven strong-field QED with Ptarmigan: Resolving wavelength-scale interference and γ -ray polarization
https://pubs.aip.org/aip/pop/article/30/9/093903/2911813/Simulations-of-laser-driven-strong-field-QED-with
Tue, 19 Sep 2023 00:00:00 GMT<span class="paragraphSection">Accurate modeling is necessary to support precision experiments investigating strong-field QED phenomena. This modeling is particularly challenging in the transition between the perturbative and nonperturbative regimes, where the normalized laser amplitude <span style="font-style:italic;">a</span><sub>0</sub> is comparable to unity and wavelength-scale interference is significant. Here, we describe how to simulate nonlinear Compton scattering, Breit–Wheeler pair creation, and trident pair creation in this regime, using the Monte Carlo particle-tracking code <span style="font-style:italic;">Ptarmigan</span>. This code simulates collisions between high-intensity lasers and beams of electrons or <span style="font-style:italic;">γ</span> rays, primarily in the framework of the locally monochromatic approximation. We benchmark our simulation results against full QED calculations for pulsed plane waves and show that they are accurate at the level of a few per cent, across the full range of particle energies and laser intensities. This work extends our previous results to linearly polarized lasers and arbitrary polarized <span style="font-style:italic;">γ</span> rays.</span>30909390310.1063/5.0159963https://pubs.aip.org/aip/pop/article/30/9/093903/2911813/Simulations-of-laser-driven-strong-field-QED-withMitigation of deceleration-phase Rayleigh–Taylor instability growth in inertial confinement fusion implosions
https://pubs.aip.org/aip/pop/article/30/9/092704/2911793/Mitigation-of-deceleration-phase-Rayleigh-Taylor
Tue, 19 Sep 2023 00:00:00 GMT<span class="paragraphSection">Rayleigh–Taylor growth during shell deceleration is one of the main limiting factors for target performance in inertial confinement fusion implosions. Using analytical scaling laws and hydrodynamic simulations, we show that such amplification can be mitigated by reducing the initial mass density in the central target region. The perturbation growth reduction is caused by a smaller hot-spot convergence ratio during deceleration, increased density scale length, and enhanced ablation stabilization. The required central density reduction can be achieved using the dynamic shell formation concept.</span>30909270410.1063/5.0164835https://pubs.aip.org/aip/pop/article/30/9/092704/2911793/Mitigation-of-deceleration-phase-Rayleigh-TaylorShock waves in strongly coupled one-dimensional dusty plasmas under Yukawa interactions
https://pubs.aip.org/aip/pop/article/30/9/093701/2911598/Shock-waves-in-strongly-coupled-one-dimensional
Mon, 18 Sep 2023 00:00:00 GMT<span class="paragraphSection">The numerical investigation of shock waves in a chain of dust particles is conducted using the molecular dynamics simulation method. Assuming that the first pulse in the shock front is a solitary wave, we derive an analytical approximate expression to demonstrate how the shock velocity depends on the piston velocity and the system parameters, such as the charge of the dust particles, the initial lattice constant, and the screening parameter. It is found that the shock wave velocity increases as the piston velocity and coupling parameter increase, while it decreases as the screening parameter increases. The analytical results are in good agreement with the molecular dynamics simulation results.</span>30909370110.1063/5.0157232https://pubs.aip.org/aip/pop/article/30/9/093701/2911598/Shock-waves-in-strongly-coupled-one-dimensionalTwo-dimensional reconstruction of filament temperatures and densities with the thermal helium beam at ASDEX Upgrade
https://pubs.aip.org/aip/pop/article/30/9/092509/2911597/Two-dimensional-reconstruction-of-filament
Mon, 18 Sep 2023 00:00:00 GMT<span class="paragraphSection">In the scrape-off layer (SOL) of fusion plasmas, radial particle and energy transport is mainly carried by plasma filaments. The plasma parameters of such filaments can be measured by the thermal helium beam diagnostic (THB). By means of an extended collisional radiative model (CRM) used for the evaluation of the diagnostic data, the light intensity response of neutral helium transitions from filaments is studied, which depends on the parameters of the filament and the background. The electron density of the filament is found to be the dominant parameter impacting the line intensities. By applying a numerical reconstruction algorithm based on the CRM, electron temperatures and densities as well as the sizes of experimentally measured filaments are obtained. This method allows for the first time measurements of the temporal decay rates of filament density and temperature in the co-moving frame of the filament and its radial propagation velocity.</span>30909250910.1063/5.0164057https://pubs.aip.org/aip/pop/article/30/9/092509/2911597/Two-dimensional-reconstruction-of-filamentAlgebraic and numerical studies on the roles of momentum conservation and self-adjointness in moment-based neoclassical particle fluxes
https://pubs.aip.org/aip/pop/article/30/9/092305/2911596/Algebraic-and-numerical-studies-on-the-roles-of
Mon, 18 Sep 2023 00:00:00 GMT<span class="paragraphSection">Linearized collision operators are model operators that approximate the nonlinear Landau collision operator, but cannot capture all the features of the Landau operator. Various linearized collision operators have been proposed, including the one that ensures the self-adjointness of the operator and another that maintains the friction–flow relations derived from the exact linearized collision operator. To elucidate the basis for choosing an appropriate model operator that derives the matrix elements used to express the friction forces, the roles of momentum conservation and the self-adjointness of the collision operator in the neoclassical particle flux are investigated theoretically, algebraically, and numerically within the framework of the moment method. Linear algebraic calculations confirm that ambipolarity only requires the property of momentum conservation, while the self-adjointness is additionally necessary to ensure the independence of poloidal flow and particle flux from the radial electric field, which must be established in an axisymmetric system. This fact is also numerically validated by the one-dimensional fluid-based transport code TASK/TX, extended to handle impurity species, and the moment-method-based neoclassical transport code Matrix Inversion. In tokamak experiments, where a parallel electric field is typically present, it induces the inward Ware flux, where even electrons can have the same or larger particle flux as main ions and impurities. The Ware flux can significantly contribute to the total neoclassical particle flux, highlighting the importance of considering the electron flux when modeling neoclassical impurity fluxes.</span>30909230510.1063/5.0164313https://pubs.aip.org/aip/pop/article/30/9/092305/2911596/Algebraic-and-numerical-studies-on-the-roles-ofThe Zap Energy approach to commercial fusion
https://pubs.aip.org/aip/pop/article/30/9/090603/2911595/The-Zap-Energy-approach-to-commercial-fusion
Mon, 18 Sep 2023 00:00:00 GMT<span class="paragraphSection">Zap Energy is a private fusion energy company developing the sheared-flow-stabilized (SFS) Z-pinch concept for commercial energy production. Spun out from the University of Washington, these experimental and computational efforts have resulted in devices with quasi-steady DD fusion yields above 10<sup>9</sup> per pulse. These devices support scaling toward energy breakeven on existing devices as well as beyond to commercially relevant engineering fusion gains. This article discusses the strategy behind Zap's development path, which is derived directly from the engineering and scientific elegance of the confinement method. Without need for external confinement or heating technologies, the SFS Z pinch relies on plasma self-organization. This compact magnetic confinement technology could, in turn, provide the basis for a cost-effective fusion power plant, vastly reduced in complexity from its competitors.</span>30909060310.1063/5.0163361https://pubs.aip.org/aip/pop/article/30/9/090603/2911595/The-Zap-Energy-approach-to-commercial-fusionThe propagation of Alfvén wave in magnetized plasma sheath of hypersonic vehicles in near space
https://pubs.aip.org/aip/pop/article/30/9/090701/2911594/The-propagation-of-Alfven-wave-in-magnetized
