Parametric Dependence of Density Limits in TEXTOR-94: Comparison ThermalInstability Theory with Experiment

摘要

The observed dependence of the TEXTOR-94 density limit on global parameters (I,B, P, etc.) and wall conditioning is compared with the predicted density limit parametric scaling of thermal instability theory. It is necessary first to relate the edge parameters of the thermal instability theory. It is necessary first to relate the edge parameters of the thermal instability theory to n and the other global parameters. Agreement is found for the dependence on magnetic field and power crossing the separatrix, and for ohmic discharges the theory predicts the observed n-1 scaling. The observed wall conditioning dependence of the density limit can be reconciled with the theory in terms of the radiative effects of different impurities in the plasma edge. The thermal instability theory also provides an explanation of why ohmic discharges are generally observed to symmetrically detach and disrupt at the density limit, whereas auxilliary heated discharges are observed to MARFE and disrupt.