Density fluctuations in JIPP T-IIU tokamak plasmas measured by a heavy ion beam probe

Multiple and small sample volume measurements of the density turbulence and potential profile measurements in tokamak plasmas were conducted using a heavy ion beam probe. The obtained wavenumber-frequency spectrum S(k,ω) shows that the cross-sections of neutral beam injection (NBI) heated plasmas are divided into three regions of different turbulence characteristics. Outside the layer where the direction of the density turbulence propagation reverses, a low frequency and low wavenumber mode travelling in the ion diamagnetic drift direction dominates. The region enclosed by this reversal layer is divided into two parts during nearly perpendicular NBI heating: a region where the propagation velocity is near the E_r/B_t poloidal rotation velocity and a bad curvature region of very small wavenumber and high propagation velocity. The region of high propagation velocity, found in NBI plasmas, disappears in the ohmic plasmas. In addition, a small component that propagates in the ion diamagnetic drift direction is observed in NBI plasmas.