Mon, 18 Sep 2023 00:00:00 GMT<span class="paragraphSection">Hypersonic plasma sheath could shield communication signals, which results in the so-called “blackout.” Blackout is a major risk to the safety of re-entry vehicles and cruise hypersonic vehicles in near space. In this study, a propagation model of Alfvén waves in plasma sheaths is developed. The impacts of the external magnetic field, the wave frequency, and the boundary conductivity on the Alfvén attenuation were investigated. According to the simulation results, once the conductivity is close to the Alfvénic conductivity near the onboard antenna, the attenuation of Alfvén waves in the plasma sheath could reach its minimum. The total attenuation of the Alfvén wave in the plasma sheath decreases with the carrier frequency. Also, the attenuation decreases with increasing magnetic field strength.</span>30909070110.1063/5.0165553https://pubs.aip.org/aip/pop/article/30/9/090701/2911594/The-propagation-of-Alfven-wave-in-magnetizedAnalysis of different modeling approaches for simulation of glow discharge in helium at atmospheric pressure
https://pubs.aip.org/aip/pop/article/30/9/093504/2911451/Analysis-of-different-modeling-approaches-for
Wed, 13 Sep 2023 00:00:00 GMT<span class="paragraphSection">One-dimensional numerical models of a direct current atmospheric pressure glow discharge in helium are developed and examined. The models use a fluid description of charged and neutral particles and a drift-diffusion approximation for particle fluxes. The effects of plasma-chemical models, the form of the electron energy distribution function (Maxwellian vs non-Maxwellian), the energy loss due to gas heating and the width of the gas gap on the discharge characteristics are analyzed. The performance of different modeling approaches is examined by superimposing computed current–voltage characteristic (CVC) curves with each other and with measured and computed CVCs available in the literature.</span>30909350410.1063/5.0161535https://pubs.aip.org/aip/pop/article/30/9/093504/2911451/Analysis-of-different-modeling-approaches-forTokamak plasma equilibrium with relativistic runaway electrons
https://pubs.aip.org/aip/pop/article/30/9/092508/2911450/Tokamak-plasma-equilibrium-with-relativistic
Wed, 13 Sep 2023 00:00:00 GMT<span class="paragraphSection">We consider axisymmetric equilibrium of a tokamak plasma that includes current carried by relativistic runaway electrons (REs). Using a guiding center approach, a qualitative picture of the equilibrium of a pure RE beam is elucidated. In a hot thermal plasma, none of the classical drifts of charged particles contribute to the net field-perpendicular current density, which is purely due to magnetization current. In the case of a runaway beam, however, the curvature drift of REs provides the Lorentz force needed to maintain the centripetal acceleration associated with the relativistic toroidal motion. Two different equilibrium formulations are derived for the general case consisting of a mix of thermal and RE current. At higher RE energies, the shift between flux-surfaces and surfaces of constant generalized angular momentum of REs in such equilibria can exceed the radial extent of a typical magnetohydrodynamic mode such that its stability properties could be altered. Simplified one-dimensional governing equations are derived for the absolute and relative orbit shifts in the case of a circular tokamak, enabling quick estimates of parameter dependencies.</span>30909250810.1063/5.0165240https://pubs.aip.org/aip/pop/article/30/9/092508/2911450/Tokamak-plasma-equilibrium-with-relativisticSimulation of neutral beam current drive on EAST tokamak
https://pubs.aip.org/aip/pop/article/30/9/092507/2911449/Simulation-of-neutral-beam-current-drive-on-EAST
Wed, 13 Sep 2023 00:00:00 GMT<span class="paragraphSection">A neutral beam current drive on the EAST tokamak is studied by using Monte Carlo test particle code TGCO. The phase-space structure of the steady-state fast ion distribution is examined and visualized. We find that trapped ions carry co-current current near the edge and countercurrent current near the core. However, the magnitude of the trapped ion current is one order smaller than that of the passing ions. Therefore, their contribution to the fast ion current is negligible (1% of the fast ion current). We examine the dependence of the fast ion current on two basic plasma parameters: the plasma current <span style="font-style:italic;">Ip</span> and plasma density <span style="font-style:italic;">ne</span>. The results indicate that the dependence of fast ion current on <span style="font-style:italic;">Ip</span> is not monotonic: with <span style="font-style:italic;">Ip</span> increasing, the fast ion current first increases and then decreases. This dependence can be explained by the change of trapped fraction and drift-orbit width with <span style="font-style:italic;">Ip</span>. The fast ion current decreases with the increase in plasma density <span style="font-style:italic;">ne</span>. This dependence is related to the variation of the slowing-down time with <span style="font-style:italic;">ne</span>, which is already well known and is confirmed in our specific situation. The electron shielding effect to the fast ion current is taken into account by using a fitting formula applicable to general tokamak equilibria and arbitrary collisionality regime. The dependence of the net current on the plasma current and density follows the same trend as that of the fast ion current.</span>30909250710.1063/5.0158503https://pubs.aip.org/aip/pop/article/30/9/092507/2911449/Simulation-of-neutral-beam-current-drive-on-EASTPerspectives on ultraintense laser-driven terahertz radiation from plasmas
https://pubs.aip.org/aip/pop/article/30/9/090602/2911448/Perspectives-on-ultraintense-laser-driven
Wed, 13 Sep 2023 00:00:00 GMT<span class="paragraphSection">High-power terahertz (THz) radiation is fundamental to numerous applications in many fields. Ultraintense laser-produced plasmas have attracted ever-increasing interest as a damage-free medium for generating high-peak-power THz pulses. This article gives the authors' perspectives on how the field of ultraintense laser-driven THz radiation from plasmas developed and where the field is headed. In particular, recent advances and some new ideas are outlined in terms of THz genesis, metrology, and applications. In addition to pushing the limits of achievable THz pulse energies and peak powers, much attention will be paid on the tunability of THz properties. Single-shot THz metrology will develop toward multi-dimensional resolution. The resulting extreme THz radiation offers immense opportunities in the THz control over matter and THz-driven strong-field physics. A selection of illustrative application cases in the field of materials, chemistry, and biology are briefly discussed. In the authors' opinion, the concerted advances in these aspects will propel this field into the bright future.</span>30909060210.1063/5.0167730https://pubs.aip.org/aip/pop/article/30/9/090602/2911448/Perspectives-on-ultraintense-laser-drivenPhase space dynamics of unmagnetized plasmas: Collisionless and collisional regimes
https://pubs.aip.org/aip/pop/article/30/9/092304/2910870/Phase-space-dynamics-of-unmagnetized-plasmas
Tue, 12 Sep 2023 00:00:00 GMT<span class="paragraphSection">Eulerian electrostatic kinetic simulations of unmagnetized plasmas (kinetic electrons and motionless protons) with high-frequency equilibrium perturbations have been employed to investigate the phase space free energy transfer across spatial and velocity scales, associated with the resonant interaction of electrons with the self-induced electric field. Numerical runs cover a wide range of collisionless and weakly collisional plasma regimes. An analysis technique based on the Fourier–Hermite transform of the particle distribution function allows to point out how kinetic processes trigger the free energy cascade, which is instead inhibited at finer scales when collisions are turned on. Numerical results are presented and discussed for the cases of linear wave Landau damping, nonlinear electron trapping, and bump-on-tail and two-stream instabilities. A more realistic situation of turbulent Langmuir fluctuations is also discussed in detail. Fourier–Hermite transform shows a free energy spread, highly conditioned by collisions, which involves velocity scales more quickly than the spatial scales, even when nonlinear effects are dominant. This results in anisotropic spectra whose slopes are compatible with theoretical expectations. Finally, an exact conservation law has been derived, which describes the time evolution of the free energy of the system, taking into account the collisional dissipation.</span>30909230410.1063/5.0160549https://pubs.aip.org/aip/pop/article/30/9/092304/2910870/Phase-space-dynamics-of-unmagnetized-plasmasThe effect of pellet injection on turbulent transport in TJ-II
