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H-mode Access and Limit Cycle Oscillations in DIII-D Negative Triangularity Plasmas

POSTER

Abstract

Negative triangularity L-mode plasmas in DIII-D exhibit H-mode-like thermal confinement and normalized pressure beta_n [1]. Their increased scrape-off layer width potentially opens a path for mitigating divertor power loading in future burning plasmas. Calculations show a reduced ballooning mode threshold prevents access to high pedestal pressure [2]. At moderate negative upper triangularity dU ~-0.2, ELMing H-mode is still sustained in DIII-D, with a moderately increased power threshold PLH ~3.5 MW compared to positive dU plasmas with similar NBI torque. However, plasmas with high negative upper triangularity (dU= -0.325) access ELMing H-mode only transiently, followed by extended limit cycle oscillations (LCO [3]), The edge electric field and normalized edge pressure gradient periodically increase but remain well below H-mode values up to the highest coupled power (~11 MW). Detailed gyrofluid stability analysis of the outer core plasma is presented.

Presenters

  • Lothar Schmitz

    University of California, Los Angeles, UCLA

Authors

  • Lothar Schmitz

    University of California, Los Angeles, UCLA

  • K. J Callahan

    UCLA

  • Lei Zeng

    University of California, Los Angeles, UCLA

  • Terry L Rhodes

    University of California, Los Angeles, UCLA

  • Max E Austin

    University of Texas at Austin, University of Texas Austin

  • Z. Yan

    University of Wisconsin, Madison

  • G. R McKee

    University of Wisconsin - Madison, University of Wisconsin, Madison

  • K. E Thome

    General Atomics

  • A. O Nelson

    Columbia University, Princeton Plasma Physics Laboratory

  • C. Paz-Soldan

    Columbia University

  • Alessandro Marinoni

    Massachusetts Institute of Technology MIT, PSFC MIT