Sherwood 2015

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approvedsherwood_plenary_ryutov.pdf2015-04-12 22:08:37Dmitri Ryutov

Divertor theory: plasma transport in complex geometries

Author: Dmitri D Ryutov
Requested Type: Consider for Invited
Submitted: 2015-02-05 18:02:27


Contact Info:
Lawrence Livermore National Laboratory
L-637, 7000 East Avenue
Livermore, California   94550

Abstract Text:
During the last decade, several suggestions have been made on improving divertor performance by modifying the geometry of the poloidal magnetic field (PF) from a canonical single-null X-point geometry to more complex geometries involving multiple PF nulls [1-5]. The speaker will briefly summarise favourable effects that these new geometries may have on the divertor power handling capability. It will be emphasized that the divertor operation is intimately related to the plasma behaviour inside the separatrix (in the pedestal region), especially in the cases where two or three PF nulls are closely spaced. There is a lot of exciting new physics arising from the cross-talk between these closely-spaced nulls. Effects involved include: the field “flattening” and related high magnetic flux expansion; change of the connection length and magnetic shear in the pedestal area; field line stochastization; interlinked primary and secondary separatrices; prompt ion losses; modified neoclassical particle orbits; sensitivity to toroidal currents in the divertor region; the onset of the plasma convection and splitting of the plasma exhaust between multiple strike-points. Configurations suitable for reaching the plasma detachment are identified. Relation of these results to recently described snowflake-like divertors on large new facilities [6, 7] is mentioned. Possible divertor configurations for future fusion reactors are discussed. Work performed for the U.S.DOE by LLNL under Contract DE-AC52-07NA27344; supported by the U.S. DOE Office of Science, OFES.

1) H. Takase. J. Phys.Soc. Japan, 70, 609, 2001. 2) M. Kotschenreuther et al., 2004 IAEA FEC, paper IC/P6-43. 3) D.D. Ryutov. Phys. Plasmas, 14, 064502, 2007. 4) M. Kotschenreuther et al., 2008 IAEA FEC, paper IC/P4-5. 5) D.D. Ryutov, M.V. Umansky. Phys. Plasmas, 20, 092509, 2013. 6) G.Y. Zheng, et al. Fus. Eng. Des., 89, 2621, 2014. 7) G. Calabrò, et al. 2014 IAEA FEC, Paper EX/P3-4.

This is an abstract for the plenary talk

March 16-18, 2015
The Courant Institute, New York University