Tungsten-rhenium filament lifetime variability in low pressure oxygen environments

Accelerated life-testing of tungsten-rhenium filaments in oxygen rich environments has been performed to investigate the longevity of the devices as a function of electron emission intensity and power cycling methodology. The lifetimes of such filaments are found to be independent of the electron emission level over typical operating ranges, but the turn-on/off sequence is found to have important life-span consequences. A gradual turn-on cycle lasting several minutes results in substantially extended lifetimes, ostensibly by reducing the thermal shock associated with more abrupt power cycling.