A. H. Guenther

Gas discharge closing switches

1 General Switching Considerations.- 2 Electrical Breakdown In Gases In Electric Fields.- 3 Gas Filled Spark Gaps.- Section 3a Self Breakdown Gaps.- Section 3b Trigatron Spark Gaps.- Section 3c Field Distortion Three Electrode Gaps.- Section 3d Electron Beam Triggering of Gas Filled Spark Gaps.- Section 3e Laser Triggering of Gas Filled Spark Gaps.- 4 Vacuum Switches.- Section 4a Electrical Breakdown in Vacuum.- Section 4b Recovery of Vacuum Spark Gaps.- Section 4c Triggered Vacuum Switch Construction and Performance.- 5 Repetitive Operation and Lifetime Considerations for Spark Gaps.- Section 5a Repetitive Spark Gap Switches.- Section 5b Lifetime Considerations.- 6 Surface Discharge Switches.- 7 Thyratrons.- Section 7a Design Principles and Operation Characteristics.- Section 7b Hydrogen Thyratrons and Their Applications as Developed in the UK.- Section 7c Studies of Fundamental Processes in Thyratrons.- Section 7d Fundamental Limitations of Hydrogen Thyratron Discharges.- 8 Metal Vapor Switches.- Section 8a The Mercury-Pool-Cathode Ignitron.- Section 8b Liquid-Metal Plasma Valves.- 9 The Pseudospark Switch.- Section 9a The Pseudospark.- Section 9b The Triggered Pseudospark Discharge.- Section 9c The Back-Lighted Thyratron.- Section 9d High Power, High Current Pseudospark Switches.- Section 9e Pseudospark Switches for High Repetition Rates and Fast Current Risetimes.- Contributors.

Concepts for Optical Control of Diffuse Discharge Opening Switches

Optical control of diffuse discharges is discussed as opening mechanism for rep-rated switches. Diffuse discharges can be sustained or terminated by making use of optogalvanic effects, that means resonant interaction of laser radiation with diffuse plasma. Independent of control mechanisms, the performance of diffuse discharge opening switches is strongly affected by such fill gas properties as attachment and electron mobility.

Laser Triggering through Fiber Optics of a Low Jitter Spark Gap

An optical filter is employed to transport a 15-ns light pulse from a high power ruby laser for precise triggering of a gas filed high voltage spark gap. The maximum power density that can be transmitted by the fiber is limited to 6 × 1012 W/m2 above which laser induced damage occurs on the fiber entrance face. The overall throughput efficiency of the optical system was measured as 62 percent. Results are presented for the switching delay time and associated jitter for various mixtures of A and N2 gas, and as a function of the voltage across a pulse-charged Blumlein generator gap. Pulse charging of the Blumlein generator was accomplished by a three-stage Marx generator, resulting in output voltages up to 250 kV. It was conclusively demonstrated that an optical fiber will transport a sufficiently intense laser pulse to evince subnanosecond jitter in the triggering of a pressurized gas switch under the conditions studied.

The use of attachers in electron-beam sustained discharge switches—theoretical considerations

Electron-beam sustained discharges can be used in opening and closing switch applications for producing bursts of energy in pulsed power systems. The incorporation of admixtures of attachers with low attachment rate at low values of E/N and high attachment rate at high values of E/N in the gaseous switch dielectric has been proposed to achieve low forward voltage drop in the conduction phase as well as rapid opening when the sustaining e-beam is terminated. This paper presents model calculations on the characteristics and transient behavior of an electron-beam sustained discharge in the high current density regime in N 2 . The influence of an attacher (N 2 O), with the property described above, and of the circuit parameters on the discharge is investigated as an illustrative example. The advantage of using such an attacher is demonstrated for the steady state conduction phases and for the opening phase, while the closing process is obstructed by the attacher. Additional possible control mechanisms, such as photodetachment to aid the closing process are discussed.

Space-Charge Effects in a Laser Fiber-Optics Triggered Multichannel Spark Gap

The dual channel triggering of a spark gap switch by fiberoptic transported ruby laser radiation is discussed. The spark gap is the output switch of a 20-ns water dielectric Blumlein generator. The Blumlein generator is pulse charged in approximately 250 ns by a three-stage Marx bank to 150 kV. The spark gap is operated at a pressure of 2540 torr with a mixture of Ar and N2 gas and an electrode separation of 2 cm. Two 1-mm diameter quartz optical fibers are used to transport 2 2-MW laser beams into the spark gap onto points 6 cm apart on the target electrode. The two beams are obtained by optical splitting of the output of a single laser. Under appropriate conditions, two arc channels are initiated by the laser beams along their paths. A small improvement in current rise time for dual channel events over single channel events is observed. Moreover, the number of successful dual channel events is observed to depend on the time of laser entry with reference to the beginning of the charging pulse, and not the gap polarity. The correlation of this behavior with the space charge build up in the slightly over-volted gap is discussed.

An Electron-Beam Triggered Spark Gap

The triggering of a high-voltage gas-insulated spark gap by an electron (e) beam has been investigated. Rise times of approximately 2.5 ns with subnanosecond jitter (~0.2 ns) have been obtained for 3-cm gaps charged at voltages as low as 50 percent of the self-breakdown voltage (varied up to 0.5 MV). The switch delay (including the e-beam diode) was 52 ns. The triggering e-beam pulse has a duration of 15 ns and a 0-50 percent rise time of 1.5 ns. The e-beam current is 0.5 kA, and the electron energy can be varied in the range from 80 to 145 keV. The working media were N2, mixtures of N2 and A, and N2 and SF6 at pressures of 1-3 atm. Voltage, current, and jitter measurements have been made for a wide range of gap conditions and e-beam parameters. Variations in the character of the discharge have been inferred using streak and open shutter photography. The photographs show that the discharge has a broad cross section and that its character varies for differing polarites and voltages. The effects of varying the e-beam width and the beam energy are discussed.

The Effect of Space Charge Induced by an Electron Beam on Spark Gap Operation

An investigation in to the effect of electron-beam (e-beam) induced space charge on the insulating property of a gas in a spark gap is presented. The characteristics of the gas transition from insulator to conductor show strong dependence on the amount and location of the space charge introduced. Investigations of the delay time and the characteristics of the conducting channel have been made. The delay time from the injection of the e-beam to the collapse of the gap voltage ranges from 10-9 to 10-3 s. From open shutter photography, we observe that the character of the conducting channel is quite varied. Dark, diffuse, filamentary, or diffuse followed by filamentary (single or multiple) channels have been observed, depending on the space-charge conditions. The fundamental processes leading to the collapse of the insulating property of the gas for various experimental conditions are discussed.

On the Road to Tomsk

From 25 June to 4 July 1989, a group of 20 US scientists and engineers from industry, academia and Federal research facilities had a singular opportunity to visit several previously “closed” Soviet scientific installationswhere research in pulsed‐power technology is conducted. These installations, many of which had never been seen by a Westerner, included the Institute of High Current Electronics and the Nuclear Physics Institute, both in Tomsk; the Leningrad Polytechnic Institute; and the Kurchatov Institute for Atomic Energys facility at Troitsk, near Moscow. Various members of the US group also visited the Yefremov Institute for Electro‐Physical Apparatus (Leningrad), the Lebedev Institute (Moscow), the USSR Research Center for Surface and Vacuum Investigation (Moscow), the Institute of High Temperatures (Moscow), the Institute of Nuclear Physics (Novosibirsk) and others. Throughout our journey, Soviet researchers conveyed the spirit of glasnost through their candor and their interest in a genuine exc...