Universidad de Sevilla PP2016-7145EUROfusion Consortium 63305

Chen, H.

Domínguez-Palacios Durán, Jesús José

Doyle, S. J.

Galdón Quiroga, Joaquín

García Muñoz, Manuel

García Vallejo, Daniel

González Martín, Javier

Rivero Rodriguez, Juan Francisco

Sanchís Sánchez, Lucía

Snicker, A.

Viezzer, Eleonora

English

Snicker, Antti

idUS. Depósito de Investigación Universidad de Sevilla

Kinetic Modelling of ELM-induced Fast-ion Transport and Accelerationin the ASDEX Upgrade TokamakJ.F. Rivero-Rodriguez1,2, M. Garcia-Muñoz2,3, J. Galdon-Quiroga2,3, A. Snicker4,J. Dominguez-Palacios2,3, H. Chen 2,3, S.J. Doyle2,3, D. Garcia-Vallejo1,J. Gonzalez-Martin5, L. Sanchis4, K. Sarkimaki6, Y. Todo7, E. Viezzer2,3the ASDEX Upgrade Team∗, and the EUROfusion MST1 Team†1 Department of Mechanical Engineering and Manufacturing, University of Seville, Spain.2 Centro Nacional de Aceleradores (CNA) (Universidad de Sevilla, CSIC, Junta de Andalucia).3 Department of Atomic, Molecular and Nuclear Physics, University of Seville, Spain.4 Aalto University, Department of Applied Physics, P.O. Box 14199, FI-00076.5 University of California, Irvine, United States.6 Max Planck Institute for Plasmaphysics, Boltzmannstr. 2, 85748 Garching, Germany.7 National Institute for Fusion Science, Toki, JapanIntroductionIn magnetically confined fusion, fast-ion confinement is essential to achieve a good plasmaperformance, while fast-ion losses may damage the tokamak wall, endangering its integrity. InH-mode regimes, tokamaks exhibit explosive and repetitive magneto-hydro dynamic (MHD)instabilities driven in the plasma edge, known as Edge Localized Modes (ELMs) [1]. ELMsrelease a great amount of energy and particles to the tokamak wall that are believed to beintolerable in future devices [2]. Besides, recent experiments in the ASDEX Upgrade tokamakhave observed accelerated fast-ion losses correlated with the ELM activity [3, 4, 5]. This workseeks to reproduce the main experimental observations in ASDEX Upgrade by first principlemodelling and to characterize the fast-ion transport and acceleration mechanism during ELMs.The ELM-induced fast-ion losses were experimentally observed and characterized in AUGusing the Fast-Ion Loss Detector (FILD) [6, 7, 8]. The FILD diagnostic provides direct measure-ments of the fast-ion losses and gives information of their velocity space. The 5 FILDs in AUGenable the measurements in different toroidal and poloidal angles. Peaks in the FILD signalsare seen to be correlated with the ELM activity, revealing different behaviours in the toroidallyand poloidally displaced FILDs. This suggests a 3D nature of the fast-ion losses during an ELMcrash. The intra-ELM velocity-space measurements of the fast-ion losses depict a population at∗See the author list of H. Meyer et al., Nucl. Fusion 59 112014 2019.†See the author list of B. Labit et al., Nucl. Fusion 59 086020 2019.47th EPS Conference on Plasma Physics O2.107energies tens of keV above the main NBI energy. A tomographic inversion of the measurementshows that this accelerated population is very localized in velocity space, suggesting a fast-ionacceleration induced by the ELM perturbation.The AUG plasma is modelled with the MHD module of the hybrid kinetic-MHD code MEGA[9], with the aim to obtain the electromagnetic perturbation during an ELM. This perturba-tion will be employed as an input in the Monte-Carlo full-orbit code ASCOT5 [10] to studythe ELM-induced fast-ion transport and acceleration with a newly developed module that ac-counts for the time-evolving electromagnetic perturbations. The MEGA simulations reproducethe main features of an ELM [11]. However, the perturbation is dominantly n = 20, well abovethe dominant n = 3 and n = 5 observed experimentally, and