ISHW09 October 2009 PPPL

Experimental study of effect of poloidal flow on stability of magnetic island in LHD and TJ-IIY. 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 Sciencea) Laboratorio Nacional de Fusión. CIEMAT 1

Experimental study of effect of poloidal flow on island

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

Experimental study of effect of poloidal flow on island

Introduction

Flow & island

Future works

Summary

2

ISHW09 October 2009 PPPL

Experimental study of effect of poloidal flow on island

Introduction

Exp. device

Flow & island

Future works

Summary

Experiment device

3

ISHW09 October 2009 PPPL

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 profile

LHD

-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

Experimental study of effect of poloidal flow on island

IntroductionRole of island

Flow & island

Future works

Summary

For a good confinement -> Nested flux surfaces

Study of dynamics of magnetic island is important

Island physics & effects on plasma

4

ISHW09 October 2009 PPPL

Control of magnetic islands is critical issue

Effect of magnetic island

[K. Ida et al. NF 44 (2004) 290]

MHD

Flattening of pressure profile

NTM

DestabilizedStabilized(?)

Transport

Island with low m/n mode number

Formation of transport barrier[K. Ichiguchi et al.

NF 41 (2001) 181][Many papers]

Dynamics of magnetic island

5

-Growth and healing depends on and -More sensitive to

-Transition of island at ~ 0.3[%]-Nonlinear behavior

ISHW09 October 2009 PPPL

Region of growth & healing

Structure of perturbed field b (by island)

0 0.2 0.4 0.6 0.8

0.01

0.1

1

10h*@/2=1

[%]@/2=1

Growth

Healing

Growth

Transition

Healing0

1

2

0 0.2 0.4 0.6 0.8

-1

0

1

c

bpl

n=1 /b e

xtn=

1

1.0>h*>0.1

(a)

[%]@/2=1

(b)

n=

1[ r

ad]

Experimental study of effect of poloidal flow on island

Introduction

Prev. study LHD

Flow & island

Future works

Summary

0 0.2 0.4 0.6 0.8

0.01

0.1

1

10h*@/2=1

[%]@/2=1

0

1

2

0 0.2 0.4

-1

0

1

HINT calc.

bpl

n=1 /b e

xtn=

1

[%]@/2=1

n=

1[ r

ad]

BS current(VENUS-f)

PS current(HINT)

BS & PS currents cannot explain

6

-b is one order or more smaller than experiment-Self-healing does not appear

ISHW09 October 2009 PPPL

Ctr- BS

Co- BS

-Direction of BS current is sensitive to rather than

Experimental study of effect of poloidal flow on island

Introduction

Prev. studyLHD

Flow & island

Future works

Summary

CERC

Positive Er increases after CERC formation

CERC phenomena

7

ISHW09 October 2009 PPPL

(Core Electron Root Confinement) Er > 0CERC formation by introducing resonances

n/m = 3/2

n/m = 4/3

[Estrada et al. PPCF 46 (2004) 277][F. Castejón et al. NF 44 (2004) 593]

Resonant surface and positive Er are important to trigger CERC formation

Experimental study of effect of poloidal flow on island

Introduction

Prev. studyTJ-II

Flow & island

Future works

Summary

CERC

dTe/d ~ 0

dTe/d 0

8

Increase of positive Er

--> Island stabilizing

ISHW09 October 2009 PPPL

Healing of island in CERC

[T. Estrada et al. NF 47 (2007) 305]

Island healing is produced just simultaneously to CERC onset

Experimental study of effect of poloidal flow on island

Introduction

Prev. studyTJ-II

Flow & island

Future works

Summary

Experimental study of effect of poloidal flow on island

Introduction

Prev. studyTJ-II

Flow & island

Future works

Summary

• 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:

Stabilising

A1

dw

dt ' A2cb p'q

q'Bpw

' A2cb

p' 'Bpw

t ~w2

w' 6 p Bp

9

In rough agreement with experimental data

ISHW09 October 2009 PPPL

Healing in CERC in TJ-IITime scale of healing

[F. Castejón, et al. 35th EPS 32D, P-1.025 (2008)][Q. Yu, et al. PoP 1 (2004) 140]

Experimental study of effect of poloidal flow on island

Introduction

Prev. studyTJ-II

Flow & island

Future works

Summary

10

Mode stabilization in CERC

-CERC without temperature flattening has been observed-Mode stabilization is observed, nevertheless

ISHW09 October 2009 PPPL

[T. Estrada et al. PPCF 47 (2005) L57]

Experimental study of effect of poloidal flow on island

Introduction

Flow & island

Future works

Summary

11

LHD-BS & PS currents cannot explain behavior of islandTJ-II-Island is stabilized in CERC

ISHW09 October 2009 PPPL

-We pay attention to radial electric field--->Poloidal flow and island

-15 -10 -5 0 5

-40

-20

0

20

40

Er[kV]

a pc

*pi2 [

a.u.

