Stability of electron-driven fishbones
Event details
| Date | 10.07.2012 |
| Hour | 10:30 › 11:30 |
| Speaker | Dr A. Merle, Institut de Recherche sur la Fusion Magnétique, CEA Cadarache, France |
| Location |
PPB 019
|
| Category | Conferences - Seminars |
In tokamaks, MHD instabilities such as electron-driven fishbone modes are frequently observed in the presence of electron heating and current-drive. These modes provide a good test bed for the linear theory of fast-particle driven instabilities as they exhibit a very high sensitivity to the details of both the equilibrium and the electronic distribution function. This has been shown by an analysis of the modes observed in Tore Supra discharges. The analysis is completed by numerical calculations using the recently developed code MIKE. Coupled to the ray-tracing and Fokker-Planck codes C3PO/LUKE for the reconstruction of the electron distribution, MIKE solves the linear dispersion relation for electron fishbones, accounting for both fluid and kinetic contributions.
In Tore Supra, electron-driven fishbones are observed during LHCD-powered discharges in which a high-energy tail of the electronic distribution function is created. Although the destabilization of those modes is related to the fast particle population, the modes are observed at relatively low frequency. A basic estimate of resonant electrons energy assuming resonance with the toroidal precession frequency of barely trapped electrons falls in the thermal range.
We analyze the stability of internal kink modes in the presence of energetic electrons using the code MIKE which has been modified to fully account for the resonance of modes with passing particles. For circulating electrons, the parallel motion contributes to the resonance condition. Using simple analytical distributions and equilibria, we show that both barely trapped and barely passing electrons resonate with the mode and can drive it unstable. More deeply trapped electrons have a stabilizing influence, while more passing particles are destabilizing. Moreover our analysis with ECRH-like distribution functions shows that a relatively low frequency is compatible with a mode that is mostly driven by energetic barely passing electrons, even in the absence of a wide q~1 region.
In Tore Supra, electron-driven fishbones are observed during LHCD-powered discharges in which a high-energy tail of the electronic distribution function is created. Although the destabilization of those modes is related to the fast particle population, the modes are observed at relatively low frequency. A basic estimate of resonant electrons energy assuming resonance with the toroidal precession frequency of barely trapped electrons falls in the thermal range.
We analyze the stability of internal kink modes in the presence of energetic electrons using the code MIKE which has been modified to fully account for the resonance of modes with passing particles. For circulating electrons, the parallel motion contributes to the resonance condition. Using simple analytical distributions and equilibria, we show that both barely trapped and barely passing electrons resonate with the mode and can drive it unstable. More deeply trapped electrons have a stabilizing influence, while more passing particles are destabilizing. Moreover our analysis with ECRH-like distribution functions shows that a relatively low frequency is compatible with a mode that is mostly driven by energetic barely passing electrons, even in the absence of a wide q~1 region.
Practical information
- General public
- Free
Organizer
- CRPP
Contact
- Paolo Ricci