R. Doerner, EU PWI Task Force Meeting, Frascati, Italy, Oct. 27-30, 2008 US-EU Collaboration on Mixed Materials for ITER: Past, Present and Future R. P.

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

R. Doerner, EU PWI Task Force Meeting, Frascati, Italy, Oct. 27-30, 2008

US-EU Collaboration on Mixed Materials for ITER: Past, Present and Future

R. P. Doerner, M. J. Baldwin, G. De Temmerman*, E. Hollmann,

D. Nishijima, G. R. Tynan, K. Umstadter and J. Yu

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

Many European co-authors (see later slide) * now @ MAST



History of US-EU Collaboration

• US withdraws from the ITER Project in 1998.• In 2000-2001, USDOE asks UCSD to develop plans for the Beryllium

decontamination of the PISCES-B facility.• Late in 2001, K. Lackner and R. Conn approached the USDOE with a

proposal to postpone the decontamination. (US was then considering to rejoin ITER.) [Federici involvement]

• The US-EU Collaboration on PISCES-B was approved by EFDA and USDOE in FY02, for a three year duration.– EU Coordinator – A. Loarte– US Coordinator – R. Doerner

• The successful collaboration was renewed in FY05 for a second three year period.

• Recently, the collaboration was extended for another three year period (FY08-10). We are currently starting the second year of this period. The EU Coordinator is now R. Zagorski.

PISCES



The US-EU Collaboration ‘fine print’

• No funding is directly transferred between the EU and US

• The EU agrees to supply manpower to assist in the experimental program on PISCES-B (mutually agreed upon scientist usually comes for a one year visit)

• Several ‘short-term’ visitors (~ month) can be proposed to investigate high priority tasks– EU visitors include: M. Balden, D. Borodin, C. Brosset, G. De

Temmerman, A. Kirschner, A. Kreter, A. Pospieszczyk, R. Pugno, J. Roth, K. Schmid, F. Tabares, A. Widdowson

• The EU supplies ‘equipment’ to facilitate the experimental task of the long-term visiting scientist

• IPP Garching provides material analysis for samples

PISCES



The US-EU Collaboration ‘fine print’

• The USDOE delayed Be decontamination of PISCES-B until the collaboration ends

• US provides logistical support for visiting EU scientists• PISCES-B experimental time can be allocated for EU proposed

experiments and model validation measurements• UCSD supports Be training and medical monitoring of long-term

EU visitors• UCSD coordinates P-B program with EU counterparts at EFDA

and in the PWI Task Force [everything is done by mutual agreement (EFDA representative, PWI TF Leader, SEWG MM leader, ITER contact, PISCES leader*)]

* Remaining permanent member of this counsel retains veto authority

PISCES



The PISCES-B divertor plasma simulator is used to simulate ITER mixed materials PSI.

PISCES ITER (edge)

Ion flux (cm2s–1) 1017–1019 ~1019

Ion energy (eV) 20–300 (bias) 10–300 (thermal)

Te (eV) 4–40 1–100

ne (cm–3) 1012–1013 ~1013

Be Imp. fraction (%) Up to a few % 1–10 (ITER)

Pulse length (s) Steady state 1000

PSI materials C, W, Be C, W, Be ..

Plasma species H, D, He H, D, T, He

• PISCES-B is contained within an isolated safety enclosure to prevent the release of Be dust.

PISCES



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

PISCES



A small beryllium impurity concentration in the plasma drastically suppresses carbon erosion with

a characteristic decay time, Be/C Chemical erosion

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

Modeling using ERO (@KFA) and WBC (@Purdue Univ.) continues to try to understand the dominant effects and timescales

10-4

10-3

10-2

10-1

100

101

0 100 200 300 400 500 600

Inte

nsity

[a.

u.]

Time [s]

ID

IBeI/ID

ICD/ID(near)-ICD/ID(far)

20060322

Be/C = 83±1 sec

PISCES



No influence of Ar on Be/C mitigation process

Comparison of CD band decay during Be seeding on C target: with and without added Ar

High ion energy case

Y(D on Be) ~3e-2, Y(Ar on Be) ~2e-2

Low ion energy case

Y(D on Be) ~1e-2, Y(Ar on Be) ~5e-5

This result may improve possibility of ITER achieving Q=10 with CFC divertor material.

