Russ Doerner - Controlled Fusion Atomic Data Center

Erosion Behavior of Carbon and Tungsten
Surfaces Exposed to Deuterium Plasma
Containing a Controlled Amount of
Beryllium Impurities
R. P. Doerner and M. J. Baldwin
Center for Energy Research, University of California – San Diego
D. G. Whyte
University of Wisconsin - Madison
K. Schmid, J. Roth and A. Wiltner
Max-Plank Institute for Plasmaphysics, Garching, Germany
UCSD
University of California San Diego
R. Doerner, March 22, 2005
PSIF workshop, ORNL

PISCES is a steady-state reflex arc plasma source that
provides parameters relevant to edge physics and PMI
issues in present and future confinement machines
Sample Manipulator
Surface
Analysis
System
Confinement
PISCES-B Devices
Ion flux (m -2 s -1 ) 10 23 10 23
Ion energy (eV)
20-300 (bias) 10-300 (thermal)
Target
C, W, Be, Li
Heat flux (MW/m 2 ) 1-10 1-10
Reciprocating
Double
Probe
Da monitor
Pyrometers
Axial
Spectroscopic views
Doppler
T (eV) e
2-40 (thermal) 1-100 (thermal)
n (m -3 ) e
10 17 -10 19 10 18 -10 20
Impurity fraction (%) 0.03-10 1-10
Pulse length continuous 10-30 sec
Target materials C,W,Be,Li C,W,Be,etc.
and coatings
(essentially any)
Plasma
Source
Plasma species H,D,He H,D,T,He
UCSD
University of California San Diego
R. Doerner, March 22, 2005
PSIF workshop, ORNL

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.
- The entire enclosure has a specially
designed ventilation system that filters all
input and output air streams.
- 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.
UCSD
University of California San Diego
R. Doerner, March 22, 2005
PSIF workshop, ORNL

US-EU Collaboration on
Mixed-Material PMI Effects for ITER
U.S. - R. Doerner – UCSD
E.U. – A. Loarte - EFDA
Three main experimental aspects:
• 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
Verification of surface and edge plasma models:
TRIDYN (IPP), ERO (KFA), WBC (ANL), UEDGE (LLNL, UCSD)
UCSD
University of California San Diego
R. Doerner, March 22, 2005
PSIF workshop, ORNL

PISCES-B linear plasma device simulates
ITER diverted field line geometry
UCSD
University of California San Diego
R. Doerner, March 22, 2005
PSIF workshop, ORNL

PISCES- B has been modified to allow exposure of
samples to Be seeded plasma
High temperature
MBE effusion cell
used to seed
plasma with
evaporated Be
12 °
153 mm
102 mm
Beryllium
impurity
seeding
195 mm
Axial spectroscopic field of view
Thermocouple
Cooled target
holder
Target
76 mm
Deposition
probe
sample
45 o
PISCES-B Plasma
Radial transport
guard
Water cooled Mo
heat dump
Heatable
deposition probe
assembly
Thermocouple
Resistive heating
coils
UCSD
University of California San Diego
R. Doerner, March 22, 2005
PSIF workshop, ORNL

PISCES-B operation above 6 eV T e provides
complete ionization of the thermal Be atom beam
0.25
0.20
Be II Plasma concentration, new Be Oven
(30.10.2002)
• Be II line emission @ 467 nm is
used to measure Be ion density
(along with ADAS rate
coefficients)
Be II / n e
[%]
0.15
0.10
0.05
0.00
Te 3eV, T Be
= 1450 °C, n e
= 3E12 cm -3
Te 7eV, T Be
= 1450 °C, n e
= 3E12 cm -3
Te 20eV, T Be
= 1450 °C, n e
= 2E12 cm -3
Te 16eV, T Be
= 1550 °C, n e
= 2E12 cm -3
Te 6eV, T Be
= 1550 °C, n e
= 3E12 cm -3
0 50 100 150 200
Distance from Target [mm]
Be oven
location
• Be oven temperature controls
Be ion density in the plasma
• Be concentration is fairly
constant along the plasma
column
UCSD
University of California San Diego
R. Doerner, March 22, 2005
PSIF workshop, ORNL

Results from experimental tasks #1 & #2
Task 1
• The erosion, deuterium retention and codeposition
properties of graphite exposed to a beryllium-containing
deuterium plasmas
Task 2
• 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)
Task 3
• The erosion and deuterium retention behavior of
beryllium exposed to deuterium plasma at temperatures
approaching the Be melting temperature
UCSD
University of California San Diego
R. Doerner, March 22, 2005
PSIF workshop, ORNL

A small beryllium impurity concentration in the
plasma drastically suppresses carbon erosion
-50 V bias, 200ºC, T e
= 8 eV, n e
= 3 e 12 cm -3
4000
Chemical erosion
Physical sputtering
3500
3000
CD band
No Be injection
0.2% Be ion concentration
2.4 10 4
No Be injection
0.2% Be ion concentration
2500
D gamma
Be I
2.8 10 4 400 450 500 550 600
2 10 4
2000
1500
1000
500
1.6 10 4
1.2 10 4
8000
4000
C I
200 400 600 800 1000
pixel number
pixel number
UCSD
University of California San Diego
R. Doerner, March 22, 2005
PSIF workshop, ORNL

