The development of 6 MeV heavy ion beam probe system in LHD

The 6 MeV Heavy Ion Beam Probe (HIBP) was installed to Large Helical Device (LHD) and it has been developed. The radial profile of potential in the region where normalized minor radius, ρ, is less than 0.5 was measured, and the electric field obtained from the fitting function of experimental data was compared with the neoclassical theory. The experimental results fairly coincided with the theory. The negative pulses were observed in potential signal in the case of the inward shifted magnetic configuration. The time constants of these pulses were less than the energy confinement time. Potential fluctuations of coherent modes were also observed, and one of their frequencies coincided with the geodesic acoustic mode (GAM). In this report, the present status of potential measurements with HIBP system in LHD is described. (author)