Modification of particle distributions by MHD instabilities I

The modification of particle distributions by low amplitude magnetohydrodynamic modes is an important topic for magnetically confined plasmas. Low amplitude modes are known to be capable of producing significant modification of injected neutral beam profiles, and the same can be expected in burning plasmas for the alpha particle distributions. Flattening of a distribution due to phase mixing in an island or due to portions of phase space becoming stochastic is a process extremely rapid on the time scale of an experiment but still very long compared to the time scale of guiding center simulations. Thus it is very valuable to be able to locate significant resonances and to predict the final particle distribution produced by a given spectrum of magnetohydrodynamic modes. In this paper we introduce a new method of determining domains of phase space in which good surfaces do not exist and use this method for quickly determining the final state of the particle distribution without carrying out the full time evolution leading to it.

Research highlights
► A new method of determining resonance location and widths of a coupled high energy particle - magnetohydrodynamic mode system is presented.
► Resonance locations and widths are used to find the diffusive relaxation of the particle distribution due to the modes.
► The method is much faster than full guiding center simulations and can give important information for burning plasma alpha particle distributions.