Quantification of Tungsten Sputtering at W/C Twin Limiters in
TEXTOR
with the Aid of Local WF Injection 6S. Brezinsek, J.W. Coenen,
M. Laengner, A. Pospieszczyk, D. Borodin, D. Kondratjew, O.
Schmitz, U. Samm, and the TEXTOR team
Institute of Energy and Climate Research - Plasma Physics,
Forschungszentrum Jülich, Association EURATOM -FZJ, Trilateral
Euregio Cluster, Germany
Introduction
Tungsten is the most promising material candidate for the
divertor plasma-facing components in the activated operation phase
of ITER. An important issue for the qualification of W as
plasma-facing material is the quantification of the W source
strength, which is connected to the components lifetime and,
finally, to the W core accumulation. W sputtering is dominated by
impinging intrinsic impurities such as O or C or seeding species
like N.
A dedicated experiment to study the W and C sputtering under
plasma impact was carried out in TEXTOR with the aid of a spherical
limiter in twin limiter design: one half made of W and the other of
C. The limiter, installed in the PWI-facilty and positioned in the
near scrape-off layer, was exposed to a set of plasma discharges
with variations of edge plasma parameters with T from 30 to 85 eV
owing to strong gas fuelling. Neutral W light was recorded and
etransferred to W sputtering fluxes and erosion yields by means of
measured effective photon efficiencies. The later have been
determined experimentally by local WF injection and observation of
WI emission in TEXTOR under 6comparable experimental conditions.
Experimental and modelled photon efficiencies (GKU code) are
compared.
Experiment
W/C twin limiter
WC
toroidalpoloidal
radial
80 120
r=60
37
r=7050
in mm
r=70
vacuumlock system
bumperlimiter
vacuumvessel
liner
limiter
toroidalfield coil
horizontalobservation
verticalobservation
toru
s a
xis
ALT-II
FMV
FMH
L 1H
equatorialplane
L 2H
M 1H
SOL
LCFS
spectroscopyal
observationsystems
IF
1.75 m
0.46 m
ICRHantenna
horizont
Compact spectrometers: temporal flux evolution
Overview spectrometer: photon flux distribution
1D radially resolved spectrometer at injection
2D ICCD camera with interference filters
TEXTOR - poloidal cut and lock system Global parameter - twin
limiter experiment
0 1 2 3 4 5 6 7
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
t [s]
Da
flu
x [
arb
. u
nit
s]
0.0
0.5
1.0
1.5
imp
uri
ty f
lux [
arb
. u
nit
s]
0
1
2
3
4
5
19
-3n
[10
m]
e,0
0
0.5
1.0
1.5
2.0
T [
keV
] e
,0
0
0.5
1.0
1.5
2.0
P [
MW
] ra
d
0
0.5
1.0
1.5
2.0
P [
MW
] to
t
0
0.5
1.0
1.5
2.0
2.5
OI
CI
Da
n e,0T e,0
P radPtot
B tI p
B [
T]
t
0
100
200
300
400
I [
kA
] p
Experimental settings
§ Deuterium fuelling
§ L-mode plasmas with 1.5 MW NBI (H beams)
§ B =2.25 T, I =0.35 MAt p
§ Limiter installed in the vacuum lock system
§ Limiter positioned close to the LCFS in the near SOL
Edge plasma conditionsEdge plasma conditions
§ Edge plasma parameters determined by He-beam diagnostic at
outer midplane
This work was done in the frame of the IEA-TEXTOR Agreement on
Plasma-Wall Interaction and the EU Task Force on Plasma-Wall
Interaction
Forschungszentrum Jülich Institute of Energy and Climate
Research - Plasma Physics Association EURATOM - FZJ
SummaryW/C twin limiter exposed in the PWI facility to TEXTOR
edge plasma with four T steps between 30eV and 85eVe Impurity
fluxes and erosion yields deduced in-situ by spectroscopy:
- Reduction of the W sputtering yield from ~5.0% to ~0.6% with
decrease in Te - Increase of C and O fluxes in the four steps. Flux
ratio of C/D and O/D remains almost constant - W sputtering mainly
by impining C and O ions. Seeding required to reach physical
threshold for W - Pentetration depths and emission pattern of W, C,
