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Experimental Study of Poloidal Flow Effect on Magnetic Island Stability in LHD and TJ-II

Explore the impact of poloidal flow on magnetic island stability in LHD and TJ-II experiments. Discuss island physics effects on plasma, previous studies, dynamics of magnetic islands, and potential for future works. Investigate MHD transport, stabilization mechanisms, and control strategies.

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Experimental Study of Poloidal Flow Effect on Magnetic Island Stability in LHD and TJ-II

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  1. Experimental study of effect of poloidal flow on island ISHW09 October 2009 PPPL Experimental study of effect of poloidal flow on stability of magnetic island in LHD and TJ-II Y. Narushima, F. Castejóna, K.Y. Watanabe, S. Sakakibara, T. Estradaa,F. Medinaa, D. Lopez-Brunaa, M. Yokoyama, K. Ida, LHD Experiment Group National Institute for Fusion Science a) Laboratorio Nacional de Fusión. CIEMAT 1

  2. Experimental study of effect of poloidal flow on island Introduction Flow & island Future works Summary ISHW09 October 2009 PPPL Outline Introduction -Experiment device -Island physics & effects on plasma -Previous study in LHD and TJ-II Poloidal flow and island --Ion polarization current effect --Application to LHD and TJ-II Future joint works Summary 2

  3. Experimental study of effect of poloidal flow on island Introduction Exp. device Flow & island Future works Summary ISHW09 October 2009 PPPL Experiment device LHD TJ-II -Major radius R0 = 1.5[m] -Minor radius a ~ 0.22[m] -Magnetic field Bt 1[T] -32 toroidal coils -Two central coils (circular and helical) -Two pairs of vertical field coils -Ohmic current can be induced, which can modify i profile -Major radius R0 = 3.5~4.1[m] -Minor radius a ~ 0.6[m] -Magnetic field Bt 3[T] -Super conductor coils A pair of helical coils L/M = 2/10 3 pairs of poloidal coils -Perturbation coil system makes static magnetic island 3

  4. Experimental study of effect of poloidal flow on island Introduction Role of island Flow & island Future works Summary ISHW09 October 2009 PPPL Island physics & effects on plasma For a good confinement -> Nested flux surfaces Effect of magnetic island MHD Transport NTM Island with low m/n mode number Flattening of pressure profile Destabilized Formation of transport barrier Stabilized(?) [K. Ichiguchi et al. NF 41 (2001) 181] [Many papers] [K. Ida et al. NF 44 (2004) 290] Control of magnetic islands is critical issue Study of dynamics of magnetic island is important 4

  5. Experimental study of effect of poloidal flow on island Introduction Prev. study LHD Flow & island Future works Summary Transition Growth Healing ISHW09 October 2009 PPPL Dynamics of magnetic island Structure of perturbed field db (by island) Region of growth & healing Growth Healing -Growth and healing depends on b and n -More sensitive to b -Transition of island at b ~ 0.3[%] -Nonlinear behavior 5

  6. Experimental study of effect of poloidal flow on island Introduction Prev. study LHD Flow & island Future works Summary ISHW09 October 2009 PPPL BS & PS currentscannot explain BS current (VENUS-df) PS current (HINT) Ctr- BS Co- BS -db is one order or more smaller than experiment -Self-healing does not appear -Direction of BS current is sensitive to n rather than b 6

  7. Experimental study of effect of poloidal flow on island Introduction Prev. study TJ-II Flow & island Future works Summary CERC n/m = 3/2 n/m = 4/3 ISHW09 October 2009 PPPL CERC phenomena (Core Electron Root Confinement) Er > 0 CERC formation by introducing resonances [F. Castejón et al. NF 44 (2004) 593] [Estrada et al. PPCF 46 (2004) 277] Positive Er increases after CERC formation Resonant surface and positive Er are important to trigger CERC formation 7

  8. Experimental study of effect of poloidal flow on island Introduction Prev. study TJ-II Flow & island Future works Summary CERC dTe/dr~ 0 dTe/dr 0 ISHW09 October 2009 PPPL Healing of island in CERC Island healing is produced just simultaneously to CERC onset [T. Estrada et al. NF 47 (2007) 305] Increase of positive Er --> Island stabilizing 8

