The Insulation of High Voltages in Vacuum

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.