STABILIZATION AND ONSET OF SAWTEETH IN TFTR

Measurements from the Tokamak Fusion Test Reactor (TFTR) of the q prof ile using motional Stark effect polarimetry and the pressure profiles have allowed detailed comparison of both supershots and L-mode dischar ges to theoretical models describing the stability of sawteeth. In TFT R supershots sawteeth are usually absent, whereas in L-mode discharges they are generally present, and in both cases q(0) is less than 1. It has been found that the omega-stabilization criterion of the two-flu id collisionless m = 1 reconnection mode agrees very well with the pre sence or absence of sawteeth in TFTR and no beta limits to the sawtoot h stabilization have been observed.