An Apparatus for Investigating 50 c/s Voltage Pre-breakdown Electron Emission in Vacuum Insulation at Low Temperature(124°K)†

An apparatus is described in which voltages up to about 100 kv a.e. can be applied to coaxial electrodes with a 5 mm radial gap, in a vacuum of 2 × 10-5 torr. Electron emission is monitored in terms of the resultant x-radiation and by superimposing the ratemeter output on a CRO display of the 50 c/s waveform, it is possible to distinguish between emission from the two electrodes. Conditioning of the aluminium electrodes is carried out by raising the voltage at constant x-radiation level, and occurs more readily at room temperature than with the electrodes cooled (inner electrode 124°K, outer electrode 200°k). The electron omission is not changed by cooling the electrodes. Anodizing one of the electrodes suppresses the electron emission from this electrode.