The measurements of magnetic field fluctuation with a heavy ion beam probe (HIBP) in the Large Helical Device (LHD) are considered in this article. Measured value reflects not only the fluctuation at the observation point (sample volume) but also the fluctuation on the beam path. These effects (called as the path integral effects) are considered and calculated for variations of fluctuations in LHD. The distortion of the measured profile by the path integral effect is not significant at the peak of the fluctuation amplitude. In contrast, in the region far from the peak, phony signals due to path integral effects are observed. Finally, the resolution of magnetic field fluctuation measurements with our HIBP system is estimated. Estimated results show that the magnitude of 4.1× 10-5 T can be measured with our system.
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