Improvement of the Bunching in Injectors for Electron Linacs

Computation results are presented showing an improvement in the final bunching characteristics when a long cavity is used at the beginning of a synchronous classical buncher. An analysis of several combinations has been done and suggests to adjoin at the entrance of such a buncher a long cavity leading to a phase-shift of about 4 ¿/3 for the electron around which the bunching occurs. An improvement by a factor of two is obtained and variations of physical parameters are not critical. Comparison with a synchronous buncher is done, including eventually the use of a modulation cavity with drift space. Results including space-charge effects are given for a practical injector.