Low-inductance gas switches for linear transformer drivers

Abstract

We are investigating several alternate gas-switch designs for use in linear transformer drivers. To meet linear-transformer-driver (LTD) requirements, these air-insulated switches must be DC charged to 200 kV, be triggerable with a jitter of 5 ns or less, have very low prefire and no-fire rates ( $ 1 in 10 4 shots), and have a lifetime of at least several thousand shots. Since the switch inductance plays a significant role in limiting the rise time and peak current of the LTD circuit, the inductance needs to be as low as possible. The switches are required to conduct current pulses with $100-ns rise times and 20-80 kA peak currents, depending on the application. Our baseline switch, designed by the High Current Electronics Institute in Tomsk, Russia, is a six-stage switch with an inductance on the order of 115 nH that is insulated with 47-67 psia of air. We are also testing three smaller two-stage switches that have inductances on the order of 66-100 nH. The smaller switches are insulated with 92-252 psia of air.

Square pulse linear transformer driver

“…Figure 5 shows the design of the modified and standard bricks of the cavity. In both types of bricks the same multigap switches with corona discharge [4,5] are used allowing these bricks to fire simultaneously when their capacitors are charged to the same voltage.…”

Pulsed power accelerator for material physics experiments

“…The two Thor brick capacitors each have a capacitance of 80 nF and are nominally charged to a voltage of þ=−100 kV. The Thor brick switch is a low inductance field distortion switch produced by High Current Electronics Institute (HCEI) in Tomsk, Russia [7]. The switch is triggered electrically from an electric trigger generator that provides a 100 kV pulse of rise time of 10-20 ns.…”

Design of a 7-MV Linear Transformer Driver (LTD) for down-hole flash x-ray radiography.

“…Sandia LDRD funds are being used to investigate several low inductance switch geometries that could replace the existing switches [24]. A new lower inductance LTD geometry has been developed at HCEI with a single capacitor in each brick and a switch made of several series and parallel spherical electrodes.…”

“…To achieve the narrower radiation pulse without peaking capacitors, the circuit must either have lower inductance or use lower capacitance per brick. Lower inductance switches are being developed using Lab Directed Research and Development (LDRD) funds at Sandia [24]. However, for this design, we have chosen to use existing switch technology.…”