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Systematic studies of Alfvén eigenmodes (AE) are performed at JET, based on the excitation via resonant interaction with fast particles generated by additional heating and by fusion reactions, and via external antennas, providing a direct measurement of the mode damping rate. Similar damping rates are observed in D-D and D-T plasmas with similar configurations. In both cases the formation of an X-point provides a strong stabilizing effect on low-n toroidal Alfvén eigenmodes (TAE). The fast particle drive is detected as a reduction in the measured damping rate as the fast particle pressure is increased. For interrupted current rise heating (ICRH) power levels above the experimentally established marginal stability limit, the magnetic fluctuation spectra indicate the destabilization of different families of AE (TAE, EAE, kTAE, NAE). In 50:50 D-T plasmas characterized by moderate fusion power, alpha particle pressure is observed to destabilize TAE in the afterglow of the neutral beam injection and ICRH heating phase. The diagnostic potential of AE is discussed along with the implications for the AE stability in ignited plasmas.

Additional information

Authors: FASOLI A, École Polytechnique Fédérale de Lausanne, Centre de Recherches en Physique des Plasmas (CH);HEETER R, Princeton University Plasma Physics Laboratory (US);BORBA D, JET Joint Undertaking, Abingdon, Oxon (GB);GORMEZANO C, JET Joint Undertaking, Abingdon, Oxon (GB);SHARAPOV S, JET Joint Undertaking, Abingdon, Oxon (GB);JAUN A, Alfvén Laboratory, Royal Institute of Technology, Stockholm (SE)
Bibliographic Reference: Article: Bulletin of the American Physical Society, Vol. 42 (1997) No. 10, p. 1860
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