Safety hazard from gas discharge interactions with the Bayard–Alpert ionization gauge

Abstract

Human contact between ground and the vacuum chamber could be lethal under conditions of open chamber ground and high pressure during ion gauge operation. At pressures of 0.1 Pa and greater, the Bayard–Alpert (BA) gauge typically generates sufficient plasma that significant coupling can occur between the grid of the BA gauge and the metal parts of the vacuum chamber. This coupling is especially severe during electron bombardment degassing, involving both glow discharge and vacuum arc mechanisms. This coupling causes significant currents to flow through the ground between the vacuum chamber and controller chassis. At high pressures, loss of the vacuum chamber ground connection floats the chamber at a voltage near that of the BA gauge grid. Contact between ground and these voltages can cause fibrillation or cardiac arrest.