17th International Toki conference / 16th International Stellarator/Heliotron Workshop 2007

Observation of Toroidal Flow on LHD
M. Yoshinuma, K. Ida, M. Yokoyama, K. Nagaoka, M. Osakabe
and the LHD Experimental Group
National Institute for Fusion Science, Toki, Japan
Contents

1. Introduction
2. Charge Exchange Spectroscopy on LHD
3. Toroidal Flow driven by NBI
4. Toroidal Flow driven by Er
5. ECH driven Toroidal Flow driven by ECH
6. Summary
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Introduction
The stabilizing and destabilizing of the magnetic confinement plasma is
considered to be sensitive to the profile of flow velocity.
A moderate shear of poloidal flow can suppress turbulence and reduce thetransport, although a large velocity shear causes instabilities such as KelvinHelmholtz instabilities.
It has been pointed out that the toroidal flow contributes the stabilization ofresistive wall mode in tokamaks. Therefore the spontaneous troidal flow
becomes important in the next fusion device such as ITER, where the toroidal
flow velocity driven by external momentum is expected to be not enough tostabilize the MHD mode.
The mechanism of driving the spontaneous troidal flow has a great interestsin the momentum transport physics.

In this presentation, we will report observations of toroidal flow and discuss themechanisms of spontaneous flow in helical plasma.

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Spontaneous and External Driven Toroidal Flow
Radial Force Balance : Er = VtBp – VpBt + 1/(Zen) dp/dr

The radial electric field is determined by the non-ambipolar loss or pressure gradientand the coupling of ExB force and viscosity tensor drives spontaneous toroidal
rotation.
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Observation of Toroidal Flow on LHD
LHD

Er control by changing collisionality

Control of NBI injection(external momentum input)
Control of radial electric field bychanging collisionality.
Density can change edge ErLocal ECH can change center Er
Measurement of both Toroidal andPoloidal flow with charge exchange
spectroscopy

Both NBI driven toroidal flow and spontaneous toroidal flow
depended on Er have been observed in LHD.
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Line of Sights of CXS on LHD
Charge exchange spectroscopy measurement can be performed
both with poloidal and toroidal line of sights.
Poloidal system
Toloidal system

Typical scheme of discharge for CXS

40keV perpendicular injection NBI with positive ion source
To acquire the background signal, the p-NBI is modulated with 100msec ON and100msec OFF.
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Profiles in the case of Counter Injection
Bt=2.85T Rax=3.6m γ=1.254 Bq=100%

5Ion temperature

4t=1.35s3t=0.95s

iT (keV)62High Ion temperature (~4.5keV) obtained in NBI
sustained plasma with electron density
ne~1.5x1019m-3.

0.8

Intensity of CVI emission

44.2

t=0.95s

t

0.4

4.4

4.6

4.8

R (m)
t=1.35s

0-10

0.6

3.8

10V (km/s)

10
3.6lhdcxs3@74282

1.2

Intensity (a.u.)

Strong toroidal flow
is observed in thecore region of theplasma and its
direction isconsistent with thedirection of the NBI.

1t=0.95s-20-30-40

t=1.35s0.2-50Toroidal flow
03.675235

3.8

4

4.2R (m)4.4

4.6

4.8-60
3.6

3.8

4

4.2
R (m)

4.4

4.6

4.8

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Profiles in the case of Co Injection
Bt=-2.769T Rax=3.575m γ=1.254 Bq=100%

lhdcxs3@74282

6Ion temperature

5t=1.15s

3i

T (keV)

4t=0.75s
21High Ion temperature (~5keV) obtained in NBI
sustained plasma with electron density
ne~1x1019m-3.

4

Intensity of CVI emission50

t=0.75s

40V (km/s)

0.8

t

0.6

4.2

4.4

20100.20

Toroidal flowt=1.15st=0.75sCo

t=1.15s
4

4.2
R (m)

4.8

30

0.4

3.8

4.6

R (m) lhdcxs3@74282

10
3.674282

3.860

lhdcxs3@74282

1.2

Intensity (a.u.)

The CXS intensity
profile shows thatthe profile of carbon
impurity is strongly
hollowed when theTi becomes high.

03.6

Ctr
4.4

4.64.8-103.6

3.844.2R (m)

4.4

4.6

4.8

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Toroidal Flow driven with NBI
Toroidal Flow driven by Externally Injection of Momentum
Toroidal flow is observed with in the case of co-injection, counter-injection, andbalanced injection to see the NBI driven component.
The NBI dominantly drives the toroidal flownear the plasma center.

