Effects of ICRF conditioning on the first wall in LHD

N. Ashikawa, K. Saito, T. Seki, M. Tokitani, Y. Ohtawa1), M. Nishiura, S. Masuzaki

K. Nishimura and A.Sagara

9th ITPA meeting on SOL/divertor physics, May 8, 2007IPP Garching, Germany

National Institute for Fusion Science, Japan

Kyushu University, Japan 1)

Introduction

Resonance layer with Bt=2.75T, Rax=3.6m, f=38.47MHz (LHD)

1.1. Investigation of effective area using material probesInvestigation of effective area using material probes

2.2. Mode Conversion experiment with different frequencyMode Conversion experiment with different frequency

ICRF conditioning (ICC) for recycling control / deducing impurities and T removal using He, D,O2 gasses

For Investigation of high energy tails, mode conversion experiment was done in 2006.

As Heating efficiency of ICRF system, it was done in JET, C-mod and LHD.

– M.-L. Mayoral et al., NF 46 (2006) S550.– Y. Lin, et al., POP 11 (2004) 2466.– K. Saito, et al., NF 41 (2001) 1021.

It is important for antenna design in ITER.

•In Helical device such as LHD, a confinement magnetic field during ICC is different in tokamaks. But a comparison between different operation scenarios using relative ratio can be possible.

Experimental setup in LHD

Hydrogen removal rate with He gasses by GDC is 10 times larger than ICC in LHD.

• Bt=2.75T, Rax=3.6m

• ICRF heating antennas at 3.5 and 7.5 port

• Working gas was He (10-3-10-1Pa)

• f=38.47MHz ， 85MHz

• Duration time is 3 second (on), and interval time is 2 second (off).

• Picrf=8-149kW (2004FY ）

-287 kW(2006FY)

Material probes setupMaterial probes setup

•From experiences (LHD, AUG, others), effective cleaning area by ICRF conditioning is considered smaller than by glow discharge

•From damages area of material probes, effective cleaning area by ICRF conditioning was estimated.

•Material holder was installed at the first wall level.

•It have three kinds of facing.

Vacuum Vessel

4.5L-Port

Probe Head

Helical Coil

Helical Coil

MaterialProbeSystem

Vacuum Vessel

4.5L-Port

Probe Head

Helical Coil

Helical Coil

MaterialProbeSystem

Plasma

１． Plasma Facing Area

３． Gap

（ slit 1.5mm)

Demonstration between divertor tiles

２．

Ver

tica

l d

irec

tio

n

Plasma facing Vertical 　 Gap×2

BBright field images,SS316LIC

RF

co

nd

itio

nin

g

(ab

ou

t 40

00s)

Transmission Electron Microscopy Transmission Electron Microscopy （（ TEMTEM ） ） AnalysisAnalysis

Damages with He bubbles are observed only plasma facing areaDamages with He bubbles are observed only plasma facing area - Vertical : small - Gap : non

Number of damages is depend on directionNumber of damages is depend on direction－－ it is suggested effective particles come to the wall straight 　 －ICC is difficult for shadow area.

200nm200nm

10-7

10-5

0.001

0.1

10

1000

105

40 60 80 100 120 140 160 180 200

SiFNA

#70819 34kW, 85MHz#70825 287kW, 38MHz#70842 257kW, 38+85MHz

Energy [keV]

Co

unts

Mode Conversion Exp.(1) Mode Conversion Exp.(1)

High energy distributions were measured by Si fast neutron High energy distributions were measured by Si fast neutron analyzer (FNA).analyzer (FNA).

