Numerical study of neutral beam probe spectroscopy for edge fluctuation measurements

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Abstract
A thermal neutral beam probing combined with a spectroscopic technique is numerically demonstrated to be available to the measurement of local electron-density fluctuations in edge plasmas, although the spatial attenuation of the beam due to the electron-impact ionization is not negligible. It is found that the fluctuations are accurately measured in the region where the density is lower than (4–6) × 1012 cm−3, and that this critical density decreases slightly for the fluctuations which propagate in the beam direction with phase velocities comparable to a thermal speed of the beam. Some results of the beam probe mounted on the TEXTOR tokamak are also described and good agreement is found between numerical and experimental results.