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Analysis of turbulent transport in the central part of high-confinement tokamak plasmas

Abstract : Turbulent transport is investigated in the central region of the high-$\beta$ JET hybrid H-mode discharge 75225 by means of linear and non-linear gyro-kinetic (GK) simulations using the GK code GKW in the local approximation limit. Compared to previous work, the analysis is extended towards the magnetic axis, $\rho < 0.3$, where the turbulence characteristics remain an open question. In contrast to the region $\rho > 0.3$ where Ion Temperature Gradient modes are the most unstable modes, the linear stability analysis indicates that Kinetic Ballooning Modes (KBM) dominate in the central region. A dedicated analysis performed at $\rho = 0.15$ reveals that the main parameters responsible for the destabilisation of KBMs in these hybrid H-modes are the high $\beta$ and low magnetic shear values. The KBMs are driven by the main ion pressure gradient with little influence of the electron temperature gradient. Including fast-ions as a kinetic species in the simulations has a slight stabilising effect. The study is then extended to the non-linear regime. It is found that the turbulence induced by these KBMs drives a significant ion and electron heat flux. Interestingly, linearly stable micro-tearing-modes (MTM) are excited non-linearly and drive a sizeable magnetic flutter electron heat flux. Standard quasi-linear models are compared to the non-linear results. The standard reduced quasi-linear models work reasonably well for the $E \times B$ fluxes, but fail to capture magnetic flutter contribution to the electron heat flux induced by the non-linear excitation of the MTMs. An extension of the quasi-linear models is proposed allowing to better capturing the magnetic flutter flux.
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https://hal-amu.archives-ouvertes.fr/tel-03368780
Contributor : Neeraj Kumar Connect in order to contact the contributor
Submitted on : Thursday, October 7, 2021 - 1:07:15 AM
Last modification on : Tuesday, October 19, 2021 - 10:59:45 PM

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Neeraj Kumar. Analysis of turbulent transport in the central part of high-confinement tokamak plasmas. Plasma Physics [physics.plasm-ph]. Aix Marseille Université, 2021. English. ⟨tel-03368780⟩

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