r. doerner, 8 th eu pwi task force meeting, warsaw, poland, nov. 4-6, 2009 directions of the us-eu...

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

R. Doerner, 8th EU PWI Task Force Meeting, Warsaw, Poland, Nov. 4-6, 2009

Directions of the US-EU Collaboration on Mixed Materials for ITER

R. P. Doerner, M. J. Baldwin, E. Hollmann,

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

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



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

* Taken from 2008 US-EU PWI Task Force talk



US-EU collaboration is contributing to several ITPA DIV/SOL High Priority ITER R&D tasks

• Changes in retention due to mixed plasma species

• Tritium release increase during 240°C - 350°C bake

• Impact of material mixing on retention

PISCES



Different materials, heating profiles and implantation doses are being studied

10-10

10-9

10-8

10-7

0

100

200

300

400

500

600

700

800

0 1000 2000 3000 4000

Be2C_2 [3.0E17 D implanted - 3.35E16 D retained]

Time (s)

Six types of material – Be on W Be on CFC Be12W Be2C C on Be W on Be

Four implantation doses - 3 E 16 D atoms (at room temp.) 3 E 17 D atoms

3 E 18 D atoms 3 E 19 D atoms

10-10

10-9

10-8

10-7

0

200

400

600

800

1000

0 500 1000 1500 2000 2500 3000 3500

Be2C_3 [2.8E18 D implanted - 7.37E16 D retained]

Time[s]

350C

PISCES



Retention and release from mixed material samples with Be-containing overlayers

• 200 nm Be layers deposited on substrates at MEdC, Romania

• Alloys formed and verified at IPP, Garching

• Samples implanted at room temperature with 200 eV D ions at IPP, Garching to a fluence of 4-5 E22 D/m2 (~3 E18 D atoms)

• TDS performed on samples at PISCES, UCSD

• Assumes all D is released from samples by TDS at 800C (to be confirmed by post-TDS NRA at IPP, Garching)

0

20

40

60

80

100

Annealed to 240CAnnealed to 350CAnnealed to 800C

Be on W Be on CFC Be2C Be12W

Total Dreleased

1.3E17 1.3E17 7.4E16 5.2E16

PISCES



Annealing to 350C is ineffective for release from C layers

W layers retain very little implanted D

10-10

10-9

10-8

10-7

0

200

400

600

800

1000

0 500 1000 1500 2000 2500 3000 3500

W on Be_3 [3E18 D implanted, 9.5E15 retained]

Time[s]

10-10

10-9

10-8

10-7

0

200

400

600

800

1000

0 500 1000 1500 2000 2500 3000 3500

C on Be_3 [3E18 D implanted - 8.3E16 retained]

Time[s]

350 C

PISCES



W Temperature & PMI are coupled

NAGDIS-II: He plasmaD. Nishijima et al. JNM (2004) 329-333 1029• Surface morphology • Shallow depth• Micro-scale

PISCES-A: D2-He plasmaM. Miyamoto et al. NF (2009) 065035600 K, 1000 s, 2.0x1024 He+/m2, 55 eV He+

• Little morphology• Occasional blisters

(b) Under focused (c) Over focused

10nm

10nm

(a) Bright field image (under focused image)

PISCES-B: pure He plasma M.J. Baldwin et al, NF 48 (2008) 0350011200 K, 4290 s, 2x1026 He+/m2, 25 eV He+

NAGDIS-II: pure He plasmaN. Ohno et al., in IAEA-TM, Vienna, 20061250 K, 36000 s, 3.5x1027 He+/m2, 11 eV He+

100 nm (VPS W on C) (TEM)

~ 600 - 700 K > 2000 K~ 900 – 1900 K

• Surface morphology • Evolving surface• Nano-scale ‘fuzz’



A small amount of He (5-20%) in deuterium plasma results in suppression of blisters on W

[from M. Miyamoto et al., NF 49(2009)065035]

Plasma exposure conditions : fluence 5e25 m-2, 300ºC, Eion ~ 55 eV, 20% He.

PISCES



Mixed D/He plasma exposure creates nano-bubbles in the near surface of W and reduces D retention

TEM image of nano voids TDS of mass 4, He and D2

[from M. Miyamoto et al., NF 49(2009)065035]

PISCES



Mixed D/He reduces D migration in W at low temperature

date D Fluence

1026 D/m2

D retained

1020 D/m2

12/08 0.75 (+He) 0.109

12/08 1 3.77

12/08 0.5 3.84

03/08 1 3.27

03/08 0.1 2.37

0

0.001

0.002

0.003

0.004

-0.5 0 0.5 1 1.5 2 2.5 3

Depth (microns)

D/W

D+He 12/08 0.75E26 D/m2no He 12/08 1E26 D/m2no He 12/08 5E25 D/m2no He 03/08 1E26 D/m2no He 03/08 1E25 D/m2

W.R.WamplerSandia National Laboratories

200°C

With He

● Addition of He to the D plasma reduced D retention by about a factor of 35.

