Alfvénic Mode-Mediated Relaxation of H Minority in a High-Field Tokamak Design.

Toroidal Alfvén Eigenmode (TAE) instabilities driven by ICRH-accelerated minority ions are analyzed using the TRANSP/NUBEAM codes. The presence of unstable TAEs leads to relaxation of fast ions including ICRH minority through diffusive and convective resonant particle transport, as prescribed by the predictive Resonance-Broadened Quasilinear (RBQ) model. Fast minority ions from ICRH are introduced into NUBEAM to capture Alfvénic effects during their slowing down. Their initial bi-Maxwellian energy distribution, characterized by parallel and perpendicular temperatures, is computed by the Fokker–Planck module of TRANSP, with wave electric field amplitudes and ICRH power deposition obtained from the TORIC-5 full-wave solver. EP kicks in the constant of motion space are verified against analytic conservation laws.

The RBQ model is used to calculate the diffusive and convective transport induced by multiple Alfvénic modes. By self-consistently relaxing the fast ion distribution function, RBQ provides a predictive, physics-based framework for quantifying energetic particle behavior in tokamak plasmas, particularly in regimes where Alfvénic instabilities strongly influence fast ion confinement.

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