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High-field side scrape-off layer investigation: Plasma profiles and impurity screening behavior in near-double-null configurations
- Source :
- Nuclear Materials and Energy, Vol 12, Iss, Pp 139-147 (2017), Elsevier
- Publication Year :
- 2017
- Publisher :
- Elsevier BV, 2017.
-
Abstract
- New experiments on Alcator C-Mod reveal that the favorable impurity screening characteristics of the high-field side (HFS) scrape-off layer (SOL), previously reported for single null geometries, is retained in double null configurations, despite the formation of an extremely thin SOL. In balanced double-null, nitrogen injected locally into the HFS SOL is better screened by a factor of 2.5 compared to the same injection into the low field side (LFS) SOL. This result is insensitive to plasma current and Greenwald fraction. Nitrogen injected into the HFS SOL is not as well screened (only a factor of 1.5 improvement over LFS) in unbalanced double-null discharges, when the primary divertor is in the direction of B×∇B. In this configuration, impurity ‘plume’ emission patterns indicate that an opposing E × B drift competes with the parallel impurity flow to the divertor. In balanced double-null plasmas, the dispersal pattern exhibits a dominant E × B motion. Unbalanced discharges with the primary divertor opposite the direction of B×∇B exhibit excellent HFS screening characteristics – a factor of 5 enhancement compared to LFS. These data support the idea that future tokamaks should locate all RF actuators and close-fitting wall structures on the HFS and employ near-double-null magnetic topologies, both to precisely control plasma conditions at the antenna/plasma interface and to maximally mitigate the impact of local impurity sources arising from plasma-material interactions. Keywords: Alcator C-Mod; Impurity screening; Double null; High field side scrape-off layer<br />United States. Department of Energy (Contract DE-FC02-99ER54512)
- Subjects :
- Nuclear and High Energy Physics
Tokamak
Field (physics)
Materials Science (miscellaneous)
Analytical chemistry
01 natural sciences
Molecular physics
010305 fluids & plasmas
law.invention
Alcator C-Mod
Impurity
law
Double null
0103 physical sciences
Impurity screening
010306 general physics
Null (radio)
Chemistry
Divertor
Plasma
lcsh:TK9001-9401
Nuclear Energy and Engineering
High field side scrape-off layer
lcsh:Nuclear engineering. Atomic power
Antenna (radio)
Subjects
Details
- ISSN :
- 23521791
- Volume :
- 12
- Database :
- OpenAIRE
- Journal :
- Nuclear Materials and Energy
- Accession number :
- edsair.doi.dedup.....fdf16c8e4838efa5613b029983ff0ed7