IT07 · Explanation of the JET n=0 chirping mode 

H. L. Berk1, C. J. Boswell2, D. Borba3,4, A. C. A. Figueiredo3, T. Johnson5, M. F. F. Nave3, S. D. Pinches6, S. E. Sharapov7, and JET EFDA contributors*

1Institute for Fusion Studies, University of Texas at Austin, Austin Texas, USA
2Plasma Science and Fusion Center, MIT, Cambridge, Massachusetts, USA
3Centro de Fusão Nuclear, Associação EURATOM/IST, Instituto Superior Ténico, Av Rovisco Pais, 1049-001 Lisboa, Portugal
4EFDA Close Support Unit, Culham Science Centre, OX14 3DB, UK
5Alfvén Laboratory, KTH, Euratom-VR Association, Sweden
6Max-Planck Institute for Plasma Physics, EURATOM Association, Boltzmannstrasse 2, D-85748 Garching, Germany
7Euratom/UKAEA, Culham Science Centre, Culham, UK
*See the Appendix of J. Pamela et al., Fusion Energy 2004 (Proc. 20th Int. Conf. Vilamoura, 2004) IAEA, Vienna (2004).

Abstract: Persistent rapid up and down frequency chirping modes with a toroidal mode number of zero (n=0) are observed in the JET tokomak when energetic ions, in the range of several hundred keV, are created by high field side ion cyclotron resonance frequency heating. Fokker-Planck calculations demonstrate that the heating method enables the formation of an energetically inverted ion distribution which supplies the free energy for the ions to excite a mode related to the geodesic acoustic mode (GAM). The large frequency shifts of this mode are attributed to the formation of phase space structures whose frequencies, which are locked to an ion orbit bounce resonance frequency, are forced to continually shift so that energetic particle energy can be released to counterbalance the energy dissipation present in the background plasma.

Note: In special issue in Nuclear Fusion - volume 46, issue 10

Synopsis (pdf)