Investigation into the formation of the scrape-off layer density shoulder in JET ITER-like wall L-mode and H-mode plasmas
Abstract
The low temperature boundary layer plasma (scrape-off layer or SOL) between the hot core and the surrounding vessel determines the level of power loading, erosion and implantation of material surfaces, and thus the viability of tokamak-based fusion as an energy source. Here, this study explores mechanisms affecting the formation of flattened density profiles, so-called 'density shoulders', in the low-field side (LFS) SOL, which modify ion and neutral fluxes to surfaces—and subsequent erosion. There is evidence against local enhancement of ionization inducing shoulder formation. We find that increases in SOL parallel resistivity, Λdiv (=[L || ν eiΩi]/c sΩe), postulated to lead to shoulder growth through changes in SOL turbulence characteristics, correlates with increases in SOL shoulder amplitude, A s, but only under a subset of conditions (D2-fuelled L-mode density scans with outer strike point on the horizontal target). Λdiv fails to correlate with A s for cases of N2 seeding or during sweeping of the strike point across the horizontal target. The limited correlation of Λdiv and A s is also found for H-mode discharges. Thus, while it may be necessary for Λdiv to be above a threshold of ~1 for shoulder formation and/or growth, another mechanism is required. More significantly,more »
- Authors:
-
- Univ. of York (United Kingdom)
- CCFE, Culham Science Centre, Abingdon (United Kingdom)
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Univ. of York (United Kingdom); Institut für Energie-und Klimaforschung—Plasmaphysik, Julich (Germany). Forschungszentrum Jülich Gmbh
- Hungarian Academy of Sciences, Budapest (Hungary)
- CCFE, Culham Science Centre, Abingdon (United Kingdom); Instituto de Plasmas e Fusao Nuclear, Instituto Superior Tecnico, Lisbon (Portugal)
- Associazione EURATOM-ENEA sulla Fusione, Frascati, Rome (Italy)
- Institut für Energie-und Klimaforschung—Plasmaphysik, Julich (Germany). Forschungszentrum Jülich Gmbh
- Association EURATOM-CEA, CEA/DSM/DRFC CEA-Cadarache (France)
- Technical Univ. of Denmark, Roskilde (Denmark)
- Publication Date:
- Research Org.:
- Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
- Sponsoring Org.:
- USDOE National Nuclear Security Administration (NNSA)
- Contributing Org.:
- JET Contributors
- OSTI Identifier:
- 1616396
- Report Number(s):
- LLNL-JRNL-806922
Journal ID: ISSN 0029-5515; 1011269; TRN: US2106444
- Grant/Contract Number:
- AC52-07NA27344
- Resource Type:
- Journal Article: Accepted Manuscript
- Journal Name:
- Nuclear Fusion
- Additional Journal Information:
- Journal Volume: 58; Journal Issue: 5; Journal ID: ISSN 0029-5515
- Publisher:
- IOP Science
- Country of Publication:
- United States
- Language:
- English
- Subject:
- 70 PLASMA PHYSICS AND FUSION TECHNOLOGY
Citation Formats
Wynn, A., Lipschultz, B., Cziegler, I., Harrison, J., Jaervinen, A., Matthews, G. F., Schmitz, J., Tal, B., Brix, M., Guillemaut, C., Frigione, D., Huber, A., Joffrin, E., Kruzei, U., Militello, F., Nielsen, A., Walkden, N. R., and Wiesen, S. Investigation into the formation of the scrape-off layer density shoulder in JET ITER-like wall L-mode and H-mode plasmas. United States: N. p., 2018.
Web. doi:10.1088/1741-4326/aaad78.
Wynn, A., Lipschultz, B., Cziegler, I., Harrison, J., Jaervinen, A., Matthews, G. F., Schmitz, J., Tal, B., Brix, M., Guillemaut, C., Frigione, D., Huber, A., Joffrin, E., Kruzei, U., Militello, F., Nielsen, A., Walkden, N. R., & Wiesen, S. Investigation into the formation of the scrape-off layer density shoulder in JET ITER-like wall L-mode and H-mode plasmas. United States. https://doi.org/10.1088/1741-4326/aaad78
Wynn, A., Lipschultz, B., Cziegler, I., Harrison, J., Jaervinen, A., Matthews, G. F., Schmitz, J., Tal, B., Brix, M., Guillemaut, C., Frigione, D., Huber, A., Joffrin, E., Kruzei, U., Militello, F., Nielsen, A., Walkden, N. R., and Wiesen, S. 2018.
"Investigation into the formation of the scrape-off layer density shoulder in JET ITER-like wall L-mode and H-mode plasmas". United States. https://doi.org/10.1088/1741-4326/aaad78. https://www.osti.gov/servlets/purl/1616396.
@article{osti_1616396,
title = {Investigation into the formation of the scrape-off layer density shoulder in JET ITER-like wall L-mode and H-mode plasmas},
author = {Wynn, A. and Lipschultz, B. and Cziegler, I. and Harrison, J. and Jaervinen, A. and Matthews, G. F. and Schmitz, J. and Tal, B. and Brix, M. and Guillemaut, C. and Frigione, D. and Huber, A. and Joffrin, E. and Kruzei, U. and Militello, F. and Nielsen, A. and Walkden, N. R. and Wiesen, S.},
abstractNote = {The low temperature boundary layer plasma (scrape-off layer or SOL) between the hot core and the surrounding vessel determines the level of power loading, erosion and implantation of material surfaces, and thus the viability of tokamak-based fusion as an energy source. Here, this study explores mechanisms affecting the formation of flattened density profiles, so-called 'density shoulders', in the low-field side (LFS) SOL, which modify ion and neutral fluxes to surfaces—and subsequent erosion. There is evidence against local enhancement of ionization inducing shoulder formation. We find that increases in SOL parallel resistivity, Λdiv (=[L || ν eiΩi]/c sΩe), postulated to lead to shoulder growth through changes in SOL turbulence characteristics, correlates with increases in SOL shoulder amplitude, A s, but only under a subset of conditions (D2-fuelled L-mode density scans with outer strike point on the horizontal target). Λdiv fails to correlate with A s for cases of N2 seeding or during sweeping of the strike point across the horizontal target. The limited correlation of Λdiv and A s is also found for H-mode discharges. Thus, while it may be necessary for Λdiv to be above a threshold of ~1 for shoulder formation and/or growth, another mechanism is required. More significantly, we find that in contrast to parallel resistivity, outer divertor recycling, as quantified by the total outer divertor Balmer D α emission, I–D α , does scale with A s where Λdiv does and even where Λdiv does not. Divertor recycling could lead to SOL density shoulder formation through: (a) reducing the parallel to the field flow (loss) of ions out of the SOL to the divertor; and (b) changes in radial electric fields which lead to E × B poloidal flows as well as potentially affecting SOL turbulence birth characteristics. Therefore, changes in divertor recycling may be the sole process involved in bringing about SOL density shoulders or it may be that it acts in tandem with parallel resistivity.},
doi = {10.1088/1741-4326/aaad78},
url = {https://www.osti.gov/biblio/1616396},
journal = {Nuclear Fusion},
issn = {0029-5515},
number = 5,
volume = 58,
place = {United States},
year = {Wed Feb 07 00:00:00 EST 2018},
month = {Wed Feb 07 00:00:00 EST 2018}
}
Web of Science
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Works referencing / citing this record:
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