Observation of Inward Turbulent Particle Transport in Edge Plasma Region of CHS Heliotron/Torsatron

Abstract

Reversal of turbulent particle flux near the plasma edge of CHS heliotron/torsatron was observed on various discharge conditions, i.e. during tangential neutral beam injection, electron cyclotron heating at the far edge, and the sawtooth crash. For all cases, the reversal is realized at a narrow particular layer near the plasma edge, when plasma parameters go into low collisionality. The reversal is caused by the change in the cross phase between density (ne) and poloidal electric field (Eθ) fluctuations. The turbulent flux is always inward when the radial electric field shear (E′r) exceeds a certain threshold of ∼1 × 106V m-2. In the sawtoothing plasmas, the arrival of a heat pulse due to the sawtooth crash enhances both ne and Eθ fluctuations but changes the cross phase to π in low-frequency range. As a result, a large inward flux is generated by the sawtooth crash. The particle flux reversal in these cases did not lead to obvious confinement improvement. Show more