Role of radial electric field shear at themagnetic island in the transport of plasmas
K.Ida, N.Ohyabu, T.Morisaki, S.Inagaki, K.Watanabe,M.Yokoyama, T.Shimozuma, Y.Takeiri, K.Itoh, Y.Liang,
K.Narihawa, K.Tanaka, Y.Nagayama, T.Tokuzawa,
K.Kawahata, H.Suzuki, A.Komori, LHD experimental group
National Institute for Fusion ScienceToki, 509-5292 Japan
１ Introduction (The effect of magnetic island on transport)
2 Er shear at the boundary of m=1 island
3 Reduction of local χe at the boundary of m=1 island
4 ITB formation inside rational surface5 Summary
Acknowledgement to Dr.C.Hidalogo (CIMAT)

Role of Er shear at the magnetic island
Magnetic island at rational surface
magnetic island might
trigger ITB formation

local heating inside
the rational surface

Reduction ofNC transport
Transition toelectron root

Er shear at the baundaryof magnetic island

Fluctuation
suppression

Increase of temperature gradientPhys. Rev. Lett.
86 (2001) 5297

Increase Er

Increase Er shear

ITBformation

Er shear and Transport at Magnetic island
When the magnetic island
is slipping

ExB

1 Narrow Transport Barrier atthe boundary magnetic island
χHeat flux

2 Internal Transport Barrier
triggered by magnetic island
Heat flux

ExB shear is expected at theboundary of magnetic island.
There are two possible effectof Er shear on transportITBχPlasma potential inside the island
0.0

Φ (V)

Flattening of space potential is observed 1/1
8cm
cm
81/1
at the rational surfaces in the wideisland-100
range of rotational transform ιι=0.25 (n/m=1/4: W <1cm) in JET -200
ι =1.0 (n/m=1/1: W<10cm) in LHD
ι =1.6 (n/m=8/5: W<few cm) in TJ-II -300

LHDLHD
1 cm ι = 1-15-10-50

R-RLCFS(cm)8/5

2.4 cm

1/4TJ-IIι =1.6
By courtesy of Dr.C.Hidalgo

JET0.7 cm ι = 0.255n/m=1/1 magnetic island in LHD
Magnetic
flux surface
1.0

Electron temperature
3LCS

2.0
(b)

0.5

without island
1.5

island2-0.5n/m=1/1 island

Ti(keV)

1.0

with island
1

0.5

-1.0
3.0

3.5

4.0
R(m)

4.5

5.0

3n0
3.8

3.9

4.0
4.1
R(m)

4.2

4.3

with island

0.0
3.85 3.90 3.95 4.00 4.05 4.10 4.15
R(m)islandwithout island2When the m/n=1/1 perturbation field isapplied to the plasma, the size ofmagnetic island can be increased and theflattening of electron/ion temperatureand density are observed

TeeT (keV), n (1019 m-3 )ewithout islandisland0.0
ECEz(m)Ion temperaturee1with island
0-1.0

-0.5

0.0
ρ

0.5

1.0

Ion temperature and radial electric fieldnear the magnetic island
Poloidal flow is zero at the magnetic island
Radial electric field
temperature
Width of Ti
flattening is smaller
than that of Er∆Ti= (2πRl χ /χ )1/2 ∆Er = (µε0ε Er/Jr)1/2µ : viscosity coefficientl|| : connection length8423290 2.5s

island width (cm)610-900A

θv (km/s)

20-2wvθ

-4

island width
8 (zero beta)

Wvθ

6WTi

4
2-6-8
3.80

3.90

4.00
R(m)

4.10

4.20

0
0.0

0.5

1.0 19 1.5-3n (10 m )
e

2.0

2.5

plasma flow spin up in the magnetic island
4

When the size of magnetic island is small,0
there are sharp flow gradient at the boundary-4of magnetic island.
1.0

no flow in island flow inisland

00.8vθ

W5T0.6Ti

i

0.4001cm
690A

4cm-4900A
00.2

Tivθ,

W500A

θi

W

no island-4v (km/s)

10i

Ti

3no island

T (ρ=0.75) (keV)

W (cm), <vθ(R-R >W (m /s)

15260A9cm-4<v (R-R )>W-50θ

i

Ti

2
46810vacuum island width (cm)120.00-41200A

However, the plasma flow along the-8
magnetic flux surface inside the island
3.8
3.9
4.0
4.1
suddenly appears (flow sin up) when theR(m)size of island exceed the critical value.
To be published in Phys Rev Lett in Jan 2002

Potential structure at O-point
Er <0 : Er’<01.00.3

Er >0 : Er’>0

E >0r

1.02dΦ/d r < 00.0z(m)

0.0

0.5

dΦ/dr = 0

Φ (kV)z(m)0.5dΦ/dr = 0

0.0

-0.3
E <0-0.5

r

-0.5

2-1.0
3.2 3.4 3.6 3.8 4.0 4.2
R(m)Ion root
Electron root

-0.6
3.90

Edge
Er < 0Er > 0dΦ/d r > 0
3.95

4.00 4.05
R(m)

4.10

X-point
Er’ < 0Er’ > 04.15-1.0
3.2 3.4 3.6 3.8 4.0 4.2R(m)O-pointdΦ/d2r > 0dΦ/d2r < 0Potential structure at O-point is determined by theEr shear at X-point.

