Measurement of current density profile modification in LHCD experiments in Alcator C-Mod

ORAL

Abstract

Recent identification and resolution of problems in the Motional Stark Effect (MSE) diagnostic in Alcator C-Mod have made it possible to measure current density profile modifications in Lower Hybrid Current Drive (LHCD) experiments. A spurious drift in measured pitch angle has been traced to thermal stress- induced birefringence on the in-vessel lenses and is avoided by measuring the change in pitch angle between a LHCD phase and a baseline Ohmic phase within a discharge. The MSE measurements imply clear off-axis current drive and the dependence on parallel refractive index in the location and the magnitude of the driven current. The measurements are compared with GENRAY/CQL3D modeling.

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Authors

  • Jinseok Ko

    MIT PSFC

  • Steve Scott

    PPPL

  • A.E. Schmidt

    MIT PSFC

  • Syun'ichi Shiraiwa

    MIT PSFC, PSFC, MIT

  • P.T. Bonoli

    MIT PSFC, PSFC-MIT, MIT, MIT Plasma Science and Fusion Center, PSFC, MIT, Cambridge, MA

  • R.R. Parker

    MIT PSFC, MIT

  • J.C. Wright

    PSFC-MIT, MIT PSFC

  • Greg Wallace

    MIT Plasma Science and Fusion Center, MIT PSFC, MIT