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Transport in three-dimensional magnetic field: examples from JT-60U and LHD

Transport in three-dimensional magnetic field: examples from JT-60U and LHD. Katsumi Ida and LHD experiment group and JT-60 group. 14th IEA-RFP Workshop April 26-28, 2010 Padova Italy. OUTLINE. １ Magnetic structure near the rational surface

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Transport in three-dimensional magnetic field: examples from JT-60U and LHD

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  1. Transport in three-dimensional magnetic field: examples from JT-60U and LHD Katsumi Ida and LHD experiment group and JT-60 group 14th IEA-RFP Workshop April 26-28, 2010 Padova Italy

  2. OUTLINE １ Magnetic structure near the rational surface (Nesting, stochastic magnetic flux, magnetic island) 2 Transport in nesting flux surface near magnetic island 2-1radial electric field structure at magnetic island 2-2 electron-ITB and magnetic island 3 Transport in stochastic magnetic flux surface 3-1Flattening of temperature profile with low shear 3-2 Heat pulse propagation experiment 4Transport in magnetic island 4-1 cold pulse propagation in magnetic island 4-2 peaked temperature profile in magnetic island 5 Summary

  3. Magnetic structure near the rational surface Flattening of Te Nesting magnetic island (confinement?) Heat flux parallel to magnetic field Heat flux perpendicular to magnetic field transition transition transition Healing of magnetic island stochastization No Te flattening Flattening of Te Flattening of Te stochastization but NOT Flattening of Te  stochastization Heat flux parallel to magnetic field is much larger than Heat flux perpendicular to magnetic field. The stochastization can be identified by the pulse propagation experiment. Fast pulse propagation is the evidence of stochastization of magnetic flux surface.

  4. Transport in nesting magnetic flux surface near rational surface and magnetic island

  5. Electron temperature profiles of ITB plasma in LHD ITB is characterized by the peaked Te profiles and the increase of Te(0) is larger than the increase of heating power  significant reduction of ce DTe = 2 kev @ PECH/ne =1.5 DTe = 8keV @ PECH/ne =4.4 K.Ida et al., Plasma Phys Control Fusion 46 (2004) A45

  6. Normalized ce profiles No ITB Thermal diffusivity normalized by Te3/2/B2 is reduced close to 0.1 (m2s-1keV-3/2T2) at the ITB region both in LHD and JT60U. However, the radial profiles of normalized ce are quite different (ce keeps decreasing toward the plasma center in LHD, while it has a minimum at r = 0.35 in JT60U)

  7. Er structure near the rational surface Er near i =1 surface Er near the i = 1/3 surface No Island i=1 K.Ida et. al., Phys Rev Lett 91 (2003) 085003 Increase the size of magnetic island Radial electric field , Er, shear are observed at the boundary of magnetic island as well as the ITB. This Er shear may contribute the reduction of thermal diffusivity at the boundary of magnetic island K.Ida et al., Phys Rev Lett 88 (2002) 015002

  8. Cold pulse propagation near rational surface Electron ITB plasma with the foot point locating near the rational surface K.Ida et. al., Phys Plasmas 11 (2004) 2551 Large delay time inside the ITB Jump of delay time at the boundary of ITB  suggests the more reduction of transport at the boundary (near rational surface)

  9. no 2/1 island with 2/1 island Electron temperature profile with and without 2/1 magnetic island ITB formation with/without magnetic island 2/1 ialsnd Cancel 2/1 magnetic island  no ITB formation with 2/1 magnetic island  Clear ITB formation K.Ida et. al., Phys Plasmas 11 (2004) 2551 The magnetic island contribute rather than suppress the formation of ITB

  10. Transport in stochastic magnetic flux

  11. Magnetic shear is controlled by NBCD Co= increase iota Ctr=decrease iota The flattening of electron temperature profile is observed in the discharge with the switch of NBI from of co- to counter, where the magnetic shear becomes weak. Ctr to co Co to ctr strong magnetic shear Weak magnetic shear

  12. Bifurcation phenomena of magnetic island no island Stochastization transition Nested magnetic island with interchange mode There is no MHD instability observed at the onset of temperature flattening. The temperature fluctuations in the frequency range of 0.8 - 1.2kH appears afterwards with a partial temperature flattening K.Ida et al., Phys. Rev. Lett, 100 (2008) 045003

  13. Relation of island width to magnetic shear Island healing island stochastization: no interchange mode stochastization nesting island  healing interchange mode is excited Clear hysteresis is observed In the relation between island width and magnetic shear K.Ida et al., Phys. Rev. Lett, 100 (2008) 045003

  14. Heat pulse propagation The direction of NBI is switched from co- to counter- during the discharge Edge iota decreases and central iota increases, which results in weaken the magnetic shear. Heat pulse propagation has been studied with modulation electron cyclotron heating Flattening of electron temperature and modulation amplitude is observed Modulation amplitude on-axis decreases Modulation amplitude off-axis increases Heat pulse propagates very quickly towards the plasma edge.

  15. Nesting and stochastic magnetic flux surface Zero temperature gradient Slow pulse propagation （ mountain shape ） Zero temperature gradient Very fast pulse propagation Finite temperature gradient Standard pulse propagation Stochastic magnetic flux Nesting magnetic flux surface Nesting magnetic island

  16. Transport in magnetic island

  17. Pellet injection experiment in LHD Small solid pellet (TESPEL) is injected near the X-point of the magnetic island Inside magnetic island outside magnetic island Pulse propagation inside the magnetic island is much slower than that outside the magnetic island

  18. Cold pulse propagation in magnetic island Significant time delay propagating from the boundary of magnetic island to the center of O-point is observed in the magnetic island where the Te profile is flat. The effective thermal diffusivity inside the magnetic island is smaller than that outside by an order of magnitude. S.Inagaki et al., Phys Rev. Lett 92 (2004) 05500

  19. Heat pulse propagation in magnetic island M.Yakovlev et. al., Phys Plasmas 12 (2005) 09250 Heat pulse due to MECH (modulation electron cyclotron heating) shows inward/outward propagation inside the magnetic island.

  20. Peaked Ti profile in magnetic island Peaked Ti profile is observed inside the magnetic island after the back-transition from H to L mode

  21. Summary 1 Transport near the magnetic island Large radial electric field shear is observed at the boundary of magnetic island. The magnetic island (not the rational surface) would contribute the formation of internal transport barrier. 2Transport in the stochastic magnetic flux Bifurcation phenomena are observed in the stochastization of magnetic flux surface (a sudden flattening of Te profile in the core region of r/a < 0.4) at the low magnetic shear of 0.15. The stochastization of magnetic flux is confirmed by the very fast heat pulse propagation in the temperature flat region. (The propagation is slow in the nesting magnetic island) 3 Transport inside the magnetic island Cold pulse propagation experiment shows good confinement insode the magnetic island Peaked temperature profile observed inside the magnetic island after the back-transition from H-mode also suggests good confinement of magnetic island.

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