  9. Experimental study of effect of poloidal flow on island Introduction Prev. study TJ-II Flow & island Future works Summary ISHW09 October 2009 PPPL Time scale of healing Healing in CERC in TJ-II Stabilising • A1=0.823, A2= 6.34, cb≈1, q is the safety factor (the inverse of the rotational transform). All the quantities are evaluated at the resonant radius. • Time Scale: [F. Castejón, et al. 35th EPS 32D, P-1.025 (2008)] [Q. Yu, et al. PoP 1 (2004) 140] In rough agreement with experimental data 9

  10. Experimental study of effect of poloidal flow on island Introduction Prev. study TJ-II Flow & island Future works Summary ISHW09 October 2009 PPPL Mode stabilization in CERC [T. Estrada et al. PPCF 47 (2005) L57] -CERC without temperature flattening has been observed -Mode stabilization is observed, nevertheless 10

  11. Experimental study of effect of poloidal flow on island Introduction Flow & island Future works Summary ISHW09 October 2009 PPPL LHD -BS & PS currents cannot explain behavior of island TJ-II -Island is stabilized in CERC -We pay attention to radial electric field --->Poloidal flow and island 11

  12. Experimental study of effect of poloidal flow on island Introduction Flow & island Theory Future works Summary ISHW09 October 2009 PPPL Radial electric field effect Theoretical prediction Index of ion polarization current effectapc [K. Itoh, et al., PoP 12 (2005) 072512] apc= w(w - w*pi)w*pi-2 w = -wEB = EB/(rsB2) EBdrift w*pi = Bpi/(rsniqiB) Ion dia. drift Er > 0 : Stabilizing Er < 0 : |wEB| > |w*pi|Stabilizing |wEB| < |w*pi| Destabilizing 12

  13. Experimental study of effect of poloidal flow on island Introduction Flow & island TJ-II Future works Summary CERC dTe/dr~ 0 dTe/dr 0 ISHW09 October 2009 PPPL Er in island healing in TJ-II Positive Er increases Healing is produced after CERC formation [T. Estrada et al. NF 47 (2007) 305] Er > 0 : Stabilizing Positive Er corresponds to stabilization 13

  14. Experimental study of effect of poloidal flow on island Introduction Flow & island LHD Future works Summary ISHW09 October 2009 PPPL Healing plasma is in Er < 0 Typical pe and Er profile Calculation Neoclassical ambipolar Er (GSRAKE) Er < 0 : Ion root Experiment Assumption Te = Ti and ne = ni Er < 0 : Ion root => Magnitude relation of wEB & w*pi 14

  15. Experimental study of effect of poloidal flow on island Introduction Flow & island LHD Future works Summary ISHW09 October 2009 PPPL |wEB| > |w*pi| is satisfied Typical wEB and w*pi profile |wEB| > |w*pi| corresponds to stabilization of the island Assumption Te = Tiand ne = ni w*pi = Bpi/(rsniqiB) w*pi <~ 5[krad/s] wEB ~ -5[krad/s] wEB = EB/(rsB2) Transition can be explained? How about b dependence? 15

  16. Experimental study of effect of poloidal flow on island Introduction Flow & island LHD Future works Summary ISHW09 October 2009 PPPL Dependence of w*pi & wEB on b Growth Healing w*pi increases with b wEB keeps constant In b ~ 0.2[%], wEB is dominant Transition cannot be explained Other mechanism should exist 16

  17. Experimental study of effect of poloidal flow on island Introduction Flow & island Future works Summary ISHW09 October 2009 PPPL Future joint works Study of magnetic island has been progressed LHD (Er < 0 Ion root) Detailed investigation of transition of magnetic island TJ-II (Er > 0 Electron root) Further studies on island width and time scale growing and healing dependences on collisionality etc. 17

  18. Experimental study of effect of poloidal flow on island Introduction Flow & island Future works Summary ISHW09 October 2009 PPPL Summary LHD -Dynamics of magnetic island depending on b and n show nonlinear behavior. -Poloidal flow might affect on island for stabilization in Er < 0 condition TJ-II -Magnetic island is present with ambient Er > 0 before CERC; at CERC onset Er becomes more intense, magnetic island is stabilized and associated coherent oscillation vanishes To clarify behavior of island, further joint works are required 18

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