Abstract
Switching can be considered to be the essence of pulsed power. Time accurate switch/trigger systems with low inductance are useful in many applications. This article describes a unique switch geometry coupled with a low-inductance capacitive energy store. The system provides a fast-rising high voltage pulse into a low impedance load. It can be challenging to generate high voltage (more than 50 kilovolts) into impedances less than $10\text{ }\text{ }\ensuremath{\Omega}$, from a low voltage control signal with a fast rise time and high temporal accuracy. The required power amplification is large, and is usually accomplished with multiple stages. The multiple stages can adversely affect the temporal accuracy and the reliability of the system. In the present application, a highly reliable and low jitter trigger generator was required for the $Z$ pulsed-power facility [M. E. Savage, L. F. Bennett, D. E. Bliss, W. T. Clark, R. S. Coats,J. M. Elizondo, K. R. LeChien, H. C. Harjes, J. M. Lehr, J. E. Maenchen, D. H. McDaniel, M. F. Pasik, T. D. Pointon, A. C. Owen, D. B. Seidel, D. L. Smith, B. S. Stoltzfus, K. W. Struve, W. A. Stygar, L. K. Warne, and J. R. Woodworth, 2007 IEEE Pulsed Power Conference, Albuquerque, NM (IEEE, Piscataway, NJ, 2007), p. 979]. The large investment in each $Z$ experiment demands low prefire probability and low jitter simultaneously. The system described here is based on a 100 kV DC-charged high-pressure spark gap, triggered with an ultraviolet laser. The system uses a single optical path for simultaneously triggering two parallel switches, allowing lower inductance and electrode erosion with a simple optical system. Performance of the system includes 6 ns output rise time into $5.6\text{ }\text{ }\ensuremath{\Omega}$, 550 ps one-sigma jitter measured from the 5 V trigger to the high voltage output, and misfire probability less than ${10}^{\ensuremath{-}4}$. The design of the system and some key measurements will be shown in the paper. We will discuss the design goals related to high reliability and low jitter. While reliability is usually important, and is coupled with jitter, reliability is seldom given more than a qualitative analysis (if any at all). We will show how reliability of the system was calculated, and results of a jitter-reliability tradeoff study. We will describe the behavior of sulfur hexafluoride as the insulating gas in the mildly nonuniform field geometry at pressures of 300 to 500 kPa. We will show the resistance of the arc channels, and show the performance comparisons with normal two-channel operation, and single channel operation.
Highlights
Pulsed-power high voltage systems often use successive stages of pulse amplification to increase a signal to levels needed to trigger a subsequent stage, reaching the desired voltage and power level
The primary trigger generator is required to be charged to its ultimate voltage for time periods up to several minutes, accept a five-volt trigger signal and produce a fast-rising high voltage output, with onenanosecond or less temporal uncertainty
The primary trigger generator effectively operates into a 5:56 resistive load
Summary
Pulsed-power high voltage systems often use successive stages of pulse amplification to increase a signal to levels needed to trigger a subsequent stage, reaching the desired voltage and power level. The primary trigger generator is required to be charged to its ultimate voltage for time periods up to several minutes, accept a five-volt trigger signal and produce a fast-rising high voltage output, with onenanosecond or less temporal uncertainty. Because of the large physical size of the Z facility, the output pulse from the primary trigger generator operates into multiple (nine) high voltage 50 cables with transit time much longer than the pulse duration. The system described here meets the rise time, amplitude, jitter, and reliability requirements for the Z primary trigger generator. While commercially available multioutput $100 kV trigger systems have been built in the past, they did not meet the jitter or rise time requirements of the primary trigger generator for Z, and were notoriously unreliable. We will show results on the observed resistance of the spark channel in different gases and for single and double channel operation
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