PISCES



2

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

3422

o C

LIQUID

Be12

W Be2W

<1750o C

<2250o C

1287

o C

Be22

W

~952100 50o C

Stable

Be-W

alloys

Be12W

W sample

Be depositedlayer

BexW alloy growth has been measured in PISCES, temperatureand availability of Be are crucial factors, growth rate is likely not

a big issue for ITER. Retention still needs to be investigated.

Thin Be2W surface layers always exist, Be12W interlayers grow when sufficient surface Be exists

PISCES



From Beryllium experiments:

D/C = 0.0204 E –0.43 (D/C)0 exp(2268/Tc) Tc > 473K

Systematic codeposition studies have provided a means tocompare different codeposit retention properties

D/Be = (5.82 x 10-5)En1.17 0.2 (

D/Be)-0.21 0.1 exp(2273 311/Tc)

D/W = (5.13 x 10-8)* En1.85 0.4 * (

D/W)0.4 0.1 * exp(736 228/Tc)

D/C = 0.0204 E –0.43 (D/C)0 exp(2268/473) Tc < 473K

From Carbon literature:

From Tungsten experiments:

0.01 0.1 1

0.01

0.1

1

Exp

erim

enta

l D/B

e

Predicted D/Be

0.001

0.01

0.1

1

0 100 200 300 400 500 600 700

Mayer, J. Nucl. Mater. 1997Causey, J. Nucl. Mater. 2002Baldwin, J. Nucl. Mater. 2005

Temperature (C)

Be scaling removes(to a large extent)the scatter in the predicted D/Be levelin Be codeposits

PISCES



Codeposition scaling can provide insight into expected trends in ITER

• C retains less T at higher particle energy locations (first wall)

• C retains more T at lower particle energy regions (dome/divertor)

• Be retains less T at low particle energy (dome/divertor)

• Be retains more T at higher particle energy regions (first wall)

0.0001

0.001

0.01

0.1

1

0 20 40 60 80 100 120

D/WD/BeD/C

Incident Particle Energy (eV)

a)

Where will codeposits preferentially form?PISCES



Normalized deuterium release behavior of Be codeposits can be used to determine cost-benefit

relationship of increasing ITER bake-out temperature

0

20

40

60

80

100

0 100 200 300 400 500 600 700 800

Porous codepositDenser codeposit

Temperature (C)

240 C 375 C

PISCES



Future Directions of PISCES Program

• Retention in, and release from, mixed-material codeposits

• Mixed-species plasma-surface interactions

• Transient heating of elemental and mixed-material surfaces during plasma exposure using laser pulses

• Ablation plume physics– Material transport along B (vapor shielding)

– Material transport across B (laser blow off, macroscopic particles)

• Angular and energy distributions of sputtered W particles

• Addition of transient particle source to the PISCES facility (longer term direction, still conceptual)

PISCES



PISCES-B calibrated spectroscopic systems allow composition measurements of mixed-species plasma

• Typically, emission from neutrals are used to quantitatively determine sputtering yield, chemical erosion, evaporation rate, etc.

• Mixed-ion species plasma effects are as important as mixed-material effects, and almost equally as unexplored– Absolute Be impurity ion concentration in plasma

– Absolute He ion composition of plasma

– Absolute Ar ion radiator concentration in plasma

– C ion content during CD4 (or C2D2) still ongoing (but difficult)

– W under consideration (photon emission coefficients?)

• Not all plasma operating scenarios are consistent with absolute spectroscopic measurements

• PISCES-B systems allow for sculpting plasma composition

PISCES



PISCES

Mixing He with D-plasma suppresses blisters on W surface and reduces D-retention in W.

Pure D2 plasma (SRWM-3b)

D-fluence ~ 5e25 m-2, D ~ 1.0e22 m-2s-1, Ts ~ 573 K, Ei ~ 60 eV

D2-He mixture plasma (SRWM-4b)

D-fluence ~ 5e25 m-2, D ~ 0.9e22 m-2s-1, Ts ~ 573 K, Ei ~ 50 eV, nHe+/ne ~ 20 %

SRWM-3b D2

Time

500 1000 1500 2000 2500 3000

Par

tial P

ress

ure

(T

orr)

10-1

110

-10

10-9

10-8

Temperature (C)

500 1000 1500

He (Torr) D2 (Torr)

SRWM-4b D2-He(20%)

Time

500 1000 1500 2000 2500 3000

Temperature (C)

500 1000 1500

He (Torr) D2 (Torr)

He ions cluster and produce nano-bubbles in the implantation zone (MD predicted) that somehow reduce D diffusion into the bulk W



PISCES-B: pure He plasma

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

Nano-scale morphology develops on high temperature W surfaces in 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

PISCES



In D2−He plasmas, nano-morphology persists, but growth rate depends on He+ flux.

