Near-millimeter free electron lasers with small period wigglers and sheet electron beams
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Electron cyclotron resonance heating (ECRH) of plasmas in magnetic fusion research and space-borne radar systems are both projected to require high power radiation sources at wavelength λ not, vert, similar 1 mm. For ECRH, a premium is placed on cw operation combined with high efficiency and moderate voltage in order to meet budgetary constraints. The space-borne radar sources must be compatible with size and weight constraints, and preferably be in the form of high gain amplifiers. In response to these needs, we are investigating the feasibility of a free electron laser (FEL) at 1 mm < λ < 2 mm utilizing a small period wiggler (0.5 cm less, approximate lw less, approximate 1 cm) and a “low” energy (not, vert, similar 0.5 MeV) sheet electron beam to produce 0.1–1.0 MW of output power. We describe a planned experiment, together with recent results of laboratory and theoretical studies of such important issues as: wiggler fabrication and performance; generation, propagation, and stability of the sheet electron beam; and energy recovery from the spent beam. Oscillators with both tapered and untapered wigglers have been considered.