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Title: 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 » distribution is presented and it is concluded that, even if the null is close to the second order, the configuration is quite robust.« less

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, vol. 15, no. 9, September 1, 2008, pp. 092501
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. doi:10.1063/1.2967900.
Ryutov, D D, Cohen, R H, Rognlien, T D, and Umansky, M V. Fri . "The Magnetic Field Structure of a Snowflake Divertor". United States. doi: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},
journal = {Physics of Plasmas, vol. 15, no. 9, September 1, 2008, pp. 092501},
issn = {1070-664X},
number = 9,
volume = 15,
place = {United States},
year = {2008},
month = {5}
}