Separating the roles of magnetic topology and neutral trapping in modifying the detachment threshold for TCV

TY - JOUR

T1 - Separating the roles of magnetic topology and neutral trapping in modifying the detachment threshold for TCV

AU - Fil, Alexandre

AU - Lipschultz, Bruce

AU - Moulton, D.

AU - Dudson, Benjamin Daniel

AU - Février, O.

AU - Myatra, Omkar

AU - Theiler, C.

AU - Verhaegh, Kevin

AU - Wensing, M.

AU - EUROfusion MST1 Team

AU - The TCV Team

N1 - © 2020 University of York. This is an author-produced version of the published paper. Uploaded in accordance with the publisher’s self-archiving policy. Further copying may not be permitted; contact the publisher for details.

PY - 2020/1/29

Y1 - 2020/1/29

N2 - Total flux expansion, a divertor magnetic topology design choice embodied in the Super-X divertor, is predicted through simple analytic models and SOLPS calculations to reduce the plasma and impurity density detachment thresholds as the outer divertor separatrix leg position and the strike-point major radius, Rt, are increased. However, those predictions are contradicted by recent TCV experimental results. In this study, utilizing the SOLPS-ITER code, we are able to both match TCV results and demonstrate that the effect of total flux expansion is counteracted by two other divertor geometry design characteristics that affect neutrals: a) the strike-point angle to the outer target; and b) the effect of physical baffles that reduce the amount of neutrals escaping from the divertor. We quantify the role of those neutral effects through developing and applying a quantitative definition of neutral trapping. The results of this study indicate that improved divertor design, properly utilizing the three design characteristics discussed should lead all effects to be additive in reducing the detachment threshold. A second implication of this study is that any assessment of alternative topologies must separate out the effects of magnetic topology from neutral design characteristics.

AB - Total flux expansion, a divertor magnetic topology design choice embodied in the Super-X divertor, is predicted through simple analytic models and SOLPS calculations to reduce the plasma and impurity density detachment thresholds as the outer divertor separatrix leg position and the strike-point major radius, Rt, are increased. However, those predictions are contradicted by recent TCV experimental results. In this study, utilizing the SOLPS-ITER code, we are able to both match TCV results and demonstrate that the effect of total flux expansion is counteracted by two other divertor geometry design characteristics that affect neutrals: a) the strike-point angle to the outer target; and b) the effect of physical baffles that reduce the amount of neutrals escaping from the divertor. We quantify the role of those neutral effects through developing and applying a quantitative definition of neutral trapping. The results of this study indicate that improved divertor design, properly utilizing the three design characteristics discussed should lead all effects to be additive in reducing the detachment threshold. A second implication of this study is that any assessment of alternative topologies must separate out the effects of magnetic topology from neutral design characteristics.

U2 - 10.1088/1361-6587/ab69bb

DO - 10.1088/1361-6587/ab69bb

M3 - Article

SN - 0741-3335

VL - 62

JO - Plasma Physics and Controlled Fusion

JF - Plasma Physics and Controlled Fusion

IS - 3

ER -