M.Osakabe, T.Itoh1, K. Ogawa3,4, M. Isobe1,2, K. Toi1,3, T.Ido1,3, A. Shimizu1, S. Kubo1,3, K.Nagaoka1,

Y.Takeiri1,2 and LHD experiment group

5th IAEA-TM on EPSeptember 5-10, 2011Austin, Texas

1National Institute for Fusion Science2Department of Fusion Science, The Graduate

University for Advanced Studies3Dept. of Energy Science and Engineering,

Nagoya University4JSPS Research Fellow

1. Introduction ◦ Background and motivation◦ Energetic-particle induced GAMs in toroidal

devices. ◦ Energetic particle induced GAM on LHD

2. Experimental results◦ LHD & experimental apparatus◦ Energetic particle induced n=0 mode associated

with neutral flux on LHD.

3. SUMMARY

Zonal Flow(ZF) and Geodesic Acostic Mode(GAM) get much attention recently, since it could be a knob to regulate turbulence in plasmas and to reduce anomalous transport.

Energetic-particle(EP) induced GAMs are observed in several toroidal devices, such as JET, DIIID and LHD. Effect of GAMs on the energetic particle behaviors needs to be investigated.

Recently, an influence of EP induced GAM was observed on LHD.⇒ The influence of EP induced GAMs on bulk ions as

well as on energetic particles needs to be investigated.

◦ JET: Global GAM H.L.Berk, et.al., Nucl. Fusion 46, S888 C.J.Boswell, et.al., Phys. Lett. A , 358, 154◦ DIIID: Energetic-particle-induced GAM (EGAM) R.Nazikian, PRL 101, 185002 G.Y.Fu, PRL 101, 185002◦ LHD: K.Toi: 22nd IAEA-FEC, EX P8-4 T.Ido : 23rd IAEA-FEC

JET

T.Ido, et.al.,

Energetic particle induced GAM on LHD

Constant at the GAM frequency in reversed shear plasmas.

Upward-shift of the frequency in monotonic shear plasmas.

p

0.8 1.0 1.2 1.4 1.6 1.8 2.0Time (s)

Co-ECCD

Rotational transform (by MSE)

Co-ECCD

= 1/

q

HIBP

n = 1 Alfvén eigenmodes(RSAEs)

eT(In this experiment, Ti < Te.)

f n=

0

0

174

2

e

A

i

iG M

TGf

T

R M

GAM frequency

These modes(n=0, 1) are not observed in plasmas without tangential NBI.

T.Ido, et.al.

n = 0

Bp [Mirnov coil]~

ne/ne[HIBP]~

[HIBP]

Heliotron configuration of l=2/m=10 field period

All superconducting coil systemPlasma major radius 3.42-4.1 mPlasma minor radius 0.6 mPlasma volume 30 m3

Toroidal field strength 0.4~2.9 T

The confining magnetic fields are externally applied on LHD. Thus, it is free from disruptions.

Combining this feature with the high-energy N-NBI and high-power gyrotrons, LHD could be a good plat home of exploring high-energy particle physics.

Heating Facility:• N-NBI:180keV/5MW x3• P-NBI: 40keV/6MW x2• ECH: 77GHz/1MW x3

84GHz/0.3MW168GHz/

Diagnostics:◦ Tangential E//B-NPA.Measurement of high

energy ions and bulk ions.◦ Mirnov-coils: Toroidal x6ch, Helical

x13ch◦ E//B-NPA

N-NB(counter)

N-NB(counter)

N-NB(co)

Standard Bt-direction

FIR-Interferometer

Mirnov-coils

E//B-NPAH measurement

Thomson scattering

Passive measurement. Measureable energy range is 0.5 – 200

[keV] for Hydrogen. Time resolution of up to 0.25ms is

possible by counting mode, and ~5s is possible to current mode.

