RADIATIVE INSTABILITIES IN THE TOKAMAK SCRAPE-OFF LAYER DURING EDGE-LOCALIZED MODE ACTIVITY

In order to reduce the heat flux entering the divertor, it is desirabl e to have strong impurity radiation in the scrape-off layer (SOL) of r eactor-size tokamaks like the International Thermonuclear Experimental Reactor [International Thermonuclear Experimental Reactor (ITER) Conc eptual Design Activity Final Report, ITER Documentation Series No. 16 (International Atomic Energy Agency, Vienna, 1991)]. Under such circum stances, however, the SOL plasma is likely to be unstable to the radia tive condensation instability. In the present paper, an investigation is undertaken to study the effects of edge-localized mode (ELM) activi ty on this instability. In the linear regime, it is demonstrated that high-frequency (''grassy'') ELM's may parametrically excite acoustic w aves. The possibility of nonlinear radiative collapse with concomitant stratification of the plasma is discussed, and solutions describing n onlinear traveling waves are derived in which the plasma goes over fro m equilibrium state to another. (C) 1995 American Institute of Physics .