We present here the detailed measurements of radial distribution of the magnetic field in a gas-puff z-pinch plasma at the final stages of the implosion phase and at stagnation. While the measurements are chordal, the radial distribution of different charge states was utilized to measure the magnetic field locally for certain radii, so that unlike chordal measurements in general, the magnetic field radial distribution was obtained with no need for the Abel inversion of the data. The distribution was measured using the Zeeman effect via a novel spectroscopic technique, at several axial locations, and demonstrates striking features such as the peak field remaining at a radius much larger than the stagnation radius at all times. Furthermore, while the distribution observed is sometimes monotonic with respect to the radius, it is often not, a behavior that can be linked to 2D features in the plasma column resulting from the Rayleigh–Taylor instability. The current flowing through the stagnating plasma was found to be a small fraction of the total current, resulting in clearly insufficient magnetic pressure to balance the plasma pressure at stagnation. The magnetic field data, taken over several axial positions, are used to obtain the true inductance in the imploding plasma for the first time; it is found that the data cannot explain the current turnover at stagnation. A simulation with the MACH2-Tabular Collisional-Radiative Equilibrium magnetohydrodynamics code in the r–z plane shows that the peak of the magnetic field pinches to a much smaller radius than is observed in the spectroscopic data. Furthermore, the depth of the computed current turnover at stagnation is smaller than the measured one. The two observed features of a radially extended magnetic field at stagnation together with a deep current turnover are a challenge to match in simulations. Various calculations and estimates of the inductive and resistive load voltages are examined to ascertain if they are responsible for the observed current notch. The results demonstrate that the knowledge of the true inductance in the driven load requires such magnetic-field-distribution measurements and that imaging data or electrical measurements are insufficient.
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February 2020
Research Article|
February 12 2020
Local measurements of the spatial magnetic field distribution in a z-pinch plasma during and near stagnation using polarization spectroscopy
G. Rosenzweig
;
G. Rosenzweig
a)
1
Faculty of Physics, Weizmann Institute of Science
, Rehovot 7610001, Israel
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E. Kroupp
;
E. Kroupp
1
Faculty of Physics, Weizmann Institute of Science
, Rehovot 7610001, Israel
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T. Queller
;
T. Queller
1
Faculty of Physics, Weizmann Institute of Science
, Rehovot 7610001, Israel
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A. Starobinets
;
A. Starobinets
1
Faculty of Physics, Weizmann Institute of Science
, Rehovot 7610001, Israel
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Y. Maron;
Y. Maron
1
Faculty of Physics, Weizmann Institute of Science
, Rehovot 7610001, Israel
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V. Tangri
;
V. Tangri
2
Research Support Instruments
, Lanham, Maryland 20706, USA
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J. L. Giuliani
;
J. L. Giuliani
3
Plasma Physics Division, Naval Research Laboratory
, Washington, DC 20375, USA
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A. Fruchtman
A. Fruchtman
4
Department of Physics, Holon Institute of Technology
, Holon 5810201, Israel
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a)
Present address: Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, MA 02139, USA. Electronic mail: [email protected]
Phys. Plasmas 27, 022705 (2020)
Article history
Received:
September 06 2019
Accepted:
January 25 2020
Citation
G. Rosenzweig, E. Kroupp, T. Queller, A. Starobinets, Y. Maron, V. Tangri, J. L. Giuliani, A. Fruchtman; Local measurements of the spatial magnetic field distribution in a z-pinch plasma during and near stagnation using polarization spectroscopy. Phys. Plasmas 1 February 2020; 27 (2): 022705. https://doi.org/10.1063/1.5126934
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