Development of high-average power FEL amplifiers using sheet electron beams and short-period wigglers

Summary form only given. A high-average-power (⩾1-MW) FEL (free-electron laser) is being developed as an ECRH (electron cyclotron resonance heating) source for RF heating of magnetic fusion plasmas. Designs for millimeter-wave (200-600-GHz) FEL amplifiers using relativistic sheet electron beams (eV_b⩾0.5 MeV, I_b ≈ 100 A) and short-period wigglers (l _w⩽1 cm) have been developed. These designs call for a large total number of wiggler periods (⩾50) as well as tapering to enhance the FEL electronic efficiency. Sheet beam stability and beam interception are two critical parameters for this radiation source concept. The effects of wiggler field errors on beam propagation have been studied using numerical simulation of beam propagation through ideal planar wigglers and wigglers with random errors. One concern was that wiggler errors could lead to a large fraction of beam loss to interception by the waveguide. The issue of beam interception, is so critical for the feasibility of the FEL amplifier that an experiment was conducted to investigate sheet beam propagation through a 60-period wiggler (l_w=1 cm)