https://pubs.aip.org/aip/pop/article/30/9/092303/2910854/The-effect-of-pellet-injection-on-turbulent
Tue, 12 Sep 2023 00:00:00 GMT<span class="paragraphSection">An improvement in confinement associated with the injection of pellets has been observed in TJ-II and other devices. By means of a simple model, we study here the modification of turbulent transport by the injection of pellets in TJ-II and how this modification affects the particle confinement time. The analysis of the results shows the relationship of the confinement improvement with the evolution of the shear flow due to turbulence, especially near low order rational surfaces. This work is based on pellet injections into the neutral beam injection heated phase of TJ-II plasmas. For this, single, double, or triple hydrogen pellet injection are considered and the post-injection evolution of selected plasma parameters are analyzed and compared.</span>30909230310.1063/5.0163832https://pubs.aip.org/aip/pop/article/30/9/092303/2910854/The-effect-of-pellet-injection-on-turbulentMonte Carlo simulations of charged particle transport in plasmas: A fast single-scattering model
https://pubs.aip.org/aip/pop/article/30/9/093902/2910853/Monte-Carlo-simulations-of-charged-particle
Tue, 12 Sep 2023 00:00:00 GMT<span class="paragraphSection">When simulating a charged particle trajectory in plasmas with Monte Carlo methods, the traditional single-scattering model is accurate but computationally expensive. The traditional multiple-scattering model reduces the computation cost but assumes an exponential distribution of the scattering angle, which overestimates the cumulative scattering angle. In this paper, we develop a new Monte Carlo method for the charged particle transport simulations. The scattering angle is naturally sampled from a modified screened Rutherford scattering cross section, in which a greatly amplified minimum deflection angle is used. With this model, the simulations give the same scattering angle distribution with the single-scattering model but only take a comparable computation cost with the multiple-scattering model when the small scattering angle and Markovian approximations can be fulfilled. This model would be especially useful for the study of inertial-confinement-fusion, which is sensitive to the alpha-particle energy deposition.</span>30909390210.1063/5.0155758https://pubs.aip.org/aip/pop/article/30/9/093902/2910853/Monte-Carlo-simulations-of-charged-particleVelocity-space sensitivity and inversions of synthetic ion cyclotron emission
https://pubs.aip.org/aip/pop/article/30/9/092109/2910559/Velocity-space-sensitivity-and-inversions-of
Mon, 11 Sep 2023 00:00:00 GMT<span class="paragraphSection">This paper introduces a new model to find the velocity-space location of energetic ions generating ion cyclotron emission (ICE) in plasmas. ICE is thought to be generated due to inverted gradients in the v ⊥ direction of the velocity distribution function or due to anisotropies, i.e., strong gradients in the pitch direction. Here, we invert synthetic ICE spectra generated from first principles PIC-hybrid computations to find the locations of these ICE-generating ions in velocity space in terms of a probability distribution function. To this end, we compute 2D ICE weight functions based on the magnetoacoustic cyclotron instability, which reveals the velocity-space sensitivity of ICE measurements. As an example, we analyze the velocity-space sensitivity of synthetic ICE measurements near the first 15 harmonics for plasma parameters typical for the Large Helical Device. Furthermore, we investigate the applicability of a least-square subset search, Tikhonov regularization, and Lasso regularization to obtain the locations in velocity space of the ions generating the ICE.</span>30909210910.1063/5.0157126https://pubs.aip.org/aip/pop/article/30/9/092109/2910559/Velocity-space-sensitivity-and-inversions-ofEffect of surface roughness on phase transition timing in megaampere pulsed-power–driven exploding conductors
https://pubs.aip.org/aip/pop/article/30/9/092108/2910555/Effect-of-surface-roughness-on-phase-transition
Mon, 11 Sep 2023 00:00:00 GMT<span class="paragraphSection">An understanding of material phase transitions in megaampere pulsed-power–driven exploding conductors is important for predicting the growth of hydrodynamic instabilities in magneto-inertial fusion concepts. This study analyzes phase transitions in electrical conductor explosions using 1D Lagrangian and 2D arbitrary Lagrangian–Eulerian resistive magnetohydrodynamic simulations to show that micrometer-scale surface roughness can lead to the electrothermal instability (ETI), a feedback effect that concentrates resistive heating and leads to early melting and ablation. Simulations of the Mykonos electrothermal instability II (METI-II) experiment show melting begins 19% sooner for machined rods with micrometer-scale surface roughness than for rods without these features. The surface magnetic field is 41 T around the initial region of melt, representing a lower magnitude than both the 86 T from 1D simulations and the 85 T threshold reported elsewhere. In 2D simulations with micrometer-scale surface roughness, temperature measurements indicate the critical point temperature of aluminum is reached 17% faster in comparison with 1D simulations. Values from 2D simulations with surface roughness align with predictions from ETI theory, and the observed temperature redistribution further supports the ETI as an underlying mechanism. Simulation results are validated against experimental photonic Doppler velocimetry data. This study shows 1D simulations are adequate to model conductors with sub-micrometer-scale surface roughness in this high-energy-density regime; however, 2D or 3D simulations are required to capture the full range of physics for accurately describing phase transitions in conductors with micrometer-scale or larger surface roughness.</span>30909210810.1063/5.0159797https://pubs.aip.org/aip/pop/article/30/9/092108/2910555/Effect-of-surface-roughness-on-phase-transitionGamma-flash generation in multi-petawatt laser–matter interactions
https://pubs.aip.org/aip/pop/article/30/9/093103/2910554/Gamma-flash-generation-in-multi-petawatt-laser
Mon, 11 Sep 2023 00:00:00 GMT<span class="paragraphSection">The progressive development of high power lasers over the last several decades enables the study of γ-photon generation when an intense laser beam interacts with matter, mainly via inverse Compton scattering at the high intensity limit. γ-ray flashes are a phenomenon of broad interest, drawing the attention of researchers working in topics ranging from cosmological scales to elementary particle scales. Over the last few years, a plethora of studies predict extremely high laser energy to γ-photon energy conversion using various target and/or laser field configurations. The aim of this article is to discuss several recently proposed γ-ray flash generation schemes, as a guide for upcoming γ-photon related experiments and for further evolution of the presently available theoretical schemes.</span>30909310310.1063/5.0158264https://pubs.aip.org/aip/pop/article/30/9/093103/2910554/Gamma-flash-generation-in-multi-petawatt-laserDiffusion–convection model of runaway electrons due to large magnetohydrodynamic perturbations in post-thermal quench plasmas
https://pubs.aip.org/aip/pop/article/30/9/092506/2909949/Diffusion-convection-model-of-runaway-electrons
