Comparison of Sawtooth Phenomenology on TFTR and DIII-D

An experiment to study sawtooth phenomena and to find the threshold for sawtooth stabilization with neutral beam injection heating, as was commonly observed on TFTR, has been done on DIII-D. In the experiments, with co-tangential neutral beam injection at powers of up to 13MW, the sawtooth period was observed to increase to of order 250 msec. Stabilization of the sawteeth for the length of the high power NBI (0.5-0.8 sec) was not observed. The sawtooth characteristics were studied with fast electron temperature (ECE) and soft x-ray diagnostics. Fast, 2 msec interval, measurements were made of the ion temperature evolution following the sawtooth to document the ion heat pulse characteristics. These data show that the ion heat pulse does not exhibit the very fast, ''ballistic'' behavior seen for the electrons. The current profile and other equilibrium profiles were measured on slower time scales. These results are compared to the data from similar studies carried out on TFTR.