Lifetime and emission stability of carbon fiber cathodes

A theoretical model is developed to predict vacuum degradation in an isolated vacuum tube during field emission cathode operation. The time dependence of emission current from single carbon fibers and bundles of carbon fibers (T-300, Amoco Performance, Inc.) are measured during 900 h. The amplitude distribution of the emission current is calculated. It is experimentally shown that the lifetime of carbon fibers in isolated vacuum tubes is mainly determined by the pressure increase caused by sputtering and desorption processes.