Effect of L-Mode Electric Field Bifurcations and Edge Stochasticity on the L-H Transition Power Threshold with Applied n$=$3 Resonant Magnetic Perturbations*

POSTER

Abstract

H-mode access in ITER-similar-shape plasmas in DIII-D ($n_{\mathrm{e}}=$1.5-5x10$^{\mathrm{19}}$m$^{\mathrm{-3}}$, $B_{\mathrm{t}}=$1.9-2T, $I_{\mathrm{p}}=$1.5MA, $q_{\mathrm{95}}=$3.6) with applied n$=$3 Resonant Magnetic Perturbations (RMP) is found to depend on edge collisionality like $P_{\mbox{LH}} /P_{\mbox{LH-08}} \sim (\nu \ast )^{-0.5}$. This is a concern for ECH-heated, low collisionality plasmas on ITER since RMP may be applied before the L-H transition to safely suppress the first ELM. Bifurcations to positive radial electric field, increased toroidal co-rotation, and reduced edge $E\times B$ shear are observed when RMP fields are screened, preventing H-mode access at high applied RMP within the heating power range explored (P$_{\mathrm{loss}}\le $4 MW). Evidence of restored H-mode access with n$=$3 RMP field penetration is presented. An edge stochasticity model accounting for electron loss in the stochastic boundary layer can explain the experimental findings. The observed increase in $P_{\mathrm{LH}}$ at low collisionality is attributed to a reduced ExB shearing rate $\omega _{\mbox{E}\times \mbox{B}} $ and an increased normalized growth rate $\gamma _{\mbox{L}} /\omega_{\mbox{E}\times \mbox{B}} $.

Authors

  • Lothar Schmitz

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

  • Terry Rhodes

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

  • Lei Zeng

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

  • Matt Kriete

    UWisc. Madison, WI, University of Wisconsin-Madison

  • Zheng Yan

    UW-Madison, University of Wisconsin-Madison, U. Wisconsin-Madison, University of Wisconsin, Madison, UWisc. Madison, WI, University of Wisconsin - Madison

  • George McKee

    University of Wisconsin, UW-Madison, University of Wisconsin-Madison, U. Wisconsin-Madison, U Wisconsin, University of Wisconsin - Madison, UWisc. Madison, WI, University of Wisconsin Madison

  • R. Wilcox

    ORNL, ORNL, Oak Ridge, TN

  • T.E. Evans

    General Atomics, GA, General Atomics, San Diego, CA

  • C. Paz-Soldan

    General Atomics, GA, General Atomics, San Diego, CA

  • Shaun Haskey

    PPPL, Princeton Plasma Physics Laboratory, PPPL, Princeton, NJ

  • B.A. Grierson

    PPPL, PPPL, Princeton, NJ

  • P. Gohil

    General Atomics, San Diego, CA

  • C.C. Petty

    General Atomics, GA, General Atomics, San Diego, CA