CERN Accelerating science

Article
Title	Acceleration of Electrons in a Diffraction Dominated IFEL
Author(s)	Musumeci, Pietro ; Joshi, Chandrashekhar ; Pellegrini, Claudio ; Ralph, J ; Rosenzweig, J B ; Sung, C ; Tochitsky, Sergei Ya ; Travish, Gil
Affiliation	(UCLA, Los Angeles, California RRC Kurchatov Institute, MoscowUCLA/DPA, Los Angeles - California)
Publication	2004
In:	26th International Free Electron Laser Conference and 11th FEL User Workshop 2004, Trieste, Italy, 29 Aug - 3 Sep 2004, pp.e-proc. THPOS57
Subject category	Accelerators and Storage Rings
Abstract	We report on the observation of energy gain in excess of 20 MeV at the Inverse Free Electron Laser Accelerator experiment at the Neptune Laboratory at UCLA. A 14.5 MeV electron beam is injected ina 50 cm long undulator strongly tapered both in period and field amplitude. A CO2 10 μ m laser with power >300 GW is used as the IFEL driver. The Rayleigh range of the laser (1.8cm) is shorter than the undulator length so that the interaction is diffraction dominated. Few per cent of the injected particles are trapped in stable accelerating buckets and electrons with energies up to 35 MeV are detected on the magnetic spectrometers. Experimental results on the scaling of the accelerator characteristics versus input parameters like injection energy, laser focus position and laser power are discussed. Three dimensional simulations are in good agreement with the electron energy spectrums observed in the experiment and indicate that substantial energy exchange between laser and electron beam only occurs in the first 25-30 cm of the undulator. An energy gradient of >70 MeV is inferred. In the second section of the undulator higher harmonic IFEL interaction is observed.