LTGS Performance and Down-Selection for the Hydrus IVA PFL

Summary form only given. Two switch designs were tested in the prototype PFL test bed at L-3 as part of the recently completed IVA design effort for flash radiographic sources in the new Hydrus hydrodynamics research facility at AWE. One design, called the slab switch, was scaled from the Phermex Laser Triggered Gas Switch (LTGS) and the other, called the diaphragm switch, was scaled from the Nike LTGS. Both switches have a single ~8 cm, laser triggered gap pressurized to 150 psig with SF6, are 42 inches in diameter, and designed to fit within the same 7-ohm PFL which is nominally charged to 2.5 MV, in 1.5 mus. The PFL and switch were tested up to 3 MV in the prototype facility. Test results for the LTGS performance based on >2730 shots are presented in this paper along with the switch type down-selection that was based on electrical, mechanical, and manufacturing criteria. The performance and reliability test results for the overall PFL are presented separately. The LTGS test results include measurements of jitter, rate of prefire, and the throughput risetime (due to inductance and resistive phase combined). The PFL design was based on a relatively low inductance prediction of between 220 to 240 nH. The effect of laser focal position in the switch gap, flow rate of the continuously flowing SF6, gas density, laser power, the mechanical deformation of the switch, and laser optic alignment on the switch jitter, risetime, and arc formation were investigated and are presented. Two dimensional EM simulations of the switch were also performed to estimate the contribution of two dimensional effects on the risetime. Circuit models that match the measured performance are presented.