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Transport and stability of the DIII-D q<sub>min</sub>~1.5 scenario

POSTER

Abstract

βN of 3.5–4 has been achieved in the DIII-D qmin~1.5 scenario using either on-axis neutral beam current drive (NBCD) or a mix of on- and off-axis NBCD. The off-axis NBCD is expected to broaden the plasma current and pressure profiles, resulting in stability and transport changes between plasmas with these different NBCD profiles. Both types of discharges are often terminated prematurely by n=1–3 tearing modes with n=1 modes being the most prevalent. However, DCON stability analysis of a discharge with off-axis NBCD finds that the n=2 ideal mode is the most unstable. These tearing modes are often triggered by bursty energetic particle modes (EPMs). Bursty n=1, 3 EPMs are often benignly present in these discharges but they are stronger and more frequent in discharges with off-axis NBCD. These discharges also have Alfvén eigenmodes (AEs) that cause fast-ion transport. However, AEs are reduced in the discharges with off-axis NBCD and the fast ion losses are closer to classical, as indicated by fluctuation diagnostics and neutron rate measurement. Local transport analysis using TRANSP and simulations using TGLF/TGYRO of these discharges will be presented.

Presenters

  • Kathreen E Thome

    General Atomics - San Diego, General Atomics

Authors

  • Kathreen E Thome

    General Atomics - San Diego, General Atomics

  • Deyong Liu

    General Atomics, University of California, Irvine

  • Craig C Petty

    General Atomics - San Diego, General Atomics

  • Christopher T Holcomb

    Lawrence Livermore Natl Lab, Lawrence Livermore National Laboratory, LLNL, Lawrence Livermore National Lab

  • Nikolas C Logan

    Lawrence Livermore Natl Lab, Lawrence Livermore National Laboratory, LLNL

  • Brian S Victor

    Lawrence Livermore Natl Lab

  • Alexander F Battey

    Columbia University, Columbia U

  • Jeremy M Hanson

    Columbia University, Columbia U

  • Francesca Turco

    Columbia University, Columbia U

  • Cami S Collins

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