Collector ion expeller

An electron collector is provided for collecting spent electrons generated by a cathode of an electron gun after passage through an interaction region of a microwave device. The collector comprises a bucket having internal walls which define an enclosed region having an entrance aperture through which electrons pass after exiting the microwave device. An electrode is disposed proximate the entrance aperture within the enclosed region. A positive potential is applied to the electrode with respect to the microwave device. The potential forms a substantially ion-free region at the entrance aperture which promotes the efficient dispersal of the spent electrons due to space charge.