Tokamak fusion test reactor poloidal rotation diagnostic (invited)

A new spectroscopic diagnostic was developed to measure poloidal velocity profiles of Tokamak fusion test reactor (TFTR) plasmas. Carbon poloidal velocities were measured using the Doppler shift of the CVI 5291 Angstrom impurity line of both intrinsic emission and charge exchange emission from neutral beams. Poloidal velocities are typically small (vθ≤104m/s) requiring small wavelength shifts (Δλ≤0.2 Angstrom) to be measured. However, the high central ion temperatures in TFTR required the use of a low dispersion spectrometer to view the entire linewidth (full width at half maximum ≤25 Angstrom). A very high throughput spectrometer/detector system was assembled to achieve the necessary precision in vθ. Statistical errors in the chord-averaged poloidal velocity less than 100 m/s have been obtained. The short focal length spectrometer features f/1.8 input optics, a transmission grating, and refractive optics. A thinned back-illuminated charge coupled device detector provided a high quantum efficiency (QE=75%). The diagnostic had 20 ms time resolution and a radial resolution of ≤3.5 cm after an inversion. Two symmetric up/down views were used to eliminate atomic physics effects that would otherwise distort the measured rotation velocity. This diagnostic complemented the measurements of Ti, vφ, and ni from a charge exchange spectroscopy system, allowing the determination of radial electric field profiles using the force balance equation. copyright 1999 American Institute of Physics