Using scaled power flow experiments at 20 MA to establish the efficacy of load current delivery on a >50 MA next-generation pulsed power facility*

The Z accelerator routinely delivers >20 MA of electrical current to centimeter-scale imploding loads. Such current delivery is made possible by the fact that the final transmission line operates in a magnetically insulated regime where charged particles are inhibited from crossing the anode-cathode gap and losses due to electrode plasma formation remain manageable. Achieving similarly effective load current delivery on a >50 MA next-generation accelerator would enable groundbreaking advances in high energy density science. To build confidence in taking this next step, it is essential to establish the efficacy of load current delivery through transmission lines operating at next-generation power flow conditions. Fortunately, such conditions can be created today at ~1/3 of the peak current by scaling down a >50 MA final transmission line both in radius to preserve the magnetic field, current density, and ohmic heating and in the anode-cathode gap to preserve the electric field. Here we report the results of the first scaled power flow experiments on Z, which are designed to test load current delivery between R = 15–27 mm on a ~60 MA accelerator. The current flowing through a 4-mm-long scaled transmission line with a 2-mm gap is measured in time and space using a line-imaging velocity interferometer. These measurements indicate that current coupling through the scaled transmission line is essentially lossless. A subsequent fourfold over-test of the electric field stress indicates a remarkable >80% current coupling through a 0.5-mm gap. The implications of the observed 80–100% coupling efficiencies are addressed with power flow theory and modeling. Finally, the design of future scaled experiments to test additional regions of a >50 MA final transmission line are presented.