Thomson scattering diagnostic for the microwave tokamak experiment

The Thomson scattering diagnostic system (TSS) on the microwave tokamak experiment (MTX) at LLNL routinely monitors electron temperature (T e ) and density. Typical measured values at the plasma center under clean conditions are 900±70 eV and 1–2×1014 (±30%) cm−3. The TSS apparatus is compact, with all elements mounted on one sturdy, two‐level optics table. Because of this, we maintain with minimum effort the alignment of both the ruby‐laser input optics and the scattered‐light collecting optics. Undesired background signals, e.g., plasma light as well as ruby‐laser light scattered off obstacles and walls, are generally small compared with the Thomson‐scattered signals we normally detect. In the MTX T e region, the TSS data are definitely fitted better when relativistic effects are included in the equations. Besides determining the temperature of the Maxwellian electron distribution, the system is designed to detect electron heating from GW‐level free‐electron laser (FEL) pulses by measuring large wavelength shifts of the scattered laser photons. TSS data suggest that we may indeed be able to detect these electrons, which can have energies up to 10 keV, according to computer simulation.