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

A model for sawtooth collapse, based on Taylor relaxation of the plasm a core in a Tokamak, is described. The relaxation is assumed to take p lace within a central zone determined by the instability of localized resistive interchange modes, and is accompanied by an ideal MHD adjust ment 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 p arameters. This model has been installed in the '1 1/2 D' resistive ev olution code LARS, and in the paper we carry out a quantitative compar ison of the simulation results with experimental data, in particular w ith the TEXTOR tokamak where detailed measurements are readily availab le.