On the feasibility of Ohmically heated negative triangularity tokamak power plants

Abstract

Negative triangularity tokamak plasmas feature naturally enhanced confinement in the so-called L-mode regime, irrespective of the power of external heating. This is in contrast to conventional scenarios, which require exceeding a given heating power threshold to induce a discrete transition to a regime of enhanced confinement called H-mode. H-mode is, however, subject to problematic instabilities and additionally suffers from confinement degradation with increasing external heating. Using simple zero dimensional power balance and standard empirical scaling laws for confinement, we analyze the impact of external heating on several different reactor-relevant devices (i.e. SPARC, MANTA, ITER and DEMO). We compare the nominal externally heated scenarios with corresponding negative triangularity cases without external heating. For devices with sufficiently high magnetic field and/or fusion gain, the internally (Ohmically) heated negative triangularity versions achieve better performance. We conclude that Ohmically heating a negative triangularity power plant is an attractive option meriting further investigation.