Comparison of detachment in Ohmic plasmas with positive and negative triangularity

Février, O.; Tsui, C. K.; Durr-Legoupil-Nicoud, G.; Theiler, C.; Carpita, M.; Coda, S.; Colandrea, C.; Duval, B. P.; Gorno, S.; Huett, E.; Linehan, B.; Perek, A.; Porte, L.; Reimerdes, H.; Sauter, O.; Tonello, E.; Zurita, M.; Bolzonella, T.; Sciortino, F.

doi:10.1088/1361-6587/ad3c1c

Title: Comparison of detachment in Ohmic plasmas with positive and negative triangularity

Journal Article · 21 April 2024 · Plasma Physics and Controlled Fusion

DOI: https://doi.org/10.1088/1361-6587/ad3c1c · OSTI ID:2339928

;

; Durr-Legoupil-Nicoud, G.;

;

; Colandrea, C.; Duval, B. P.;

; Huett, E.;

;

; Porte, L.;

;

; Zurita, M.; Bolzonella, T.;

Abstract In recent years, negative triangularity (NT) has emerged as a potential high-confinement L-mode reactor solution. In this work, detachment is investigated using core density ramps in lower single null Ohmic L-mode plasmas across a wide range of upper, lower, and average triangularity (the mean of upper and lower triangularity: δ ) in the TCV tokamak. It is universally found that detachment is more difficult to access for NT shaping. The outer divertor leg of discharges with $δ \approx - 0.3$ could not be cooled to below $5 eV$ through core density ramps alone. The behavior of the upstream plasma and geometrical divertor effects (e.g. a reduced connection length with negative lower triangularity) do not fully explain the challenges in detaching NT plasmas. Langmuir probe measurements of the target heat flux widths ( λ _q ) were constant to within 30% across an upper triangularity scan, while the spreading factor S was lower by up to 50% for NT, indicating a generally lower integral scrape-off layer width, λ _int . The line-averaged core density was typically higher for NT discharges for a given fuelling rate, possibly linked to higher particle confinement in NT. Conversely, the divertor neutral pressure and integrated particle fluxes to the targets were typically lower for the same line-averaged density, indicating that NT configurations may be closer to the sheath-limited regime than their PT counterparts, which may explain why NT is more challenging to detach.

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Sponsoring Organization:: USDOE

Grant/Contract Number:: SC0010529

OSTI ID:: 2339928

Alternate ID(s):: OSTI ID: 2335546

Journal Information:: Plasma Physics and Controlled Fusion, Journal Name: Plasma Physics and Controlled Fusion Journal Issue: 6 Vol. 66; ISSN 0741-3335

Publisher:: IOP PublishingCopyright Statement

Country of Publication:: United Kingdom

Language:: English

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