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What can an edge gyrokinetic code do about the integrated tokamak exhaust and pedestal performance gap?

ORAL

Abstract

Edge pedestal an important object in determining the core plasma performance that is experimentally observed to be coupled to the power exhaust issue. Multiple methods can predict the performance of the core plasma from the pedestal performance. The unknown gap is in the integrated relationship between the tokamak exhaust and the pedestal performance. To date, the edge gyrokinetic code XGC reproduces [1] the experimental heat-load width observed in various tokamaks (Eich/Goldston) and predicts that ITER’s heat-load width, during fusion operation phase (FPO), will be much wider than the one predicted by extrapolation of experimental data. This is due to the enhanced kinetic turbulent transport occurring at ITER’s extremely large value of a/ρi [1]. This enhanced near-SOL turbulence across the magnetic separatrix could yield more intimate relationship between power-exhaust and pedestal performance than what have been observed in the present tokamaks. Moreover, a gyrokinetic evidence says that the parallel force-balance relationship between upstream and downstream plasmas may not be well-described by simplified fluid equations [2]. The relationship between the pedestal performance - including the RMPs and the onset windows of ELM and density-limit electromagnetic instabilities - and the power exhaust in detached/semi-detached divertor condition in FPO ITER may be best predicted by gyrokinetic simulations that include neutral particles, heavy and light impurity particles with power radiation, and atomic physics. Recent XGC discovery of the micro-turbulent homoclinic tangle offers further evidence for closer connection between pedestal and divertor plasma in FPO ITER [3].

[1] C.S. Chang et al., Phys. Plasmas 28, 022501 (2021); Nucl. Fusion 57, 116023 (2017)

[2] R.M. Churchill, C.S. Chang et al., Nucl. Fusion 59 (2019) 096002

[3] C.S. Chang et al., at this conference, to be submitted to Nature Physics

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Publication: [1] C.S. Chang et al., ""Constructing a new predictive scaling formula for ITER's divertor heat-load width informed by a simulation-anchored machine learning," Phys. Plasmas 28, 022501 (2021)<br>[2] C.S. Chang et al., Nucl. Fusion 57, 116023 (2017)<br>[3] R.M. Churchill, C.S. Chang et al., Nucl. Fusion 59 (2019) 096002<br>[4] Robert Hager, C.S. Chang et al., Physics of Plasmas 27, 062301 (2020)<br>[5] R.M. Churchill, C.S. Chang and S. Ku, IEEE Trans. Plasma Sci., 48:2661 (2020) <br>[6] C.S. Chang et al., "X-point ion orbit physics in scrape-off layer and generation of a localized electrostatic potential perturbation around X-point," Phys. Plasmas 26, (2019) 014504<br>[7] C.S. Chang et al., "Gyrokinetic projection of the divertor heat-flux width from present tokamaks to ITER," Nucl. Fusion 57, 116023 (2017)<br>[8] C.S. Chang et al., "A fast low-to-high confinement mode bifurcation dynamics in a tokamak edge plasma gyrokinetic simulation, Phys. Rev. Lett. 118, 175001 (2017)<br>[9] C.S. Chang et al., manuscript in preparation, to be submitted to Nature Physics

Presenters

  • Choongseok Chang

    Princeton Plasma Physics Laboratory, PPPL, Princeton Plasma Physics Laboratory, Princeton University

Authors

  • Choongseok Chang

    Princeton Plasma Physics Laboratory, PPPL, Princeton Plasma Physics Laboratory, Princeton University

  • Seung-Hoe Ku

    Princeton Plasma Physics Laboratory

  • Robert Hager

    Princeton Plasma Physics Laboratory

  • Michael Churchill

    Princeton Plasma Physics Laboratory

  • Julien Dominski

    Princeton Plasma Physics Laboratory

  • George J Wilkie

    Princeton Plasma Physics Laboratory