Thu, 07 Sep 2023 00:00:00 GMT<span class="paragraphSection">Systematic test particle tracing simulations for runaway electrons (REs) are performed for six post-thermal quench equilibria from DIII-D and ITER, where large scale, kink-like <span style="font-style:italic;">n</span> = 1 (<span style="font-style:italic;">n</span> is the toroidal mode number) magnetohydrodynamic (MHD) instabilities are found. The modeled particle guiding center orbits allow extraction of the effective diffusion–convection coefficients of REs in the presence of <span style="font-style:italic;">large</span> three-dimensional (3D) perturbations up to 10% of the equilibrium toroidal field. With a fixed spatial distribution of the field perturbation, the RE transport coefficients along the plasma radial coordinate track reasonably well with the surface-averaged perturbation level. A substantial variation in the value of the transport coefficients—by three orders of magnitude in most cases, however, occurs with varying launching location of REs along the plasma radius. Large 3D perturbations almost always lead to comparable diffusion and convection processes, meaning that diffusion alone is insufficient to describe the particle motion. At lower (but still high) level of perturbation, the RE convection is found to be dominant over diffusion. A similar observation is made when the perturbation is too strong. In the presence of large perturbation, the dependence of the RE transport on the particle energy is sensitive to the spatial distribution of the perturbation. Based on numerically obtained RE transport coefficients, an analytic fitting model is proposed to quantify the particle diffusion and convection processes due to large MHD events in post-thermal quench plasmas. The model is shown to reasonably well reproduce the direct test particle tracing results for the RE loss fraction and can, thus, be useful for incorporating into other kinetic RE codes in order to simulate the RE beam evolution in the presence of large 3D perturbations.</span>30909250610.1063/5.0159923https://pubs.aip.org/aip/pop/article/30/9/092506/2909949/Diffusion-convection-model-of-runaway-electronsEmpirical probability and machine learning analysis of m , n = 2, 1 tearing mode onset parameter dependence in DIII-D H-mode scenarios
https://pubs.aip.org/aip/pop/article/30/9/092505/2909948/Empirical-probability-and-machine-learning
Thu, 07 Sep 2023 00:00:00 GMT<span class="paragraphSection"><span style="font-style:italic;">m</span>, <span style="font-style:italic;">n</span> = 2, 1 tearing mode onset empirical probability and machine learning analyses of a multiscenario DIII-D database of over 14 000 H-mode discharges show that the normalized plasma beta, the rotation profile, and the magnetic equilibrium shape have the strongest impact on the 2,1 tearing mode stability, in qualitative agreement with neoclassical tearing modes (<span style="font-style:italic;">m</span> and <span style="font-style:italic;">n</span> are the poloidal and toroidal mode numbers, respectively). In addition, 2,1 tearing modes are most likely to destabilize when <span style="font-style:italic;">n</span> > 1 tearing modes are already present in the core plasma. The covariance matrix of tearing sensitive plasma parameters takes a nearly block-diagonal form, with the blocks incorporating thermodynamic, current and safety factor profile, separatrix shape, and plasma flow parameters, respectively. This suggests a number of paths to improved stability at fixed pressure and edge safety factor primarily by preserving a minimum of 1 kHz differential rotation, increasing the minimum safety factor above unity, using upper single null magnetic configuration, and reducing the core impurity radiation. In addition, lower triangularity, lower elongation, and lower pedestal pressure may also help to improve stability. The electron and ion temperature, collisionality, resistivity, internal inductance, and the parallel current gradient appear to only weakly correlate with the 2,1 tearing mode onsets in this database.</span>30909250510.1063/5.0165859https://pubs.aip.org/aip/pop/article/30/9/092505/2909948/Empirical-probability-and-machine-learningA simulation study of electron-scale turbulence generation by nonlinear wave–wave interaction in laser-produced plasmas
https://pubs.aip.org/aip/pop/article/30/9/092107/2909947/A-simulation-study-of-electron-scale-turbulence
Thu, 07 Sep 2023 00:00:00 GMT<span class="paragraphSection">A laboratory simulation of a model based on the nonlinear interaction of plasma waves is presented to study the electron-scale magnetic turbulence in the magnetized plasma. In this perspective, the model equations of the Trivelpiece–Gould (TG) mode and extraordinary mode (pump wave) are developed, taking the relativistic change in electron mass and the ponderomotive force into account. Laboratory simulations utilizing the pseudo-spectral method along with the predictor–corrector scheme and finite difference method are performed to solve the formulated coupled model equations. The propagation angle ( θ ) of the TG mode from the magnetic field affects the dispersive properties of the dynamics (TG mode), which, in turn, impact the density perturbation, scale size of the filamentary structures, density harmonics, magnetic field enhancement, and the spectral index of the turbulence generation. The simulation results reveal that the observed turbulent spectra resemble the magnetic turbulence reported in various studies of the interaction of the intense laser with plasma at the laboratory astrophysics scale relevant to astrophysical events. A simplified model in the paraxial limit is also given to understand the effect of the propagation direction (angle of propagation <span style="font-style:italic;">θ</span>) of the TG mode on the localized structures of the pump laser beam in the magnetized plasma.</span>30909210710.1063/5.0166871https://pubs.aip.org/aip/pop/article/30/9/092107/2909947/A-simulation-study-of-electron-scale-turbulenceEvolution and hot electron generation of laser–plasma instabilities in direct-drive inertial confinement fusion
https://pubs.aip.org/aip/pop/article/30/9/092701/2909946/Evolution-and-hot-electron-generation-of-laser
Thu, 07 Sep 2023 00:00:00 GMT<span class="paragraphSection">A series of 2D in-plane plane wave particle-in-cell simulations find distinctive paths of laser-plasma instability evolution in OMEGA-scale implosions, depending on the initial electron temperature. At low temperatures, two-plasmon decay (TPD) dominates in both initial growth and the steady state. At high temperatures, the initial dominant modes switch to stimulated Raman scattering, but TPD still dominates a steady state characterized by cavitation and Langmuir turbulence. A hot electron scaling is also obtained from the simulations that, when combined with laser/plasma conditions from hydro simulations, can predict hot electron generation in implosions that do not employ smoothing-by-spectral-dispersion (SSD). It also shows that under the same laser/plasma conditions, SSD can reduce hot electron generation.</span>30909270110.1063/5.0161865https://pubs.aip.org/aip/pop/article/30/9/092701/2909946/Evolution-and-hot-electron-generation-of-laserBounce-averaged drifts: Equivalent definitions, numerical implementations, and example cases
https://pubs.aip.org/aip/pop/article/30/9/093901/2909931/Bounce-averaged-drifts-Equivalent-definitions
Thu, 07 Sep 2023 00:00:00 GMT<span class="paragraphSection">In this article, we provide various analytical and numerical methods for calculating the average drift of magnetically trapped particles across field lines in complex geometries, and we compare these methods against each other. To evaluate bounce integrals, we use a generalization of the trapezoidal rule which is able to circumvent integrable singularities. We contrast this method with more standard quadrature methods in a parabolic magnetic well and find that the computational cost is significantly lower for the trapezoidal method, though at the cost of accuracy. With numerical routines in place, we next investigate conditions on particles which cross the computational boundary, and we find that important differences arise for particles affected by this boundary, which can depend on the specific implementation of the calculation. Finally, we investigate the bounce-averaged drifts in the optimized stellarator NCSX. From investigating the drifts, one can readily deduce important properties, such as what subset of particles can drive trapped-particle modes and in what regions radial drifts are most deleterious to the stability of such modes.</span>30909390110.1063/5.0160282https://pubs.aip.org/aip/pop/article/30/9/093901/2909931/Bounce-averaged-drifts-Equivalent-definitionsObservations of plasma waves generated by charged space objects
https://pubs.aip.org/aip/pop/article/30/9/092106/2909887/Observations-of-plasma-waves-generated-by-charged
