Poloidal asymmetries in edge transport barriers
[3];
[4];
[5];
- Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA; Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543, USA
- Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA; Centre de Recherches en Physique des Plasmas École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland
- Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA; Department of Physics, University of York, Heslington, York YO10 5DD, United Kingdom
- Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
- Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA; Department of Physics, University of Maryland, College Park, Maryland 20742, USA
- Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543, USA
Measurements of impurities in Alcator C-Mod indicate that in the pedestal region, significant poloidal asymmetries can exist in the impurity density, ion temperature, and main ion density. In light of the observation that ion temperature and electrostatic potential are not constant on a flux surface [Theiler et al., Nucl. Fusion 54, 083017 (2014)], a technique based on total pressure conservation to align profiles measured at separate poloidal locations is presented and applied. Gyrokinetic neoclassical simulations with XGCa support the observed large poloidal variations in ion temperature and density, and that the total pressure is approximately constant on a flux surface. With the updated alignment technique, the observed in-out asymmetry in impurity density is reduced from previous publishing [Churchill et al., Nucl. Fusion 53, 122002 (2013)], yet remains substantial (nz,H/nz,L~6). Candidate asymmetry drivers are explored, showing that neither non-uniform impurity sources nor localized fluctuation-driven transport are able to explain satisfactorily the impurity density asymmetry. Since impurity density asymmetries are only present in plasmas with strong electron density gradients, and radial transport timescales become comparable to parallel transport timescales in the pedestal region, it is implied that global transport effects relating to the strong electron density gradients in the pedestal are the main driver for the pedestal in-out impurity density asymmetry.
- Research Organization:
- Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Fusion Energy Sciences (FES)
- Contributing Organization:
- Alcator C-Mod Team
- Grant/Contract Number:
- FC02-99ER54512; AC02-09CH11466; FG02-06ER54845; FG02-86ER53223
- OSTI ID:
- 1548280
- Alternate ID(s):
- OSTI ID: 1228306
- Journal Information:
- Physics of Plasmas, Vol. 22, Issue 5; ISSN 1070-664X
- Publisher:
- American Institute of Physics (AIP)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
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