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ISHW09 October 2009 PPPL

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. Castejón a , K.Y. Watanabe, S. Sakakibara, T. Estrada a , F. Medina a ,

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ISHW09 October 2009 PPPL

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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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