the growth rate of the perturba-tion is γ = 105 s−1, an order of magnitude above that observed experimentally [12, 13]. Be-sides, the time scale of the perturbation have been adjusted to be above the orbital time scaleswith the aim to observe an interaction between the ELM perturbation and the fast ions. Thus,only qualitative comparisons between the modelled results and the experiments are adressedFILD2 NBI1-0.6 -0.5 -0.4 -0.3 -0.1-0.2 0.0Pitch140Energy [keV]1201008060402001.00.50.0Particles [a.u.]ASCOT5Figure 1: Velocity space distribution of theELM-induced fast-ion losses reaching FILD2from NBI1, as estimated in ASCOT5.here.Effect of ELMs on the NBI distributionThe transport and acceleration of the NBI-bornfast-ion distribution in AUG are assessed by mod-elling the 8 beams with BBNBI [14]. BBNBI pro-duces a distribution of 6 million markers for eachbeam. The markers are first tracked in an unper-turbed field to filter out the NBI prompt losses.Then, the orbits of the confined fast ions are trackedduring the ELM perturbation. Simulations withan axisymmetric wall show that the ELM-inducedlosses concentrate on the LFS near the midplane,following the high-n, field-aligned patterns of theELM perturbation. This illustrates the strong impact of the ballooning perturbation on the fast-ion confinement. The NBI fast-ion energy distribution spreads over high energies during thesimulation, forming a local maximum at 30 keV above the injection energy, resulting in a dis-tinguishable accelerated population. The velocity space of the fast ions colliding with the FILDprobes can be used as an estimate of the FILD signal. Figure 1 shows the velocity space of theNBI1 distributions colliding with FILD2. A high energy component, 30 keV above the injectionenergy, that converges to a narrow pitch angle range, can be observed.47th EPS Conference on Plasma Physics O2.107Modelled Transport and Acceleration Mechanism2.281.711.140.570.00-0.57-1.14-1.71-2.28-2.854.53.62.71.80.90.0-0.9-1.8-2.7-3.6-0.2-0.4-0.6-0.8-1.0-0.2-0.4-0.6-0.8-1.0x10-21[keV][kg·m2/s]separatrixPitchPitchb) ƐΔa) PΔφ 3.5 3.02.32.01.61.20.2300.380trappedpassing3.5 3.02.32.01.61.20.2300.380trappedpassing1.90 1.95 2.00 2.102.05 2.15 2.20R [m]1.90 1.95 2.00 2.102.05 2.15 2.20R [m]separatrix2200176013208804400-440-880-1320-1760-0.2-0.4-0.6-0.8-1.0[J/T]Pitchc) μΔ3.5 3.02.32.01.61.20.2300.380trappedpassing1.90 1.95 2.00 2.102.05 2.15 2.20R [m]separatrixFigure 2: (a) Variation of the toroidal canon-ical momentum , (b) the kinetic energy and (c)the magnetic moment. ωpol/ωtor contour linesin white.The fast-ion transport and acceleration during theELM perturbation is assessed by tracking the varia-tion of the orbits constants of motion and adiabaticinvariants. The variation of the toroidal canonicalmomentum (∆Pϕ ) is associated with the particle ra-dial transport, the variation of the kinetic energy(∆ε) with acceleration and the variation of the mag-netic moment (∆µ) with a variation of the perpen-dicular velocity in the cyclotron time scale. A set ofmarkers is used as a representation of the particlephase-space, distributed in a grid with initial con-ditions ϕ = 0, z = 0, ε = 80keV and the initial ra-dial position and pitch angle of the grid. The mark-ers are followed during 10 poloidal turns. Besides,to evaluate a resonant interaction, the orbits reso-nance condition, expressed in terms of the fractionωpol/ωtor [15], are shown as white contour lines.A clear correlation between the ∆Pϕ lines and theωpol/ωtor contour lines can be observed in figure2(a). This suggests a resonant transport between thefast-ion orbits and the magnetic perturbation. Be-sides, it is observed that passing particles are af-fected by the chaotic field lines near the edge, eventhough the