Wed, 06 Sep 2023 00:00:00 GMT<span class="paragraphSection">A sampling of the environment around inert space objects has determined, which linear and nonlinear waves are created by moving space debris of all sizes. Plasma waves excited by satellites and space debris moving through the Earth's plasma in low earth orbit have been measured with <span style="font-style:italic;">in situ</span> electric field sensors on other satellites. These orbit driven plasma waves are of interest for proximity detection of space debris and sources of electrostatic and electromagnetic noise on spacecraft. Satellites and other space objects moving through the near-earth ionosphere between 200 and 1000 km altitude become electrically charged by both electron collection and photo emission in sunlight. These hypersonic, charged objects can excite a wide range of plasma waves. Measurements with the Radio Receiver Instrument (RRI) on the Swarm-E satellite have shown that electromagnetic plasma waves from known objects can be observed out to ranges of tens of kilometers. The amplitude, spectral, and polarization changes of the RRI data are consistent with electromagnetic, compressional Alfvén waves launched by charged space objects traveling across magnetic field lines. In addition, electrostatic lower hybrid waves or nonlinear ion acoustic pinned oscillations may have been self-generated and measured on the Swarm-E satellite. It is proposed that measurements of these waves with local electric field measurements or remote electromagnetic wave scatter may be useful to design systems for the location of orbiting objects. Spatial and temporal details of spacecraft charging are key to understanding the extent of waves associated with the object motion in space plasmas.</span>30909210610.1063/5.0155454https://pubs.aip.org/aip/pop/article/30/9/092106/2909887/Observations-of-plasma-waves-generated-by-chargedElectron inertia effects in 3D hybrid-kinetic collisionless plasma turbulence
https://pubs.aip.org/aip/pop/article/30/9/092302/2909879/Electron-inertia-effects-in-3D-hybrid-kinetic
Wed, 06 Sep 2023 00:00:00 GMT<span class="paragraphSection">The effects of the electron inertia on the current sheets that are formed out of kinetic turbulence are relevant to understand the importance of coherent structures in turbulence and the nature of turbulence at the dissipation scales. We investigate this problem by carrying out 3D hybrid-kinetic Particle-in-Cell simulations of decaying kinetic turbulence with our CHIEF code. The main distinguishing feature of this code is an implementation of the electron inertia without approximations. Our simulation results show that the electron inertia plays an important role in regulating and limiting the largest values of current density in both real and wavenumber Fourier space, in particular, near and, unexpectedly, even above electron scales. In addition, the electric field associated with the electron inertia dominates most of the strongest current sheets. The electron inertia is thus important to accurately describe the properties of current sheets formed in turbulence at electron scales.</span>30909230210.1063/5.0148818https://pubs.aip.org/aip/pop/article/30/9/092302/2909879/Electron-inertia-effects-in-3D-hybrid-kineticPlasma flows during the ablation stage of an over-massed pulsed-power-driven exploding planar wire array
https://pubs.aip.org/aip/pop/article/30/9/092104/2909871/Plasma-flows-during-the-ablation-stage-of-an-over
Wed, 06 Sep 2023 00:00:00 GMT<span class="paragraphSection">We characterize the plasma flows generated during the ablation stage of an over-massed exploding planar wire array, fielded on the COBRA pulsed-power facility (1 MA peak current, 250 ns rise time). The planar wire array is designed to provide a driving magnetic field ( 80 – 100 T) and current per wire distribution (about 60 kA), similar to that in a 10 MA cylindrical exploding wire array fielded on the Z machine. Over-massing the arrays enables continuous plasma ablation over the duration of the experiment without implosion. The requirement to over-mass on the Z machine necessitates wires with diameters of 75 – 100 μ m, which are thicker than wires usually fielded on wire array experiments. To test ablation with thicker wires, we perform a parametric study by varying the initial wire diameter between 33 and 100 <span style="font-style:italic;">μ</span>m. The largest wire diameter (100 <span style="font-style:italic;">μ</span>m) array exhibits early closure of the cathode-wire gap, while the gap remains open over the duration of the experiment for wire diameters between 33 and 75 <span style="font-style:italic;">μ</span>m. Laser plasma interferometry and time-gated extreme-ultraviolet (XUV) imaging are used to probe the plasma flows ablating from the wires. The plasma flows from the wires converge to generate a pinch, which appears as a fast-moving ( V ≈ 100 kms − 1) column of increased plasma density ( n ¯ e ≈ 2 × 10 18 cm − 3) and strong XUV emission. Finally, we compare the results with three-dimensional resistive-magnetohydrodynamic (MHD) simulations performed using the code GORGON, the results of which reproduce the dynamics of the experiment reasonably well.</span>30909210410.1063/5.0160893https://pubs.aip.org/aip/pop/article/30/9/092104/2909871/Plasma-flows-during-the-ablation-stage-of-an-overSPARC as a platform to advance tokamak science
https://pubs.aip.org/aip/pop/article/30/9/090601/2909870/SPARC-as-a-platform-to-advance-tokamak-science
Wed, 06 Sep 2023 00:00:00 GMT<span class="paragraphSection">The unique capabilities of the SPARC tokamak mean that it has the potential to contribute significantly to tokamak science and plasma physics, motivating further collaboration and broader data access beyond the CFS and MIT teams. SPARC is a compact, high-field tokamak that is currently under construction and is predicted to achieve burning plasma conditions once in operation. SPARC experimental data has the potential to advance the understanding of many aspects of tokamak physics, including but not limited to confinement and stability at high field and high density, burning plasma physics, disruption physics, and boundary physics and heat flux management in power plant-relevant conditions. The SPARC team is already a combination of members from Commonwealth Fusion Systems (CFS), a privately funded company, and the Massachusetts Institute of Technology (MIT), a non-profit university. This article describes the opportunities for the SPARC team to work with other researchers to advance toward a fusion power plant on the fastest possible time scales and to simultaneously broaden scientific understanding of plasma physics, meeting the missions of both CFS and academic partners.</span>30909060110.1063/5.0162457https://pubs.aip.org/aip/pop/article/30/9/090601/2909870/SPARC-as-a-platform-to-advance-tokamak-scienceGeneral dispersion relations for resistive wall modes in tokamaks
https://pubs.aip.org/aip/pop/article/30/9/092504/2909849/General-dispersion-relations-for-resistive-wall
Wed, 06 Sep 2023 00:00:00 GMT<span class="paragraphSection">The dispersion relation for the resistive wall modes (RWMs) is derived without the use of the trial function b H F proposed in S. W. Haney and J. P. Freidberg [Phys. Fluids B <strong>1</strong>, 1637 (1989)] for the magnetic perturbation b outside the plasma. Another difference from the Haney–Freidberg (HF) approach is the incorporation of non-ideal effects in the plasma description. These enter the final result through the energy functional and affect the external solution for b through the boundary conditions only. This allows to perform the derivations in a general form without constraints on the dissipation mechanisms in the plasma. Then, the main mathematical difficulties are related to the description of the energy flow outside the plasma. This part of the task is presented with details allowing easy comparisons with the reference HF case. Being universally applicable, the resulting dispersion relation covers the existing variants, including those based on the so-called kinetic approaches. It shows that, because of its integral nature, the same predictions can be expected from various models for the plasma. Another conclusion is that, with a non-ideal contribution, just one or two free parameters would be enough to get agreement with experimental data on the plasma stability boundary. This, however, does not guarantee that the same choice of the fitting coefficients will be similarly efficient on other devices. The proposed relations provide a unified approach to the problem of plasma stability against RWMs.</span>30909250410.1063/5.0159762https://pubs.aip.org/aip/pop/article/30/9/092504/2909849/General-dispersion-relations-for-resistive-wallKinetic theory for spin-polarized relativistic plasmas
https://pubs.aip.org/aip/pop/article/30/9/093102/2909847/Kinetic-theory-for-spin-polarized-relativistic