10NBI2(Co)Co-injection case (NBI2) :Toroidal flow drive inside the R of 3.9m

5Counter-injection case (NBI1) :Toroidal flow drive inside the R of 4.1m

0The NBI driven component is small at theplasma edge.
It is considered to be the result come from thestrong helical ripple and small deposition ofthe NBI power at the plasma edge.
Bt=1.5T Rax=3.6m γ=1.174 Bq=100% 75488,75489,75493-5t

V (km/s)Balanced-injection case :Spontaneous component is observed.

NBI1&2(Balance)-10-15
NBI1(Ctr)
-20
3.6

3.8

4

4.2

4.4

4.6

R (m)

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Toroidal Flow driven by Radial Electric Field
Positive and negative Er can be formed at the plasma edge by controlling thedensity and input power.

Toroidal flow at the plasma edge changed associated with the changing theradial electric field.
Vp < 0 (Ion root）
Vp > 0 (Electron root）

Drives Vt in co-direction.
Drives Vt in counter-direction.

Poloidal flow velocity

Toroidal flow velocity

155
Ion Root

Electron Root
1019-3190.55x10 m (Co with ECH)

Near Zero-3

19

1.0x10 m (Ctr)-30.45x10 m (Co)

0V (km/s)

019-5-30.45x10 m (Co)

Ion Root
19-5t

Near ZeropV (km/s)

5-10-3

1.0x10 m (Ctr)-10Electron Root
19-3

0.55x10 m (Co with ECH)

-15
4.2

4.25

4.3 4.35R(m)Bt=1.5T Rax=3.6m γ=1.174 Bq=100%

4.4

4.45 4.5-15
4.2

4.25

4.3 4.35

4.4

4.45

4.5R(m)9/13

Toroidal Flow driven by Radial Electric Field
Dependence of toroidal flow velocity on radial electric field

5R=4.4m t=1.5s
NBI 1 and 2t

V (km/s)

0-5-100

5101520E (kV/m)r

ΔEr=15kV/m => ΔVt=5km/s
Counter flow is increased associated with growing
up the positive Er (electron root)
The direction of the poloidal flow driven by Er x B ischanged to the direction of helical pitch which has
minimum gradient of magnetic field strength.

10/13Toroidal Flow driven by ECH (1)ECH is injected into the NBI sustained plasma (<ne>~0.4x1019 m-3).
The NBI is injected with balanced combination to make the NBI driven flow small.
Modulated injection of NBI4 is just used for CXS measurement.
54

ECH ON 1.3s - 1.8s
1.5s (with ECH)

1.5T (keV)ECH ON 1.3s - 1.8s
1.25s (without ECH)

2iT (keV)

e13

1

0.5

1.2s(without ECH)

1.45s
(with ECH)
0
3.60
3.84

4.2R(m)

4.4

4.6

2.8

3.2

3.64

4.4

R (m)

The CERC (Core Electron Root Confinement) profile is observed in the electrontemperature, while the ion temperature has no significant change with the ECH.

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Toroidal Flow driven by ECH (2)3010ECH ON 1.3s - 1.8s
5ECH ON 1.3s - 1.8s

E (kV/m)t-5

0-10-10-15-20
3.6-20
3.6

1.25s(without ECH)
3.84

4.2R(m)1.5s (with ECH)

10r

0V (km/s)

201.45s (with ECH)

1.2s(without ECH)
3.84

4.2

4.4

4.6R(m)4.4

4.6

Toroidal flow is driven into codirection near the plasma core
(ΔVt~10 km/s) during the ECH.

During ECH, the positive radial electric field appears associated with theformation of the CERC.
Positive Er drives the flow in the co-direction near the plasma core.
Bt=1.5T Rax=3.6m γ=1.174 Bq=100% #75493

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Summary(1) The profiles of ion temperature, toroidal flow velocity and carbon impurity aremeasured with charge exchange spectroscopy using the charge exchange line offully ionized carbon.
(2) Toroidal flow driven by external momentum
Strong toroidal flow parallel to the momentum input of NBI is observed in the coreregion of the plasma.
(3) Spontaneous flow(3-1) At the plasma edge
The relation between the spontaneous toroidal flow and radial electirc field isinvestigated and the positive radial electric field drives spontaneous rotation in thecounter direction (anti parallel to the <ExBp>) at the plasma edge.
(3-2) In the plasma core
Toroidal flow driven in the co direction is observed when the ECH is injected. Thisobservation shows the spontaneous rotation at the plasma core is opposite to that at
the plasma edge (parallel to the <ExBp>).
(3-3) The differences between core and edge can be explained by the differences in
the ratio of εt/εh.

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