Two Point Correlation Technique for the Measurements of Poloidal Plasma Rotation by Heavy Ion Beam Probe

摘要

The paper proposes a method to measure poloidal rotation velocity of toroidal plasma v _pol using Heavy Ion Beam Probe (HIBP) with a multi-slit energy analyzer. The method is based on calculation of phase shift between broadband density turbulence measured simultaneously in two sample volumes, located at the same magnetic surface but separated poloidally. Oscillatory component of HIBP beam current is used as a density turbulence characteristic. HIBP is capable to provide the temporal evolution of the v _pol in a fixed radial position and also the v _pol profile by periodic radial scan. Method was verified in real plasma experiment in ECRH and NBI discharges on the TJ-II stellarator. Result shows that in low density discharges ( n _e ≈ 0.3-0.5×1019 m?3) absolute values of local v _pol is about 4-6 km/s, oriented in the ion diamagnetic drift direction. When HIBP operates for radial scans, it is conventionally measuring the plasma potential profile, and so provides the radial electric field E _r and velocity of E × B drift ( v _E×B) at the same time as plasma rotation. Experimental data shows that in low density ECRH plasma the rotation velocity coincides with E × B velocity within achieved experimental accuracy. When the density is increasing, both v _E×B and v _pol tends to decrease and then change the sign at threshold plasma densities in the range of n _e ≈ 0.7-1×1019 m?3. With this new proposed technique HIBP becomes the new effective tool to study plasma rotation and turbulence characteristics in toroidal plasmas.