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Impact of microtearing on electron transport in magnetized plasmas

par Elodie PICO - publié le

Thesis advisor : Xavier Garbet
Email and address : xavier.garbet
IRFM, CEA, St-Paul-Lez-Durance 13108, France
Co-advisor : Magali Muraglia (magali.muraglia,
Centre Saint Jérôme, Case 322
Avenue Escadrille Normandie-Niemen,
13397, Marseille Cedex 20, France)

Subject description :

Several instabilities can deteriorate the magnetic confinement in tokamaks. These instabilities are driven by strong gradients in the core plasma. In particular, fluctuations of the magnetic field associated with the current gradient can generate MagnetoHydroDynamic (MHD) instabilities, called tearing modes, that lead to a modification of the magnetic field lines topology. This phenomenon, called "magnetic reconnection", also takes place in solar flares [1]. The size of the island shaped magnetic structures generated by MHD instabilities is usually of about a few centimetres, and may reach a significant fraction of the machine size. However, recent experiments, in spherical torus and/or high aspect ratio tokamaks, indicate that magnetic reconnection also occurs at small scales [2, 3], in relation with microtearing instabilities. The stochasticity of field lines and the destruction of magnetic surfaces have a strong impact on electron transport [4]. Early theoretical studies [5] have shown that the tearing mode is stable at small scales while microtearing modes have been observed in experiments recently. Thus a lot of questions are still open. More precisely, we propose to study, by means of numerical simulations, the mechanism (still unknown) that underlies the microtearing instability, the non linear evolution of these modes and their impact on electron transport.
Scales at play for this problem are of the same order as the ion Larmor radius and
a gyro-kinetic plasma description is required. We plan to use the gyro-kinetic GKW code [6] to work on this project.

Bibliography :
[1] D. Biskamp, Magnetic Reconnection in Plasma, Cambridge University Press, Cambridge, England (2000)
[2] K.L. Wong et al., Phys. Rev. Lett. 99, 135003 (2007)
[3] M. Zuin et al., Phys. Rev. Lett. 110, 055002 (2013)
[4] W. Guttenfelder et al., Phys. Plasma 19, 056119 (2012)
[5] H.P. Furth et al., Phys. Fluids 6, 459 (1963)
[6] A.G. Peeters et al., Computer Physics Communication 180, 2650 (2009)