Regimes of weak ITG/TEM modes for transport barriers without velocity shear

POSTER

Abstract

Electrostatic modes (ITG and TEM) usually dominate core transport, but we show there exists a regime where these modes are hugely weakened, enabling transport barriers without velocity shear. This regime has apparently arisen in multiple contexts: high beta poloidal ITB in DIII-D, ITB in JET with pellet injection, ITB observed in Wendelstein 7X, wide pedestal QH-mode pedestals and other pedestals. In all these cases the processes that greatly weaken ITG/TEM modes are similar. Through gyrokinetic simulations in model geometries and actual geometries, and a semi-analytic, Simplified Kinetic Model, we arrive at a clear understanding of these fusion friendly regimes made possible only by specific magnetic geometry characteristics plus substantial density gradients. Comprehensive electrostatic and electromagnetic gyrokinetic simulations with GENE show that for plasmas in this regime, linear modes are weak, and the nonlinear transport can be reduced by two orders of magnitude. Various experimental transport barriers on DIII-D will be used as examples, and stellarator geometries such as Wendelstein 7X, NCSX and HSX will also be considered.

Authors

  • M. Kotschenreuther

    University of Texas at Austin, UT Austin

  • X. Liu

    University of Texas

  • David Hatch

    IFS/University of Texas, University of Texas at Austin, Institute for Fusion Studies, Institute of Fusion Studies, University of Texas at Austin, UT Austin

  • S. Mahajan

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

  • M.J. Pueschel

    University of Texas at Austin

  • M. Halfmoon

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

  • I. J. McKinney

    University of Wisconsin at Madison, University of Wisconsin-Madison, Madison, Wisconsin, USA, University of Wisconsin - Madison

  • P. Xanthopoulos

    Max Plank Institute for Plasma Physics

  • Andrea Garofalo

    General Atomics, GA

  • Joseph McClenaghan

    General Atomics

  • Siye Ding

    Institute for Plasma Physics, ORNL

  • Xi Chen

    General Atomics - San Diego, General Atomics, GA

  • Mike Zarnstorff

    Princeton Plasma Physics Laboratory, Princeton Plasma Physics Lab