PRS Load B-Dot Current Measurements on Argon Z-Pinches

Summary form only given. PRS implosion kinematics depend on the load current's time-dependent spatial distribution and magnitude. Time-dependent axial shunting of the load current to the return current posts can contribute to non-optimum assembly of the pinch on-axis, reducing the ideally achievable K-shell yield. The presence of plasma and the harsh environment in the PRS load region typically make current measurements close to the load difficult. Previously, we reported on the use of axially distributed, single loop B-dots mounted azimuthally between the return current posts. Those measurements suggested initial axial current propagation delays and exhibited plasma shielding which depended on the nozzle outer-plenum gas pressure. We present here new current measurements in the downstream PRS load region on pulsed power simulators using a 12-cm diameter argon gas puff Z-pinch. The data were taken under two drive conditions: 1) at peak currents up to 3.5 MA with implosion times exceeding 200 ns; and 2) at about 6 MA for 250-300 ns implosions. We used three different magnetic probe configurations: B-dots between current return posts (as previously reported), a hidden post B-dot (located in a recess on the back side of a current return post), and recessed in an azimuthally continuous, return current ring. A comparison of current measurements taken in the different magnetic probe configurations will be presented. All show some degree of plasma shielding of the probes. Much of the new data comes with significantly higher statistics, allowing the level of reproducibility of the measurements to be ascertained. Differences between the current measurements at the two current levels will be contrasted