O/X-point cold pulse propagation
X-points injection

0.0-0.5TESPEL

φ = -50.11 deg

0.5

φ = -50.11 deg

0.0TESPEL-0.5Rax = 3.5 m, γ = 1.259, LID = +800 A

3.0ECE

4.0LHDφ = 18 deg

0.5

Z (m)

Z (m)

0.0ECE RadiometerLHD

φ = 18 deg

0.5

3.5R (m)O-points transportX-points transport

ECE Radiometer

LHD

TESPELZ (m)TESPELplasma pellet

Z (m)Presented at P-I-71 O-points injection
0.5by N.Tamura

ECE
0.0ECE-0.5

Rax = 3.5 m, γ = 1.259, LID = -1200 A-0.5

Rax = 3.5 m, γ = 1.259, LID = +800 A

3.0
3.5
4.0
3.0
3.5
4.0LHDR (m)R (m)The electron thermal diffusivity is evaluated from the cold pulse
propagation produced by small hydro-carbon pellet (TESPEL).

Heat transport near the magnetic island
2.0X-points
0O-point(0.5 m /s)
20.2 m /s
0.0
2.8
2.9
3.0
3.1
R (m)

-0.1
0

Presented at P-II-02 by S.Inagakiχe = 0.2 m2/s @ O-pointχe = 2.0 m2/s @ X-point∆T (keV)2.2

χ = 2.0 m 2/s
2.22
2.24
2.26-0.1
0
R
=
2.966
m
Time (s)2.2

χ = 2.0 m 2/s
-0.1
2.22
2.24
2.26 0R = 2.984m
Time (s)3.2-0.1
02.2∆T (keV)

2.26-0.10∆T (keV)

22.22
2.24
R =Time2.948(s)
m2.2

2.2

2.22
2.24
Time (s)-0.12.26

2.22 R =2.24
2.26
2.911 mTime (s)χ = 0.2 m 2/s
2.2

2.22R = 2.901
2.24 m 2.26
Time (s)χ = 0.2 m 2/s

χ = 2.0 m 2/s
-0.1

2.22
2.24 m 2.26
R = 2.929
Time (s)χ = 0.2 m 2/s∆T (keV)

0.5

LHD #029555

R = 2.948 m∆T (keV)2

2.2∆T (keV)-0.1
00.5 m /s0

R = 2.929 m∆T (keV)1.0

O-points∆T (keV)22.0 m /seT (keV)

O-point
X-point 2(0.5 m /s)
1.5 magnetic island

2.2

2.22
2.24
Time (s)Significant reduction of thermal diffusivity is observed near orinside the magnetic island

2.26

Particle transport near the magnetic island

Magneticisland

TJ-II

The ExB fluctuation particle flux isinwards at ι = 2 resonant surface
Transport near the rational surface
Particle transport à Inward flux
Heat transport à Reduction of χ
These improvement of transport near themagnetic island is localized to compensate theloss of confinement due to the flattening ofpressure inside the island

TJ-II
By courtesy of Dr.C.Hidalgomagnetic island at therational surface might
trigger the ITB formation

ITB near the ι=1/2 surface in LHD
transition
with ITB
no ITB

61922n =0.3x10 m-3ePECH∆Te0-10.5

0.6
decay time (s)0.20.4PECH (MW)PNBI = 4 MWTe(0)

ι = 0.54e400with ITB(358kW)
no ITB(253kW)ι = 0.56e

T (0) [keV]

88

T [keV]

10-0.50ρ

0.50.4

no ITB

0.3[d(ln∆T )/dt]

1with ITB-1e0.2
0.10
2.0

2.5

3.0
3.5
Te (keV)

4.0

Internal transport barrier (ITB) is observed near the rationalsurface of ι = 1/2 (q=2).

Er profiles of the plasma with ITB
Er shear at the magnetic island
might trigger the ITB formation.
Er shear nearmagnetic island

Reduction ANtransport
Transition to large
Er and Er shear

Increase ofTe gradienttrigger

Reduction NC
transport
10580

1/5

10
3.060
4020

e

2

1/2

3.5R(m)4.0

4.5

NBI+ECH
NBI

Er(kV/m)

31.5s
2.1s

χ (m2/s)Te(keV)

4100

1-51/51/2

4.0R(m)4.1005 10E (kV/m)
r15-203.8

3.9

4.2

SummaryObservations
1

The localized radial electric field shear (Er shear) is observedat the boundary the magnetic island at the O-points. (Theflow spin up start inside the magnetic island, when the island
size is too large).

2

The electron thermal diffusivity near or inside the magnetic
island at the O-point is much smaller than that at the X-point.

3

The internal transport barrier (ITB) appears near therational surface.
Speculation
These observations support the hypothesis that Er shear
near the boundary of magnetic island may trigger the ITB
formation.