The Los Alamos photoinjector program

Abstract

Free electron lasers (FELs) require electron beams of high peak brightness. In this presentation, we describe the design of a compact high-brightness electron source for driving short-wavelength FELs. The experiment uses a laser-illuminated Cs3Sb photoemitter located in the first rf cavity of an injector linac. The photocathode source and associated hardware are described. The doubled YAG laser (532 nm), which is used to drive the photocathode, produces 75 ps micropulses at 108 MHz repetition rate and peak powers of approximately 300 kW. Diagnostics include a pepper-pot emittance analyzer, a magnetic spectrometer, and a 4 ps resolution streak camera. Present experiments give the following results: micropulse current amplitudes of 100 mA to 400 A, beam emittances ranging from 10 π mm mrad to 40 π mm mrad, an energy spread of ± 3%, and peak current densities of 600 A/cm2 The design of experiment has now been changed to include a separately phased rf cavity immediately following the first cavity. This modification enables us to study the effects of phasing with the possibility of improving the injector performance. Also, this change will improve the vacuum conditions in the photoelectron source with a consequent improvement in lifetime performance. A brief discussion on the possible applications of this very bright and compact electron source is presented.