Assessing the Impact of Alpha Particles on Thermal Confinement in JET D-T Plasmas through Global GENE-Tango Simulations

TL;DR

This study uses advanced simulations to evaluate how alpha particles influence plasma behavior in JET, finding minimal impact on turbulence at current levels but potential destabilization at higher concentrations relevant to future reactors.

Contribution

It demonstrates the negligible effect of alpha particles on turbulence in JET and explores their potential impact at higher densities expected in ITER using global gyrokinetic simulations.

Findings

Alpha particles have minimal impact on turbulent transport in JET.

Alpha heating influences electron temperature peaking.

Higher alpha densities can destabilize turbulence.

Abstract

The capability of the global, electromagnetic gyrokinetic GENE code interfaced with the transport Tango solver is exploited to address the impact of fusion alpha particles (in their dual role of fast particles and heating source) on plasma profiles and performance at JET in the discharges with the highest quasi-stationary peak fusion power during the DTE2 experimental campaigns. Employing radially global nonlinear electromagnetic GENE-Tango simulations, we compare results with/without alpha particles and alpha heating. Our findings reveal that alpha particles have a negligible impact on turbulent transport, with GENE-Tango converging to similar plasma profiles regardless of their inclusion as a kinetic species in GENE. On the other hand, alpha heating is found to contribute to the peaking of the electron temperature profiles, leading to a 1keV drop on the on-axis electron temperature when alpha heating is neglected in Tango. The minimal impact of alpha particles on turbulent transport in this JET discharge - despite this being the shot with the highest fusion output - is attributed to the low content of fusion alpha in this discharge. To assess the potential impact of alpha particles on turbulent transport in regimes with higher alpha particle density, as expected in ITER and fusion reactors, we artificially increased the alpha particle concentration to levels expected for ITER. By performing global nonlinear GENE standalone simulations, we found that increasing the alpha particle density beyond five times the nominal value lead to significant overall turbulence destabilization.