PFC Meeting, PRINCETON, May 05

Be/W mixed material experiments

M. J. Baldwin, R. P. Doerner and D. Nishijima Center for Energy Research, University of California – San Diego

K. Ertl, J. Roth, Ch. Linsmeier, K. Schmid and A. WiltnerMax-Plank Institute for Plasmaphysics, Garching, Germany

PFC Meeting, PRINCETON, May 05

Motivation

UC San Diego PISCES and EFDA are investigating the influence of Beplasma impurities on exposed materialsinteractions relevant to ITER.

The ITER design: Be first-wall,W divertor, C (graphite) strike points.

Diverted plasma expected to be ‘dirty’:Eroded Be impurity conc. up to 10 %.

Amongst others, Be/W PMI is an issue.

PFC Meeting, PRINCETON, May 05

Thermo - couple

PISCES -B Plasma column

153 mm

Plasma source

Magnetic axis

Evaporative Be Impurity seeding

W Target

PISCES-B can investigate Be-W PMI relevent to ITER divertor

Cooled target assembly

ion (cm2s–1) 1018–1019

E ion (eV) 50 (bias) Te (eV) 6–10 ne (cm–3) 1012–1013 Be fraction 0.05–1 %

PFC Meeting, PRINCETON, May 05

Be layers on plasmaexposed W surfaces? Be can alloy with W W structural integrity

is reduced at significantlylower temperatures.Liq. phase precipitates at

Be2W ~ 2200°CBe12W ~ 1500°CBe22W ~ 1300°C

ITER should be concernedabout these alloys since littlePMI data on Be-W exists.

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.

PFC Meeting, PRINCETON, May 05

Tungsten crucible

Be ingot

45°

PISCES-B Be oven: W crucible melted.

Be oven temperaturenever exceeded 1550°C

Typical operation andoperating temperaturewhen the oven failedwas 1200°C

Total lifetime ofcrucible was 100 hrs. Be ingot

Zone B(melt region)

Zone A

Intact W wall (97%W, 3%O)

Inner wall coating(4% W, 95% Be, 1%O) Be22W?

Crucible wall fragments fromBe rich failure zone(9% W, 70% Be, 14% C, 7% O) Be12W?

PFC Meeting, PRINCETON, May 05

Alloy formation studies(US-EU collaboration)

Polished Be substrate

Annealing in vacuum up to 800°C for up 600 min

RBS ion beam analysisH (1 MeV)

230 nm deposited W

No visible reaction up to 700°C

Alloy formation starts at 800°C

Be diffuses through Be/W alloy and W layer to the surface

PFC Meeting, PRINCETON, May 05

Is layer growth diffusion limited?

Be12W

Reaction controlled by chemicalpotential or diffusion not clear. A. Vasina et.al, Russian Metally, 1(1974)119.

After 600 min the wholelayer is transformed intoBe12W

The Be12W phase seemsthermodynamically morestable than Be2W and Be22W

D800°C ~ 1.7 10-13 cm2/s

PFC Meeting, PRINCETON, May 05

PISCES plasma exposure induces beryllides (570-1050 oC).

XPS confirmsberyllides(E.g. Wiltner et al. J. Nucl.Mater. 337-339 (2005) 951)

AES Concentrationsare close to Be12W

Need to investigatePMI layer growth

Will diffusion limitlayer growth underplasma operation?

Binding energy (eV)

110115

N(E

) (

Arb

uni

ts)

050

010

0015

0020

00

Be 1s

Me

talli

c B

e

11

1.8

0 e

V

Be

oxi

de

3035

020

0040

00

W 4f

Ber

yllid

e

11

1.1

5 e

V

W

31

.0 e

V

Beryllidedoubletshifts-0.25 eV

STD

1050 oC

750 oC

570 oC

W 17% Be 83%

W 15% Be 85%

W 23% Be 77%

10-10

10-9

10-8

10-7

10-6

10-5

0.0001

0.0004 0.0006 0.0008 0.001 0.0012 0.0014 0.0016 0.0018

Be12

W from E. Vasina [9]

Be22

W from E. Vasina [9]

PISCES-B data

y = 0.0040771 * e (̂-15099x) R= 0.98313

y = 3.3293e+05 * e (̂-39364x) R= 0.98877

1/T (K)A. Vasina and A. S. Panov, Russian Metallurgy (Metally), 1(1974)119.

PFC Meeting, PRINCETON, May 05

Retention and blistering w/ & w/o BeW layers

Initial results suggest that Be impurity flux inhibits blistering. Why?

Retention in Be coated W is is found to be comparable to retention in unblistered W at temperatures of 300 °C and 1000 °C.

No Be ~0.1 % Be seeding.Eion: 75 eV

T: ~ 300 oC

D+: 1 x 1022 m-2 s-1

Fluence: 5 x 1025 m-2

Time (s)

1000 2000

Pre

ssur

e (

Tor

r)

010

-72x

10-7

Tem

pera

ture

(K

)

400

600

800HDD2

Time (s)

1000 2000

Pre

ssur

e (

Tor

r)

010

-72x

10-7

Tem

pera

ture

(K

)

400

600

800HDD2

PFC Meeting, PRINCETON, May 05

Summary

Be-W PMI not well understood. Important for ITER & JET. Be-W interaction produces low melting point (< 1750 °C) phases.

The Be12W phase seems more stable than Be2W and Be22W.Observed with WDS, AES, XPS (UCSD) and RBS (IPP).

Be-W layer growth occurs at (~800 oC). Possibly diffusion limited.Activation energy to be determined (IPP) by further phase formation vs temperature studies.

PMI can induce beryllides at even lower temperature (570 oC) Layer growth studies are required (PISCES).Is PMI diffusion limited or kinetics controlled?

Be-W layer reduces blistering/retention (~300 °C). No blistering/retention (~ 1000°C). More data needed. (PISCES)

Retention consistent with unblistered W.