Arc initiation at metal surfaces in a hydrogen Penning discharge

The arcing behaviour of a number of refractory metals and graphite has been examined by negatively biasing specimen electrodes in the presence of a pulsed rf discharge. The main object of this work was to select anode materials for gas-filled valves which would reduce their tendency to arc-back under severe Commutation conditions.The voltage at which about 5 % of the pulses resulted in an arc, at an argon ion current density of 1.2 kA m-2, was used as a figure of merit. Of the materials examined, tungsten was the best with a figure of merit of 15 kV and graphite the worst with 6 kV.A good correlation was obtained between the results and the published values for the vacuum arc voltages.

Section: Discussionsupporting

confidence: 90%

Section: Introductionmentioning

confidence: 99%

The initiation of arcs by ion bombardment

Lloyd¹,

Gozna²,

Jervis-Hunter³

1970

“…It seems unlikely that this mechanism could apply to small surface impurities either in particulate or layer form since any electrons formed at the dielectric-metal junction could not attain sufficient energy to produce positive charging by secondary electron emission with the fields under consideration. In studies of the glow to arc transition (Holliday andIsaacs 1966, Maskrey andDugdale 1966) breakdown across the plasma-cathode sheath was attributed to positive ion charging and heating of the impurity inclusions. It is clear that if a mechanism for charging of impurities exists then breakdown may be initiated by a trigger discharge across the surface of or through the impurity itself.…”

Section: Model For Electroluminescence Breakdown Initiation and Elect...mentioning

confidence: 99%

Electrical phenomena at the surface of electrically stressed metal cathodes. I. Electroluminescence and breakdown phenomena with medium gap spacings (2-8 mm)

Hurley¹

1979

Spectral intensity measurements have been made of the light emitted from discrete points on the surface of electrically stressed metal cathodes. DC and pulsed breakdown voltage measurements have also been made immediately following surface arcing treatment. These show that the significant differences occur between different electrode materials. It is shown that the phenomena of electroluminescence, electron emission and vacuum breakdown, are all consistent with a model based on the production of conducting filamentary channels, electroformed through surface oxide or oxide type impurities by the action of the applied field.

“…The resulting values of E varied in a random fashion by only 25% from a median 2.1 MV cm-l as YO was increased from 7 to 13 kv, despite a wide range of plasma parameters. While this field was insufficient for adequate field emission from a smooth surface, it was probably able to initiate cathode spots at surface defects or inclusions (Holliday and Isaacs 1966). Support for the field-emission spot mechanism was obtained from the voltage-current characteristics.…”

Section: Vomentioning

confidence: 90%

“…More recently several mechanisms have been proposed to explain arc initiation and the cathode 'conditioning' effect. These include field emission at surface irregularities, impurity centres or deposits (Holliday and Isaacs 1966), the electrical !breakdown and vaporization of insulating surface inclusions, perhaps involving the evaporation of surface contaminants (Maskrey and Dugdale 1966), and the vaporization of particles in poor thermal contact with the surface (Holliday and Isaacs 1966).…”

Section: Vomentioning

confidence: 99%

An investigation of the electrical breakdown of a plasma - electrode system

Fearn¹

1969

Electrical breakdown between a pair of electrodes immersed in a flowing plasma corresponds to the transition between low- and high-current conduction régimes and has been attributed to many causes. In the work reported here, which involved cold electrodes in contact with the plasma produced by an electromagnetic shock tube, it was found that the minimum breakdown voltage corresponded to an average electric field in the cathode sheath of about 2 MV cm−1 over a wide range of plasma conditions. This was probably adequate to initiate the formation of non-thermionic cathode spots, and the voltage-current characteristics in the high-current régime were consistent with a field-emission theory of this mechanism, originally suggested by Smy. Moreover, electric fields in the plasma, sheath thicknesses and mean free paths were such that alternative explanations of the high-current régime were reasonably eliminated.