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 injector for any linear accelerator needing intense and/or small emittance beams. When designing such a gun under given specifications, it is helpful to have some simple rules to choose the most adequate set of parameters. This paper gives a quick overview of the basic theory of rf guns and of the presently achievable technical parameters, thus providing some guidelines to help the designer in his choices. Simple scaling laws and formulas for both beam dynamics and technical parameters are proposed and compared to corresponding values for existing photo-injectors. Finally, the various sophisticated schemes used to improve the performances beyond those given by a straightforward approach are reviewed.