•38MHz,1.5T38MHz,1.5T

•38MHz, 2.75T : He 238MHz, 2.75T : He 2ndnd harmonics harmonics

•85MHz, 2.75T : electron 85MHz, 2.75T : electron accelerated modeaccelerated mode

•85MHz(30%)+38MHz(70%) : mix85MHz(30%)+38MHz(70%) : mix

High energy tails are observed on He 2High energy tails are observed on He 2ndnd harmonics mode (38MHz, 2.75T)harmonics mode (38MHz, 2.75T)

0.1

1

10

100

1000

104

40 60 80 100 120 140 160 180 200

#70842 257kW

#70840 116kW

Energy [keV]

Co

un

ts

•High energy ion particles were High energy ion particles were not not observed at observed at electron accelerated modeelectron accelerated mode..

•Tail distribution does not depend on an Tail distribution does not depend on an input power.input power.

•Natural Diamond DetectorNatural Diamond Detector measured particle flux by measured particle flux by ICC.ICC.

1.6 – 3.2 x 101.6 – 3.2 x 1055 at #70825 (38MHz, 2.85T, 287kW). at #70825 (38MHz, 2.85T, 287kW).

Mode Conversion Exp. (2) Mode Conversion Exp. (2)

0

50

100

150

200

250

300

0

1

2

3

4

5

6

70793 70817 70840

PowerH2

Ne

t in

pu

t p

ow

er

(kW

)

H2 R

em

ova

l rate

(Pa

m3/h

)

shot number

•38MHz,1.5T : Low removal rate38MHz,1.5T : Low removal rate

•Comparison of 38MHz and 85MHz Comparison of 38MHz and 85MHz with 2.75T : ?? (difficult) with 2.75T : ?? (difficult)

0

50

100

150

200

250

300

0

1

2

3

4

5

6

70815 70820 70825 70830

Power H2

Ne

t in

pu

t p

ow

er

(kW

)

H2 R

em

ova

l rate

(Pa

m3/h

)

shot number

85MHz85MHz

38MHz38MHz

38MHz, 1.5T38MHz, 1.5T

•From comparison of modes with 1.5T, 38MHz w/o tails and 2.75T, 38MHz with tails, with high energy distribution mode have higher hydrogen removal rate.

1

10

100

1000

104

105

1 10 100 1000

Pic

rf(k

W)/

P(P

a)

V(m

3 )

Volume (m3)

ITER

LHD

TEXTOR

Tore SupraHT-7

W7-AS

ASDEX

Function of power density, PFunction of power density, Pinin/(/(ppV)V)1)1)

V; Volume of vacuum camber

Pin; Input power of ICRF antenna.

p; He partial pressure

Powers: -800kW(TEXTOR)

He Pressures: 0.55 Pa( HT-7)

•Minimum estimation for ITER, about 100 kW/Pa m3 is shown using 0.01 Pa and 3MW (using pulse mode).

Function of power density is used as a function of accelerating power to particles

0

500

1000

1500

2000

0

1

2

3

4

5

6

70793 70817 70840

Power density H2

Pic

rf(k

W)/

P(P

a) V

(m3 )

H2 R

em

ova

l rate

(Pa

m3/h

)

shot number

Power density related to hydrogen removal ratePower density related to hydrogen removal rate

1)E. de la Cal PPCF(2005)

0

500

1000

1500

2000

0

1

2

3

4

5

6

70820 70830 70840

Power density

H2

Pic

rf(k

W)/

P(P

a) V

(m3 )

H2 R

em

ova

l rate

(Pa

m3/h

)

shot number

SummarySummary

•Using material probes, damaged area is observed in LHD. On the first wall level, only plasma facing area have damages with helium bubbles. A shadowed area have no damage. In future, we have a planning the same experiment in EAST.

•From mode conversion experiment, different high energy distributions were measured during ICC. From comparison of modes with 1.5T, 38MHz w/o tails and 2.75T, 38MHz with tails, with high energy distribution mode have higher hydrogen removal rate.

•Particle flux measured by NDD is 1.6 – 3.2 x 105.

•Comparison of hydrogen removal rate and power density of ICC shows a good relation.

•Using new design parameters of -3 MW with 0.01 Pa for ICRF antenna, a power density of ICC in ITER is same level in current devices.