X-point and divertor filament dynamics from gas puff imaging on TCV

Wüthrich, C.; Theiler, C.; Offeddu, N.; Galassi, D.; Oliveira, D. S.; Duval, B. P.; Février, O.; Golfinopoulos, T.; Han, W.; Marmar, E.; Terry, J. L.; Tsui, C. K.; the TCV Team,

doi:10.1088/1741-4326/ac8692

X-point and divertor filament dynamics from gas puff imaging on TCV

Journal Article · Wed Sep 07 00:00:00 EDT 2022 · Nuclear Fusion

DOI:https://doi.org/10.1088/1741-4326/ac8692· OSTI ID:1885851

; ; ; ; ; Duval, B. P.; ; Golfinopoulos, T.; ; Marmar, E.; ; ; the TCV Team,

Abstract

A new gas puff imaging diagnostic has been installed on the TCV tokamak, providing two-dimensional insights into scrape-off-layer (SOL) turbulence dynamics above, at and below the magnetic X-point. A detailed study in L-mode, attached, lower single-null discharges shows that statistical properties have little poloidal variations, while vast differences are present in the 2D behaviour of intermittent filaments. Strongly elongated filaments, just above the X-point and in the divertor far-SOL, show a good consistency in shape and dynamics with field-line tracing from filaments at the outboard midplane, highlighting their connection. In the near-SOL of the outer divertor leg, short-lived, high frequency and more circular (diameter ∼15 sound Larmor radii) filaments are observed. These divertor-localised filaments appear born radially at the position of maximum density and display a radially outward motion with velocity ≈400 m s ⁻¹ that is comparable to radial velocities of upstream-connected filaments. Conversely, in these discharges ( $\vec{B} \times \nabla B$ pointing away from the divertor), these divertor filaments’ poloidal velocities differ strongly from those of upstream-connected filaments. The importance of divertor-localised filaments upon radial transport and profile broadening is explored using filament statistics and in situ kinetic profile measurements along the divertor leg. This suggests that these filaments contribute significantly to electron density profile broadening in the divertor.

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Research Organization:: Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States); Univ. of California, San Diego, CA (United States)

Sponsoring Organization:: USDOE; USDOE Office of Science (SC)

Contributing Organization:: TCV Team

Grant/Contract Number:: SC0010529; SC0020327

OSTI ID:: 1885851

Alternate ID(s):: OSTI ID: 2420051
OSTI ID: 1879594

Journal Information:: Nuclear Fusion, Journal Name: Nuclear Fusion Journal Issue: 10 Vol. 62; ISSN 0029-5515

Publisher:: IOP PublishingCopyright Statement

Country of Publication:: IAEA

Language:: English

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X-point and divertor filament dynamics from gas puff imaging on TCV

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