Wed, 06 Sep 2023 00:00:00 GMT<span class="paragraphSection">The investigation of spin and polarization effects in ultra-high intensity laser–plasma and laser–beam interactions has become an emergent topic in high-field science recently. In this paper, we derive a relativistic kinetic description of spin-polarized plasmas, where quantum-electrodynamics effects are taken into account via Boltzmann-type collision operators under the local constant field approximation. The emergence of anomalous precession is derived from one-loop self-energy contributions in a strong background field. We are interested, in particular, in the interplay between radiation reaction effects and the spin polarization of the radiating particles. For this, we derive equations for spin-polarized quantum radiation reaction from moments of the spin-polarized kinetic equations. By comparing with the classical theory, we identify and discuss the spin-dependent radiation reaction terms and radiative contributions to spin dynamics.</span>30909310210.1063/5.0165836https://pubs.aip.org/aip/pop/article/30/9/093102/2909847/Kinetic-theory-for-spin-polarized-relativisticOptical probing of magnet-induced transparent over-dense plasma in a whistler mode
https://pubs.aip.org/aip/pop/article/30/9/092105/2909843/Optical-probing-of-magnet-induced-transparent-over
Wed, 06 Sep 2023 00:00:00 GMT<span class="paragraphSection">For the first time, optical probing of the highly magnetized over-dense plasma in a whistler mode is theoretically investigated, where the over-dense plasma becomes magnet-induced transparent (MIT) for right hand circularly polarized laser when the electron cyclotron frequency is higher than laser frequency. Applications of the popular optical diagnostics technologies (i.e., absorption, interferometry, shadowgraphy, and schlieren imaging) in the MIT plasma are studied in the measurement of plasma density, temperature, and strength of magnetic field. The “normal” Faraday rotation is expanded to region of <span style="font-style:italic;">B</span> > 1 (B is the dimensionless magnetic field) for both over-dense plasma (<span style="font-style:italic;">n</span> > 1, n is the dimensionless plasma density) and under-dense plasma (<span style="font-style:italic;">n</span> < 1). For probing laser with higher intensity as to be able to heat up plasma collisionally, the power transmission is increased and intense laser is found to deposit more energy in the region of higher plasma density or weaker magnetic field.</span>30909210510.1063/5.0156320https://pubs.aip.org/aip/pop/article/30/9/092105/2909843/Optical-probing-of-magnet-induced-transparent-overInfluence of ambient pressure and laser energy on the plasma dynamics and parameters of laser-irradiated polyvinyl chloride
https://pubs.aip.org/aip/pop/article/30/9/093503/2909842/Influence-of-ambient-pressure-and-laser-energy-on
Wed, 06 Sep 2023 00:00:00 GMT<span class="paragraphSection">The dependence of propulsion performance generated by laser ablation of polyvinyl chloride on laser energy and pressure is investigated using Q-switched Nd: YAG laser with the wavelength of 1064 nm. When the pressure is decreased, the impulse and coupling coefficient rise first and then decline. Such a trend is also reflected in the variation of coupling coefficient with laser energy in the whole pressure range. However, the change in impulse with laser energy at atmospheric pressure is not completely consistent with that at low pressure levels. The dynamic behavior and duration of plasma plume are considered to be the factors for the difference in propulsion performance. By capturing the fast exposure images of plume, the separation at atmospheric pressure and severe expansion accompanied by rapid quenching in near vacuum are observed. Moreover, the plasma plume lasts longer time at high pressures. It is ascribed to the higher electron temperature, which promotes background gas to excite and ionize. Since the electron density increases with the improvement of laser energy and pressure, the absorption of electrons to laser energy becomes stronger through the inverse bremsstrahlung mechanism. Accordingly, the shielding effect of plasma is enhanced, causing the weak laser-target interaction. The result is that the crater depth and ablative mass increase with decreasing pressure. This work is important for understanding the energy conversion mechanism and optimizing the laser propulsion performance.</span>30909350310.1063/5.0152768https://pubs.aip.org/aip/pop/article/30/9/093503/2909842/Influence-of-ambient-pressure-and-laser-energy-onInvestigation of spatial distribution of EEPFs and neutral species in nitrogen inductively coupled plasmas by 2D hybrid simulation
https://pubs.aip.org/aip/pop/article/30/9/093502/2909546/Investigation-of-spatial-distribution-of-EEPFs-and
Tue, 05 Sep 2023 00:00:00 GMT<span class="paragraphSection">Neutral species in nitrogen plasmas play a crucial role in many applications related to semiconductor fabrication. In this research, a two-dimensional fluid/electron Monte Carlo hybrid model is employed to simulate nitrogen inductively coupled plasmas, and the spatial distributions of electron energy probability distributions (EEPFs), as well as their influence on the neutral species, are discussed under various pressures. It is found that the EEPF in the bulk region is relatively uniform, and it exhibits a bi-Maxwellian distribution at 3 mTorr. As pressure increases, the high energy tail declines due to the more frequent collisions. Moreover, a hole appears at around 3 eV in the EEPF above the substrate, and it becomes less obvious toward the skin layer below the dielectric window. Moreover, the maxima of metastable species densities, i.e., N 2 ( A 3 Σ u + ), N ( 2 D ), and N ( 2 P ), are located at the center of the chamber at low pressure, and they gradually move to the skin layer under the coils as pressure increases. The behaviors of neutral species can be understood by examining the reactant densities of the main generation and loss mechanisms, as well as the corresponding rate coefficients which are calculated according to EEPFs. In addition, since the ground state N ( 4 S ) is mainly produced by the quenching of metastable atoms and neutralization of ions at the walls, the maximum of the N ( 4 S ) density appears below the dielectric window and above the substrate at 3 mTorr, and the peak under the dielectric window becomes more obvious at higher pressure due to the stronger locality.</span>30909350210.1063/5.0159577https://pubs.aip.org/aip/pop/article/30/9/093502/2909546/Investigation-of-spatial-distribution-of-EEPFs-andPolarization and properties of low-frequency waves in warm magnetized two-fluid plasma
https://pubs.aip.org/aip/pop/article/30/9/092901/2909541/Polarization-and-properties-of-low-frequency-waves
Tue, 05 Sep 2023 00:00:00 GMT<span class="paragraphSection">This paper presents the derivation of a general wave dispersion relation for warm magnetized plasma under the two-fluid formalism. The discussion is quite general except for the assumption of low frequency and slow phase speed, for which the displacement current is negligible, under the implicit assumption that the plasma is sufficiently dense to satisfy the condition ω p e > ω c e, where <span style="font-style:italic;">ωpe</span> and <span style="font-style:italic;">ωce</span> denote the plasma oscillation frequency and electron gyro frequency, respectively. The present discussion does not invoke charge neutrality associated with the fluctuations although it is implicitly satisfied. The resulting dispersion relation that includes the fluid thermal effects shows that there are three eigen modes, which include those corresponding to ideal MHD, namely, fast, slow, and kinetic Alfvén waves, as well as higher-frequency modes including the ion and electron cyclotron and lower-hybrid resonances. The fluid effects in the ideal MHD wave branches are influenced by the finite Larmor radius scales, and when the wave number in the cross field direction is comparable to these values, the fluid effects become significant. It is found that the Larmor radius should be interpreted in the sense as ion-acoustic gyro-radius instead of ion thermal gyro radius only. That is, it is found that the electrons also contribute to the non-ideal effect associated with the kinetic Alfvén wave. A comprehensive explanation of the polarization of each mode is also presented. The present findings indicate that the polarity may change its sign only for the kinetic Alfvén mode branch and that such a transition is based on the propagation angle. When such a change does take place, it is found that the kinetic Alfvén wave transits to an ion-acoustic mode. For each branch, it is also found that the electric field along the ambient magnetic field is purely transverse.</span>30909290110.1063/5.0149227https://pubs.aip.org/aip/pop/article/30/9/092901/2909541/Polarization-and-properties-of-low-frequency-wavesHot spots of the main limiter induced by fast ions in experimental advanced superconducting tokamak (EAST)
https://pubs.aip.org/aip/pop/article/30/9/092503/2909346/Hot-spots-of-the-main-limiter-induced-by-fast-ions
