Current re-distribution in an experiment of magnetic flux compression by an imploding plasma*

This talk 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.
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 (B_z0) has a dramatic effect on the implosion dynamics affecting significantly the current distribution in the plasma. It was found that in the presence of B_z 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 B_z0. 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.