resonant transport is dominant. The pat-terns in figures 2(b) and 2(c) are different to thoseobserved in figure 2(a). Nonetheless, they are anal-ogous to each other, depicting that the energy variation is associated with a variation of theperpendicular velocity component in the cyclotron time scale. The electric field, which is calcu-lated in MEGA by a simplified Ohm’s law (E =−v×B+ηJ), is dominated by the v×B term,while the resistive term has a negligible effect. Therefore, the electric perturbation is mostlyperpendicular to the magnetic field lines in spatial scales below the gyroradius size. This pro-duces a net variation in the magnetic moment, that is reflected in an acceleration due to an orbitdrift resonance with the perpendicular electric field. This cannot be observed in a guiding center47th EPS Conference on Plasma Physics O2.107approach, as the perpendicular electric field is there interpreted as a drift in the fast-ion orbit.These results are in line with the proposed acceleration of energetic particles due to propagatingplasma blobs [16], where vertically polarized blobs with sizes below the fast-ion gyroradiusinteract with the fast particle gyromotion thus producing a fast-ion acceleration.ConclusionsThe main observations in ASDEX Upgrade of accelerated fast-ion losses during ELMs havebeen qualitatively reproduced using MEGA and ASCOT5. MEGA is employed to resolve theelectromagnetic perturbation during an ELM, while ASCOT5 is employed to trace the fast-ion orbits during the time-evolving perturbations. The results show field-aligned patterns of thelosses on the wall near the midplane and have reproduced an accelerated population on the FILDprobe very localized in phase space. The models reveal a resonant transport and acceleration inthe fast-ion perpendicular velocity.AcknowledgementThis research received funding from the V Plan Propio de Investigación de la Universidadde Sevilla (PP2016-7145). The simulations were partly performed on the MARCONI super-computer (CINECA). This work has been carried out within the framework of the EUROfusionConsortium and has received funding from the Euratom research and training programme 2014-2018 and 2019-2020 under Grant Agreement No. 633053. The views and opinions expressedherein do not necessarily reflect those of the European Commission.References[1] H. Zohm. Edge localized modes (ELMs). Plasma Phys. Controlled Fusion, 38(2):105, 1996.[2] T. Eich et al. Nuclear Materials and Energy, 12:84–90, 2017.[3] M. García-Muñoz et al. Plasma Phys. Controlled Fusion, 55(12):124014, 2013.[4] J. Galdon-Quiroga et al. Phys. Rev. Lett., 121:025002, 2018.[5] J. Galdon-Quiroga et al. Nucl. Fusion, 59(6):066016, 2019.[6] M. García-Muñoz et al. Rev. Sci. Instrum., 80(5):053503, 2009.[7] J. Gonzalez-Martin et al. Rev. Sci. Instrum., 89(10):10I106, 2018.[8] J. Gonzalez-Martin et al. J. Instrum., 14(11):C11005–C11005, 2019.[9] Y. Todo and T. Sato. Phys. Plasmas, 5(5):1321–1327, 1998.[10] J. Varje, K. Sarkimaki, et al., 2019. preprint.[11] G. T. A. Huysmans and O. Czarny. Nucl. Fusion, 47(7):659, 2007.[12] F. Mink et al. Plasma Phys. Control. Fusion, 58(12):125013, 2016.[13] F. Mink et al. Nucl. Fusion, 58(2):026011, 2018.[14] O. Asunta et al. Comput. Phys. Commun., 188:33–46, 2015.[15] L. Sanchis et al. Plasma Phys. Controlled Fusion, 61(1):014038, 2018.[16] V. S. Marchenko and S. N. Reznik. Phys. Plasmas, 25(8):084502, 2018.47th EPS Conference on Plasma Physics O2.107

Kinetic Modelling of ELM-induced Fast-ion Transport and Acceleration in the ASDEX Upgrade Tokamak

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Kinetic Modelling of ELM-induced Fast-ion Transport and Acceleration in the ASDEX Upgrade Tokamak

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