Combination of multichannel detection and fast time response in a multichord spectrometer

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Abstract
A high resolution spectrometer has been used to measure simultaneously plasma impurity ion temperatures and rotational velocities, with submillisecond temporal resolution. The dual requirements of detailed spectral detection and fast time response are satisfied by having two detection systems viewing the same dispersed spectrum. The first is a multichannel system (e.g., a two-dimensional charge coupled device camera, for multichord detection) and the other an assembly comprising of three photomultipliers. A matched double spectrometer (f=1.26 m) is used to disperse the spectrum and giving an overall inverse dispersion of 0.04 nm/mm. The dispersive power is about 20× greater than the more conventional systems and has a corresponding increase in etendu, or light throughput, for the same resolution. The combination has been successfully used for magnetohydrodynamics mode locking experiments on COMPASS-C tokamak where velocity shifts of ∼30 km−1 were measured to an accuracy of ∼1 km s−1 with a 40 μs time resolution.

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