Investigation of multi-ion heat and neoclassical transport using new edge main ion measurements at ASDEX Upgrade

Abstract This study provides new insights into multi-ion heat transport and the validation of neoclassical theory at the edge of H-mode plasmas. Utilizing a high-resolution main ion charge exchange recombination spectroscopy system, the first characterization of edge deuterium temperature ( T D ) and toroidal velocity ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>v</mml:mi> <mml:mrow> <mml:mi>ϕ</mml:mi> <mml:mo>,</mml:mo> <mml:mi>D</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> ) in a metal wall environment is presented. Dedicated experiments which examine the impact of the heating mix on T D and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>v</mml:mi> <mml:mrow> <mml:mi>ϕ</mml:mi> <mml:mo>,</mml:mo> <mml:mi>D</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> in the ASDEX Upgrade tokamak are discussed. An unexpected temperature difference between main ions ( T D ) and impurities ( T z ) was discovered when increasing <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>P</mml:mi> <mml:mrow> <mml:mi>ECRH</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>T</mml:mi> <mml:mi>D</mml:mi> </mml:msub> <mml:mo>&gt;</mml:mo> <mml:msub> <mml:mi>T</mml:mi> <mml:mi>z</mml:mi> </mml:msub> </mml:mrow> </mml:math> . The new temperature measurements have been used to solve the multi-ion heat transport equations with the astra transport code. The interpreted deuterium ( χ D ) and impurity ( χ z ) heat diffusivities have been compared to fluid ( tglf ) and gyrokinetic ( gkw ) models. While the dependence of a qualitatively similar <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>χ</mml:mi> <mml:mi>D</mml:mi> </mml:msub> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:msub> <mml:mi>χ</mml:mi> <mml:mi>z</mml:mi> </mml:msub> </mml:mrow> </mml:math> on the ion to electron heat flux ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>Q</mml:mi> <mml:mi>i</mml:mi> </mml:msub> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:msub> <mml:mi>Q</mml:mi> <mml:mi>e</mml:mi> </mml:msub> </mml:mrow> </mml:math> ) was identified in both experiment and simulation, discrepancies in the absolute value between the two are found when temperature differences between deuterium and impurities are present. The mechanism for the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>χ</mml:mi> <mml:mi>D</mml:mi> </mml:msub> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:msub> <mml:mi>χ</mml:mi> <mml:mi>z</mml:mi> </mml:msub> </mml:mrow> </mml:math> dependence on <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>Q</mml:mi> <mml:mi>i</mml:mi> </mml:msub> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:msub> <mml:mi>Q</mml:mi> <mml:mi>e</mml:mi> </mml:msub> </mml:mrow> </mml:math> is the stronger resonant interaction of impurities with low drift frequency turbulence modes in comparison to deuterium. Importantly, it is shown that considering a single ion species (i), and assuming <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>T</mml:mi> <mml:mi>D</mml:mi> </mml:msub> <mml:mo>=</mml:mo> <mml:msub> <mml:mi>T</mml:mi> <mml:mi>z</mml:mi> </mml:msub> </mml:mrow> </mml:math> gives reasonable estimates of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>χ</mml:mi> <mml:mi>D</mml:mi> </mml:msub> <mml:mo>≈</mml:mo> <mml:msub> <mml:mi>χ</mml:mi> <mml:mi>i</mml:mi> </mml:msub> </mml:mrow> </mml:math> for the cases studied here. On the contrary, the evaluation of χ z is very sensitive to ion temperature differences, which must be considered for accurate impurity ion heat transport description. Additionally, differences between <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>v</mml:mi> <mml:mrow> <mml:mi>ϕ</mml:mi> <mml:mo>,</mml:mo> <mml:mi>D</mml:mi>