On the feasibility of Ohmically heated negative triangularity tokamak power plants

Negative triangularity (NT) plasmas achieve enhanced confinement without edge localized modes nor the need to exceed the L-H heating power threshold. Removing this H-mode accessibility constraint opens a new region of parameter space: scenarios with low external heating power. 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 determine the ideal amount of external heating to maximize performance and test whether it is possible to reach satisfactory performance with no external heating at all. For devices with sufficiently high magnetic field and/or fusion gain, Ohmically heated NT scenarios achieve better performance than positive triangularity H-mode scenarios with external heating. We conclude that NT enables attractive low input power scenarios that merit further investigations with more comprehensive models. Such low power scenarios appear particularly well suited for attaining high fusion gain Q (e.g. a burning plasma experiment).