DESIGN OF A SUBMILLIMETER-WAVE ALPHA-PARTICLE THOMSON SCATTERING DIAGNOSTIC FOR FUSION PLASMAS

A collective Thomson scattering system based on a NH3 laser master oscillator and a free-electron laser (FEL) amplifier operating at a wavelength of 152 μm is described. The FEL is driven by a compact, high repetition rate induction linear accelerator developed at SRL. Operation of a prototype linac at a repetition rate of 1 kHz has been demonstrated. Simulations show that the FEL is capable of supplying the required 11 kW average (220 MW peak) radiated power for a successful Thomson scattering measurement with a measurement time of 100 ms. A detailed design of the tapered FEL wiggler and beam transport system has been completed. A high repetition rate CO2 pump laser to be used in the FIR master oscillator has also been designed. This laser will employ a compact closed flow loop to achieve 1 kW average power, narrow line operation at a 1 kHz pulse rate.