The UCLA high gain infrared FEL

Abstract

The Particle Beam Physics Laboratory (PBPL) at UCLA is constructing a short period FEL which will operate in the high gain regime. The focus of the work has been the production of a high brightness electron beam suitable for short wavelength FELs. Once operational the FEL will be used to study phenomena of significance to short wavelength devices such as SASE and performance sensitivity to various beam parameters. Future studies may include the addition of a second undulator or amplification of an input source (CO, laser) to study saturation, superradiante, and optical guiding. The electron beam is provided by a linac whose major components are a S-band copper photocathode gun and a Plane Wave Transformer (PWT) accelerator section. The UCLA photocathode gun is driven by a frequency quadrupled, pulse compressed Nd:YAG laser (UVl and has been characterized and described in detail elsewhere [l]. Solenoidal focusing controls the highly divergent beam as it exits the gun and provides for emittance compensation [2] into the PWT which accelerates the electrons to roughly 17 MeV [3]. During recent conditioning, the PWT has been operated at high power and the dark current measured at 7.5 MeV. The UCLA experiment was designed to study issues important to future short wavelength devices. The short period undulator, combined with our moderate energy beam produces radiation in the infrared where a large number of diagnostics are available, without the added complexity of producing a higher energy beam that would be necessary for operation at shorter wavelengths. Further, working in the infrared (IR) does not suffer from the beam noise problems associated with past microwave FELs. The lack of suitable sources at short wavelengths makes the feasibility of start up from noise (SASE) important [4]. Lack of suitable mirrors makes an oscillator configuration