Stability of Alfvénic fluctuations driven by anisotropic energetic particles in tokamak plasmas

Abstract Energetic particle (EP)-driven Alfvénic fluctuations pose a significant challenge to plasma confinement and stability in future reactor relevant tokamak plasmas like Divertor Tokamak Test (DTT) facility. While previous studies often relied on isotropic EP distributions, this work presents a novel investigation into the stability of toroidal Alfvén eigenmodes (TAEs) in DTT, focusing on anisotropic EP distribution functions characteristic of negative neutral beam injection (NNBI) and ion cyclotron resonance heating (ICRH) schemes. Utilizing the local gyrokinetic code DAS (Drift Alfvén Stability), which employs a ballooning-mode representation and incorporates realistic magnetic equilibria, we model NNBI-driven EPs with an anisotropic slowing-down distribution and ICRH-driven EPs with an anisotropic gamma distribution. Our analysis reveals the distinct TAE stability characteristics for NNBI and ICRH scenarios, leading to different optimal toroidal mode numbers and growth rate dependencies. Parameter scans for ICRH demonstrate that TAE stability is profoundly influenced by the minority species, minority concentration, effective temperature, and critically, pitch-angle anisotropy. The numerical results are well consistent with our physical understanding based on the analyses of wave-particle resonance condition and coupling strength developed in our previous work Wei et al (2025 Nucl. Fusion 65 106035). More specifically, TAE instabilities driven by NNBI are generally weaker than those driven by ICRH, and for ICRH heating, using 3 He minority with relatively high concentration and prevalence of barely trapped particle population may yield to the suppression of TAE instabilities. This study provides crucial insights for optimizing heating strategies and EP management in DTT and other next-generation fusion devices, offering a more predictive understanding of EP-driven instabilities for robust plasma performance.