Development of 2D potential profile measurements using the heavy ion beam probe on the large helical device

Two-dimensional potential fluctuation profiles were measured with the heavy ion beam probe (HIBP) on the Large Helical Device. For two-dimensional measurements with HIBP, the probe beam energy had to be changed, and subtle adjustment of the beam trajectory along the long beam transport line (~20 m) was required. An automatic beam adjustment system was developed for the beam transport line, and used to easily adjust the probe beam trajectory. Potential fluctuations in the high-frequency range (~200 kHz) were measured, and the probe beam energy was changed shot to shot. Two-dimensional potential phase structures were successfully obtained by analyzing the coherence between potential and magnetic field fluctuation, which is used as a reference signal.