Simultaneous Measurements of Plasma Potential and Density Fluctuations in a Bumpy Torus by a Heavy Neutral Beam Probe

A heavy neutral beam probe was developed for simultaneous measurements of local space potential and density fluctuations in a plasma. It was applied to both electron cyclotron heated (ECH) and radio frequency heated (RF) plasmas in the bumpy torus NBT-1M, and the feasibility of this method was successfully demonstrated by observing a low frequency m = 1 interchange mode which was rotating poloidally at a frequency near the E X B drift frequency. It was shown that use of this probe results in extension of the range of fluctuation measurement by beam probe technique to relatively low temperature plasmas. It is applicable to a plasma with a strong RF field with which Langmuir probes cannot be used.