• The presence of D2 does not appear to affect nano-morphology structure.

• But growth rate can be affected.

• After a little more than 1 h of He plasma exposure in D2−0.1He, layer thickness is only ~0.5 m.

• Layer thickness, ~2.0 m in D2−0.2He is comparable to pure He.

D+He= 4–6×1022 m–2s–1

PISCES



He+(m-2s-1)

1021 1022 1023

Laye

r th

ickn

ess

( m

)

0.01

0.1

110

Ts= 1120 K

t = 3600 s

He

D2-He

Nano-morphology growth rate depends on He+ flux below 7×1021 m-2s-1.

• Two regions of interest: - Layer growth rate increases exponentially for He+ fluxes up to ~7×1021 m-2s-1.- Layer growth rate is optimal for He+ fluxes above this.

• D2 does not likely affect nano-structured layer growth rate.

- Lowest He+ flux data point (pure He) fits trend.

• Nano-structure growth may require surface saturation or mechanism that traps He.

ITER (Outer strike plate)A. Kukushkin, ITER Report, [ITER_D_27TKC6] 2008

PISCES


R. Doerner, EU PWI Task Force Meeting, Frascati, Italy, Oct. 27-30, 2008 8

A thick Be or C layer inhibits nano-morphology.

• At ~ 15 eV, PMI conditions favor net Be or C deposition. He induced nano-scopic morphology is inhibited.

• A ~Be12W alloy layer is observed on W in a D2−0.1He plasma w/ Be injection.

• A C rich layer forms on W in a D2−0.1He plasma w/ CD4 injection.

• At ~15 eV, the stopping range for both D+ and He+ is under 1 nm in Be or C. D+He= 3×1022 m–2s–1

PISCES



Q-Switched Nd:YAG Laser

1064nm

<850 mJ

~5 nsec pulse

<1 mrad

Two laser systems exist at PISCES to investigate simultaneous laser and plasma irradiation

Presently being used on PISCES-A

Developing safety systemsDebugging delivery opticsDiagnostic developmentCan double as diagnostic beam

Long-pulse Laser System

0.3-10 msec pulse

Epulse = 1.5 - 50 J

Up to 50 MJ/m2-sec1/2

Fiber Delivery Available

Being installed into PISCES-ASafety systems designed and being incorporated into PISCES-B enclosureOperational in PISCES-B by Jan. 09

PISCES



Effects of D Loading on W Surface Damage

F = 5x1022/m2

F = 5x1023/m2

F = 2x1024/m2

Fluence to surface before

laser pulse variedAbsorbed

Energy Impact ~45 MJ/m2 s1/2

(RW (=1064nm) ~ 70%)

Vbias= -125V=2x1022/m2-sec

Te=11eVne=2x1024/m3

Ts ~ 50°C

SA

MP

LE

PISCES



Something completely different, angular distributions of sputtered C atoms and clusters (Mo done, W underway)

• RF plasma source is used to investigate sputtering details

• Hiden EQP analyzer can differentiate mass and energy of incoming ions and neutrals

• Variation in target angle allows measurement of angular distribution of sputtered species (always normal incident plasma ions)

• Sputtering of C atoms and clusters are investigated with different noble gas plasma

E. Oyarzabal et al., J. App. Phys. 100(2006)063301

PISCES



Angular distribution of

sputtered atoms, dimers and

trimers become more cosine with lower mass ions

E. Oyarzabal et al., J. App. Phys. 104(2008)043305



Conclusion

• US-EU collaboration on mixed materials for ITER has been very successful (at least 26 publications)

• In 2007, PISCES entered the US-Japan TITAN collaboration which should promote US-EU-Japan PMI interactions

• PISCES participates in bilateral exchanges with ASIPP (China)

• ITER has expressed interest in also working directly with the PISCES Program

PISCES

R. Doerner, EU PWI Task Force Meeting, Frascati, Italy, Oct. 27-30, 2008 US-EU Collaboration on Mixed Materials for ITER: Past, Present and Future R. P.

Documents

eu collaboration us

useu collaboration

eu coordinator

eu pwi task force meeting

eu counterparts

pisces leader

samples pisces slide

decontamination of pisces