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 C VI 5291 Angstrom impurity line of both intrinsic emission and charge exchange emission from neutral beams. Poloidal velocities are typically small (upsilon(theta) less than or equal to 10(4) m/s) requiring small wavelength shifts (Delta lambda less than or equal to 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 less than or equal to 25 Angstrom). A very high throughput spectrometer/ detector system was assembled to achieve the necessary precision in upsilon(theta) upsilon(theta). 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 less than or equal to 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 T-i, upsilon(phi), and n(i) from a charge exchange spectroscopy system, allowing the determination of radial electric field profiles using the force balance equation. (C) 1999 American Institute of Physics. [S0034-6748(99)73801-3].