Abstract
The impact of triangularity on edge plasma transport and turbulence is addressed from full 3D turbulence simulations performed with TOKAM3X. Flux driven fluid simulations are run on analytical magnetic equilibria generated with positive and negative triangularity δ in a bottom limiter configuration. The conservation of the energy is assured by the increase of the bottom limiter radial position from δ > 0 to δ < 0 . Changing the triangularity impacts both the plasma equilibrium and the turbulence. In particular, negative triangularity leads to a reduction of the density and electron temperature decay lengths in agreement with the literature. Concerning the turbulence, in all the simulations, it remains ballooned with an enhanced level of fluctuations at low field side in comparison to the high field one. Moreover, no clear trend is visible on the relative level of fluctuations of both density and electron temperature in the CFR whereas an enhancement (resp. reduction) is visible in the scrape-off layer at the low field side midplane for the negative (resp. positive) triangularity simulations. This behaviour differs from TCV and DIII-D measurements which show the benefit of negative triangularity in terms of turbulence reduction and increased confinement. However, no conclusion is drawn from our preliminary study concerning the impact of triangularity on the turbulent transport. Change in triangularity impacts many simulation control parameters, as in the experiments, and that the analysis of its impact alone on the dynamics of the plasma is not obvious in this configuration.
Highlights
The success of future fusion devices as ITER is conditional on the access to long enough energy confinement time and high enough pressure of the plasma
Low Field Side MidPlane (LFS MP) radial profiles of density and electron temperature averaged on time and toroidal direction are represented in figure 2
A scan in triangularity has been performed in full 3D fluid turbulence simulations with the TOKAM3X code in a bottom limited configuration encompassing the edge last closed field lines region (CFR) and the scrape-off layer (SOL)
Summary
The success of future fusion devices as ITER is conditional on the access to long enough energy confinement time and high enough pressure of the plasma. The effect of shaping including negative triangularity on the scrape-off layer plasma has been investigated in TCV high field limited plasmas and by the 3D turbulent fluid code GBS [6, 7]. The fluid edge electrostatic 3D code TOKAM3X includes the physics suspected to play a significant role in the particle and energy transport in the edge plasma (diffusion, mean drifts convection, turbulence triggered by electrostatic interchange and electrostatic resistive drift waves) in arbitrary axisymmetric magnetic geometry In this contribution, we propose to study the impact of analytical negative triangularity magnetic equilibria on both the edge closed field lines region (CFR) and the scrape-off layer (SOL) plasma in a bottom limited configuration.
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