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Ion cyclotron emission (ICE) has been observed during neutral beam heated supershot discharges in the Tokamak Fusion Test Reactor (TFTR) deuterium-tritium campaign at sequential cyclotron harmonics of both fusion products and beam ions. The emission originates from the outer midplane edge plasma, where, during the initial phase of the discharge, fusion products are likely to have a drifting ring-type velocity-space distribution which is anisotropic and sharply peaked. The birth velocity of fusion products is smaller than the local Alfvén speed at the outer midplane in the TFTR supershot discharges considered here. In this paper it is shown that the magnetoacoustic cyclotron instability, which results in the generation of obliquely propagating fast Alfvén waves at low cyclotron harmonics of the fusion ions, can occur under such conditions. Moreover, the time evolution of the maximum growth rate closely follows the observed time evolution of ICE amplitude, averaged over several TFTR supershot discharges. The magnetoacoustic cyclotron instability is supressed if the sub-Alfvénic fusion ions undergo even a moderate degree of thermalisation, or are isotropic. In contrast, the super-Alvénic fusion products which are present in the outer midplane of the Joint European Torus (JET) can drive the magnetoacoustic cyclotron instability even if they are isotropic or have a relatively broad distribution of speeds. These conclusions may help to account for the observation that product-driven ICE in JET persists for longer than fusion product-driven ICE in TFTR supershot discharges.

Additional information

Authors: MCCLEMENTS K G ET AL., AEA Fusion, Culham Laboratory, Abingdon, Oxon. (GB)
Bibliographic Reference: Report: UKAFA FUS 280 EN (1995) 26 pp.
Availability: Available from the Librarian, UKAEA, Culham Laboratory, Abingdon, Oxon. OX14 3DB (GB)
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