Poloidal rotation velocity and ion temperature measurements in edge plasma region

Diagnostic description:

The pasive spectroscopic diagnostic with a high spectral resolution based on observations of impurity lines, such as carbon or oxygen, is used on the COMPASS tokamak for measurements of both poloidal rotation and ion temperature in the plasma edge. Poloidal rotation of the plasma directly influences particle confinement time, meanwhile, ion temperature is an important parameter for determination of plasma energetic balance.

To determine edge plasma rotation, Doppler shift of the spectral lines of two times ionized carbon using the spectrometer with a high dispersion can be used. There, ion temperature can be extracted from Doppler broadening of the observed lines. The two-grating spectrometer, see Fig. 1 (left), which has been already successfully used for similar measurements on the ISTTOK tokamak in Portugal [Gomes, et al., Rev. Sci. Instrum. 74, 2071 (2003)], was borrowed to IPP Prague in 2009. The spectrometer is coupled with the COMPASS tokamak by the set of optical fibres, and is optimized for measurements in a narrow spectral band of about 2 nm (at 465 nm). It allows to observe the triplet of the carbon lines CIII 464.74 nm, 465.03 nm, and 465.15 nm. Spectra are recorded by the high-speed spectroscopic camera Andor iXon EM+ DU-897 with a high quantum efficieny and providing a typical time resolution of 20 ms.

Fig. 1: Spectorgraph set-up (left) and C 2+ spectra from COMPASS tokamak (right)