Numerical Marfe simulations at ASDEX and ASDEX-Upgrade
It has been shown by numerical simulations that for certain ranges of the discharge parameters (particularly for high plasma density and impurity concentration) Marfes will occur in the edge plasma of ASDEX-Upgrade. The limit for Marfe onset has been determined as a function of the plasma density, the power influx into the edge plasma and the safety factor. On raising the plasma density, for sufficiently high impurity concentration, there exists a sharply defined critical value above which the plasma state abruptly reorganises and a Marfe is formed. For fixed impurity concentrations, this density increases for increasing input power but is nearly independent of the safety factor although the relative density enhancement of the Marfe increases with q (i.e. the Marfe becomes more pronounced for high q and flattens for decreasing q). Starting from the Marfe plasma state and lowering the density, the plasma returns to the Marfe-free state at another critical density which is usually lower than the first one. This hysteresis increases with the energy input and nearly vanishes below about 1 MW. However, Marfe formation as a highly nonlinear process also depends crucially on the details of the model, so at this stage the results have only a qualitative meaning. The time dependent multi-fluid calculations show that Marfes are usually not in steady state, but deform and move around the lower x-point region with an intensity which depends on how far the density is beyond the limit for Marfe onset. This behaviour is coupled to the motion of the lower impurity charge states which provide effective radiative energy losses and thus cool the plasma.
Bibliographic Reference: Article: Proceedings of the 20th European Conference on Controlled Fusion and Plasma Physics, Vol. II (1993) pp. 807-810
Record Number: 199311151 / Last updated on: 1994-11-29
Original language: en
Available languages: en