CALCULATION OF THE POSTCRASH STATE AND 1-1/2-D SIMULATION OF SAWTOOTH CYCLES

A model for sawtooth collapse, based on Taylor relaxation of the plasma core in a Tokamak, is described. The relaxation is assumed to take place within a central zone determined by the instability of localized resistive interchange modes, and is accompanied by an ideal MHD adjustment of the external region so as to maintain force balance across the interface. Using an aspect ratio expansion, equations determining the post-crash equilibrium are derived and solved in terms of equilibrium quantities prior to collapse. The crash model contains no arbitrary parameters. This model has been installed in the '1 1/2 D' resistive evolution code LARS, and in the paper we carry out a quantitative comparison of the simulation results with experimental data, in particular with the TEXTOR tokamak where detailed measurements are readily available.