A foreword to the special issue: Proceedings of PLASMA 2023—International Conference on Research and Applications of Plasmas Free

Plasma physics resembles a magnificent city: vast and clustered suburbs emerge from the surrounding darkness with their glittering lights. Lamps by the roads highlight communication tracks connecting larger and larger congregates. Streets converge, and illuminations become dense so that central parts appear more and more distinctively, mesmerizing with their radiance, seducing with visions of splendor, brilliance, and opulence.

Similarly, in plasma physics, we have immense areas of research, seemingly dissolved, but all connected with phenomena occurring in the ionized gas—produced here on Earth by electric dischargers, laser beams, in flames, and in lamps, but also in infinite space, in stars, in aurora borealis. Connected by manuscripts in scientific journals, by conference talks, following the streets of increasing knowledge, they lead to several central points, which are key issues crucial for the further existence of humankind. The need for limitless and clean energy is among them, represented by the brightest castle in the city of knowledge, still invulnerable, but so magnetic and illuminating.

This is the domain that attracts the majority of scientists—thermonuclear fusion-oriented research. Plasma 2023 was the first conference after breakthroughs in both magnetic and inertial confinement fusion. At JET, the first 21st-century deuterium–tritium campaign set the record in energy released in a nuclear fusion reaction. In fact, it delivered much more: the proof of efficient plasma control in scenarios that reproduced at ITER will produce ten times more energy than needed to ignite the reaction. At NIF, a similar breakthrough has been achieved: fusion produced 3.15 MJ, which was 1.5 more than the energy of the laser beam and almost 1% of the total energy employed for firing the pulse.

To highlight these two groundbreaking achievements, the PLASMA 2023 program featured a dedicated plenary session. This session showcased presentations by leading scientists who had made substantial contributions to the experiments and provided them with a platform to address questions from both the press and the general public. Given these efforts, it is unsurprising that the majority of publications in this special issue relate to fusion research. However, this focus should not be interpreted as indicative of a narrow conference scope. On the contrary, a review of the manuscripts reveals the interdisciplinary and interconnected nature of thermonuclear fusion research and underscores the rich and diverse landscape it encompasses.

As has been stressed in the Introduction, the conference topics were dominated by thermonuclear fusion research. The most direct reference to the deuterium–tritium campaign at JET can be found in two manuscripts. The “Study of impurity behavior in JET-ILW hybrid scenario with deuterium, tritium, and deuterium–tritium plasmas” by Wendler et al.,¹ which was chosen as a Featured Article, presents important conclusions in terms of impurity influence on the development of further plasma scenarios at ITER. The research is followed by Gromelski et al., “Investigation of triangularity impact on impurity content in JET-ILW H, D, T, and DT plasmas,”² mostly contributed to the influence of the plasma shape on its content. The topic of impurity, yet in the outer plasma region, is further addressed in the paper by Grzybicka et al., “TECXY simulations of the power exhaust in the multi-impurity plasma of DTT reactor”³ in which the authors present interesting calculations for Divertor Test Tokamak being at the development at Frascati, Italy.

Even more advanced and related to a more distant future are the calculations and designs contributed to three DEMO related manuscripts. First two, by Akbas et al., “Neutron shielding calculation for DEMO-Prad/SXR measurement system”⁴ and Jagielski et al., “Magnetic field influence on electron transport in planned GEM-based radiated power diagnostic for DEMO,”⁵ bring forth designs of crucial diagnostic systems. The conceptual DEMO area of future diagnostic systems is perfectly complemented by Chernyshova et al., “Conceptual research on meeting tomographic reconstruction and measurement accuracy requirements: Key factors in the development of a radiated power diagnostics for DEMO”⁶ which provides a comprehensive insight into diagnostic systems of thermonuclear powerplant.

The topics connected with diagnostics are also important components. There is a group of three papers addressing the issues of fuel retention and the wall composition diagnostics: Wüst et al., “Depth-resolved deuterium retention analysis in displacement-damaged tungsten using laser-induced breakdown spectroscopy,”⁷ Ladygina et al., “LIBS diagnostics of Be-based samples with different gas impurities,”⁸ and Gąsior et al., “ANN based LIBS models for quasi-experimental spectra relevant for materials for next-step fusion reactors.”⁹ The last of the three introduces the application of machine learning, which starts to permeate plasma physics as it did many other scientific areas. Other aspects of laser plasma are explored in the work of Bartnik et al., “Time-resolved spectral investigation of low-temperature plasma induced in gas mixtures by laser-produced plasma or nanosecond pulses of extreme ultraviolet radiation.”¹⁰ 

Other important diagnostics are dedicated to neutrons and x-rays. These topics are present in the contributions Jardin et al., “Energy-resolved x-ray and neutron diagnostics in tokamaks: prospect for plasma parameters determination,”¹¹ Syrocki et al., “Theoretical interpretation of W soft x-ray spectra collected by the pulse height analysis system on Wendelstein 7-X stellarator,”¹² and Jabłoński et al., “X-ray tomography system concept for stellarator TJ-II.”¹³ Two of the articles concern the topic of stellarators, which is also present in Kovtun et al., “ICRF production of plasma with hydrogen minority in Uragan-2M stellarator by two-strap antenna,”¹⁴ and Langenberg et al., “Achieving stationary high performance plasmas at Wendelstein 7-X.”¹⁵ Notably, the second of these papers may be considered especially influential as it addresses the advanced plasma scenarios at the W7-X—the most cutting-edge stellarator in the world.

Equally important are manuscripts concerning materials as well as plasma phenomena resulting from interactions with them. These topics are covered in Nowakowska-Langier et al., “The study of interaction of the high energetic plasma and electron pulses with multicomponent alloy surface,”¹⁶ Pawelec et al., “Internal energy distributions of BeH, BeD, and BeT molecules created during chemically assisted physical sputtering in JET tokamak plasma,”¹⁷ and Wu et al., “Relativistic R-matrix calculations for the photoionization of W⁶¹⁺ ions.”¹⁸ Whereas the first of them describes interesting experiments with plasma produced by discharges, the following two offer excellent insight into the physics of plasma processes.

To ensure that interesting plasma physics can also be found separately from tokamaks and stellarators, there are two interesting papers on plasma-drives: Jakubczak et al., “Analysis of composition and dynamics of the plasma plume emitted by a 1 J pulsed plasma thruster fed with polytetrafluoroethylene and determination of thruster efficiency components”¹⁹ and Jardin and Lubiński, “Searching for chaotic behavior in the experimental ion current and discharge current waveforms of a Hall effect thruster.”²⁰ The last paper seasons the collection with the chaos flavor which makes the outcome utterly enthralling but still balanced.

PLASMA 2023 was undoubtedly successful in both the scientific and social aspects. The lectures and discussions facilitated the proliferation of knowledge and were reinforced by sponsors' sessions presenting advanced equipment solutions for science. Social events encouraged scientists to exchange their views and initiate or continue collaborations. The event provided a comprehensive overview of contemporary plasma physics and made the researchers aware of the challenges, such as the need for the modification of the first wall in ITER or the development of more efficient lasers for ICF. As editors, we believe that the choice of the manuscripts in this special issue reflects all main topics of the conference, and we hope that it will be enjoyed by readers.

The conference was supported by Polish Ministry of Education and Science, Grant Agreement No KONF/SN/0198/2023/01.