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Explaining the lack of power degradation of the energy confinement in the wide pedestal quiescent H-mode via transport modelling

ORAL

Abstract

The large Shafranov shift resulting from increased near-zero-torque injected beam power (PNBI) in the wide pedestal quiescent H-mode (WPQH) stabilizes turbulence and enables high-confinement ELM-free plasmas. Compared to the standard QH-mode, WPQH is characterized by formation of a wider and higher pedestal, and strong broadband fluctuations in the pedestal. However, unlike conventional H-modes where the energy confinement time reduces with increasing heating power, WPQH modes do not show power degradation of the energy confinement, posing a riddle. As the PNBI was increased, reduced transport, as well as increased core diamagnetic E×B shear rate are observed, suggesting the formation of an ion internal transport barrier (ITB). In this work, TGLF code was used to predict the ITB and its stability analysis. The energy confinement time calculated from the new constructed equilibria with the modelled profiles show insensitivity to the increased PNBI; these modelled profiles use the TGYRO transport solver with TGLF/TRANSP matched energy fluxes. Linear stability analysis reveals that drift-wave instabilities in the core are stabilized by E×B shear, the Ti/Te ratio and the Shafranov shift; the latter was found to have the strongest effect on the turbulence suppression.

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Presenters

  • Saeid Houshmandyar

    University of Texas at Austin, The University of Texas at Austin

Authors

  • Saeid Houshmandyar

    University of Texas at Austin, The University of Texas at Austin

  • Keith H Burrell

    General Atomics - San Diego, General Atomics

  • Michael R Halfmoon

    University of Texas at Austin

  • Brian A Grierson

    Princeton Plasma Physics Laboratory

  • Joseph T Mcclenaghan

    General Atomics, General Atomics - San Diego, Oak Ridge National Laboratory

  • Gary M Staebler

    General Atomics - San Diego, General Atomics

  • Rongjie Hong

    Oak Ridge Assoc Univ, UCLA, University of California, Los Angeles

  • David R Hatch

    University of Texas at Austin, Institute for Fusion Studies, University of Texas at Austin

  • Lei Zeng

    UCLA, University of California, Los Angeles, University of California Los Angeles

  • Max E Austin

    University of Texas at Austin