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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
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}
}

Works referenced in this record:

On heat loading, novel divertors, and fusion reactors
journal, July 2007


Recent liquid lithium limiter experiments in CDX-U
journal, May 2005


On scrape off layer plasma transport
journal, May 2001


Dynamics of an Isolated Blob in the Presence of the X-Point
journal, September 2006


Theory and fluid simulations of boundary-plasma fluctuations
journal, June 2007


Exhaust, ELM, and halo physics using the MAST tokamak
journal, September 2003


The dynamics of an isolated plasma filament at the edge of a toroidal device
journal, December 2006


Effect of the magnetic field geometry on the flute-like perturbations near the divertor X point
journal, September 1993


Resistive modes in the edge and scrape-off layer of diverted tokamaks
journal, November 2000


The effect of lithium surface coatings on plasma performance in the National Spherical Torus Experiment
journal, May 2008


On description of magnetic stochasticity in poloidal divertor tokamaks
journal, January 2008


Stochastic transport modeling of resonant magnetic perturbations in DIII-D
journal, June 2007


Geometrical Effects in Plasma Stability and Dynamics of Coherent Structures in the Divertor
journal, March 2008


Overview of the ARIES-RS reversed-shear tokamak power plant study
journal, December 1997


Blob Dynamics in 3D BOUT Simulations of Tokamak Edge Turbulence
journal, December 2004


Toward deeper understanding of a plasma [????????????????????????]
journal, January 2004


Structure and motion of edge turbulence in the National Spherical Torus Experiment and Alcator C-Mod
journal, May 2006


Compatibility of the radiating divertor with high performance plasmas in DIII-D
journal, June 2007


Instability Driven by Sheath Boundary Conditions and Limited to Divertor Legs
journal, April 2004


Edge instability regimes with applications to blob transport and the quasicoherent mode
journal, September 2005


Edge localized modes and the pedestal: A model based on coupled peeling–ballooning modes
journal, May 2002