Triangularity dependence of the divertor heat flux profile and SOL filamentary turbulence on TCV

Abstract The role of positive and negative triangularity on the divertor heat flux profile and on the SOL filamentary (blobby) turbulence is investigated experimentally in lower single-null, attached, L-mode plasmas on TCV. The divertor heat flux profile is determined by Langmuir probe measurements and is analyzed across a large data-set with varying triangularity, revealing a clear positive correlation of the divertor heat flux width λ q with the upper triangularity δ u , while no dependence on the lower triangularity δ l is observed. A secondary peak often observed in target particle and heat flux profiles is investigated, finding a dependence of its radial position on the outer wall gap. This is hypothesized to be connected to the deceleration of the blobs by the wall, as suggested by experimental data. The gas puff imaging analysis of blobs reveals significant differences in their radial velocity when triangularity is changed, especially in the X -point region. A heuristic blob transport model is developed to investigate a mechanism by which the blob behavior could directly affect the target profiles and the reported <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>λ</mml:mi> <mml:mi>q</mml:mi> </mml:msub> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mi>δ</mml:mi> <mml:mi>u</mml:mi> </mml:msub> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> </mml:math> dependency; the resulting predictions are found to be reasonably consistent with experimental observations.