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abstract:
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We report on the observation of energy gain in excess of
20 MeV at the Inverse Free Electron Laser Accelerator ex-
periment at the Neptune Laboratory at UCLA. A 14.5 MeV
electron beam is injected in a 50 cm long undulator strongly
tapered both in period and field amplitude. A CO2 10.6 μm
laser with power > 300 GW is used as the IFEL driver. The
Rayleigh range of the laser (
∼ 1.8 cm) is shorter than the
undulator length so that the interaction is diffraction dom-
inated. 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 spectrometer.
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.
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