Millimeter wave amplification in a free electron laser with a focusing wiggler

Abstract

A mm wave amplifier experiment on a free electron laser was performed using an intense, mildly relativistic electron beam (0.7–0.9 MeV) with a combination of a focusing planar wiggler and a weak additional axial magnetic field in the so-called ‘‘group 1’’ region. A beam transport ratio of over 80%, through the whole wiggler length, was realized. In an amplification experiment, a spatial growth rate of 56 dB/m was obtained at a frequency of 45 GHz, and a power saturation was observed at a level of 6 MW, where the total gain was estimated to be 52 dB. It was shown that the off-axis component of the beam contributes considerably to the rf amplification in the focusing wiggler.

Nonlinear simulation of TM mode free electron laser in rectangular waveguide with ion-channel

“…Usually, an external magnetic field is employed as a guide for beam transportation and keeping electrons inside the effective interaction medium. Unfortunately, for the case of the planar wiggler, the applied magnetic field (B 0 ) causes − → B 0 × − → ∇B w drift and other destructive effects such as beam breakup instability which diverges electrons toward the waveguide wall and dissipation [13,14]. Some HPM devices like PASTRON use plasma medium as a background for beam-wave interactions [15,16], where the ion channel plays the role of beam convergence.…”