Ralph, J.
(J. Ralph)

THPOS57 Acceleration of Electrons in a Diffraction Dominated IFEL
Pietro Musumeci, Chan Joshi, Claudio Pellegrini, J. Ralph, James B Rosenzweig, C. Sung, Sergei Tochitsky, Gil Travish (UCLA, Los Angeles, California), Sergey Tolmachev, Alexander Varfolomeev, Alexander Varfolomeev Jr., Timofey Yarovoi (RRC Kurchatov Institute, Moscow), Salime Boucher, Adnan Doyuran, Robert England, Rodney Yoder (UCLA/DPA, Los Angeles - California)

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.