Tokamak fusion test reactor poloidal rotation diagnostic (invited)

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Abstract
A new spectroscopicdiagnostic was developed to measure poloidal velocity profiles of Tokamakfusion test reactor (TFTR) plasmas. Carbon poloidal velocities were measured using the Doppler shift of the C VI 5291 Å impurity line of both intrinsic emission and charge exchange emission from neutral beams. Poloidal velocities are typically small (v θ ⩽10 4 m/s ) requiring small wavelength shifts (Δλ⩽0.2 Å) 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 Å). A very high throughput spectrometer/detector system was assembled to achieve the necessary precision in v θ . 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 T i , v φ , and n i from a charge exchangespectroscopy system, allowing the determination of radial electric field profiles using the force balance equation.