SCALING MICROSECOND-CONDUCTION-TIME PLASMA OPENING SWITCH OPERATION FROM 2 TO 5 MA

We describe experiments in which conduction currents were successfully scaled from 2 to 5 MA for conduction times around 1 mu s in a coaxial geometry plasma opening switch (POS) on the 4 MJ ACE 4 driver, Simple models of POS operation, derived from previous work, were used to sca le successful results from drivers that operate at microsecond conduct ion times, but at currents below 1 MA, An MHD model for the conduction phase was verified in which the square root of the plasma density is approximately proportional to the product of conduction time and peak conduction current divided by the switch radius and length, For the op ening phase, a model where the POS gap is approximately constant when the local plasma conditions at the beginning of the conduction phase a re kept roughly the same is consistent with the observed POS opening v oltages of at least 1 MV. The conduction current was increased by incr easing the POS cathode radius from 6 to 20 cm while maintaining roughl y the same plasma density. This increase in radius resulted in the obs erved increase in the conduction-current/conduction-time product from 2 to 5 MA . mu s while maintaining MV POS voltages.