Be rich surface layers form during exposure
and shield underlying carbon from erosion
T surface = 700ºC T surface = 800ºC
100
100
80
80
60
60
40
40
20
T surface ~ 250C
T surface ~ 700C
20
T surface ~ 900C
T surface ~ 1000C
0
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35
Be plasma concentration (%)
0
0 0.1 0.2 0.3 0.4 0.5
Be plasma concentration (%)
• Be surface concentration after 5000 sec. P-B exposure.
• ITER will have 1-10% Be impurity concentration in the
divertor plasma
UCSD
University of California San Diego
R. Doerner, March 22, 2005
PSIF workshop, ORNL

Be layer formation effectively eliminates
erosion from carbon substrate
CD band intensity
(i.e. chemical erosion)
decreases With increasing
Weight loss data
confirms reduction in
erosion seen spectroscopically
Be concentration in the plasma
100
CD-Band intensity [%]
80
60
40
20
CD-Band intensity [%]
Linear Fit: CD = 100.0 - 580.6 * C Be
0
0.00 0.05 0.10 0.15
Be plasma concentration [%]
Normalized weightloss [10 -26 mg m 2 ]
Weight loss (mg/cm 2 )
0
-10
-20
-30
Bias: 50V
~500K
No Be
Be seeding
~1000K
No Be
Be seeding
0.00 0.05 0.10 0.15 0.20
Be 1+ plasma concentration [%]
Decreasing erosion
UCSD
University of California San Diego
R. Doerner, March 22, 2005
PSIF workshop, ORNL

Be layer forms on C targets with a complicated
three dimensional structure
~0.1 % Be seeding
∆m = - 5 mg
AES - 85 % Be,
10% O & 5% C
ATJ graphite
Not exposed
No Be seeding
∆m = - 62 mg
Plasma
conditions:
Γ D
~3x10 18 cm -2 s -1 , T e
~ 6eV, n e
~ 10 12 cm -3 , T ~500 K, D Ion Fluence ~2x10 22 cm -2
UCSD
University of California San Diego
R. Doerner, March 22, 2005
PSIF workshop, ORNL

Do we understand why these Be layers form?
In equilibrium:
Deposition Rate of Be = Removal Rate of Be
Be Deposition Rate = f Be
Γ pl
(1 – R f
)
~0 for Be on C
where, f Be
= plasma Be concentration, Γ pl
= plasma flux, R f
= reflection coefficient
Be Removal Rate = c Be
Y Be
Γ pl
(1-R d
)
where, c Be
= Be surface concentration, Y Be
= sputtering yield of Be due to 50 eV
deuterium ions (=0.02), R d
= redeposition fraction (~20% from WBC simulation)
So the equilibrium surface concentration of Be, c Be
, should be:
c Be
= f Be
/ Y Be
(1-R d
) = 0.001 / 0.02(1-0.2) = ~ 6%
Beryllium-carbide formation may be responsible for erosion suppression.
If Be 2
C surface layer, then Y = 0.002 (from TRIMSP) and
c Be
= f Be
/ Y Be2C
(1-R d
) = 0.001 / 0.002(1-0.2) = ~ 60%
UCSD
University of California San Diego
R. Doerner, March 22, 2005
PSIF workshop, ORNL

*
*
*
* Be oven became depleted during exposure
UCSD
University of California San Diego
R. Doerner, March 22, 2005
PSIF workshop, ORNL

WPM samples show collection of beryllium
rich deposits during Be seeding runs
Data from IPP-Garching sputter XPS system
100
profile, WPMTA01
300ºC target exposure
100
700ºC target exposure
composition (%)
90
80
70
60
50
40
30
Be%
C%
O%
Ta%
90
80
70
60
50
40
30
Atomic %
100
90
80
70
60
50
40
30
Be%
C%
O%
Ta-%
20
20
20
10
10
10
0
0 5000 10000 15000 20000 25000 30000 35000 40000 45000
0
0
Be seeding on
time (s)
Plasma setup
C sample, No Be
Ta
substrate
0 20 40 60 80 100 120
Fluence [cm -2 ]
Be seeding on
Plasma on
Ta
substrate
UCSD
University of California San Diego
R. Doerner, March 22, 2005
PSIF workshop, ORNL

T retained in Be rich codeposits can be more
easily removed during divertor bakeout
D/Be in codeposits (at. %)
1 10 100
Baldwin et al.
PSI-16 Maine USA (2004)
J. Nucl. Mater. (accepted)
50 o C (O ~ 3 at. %)
ITER bake
150 o C (O ~ 30 at. %)
Co-deposited a:CH layer
Causey et al. J. Nucl.
Mater. 176-7 (1990) 987
300 o C (O ~ 33 at. %)
1 10 100
H/C in codeposits (at. %)
• 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-ofsight
of erosion location
200 400 600 800 1000
• Oxygen bake may not be
Temperature ( o C)
needed
UCSD
University of California San Diego
R. Doerner, March 22, 2005
PSIF workshop, ORNL

