Calibration procedure and data processing for a TV Thomson scattering system

Calibration procedures for Thomson scattering systems based on television-like cameras, so-called TVTS systems, are described. The TVTS systems of the Rijnhuizen Tokamak Project (RTP), the TJ-II stellarator, and the Torus Experiment for Technology Oriented Research (TEXTOR) tokamak combine a 10-15 J ruby laser as a source with an intensified charge coupled device camera as a detector. A tungsten strip lamp in combination with an integrating sphere is used to calibrate all similar to 10(5) pixels of the camera relatively to each other. Rayleigh scattering on hydrogen or nitrogen is used to perform an absolute calibration of the complete detection system. Great emphasis is placed on possible systematic errors on the determination of the electron temperature T-e and density n(e) due to the calibration, such as tungsten lamp temperature, detoriation of the detection window, long term stability, laser beam alignment, and detector linearity. The long term stability of the system was tested by comparing different sets of calibration factors. Over a period of 1/2 yr the values of the calibration factors varied by less than 5%. Using the same Thomson scattering data but different sets of calibration factors the T-e values varied even less than 1%. A two camera technique was used to search for possible unknown systematic errors in the determination of T-e profiles. It appears that these systematic errors are about half of the observational error on T-e. Density fluctuations can be determined with an accuracy equal to the statistical error of similar to3%, while the systematic error on n(e) appeared to be similar to 10%, which can be corrected for using interferometer data. As a result, these TVTS systems can measure T-e and n(e) profiles with similar to 100 (RTP) or 120 (TEXTOR) spatial elements along the full plasma diameter with observational errors on T-e of similar to6% in the range of 25 eV-6 keV, at n(e) = 2 x 10(19) m(-3) and 10 J laser energy. (C) 2001 American Institute of Physics.

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