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

| openaire: EC/H2020/633053/EU//EUROfusion Funding Information: The author (X. D. Du) would like to thank M. Podestà, G. J. Kramer, and R.Nazikian for fruitful discussions. This work was supported by the US DOE under DE-AC05-00OR22725, DE-FC02-04ER54698, DE-AC02-09CH11466, and DE-SC0015878. The ASCOT5 project has received funding from the European Research Council under Grant Agreement No. 647121. This ASCOT5 project has been carried out within the framework of the EUROfusion consortium and has received funding from the Euratom research and training programme under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. The ASCOT5 project was also partially funded by the Academy of Finland projects No. 324759 and No. 298126. We acknowledge the computational resources provided by Aalto Science-IT project. The MEGA simulation used resources of the National Energy Research Scientific Computing Center (NERSC), a U.S. Department of Energy Office of Science User Facility located at Lawrence Berkeley National Laboratory, operated under Contract No. DE-AC02-05CH11231. Publisher Copyright: © 2021 American Physical Society.Fast ion phase-space flow, driven by Alfvén 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-(ω/n)Pζ surfaces, where E, Pζ are the energy and canonical toroidal momentum of ions; ω 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.Peer reviewe