Pushing the capture limit of thermionic gun linacs

Although accelerator technology has matured sufficiently, state-of-the-art x-ray linacs for radiotherapy and cargo-scanning capture merely 30%--50% of the electrons from a thermionic cathode, requiring higher cathode current leaving uncaptured to cause problems such as back bombardment on leading shortening life. Any solution increase should be effective, simple, reliable, compact, low cost in order adopted by industry. To address this, we present design 6 MeV high efficiency S-band electron linac that captures 90% initial dc beam. This does not require any extra parts would is achieved via low-field amplitude first bunching cell decrease number back-streaming electrons, velocity bunch beam, recapture electrons. Under field amplitude, launched at decelerating phases travel backward with speeds, thus most them can catch next rf cycle, get reaccelerated/recaptured. As speed low, length also shorter than existing linacs. Such short use asymmetric cells differential coupling side-coupled cells. Our novel implications all commercial gun increasing beam lifetime.