The Magnetic Field Structure of a Snowflake Divertor

Ryutov, D D; Cohen, R H; Rognlien, T D; Umansky, M V

doi:10.1063/1.2967900

The Magnetic Field Structure of a Snowflake Divertor

Journal Article · Fri May 30 04:00:00 EDT 2008 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.2967900· OSTI ID:945775

Ryutov, D D; Cohen, R H; Rognlien, T D; Umansky, M V

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.

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Research Organization:: Lawrence Livermore National Laboratory (LLNL), Livermore, CA

Sponsoring Organization:: USDOE

DOE Contract Number:: W-7405-ENG-48

OSTI ID:: 945775

Report Number(s):: LLNL-JRNL-404468

Journal Information:: Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 9 Vol. 15; ISSN PHPAEN; ISSN 1070-664X

Country of Publication:: United States

Language:: English

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