Session 6Q - TFTR, JT-60, JET.
POSTER session, Wednesday afternoon, November 13
Exhibit Hall - Concourse Level, Adam's Mark
A design study is presented for a collective CO_2 Thomson scattering measurement of confined fusion alphas in high power, deuterium-tritium plasmas in TFTR. The collective regime for these plasmas (n_e=1.0x10^20 m^-3, Te = 10 keV, Ti = 35 keV, n_D = n_T, n_\alpha/n_e = 0.2%) requires scattering angles of about 0.5 deg (k\lambda_D = 0.5), resolution lengths along the beam of about 0.4 m, and access windows of 0.1 m diameter. A few spatial resolution elements in the alpha profile are possible. We assume a 50 MW, 1 \mus, 30 pps laser and heterodyne detection with P_N \sim 5x10^-20 W/Hz resolving the alpha ion feature with \Delta f \sim 2 GHz(\Delta \theta/\theta = \Delta v_\alpha/v_\alpha \sim 0.2). We estimate the maximum signal-to-noise per pulse of about 10 at 5 GHz for an equilibrium alpha slowing down spectrum. Detection is simplified with quantum well detectors which have a bandwidth of 30 GHz permitting double sideband detection and with the use of a hot CO_2 gas absorption cell to eliminate the unscattered laser light from the detection. At 10 \mum plasma light, refraction, and Faraday rotation are unimportant. Magnetic effects modify the spectrum only for k \cdot B / kB < 0.1 and can be avoided. Estimates for TFTR are similar to those for ITER where the radial resolution can be better than 0.3 m across the full diameter of 5.8 m.