Speaker
Description
The impact of $\alpha$ heating on collisional transport of thermal species and the influence of Alfv\'en waves on fast ion transport are crucial mechanisms driving reactor-scale physics, though both remain important open questions for stellarator fusion power plants (FPPs). To better understand the latter, we compute the linear growth rates of Alfv\'en eigenmodes (AEs) in a reactor scale version of W7-X and in Thea Energy’s Helios equilibrium using fully kinetic linear models in the flux-tube gyrokinetics code GX. Large mode numbers for AEs at reactor scale enable use of the flux tube code for rapid computation of AE growth rates.
Benchmarking against existing flux tube studies of toroidal Alfv\'en eigenmodes in a simple tokamak geometry confirms AE growth can be captured in GX. Extension to W7-X shows growth rates of around $\gamma/\omega_A = 4%$ at an $\alpha$ fraction of 2.5% and a fast ion temperature ratio of $T_{\alpha}/T_i = 350$. Growth rates scale linearly with $\alpha$ density, temperature, and density gradient.
Operational points selected along curves of constant fusion output power of P = 958 MW provide self-consistent profiles for the FPP. A $\beta$-driven transition from AE growth to KBM growth is observed as well as $\beta$-induced frequency gap transitions. AE growth rates of around $\gamma/\omega_A =10%$ are observed at a volume-averaged $\beta$ of 1.9%, before a transition to KBM growth at 2% volume-averaged $\beta$ with growth rates at $\gamma/\omega_A =20%$.
Collisional heating of thermal species induced by $\alpha$ transport is captured using Monte-Carlo simulations of fast ions in firm3d with guiding-center tracing. Global transport solver Trinity updates fusion reactivity profiles handled in firm3d. Nonlinear GX simulations provide heat and particle fluxes of the thermal species to update thermal profiles in Trinity. Preliminary results in the absence of waves are presented.