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Impact of shear flows on turbulent transport in the edge plasma of tokamaks

Turbulent transport taking place at the edge of tokamak plasmas has two crucial impacts on reactor operation:
1) global confinement performances by controlling losses across separatrix,  
2) peak heat load onto plasma facing components by controlling the width of the scrape off layer.  

Besides turbulence developping against magnetic confinement, large scale flows are also generated along magnetic flux surfaces. These flows do not directly participate in transport losses, but they can interact with turbulence through shearing process. The ultimate illustration of such coupling is the transition to high confinement mode, caracterized by a strong flow shear and reduced trubulence activity at the boundary of the confined plasma.
Consequences are two fold:
1) improved global confinement and 2) narrower SOL width, which complexifies the power exhaust issue. 

Objective of the internship:
The project aims at investigating the coupling mechanism between imposed shear flows and interchange turbulence in 2D simulations; and based on these investigations, develop a reduced transport model able to predict the scrape off layer width in presence of shear flows.  The project will be divided into several progression steps:
1) Understand the basic theory of interchange turbulence and interaction with shear flows,
2) Prepare a simulation plan,
3) Analyses of simulation results:  impact of shear flows on pressure gradients, turbulence spectra, vortex deformation, etc,
4) Synthesize the relevant mechanims into a reduced model of SOL transport.      

Mise à jour : 22/11/2017
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