MHD stability of negative triangularity DIII-D plasmas
W. Boyes, F. Turco, J.M. Hanson, A. Marinoni, A. Turnbull, M. E. Austin, G.A. Navratil
Abstract
Abstract Negative triangularity (NT) experiments in DIII-D point to an emergent reactor scenario free of sawteeth, endowed with benign, nondisruptive n = 2 tearing modes, which experience q min <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>⩾</mml:mo> </mml:math> 1 similar to the positive triangularity hybrid scenario. Plasmas exhibiting this behavior attain <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>β</mml:mi> <mml:mrow> <mml:mtext>N</mml:mtext> </mml:mrow> </mml:msub> </mml:mrow> <mml:mo>></mml:mo> <mml:mn>3</mml:mn> </mml:math> , high enough to reconsider long held views of NT stability. Ideal MHD and tearing stability analysis of well-diagnosed equilibrium reconstructions of experimental hybrid-like plasmas predict that among shape parameters, MHD stability limits are only sensitive to average triangularity. Operation is predicted to be possible at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>β</mml:mi> <mml:mrow> <mml:mtext>N</mml:mtext> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> relevant to upcoming tokamaks and commercial NT reactors.