Influence of limiter bias and interchange instabilities on the structure of the tokamak plasma edge
The Jülich 2d boundary layer code SOLXY has proved to be a useful tool for investigating specific physical questions in the plasma edge of limiter tokamaks. The present paper considers two different problems related to a toroidal belt limiter such as the ALT-II of TEXTOR. An investigation into limiter bias led to the proposal of an electrically biased pump limiter that creates a potential ditch. This channels the particles (D,T-ions and impurities) into the limiter scoops, while reducing the particle load and material sputtering at the neighbouring parts of the limiter, i.e. the leading edge of the blade and the side faces of the pumping duct. For the investigation into interchange instabilities, a numerical experiment was performed by triggering and cultivating unstable short wavelength modes in the boundary layer. It has been predicted theoretically that the anomalous transport in the plasma edge is due to the destabilising action of interfering material surfaces (limiter or divertor targets) on parallel electric currents along the open field lines. A major candidate for inducing microturbulence is interchange instabilities (flutes) in regions of unfavourable curvature and indeed an instability of this kind is found, growing predominantly near the outboard midplane and close to the separatrix.
Bibliographic Reference: Article: 18th European Conference on Controlled Fusion and Plasma Physics, Vol. III (1991) pp. 13-16
Record Number: 199111383 / Last updated on: 1994-12-02
Original language: en
Available languages: en