Theory and Fluid Simulations of Boundary Plasma Fluctuations
Abstract
Theoretical and computational investigations are presented of boundary plasma microturbulence that take into account important effects of the geometry of diverted tokamaksin particular, the effect of xpoint magnetic shear and the termination of field lines on divertor plates. We first generalize our previous 'heuristic boundary condition' which describes, in a lumped model, the closure of currents in the vicinity of the xpoint region to encompass three currentclosure mechanisms. We then use this boundary condition to derive the dispersion relation for lowbeta flutelike modes in the divertorleg region under the combined drives of curvature, sheath impedance, and divertor tilt effects. The results indicate the possibility of strongly growing instabilities, driven by sheath boundary conditions, and localized in either the private or common flux region of the divertor leg depending on the radial tilt of divertor plates. We revisit the issue of xpoint effects on blobs, examining the transition from blobs terminated by xpoint shear to blobs that extend over both the main SOL and divertor legs. We find that, for a mainSOL blob, this transition occurs without a freeacceleration period as previously thought, with xpoint termination conditions applying until the blob has expanded to reach the divertor plate. We also derivemore »
 Authors:
 Publication Date:
 Research Org.:
 Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
 Sponsoring Org.:
 USDOE
 OSTI Identifier:
 936982
 Report Number(s):
 UCRLJRNL227892
TRN: US0806151
 DOE Contract Number:
 W7405ENG48
 Resource Type:
 Journal Article
 Resource Relation:
 Journal Name: Nuclear Fusion, vol. 47, July 2007, July 1, 2007, pp. 612; Journal Volume: 47
 Country of Publication:
 United States
 Language:
 English
 Subject:
 70 PLASMA PHYSICS AND FUSION; BOUNDARY CONDITIONS; CLOSURES; DISPERSION RELATIONS; DIVERTORS; FLUCTUATIONS; GEOMETRY; IMPEDANCE; PLASMA; PLATES; SHEAR; SOLS; TURBULENCE
Citation Formats
Cohen, R H, LaBombard, B, LoDestro, L L, Rognlien, T D, Ryutov, D D, Terry, J L, Umansky, M V, Xu, X Q, and Zweben, S. Theory and Fluid Simulations of Boundary Plasma Fluctuations. United States: N. p., 2007.
Web. doi:10.1088/00295515/47/7/012.
Cohen, R H, LaBombard, B, LoDestro, L L, Rognlien, T D, Ryutov, D D, Terry, J L, Umansky, M V, Xu, X Q, & Zweben, S. Theory and Fluid Simulations of Boundary Plasma Fluctuations. United States. doi:10.1088/00295515/47/7/012.
Cohen, R H, LaBombard, B, LoDestro, L L, Rognlien, T D, Ryutov, D D, Terry, J L, Umansky, M V, Xu, X Q, and Zweben, S. Tue .
"Theory and Fluid Simulations of Boundary Plasma Fluctuations". United States.
doi:10.1088/00295515/47/7/012. https://www.osti.gov/servlets/purl/936982.
@article{osti_936982,
title = {Theory and Fluid Simulations of Boundary Plasma Fluctuations},
author = {Cohen, R H and LaBombard, B and LoDestro, L L and Rognlien, T D and Ryutov, D D and Terry, J L and Umansky, M V and Xu, X Q and Zweben, S},
abstractNote = {Theoretical and computational investigations are presented of boundary plasma microturbulence that take into account important effects of the geometry of diverted tokamaksin particular, the effect of xpoint magnetic shear and the termination of field lines on divertor plates. We first generalize our previous 'heuristic boundary condition' which describes, in a lumped model, the closure of currents in the vicinity of the xpoint region to encompass three currentclosure mechanisms. We then use this boundary condition to derive the dispersion relation for lowbeta flutelike modes in the divertorleg region under the combined drives of curvature, sheath impedance, and divertor tilt effects. The results indicate the possibility of strongly growing instabilities, driven by sheath boundary conditions, and localized in either the private or common flux region of the divertor leg depending on the radial tilt of divertor plates. We revisit the issue of xpoint effects on blobs, examining the transition from blobs terminated by xpoint shear to blobs that extend over both the main SOL and divertor legs. We find that, for a mainSOL blob, this transition occurs without a freeacceleration period as previously thought, with xpoint termination conditions applying until the blob has expanded to reach the divertor plate. We also derive propagation speeds for divertorleg blobs. Finally, we present fluid simulations of the CMod tokamak from the BOUT edge fluid turbulence code, which show mainSOL blob structures with similar spatial characteristics to those observed in the experiment, and also simulations which illustrate the possibility of fluctuations confined to divertor legs.},
doi = {10.1088/00295515/47/7/012},
journal = {Nuclear Fusion, vol. 47, July 2007, July 1, 2007, pp. 612},
number = ,
volume = 47,
place = {United States},
year = {Tue Jan 09 00:00:00 EST 2007},
month = {Tue Jan 09 00:00:00 EST 2007}
}

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