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PhD : Turbulence Flow Interaction in magnetized plasmas

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Date Limite Candidature : vendredi 22 octobre 2021

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General information

Reference : UMR7648-EDOBOU-008
Workplace : PALAISEAU
Date of publication : Friday, October 1, 2021
Scientific Responsible name : Pascale HENNEQUIN
Type of Contract : PhD Student contract / Thesis offer
Contract Period : 36 months
Start date of the thesis : 1 December 2021
Proportion of work : Full time
Remuneration : 2 135,00 € gross monthly

Description of the thesis topic

Plasma turbulence plays a crucial role in the performance of future fusion devices. Turbulence transport indeed determines the typical size of the hot confined plasma expected to sustain fusion reactions. Turbulence control has been achieved in the edge of tokamak plasma in High confinement regime (Low to High confinement transition). However the mechanisms that underlie the bifurcation are still elusive. Prediction of confinement in next step machines remains the primary challenge for transport models and first principle codes, which need to be validated against experiment.
The underlying mechanism suggested in the transport reduction is the effect of the shear of the plasma velocity, which is expected to tear apart the turbulent eddies, then limit their growth and radial extent. Moreover the tilting of turbulent eddies participate in a positive loop by enhancing the flow shear. The nonlinear decorrelation effect plays a role through the decrease of the radial correlation length and the change in the phase between density, temperature and potential fluctuations. However only indirect measurements have corroborated this mechanism, which is still to be directly proven in measurements and simulations.
The thesis will be focused on the experimental study of the interaction between these flows and the fluctuations, in well characterized experiments which can then be compared in detail to gyrokinetic simulations.
Experiments will be conducted both on large European Tokamaks (WEST at Cadarache, ASDEX Upgrade at Garching) and on our small local magnetized plasma Torix. They will make use of different fluctuation measurement techniques among them Doppler back-scattering which has been developed and implemented on these tokamaks by the team. The comparison to simulations of these plasmas and theoretical interpretation will also be performed in collaboration between CEA and LPP

Work Context

The thesis will be conducted in the framework of a collaboration between LPP/Ecole Polytechnique and CEA/IRFM.
The Fusion Plasmas Group at LPP develops both experimental and theoretical studies of plasma turbulence. In particular the team designs fluctuation diagnostics based on microwave or optical range wave scattering (Doppler reflectometry) and operates them on different tokamaks in Europe: WEST (Cadarache) and ASDEX Upgrade (IPP Garching, Germany). They allow to probe turbulence at different scales and trace fluctuations to infer their velocity through Doppler effect. This is a well suited diagnostic to study turbulence flows interaction.
CEA IRFM (Institut de Recherches sur la Fusion Magnétique) at Cadarache operates the WEST tokamak ("Tungsten (W) Environment in Steady-state Tokamak", upgrade of the former Tore Supra including a divertor to study and mitigate power exhaust) and develops experiments and state of the art models to prepare ITER operation with burning. First principle codes among them the gyrokinetic code GYSELA are developed and extensively used (HPC).
The student will be mainly located at Cadarache, with regular stays at LPP and possibly other European laboratories (IPP, Germany) for experimental campaigns.

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