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Effects of ICRF conditioning on the first wall in LHD. N. Ashikawa , K. Saito, T. Seki, M. Tokitani, Y. Ohtawa 1) , M. Nishiura, S. Masuzaki K. Nishimura and A.Sagara. National Institute for Fusion Science, Japan Kyushu University, Japan 1). Introduction. - PowerPoint PPT Presentation
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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.