On 23rd October 2019, our Laboratory member Marko Cvejić held an open lecture at the Institute of Physics Belgrade. The lecture was “Challenges in the investigation of compression of magnetized plasma“, where he presented his results obtained at the Weizmann Institute of Science.
The seminar will refer to a compression of magnetic flux that is initially embedded in a plasma that undergoes an implosion. The plasma is produced in a Z-pinch configuration in which a gas puff load is ionized and implodes under the J×B forces resulting from a 1-μs long, 300 kA, current pulse.
The subject of compression of magnetic flux and magnetized plasma is a fundamental problem manifested in a variety of conducting fluid phenomena in laboratory plasmas and astrophysics. Recently, this subject has gained particular interest due to the advances in producing plasmas of high temperature and density for fusion purposes, based on the approach of magnetized plasma compression.
We report the first-time development and employment of spectroscopic methods, based on the Zeeman effect and polarization techniques, to measure both the compressed (axial) and the compressing (azimuthal) magnetic fields throughout the implosion and stagnation processes.
Time and space resolved spectroscopic measurements showed that the application of a relatively weak axial magnetic field (Bz0) has a dramatic effect on the implosion dynamics affecting significantly the current distribution in the plasma . It was found that in the presence of Bz a large part of the current does not flow in the imploding plasma, rather it flows through a slow-imploding low-density plasma (LDP) residing at large radii. Furthermore, it is observed that the fraction of total current that flows in the LDP increases with Bz0.
We suggest an explanation of the phenomena, based on the development of a force-free current configuration. Previously unpredicted observations in high-power magnetized-plasma experiments, including recent unexplained structures observed in the Magnetized Liner Inertial Fusion experiment, may be connected to the present discovery.
 Mikitchuk, D., Cvejić, M., Doron, R., Kroupp, E., Stollberg, C.,
Maron, Y., Velikovich, A. L., Ouart, N. D., Giuliani, J. L., Mehlhorn,
T. A., Yu, E. P., and Fruchtman, A. “Effects of a preembedded axial
magnetic field on the current distribution in a Z-pinch implosion”,
Phys. Rev. Lett. 122, 045001 (2019).