Nitrogen-seeded divertor detachment in TCV L-mode plasmas

Février, O.; Theiler, C.; Harrison, J. R.; Tsui, C. K.; Verhaegh, K.; Wüthrich, C.; Boedo, J. A.; De Oliveira, H.; Duval, B. P.; Labit, B.; Lipschultz, B.; Maurizio, R.; Reimerdes, H.

doi:10.1088/1361-6587/ab6b00

Nitrogen-seeded divertor detachment in TCV L-mode plasmas

Journal Article · Sun Feb 09 23:00:00 EST 2020 · Plasma Physics and Controlled Fusion

DOI:https://doi.org/10.1088/1361-6587/ab6b00· OSTI ID:1802121

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Ecole Polytechnique Federale Lausanne (Switzerland); OSTI
Ecole Polytechnique Federale Lausanne (Switzerland)
Culham Science Centre, Abingdon (United Kingdom). Culham Centre for Fusion Energy (CCFE)
Ecole Polytechnique Federale Lausanne (Switzerland); Univ. of California, San Diego, La Jolla, CA (United States)
Ecole Polytechnique Federale Lausanne (Switzerland); Univ. of York (United Kingdom)
Univ. of California, San Diego, La Jolla, CA (United States)
Univ. of York (United Kingdom)

Most of the detachment experiments done to date on the tokamak à configuration variable (TCV), both in standard and alternative divertor geometries, focused on L-mode integrated core density ramps. In view of extending these studies to high-power, high-confinement regimes, where impurity seeding will be necessary for detachment, the properties of nitrogen seeded L-mode detachment in TCV are assessed here with the extensive set of edge and divertor diagnostics and similarities and differences with integrated core density ($$\langle n_e \rangle$$) ramp detachment experiments are elucidated. It is found that in high current, reversed field plasmas, detachment at the outer target is achieved with N₂-seeding and density ramps, with target heat flux reductions of up to 90%, while the inner target only detaches with seeding. The Scrape-Off Layer radiation fraction reaches values of 60%–80% and in all situations, a stable radiator can form around the X-point. In this work, the most striking difference between seeding and density ramp is the behavior of the upstream quantities. During the $$\langle n_e \rangle$$-ramp, a broadening of the upstream density profile (density ‘shoulder’) occurs, concurrent with the outer target ion flux roll-over, while no such behavior occurs during nitrogen seeded detachment. Separatrix density, electron temperature and pressure also evolve strongly with increasing density, and are largely unaffected by the injection of nitrogen. Comparison of upstream and target pressures reveals that, in all cases, the outer target ion flux reduction coincides with the development of a parallel gradient of the total pressure. Common to all cases is also a reduction of energy confinement time with detachment, although this effect is weak for seeding at relatively high density. Studying the impact of the ∇B-drift direction in both nitrogen seeding and core density ramps reveals that drifts mainly affect the behavior at the inner strike point, highlighting the need to include them in edge transport simulations.

View Accepted Manuscript (DOE)

Research Organization:: Univ. of California, San Diego, CA (United States)

Sponsoring Organization:: USDOE Office of Science (SC); Swiss National Science Foundation (SNF); Euratom

Contributing Organization:: The TCV Team; The EUROfusion MST1 Team

Grant/Contract Number:: SC0010529

OSTI ID:: 1802121

Alternate ID(s):: OSTI ID: 23027370

Journal Information:: Plasma Physics and Controlled Fusion, Journal Name: Plasma Physics and Controlled Fusion Journal Issue: 3 Vol. 62; ISSN 0741-3335

Publisher:: IOP ScienceCopyright Statement

Country of Publication:: United States

Language:: English

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