Comparison of high density and nitrogen seeded detachment using SOLPS-ITER simulations of the tokamak á configuration variable

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Smolders, A. and Wensing, M. and Carli, S. and de Oliveira, H. and Dekeyser, W. and Duval, B. P. and Février, O. and Gahle, D. and Martinelli, L. and Reimerdes, H. and Theiler, C. and Verhaegh, K. (2020) Comparison of high density and nitrogen seeded detachment using SOLPS-ITER simulations of the tokamak á configuration variable. Plasma Physics and Controlled Fusion, 62 (12). 125006. ISSN 0741-3335 (https://doi.org/10.1088/1361-6587/abbcc5)

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Abstract

First of a kind SOLPS-ITER simulations on tokamak á configuration variable (TCV) that include nitrogen have been performed to model recent nitrogen seeded detachment experiments. Based on spectroscopic measurements, a nitrogen recycling coefficient RNp ≈ 0.3–0.5 on the graphite walls of TCV is estimated. The experimentally observed decrease of core nitrogen density with increasing plasma density is reproduced and linked to a reduction of the ionisation mean free path in the scrape-off layer. Although the influence of sputtered carbon impurities from TCV’s graphite wall cannot be fully eliminated, seeding nitrogen increases control over the total impurity density. This facilitates disentangling the effect of impurities from that of high upstream density on the main characteristics of detachment, namely target power and ion current reductions and the development of a parallel pressure drop. Increasing the density and the seeding rate reduce the power on the divertor targets in a different way: with density, the ion current increases and the target temperature strongly decreases, whereas seeding impurities decreases the ion current and affects less strongly the temperature. The reduction in ion current when seeding nitrogen is due to a lower ionisation source, which is not related to power limitation nor an increased momentum loss, but to a decrease of the ionisation reaction rate. Impurity seeding leads to less volumetric momentum losses (and hence pressure drop) than density ramps, for the same level of energy flux reduction. Additionally, main chamber sputtering of carbon is identified as a possible explanation for the missing target ion current roll-over during density ramps in the simulations.

ORCID iDs

Smolders, A., Wensing, M., Carli, S., de Oliveira, H., Dekeyser, W., Duval, B. P., Février, O., Gahle, D. ORCID logoORCID: https://orcid.org/0000-0002-4434-7626, Martinelli, L., Reimerdes, H., Theiler, C. and Verhaegh, K.;
  • Item type:Article
    ID code:78136
    Dates:
    Date
    Event
    26 October 2020
    Published
    29 September 2020
    Accepted
    Subjects:Science > Physics
    Department:Faculty of Science > Physics
    Depositing user: Pure Administrator
    Date deposited:12 Oct 2021 11:28
    Last modified:18 Dec 2024 16:25
    Related URLs:
    URI:https://strathprints.strath.ac.uk/id/eprint/78136
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