D determined. Input for ERO modelling
WF injected through a gas inlet inthe PWI facility in TEXTOR to
mimic W source6 - WF dissociates quickly and provide well-known
source of W atoms (population to be determined)6
- Effective photon efficiencies for various WI lines obtained
and compared with GKU modelling - Effective photon efficiencies
applied to W/C twin limiter experiment
Experiments with impurity seeding by nitrogen started to reduce
the local T further e
Experiment: W sputtering at W/C twin limiters in TEXTOR
Experiment
W photon efficiency calibration Diagnostic set-up
Experiment: WF injection for W sputtering calibration 6
Edge plasma conditionsExperimental results: Spatial distribution
with filtered cameras (side view)
§ C limiter faces ids and W limiter faces eds
§ 19 -34 density steps per discharge (2,3,4,5x10 m )
§ Repetition of discharges for full diagnostic coverage
Here:C is facing the
ids: ion drift sideW is facing the
eds: el. drift side
Experimental results: Spatial distribution with filtered cameras
(top view)
Experimental results: Impurity fluxes and erosion yields
(integral from spectrometer)
47
48
49
50
51
46
45
44
43
LCFS
rad
ius
/ c
m
toroidal direction / cm
profiles
0 1 2 0 3 2 5 4 -5 -3 -4 -1 -2
CII (515.0+/-1.5)nm
# 113114
C limiter W limiter
phase II
47
48
49
50
51
46
45
44
43
LCFS
rad
ius
/ c
m
toroidal direction / cm
profiles
0 1 2 0 3 2 5 4 -5 -3 -4 -1 -2
CII (515.0+/-1.5)nm
# 113114
C limiter W limiter
phase I
47
48
49
50
51
46
45
44
43
LCFS
rad
ius
/ c
m
toroidal direction / cm
profiles
0 1 2 0 3 2 5 4 -5 -3 -4 -1 -2
CII (515.0+/-1.5)nm
# 113114
C limiter W limiter
phase III
47
48
49
50
51
46
45
44
43
LCFS
rad
ius
/ c
m
toroidal direction / cm
profiles
0 1 2 0 3 2 5 4 -5 -3 -4 -1 -2
CII (515.0+/-1.5)nm
# 113114
C limiter W limiter
phase IV
47
48
49
50
51
46
45
44
43
LCFS
rad
ius
/ c
m
toroidal direction / cm
profiles
0 1 2 0 3 2 5 4 -5 -3 -4 -1 -2
WI (400.8+/-0.5)nm
# 113112
C limiter W limiter
phase I
47
48
49
50
51
46
45
44
43
LCFS
rad
ius
/ c
m
toroidal direction / cm
profiles
0 1 2 0 3 2 5 4 -5 -3 -4 -1 -2
WI (400.8+/-0.5)nm
# 113112
C limiter W limiter
phase II
47
48
49
50
51
46
45
44
43
LCFS
rad
ius
/ c
m
toroidal direction / cm
profiles
0 1 2 0 3 2 5 4 -5 -3 -4 -1 -2
WI (400.8+/-0.5)nm
# 113112
C limiter W limiter
phase III
47
48
49
50
51
46
45
44
43
LCFS
rad
ius
/ c
m
toroidal direction / cm
profiles
0 1 2 0 3 2 5 4 -5 -3 -4 -1 -2
WI (400.8+/-0.5)nm
# 113112
C limiter W limiter
phase IV
47
48
49
50
51
46
45
44
43
LCFS
rad
ius
/ c
m
toroidal direction / cm
profiles
0 1 2 0 3 2 5 4 -5 -3 -4 -1 -2
Da (656.3+/-1.5)nm
# 113108
C limiter W limiter
phase I
47
48
49
50
51
46
45
44
43
LCFS
rad
ius
/ c
m
toroidal direction / cm
profiles
0 1 2 0 3 2 5 4 -5 -3 -4 -1 -2
Da (656.3+/-1.5)nm
# 113108
C limiter W limiter
phase II
47
48
49
50
51
46
45
44
43
LCFS
rad
ius
/ c
m
toroidal direction / cm
profiles
0 1 2 0 3 2 5 4 -5 -3 -4 -1 -2
Da (656.3+/-1.5)nm
# 113108
C limiter W limiter
phase III
47
48
49
50
51
46
45
44
43
LCFS
rad
ius
/ c
m
toroidal direction / cm
profiles
0 1 2 0 3 2 5 4 -5 -3 -4 -1 -2
Da (656.3+/-1.5)nm
# 113108
C limiter W limiter
phase IV
Filter: WI=(400.8+/-0.5)nm
radial resolvedspectrometer
integral measurements
2D imaging
Gas inletLCFS
Photon efficiency calibration: WF injection6
W photon efficiency calibrationWI spectra comparison between
injected and sputtered WW photon efficiency calibrationWI and WII
spectra comparison between injected and sputtered W
W photon efficiency calibrationWI spectra comparison between
injected and sputtered WW photon efficiency calibrationEffective
photon efficiency for WI (400.8 nm) ouf of WF6
416,0 417,0 418,0
0
2
4
6
8
10
WII
W/C limiter