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
Surface composition of a W target
exposed to a Be seeded deuterium
plasma in PISCES-B
• Plasma exposure conditions
– Be conc. ~0.1%
100
– E ion
~ 75 eV
90
– T W
~ 300°C
– Ion flux ~ 1x10 22 m -2 s -1
– Exposure time = 5000 sec.
• Estimated Be layer thickness
on W is 10 nm
Composition (at. %)
80
70
60
50
40
30
20
Be (at %)
O (at %)
W (at %)
10
• Surface has 12 times as much
Be as W
0
0 5 10 15 20
Sputtering Time (min)
0 10 20 30 40
Estimated Thickness (nm)
50 60
UCSD
University of California San Diego
R. Doerner, March 22, 2005
PSIF workshop, ORNL

Be on W should be even less likely to form
Be surface layers.
Again, in equilibrium:
Deposition Rate of Be = Removal Rate of Be
Be Deposition Rate = f Be
Γ pl
(1 – R f
)
where, R f
= reflection coefficient is now R f
~ 0.6 (for Be on W)
Be Removal Rate = c Be
Y Be
Γ pl
(1-R d
)
Now, Y Be
= 0.026 for 75 eV D ions on Be
So the equilibrium surface concentration of Be on W, c Be-W
, should be:
c Be-W
= f Be
(1-R f
)/ Y Be
(1-R d
) = 0.001(1-0.6) / 0.026(1-0.2) = ~ 2%
Are tungsten beryllides (i.e. Be x
W) responsible?
UCSD
University of California San Diego
R. Doerner, March 22, 2005
PSIF workshop, ORNL

What will be the result of Be layers on
plasma exposed W surfaces?
• Be can alloy with W
• Resulting alloys (Be W 22
and Be W) have lower
12
melting temperatures
(~1500°C)
• Should ITER/JET be
concerned about these
alloys? (Ongoing research)
From H. Okamoto and L.E. Tanner, in “Phase Diagrams of
Binary Tungsten Alloys”, Ed. S.V. Naidu and P. Rao,Indian
Institute of Metals, Calcutta, 1991.
UCSD
University of California San Diego
R. Doerner, March 22, 2005
PSIF workshop, ORNL

If alloy formation (carbide or beryllide) is responsible for Be
layers, then subsequent Be deposition should be quickly
re-eroded. Be alloy layers should be thin.
C sample, 175°C, f Be
~0.15%
W sample (AES data)
f Be
= 0.1%, 5000 sec., T W
= 300°C
100
90
Composition (at. %)
80
70
60
50
40
30
20
10
0
Be (at %)
O (at %)
W (at %)
0 5 10 15 20
Sputtering Time (min)
0 10 20 30 40
Estimated Thickness (nm)
50 60
UCSD
University of California San Diego
R. Doerner, March 22, 2005
PSIF workshop, ORNL

The dynamic behavior of the Be layer may help
decipher the mechanism responsible for
surface layer formation.
1.6
• At PISCES-B conditions:
f ~ 0.001
Be
Γ = 3e18 cm -2 s -1
pl
Γ = 3e15 Be/cm 2 s
Be
or 1 Be monolayer/sec
CD/Dg
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0 50 100 150 200
Distance from Target [mm]
Discharge time [s]
1940
2670
3500
4100
7050
For 50 eV Be on C the stopping
distance is only ~0.5nm, or
~2-3 monolayers
Erosion suppression (i.e. CD
band decrease) takes much
longer
Upstream Be conc. (%)
1
0.1
UCSD
University of California San Diego
R. Doerner, March 22, 2005
PSIF workshop, ORNL
0.01
10 1 10 2 10 3 10 4
CD Band strength e-folding time (s)

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 a model that can predict the dynamic behavior
of the Be coating process
• Investigate concurrent Be and C injection into D plasma
• Investigate similarities and differences of W & C targets
• W-Be alloy formation is a critical issue needing
immediate attention (melting temperature, thermal
properties, formation rates, tritium retention, etc.)
UCSD
University of California San Diego
R. Doerner, March 22, 2005
PSIF workshop, ORNL

Be impurities may dominate PMI
(specifically tritium accumulation) in
devices with large area Be walls
• Need to predict first wall erosion rates (CX, diffusion,
blob transport, ELMs, …)
• Understanding SOL flows in confinement devices is
crucial to predicting divertor impurity content and
likelihood of layer growth
• Subject layers to ELM style heat pulses during formation
• Investigate role of other impurities (i.e. oxygen, Ne, Ar)
UCSD
University of California San Diego
R. Doerner, March 22, 2005
PSIF workshop, ORNL