]

Unstable

Stable

(dpi/dr)/eni

0 5[kV/m] 10[kV/m]

Radial electric field effectTheoretical predictionIndex of ion polarization current effect apc

[K. Itoh, et al., PoP 12 (2005) 072512]

12

Er > 0 : Stabilizing

Er < 0 : |EB| > |*pi| Stabilizing|EB| < |*pi| Destabilizing

ISHW09 October 2009 PPPL

apc= (- *pi)*pi-2

= -EB = EB/(rsB2)EB drift

*pi = Bpi/(rsniqiB)Ion dia. drift

Experimental study of effect of poloidal flow on island

Introduction

Flow & island

Theory

Future works

Summary

Er > 0 : Stabilizing

Er in island healing in TJ-II

13

Positive Er corresponds to stabilization

ISHW09 October 2009 PPPL

Experimental study of effect of poloidal flow on island

Introduction

Flow & island

TJ-II

Future works

Summary

Positive Er increases Healing is produced

CERC

dTe/d ~ 0

dTe/d 0

[T. Estrada et al. NF 47 (2007) 305]

after CERC formation

-10

-5

0

0 0.2 0.4 0.6 0.8 1.00

5

10

15

#86405 t = 4.3[s]

Er[k

v/m

]p e

[kPa

]

Typical pe and Er profile

0 0.2 0.4 0.6 0.8

0.01

0.1

1

10

Healing

Growth

h*@

/2=

1

[%]@/2=1

Er < 0 : Ion root

Assumption Te = Ti

and ne = ni

Neoclassical ambipolar Er

(GSRAKE)

14

Er < 0 : Ion root=> Magnitude relation of EB & *pi

ISHW09 October 2009 PPPL

Healing plasma is in Er < 0

Calculation

Experiment

Experimental study of effect of poloidal flow on island

Introduction

Flow & island

LHD

Future works

Summary

|EB| > |*pi| is satisfied

0 0.2 0.4 0.6 0.8 1.0-10

-5

00

5

10

ExB

[kra

d/s]

#86405 t = 4.3[s] *

pi[k

rad/

s]

EB = EB/(rsB2)

Typical EB and *pi profile

15

|EB| > |*pi| corresponds to stabilization of the island

ISHW09 October 2009 PPPL

AssumptionTe = Ti and ne = ni

*pi = Bpi/(rsniqiB)

*pi <~ 5[krad/s]

EB ~ -5[krad/s]

Transition can be explained? How about dependence?

0 0.2 0.4 0.6 0.80

1

2

[%]@/2=1b

pln=

1 /b e

xtn=

1

Experimental study of effect of poloidal flow on island

Introduction

Flow & island

LHD

Future works

Summary

0 0.2 0.4 0.6 0.8

-10

-5

0

5

10 *pi ExB

[10

3 rad

/s]@

/2=

1

@/2=1[%]

16

Dependence of *pi & EB on

Transition cannot be explainedOther mechanism should exist

*pi increases with EB keeps constantIn ~ 0.2[%], EB is dominant

Healing

ISHW09 October 2009 PPPL

0 0.2 0.4 0.6 0.80

1

2

[%]@/2=1

bpl

n=1 /b e

xtn=

1

Growth

Experimental study of effect of poloidal flow on island

Introduction

Flow & island

LHD

Future works

Summary

Future joint works

17

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.

ISHW09 October 2009 PPPL

Experimental study of effect of poloidal flow on island

Introduction

Flow & island

Future works

Summary

Experimental study of effect of poloidal flow on island

Introduction

Flow & island

Future works

Summary

Summary

18

LHD-Dynamics of magnetic island depending on and show nonlinear behavior. -Poloidal flow might affect on island for stabilization in Er < 0 condition

ISHW09 October 2009 PPPL

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