l [nm]
TEXTOR # 114536
TEXTOR # 113112
0,0
2,0
4,0WF
6 injection
429,0 430,0
0
20
40
60
80
100
120
W/C limiter
l [nm]
TEXTOR # 114536
TEXTOR # 113112
0,0
2,0
4,0
6,0
8,010,0
12,0
14,0
16,0
18,0
20,0
WI
WF6 injection
inte
nsi
ty [
arb
. units
]in
tensi
ty [
arb
. units
]
522,0 523,0 524,0
0
20
40
W/C limiter
l [nm]
TEXTOR # 114536
TEXTOR # 113112
0,0
1,0
2,0
3,0
4,05,0
6,0
7,0
8,0
9,0
10,0
WI
WF6 injection
inte
nsi
ty [
arb
. units
]in
tensi
ty [
arb
. units
]
400,0 401,0 402,0
0
20
40
60
80
100
120
W/C limiter
l [nm]
TEXTOR # 114536
TEXTOR # 113112
0,0
2,0
4,0
6,0
8,010,0
12,0
14,0
16,0
18,0
20,0
WI
WF6 injection
inte
nsi
ty [
arb
. units
]in
tensi
ty [
arb
. units
]
inte
nsi
ty [
arb
. units
]in
tensi
ty [
arb
. units
]
§ Complete spectrum coverage from 363 nm-715 nm. More WI lines
identified and quantified: model benchmark
§ WII lines identified and quantified at 434.8 nm, 417.5 nm,
385.2 nm
§ Line ratio of WI to WII lines is different between injected
and sputtered W => issue of prompt redeposition
§ Four plateaus with different pairs of edge T and ne e:phase I:
T ~85 eVe § phase II: T ~60 eVe § phase III: T ~45 eVe § phase IV:
T ~30 eVe
0 10 20 30 40 50 60 70 80 90 100 110
0
20
40
60
80
100
120
140
160
180
200
220
240 WF6 injection (Spectrelle)
[S/X
B]
WF
6->
W
WI
(40
0.8
nm
)
Te [eV]
W/C twin limiter experiment
GKU Vainshtein/Beigman
Tw=0.1 eV
Tw=0.2 eV
Tw=0.3 eV
Tw=1.0 eV
Tw=2.0 eV
TEXTOR: #113966-70,73-74
Normalisarion on WI at 400.8 nm
The effective photon efficiencies
WI at 429.5 nm => ~80
WI at 505.2 nm => ~245
are in fair agreement with GKU modelling but higher thanvalues
deduced in PISCES-B[Nishijima 2010]
WI at 400.8nm
Photon flux proportional to particle flux§
§
§Fraction of injected WF could be 6dissociated and deposited in
gas inlet => eff. S/XB is upper limit
Measured eff. photon efficienciesshow moderate reduction with T
ein the TEXTOR experimental range
Averaged value for W/C twin limiterexperiment is for WI at 400.8
nm
about 85 = [S/XB]WF6->W
§ §
§
WF6
plasma
SOL
Proportionality factor: inv. photon efficiency S/XB§
Simulate W source by calibrated WF injection6§
Assumption: WF dissociates quickly and produces6 W atoms
comparable to sputtered W
§
Full ionising plasma conditions in TEXTOR edge§
Analyse W line ratios to qualify initial populationin the
complex atomic ground state (T ) w
§
0 1 2 3 4 5 6 7
0,00
0,02
0,04
0,06
0,08
0,10
S/XB Dg 434.0nm=1000(exp)S/XB WI 400.9nm=85 (exp)
#113112
Yie
ldin
%
time [s]
W/D C/D O/D
S/XB CII 426.7nm=80(exp)S/XB OII 441.6nm=45(exp)
0 1 2 3 4 5 6 7
0,00
0,25
0,50
0,75
1,00
1,25
1,50
1,75
2,00
2,25
2,50
2,75
3,00
WI
OII
Dd
CII
Dg
time [s]
WI,
OII,Dd
inte
nsi
ty[a
rb.u
nits
]
0
2
4
6
8
10
12#113112
CII
CII,Dg
inte
nsity
[arb
.u
nits
]
Dg
0 1 2 3 4 5 6 7
0,00
0,02
0,04
0,06
0,08
0,10
time [s]
Yie
ldin
%
S/XB CII 426.7nm=80(exp)S/XB OII 441.6nm=45(exp)
S/XB Dg 434.0nm=1000(exp)S/XB WI 400.9nm=85 (exp)
W/D C/D O/D
#113118
0 1 2 3 4 5 6 7
-0,50
-0,25
0,00
0,25
0,50
0,75
1,00
1,25
1,50
1,75
2,00
2,25
2,50
2,75
3,00
time [s]
WI,
OII,Dd
inte
nsi
ty[a
rb.u
nits
]
CII,Dg
inte
nsity
[arb
.u
nits]
WI
Dd
OII
CII
Dg
Dg
CII
#113118
-2
0
2
4
6
8
10
12
14
16
18
§ Decrease of WI emission with decrease of local electron
temperature,but with increase of impurity flux (~CII) and ion flux
(~Da)
§ Short penetration depth of WI emission ( V. Philipps JNM
1998
phase I phase II phase III phase IV phase I phase II phase III
phase IV
phase I phase II phase III phase IVphase I phase II phase III
phase IV
gas inlet position at r=47.0cm
WI 400.8nm Dd 410.2nm
48.0
46.0
Dl~26nm
47.0
confined plasma
45.0
44.0
43.0
42.0
41.0
rad
ius
[c
m]
wavelength [nm]
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