Quasilinear drift kinetic theory of alpha particle transport by neoclassical tearing modes

TL;DR

This paper develops a quasilinear kinetic theory to understand how neoclassical tearing modes in tokamaks can cause significant transport of alpha particles, which are crucial for fusion energy.

Contribution

It extends kinetic theory to alpha particle interactions with NTMs, revealing conditions for significant particle transport and emphasizing the need for nonlinear analysis.

Findings

NTMs can cause substantial alpha particle transport in tokamaks.

Quasilinear theory applies to small amplitude NTMs, indicating limits for its use.

Nonlinear effects are important for larger amplitude NTMs.

Abstract

Kinetic theory of particles near resonances is a current topic of discussion in plasma physics and astrophysics. We extend this discussion to the kinetic theory of the interaction between alpha particles (energetic particles predicted to exist in large quantities in next-generation fusion experiments) and a neoclassical tearing mode (NTM), a resistively-driven perturbation that sometimes exists in a tokamak. We develop a quasilinear treatment of the interaction between alphas and an NTM, showing why an NTM can be a source of significant passing alpha particle transport in tokamaks. The limitations on quasilinear theory constrain our theory's applicability to small amplitude NTMs, highlighting the importance of nonlinear studies.