Details |
|
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 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
|