Simulations of the effects of ion space-charge on vacuum power flow in inductive energy store pulsed power systems

In this paper we present results from particle-in-cell (PIC) simulations regarding power-flow between a plasma opening switch (POS) and a Bremsstralung diode. A realistic geometry that closely approximates the Decade Module 1 (DM1) was used in conjunction with a switch opening model to simulate power-flow in an inductive energy store pulsed-power system. Several assumptions were made concerning the emission of ions from the high density POS plasma (n/spl sim/10/sup 15/ cm/sup -3/) and the downstream anode, as well as the distribution of plasma in the POS-to-load region to assess the role of ion space-charge on the delivery of energy to the diode load. It is found that ion emission from the POS plasma allows a low density plasma (n/spl sim/10/sup 12/ cm/sup -3/) to propagate down the transmission line between the POS and load at about 1 cm/ns. The simulations also show that a large fraction of the current arrives at the load coincidentally with the arrival of this low density plasma. However, the load currents predicted from simulations are too low to explain the measured radiation on DM1. When ion emission is allowed from the anode between the POS and load, additional electron current can propagate along the anode and into the load. When plasma is placed in the POS-to-load region it is found that current transfer is enhanced by the presence of ion space-charge in the POS-to-load region. The enhancement is evident only in regions where the plasma density is highest and goes away as plasma ions are removed.