Electrode plasma transport into the gap of high-current Z pinch accelerators*

The transport of electrode plasmas into the gap of the inner MITL (magnetically insulated transmission line) of the high current accelerators such as Z leads to current loss and degradation of Z pinch performance.  The process of current loss across the magnetized gap in these devices has been carefully studied and attributed to a Hall mechanism proportional to plasma density and electric field.[1] Theory and simulation of the transport of electrode plasmas have focused on stability of the electron sheath emitted from a resistive cathode plasma.[2][3]   The instability of the system drives a longitudinal electric field of sufficient strength to accelerate ions leading to a fast plasma penetration into the gap.  The plasma densities reach 10¹⁴-10¹⁵ cm^-3 in several nanoseconds. Plasma ExB drift further compresses the plasma to densities exceeding 10¹⁶ cm^-3 which is sufficient to transport significant current loss.  In this paper, we describe the instability and plasma transport into the gap of a characteristic high current inner MITL with theory and detailed CHICAGO kinetic simulations.

[1] N. Bennett, D. R. Welch, G. Laity, D. V. Rose, and M. E. Cuneo, Phys. Rev. Accel. Beams 24, 060401 (2021).

[2] C. L. Chang, T. M. Antonsen Jr., E. Ott, and A. T. Drobot, Phys. Fluids 27, 2545 (1984).

[3] D. R. Welch, N. Bennett, T. C. Genoni, D. V. Rose, C. Thoma, C. Miller, and W. A. Stygar, Phys. Rev. Accel. Beams 24, 060401 (2021).