Predictions of improved confinement in SPARC via energetic particle turbulence stabilization

TL;DR

This paper demonstrates through gyrokinetic simulations that energetic particles generated by ICRH can significantly suppress turbulence and enhance fusion gain in the SPARC tokamak, offering a promising pathway for improved confinement.

Contribution

It introduces a novel fast ion stabilization mechanism in SPARC, showing how energetic particles can trigger an anomalous transport barrier to improve confinement.

Findings

Supra-thermal particles suppress ion-scale turbulence.

Fusion gain could increase up to 80% with energetic particle stabilization.

Optimized energetic particle profiles may further enhance performance.

Abstract

The recent progress in high-temperature superconductor technologies has led to the design and construction of SPARC, a compact tokamak device expected to reach plasma breakeven with up to $25$MW of external ion cyclotron resonant heating (ICRH) power. This manuscript presents local (flux-tube) and radially global gyrokinetic GENE (Jenko et al 2000 Phys. Plasmas {\bf 7} 1904) simulations for a reduced-field and current H-mode SPARC scenario showing that supra-thermal particles - generated via ICRH - strongly suppress ion-scale turbulent transport by triggering a fast ion-induced anomalous transport barrier (F-ATB). The trigger mechanism is identified as a wave-particle resonant interaction between the fast particle population and plasma micro-instabilities (Di Siena et al 2021 Phys. Rev. Lett. {\bf 125} 025002). By performing a series of global simulations employing different profiles for the thermal ions, we show that the fusion gain of this SPARC scenario could be substantially enhanced up to $\sim 80\%$ by exploiting this fast ion stabilizing mechanism. A study is also presented to further optimize the energetic particle profiles, thus possibly leading experimentally to an even more significant fusion gain.