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PISCES ITER-simulation experiments on Mixed-Materials (Be, C, W) R. P. Doerner, M. J. Baldwin and D. Nishijima Center for Energy Research, University of California – San Diego D. G. Whyte University of Wisconsin - Madison K. Schmid, J. Roth and A. Wiltner - PowerPoint PPT Presentation
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U C S DU niversity o f C alifo rn ia S a n D iego
R. Doerner, May 9, 2005PFC Program Review, PPPL
PISCES ITER-simulation experiments on Mixed-Materials (Be, C, W)
R. P. Doerner, M. J. Baldwin and D. Nishijima Center for Energy Research, University of California – San Diego
D. G. WhyteUniversity of Wisconsin - Madison
K. Schmid, J. Roth and A. WiltnerMax-Plank Institute for Plasmaphysics, Garching, Germany
U C S DU niversity o f C alifo rn ia S a n D iego
R. Doerner, May 9, 2005PFC Program Review, PPPL
US-EU Collaboration on Mixed-Material PMI Effects for ITER has
been extended for 3 years
• The erosion, deuterium retention and codeposition properties of graphite exposed to a beryllium-containing deuterium plasmas
• The erosion, deuterium retention and codeposition properties of tungsten exposed to deuterium plasma containing beryllium impurities (as well as with and without (in TPE) carbon impurities)
• The erosion and deuterium retention behavior of beryllium exposed to deuterium plasma at temperatures approaching the Be melting temperature
U.S. - R. Doerner – UCSD E.U. – A. Loarte - EFDA
Focused on two main experimental aspects:
Verification of surface and edge plasma models:TRIDYN (IPP), ERO (KFA), WBC (ANL), UEDGE (UCSD)
U C S DU niversity o f C alifo rn ia S a n D iego
R. Doerner, May 9, 2005PFC Program Review, PPPL
PISCES-B, and Its Associated Surface Analysis Laboratory, Are Compatible with
Beryllium Operations.
- The PISCES-B plasma generator is contained in a separate enclosure to prevent release of beryllium particulates into the general lab.
- All personnel entering the enclosure wear full coverage personal protective equipment and follow strict entry and exit procedures when performing routine maintenance, machine repair, or sample handling/exchange operations.
- The entire enclosure has a specially designed ventilation system that filters all input and output air streams.
U C S DU niversity o f C alifo rn ia S a n D iego
R. Doerner, May 9, 2005PFC Program Review, PPPL
PISCES-B linear plasma device simulates ITER diverted field line geometry
U C S DU niversity o f C alifo rn ia S a n D iego
R. Doerner, May 9, 2005PFC Program Review, PPPL
PISCES-B has been modified to allow exposure of samples to Be seeded plasma
Radial transport guard
102 mm
153 mm
76 mm
195 mm
45 o
Cooled target holder
Heatable deposition probe assembly
Thermocouple
Thermocouple
Water cooled Mo heat dump
Resistive heating coils
High temperature MBE effusion cell used to seed plasma with evaporated Be
12 °
PISCES-B PlasmaTarget
Depositionprobesample
Axial spectroscopic field of view
Berylliumimpurityseeding
Radial transport guard
102 mm
153 mm
76 mm
195 mm
45 o
Cooled target holder
Heatable deposition probe assembly
Thermocouple
Thermocouple
Water cooled Mo heat dump
Resistive heating coils
High temperature MBE effusion cell used to seed plasma with evaporated Be
12 °
PISCES-B PlasmaTarget
Depositionprobesample
Axial spectroscopic field of view
Berylliumimpurityseeding
U C S DU niversity o f C alifo rn ia S a n D iego
R. Doerner, May 9, 2005PFC Program Review, PPPL
A small beryllium impurity concentration in the plasma drastically suppresses carbon erosion
-50 V bias, 200ºC, Te = 8 eV, ne = 3 e 12 cm-3
Chemical erosion Physical sputtering
500
1000
1500
2000
2500
3000
3500
4000
No Be injection0.2% Be ion concentration
Wavelength (nm)
CD band
D gamma Be I
459445431 452438
4000
8000
1.2 104
1.6 104
2 104
2.4 104
2.8 104
No Be injection0.2% Be ion concentration
Wavelength (nm)
C I
941.5940.5939.5938.5937.5
U C S DU niversity o f C alifo rn ia S a n D iego
R. Doerner, May 9, 2005PFC Program Review, PPPL
Be rich surface layers form during exposure and shield underlying carbon from erosion
0
20
40
60
80
100
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35
T surface ~ 250CT surface ~ 700C
Be plasma concentration (%)
• ITER will have 1-10% Be impurity concentration in the divertor plasma
0.00 0.05 0.10 0.15 0.20-30
-20
-10
0
Bias: 50V~500K
No Be Be seeding
~1000K No Be Be seeding
No
rma
lize
d w
eig
htl
os
s [
10
-26 m
g m
2]
Be1+ plasma concentration [%]
De
cre
as
ing
ero
sio
n
Weight loss dataconfirms reduction in
erosion seen spectroscopically
Be surface concentration after 5000 sec. P-B exposure.
