An Experimental Test of the Streamer Breakdown Criterion

Abstract

The filamentary spark channel, resulting from the electrical breakdown of a gas, generally forms in one of two ways. At voltages close to the minimum breakdown potential the spark channel has been shown to develop from the constriction of the diffuse glow discharge formed from the superposition of many generations of electron avalanches (Cavenor and Meyer 1969). At large overvoltages, however, single avalanches have been observed to develop into luminous conducting filaments, called streamers, which completely bridge the electrode gap within the transit time of the initial avalanche (Wagner 1966).The criterion proposed for the occurrence of this streamer mode of development is that the charge carrier number in the initial avalanche should attain a value of some lO9 ions and electrons and that the electrons be concentrated within the diffusion radius of the avalanche. Under such conditions it is suggested that enhancement of the electric field by the space charge, in the vicinity of the avalanche, is sufficient to allow gas ionizing radiation to extend the ionized region simultaneously towards both electrodes (Raether 1964). For avalanches initiated by single photoelectrons the amplification of the avalanche, expad, must therefore be lO9 and thus ad, the product of the primary ionization coefficient and the gap length, must be of the order of 20 ion pairs. For the case of hydrogen, with a given value of pd it is possible to compute, from values of alp versus E Ip and experimentally determined breakdown voltages, the percentage overvoltage required to establish the condition ad = 20. This information is given in Figure 1 where the corresponding curve for ad = 18 is added to show * Manuscript

Analysis of the radiation characteristics of large-aperture exciplex laser systems utilizing a three-dimensional transfer equation

“…Our observations with conditioned electrodes are in general agreement with the Australian work (Cavenor andMeyer 1969, Cavenor 1970) who used conditioned electrodes in their experiments.…”

“…Recently Meyer and Lee (1971) have shown that the glow characteristics are independent of the source impedance. Cavenor (1970) has confirmed the existence of the glow phase at overvoltages up to 100% and a pressure of 500 Torr, and Cavenor and Meyer (1969) also showed that this diffuse glow subsequently constricts to a filamentary discharge which still shows a cathode dark space at the cathode and which causes a further drop in the gap voltage. There is a progressive increase in the current through the filament until, finally, a discontinuity at the cathode accompanied by the disappearance of the dark space leads to a sudden increase in luminosity and electrical conductivity and the gap voltage collapses to very low values.…”

Streamer breakdown: cathode spot formation, Trichel pulses and cathode-sheath instabilities

“…terminology can be exemplified by the following claim by Cavenor [106]: 'The filamentary spark channel, resulting from the electrical breakdown of a gas, generally forms in one of two ways. At voltages close to the minimum breakdown potential the spark channel has been shown to develop from the constriction of the diffuse glow discharge formed from the superposition of many generations of electron avalanches.…”

Spark discharges in iodine vapour

“…The development of spark discharges is known to proceed in several different ways, depending on the gas and its pressure, the discharge gap and electrode geometry, the external circuit and the magnitude of the overvoltage applied to the discharge gap (cf Haydon 1968, Craggs 1978. The role of overvoltage, for example, is regarded as important at gas pressures of several hundred Torr and under uniform field conditions (Cavenor andMeyer 1969, Kekez er aZ1970). At low overvoltage, under these conditions, the spark develops by the Townsend mechanism, and at high overvoltage, generally by the so-called streamer mechanism.…”

“…At low overvoltage, under these conditions, the spark develops by the Townsend mechanism, and at high overvoltage, generally by the so-called streamer mechanism. This is not an exact rule however, and the Townsend mechanism has been observed to operate for overvoltages as high as 100% (Cavenor 1970). In this paper, we are more concerned with the later stages of development which follow the establishment of a diffuse glow discharge; this is a quasi-stable stage in the spark development which often follows the initial breakdown process.…”