MAGNETIC BUNCHING AND BRIGHTNESS MEASUREMENTS AT ELSA

A non-isochronous beam transport system can be used to reduce the puls e length of an electron beam with a proper correlation in energy and t ime. By performing magnetic bunching at relativistic beam energies a h igh-peak current is achieved while the emittance growth due to space c harge forces is minimized. When combined with an rf-gun photocathode i njector, magnetic bunching has the potential to produce an electron be am with a low transverse emittance and a high-peak current necessary f or efficient free-electron laser operation. The ELSA rf photocathode a ccelerator beam line contains a 180-degrees, three dipole, non-isochro nous bend which has been used to bunch the electron beam. A compressio n factor of 3 has been achieved in preliminary tests. Pulse length mea surements over a range of compression factors can provide the longitud inal emittance using an emittance analysis technique similar to that f or the transverse emittance. Experimental results of beam bunching, lo ngitudinal and transverse emittances and a discussion of beam brightne ss are presented.