A challenge for the TW-class accelerators driving $Z$-pinch experiments, such as Sandia National Laboratories’ $Z$ machine, is to efficiently couple power from multiple storage banks into a single multi-MA transmission line. The physical processes that lead to current loss are identified in new large-scale, multidimensional simulations of the $Z$ machine. Kinetic models follow the range of physics occurring during a pulse, from vacuum pulse propagation to charged-particle emission and magnetically-insulated current flow to electrode plasma expansion. Simulations demonstrate that current is diverted from the load through a combination of standard transport (uninsulated charged-particle flows) and anomalous transport. Standard transport occurs in regions where the electrode current density is a few $10^4-{10}^5\mathrm{A}/{\mathrm{cm}}^2$ and current is diverted from the load via transport without magnetic insulation. In regions with electrode current density $>{10}^6\mathrm{A}/{\mathrm{cm}}^2$, electrode surface plasmas develop velocity-shear instabilities and a Hall-field-related transport which scales with electron density and may, therefore, lead to increased current loss.

• Received 24 July 2019

DOI:https://doi.org/10.1103/PhysRevAccelBeams.22.120401

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Published by the American Physical Society