Transport in three dimensional magnetic field examples from jt 60u and lhd
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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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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

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


Magnetic structure near the rational surface

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.


Transport in three dimensional magnetic field examples from jt 60u and lhd

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


Electron temperature profiles of itb plasma in lhd

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


Normalized c e profiles

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)


E r structure near the rational surface

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


Cold pulse propagation near rational surface

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)


Itb formation with without magnetic island

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


Transport in three dimensional magnetic field examples from jt 60u and lhd

Transport in stochastic magnetic flux


Magnetic shear is controlled by nbcd

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


Bifurcation phenomena of magnetic island

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


Relation of island width to magnetic shear

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


Heat pulse propagation

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.


Nesting and stochastic magnetic flux surface

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


Transport in three dimensional magnetic field examples from jt 60u and lhd

Transport in magnetic island


Pellet injection experiment in lhd

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


Cold pulse propagation in magnetic island

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


Heat pulse propagation in magnetic island

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.


Peaked ti profile in magnetic island

Peaked Ti profile in magnetic island

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


Summary

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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