The Magnetic Field Structure of a Snowflake Divertor
Abstract
The snowflake divertor exploits a tokamak geometry in which the poloidal magnetic field null approaches second order; the name stems from the characteristic hexagonal, snowflake-like, shape of the separatrix for an exact second-order null. The proximity of the poloidal field structure to that of a second-order null substantially modifies edge magnetic properties compared to the standard X-point geometry; this, in turn, affects the edge plasma behavior. Modifications include: (1) The flux expansion near the null-point becomes 2-3 times larger; (2) The connection length between the equatorial plane and divertor plate significantly increases; (3) Magnetic shear just inside the separatrix becomes much larger; and (4) In the open-field-line region, the squeezing of the flux-tubes near the null-point increases, thereby causing stronger decoupling of the plasma turbulence in the divertor legs and in the main SOL. These effects can be used to reduce the power load on the divertor plates and/or to suppress the 'bursty' component of the heat flux. It is emphasized that the snowflake divertor can be created by a relatively simple set of poloidal field coils situated beyond the toroidal field coils. Analysis of the robustness of the proposed divertor configuration with respect to changes of the plasma currentmore »
- Authors:
- Publication Date:
- Research Org.:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Org.:
- USDOE
- OSTI Identifier:
- 945775
- Report Number(s):
- LLNL-JRNL-404468
Journal ID: ISSN 1070-664X; PHPAEN; TRN: US0901093
- DOE Contract Number:
- W-7405-ENG-48
- Resource Type:
- Journal Article
- Journal Name:
- Physics of Plasmas
- Additional Journal Information:
- Journal Volume: 15; Journal Issue: 9; Journal ID: ISSN 1070-664X
- Country of Publication:
- United States
- Language:
- English
- Subject:
- 70 PLASMA PHYSICS AND FUSION; CONFIGURATION; DECOUPLING; DISTRIBUTION; DIVERTORS; ELECTRIC CURRENTS; GEOMETRY; HEAT FLUX; MAGNETIC FIELDS; MAGNETIC PROPERTIES; MODIFICATIONS; PLASMA; SHAPE; SHEAR; TURBULENCE
Citation Formats
Ryutov, D D, Cohen, R H, Rognlien, T D, and Umansky, M V. The Magnetic Field Structure of a Snowflake Divertor. United States: N. p., 2008.
Web. doi:10.1063/1.2967900.
Ryutov, D D, Cohen, R H, Rognlien, T D, & Umansky, M V. The Magnetic Field Structure of a Snowflake Divertor. United States. https://doi.org/10.1063/1.2967900
Ryutov, D D, Cohen, R H, Rognlien, T D, and Umansky, M V. 2008.
"The Magnetic Field Structure of a Snowflake Divertor". United States. https://doi.org/10.1063/1.2967900. https://www.osti.gov/servlets/purl/945775.
@article{osti_945775,
title = {The Magnetic Field Structure of a Snowflake Divertor},
author = {Ryutov, D D and Cohen, R H and Rognlien, T D and Umansky, M V},
abstractNote = {The snowflake divertor exploits a tokamak geometry in which the poloidal magnetic field null approaches second order; the name stems from the characteristic hexagonal, snowflake-like, shape of the separatrix for an exact second-order null. The proximity of the poloidal field structure to that of a second-order null substantially modifies edge magnetic properties compared to the standard X-point geometry; this, in turn, affects the edge plasma behavior. Modifications include: (1) The flux expansion near the null-point becomes 2-3 times larger; (2) The connection length between the equatorial plane and divertor plate significantly increases; (3) Magnetic shear just inside the separatrix becomes much larger; and (4) In the open-field-line region, the squeezing of the flux-tubes near the null-point increases, thereby causing stronger decoupling of the plasma turbulence in the divertor legs and in the main SOL. These effects can be used to reduce the power load on the divertor plates and/or to suppress the 'bursty' component of the heat flux. It is emphasized that the snowflake divertor can be created by a relatively simple set of poloidal field coils situated beyond the toroidal field coils. Analysis of the robustness of the proposed divertor configuration with respect to changes of the plasma current distribution is presented and it is concluded that, even if the null is close to the second order, the configuration is quite robust.},
doi = {10.1063/1.2967900},
url = {https://www.osti.gov/biblio/945775},
journal = {Physics of Plasmas},
issn = {1070-664X},
number = 9,
volume = 15,
place = {United States},
year = {Fri May 30 00:00:00 EDT 2008},
month = {Fri May 30 00:00:00 EDT 2008}
}
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