abstract_PPCF_Toi
Observation of inward turbulent particle
transport in edge plasma region of CHS heliotron/torsatron.
Toi K. Ohkuni K. Shats MG. Akiyama
R. Goto M. Isobe M. Matsunaga G. Matsuoka K. Minami T. Morita S. Nishimura
S. Nomura I. Okamura S. Osakabe M. Shimizu A. Suzuki C. Takagi S.
Takahashi C. Takechi M. Tanaka K. Yoshimura Y.
Plasma Physics & Controlled Fusion,
vol.44, suppl.5A, May 2002, pp.A237-43. UK.
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 (n/sub
e/) and poloidal electric field (E/sub theta /) fluctuations. The turbulent
flux is always inward when the radial electric field shear (E'/sub r/) exceeds
a certain threshold of ~1*10/sup 6/ V m/sup -2/. In the sawtoothing plasmas,
the arrival of a heat pulse due to the sawtooth crash enhances both n/sub
e/ and E/sub theta / fluctuations but changes the cross phase to pi 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. (
