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The theory of the magnetoacoustic cyclotron instability, which has been proposed as a mechanism for suprathermal ion cyclotron harmonic emission observed in large tokamaks, is generalised to include finite parallel wavenumber k(parallel). This extension introduces significant new physics: the obliquely propagating fast Alfvén wave can undergo cyclotron resonant interactions with thermal and fusion ions, which affects the instability driving and damping mechanisms. The velocity-space distribution of the fusion ions is modelled by a drifting ring, which approximates the distribution calculated for the emitting region in tritium experiments on JET. Linear instability can occur simultaneously at the fusion ion cyclotron frequency and all its harmonics when the fusion ion concentration is extremely low, because the finite k(parallel) gives rise to a Doppler shift which decouples cyclotron damping due to thermal ions from wave growth associated with fusion ions. Doppler shifts associated with finite k(parallel) may also be related to the observed splitting of harmonic emission lines.

Additional information

Authors: DENDY R O, AEA Fusion, Culham Laboratory, Abingdon, Oxon. (GB);LASHMORE-DAVIES C N, AEA Fusion, Culham Laboratory, Abingdon, Oxon. (GB);MCCLEMENTS K G, AEA Fusion, Culham Laboratory, Abingdon, Oxon. (GB);COTTRELL G A, JET Joint Undertaking, Abingdon, Oxon. (GB)
Bibliographic Reference: Report: AEA FUS 255 EN (1993)
Availability: Available from the Librarian, UKAEA, Culham Laboratory, Abingdon, Oxon. OX14 3DB (GB)
Record Number: 199311645 / Last updated on: 1994-11-28
Original language: en
Available languages: en