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PRODID:-//Memento EPFL//
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SUMMARY:Stability of electron-driven fishbones
DTSTART:20120710T103000
DTEND:20120710T113000
DTSTAMP:20260410T094924Z
UID:a1b36d78f786e829334fcb25a13c01cc2567c478dd01f69df672be0f
CATEGORIES:Conferences - Seminars
DESCRIPTION:Dr A. Merle\, Institut de Recherche sur la Fusion Magnétique
 \, CEA Cadarache\, France\nIn tokamaks\, MHD instabilities such as electr
 on-driven fishbone modes are frequently observed in the presence of electr
 on 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 electroni
 c distribution function. This has been shown by an analysis of the modes o
 bserved in Tore Supra discharges. The analysis is completed by numerical c
 alculations using the recently developed code MIKE. Coupled to the ray-tra
 cing and Fokker-Planck codes C3PO/LUKE for the reconstruction of the elect
 ron distribution\, MIKE solves the linear dispersion relation for electron
  fishbones\, accounting for both fluid and kinetic contributions.\n\nIn To
 re Supra\, electron-driven fishbones are observed during LHCD-powered disc
 harges 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 frequ
 ency. A basic estimate of resonant electrons energy assuming resonance wit
 h the toroidal precession frequency of barely trapped electrons falls in t
 he thermal range.\n\nWe analyze the stability of internal kink modes in th
 e presence of energetic electrons using the code MIKE which has been modif
 ied to fully account for the resonance of modes with passing particles. Fo
 r 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 m
 ode and can drive it unstable. More deeply trapped electrons have a stabil
 izing influence\, while more passing particles are destabilizing. Moreover
  our analysis with ECRH-like distribution functions shows that a relativel
 y low frequency is compatible with a mode that is mostly driven by energet
 ic barely passing electrons\, even in the absence of a wide q~1 region.
LOCATION:PPB 019
STATUS:CONFIRMED
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