Plasma performance and operational space without ELMs in DIII-D

Abstract

Abstract A database of DIII-D plasmas without edge-localized modes (ELMs) compares the operating space and plasma performance of stationary no-ELM regimes found in conventional tokamaks: ELM suppression with resonant magnetic perturbations (RMPs), quiescent H-mode (QH, including wide-pedestal variant), improved confinement mode (I-mode), enhanced D-alpha H-mode (EDA-H), conventional low-confinement mode (L-mode), and negative triangularity L-mode (Neg-D). Operational space is documented in terms of engineering and physics parameters, revealing divergent constraints for each regime. Some operational space discriminants (such as pedestal collisionality) are well known, while others, such as low torque &amp; safety factor, or high power &amp; density, are less commonly emphasized. Normalized performance (confinement quality and normalized pressure) also discriminate the no-ELM regimes and favor the regimes tolerant to power in DIII-D: RMP, QH, and Neg-D. Absolute performance (volume-averaged pressure <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mfenced close="⟩" open="⟨"> <mml:mi>p</mml:mi> </mml:mfenced> </mml:math> , confinement time τ , and triple product <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mfenced close="⟩" open="⟨"> <mml:mi>p</mml:mi> </mml:mfenced> <mml:mi>τ</mml:mi> </mml:math> ) also discriminates no-ELM regimes and is found to rise linearly with IaB (a metric for the magnetic configuration strength, the product of current I , minor radius a , and field B that has units of force), and also benefits from tolerance to power. The highest normalized performance using the metric <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mfenced close="⟩" open="⟨"> <mml:mi>p</mml:mi> </mml:mfenced> <mml:mi>τ</mml:mi> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:mi>I</mml:mi> <mml:mi>a</mml:mi> <mml:mi>B</mml:mi> </mml:math> is found in QH and RMP regimes. Focusing on ITER-shaped no-ELM plasmas, Q = 10 at 15 MA scaled global performance is met with some metrics ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>β</mml:mi> <mml:mrow> <mml:mi>N</mml:mi> </mml:mrow> </mml:msub> <mml:msub> <mml:mi>H</mml:mi> <mml:mrow> <mml:mn>98</mml:mn> </mml:mrow> </mml:msub> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:msubsup> <mml:mi>q</mml:mi> <mml:mrow> <mml:mn>95</mml:mn> </mml:mrow> <mml:mn>2</mml:mn> </mml:msubsup> </mml:math> , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mi>H</mml:mi> <mml:mrow> <mml:mn>98</mml:mn> </mml:mrow> <mml:mn>3</mml:mn> </mml:msubsup> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:msub> <mml:mi>β</mml:mi> <mml:mrow> <mml:mi>N</mml:mi> </mml:mrow> </mml:msub> <mml:msubsup> <mml:mi>q</mml:mi> <mml:mrow> <mml:mn>95</mml:mn> </mml:mrow> <mml:mn>2</mml:mn> </mml:msubsup> </mml:math> ), but not others ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>β</mml:mi> <mml:mrow> <mml:mi>N</mml:mi> </mml:mrow> </mml:msub> <mml:msub> <mml:mi>H</mml:mi> <mml:mrow> <mml:mn>89</mml:mn> </mml:mrow> </mml:msub> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:msubsup> <mml:mi>q</mml:mi> <mml:mrow> <mml:mn>95</mml:mn> </mml:mrow> <mml:mn>2</mml:mn> </mml:msubsup> </mml:math> , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mfenced close="⟩" open="⟨"> <mml:mi>p</mml:mi> </mml:mfenced> <mml:mi>τ</mml:mi> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:mi>I</mml:mi> <mml:mi>a</mml:mi> <mml:mi>B</mml:mi> </mml:math> ), and only thus far at high torque ( β N is normalized pressure, H 89,98 is the confinement quality by scaling law, and q 95 is the safety factor). Though comparable QH and RMP performance is found, the pedestal pressure ( p ped ≈ 2 p e , ped ) is very different. p ped in RMP plasmas is relatively low, and the best performance is found with a high core <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mfenced close="⟩" open="⟨"> <mml:mi>p</mml:mi> </mml:mfenced>

Topics & Concepts