Gas Switch Studies for Linear Transformer Drivers

Abstract

Linear Transformer Drivers (LTDs) represent a new pulsed power architecture that could dramatically reduce the size and cost of large pulsed-power drivers. Large LTD systems, however, will require hundreds, to tens-of-thousands, of lowinductance gas switches that can be DC-charged to -200kV and then be triggered with low jitter and low prefire probability. We are studying several competing gas switch geometries in an attempt to design an optimum switch for these applications as well as to increase our knowledge of the physics of the switching process. In addition to standard electrical diagnostics (V, I), we are studying the switches with a variety of optical diagnostics including fast photodiodes, a framing camera and a time-resolved spectroscopy system. In our test system, 20-nF capacitors on top and bottom of the switch are charged to voltages up to +100 kV, then the switch is triggered and current flows through the switch and a load resistor in a geometry that resembles the LTD architecture.Initial results have been obtained with a 6-stage, air-insulated switch based on a design by B. Koval'chukl. When the trigger arrives at the switch, two of the 6 gaps break down promptly but there is a delay of up to 50 ns before the other 4 gaps break down. Despite this delay, the 1-sigma jitter is + 10 ns. The 10%-to-90% risetime of the current pulse is 45 ns. Results from several competing switches will be presented.

Design and construction of a ±100 kV gas switch for linear transformer drivers

“…1 1   f [12,15]. In order to improve triggering performance of the switch, we have designed a 1mm preionization gap in the center of the trigger plane, the pre-ionization gap is formed by a ceramic spark plug and its opposite trigger pin.…”

“…And the lower picture of Figure 2 shows that -120 kV trigger pulse applied to the trigger plane, the maximum electric field intensity distorted to 255 kV/cm. When the air pressure is 0.5 MPa, the breakdown field calculated to be about 138 kV/cm by formula (1). 255 kV/cm is 1.85 times of the breakdown field, so the switch can be easily triggered.…”

“…Our trigger system is based on a 60:1 pulse transformer, Figure 3 shows the basic circuit of our trigger system. As show in Figure 3, 0 C is the pulse transformer primary capacitor which is charged by an autotransformer 1 T through silicon rectifier stack 1 D and the current limiting resistor 2 R . When 0 C is fully charged, the low voltage control system produce a signal to trigger the silicon controlled rectifier 1 S , 0 C is discharged through 1 S and then the secondary of the pulse transformer 2 T will induce a negative pulse, the pulse amplitude can be easily changed by the charge voltage of 0 C .…”

“…AS a new kind of pulse power technology, the lineartransformer-driver (LTD) can dramatically reduce the size and cost of pulsed power generator [1][2][3][4]. Linear transformer drivers, however, require gas switches that can be DC charged to ±100 kV, triggered with a jitter of 5 ns or less, be low inductance, have very low pre-fire and nofire rates, and have a at least tens of thousands shots lifetimes.…”

“…The switch has the following advantages: high stability breakdown, multichannel discharge tends to reduce the inductance and the electrode erosion and relatively low trigger pulses required. By adopting the three-electrode field distortion switch with UV illumination designed by L3 instead of the of the multi-gap switch, LTD2 built in Sandia Laboratories, decreases switching inductance, and the output peak current and pulse rise time are improved [1][2][3][4][7][8][9][10][11]. In this paper, a ±100 kV gas switch with low inductance and jitter was designed.…”