### Abstract

Fusion-born α particles moving parallel to the magnetic field can resonate with toroidal Alfvén eigenmodes (TAE) leading to anomalous α-orbit diffusion across the α-loss boundaries in a tokamak. This is analyzed using the Hamiltonian guiding center code ORBIT in conjunction with the kinetic magnetohydrodynamics (MHD) eigenmode solving code NOVA-K. Resonant single a orbits are studied below and above the threshold for orbit stochasticity and Monte Carlo randomized ensembles of alphas subjected to a finite amplitude time-dependent TAE are followed with respect to their radial losses using realistic MHD equilibria and numerically computed toroidal Alfvén eigenfunctions for one toroidal eigenmode n = 1 and the full Fourier spectrum of poloidal harmonics m involved in the "gap mode." The α-loss mechanisms are resonant drift motion across the loss boundaries of alphas born near these boundaries and stochastic diffusion to the boundaries in constants of the motion (phase) space. After a first transient of resonant drift losses scaling as B̃_{r}/B_{0}, the number of alphas lost via diffusion scales as (B̃_{r}/B_{0})^{2}. For TAE amplitudes B̃_{r}/B_{0}≥10^{-3}, α orbit stochasticity sets in and, depending on the radial width of the fast α density n_{α} (r), a substantial fraction of alphas can be lost in one slowing down time. For B̃_{r}/B_{0}<10 ^{-4}, the losses become insignificant.

Original language | English |
---|---|

Pages (from-to) | 1506-1516 |

Number of pages | 11 |

Journal | Physics of Fluids B |

Volume | 4 |

Issue number | 6 |

DOIs | |

Publication status | Published - 1992 Jan 1 |

### All Science Journal Classification (ASJC) codes

- Computational Mechanics
- Condensed Matter Physics
- Mechanics of Materials
- Physics and Astronomy(all)
- Fluid Flow and Transfer Processes

## Fingerprint Dive into the research topics of 'Alpha-particle losses from toroidicity-induced Alfvén eigenmodes. Part II: Monte Carlo simulations and anomalous alpha-loss processes'. Together they form a unique fingerprint.

## Cite this

*Physics of Fluids B*,

*4*(6), 1506-1516. https://doi.org/10.1063/1.860061