Cathode plasma expansion in magnetically insulated transmission lines

Summary form only given. Cathode plasma expansion is a concern in MITLs such as those being developed for ZR, an upgrade of the Z machine at Sandia National Laboratories. To minimize the vacuum-region inductance, one would like to make the MITL AK gap, d, as small as possible, while avoiding a significant increase in the sheath electron current (which scales as 1/d/sup 2/) due to expansion of the cathode plasma. This is a more severe constraint than simply avoiding complete gap closure. We investigate this issue using both an MHD model and particle-in-cell simulations with LSP. The magnetic field diffuses rapidly into the plasma, so the expansion of the plasma is of order of the local sound speed even though /spl beta/=8/spl pi/nkT/B/sup 2/ /spl Lt/ 1. calculations for ZR parameters will be presented.