Bursts of electron cyclotron emission during disruptions of high β discharges in TFTR

During sudden disruptions of tokamak plasma discharges at high β, short and intense bursts of electron cyclotron emission (ECE) are observed. A unique combination of two fast grating polychromator instruments located at different toroidal positions is used to measure the emission and characterize these bursts. New insights into the 3D dynamics of these disruptions and the accompanying bursts of ECE have been obtained. An explanation of the bursting is presented which is consistent both qualitatively and quantitatively with observations, predicting for example radiation enhancement factors of about 10. Bursting can be explained not in terms of enhanced excitation of emission but rather in terms of reduction of absorption of thermal emission. Bursting is consistent with a modification to the electron distribution function fe due to a rapid energy or particle exchange between hot electrons and cold electrons from the edge, momentarily reducing the velocity gradient of fe in the thermal region. Large ELM (edge-localized mode) events also exhibit bursts of ECE due to a similar sequence of events.