We
igh
t lo
ss
(m
g/c
m2
)
U C S DU niversity o f C alifo rn ia S a n D iego
R. Doerner, May 9, 2005PFC Program Review, PPPL
Plasma conditions:
D ~3x1018 cm-2 s-1, Te~ 6eV, ne~ 1012 cm-3, T ~500 K, D Ion Fluence ~2x1022 cm-2
No Be seeding m = - 62 mg
ATJ graphiteNot exposed
~0.1 % Be seeding m = - 5 mg AES - 85 % Be, 10% O & 5% C
Be layer forms on C targets with a complicated three dimensional structure
U C S DU niversity o f C alifo rn ia S a n D iego
R. Doerner, May 9, 2005PFC Program Review, PPPL
Be impurities from the ITER first wall can also form Be-rich surfaces on the tungsten baffle plates
• Be layers have been observed on on W surfaces, as well as C
• Plasma exposure conditions– Be conc. ~0.1%– Eion ~ 75 eV– TW ~ 300°C– Ion flux ~ 1x1022 m-2s-1
– Exposure time = 5000 sec.
• Surface has 12 times as much Be as W indicating formation of Be12W tungsten beryllide alloy (Tmelt of Be12W ~ 1500°C)
Surface morphology of a W targetexposed to a Be seeded deuterium
plasma in PISCES-B
U C S DU niversity o f C alifo rn ia S a n D iego
R. Doerner, May 9, 2005PFC Program Review, PPPL
If alloy formation (carbide or beryllide) is responsible for Be layers, then subsequent Be deposition should be quickly re-
eroded, which means Be alloy layers should be thin.
0 5 10 15 200
10
20
30
40
50
60
70
80
90
100
Be (at %) O (at %) W (at %)
Co
mp
osi
tion
(a
t. %
)
Sputtering Time (min)
W sample (AES data)fBe = 0.1%, 5000 sec., TW = 300°C
0 10 20 30 40
Estimated Thickness (nm)50 60
C sample, 175°C, fBe ~0.15%
U C S DU niversity o f C alifo rn ia S a n D iego
R. Doerner, May 9, 2005PFC Program Review, PPPL
Time (s)
0 500 1000 1500 2000
Nor
m. C
D B
and
stre
ngth
(A
rb. u
nits
)
0.1
1
Sur
face
car
bon
conc
entr
atio
n
0.1
1
0.18 % Be0.41 % Be
0.13 % Be
1.10 % Be
0.03 % Be
The dynamic behavior of the Be layer may help decipher the mechanisms responsible for
surface layer formation on C and W substrates• PISCES-B conditions: fBe ~ 0.001, pl = 3e18 cm-2s-1, Be = 3e15 Be/cm2s or 1 Be monolayer/sec
0.04% Be
0.16% Be
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 5 10 15 20 25 30
CD/Dg (C sample)Be/Dg (C sample)Be/Dg (W sample)
Time (min)
Be layers can form slowly on C samples under PISCES-B conditions
Be layers appear to form rapidly on W samples under PISCES-B plasma conditions
U C S DU niversity o f C alifo rn ia S a n D iego
R. Doerner, May 9, 2005PFC Program Review, PPPL
Erosion mechanism will determine fuel retention.Fuel accumulation within ITER is a critical
operational and safety issue
• PISCES witness plate manipulator (WPM) allows investigation of codeposited material eroded from targets
• PISCES target analysis examines implantation and saturation issues associated with high-flux plasma interaction locations
• NRA (at IPP and UW-Madison) and TDS (at UCSD) allow quantitative comparison of retention measurements
U C S DU niversity o f C alifo rn ia S a n D iego
R. Doerner, May 9, 2005PFC Program Review, PPPL
WPM samples show collection of beryllium rich deposits during Be seeding runs
0 5000 10000 15000 20000 25000 30000 35000 40000 450000
10
20
30
40
50
60
70
80
90
100
0
10
20
30
40
50
60
70
80
90
100
com
po
sitio
n (
%)
time (s)
Be% C% O% Ta%
