R. Doerner, EU SEWG meeting, JET. July 9-10, 2007 Recent Results from PISCES Program R. P. Doerner,...

U C S DU niversity o f C alifo rn ia S a n D iego

R. Doerner, EU SEWG meeting, JET. July 9-10, 2007

Recent Results from PISCES Program

R. P. Doerner, M. J. Baldwin, G. De Temmerman, J. Hanna, D. Nishijima, G. Tynan and K. Umstadter

Center for Energy Research, University of California – San Diego, USA

Work performed as part of:

US-EU Collaboration on Mixed-Material PMI Effects for ITER

TITAN US-Japan Collaboration

UCSD – SNLL Collaboration on Be/W alloys



Outline - Recent PISCES Results

• Erosion of Be layers

• Laser irradiation of plasma exposed targets– Preparation for ELM simulation studies

• Be/W formation conditions

• Mixed species (D/He) plasma studies

• W exposure to mixed species plasma– Impact of Be and C impurities on W surface evolution

• Codeposition studies (presented tomorrow)

• Summary



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

P-B experiments simulateBe erosion from ITER wall,subsequent sol transport and interaction with W bafflesor C dump plates, as well asinvestigation of codepositedmaterials using witness plates



Plasma deposited Be (from oven) erodes differently than other Be layers

• Erosion calibration measurements for JET ILW erosion marker tiles

• Plasma deposited Be is easily re-eroded from deposited locations (remember for tomorrow)

• Erosion of Be from Be2C are underway10-5

10-4

10-3

10-2

10-1

0 20 40 60 80 100 120 140

PC-BeGA-BeRomainian-BeBe on Be

Eckstein(D,D2,D3->Be) x0.133

Ei [eV]



ELM simulation experiments are beginning, using laser irradiation of plasma exposed targets

• Laser heating method allows use of background plasma as diagnostic tool

• High-speed diagnostics implemented using 750mJ YAG laser (0.5 nsec)– 10000 fps, 10 msec camera, also single frame 2-100 nsec camera

– Gated imaging spectrometer w/ ICCD (50 nsec gate)

• Hydrogen saturation of surface produces much different effects– Macroscopic material ejection observed both w&w/o plasma

– 10x more material lost from plasma exposed samples during laser shots

– Laser irradiation of samples can induce plasma arcing (e- emission?)

• Acquired welding laser capable of simulating ELM conditions– 1.5 – 50 J, 0.3 – 10 msec adjustable pulse, fiber delivery to P-B



2

Stable Be-W alloys are known and have melting points closer to that of Be than W.

Atomic percent Tungsten

0 10 20 30 40 50 60 70 80 90 100

Tem

pera

ture

(o

C)

1000

2000

3000

Weight percent Tungsten

0 70 80 90 100

Be W

34

22

o C

LIQUID

Be

12W Be

2W

<1750o C

<2250o C

12

87

o C

Be

22W

~952100 50o C

Stable Be-W alloys

• Stable Be-W inter-metallics are:

~2200°C (Be2W)

~1500°C (Be12W)

~1300°C (Be22W)

• What will happen if Be transport into the W bulk is rapid enough that alloy formation is not limited to the near surface?



XPS confirms Be-W alloy formation on W target surfaces exposed in range 850-1320 K.

• Be-W alloy line shifts are consistent with:Wiltner & Linsmeier,JNM 337–339 (2005)

Binding energy (eV)

110115

N(E

) (

Arb

uni

ts)

050

010

0015

0020

00

Be 1s

Met

allic

Be

111

.80

eV

Be

oxid

e

3035

020

0040

00

W 4f

Ber

yllid

e 1

11.1

5 eV

W 3

1.0

eV

Beryllidedoubletshifts-0.25 eV

STD

1320 K

1020 K

850 K

W 17% Be 83%

W 15% Be 85%

W 23% Be 77%

D ion fluence ~ 1.2x1026 m-2

nBe+/ne ~ 0.1 %,



The availability of surface Be is found to be critical for Be-W alloy formation (t ~ 1 h).

• A 0.3 m Be12Wlayer forms at W-Beinterface.

• Be12W nucleation

on W rich surface.

