Reduced Models for Anomalous Resistivity and Vacuum Density Floors for Z-Pinch Implosions Based On Kinetic Simulations Using the Particle-in-Cell Code Chicago*

Kinetic simulations of Z-pinch implosions are prohibitively slow and expensive for high current(>20 MA) high convergence ratio( r < 1mm) experiments.  Kinetic simulations can benefit Z-pinch modeling by validating analytic models of kinetic effects which can be added to the fluid codes which can model the experiments.  Two kinetic effects that will be discussed are anomalous resistivity due to lower-hybrid-drift instabilities(LHDIs) and the vacuum density and vacuum plasma environment near the load.  Unlike ion acoustic modes or Buneman modes, LHDIs are unstable in plasmas with arbitrary temperature ratios ZT_e/T_i  and with drift speeds slower than electron thermal speeds.  They are destabilized by the relative drift in plasmas with a density gradient and are expected to be widely active in Z-pinch environments of interest.  These small-scale instabilities are modeled using the PIC code Chicago under a range of conditions relevant to Z-pinches on the Z-machine at Sandia to validate a new anomalous resistivity model for high-drift speeds and very low plasma beta.  Chicago is also used to model the low-density weakly-collisional plasmas that evolve off the surfaces of magnetically insulated transmission lines(MITLs).  These simulations are used to predict parasitic current loss in the MITLs and to estimate the vacuum quality near the Z-pinch target as this low density plasma is swept radially inward at the ExB velocity.  The target performance predicted in fluid simulations can be sensitive to the vacuum quality that is imposed upstream of the target.  Kinetic simulations can constrain these fluid simulations.