Verhaegh, K., Lipschultz, B. orcid.org/0000-0001-5968-3684, Harrison, J. R. et al. (18 more authors) (2022) Spectroscopic investigations of detachment on the MAST Upgrade Super-X divertor. Nuclear Fusion. 016014. ISSN 1741-4326
Abstract
We present the first analysis of the atomic and molecular processes at play during detachment in the MAST-U Super-X divertor using divertor spectroscopy data. Our analysis indicates detachment in the MAST-U Super-X divertor can be separated into four sequential phases: first, the ionisation region detaches from the target at detachment onset leaving a region of increased molecular densities downstream. The plasma interacts with these molecules, resulting in molecular ions ( D 2 + and/or D 2 − → D + D − ) that further react with the plasma leading to molecular activated recombination and dissociation (MAR and MAD), which results in excited atoms and significant Balmer line emission. Second, the MAR region detaches from the target leaving a sub-eV temperature region downstream. Third, an onset of strong emission from electron-ion recombination (EIR) ensues. Finally, the electron density decays near the target, resulting in the bulk of the electron density moving upstream. The analysis in this paper indicates that plasma-molecule interactions have a larger impact than previously reported and play a critical role in the intensity and interpretation of hydrogen atomic line emission characteristics on MAST-U. Furthermore, we find that the Fulcher band emission profile in the divertor can be used as a proxy for the ionisation region and may also be employed as a plasma temperature diagnostic for improving the separation of hydrogenic emission arising from electron-impact excitation and that from plasma-molecular interactions. We provide evidences for the presence of low electron temperatures (≪0.5 eV) during detachment phases III-IV based on quantitative spectroscopy analysis, a Boltzmann relation of the high-n Balmer line transitions together with an analysis of the brightness of high-n Balmer lines.
Metadata
Item Type: | Article |
---|---|
Authors/Creators: |
|
Copyright, Publisher and Additional Information: | © 2022 Crown copyright. Funding Information: This work has been carried out within the framework of the EUROfusion Consortium, funded by the European Union via the Euratom Research and Training Programme (Grant Agreement No 101052200—EUROfusion), from the RCUK Energy Programme and EPSRC Grants EP/T012250/1 and EP/N023846/1. It has been supported in part by the Swiss National Science Foundation. To obtain further information on the data and models underlying this paper please contact publicationsmanager@ukaea.uk . Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Commission. Neither the European Union nor the European Commission can be held responsible for them. |
Keywords: | Balmer emission,divertor detachment,Fulcher emission,MAST Upgrade,plasma spectroscopy,plasma-neutral interactions,Super-X divertor |
Dates: |
|
Institution: | The University of York |
Academic Units: | The University of York > Faculty of Sciences (York) > Physics (York) The University of York > Faculty of Arts and Humanities (York) > Archaeology (York) |
Depositing User: | Pure (York) |
Date Deposited: | 05 Jan 2023 16:30 |
Last Modified: | 27 Nov 2024 00:44 |
Published Version: | https://doi.org/10.1088/1741-4326/aca10a |
Status: | Published |
Refereed: | Yes |
Identification Number: | 10.1088/1741-4326/aca10a |
Related URLs: | |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:194963 |
Download
Filename: Verhaegh_2023_Nucl._Fusion_63_016014.pdf
Description: Spectroscopic investigations of detachment on the MAST Upgrade Super-X divertor
Licence: CC-BY 2.5