Transport in three-dimensional magnetic field: examples from JT-60U and LHDKatsumi Ida and LHD experiment group and JT-60 group14thIEA-RFP Workshop

April 26-28, 2010Padova Italy

OUTLINE 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

Magnetic structure near the rational surfacestochastizationNesting magnetic island(confinement?)Healing of magnetic island transitionFlattening of TetransitiontransitionNo Te flatteningFlattening 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.Flattening of TeHeat flux perpendicular to magnetic fieldHeat flux parallel to magnetic field

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

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

Normalized ce profilesThermal 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)No ITB

Er structure near the rational surfaceRadial electric field , Er, shear are observed at the boundary of magnetic island as well as the ITB.Er near i =1 surfaceEr near the i = 1/3 surfaceThis Er shear may contribute the reduction of thermal diffusivity at the boundary of magnetic islandNo IslandIncrease the size of magnetic islandi=1K.Ida et al., Phys Rev Lett 88 (2002) 015002K.Ida et. al., Phys Rev Lett 91 (2003) 085003

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

ITB formation with/without magnetic islandThe magnetic island contribute rather than suppress the formation of ITB with 2/1 magnetic island Clear ITB formationCancel 2/1 magnetic island no ITB formationElectron temperature profile with and without 2/1 magnetic islandno 2/1 islandwith 2/1 island2/1 ialsndK.Ida et. al., Phys Plasmas 11 (2004) 2551

Transport in stochastic magnetic flux

Magnetic shear is controlled by NBCDCo to ctrCtr to coWeak magnetic shearstrong magnetic shearCo= increase iotaCtr=decrease iotaThe 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.

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

Bifurcation phenomena of magnetic islandno islandStochastizationNested magnetic islandwith interchange mode transitionK.Ida et al., Phys. Rev. Lett, 100 (2008) 045003

Relation of island width to magnetic shearClear hysteresis is observedIn the relation between island width and magnetic shearIsland healing island stochastization: no interchange modestochastization nesting island healing interchange mode is excitedK.Ida et al., Phys. Rev. Lett, 100 (2008) 045003

Heat pulse propagationHeat pulse propagation has been studied with modulation electron cyclotron heatingThe 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. Flattening of electron temperature and modulation amplitude is observedModulation amplitude on-axis decreasesModulation amplitude off-axis increases

Heat pulse propagates very quickly towards the plasma edge.

Nesting and stochastic magnetic flux surfaceFinite temperature gradientStandard pulse propagationZero temperature gradientVery fast pulse propagationZero temperature gradientSlow pulse propagation mountain shape Nesting magnetic flux surfaceStochastic magnetic fluxNesting magnetic island

Transport in magnetic island

Pellet injection experiment in LHDPulse propagation inside the magnetic island is much slower than that outside the magnetic islandSmall solid pellet (TESPEL) is injected near the X-point of the magnetic islandInside magnetic islandoutside magnetic island

Cold pulse propagation in magnetic islandSignificant 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

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

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

Summary1 Transport near the magnetic islandLarge 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 fluxBifurcation 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 islandCold 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.