BURSTS OF ELECTRON-CYCLOTRON EMISSION DURING DISRUPTIONS OF HIGH-BETADISCHARGES IN TFTR

During sudden disruptions of tokamak plasma discharges at high beta, s hort and intense bursts of electron cyclotron emission (ECE) are obser ved. A unique combination of two fast grating polychromator instrument s located at different toroidal positions is used to measure the emiss ion and characterize these bursts. New insights into the 3D dynamics o f these disruptions and the accompanying bursts of ECE have been obtai ned. An explanation of the bursting is presented which is consistent b oth qualitatively and quantitatively with observations, predicting for example radiation enhancement factors of about 10. Bursting can be ex plained not in terms of enhanced excitation of emission but rather in terms of reduction of absorption of thermal emission. Bursting is cons istent with a modification to the electron distribution function f(e) due to a rapid energy or particle exchange between hot electrons and c old electrons from the edge, momentarily reducing the velocity gradien t of f(e) in the thermal region. Large ELM (edge-localized mode) event s also exhibit bursts of ECE due to a similar sequence of events. (C) 1997 Elsevier Science S.A.