An efficient physics-based Monte Carlo algorithm for simulating alpha-particle orbits in tokamak fusion-reactor plasmas with toroidal-field ripple

Abstract

A Monte Carlo code ALPHANET, designed to simulate the energetic alpha-particle behavior in tokamak fusion-reactor plasmas with toroidal-field ripple, has been developed. ALPHANET employs a physically well-justified approach to speed up the particle simulation: far from the bounce points, the trajectory is approximated by assuming only the axisymmetric magnetic-field term in the guiding-center equations. Since the ripple term is only dropped after a careful procedure, the physical trajectory is well reproduced. In this paper we give the rationale for our approach, we describe the physics embedded in the code, we point out some of the pitfalls of the algorithm, and, we evaluate the final results from both physical and numerical standpoints.