Fri, 01 Sep 2023 00:00:00 GMT<span class="paragraphSection">The main limiter in EAST was observed to endure a high heat load and was cracked near the midplane at the right side during the plasma operation. To explore the heat load carried by fast ion loss toward the main limiter, the neutral beam injection (NBI) and radio frequency power proportion experiment was conducted in EAST where the plasma stored energy and line integrated density were kept almost constant. The hot spot at the right side of the main limiter was observed to be enhanced by co-current perpendicular (co-perp) NBI. An NBI ion loss simulation was performed in the presence of the toroidal field ripple and the Coulomb collision by using the orbit code GYCAVA and the NBI code TGCO. The result indicates that the NBI ion loss by ripple and collision mainly causes a bright area below the midplane of the right side of the main limiter as observed in the EAST experiment. The peak heat load of lost fast ions generated by co-perp NBI is ∼0.5 MW/m<sup>2</sup> as obtained by 1 MW of NBI deposited power and comparable with the heat load carried by fast electrons induced by lower hybrid current drive. In addition, increasing the gap between the separatrix and the first-wall limiters in the simulation is found to reduce this heat load.</span>30909250310.1063/5.0156815https://pubs.aip.org/aip/pop/article/30/9/092503/2909346/Hot-spots-of-the-main-limiter-induced-by-fast-ionsStudy of trigger mechanisms of a pseudospark switch configuration with a steady-state auxiliary glow discharge
https://pubs.aip.org/aip/pop/article/30/9/093501/2909326/Study-of-trigger-mechanisms-of-a-pseudospark
Fri, 01 Sep 2023 00:00:00 GMT<span class="paragraphSection">This paper presents data on investigation of the pseudospark switch whose trigger unit uses a low-current auxiliary glow discharge with hollow cathode and hollow anode. The electrode system of this unit communicates with the main high-voltage gap of the switch due to the aperture in the flat part of one of the trigger electrodes. It is shown that when the electrode with the aperture plays of role of the hollow cathode of the auxiliary discharge, a low parasitic current through the aperture is provided by the ion flow. This ion current does not practically influence on the static breakdown voltage of the main gap. Applying the trigger pulse between the trigger electrodes leads to the pulsed trigger discharge with an enhanced current. At a negative polarity of the trigger pulse, the cavity with aperture turns out into the hollow anode so that the current is able to be intercepted through the aperture to the grounded cavity of the main gap. The plasma is generated in the cavity and the switch is triggered. With the proper selection of the geometry of the trigger electrodes, the delay time to trigger at a level of several tens of nanoseconds is achievable.</span>30909350110.1063/5.0155949https://pubs.aip.org/aip/pop/article/30/9/093501/2909326/Study-of-trigger-mechanisms-of-a-pseudosparkBifurcation of coherent vortex flow in a magnetic island through nonlinear parity instability
https://pubs.aip.org/aip/pop/article/30/9/092103/2909325/Bifurcation-of-coherent-vortex-flow-in-a-magnetic
Fri, 01 Sep 2023 00:00:00 GMT<span class="paragraphSection">The topology of the vortex flow associated with the magnetic island plays a significant role in modulating the turbulent transport near the magnetic island. In this paper, self-consistent nonlinear simulations of multi-scale interactions among large scale tearing mode, vortex flow, and small scale ion temperature-gradient (ITG) mode are numerically investigated based on the five-field Landau-fluid model. We found that the coherent vortex flow in a magnetic island has different parities in the nonlinear quasi-steady state, and this can be described by a theoretical framework—nonlinear parity instability. In the ITG stable case, the structure of the vortex flow bifurcates from tearing parity to twisting parity, which is characterized by modulational parity instability, modeled by a four-wave nonlinear coupling process. In the ITG unstable case, the vortex flow stays in tearing parity without parity bifurcation, and the energy is transferred from the twisting parity modes to the tearing parity modes. The impact of the parity instability on the magnetic island width is discussed as well.</span>30909210310.1063/5.0161167https://pubs.aip.org/aip/pop/article/30/9/092103/2909325/Bifurcation-of-coherent-vortex-flow-in-a-magneticReversed Cherenkov radiation amplifier with compact structure and high efficiency
https://pubs.aip.org/aip/pop/article/30/9/093301/2909324/Reversed-Cherenkov-radiation-amplifier-with
Fri, 01 Sep 2023 00:00:00 GMT<span class="paragraphSection">Based on the reversed Cherenkov radiation excited in metamaterials, a novel S-band reversed Cherenkov radiation amplifier (RCRA) with two output ports is proposed in this paper. Its metamaterial slow-wave structure (MSWS) consists of a hollow circular waveguide periodically loaded with all-metal double-ridge complementary electric split-ring resonators (CeSRRs). The CeSRR exhibits subwavelength and strong resonance characteristics, which lead to miniaturization and high interaction impedance of the MSWS. The period of the MSWS is optimized using the phase velocity jump technique to further increase the output power and electronic efficiency. The simulation results demonstrate that when the microwave signal of 7.8 W at 2.286 GHz is inputted at port 2, the output power at port 1 is 307 W, and the saturated output power and saturated gain at port 3 are 5.48 kW and 28.47 dB, respectively. Notably, the total electronic efficiency of the RCRA is predicted as 33.84%. The RCRA features high electronic efficiency and miniaturization and may meet special application scenarios that require two output microwave signals at the same frequency.</span>30909330110.1063/5.0159757https://pubs.aip.org/aip/pop/article/30/9/093301/2909324/Reversed-Cherenkov-radiation-amplifier-withA physics-informed deep learning model of the hot tail runaway electron seed
https://pubs.aip.org/aip/pop/article/30/9/092501/2909323/A-physics-informed-deep-learning-model-of-the-hot
Fri, 01 Sep 2023 00:00:00 GMT<span class="paragraphSection">A challenging aspect of the description of a tokamak disruption is evaluating the hot tail runaway electron seed that emerges during the thermal quench. This problem is made challenging due to the requirement of describing a strongly non-thermal electron distribution, together with the need to incorporate a diverse range of multiphysics processes, including magnetohydrodynamic instabilities, impurity transport, and radiative losses. This work develops a physics-informed neural network (PINN) tailored to the solution of the hot tail seed during an axisymmetric thermal quench. Here, a PINN is developed to identify solutions to the adjoint relativistic Fokker–Planck equation in the presence of a rapid quench of the plasma's thermal energy. It is shown that the PINN is able to accurately predict the hot tail seed across a range of parameters, including the thermal quench timescale, initial plasma temperature, and local current density, in the absence of experimental or simulation data. The hot tail PINN is verified by comparison with direct Monte Carlo simulations, with excellent agreement found across a broad range of thermal quench conditions.</span>30909250110.1063/5.0164712https://pubs.aip.org/aip/pop/article/30/9/092501/2909323/A-physics-informed-deep-learning-model-of-the-hotForeword to special issue: Papers from the 64th Annual Meeting of the APS Division of Plasma Physics, October 17–21, 2022
https://pubs.aip.org/aip/pop/article/30/9/090401/2909322/Foreword-to-special-issue-Papers-from-the-64th
