The development of potential measurements with 6 MeV Heavy Ion Beam Probe on LHD

In order to measure the potential in Large Helical Device (LHD), 6 MeV heavy ion beam probe (HIBP) has been developed. The temporal evolvements of potential in the central region of plasmas, which were produced by neutral beam injection (NBI) and additionally heated by electron cyclotron heating (ECH), were measured with our HIBP system. The line averaged density of these shots were about 1 ~ 5 × 10 18 m -3 . At the time of ECH was applied, a rapid change of potential to positive direction was observed. In this ECH phase, negative pulses were observed in the potential signal, which were very similar to "pulsation" that was firstly found in Compact Helical System (CHS), however, the time constant of these pulses were larger than in the case of CHS. In the NBI phase, the fluctuation was observed with HIBP, of which frequency was correlated with potential of equilibrium. It is considered that this frequency was influenced by E × B drift.