● With He, D retention is mainly at the surface,whereas without He, D retention peaks ~ 1 micron beneath the surface.

NRA measurements byW. Wampler - SNLA

1e21 D/m2 ~ 3 mg/m2

PISCES



Above 900 K, W ‘fuzz’ occurs.Fuzz is approx. 95% space

• SEM used to profile ‘fuzz’ layer thickness over sample surface.

• Geometric vol. of ‘fuzz’ layer est. (7.8 x10-10 m3 ±10%).

Distance from center of target (mm)

-10 0 10

Cro

ss s

ectio

nal h

eigh

t (

m)

-150

00

24

6 t = 3600 sEion = 30 eV

Ts=1120 K

He

nano-structuredlayer

W bulk

• ‘Fuzz’ layer removed. Mass change (Dm=0.87 mg ±1%).

Comp. w/ pure W, ( = 19.25 x103 kgm-3), ‘fuzz’ layer is 94 % porous.

PISCES



‘Fuzz’ growth consumes W bulk

22000 s, 1120 K60 eV He+ PISCES-Bpure He plasma

~50 ITER shots


~20 ITER shots


~4 ITER shots RN

061

5200

7

RN 0

9272

005

RN 0

6182

007

Confirmation of fuzz growth out of the surface, first suggested by Prof. Yoshida. This growth mechanism may present a concern for W divertor operation where surface fuzz may, or may not, withstand the harsh plasma bombardment environment.

PISCES



Effect of He plasma on various grades of W PISCES

Japanese ultra-fine-grain W



Re-crystalized W responds very differently.

Re-crystalization may lead to greater ‘space’ in grain boundaries, due to defect migration to grain boundaries, (i.e. grain growth). Such space permits deep ‘fuzz’ growth at grain boundaries and may affect adhesion of W grains.

PISCES



Evidence of surface grain ejection ?

30 o ~20 m

Surface

X-section

beam

beam

X-section

Surface

SR WHeT ~1120 Kt = 2.2 x104 sHe

+ ~5 x1022 m-2s-1

EHe+ ~ 50 eV

PISCES



Small pits ~1m, are found on UFG-W nano-‘fuzz’. Grain ejection?

UFG-W (1.5 wt% TiC)He, T ~1120 K, t = 3.6 x103 s, He

+ ~2.5 x1022 m-2s-1, EHe+ ~40 eV

30 o

beam

Surface

Small impressions in the surface that have also developed nano-‘fuzz’

Typically, nano-‘fuzz’ is uniform in appearance

PISCES



Angular distribution measurements of sputtered W atoms (flat surface done, fuzz 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 W atoms from flat and fuzzy surfaces (made in P-A) are being compared

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

PISCES



Erosion rate of W fuzz

• Measurements are underway to determine erosion yield and angular distribution of eroded W fuzz

0.01

0.1

1

0 100 200 300 400 500

W I/

Ar

II

Time [s]

Ei ~ 45 eV

Ei ~ 65 eV

Ei ~ 85 eV

Ei = 105 V

Integrated W atom surface loss rate from a nanostructured surface (in P-B)

Sputtered Ar on W angular distribution from a smooth surface in rf etcher

W fuzz

Smooth W

PISCES



PISCES collaborates in several areas within the EU fusion program

• MD simulations of Be chemical sputtering predicted ion energy dependence

• ERO modeling of mixed material effects

• JET ILW marker tiles being produced (with GA)

• W S/XB measurements

• Effects of nitrogen impurity seeding, performance test show PISCES can run N2 plasma (future direction)

MD simulations of D on Be predicted subsequent erosion measurements

PISCES

Exp. from D. Nishijima et al, PPCF 50(2008)125007.Sim. from C. Bjorkas, submit. to New J. Physics (2009).



UCSD, MIT and UC Berkeley recently received funding for a 5 yr. Plasma Science Center

• Center will focus on a multi-scale (experiment and modeling) approach to PMI

• Effort to focus on fundamental, rather than machine specific, PMI issues

• Collaborative possibilities abound

• Several postdoctoral positions available

PMI Center

r. doerner, 8 th eu pwi task force meeting, warsaw, poland, nov. 4-6, 2009 directions of the us-eu...

Documents

w fuzz

w pure w

c pisces slide

th eu pwi task force

w total d

retention pisces slide

d migration

2e16 pisces slide