High Voltage, Small Back-lighted Thyratrons

Abstract

We report comparative studies of mini (6.3 Apelt e 2Lm p mm diameter electrodes) and medium sized (19 mm I diameter electrodes) pseudospark and back-lighted 355nm 6.3 m To Vacuum sysem thyratron (BLT) switches. Currents greater than 9 Laser kA, and hold-off voltages in excess of 40 kV have been achieved, the highest hold-off occurring in the smaller HV diameter switch. The switches are optically triggered; Load Resistor we consider here with helium and hydrogen fill. The results suggest that the switches can be optimized for miniaturized high voltage pulse generation, and that Fig.lExperimentalsetup smaller switches have potential for compact repetitiveThe inside structure of the mini-BLT and the mediumpulsed power applications.BLT is similar. For the mini-BLT, a 3mm thick molybdenum disk with a 3mm central hole is capped on a hollow OFHC 1/4" diameter copper tube. In the medium-BLT, a 15mm molybdenum disk with a 3mm central hole is I. INTRODUCTION inserted in a 3/4" diameter OFHC copper tube. 2mm electrodes gap is maintained in both the mini-BLT and the The pseudospark is a low pressure glow discharge medium-BLT. A 2.2Q stack resistor, 6nF or 1 5nF switch [1] which is distinguished from a traditional capacitor is included in the system. In order to reduce the thyratron by a self-heated, initially cold cathode that is system inductance, compact structure is installed. highly emissive (10,000A/cm2). The emission process involves initially a hollow cathode discharge mode, and a III. DIscusSION subsequent so-called super-emissive mode.The cathode does not require an external cathode heater. A. Hold-off Voltage Psuedospark lifetimes in excess of 108 shots have been The BLT is worked at the left side of the Paschen curve reported [2]. The optically triggered version of the switch in a low pressure glow discharge mode. Lower pressure is referred to as a Back-Lighted Thyratron (BLT), reflecting can result in higher hold-off voltage for the 2mm similarity between psuedosparks and thyratrons as low electrode distance. However, the higher gas pressure can pressure, high hold off voltages characteristics. bring smaller delay and jitter [3], reduce current quenching [4], and acquire higher maximum peak current. In addition, the gas discharge demands a certain critical II. EXPERIMENTAL SETUP gas density [5] which can be easily achieved in higher pressure. So, a comparative high pressure gas switch Fig. 1 shows the experimental system setup of the mini-without sacrificing high hold-off voltage is attractive.BLT (6.3mm electrode diameter) and the medium-BLT Fig. 2 shows that the mini-BLTs hold higher voltages (19mm electrode diameter). The mini-BLT is comprised than the medium-BLT under the same gas conditions. In of a glass cylinder 7.62cm (3 inch) long and 1.27cm (1/2 addition, helium can withstand higher breakdown voltage inch) in diameter. This is more than ten times smaller than than hydrogen such that an arc happens much more often the traditional thyratron and pseudospark in magnitude. in the medium-BLT than in the min...

Energy Efficient Transient: Plasma Ignition: Physics and Technology

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“…Continuing the development of miniature pseudospark switches for reliable and long-life operation of transient plasma ignition systems, an optically triggered switch (BLT) with an inverse dependence on electrode area and holdoff voltage was found. July [9][10][11][12][13]2006, studies were conducted at AFRL with collaboration between USC (C. Cathey, M.G.) and Dr. F. Schauer's PDE research group.…”

“…The ignition system typically consists of a pseudospark based pulse generator, a rapid charger or HV DC supply, and an electrode interface assembly [10,11] Research directed towards more compact versions of the pulse generation technology to ensure it is a viable option for airborne platforms and for use in other applications, is briefly discussed. A miniaturized back-lighted thyratron (BLT) switch is to be discussed as a feasible replacement for the relatively large pseudospark switch [12]. The BLT is a laser triggered (can be electrically triggered also) hollow cold cathode thyratron and is able to switch 40 kV, 9 kA.…”