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Accueil > Séminaires et conférences > Séminaires, soutenances de thèses et HDR précédents > 2014 > Séminaires 2014 > Le jeudi 11 septembre à 14h

Le jeudi 11 septembre à 14h

R Ganesh - Global Gyrokinetic Stability of Collisionless Microtearing Modes in Large Aspect Ratio Tokamaks

Lieu  : Palaiseau, salle de l’aile 0 (exLIX)

Abstract :
Linear full radius gyrokinetic calculations show the existence of unsta-
ble microtearing modes in purely collisionless, high temperature, large
aspect ratio tokamak plasmas. The first part of the present study takes
into account fully gyrokinetic highly passing ions and electrons. The
global 2-D structures of the collisionless mode with full radius
coupling of the poloidal modes is obtained and compared with another
electromagnetic mode, namely the Alfven ITG Mode (or Kinetic Ballooning
Mode) for the same equilib- rium profile. Several important
characteristics of the modes are brought out and compared, such as a
clear signature in the symmetry properties of the two modes, the plasma
β dependence and radial and poloidal length scales of the electrostatic
and magnetic vector potential fluctuations. Extensive parameter scans
for this collisionless microtearing mode reveal the scaling of the
growth rate with β and the electron temperature gradient ηe. Scans at
different β values show an inverse relationship between the ηe
threshold and β, leading to a stability diagram, and implying that the
mode might exist at moderate to strong temperature gradients for finite
β plasmas in large aspect ratio tokamaks. In contrast to small aspect
ratio tokamaks where the trapped electron magnetic drift resonance is
found to be important, in large aspect ratio tokamaks, a strong
destabilization due to the magnetic drift resonance of passing
electrons is observed and is identified as a possible collisionless
drive mechanism for the collisionless MTM. In the second part, nonadia-
baticity of trapped electrons is included. It is demonstrated that while
growth rates are modified moderately, for a given ηe, presence of
trapped electrons lowers the cricital β above which MTM is unstable.
Many of these results will be discussed in detail and outstanding
issues will be pointed out.


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Tutelles : CNRS Ecole Polytechnique Sorbonne Université Université Paris Sud Observatoire de Paris Convention : CEA
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Mentions légales
Exploitant du site : Laboratoire de Physique des Plasmas, Ecole Polytechnique route de Saclay F-91128 PALAISEAU CEDEX
Hébergeur : Laboratoire de Physique des Plasmas, Ecole Polytechnique route de Saclay F-91128 PALAISEAU CEDEX
Directeur de la publication : Pascal Chabert (Directeur)