Abstract
During ohmically heated high current deuterium discharges in JET, inverted sawtooth oscillations in the superthermal ion cyclotron emission (ICE) have been detected which cannot be accounted for by fluctuations in the antenna-plasma coupling efficiency. This observation confirms the spatial localization of the ICE source in the edge plasma, close to the position of the detecting RF antenna on the low field side of the torus. Strong time correlation is observed between the inverted ICE sawteeth and those seen in an outer soft X-ray channel and in Dα emission from the limiter. Time delay data show that the ICE sawtooth peaks coincide with the arrival of sawtooth heat pulses in the edge plasma which are delayed by 17 ms with respect to the central sawtooth crash. The ICE sawtooth oscillations are interpreted in terms of local changes in the thermonuclear D-D fusion reactivity in the edge plasma. The observations are consistent with the interpretation of ICE as the result of maser action by an energetic ion population.
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