Use of discrete B-dot loops for load current measurements very close to an argon Z-pinch on Double Eagle

Summary form only given. We report here load current measurements using ceramic encapsulated, single loop B-dots mounted less than a centimeter outside the return current posts. DE was operating in a long pulse mode, delivering peak currents up to 3.5 MA and enabling implosions times up to 250 ns to be investigated. The principal goal of the test series was to study the K-shell yield dependence on changes in gas distribution for two different nozzle designs. The load current B-dots showed initial axial current propagation. This is consistent with nozzle gas flow calculations that show the presence of some gas from the nozzle extending out to the return post radius. For shots with reduced gas densities in the region of the current return posts, corresponding to the best K-shell yield conditions, the shape of the load current monitors tracked each other significantly better in the later time leading up to the implosion. Even under those conditions, they showed evidence of plasma shielding in that the current bite associated with the implosion was muted and delayed relative to that seen in the standard upstream load current monitor. The degree to which the B-dots provided qualitative or quantitative information on the PRS implosion is discussed.