100 Hz, 5 To 40kV Triggered Spark Gap For Medium Power Modulators

Abstract

A trigatron spark gap, T-150, rated at 300 kA for a single shot, has been evaluated for repetition rate applications towards 100 Hz at reduced currents. Switching voltage range was varied from 10 to 40 kV via gap-pressure and gas flow settings. Its trigger generator, producing 8-20 kV pulses, is solid-state based and fiber optically linked for electrical isolation. Trigger energy has been minimized to prolong the overall switch life, drawing input power of <75 W at up to 100 Hz. Demonstrated repetition rate, lifetime, and prefire performance indicated the use of the switch as an alternative to ignitrons or thyratrons in medium power modulators. Introduction Physics International (PI) has fielded a number of single-pulse closing switches172 for high energy capacitor banks to drive electric launchers.3-5 To reduce size and weight of the switch, add a repetitive firing capability, and minimize trigger power, a trigatron gas switch, T-150, has been developed along with the TG-10 trigger generator.6 In this paper, we report on initial results in repetitive firing of the switch at reduced currents. Figure 1 shows a photograph of the switch-trigger package. The highly compact TG1 OB trigger generator is solid-state based and battery powered, producing 20 kV open circuit output voltage. The generator employs fiber-optic isolation to ensure safe, reliable operation in a noisy environment. An ac-powered version (TG-1292R in Figure 1) is customized for increased power, higher repetition rate applications. Trigger energy is minimized to limit the trigger power. The generator draws <75 W at up to 100 Hz. The switch-trigger package can be controlled via fiber optic links, allowing their use in a "floating" configuration in modulator or capacitor bank circuits. T-I50 TG-100 TG-1292R Figure 1. Photograph of T-150 spark gap, batteryoperated TG-lOB, and enhanced ac-powered TG-1292R trigger generator. Single pulse performance of the T-150 lies between those for the high charge transfer spark gaps (namely, PI's two-electrode, seriesinjected trigger switches Table 1-A) and high voltage mid-plane trigger switches (see PI T-508 Table 1-C). TG-10 is distinguishable from other trigger generators in its compactness and low power requirement even at high repetition rates. Table 1. T-150 switch's single pulse ratings relative to electric gun switches (A), Marx switches (C), and ignitrons. A . B . C . Series Injection Trigatron MidIgnitron Gas Switch Plane Trigger Switch ST-4198 ST-3OOA T-150 T-508 "C"-"D" 540 120 50-200 Transfer (C) Integral (MJ/R) Action 135 0.2 T150/TG-10 performance is comparable to size "D" ignitrons, suitable for coil gun drivers or other medium power modulators. The switch and the TG-1292R generator has recently been used as an output switch for the 10 Hz, 16 kJ/s pulser intended for food pasteurization? T-150 Demonstrated Performance T-150 handles currents to 300 kA and transfers 120 C in a single shot with no damage. Operating parameters for the T-150 are listed in Table 2. To date, repetition rate performance has been demonstrated only to 10 Hz and over 9 kA peak current, 3 ps pulse width (FWHM), owing to power supply limitation. Short bursts have been performed at 20 Hz also at 9 kA. Ultimate capabilities are not yet established. Table 2. T-150 demonstrated operating parameters. Operating Voltage 4QkV Demonstrated Peak Current Repetition Rate Demonstrated Charge Transfer 120 C/shot Action (Single Shot) 16 MJIR Size and Weight 300 kA (Single Shot) 10 Hz, at 9 kA p e a 3 ps 3 Hz, at 15 kA p e a l 3 ps Switching Gas Air 8 in. dia, 11 in. high; 20 lbs