Numerical investigation of alpha particle confinement under the perturbation of Neoclassical Tearing Modes and toroidal field ripple in CFETR

The confinement of alpha particles in burning plasma is a key issue in fusion reactor design, including particle interaction with instabilities. This paper includes two topics, one is the effect of Neoclassical Tearing Modes (NTM) and toroidal field ripple on alpha particle loss, and another is the assessment of particle redistribution under NTM with a reduced model. We consider Chinese Fusion Engineering Test Reactor (CFETR) parameters, the alpha particle distribution given by TRANSP/NUBEAM and the NTM perturbation function given by the initial value code TM1. We show the synergistic effect of NTM and ripple is negligible; the particle loss fraction does not change with increasing NTM amplitude. Only passing particles are affected by the mode particle resonance, producing profile flattening but no increased loss because only trapped particles are influenced by ripple. To study alpha particle profile flattening, the work adopts an innovative method of phase vector rotation to determine regions of good and broken Kolmogorov Arnold Moser (KAM) surfaces and equilibrates the particle density according to local stochasticity.