profile, WPMTA01Carbon target : 300ºC target exposure
0 20 40 60 80 100 120
0
10
20
30
40
50
60
70
80
90
100
Be% C% O% Ta-%
Ato
mic
%Fluence [cm
-2]
Carbon target : 700ºC target exposure
No WPM data yet from W targets, but large loss rate of incident Be ions on W targets (re-erosion or reflection) quickly causes coating of diagnostic windows during Be seeding runs
U C S DU niversity o f C alifo rn ia S a n D iego
R. Doerner, May 9, 2005PFC Program Review, PPPL
T retained in Be rich codeposits can be more easily removed during divertor bakeout
• Although more hydrogen isotopes are retained during lower temperature codeposition, they are more easily desorbed
• ITER can bake divertor to 375°C (after coolant drain)
• Codeposits will be in line-of-sight of erosion location
• Oxygen bake may not be needed to remove fuel atoms from codeposits
Temperature (o C)
200 400 600 800 1000
D/B
e in
cod
epos
its (
at. %
)
110
100
H/C
in c
odep
osits
(at
. %)
110
100
50o C (O ~ 3 at. %)
150o C (O ~ 30 at. %)
300o C (O ~ 33 at. %)
Co-deposited a:CH layerCausey et al. J. Nucl.
Mater. 176-7 (1990) 987
Baldwin et al. PSI-16 Maine USA (2004)J. Nucl. Mater. (accepted)
ITER bake
U C S DU niversity o f C alifo rn ia S a n D iego
R. Doerner, May 9, 2005PFC Program Review, PPPL
Hydrogen isotopes are not so easily removed from locations of direct plasma contact
• Data from erosion dominated regimes in PISCES
• More fuel atoms are retained in targets during Be seeding runs
• Presence of Be has little influence on desorption characteristics of C targets
• Flash heating of strikepoints (i.e. laser, flashlamp or controlled plasma power deposition) could be used if target retention becomes an issue for ITERTime (s)
1500 3000
Par
tial p
ress
ure
(T
orr)
10-9
10-8
10-7
Temperature (K)
500 1000
1500 3000
500 1000
Texp~600 K
Texp~1000 K
(a) (b)
0.1% Be
No Be
TDS of C targets w/ & w/o Be seeding
U C S DU niversity o f C alifo rn ia S a n D iego
R. Doerner, May 9, 2005PFC Program Review, PPPL
US-EU Collaboration on Be/C/W has produced significant new results, but more work is needed.
• Understand mechanism responsible for Be-rich layer formation at very low impurity Be concentration (~0.1%)
• Develop/benchmark models that can predict the dynamic behavior of the Be coating process
• Subject layers to ELM style heat pulses during formation• Investigate similarities and differences of W & C targets• Investigate concurrent Be and C injection into D plasma• Investigate role of other impurities (i.e. oxygen, carbon,
radiating noble gases)• W-Be alloy formation is a critical issue needing
immediate attention (melting temperature, thermal properties, formation rates, tritium retention, etc.)
See talk by M. Baldwin
U C S DU niversity o f C alifo rn ia S a n D iego
R. Doerner, May 9, 2005PFC Program Review, PPPL
Be impurities may dominate PMI (specifically tritium accumulation) in devices with large area Be walls
• Need to accurately predict first wall erosion rates (CX, diffusion, convective transport)
• Understanding SOL flows in confinement devices is crucial to predicting divertor impurity content
• Need benchmarked PMI models to predict behavior of surfaces with some confidence