Observation of Energy Gain at the BNL Inverse Free-Electron-Laser Accelerator

A 40MeV electron beam, using the inverse free-electron-laser interaction, has been accelerated by {Delta}{ital E}/{ital E}=2.5{percent} over a distance of 0.47m. The electrons interact with a 1{endash}2GW CO{sub 2} laser beam bounded by a 2.8mm i.d.sapphire circular waveguide in the presence of a tapered wiggler with {ital B}{sub max}{approx_equal}1T, and a period 2.89{le}{lambda}{sub {ital w}}{le}3.14cm. The experimental results of {Delta}{ital E}/{ital E} as a function of electron energy {ital E}, peak magnetic field {ital B}{sub {ital w}}, and laser power {ital W}{sub {ital l}} compare well with analytical and 1D numerical simulations and permit scaling to higher laser power and electron energy. {copyright} {ital 1996 The American Physical Society.}