Manipulating Turbulence via Flux-Surface Triangularity and Electron Cyclotron Heating

Based on TCV discharges with large triangularity |δ|, the impact of extreme |δ| > 0.6 on microturbulence is assessed. Focusing on profiles for an experimental δ = 0.3 in a TEM turbulence regime, nonlinear gyrokinetic simulations are found to be consistent with the experimental flux. Varying δ, growth rates are suppressed at large |δ|, with negative δ experiencing stronger stabilization and little dependence on radial wavenumber; this is the case irrespective of collisionality and despite more energy being available for instability and turbulence at δ < 0, suggesting a mechanism by which flux-surface shaping can avoid available energy being injected by the instability. Heat fluxes dip as |δ| > 0.6, although the ion fluxes rise at strongly negative δ, where a transition to ITG modes occurs. Quasilinear transport modeling captures trends well in an ITG regime, whereas TEM-based predictions tend to overestimate fluxes at large positive δ. This is due to substantially stronger and larger-scale zonal flows at positive δ.

Preliminary gyrokinetic results are shown of electron cyclotron heating, with explicit heat deposition during simulations. The generation of corrugations in the electron temperature and electric field can, depending on the deposition location, regulate - and indeed lower - TEM fluxes. A concurrent effect is the local destabilization of ETG modes that can drive additional flux.