Modelling the Alfvén eigenmode induced fast-ion flow measured by an imaging neutral particle analyzer

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A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
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Nuclear Fusion, Volume 62, issue 11
An imaging neutral particle analyzer (INPA) provides energy and radially resolved measurements of the confined fast-ion population ranging from the high-field side to the edge on the midplane of the DIII-D tokamak. In recent experiments, it was used to diagnose fast-ion flow in the INPA-interrogated phase-space driven by multiple, marginally unstable Alfvén eigenmodes (AEs). The key features of this measured fast-ion flow are: (I) a fast-ion flow from q min and the injection energy (81 keV) towards lower energies and plasma periphery.(II) A flow from the same location towards higher energies and the plasma core, (III) a phase-space 'hole' at the injected energy and plasma core and (IV) a pile-up at the plasma core at lower energies ( 1/460 keV). Ad hoc energetic particle diffusivity modelling of TRANSP significantly deviates from the observation. Comparably, a reduced modelling, i.e. a combination of NOVA-K and ASCOT5 code with the measured mode structure and amplitude, generally reproduce some key features of the observed phase-space flow, but largely failed to interpret fast ion depletion near the plasma axis. At last, self-consistent, first-principle multi-phase hybrid simulations that include realistic neutral beam injection and collisions are able to reproduce most features of the time-resolved phase-space flow. During consecutive hybrid phases, an RSAE consistent with the experiment grows and saturates, redistributing the injected fast ions. The resulting synthetic INPA images are in good agreement with the measurement near the injection energy. The simulations track the fast-ion redistribution within the INPA range, confirming that the measured fast-ion flow follows streamlines defined by the intersection of phase-space surfaces of constant magnetic moment μ and constant E′ = nE + ωP φ, where n and ω are the instability toroidal mode number and frequency, and E and P φ the ion energy and toroidal canonical momentum. Nonperturbative effects are required to reproduce the depletion of fast ions near the magnetic axis at the injection energy.
Funding Information: This work is supported by US DOE Contracts DE-SC0020337, DE-AC05-00OR22725, DE-FC02-04ER54698, DE-AC02-09CH11466 and DE-SC0015878. This research used resources of the National Energy Research Scientific Computing Center (NERSC), a US Department of Energy Office of Science User Facility located at Lawrence Berkeley National Laboratory, operated under Contract No. DE-AC02-05CH11231 using NERSC Award FES-ERCAP20598. The ASCOT5 project was partially funded by the Academy of Finland Project Nos. 324759 and 298126. 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. X. Wang’s work has been carried out within the framework of the EUROfusion Consortium, funded by the European Union via the Euratom Research and Training Programme (Grant Agreement No. 101052200—EUROfusion). The views and opinions expressed herein do not necessarily reflect those of the European Commission. | openaire: EC/H2020/647121/EU//PLASMA | openaire: EC/H2020/633053/EU//EUROfusion
Alfvénic instabilities, fast ion flow, imaging neutral particle analyzer
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Gonzalez-Martin , J , Du , X D , Heidbrink , W W , Van Zeeland , M A , Särkimäki , K , Snicker , A , Wang , X & Todo , Y 2022 , ' Modelling the Alfvén eigenmode induced fast-ion flow measured by an imaging neutral particle analyzer ' , Nuclear Fusion , vol. 62 , no. 11 , 112003 , pp. 1-14 .