Gas evolution during operation of a CsI-coated carbon fiber cathode in a closed vacuum system

In order to quantify the gases generated during operation of an explosive emission cathode, residual gas analysis was performed on a closed vacuum system. Two different anode materials were tested using an identical CsI-coated carbon fiber cathode. For both the nearly transparent molybdenum mesh and the carbon fiber anode, the largest pressure increases were observed in hydrogen and carbon dioxide. Use of the molybdenum mesh resulted in the generation of approximately 0.38 neutrals per electron compared to 0.73 neutrals per electron while using the carbon fiber anode. While the background vacuum pressure was typically in the low 10^-7 torr scale, it was found that gas generation during these explosive emission pulses led to local diode pressures of 0.5 mtorr up to several tens of mtorr. Such pressures are consistent with the ability to generate ion densities that can drastically effect the space charge-limited current.