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Analysing divertor magnetic fields with multiple nulls

Author: Dmitri D Ryutov
Requested Type: Consider for Invited
Submitted: 2015-01-14 18:33:54

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Lawrence Livermore National Laboratory
L-637, 7000 East Avenue
Livermore, California   94550
USA

Abstract Text:
A general analysis of divertor magnetic configurations created by remote coils is presented, with the interplay of two (snowflake-like) or three (cloverleaf-like) closely-spaced nulls assessed in a systematic manner. A set of “proximity conditions” that characterizes the influence of the cross-talk between the nulls on various divertor effects is presented. Among these effects are: the field “flattening” and related flux expansion; position of the secondary separatrices with respect to the primary one; sensitivity to toroidal currents in the divertor region; prompt ion loss, neoclassical particle orbits; the onset of the “churning mode” [1]. Interplay between the divertor field structure and pedestal width is described. Configurations most suitable for reaching regimes of the plasma detachment are identified. Application of these results to recently described snowflake-like configurations on new tokamaks [2, 3] is described. Most promising configurations for future facilities are discussed.
This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Fusion Energy Sciences.
1.D.D. Ryutov, R.H. Cohen, W.A. Farmer, et al. The “Churning Mode” of plasma convection in the tokamak divertor region.” “Physica Scripta,” 89, 088002, 2014
2.G.Y. Zheng, et al. “Magnetic configuration flexibility of snowflake divertor for HL-2M.“ Fusion Engineering and Design, 89, 2621, 2014.
3.G. Calabrò, et al “EAST Snowflake Experiment: Scenario Development and Edge Simulations.” Paper EX/P3-4, IAEA FEC, St Petersburg, October 2014

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