RF phase focusing and asymmetric field shape in standing-wave electron linacs

In order to minimize the size and weight of the low energy standing-wave linacs and to improve the beam spots as well as the transmission, the RF fields are used for radial focusing without external magnetic focusing devices. By choosing the proper phase velocity distribution and by adjusting the amplitudes of the buncher fields from cavity to cavity, the RF fields in the buncher region provide transverse focusing as well as longitudinal bunching and acceleration. The RF phase focusing is more effective by proper choice of an asymmetric cell geometry in the first cavity. 1.