Visualization of Fast Ion Phase-Space Flow Driven by Alfven Instabilities

Fast ion phase-space flow, driven by Alfven eigenmodes (AEs), is measured by an imaging neutral particle analyzer in the DIII-D tokamak. The flow firstly appears near the minimum safety factor at the injection energy of neutral beams, and then moves radially inward and outward by gaining and losing energy, respectively. The flow trajectories in phase space align well with the intersection lines of the constant magnetic moment surfaces and constant E - (omega / n)P-zeta surfaces, where E, P-zeta are the energy and canonical toroidal momentum of ions; omega and n are angular frequencies and toroidal mode numbers of AEs. It is found that the flow is so destructive that the thermalization of fast ions is no longer observed in regions of strong interaction. The measured phase-space flow is consistent with nonlinear hybrid kinetic-magnetohydrodynamics simulation. Calculations of the relatively narrow phase-space islands reveal that fast ions must transition between different flow trajectories to experience large-scale phase-space transport.

Automated summary

In the DIII-D tokamak, fast ion phase-space flow driven by Alfven eigenmodes (AEs) exhibits different trajectories in different regions and is influenced by energy. The flow trajectories in phase space align with the intersection lines of constant magnetic moment and constant E-(omega/n)P-zeta surfaces, indicating large-scale phase-space transport of fast ions at those points. This destructive flow behavior of fast ions is consistent with nonlinear hybrid kinetic-magnetohydrodynamics simulation, where ions transition between different flow trajectories for phase-space transport.