ALT-II toroidal belt limiter biasing experiments on TEXTOR
Edge electric fields have been related to H-mode-like behaviour. The experiments reported are an attempt to control the SOL profiles by electrostatic biasing of the full toroidal-belt limiter ALT-II. The specific goals are to influence the edge particle flows, particle removal, power deposition and the global confinement. Experiments have been performed with levels of biasing power of up to 180 KW and in discharges characterised by B(t)=2.25 T, I(p)=340 KA and n(e)=2.5 to 3.0 x 1.0 E13/cm3. The typical time sequence consists of an initial ohmic phase, followed by a biasing phase from 1.0 to 2.0 sec. and an overlapping neutral beam injection (NBI) phase from 1.5 to 2.5 sec. The gas feed is switched off at 0.8 sec. For the data presented, a helium puff lasting 15 msec was injected at 0.8 sec. The biasing voltage is referenced to the liner. Two biasing configurations are examined: 1) biasing ALT-II with the plasma positioned on ALT-II and 2) biasing ALT-II with the plasma positioned to contact both the inner-bumper limiter (at liner potential) and ALT-II (creating enhanced poloidal electric fields). Comparisons are made for both bias polarities with co-NBI, counter-NBI and ohmic discharges. Radial profiles of floating potential, poloidal field, n(e) and T(e) are obtained using a fast-reciprocating probe.
Bibliographic Reference: Article: 18th European Conference on Controlled Fusion and Plasma Physics, Vol. IV (1991) pp. 369-372
Record Number: 199111403 / Last updated on: 1994-12-02
Original language: en
Available languages: en