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MHD simulation on pellet plasmoid in LHD

MHD simulation on pellet plasmoid in LHD. R. Ishizaki and N. Nakajima. National Institute for Fusion Science. 6 th Japan-Korea Workshop on Theory and Simulation of Magnetic Fusion Plasmas NIFS, Toki, JAPAN July 28 – 29, 2011. Plasmoid. Pellet. Introduction.

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MHD simulation on pellet plasmoid in LHD

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  1. MHD simulation on pellet plasmoid in LHD R. Ishizaki and N. Nakajima National Institute for Fusion Science 6th Japan-Korea Workshop on Theory and Simulation of Magnetic Fusion Plasmas NIFS, Toki, JAPAN July 28 – 29, 2011

  2. Plasmoid Pellet Introduction. • It is observed in tokamak experiments that the ablation cloud drifts to the lower field side. • The ablation cloud dose not approach the core plasma in LHD even if the pellet is injected from the high field side. Baylor, Phys. Plasmas 7, 1878 (2000) High field Low field Sakamoto, 29th EPS conference on Plasma Phys. and Contr. 26B, P-1.074 (2002)

  3. The other works on motion of the ablation cloud. Topics : Drift motion 1. P.B.Parks and L.R.Baylor, Phys. Rev. Lett. 94, 125002 (2005). • Theory, no resistivity, constant B-field 2. R.Samtaney et al., Comput. Phys. Commun. 164, 220 (2004). • Ideal MHD simulation, pellet is point source with ablation model 3. V.Rozhansky et al., Plasma Phys. Control. Fusion 46, 575 (2004). • No resistivity, constant B-field, pellet is point source, mass and moment equations 4. H.R.Strauss and W.Park, Phys. Plasmas 7, 250 (2000). • Ideal MHD simulation, pellet is plasmoid, no heating • In order to clarify the drift motion in LHD plasmas, MHD simulation has been carried out. • The plasmoid motions are evaluated in various configurations (LHD, tokamak, RFP and vacuum field) in order to obtain the universal understanding.

  4. OUTLINE. • Code, geometry and basic equations. • Simulation results on drift motions of plasmoids • Tokamak • LHD • RFP • Vacuum field • Consideration about simulation results.

  5. CAP code and numerical scheme. • We are developing the CAP code in order to investigate the dynamics of the pellet ablation. (Multi-phase code) R. Ishizaki et al, Phys. Plasmas, 11 4064 (2004). • MHD version of the code has been developed in order to investigate the plasmoid motion in torus plasmas. R. Ishizaki and N. Nakajima, J. Plasma and Fusion Res. SERIES 8, 995 (2009). • A plasmoid induced by pellet ablation has locally and extremely large perturbation, namely nonlinear one, in which the plasma beta is > 1. Therefore, Cubic-interpolated pseudoparticle (CIP) method is used in the code in order to solve such a large perturbation stably. T. Yabe and P.Y. Wang, J. Phys. Soc. Jpn 60, 2105 (1991).

  6. Z f R Geometry and basic equations.

  7. Lowest field Highest field Poloidal cross sections in LHD. Direction of lower field side Saddle point Coil Saddle point R Horizontally elongated cross section Vertically elongated cross section

  8. OUTLINE. • Code, geometry and basic equations. • Simulation results on drift motions of plasmoids • Tokamak • LHD • RFP • Vacuum field • Consideration about simulation results.

  9. Lowest field Highest field Configurations and plasmoid locations. LH-i : LHD LH-o : LHD LV-i : LHD Direction of lower field side T-i : Tokamak R-i : RFP V : Vacuum field

  10. A plasmoid is located inside in the horizontal cross section. LH-i : LHD

  11. A plasmoid is located outside in the horizontal cross section. LH-o : LHD

  12. A plasmoid is located inside in the vertical cross section. LV-i : LHD

  13. A plasmoid is located inside in the tokamak. T-i : Tokamak

  14. A plasmoid is located inside in a RFP-like plasma. R-i : RFP e ~ 0.15 q ~ 0.1 b ~ 1 Bp/BT ~ 1

  15. A plasmoid is located in a 1/R vacuum field. V : Vacuum field

  16. Back and forth Outward Hardly drift Inward Outward Outward Simulation results. LV-i LH-i LH-o Outward/inward : positive/negative direction of major radius Direction of lower field side T-i R-i V

  17. OUTLINE. • Code, geometry and basic equations. • Simulation results on drift motions of plasmoids • Tokamak • LHD • RFP • Vacuum field • Consideration about simulation results.

  18. is dominant among forces in all cases. 0 : equilibrium 1 : perturbation LH-i : LHD LH-o : LHD LV-i : LHD T-i : Tokamak R-I : RFP V : Vacuum field

  19. LH-i : LHD LH-o : LHD LV-i : LHD First term First term T-i : Tokamak R-I : RFP V : Vacuum field Second term Second term First term FR consists of two forces.

  20. Plasmoid The first term in FR depends on the connection length. T-i : Tokamak LH-i : LHD

  21. A leading term in FR is determined by the connection length. T-i Tokamak 1/R force Freidberg, Ideal MHD LHD LH-i LV-i Vacuum field RFP-like LH-o

  22. B1 B1 FR B1 dense sparse B1 Perturbed magnetic field becomes Dipole field. The dipole field is created around the plasmoid. What is the first term? LH-i : LHD

  23. B1 dense sparse B1 Dipole field A plasmoid is located inside in the horizontal cross section. LH-i : LHD

  24. Summary. ◯ For systematic understanding of the drift of pellet plasmoid,   • An MHD version of CAP code has been developed with CIP scheme.    • Various configurations; LHD, Tokamak, RFP-like and vacuum field, are investigated for the first time. ◯ The drifts of the pellet plasmoid are summarized as follows: • It is found that the pellet plasmoid motions in various configurations can be explained by using the connection length. • Especially, the motions in LHD are different from one in tokamak. This fact qualitatively explains the difference on the experimental results between tokamak and LHD. ◯ Future work: • We will obtain the results about drift motion of a plasmoid induced by ablation from a moving pellet.

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