AN INTRODUCTION TO PHOTO-INJECTOR DESIGN

Over the past ten years, photo-injectors have proven their ability to produce very bright electron beams, thus becoming a very attractive in jector for any linear accelerator needing intense and/or small emittan ce beams. When designing such a gun under given specifications, it is helpful to have some simple rules to choose the most adequate set of p arameters. This paper gives a quick overview of the basic theory of rf guns and of the presently achievable technical parameters, thus provi ding some guidelines to help the designer in his choices. Simple scali ng laws and formulas for both beam dynamics and technical parameters a re proposed and compared to corresponding values for existing photo-in jectors. Finally, the various sophisticated schemes used to improve th e performances beyond those given by a straightforward approach are re viewed.