Installed at tangential port and its sight line locates 10cm below the mid-plane. Thus, inner most observable location is limited to r/a =0.16

Thanks to the collaboration with PPPL

0.0

0.5

1.0

1.5

0

30

60

90

120

150

180

0.0 2.0 4.0 6.0 8.0 10.0

E//B-NPA Line of sights for Raxis

=3.75m configuration

r/a

Pitch Angle [deg.]

distance from port [m]

Gas cell

ＭＣＰ x 3

Ｈ０

Magnet

E,B

• The typical initial frequencies are 50 -70kHz and their frequencies chirp-up during their mode activity activities.

• No significant increase of H-signals were observed.

• Typical estimated slowing-down time is ~8[s] at the core.

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

0.0

2.0

4.0

6.0

8.0

10.0

0.0 0.2 0.4 0.6 0.8 1.0 1.2

Te

ne

se/2

Te[keV], ne [x

1017 m-3]

se /2 [s]

r/a

ne ~8x1017 ne~7x1017 ne ~1.5x1018

Up-sweeping n=0 mode NOT observed during ECH-only phase

Up-sweeping n=0 mode disappearsquickly after ECH turn-off.

The initial frequency of the mode is much smaller than expected n=0 GAE frequencies (f>500kHz).

-360

-270

-180

-90

0

90

180

270

360

0 45 90 135 180 225 270 315 360

Toroidal/#94839@t=1.7983s

Phase [deg.]

[deg.]

n=0

-360

-270

-180

-90

0

90

180

270

360

-180-135-90 -45 0 45 90 135 180

Poloidal/#94839@t=1.7983s

Phase [deg.]

[deg.]

m=1

m=2

One has the Te 0.5-dependence of its mode frequency. This mode can be considered to be similar to the energetic particle induced GAM on LHD.

The other mode has weak dependence of its mode frequency on Te. The mode frequency is larger than the usual GAM mode and is close to the orbital frequency of the NB produced energetic particles.

Neutral flux increase was observed for both cases.

10

100

1 10

a)

Ido, et.al.#94834#94839#94839 with N-Flux increase

Freq. [kHz]

Te(0) [keV]

Te(0)1/2

0

20

40

60

80

100

0 50 100 150 200

fb0 (=vb0/2R

)[kHz]

Energy [keV]

R=3.75m, =0.35

ENB

inj.

b)

The mode grows very quickly at its initial phase (eff=~4.6x103[s-1]).

The ion temperature starts to increase when the mode amplitude reaches a certain value (~2x10-2

[a.u.]), and the effective growth rate of the mode decreases (eff=~2.3x102 [s-1]), simultaneously.

When the mode frequency reaches to a certain frequency close to the orbital frequency of the energetic particle produced by the NB, the mode amplitude starts to decrease gradually (eff=~ -69 [s-1]) .

1018

1019

1020

1021

1022

1023

0.0 2.0 4.0 6.0 8.0 10.0

a)1.79128s1.79378s1.79628s

Neutral flux [a.u.]

Energy[keV]

t=2.5ms

0

50

100

150

200

10-5

10-4

10-3

10-2

10-1

b)Frequency [kHz]

Peak Amplitude [a.u.]

1017

1018

1019

1020

1021

1022

1023

1.790 1.795 1.800 1.805 1.810

d) 1.1keV2.2keV3.9keV

5.1keV7.6keV

NeutralFlux [a.u.]

time[sec]

0.00

0.50

1.00

1.50

2.00c)

Ti-fit

Ti[keV]

At low density intensive EC heated LHD plasmas, energetic particle induced n=0/m=1 modes being associated with the flux increase of low energy neutrals are observed.

The modes can be categorized into two type. ◦ The one has Te0.5 dependence of its frequency and is considered as

energetic particle induced GAM.◦ The other has weak Te dependence of its frequency. The frequency

is almost constant at around the orbital frequency of the NB-produced fast-ions.

For both modes, the neutral flux increase was observed at the energy ranges close to the bulk ions.

The temporal behavior of the mode and the neutral flux indicates an anomalous heating or radial transport of bulk ions by the n=0 mode.