• No Be sub-surface.



Similar layered structure observed in SNLL vacuum deposition measurements



Be re-erosion and evaporation reduce surface Be availability, reducing alloy formation rate.

• Surface composit-ion below stoichio-metry for Be2W. No Besub-surface.

• Be12W surfacenucleation over almostidentical surface to (d).



Simple particle transport model predicts Be overlayer formation (most efficient alloying).

More detailed modeling needed.

Ts (K)1100 1200 1300 1400 1500 1600

f Be+

10-3

10-2

10-1

10 eV

25 eV

50 eV

100 eV

D+=2 x1018 cm-2s-1

PISCES

D+=2 x1019 cm-2s-1

ITER

Be layerwill form

Be layerdoesn'tform

rDBe

Bein 1 RfJ

[9] yieldssputter , , BeBeBeD YYfractions redep. , , ed RR

see

dDBeBeBe

dDBeDBeout

1

1

1

TR

RYf

RYJ

flux diffusion bulk ,sT

[9] coef refl. WBe ,r R

[10]flux evap. ,e

Values taken from: W. Eckstein, IPP Report 9/17, (1998)D. R. Lide, CRC Handbook of Chem. & Phys., Internet Version (2005)



Mixed D-Be/C-He on W experiments

Effects of He and D-He plasma on W.

Influence of plasma impurities Be and C on these effects.



PISCES-B: pure He plasma

Ts = 1200 K, t = 4290 s, Fluence = 2x1026 He+/m2, Ei = 25 eV

Plasma simulators observe morphology change on W surfaces exposed to pure He plasma.

Transmission electron microscope (TEM)in Kyushu Univ.

Scanning electron microscope (SEM)

NAGDIS-II: pure He plasma

Ts = 1250 K, t = 36,000 s, Fluence = 3.5x1027 He+/m2, Ei = 11 eV

N. Ohno et al., in IAEA-TM, Vienna, 2006



D2-He plasma, Ei = 60 eV nHe+/ne ~ 10 %t = 4200 s1025 He+/m2

Effect of D2-He plasmas at Ts = 1100-1200 K.

• Plasma exposure time, t, is a stronger influence than He ion flux or fluence

He plasma, Ei = 60 eV

t = 420 s1025 He+/m2

He plasma, Ei = 25 eV

t = 4290 s2x1026 He+/m2



Ei = 60 eV, Ts = 1100 K, Fluence = 1025 He+/m2

D2-He plasma D2-He plasma with BenHe+/ne ~ 10 %, nBe+/ne ~ 0.2 %, t = 4200 s

D2-He mixture plasma w/wo Be induces morphology on W at Ts = 1100 K & Ei = 60 eV.

Finger-like structures observed, similar to pure He plasma

Ion bombardment at Ei = 60 eV prevents Be layer growth.

But, Be somewhat inhibits morphology.

nHe+/ne ~ 10 %,t = 4200 s



RN01312007

Be12Wlayer

RN01292007

95% Clayer

Be or C plasma impurities can inhibit morphology at Ts = 1100 K & Ei = 15 eV.

Ei = 15 eV, Ts = 1100 K, Fluence = 1025 He+/m2

D2-He plasma with BenHe+/ne ~ 10 %, nBe+/ne ~ 0.5 %, t = 5000 s

D2-He plasma with CnHe+/ne ~ 10 %, nC+/ne < 0.1 %, t = 3600 s

Surface layer composition determined by x-ray microanalysis (WDS).

Be-W alloy and W-C layers inhibit He induced morphology.

At Ei = 15 eV, Be and C deposited on W are not sputtered away.



In conclusion

• Tungsten as PFM has unique issues for an all-W ITER, and beyond

• Mixed-material issues are critical, even in a device with only one element as a PFM– Helium ash, Argon/Neon radiator gas, Oxygen

• How will mixed-species plasmas effect Be mitigation of C chemical erosion

• Stay tuned for tomorrow’s discussion on codeposition (and the role of mixed species plasmas there)

R. Doerner, EU SEWG meeting, JET. July 9-10, 2007 Recent Results from PISCES Program R. P. Doerner,...

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