The Insulation of High Voltages in Vacuum

Abstract

Breakdown studies have been made between electrodes in high vacuum at constant voltages from 50 to 700 kv. These further demonstrate the inadequacy of the field emission theory to account generally for high voltage breakdown in vacuum. Experiments are described which investigate some of the ``total voltage'' breakdown mechanisms, including positive-ion emission by electron impact, electron emission by positive-ion impact and by photons. In the d.c. case these processes contribute to a steady interchange of charged particles between cathode and anode which increases with voltage until breakdown ensues. At higher breakdown voltages the cathode gradient has diminished far below the value for field emission. Measurements of electron emission by electrons with energies up to 300 kv for tungsten, steel, aluminum, and graphite are reported. The possibilities of predicting and of improving the insulating strength of electrode gaps in high vacuum by the study of the coefficients of the electrode materials are discussed.

Electrical discharges in high vacuum

“…VAN DE GRAAFF and his collaborators as well as other authors have made many measurements to determine A and B [1], [21, [3], [4] and [5]. The results of all these measurements contradict the above theory namely AB always proved to be much smaller than 1.…”

“…1957 produced by the strong field ocr at the cathode. Measurements have been made by VAN DE GRAArT and TRUMP concerning the breakdown occurring between a stainless steel ball anda plane electrode at voltages up to 700 kV [1]. They found that the field strength at the cathode producing a breakdown was more than 3 Mu at 0,1 mm distance of the electrodes, where as it was lower than 100 kV/cm at 70 mm distance.…”

Experimental investigation of an optimum configuration for a high-voltage photoemission gun for operation at≥500 kV

“…However, the maximum of secondary electron emission coefficient of titanium, which our gun chamber is made of, is 0.9 at electron beam energy of 0.28 keV [26]. The coefficient is generally much less than the maximum for electron beam energy from 200 to 500 keV according to experimental results for other metals [27]. If one uses Y SE ¼ 0.2 instead of Y SE ¼ 50 given in the textbook [25], K ¼ 4.8 × 10 −3 is derived.…”

Physical processes controlling dark current emission and resulting breakdown in Linacs.

“…Then, if a positive ion produces B secondary electrons and the one photon produces D secondary electrons at the cathode, a runaway phenomenon is established when AB+CD≥ 1. The authors of this hypothesis found that the secondary emission factors were too small for the development of a cumulative process [3].…”