Modelling of Sawtooth Destabilization during Radio-Frequency Heating Experiments in the Joint European Torus
Sawtooth oscillations have been stabilized in the Joint European Torus (JET) using radio-frequency waves which deposit their energy in the plasma via ion cyclotron resonance heating (ICRH). Sawteeth often reappear, however, while ICRH is still occurring. In this paper it is shown quantitatively that the reappearance of sawteeth in such cases may be associated with a change of sign in the total potential energy gammaW associated with m = 1 internal kink displacements. To compute gammaW, a realistic model is used for the distribution function of minority ions heated by ICRH, which takes into account strong heating of ions whose banana tips lie in the heated region. At low frequencies, trapped minority ions have a stabilizing effect which arises from conservation of the third adiabatic invariant. However, heated minority ions also contribute to the Shafranov shift of magnetic flux surfaces, which is destabilizing.
Bibliographic Reference: Report: UKAEA FUS 326 (1996) 22pp.
Availability: Available from the Librarian, UKAEA, Culham Laboratory, Abingdon, Oxon, OX14 3DB (GB)
Record Number: 199610336 / Last updated on: 1996-03-29
Original language: en
Available languages: en