R. Doerner, May 9, 2005 PFC Program Review, PPPL PISCES ITER-simulation experiments on Mixed-Materials (Be, C, W) R. P. Doerner, M. J. Baldwin and D. Nishijima

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



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)



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.



PISCES-B linear plasma device simulates ITER diverted field line geometry



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



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



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

)



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



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



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%



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



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



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



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



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



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



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

Documents

R. Doerner, May 9, 2005 PFC Program Review, PPPL PISCES ITER-simulation experiments on Mixed-Materials (Be, C, W) R. P. Doerner, M. J. Baldwin and D. Nishijima