Alpha Particle Dynamics in ARC Burning Plasmas

The ARC tokamak is expected to operate in a burning plasma regime with a large fusion-born alpha population. Alfvén eigenmode (AE)-driven effects are analyzed analytically and then numerically including alpha drive, ion Landau damping, and collisional damping from trapped electrons. Unstable and near-threshold unstable AE domains are identified within ARC's operational space. The NOVA code finds multiple AEs unstable up to toroidal mode numbers n=30. NUBEAM evaluates the alpha transport on timescales beyond the slowing-down time from RBQ computed transport coefficients. These global simulations identify favorable and unfavorable operating regimes in terms of alpha confinement, pressure redistribution, and heating efficiency. NTM, sawtooth, and toroidal-field ripple induced alpha transport are evaluated using the ORBIT-kick guiding center code. The kick-transport is integrated into TRANSP for more self-consistent calculations of alpha-driven current and overall sustainment of the ARC scenario. Sensitivity scans are performed in mode frequency, rational surface location, island width, mode amplitude, q=1 location, and limiter proximity. This study delivers physics-based insights to guide machine design, equilibrium control, and ensure adequate alpha heating.