Tests of a prototype gas-switched 1.4 MV pulse forming line

Abstract

Summary form only given. The 14 MV induction voltage adder (IVA) being designed by L-3 Pulse Sciences for AWE Aldermaston , UK, is powered by water-dielectric pulse forming lines (PFL) that drive each induction cell with ~60 ns 1.4 MV pulses and currents up to 140 kA. The PFL design selected is a simple water coax switched out by a 150 psig SF 6 gas switch in order to minimize prepulse. Specifications on IVA output rise-time and pulse shape require an adequately low gas-switch inductance and a self-closing water pulse-sharpening switch, plus a gas switch jitter of <2 ns rms, achieved by laser triggering. Operational specifications include a failure rate of less than 1 in 7500 shots for each PFL and refurbishment only every 210 shots. The gas switch is the main concern in the prototype PFL tests reported here. Two identical prototype gas switches are tested sequentially in a test-bed that also replicates the PFL and its input and output hardware in detail. The charge time planned for ten PFLs in the IVA is obtained using a smaller Marx with added series inductance, and the test-bed drives a dummy load. With each gas switch, five series of 210 shots are carried out, separated by switch disassembly, inspection and cleaning. A switch design with two radial nylon insulators allows easy disassembly. The switch insulators and electrodes show minimal effects after 210 shots. Waveforms measured at various points are compared with calculations based on both TL models and LSP models. A sequence of test voltages from the 2.5 MV maximum PFL operating voltage in the IVA up to a 20% over-stress at 3 MV is used to give reasonable confidence that the reliability requirements will be met