Fri, 01 Sep 2023 00:00:00 GMT<span class="paragraphSection">The 64th Annual Meeting of the APS Division of Plasma Physics (DPP) was held October 17–21, 2022 in Spokane, Washington at the Spokane Convention Center. More than 1800 physicists attended, safely, in-person. With both virtual and on-site participants, discussions were lively, and the research presentations shared the most exciting developments in the modern observation, theory, simulation, and manipulation of plasma. The presentations included four invited review talks, 98 invited talks, four tutorials, and four presentations from this year's prize and award recipients. There were 1149 contributed poster presentations and 945 contributed oral presentations. Including both in-person and remote attendees, DPP 2022 had a record 2232 participants. In keeping with APS guidance for hybrid meetings, in-person presentations of all invited presentations were broadcast live and were accompanied by a Q&A discussion. All contributed oral presentations were live-streamed and poster presentations were prerecorded along with options to schedule in-person discussions on demand. Six mini-conferences were held: “<span style="font-style:italic;">Heating and Non-Thermal Particle Acceleration during Magnetic Reconnection in Laboratory,</span>” “<span style="font-style:italic;">Public-Private Partnerships for Fusion Energy,</span>” “<span style="font-style:italic;">Workforce Development Through Research-Based, Plasma-Focused Science Education and Public Engagement,</span>” “<span style="font-style:italic;">Charged Particle Transport in High-Energy-Density Plasma,</span>” “<span style="font-style:italic;">The Integrated Tokamak Exhaust and Performance Gap,</span>” and “<span style="font-style:italic;">Relativistic Plasma Physics in Supercritical Fields.</span>” Building on the success of last year's “Student Day,” Sunday afternoon's session “for students, by students” included lightning talks, plasma trivia, and an informal occasion to connect with other students, learn how to get the most from the DPP Annual Meeting, and share successful ways to connect with colleagues and advance their professional careers.</span>30909040110.1063/5.0169071https://pubs.aip.org/aip/pop/article/30/9/090401/2909322/Foreword-to-special-issue-Papers-from-the-64thRadiative cooling effects on reverse shocks formed by magnetized supersonic plasma flows
https://pubs.aip.org/aip/pop/article/30/9/092102/2909321/Radiative-cooling-effects-on-reverse-shocks-formed
Fri, 01 Sep 2023 00:00:00 GMT<span class="paragraphSection">We study the structure of reverse shocks formed by the collision of supersonic, magnetized plasma flows driven by an inverse (or exploding) wire array with a planar conducting obstacle. We observe that the structure of these reverse shocks varies dramatically with wire material, despite the similar upstream flow velocities and mass densities. For aluminum wire arrays, the shock is sharp and well-defined, consistent with magneto-hydrodynamic theory. In contrast, we do not observe a well-defined shock using tungsten wires, and instead we see a broad region dominated by density fluctuations on a wide range of spatial scales. We diagnose these two very different interactions using interferometry, Thomson scattering, shadowgraphy, and a newly developed imaging refractometer that is sensitive to small deflections of the probing laser corresponding to small-scale density perturbations. We conclude that the differences in shock structure are most likely due to radiative cooling instabilities, which create small-scale density perturbations elongated along magnetic field lines in the tungsten plasma. These instabilities grow more slowly and are smoothed by thermal conduction in the aluminum plasma.</span>30909210210.1063/5.0160809https://pubs.aip.org/aip/pop/article/30/9/092102/2909321/Radiative-cooling-effects-on-reverse-shocks-formedNon-linear dynamics of the double tearing mode
https://pubs.aip.org/aip/pop/article/30/9/092502/2909302/Non-linear-dynamics-of-the-double-tearing-mode
Fri, 01 Sep 2023 00:00:00 GMT<span class="paragraphSection">3D non-linear magnetohydrodynamics simulations of a double tearing mode with the JOREK code are presented in the context of trying to better understand the benign termination of runaway electron beams observed in some experiments. It is shown that the non-linear behavior qualitatively depends on the resistivity <span style="font-style:italic;">η</span> via its effect on how fast secondary, non-linearly destabilized, tearing modes grow relative to the primary mode. Within a certain range of <span style="font-style:italic;">η</span>, a violent and global relaxation is observed, consistent with the “Kadomtsev-predicted” reconnection region extending from almost the very center up to the edge of the plasma.</span>30909250210.1063/5.0162608https://pubs.aip.org/aip/pop/article/30/9/092502/2909302/Non-linear-dynamics-of-the-double-tearing-modeElectron heat flux and propagating fronts in plasma thermal quench via ambipolar transport
https://pubs.aip.org/aip/pop/article/30/9/092301/2909301/Electron-heat-flux-and-propagating-fronts-in
Fri, 01 Sep 2023 00:00:00 GMT<span class="paragraphSection">The thermal collapse of a nearly collisionless plasma interacting with a cooling spot, in which the electron parallel heat flux plays an essential role, is both theoretically and numerically investigated. We show that such thermal collapse, which is known as thermal quench in tokamaks, comes about in the form of propagating fronts, originating from the cooling spot, along magnetic field lines. The slow fronts, propagating with local ion sound speed, limit the aggressive cooling of plasma, which is accompanied by a plasma cooling flow toward the cooling spot. The extraordinary physics underlying such a cooling flow is that the fundamental constraint of ambipolar transport along the field line limits the spatial gradient of electron thermal conduction flux to the much weaker convective scaling, as opposed to the free-streaming scaling, so that a large electron temperature and, hence, pressure gradient can be sustained. The last ion front for a radiative cooling spot is a shock front where cold but flowing ions meet hot ions.</span>30909230110.1063/5.0163411https://pubs.aip.org/aip/pop/article/30/9/092301/2909301/Electron-heat-flux-and-propagating-fronts-inA magnetically insulated coaxial vacuum diode providing a reduced energy spread in the leading edge of a high-current electron beam
https://pubs.aip.org/aip/pop/article/30/9/093101/2909300/A-magnetically-insulated-coaxial-vacuum-diode
Fri, 01 Sep 2023 00:00:00 GMT<span class="paragraphSection">A magnetically insulated vacuum diode was modified to reduce the fraction of low-energy electrons in the leading edge of a high-current beam. The voltage pulse of duration ≈1 ns, rise time ≈250 ps, and amplitude ≈ –230 kV that arrives at the diode cathode from a transmission line is split in coupled coaxial lines (CLs) into two pulses with an amplitude ratio <span style="font-style:italic;">U</span><sub>2</sub>/<span style="font-style:italic;">U</span><sub>1</sub> >1. The end of the common electrode of the CLs is close in profile to an equipotential surface and forms two gaps in the diode. In the first injection gap, at <span style="font-style:italic;">U</span><sub>0</sub> < <span style="font-style:italic;">U</span><sub>1</sub>, explosive electron emission starts at the cathode. The pulse <span style="font-style:italic;">U</span><sub>1</sub> arrives here with a delay at least equal to the duration of the leading edge, since there is a dielectric insert in the inner CL. The beam enters, through the window in the intermediate electrode, the acceleration gap, where the leading pulse <span style="font-style:italic;">U</span><sub>2</sub>, delivered from the outer CL, has already peaked. In the proposed device, unlike the one-gap prototype diode, electrons start from the cathode at a much smaller spread of the leading edge voltage. As a result, after acceleration of these electrons in the second gap, their energy spread relative to the maximum energy decreases multiply. This is confirmed by calculations and measurements of the beam current for a beam passed through aluminum filters.</span>30909310110.1063/5.0161097https://pubs.aip.org/aip/pop/article/30/9/093101/2909300/A-magnetically-insulated-coaxial-vacuum-diodePropagation of short-wavelength electromagnetic surface waves along the transition layer between two plasma-like half-spaces in the Voigt geometry
https://pubs.aip.org/aip/pop/article/30/9/092101/2909295/Propagation-of-short-wavelength-electromagnetic
Fri, 01 Sep 2023 00:00:00 GMT<span class="paragraphSection">The dispersion properties of surface type electromagnetic waves are studied. The waves are considered to propagate along a slab transition layer located between two infinite homogeneous plasma regions of different particle densities. The wavelength is assumed to be short as compared with the layer width. The waves propagate across a static magnetic field, which is parallel to the layer interface. The influence of the smoothness of the gradient of the plasma particle density within the layer on the surface wave propagation/disappearance is discussed. The conclusions derived in the present paper are of interest in the fields of plasma electronics, nano-technologies, plasma-antenna systems, plasma production, and magnetic confinement fusion.</span>30909210110.1063/5.0165416https://pubs.aip.org/aip/pop/article/30/9/092101/2909295/Propagation-of-short-wavelength-electromagnetic