Inward turbulent particle transport in a helical plasma heated by neutral beam injection

In neutral-beam-injection (NBI) heated plasmas of the Compact Helical Syste m (CHS) heliotron/torsatron [K. Matsuoka , Plasma Physics and Controlled Nu clear Fusion Research, 1988 (International Atomic Energy Agency, Vienna, 19 89), Vol. 2, p. 441], inward turbulent particle flux is observed at a parti cular radial location near the plasma edge. The observed reversal of the pa rticle flux is connected to the change in the cross-phase between electron density and poloidal electric field fluctuations. This phenomenon is observ ed in the parameter regime of low collisionality at the electron temperatur e T-e > 15 eV, electron density n(e) < 3 x 10(18) m(-3), which approximatel y corresponds to the effective collision frequency normalized by the transi t frequency of a circulating particle nu (*) less than or similar to 1. The large inward particle flux (greater than or similar to1 x 10(20) m(-2) s(- 1)) correlates with the positive shear of the radial electric field E-r(') (greater than or similar to1 x 10(6) V m(-2)), but does not have clear corr elation with the radial electric field E-r and the curvature E-r'. (C) 2001 American Institute of Physics.