Disruptions in the TFTR tokamak

For a successful reactor, it will be useful to predict the occurrence of disruptions and to understand disruption effects, including how a plasma disrupts onto the wall and how reproducibly it does so. Studies of disruptions on TFTR at both high βpol and high density have shown that, in both types, a fast growing m/n = 1/1 mode plays an important role. In high-density disruptions, a newly observed fast m/n = 1/1 mode occurs early in the thermal decay phase. For the first time in TFTR, q-profile measurements just prior to disruptions have been made. Experimental studies of heat deposition patterns on the first wall of TFTR due to disruptions have provided information on MHD phenomena prior to or during the disruption, how the energy is released to the wall, and the reproducibility of the heat loads from disruptions. This information is important in the design of future devices such as ITER. Several new processes of runaway electron generation are theoretically suggested to be effective in large-tokamak disruptions (including TFTR and ITER) for a sizeable range of discharge parameters. A preliminary assessment of hard x-ray data from TFTR appears consistent with their generation from disruption-generated runaways. (author). 15 refs, 7 figs, 1 tab