High-current Cathode for Electron Linear Accelerator

Abstract

FOR many years, the bombarded tantalum cathode gun has acted as a reliable source of electrons for injection into demountable linear accelerator systems^1,2. An important advantage of the pure metal cathode, such as tantalum or tungsten, is its high resistance to poisoning under adverse vacuum conditions which exist in linear accelerators during multipactor resonances, during high energy beam collision and clipping on inner surfaces, and, in particular, when the microwave structure is initially out-gassed by application of the radio-frequency power. Furthermore, after the cathode has cooled, the accelerator may repeatedly be opened to atmosphere, re-evacuated and the cathode returned to operating temperature without loss of emission and without additional precautions or special restrictions. On several occasions, vacuum systems containing pure metal cathodes at elevated temperatures have been inadvertently opened to atmosphere, and it has been possible to re-operate these guns satisfactorily.