PISCES W fuzz experiments: A summary of work up to now. · PISCES Why do we care about fuzz? •W...
Transcript of PISCES W fuzz experiments: A summary of work up to now. · PISCES Why do we care about fuzz? •W...
![Page 1: PISCES W fuzz experiments: A summary of work up to now. · PISCES Why do we care about fuzz? •W is an excellent FW material. •Low sputter yield in detached plasma. •High melt](https://reader036.fdocuments.net/reader036/viewer/2022070720/5ee07e0aad6a402d666baad1/html5/thumbnails/1.jpg)
PISCES
FNST/PFC/MASCO meeting, UCLA Aug. 2-6, 2010
PISCES W fuzz experiments:A summary of work up to now.
M.J. Baldwin, R.P. Doerner, D. NishijimaUniversity of California, San Diego, USA
![Page 2: PISCES W fuzz experiments: A summary of work up to now. · PISCES Why do we care about fuzz? •W is an excellent FW material. •Low sputter yield in detached plasma. •High melt](https://reader036.fdocuments.net/reader036/viewer/2022070720/5ee07e0aad6a402d666baad1/html5/thumbnails/2.jpg)
PISCES
Why do we care about fuzz?• W is an excellent FW material.
• Low sputter yield indetached plasma.
• High melt point (3695 K).
• Low D/T inventory >700 K.
• ITER divertor‐liner/domeare to be fabricatedfrom W. TWsurf < 1000 K.
• In the DT phase, ITERdivertor will be‘all W metal’. TWsurf > 1000 K.
• But . . . . PMI research indicates that energetic He in contact w/ hot W will cause W fuzz.
• PISCES, Baldwin et al. NF 48 (2008)
• NAGDIS‐II, Takamura, et al. Plasma and Fusion Res. 51 (2006)
• LHD, Tokitani et. al. JNM 337–339 (2005)
• LP RF devices, Baldwin et al. 2010 PSI San Diego P1‐1
• GLADIS device ‐ IPP Garching, H Greuner(2009) personal comm.
• IEC device walls ‐ Univ. of Wisconsin, Zenobia, JNM 389 (2009)
• PILOT PSI, G. Wright, G deTemmerman, (2009) personal comm.
![Page 3: PISCES W fuzz experiments: A summary of work up to now. · PISCES Why do we care about fuzz? •W is an excellent FW material. •Low sputter yield in detached plasma. •High melt](https://reader036.fdocuments.net/reader036/viewer/2022070720/5ee07e0aad6a402d666baad1/html5/thumbnails/3.jpg)
PISCES
What causes fuzz?
5.47 eV4.15 eV
0.24 eV
W. Schilling, in Point Defects and Defect Interactions in Metals, Eds J.Takamura, M. Doyama, and M. Kiritani(North‐Holland, Amsterdam, 1982), p. 303.
In W, He will bind readily with:
• Vacancies (4.15 eV)Abd El Keriem et al. PR‐B 47 (1993) 14771
• Impurities (1‐3 eV). Kornelsen et al. JNM 92 (1980) 79
• Hei‐V.Abd El Keriem et al. PR‐B 47 (1993) 14771
• Interstititial He (~1 eV).Becquart et al. PRL 97 (2006) 196402‐1 (supported by calculation)
![Page 4: PISCES W fuzz experiments: A summary of work up to now. · PISCES Why do we care about fuzz? •W is an excellent FW material. •Low sputter yield in detached plasma. •High melt](https://reader036.fdocuments.net/reader036/viewer/2022070720/5ee07e0aad6a402d666baad1/html5/thumbnails/4.jpg)
PISCES
What causes fuzz?
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) (in press)600 K, 1000 s, 2.0x1024 He+/m2, 55 eV He+
• Little morphology• Occasional blisters
10nm
(a) Bright field image (under focused image)
PISCES‐B: pure He plasmaM.J. Baldwin et al, NF 48 3 (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’
![Page 5: PISCES W fuzz experiments: A summary of work up to now. · PISCES Why do we care about fuzz? •W is an excellent FW material. •Low sputter yield in detached plasma. •High melt](https://reader036.fdocuments.net/reader036/viewer/2022070720/5ee07e0aad6a402d666baad1/html5/thumbnails/5.jpg)
PISCES
Are any W or W alloy grades resilient to fuzz? Not yet.
PISCES, Baldwin et al. JNM (2010) in press
![Page 6: PISCES W fuzz experiments: A summary of work up to now. · PISCES Why do we care about fuzz? •W is an excellent FW material. •Low sputter yield in detached plasma. •High melt](https://reader036.fdocuments.net/reader036/viewer/2022070720/5ee07e0aad6a402d666baad1/html5/thumbnails/6.jpg)
PISCES
Can it get worse? Possibly.
PISCES,Baldwin et al.JNM (2010)in press
![Page 7: PISCES W fuzz experiments: A summary of work up to now. · PISCES Why do we care about fuzz? •W is an excellent FW material. •Low sputter yield in detached plasma. •High melt](https://reader036.fdocuments.net/reader036/viewer/2022070720/5ee07e0aad6a402d666baad1/html5/thumbnails/7.jpg)
PISCES
What does fuzz do the W surface?
22000 s, 1120 K60 eV He+
PISCES‐Bpure He plasma
~50 ITER shots
9000 s, 1120 K60 eV He+
PISCES‐Bpure He plasma
~20 ITER shots
2000 s, 1120 K60 eV He+
PISCES‐Bpure He plasma
~4 ITER shots
RN
061
5200
7
RN
092
7200
5
RN
061
8200
7
Comparable to
![Page 8: PISCES W fuzz experiments: A summary of work up to now. · PISCES Why do we care about fuzz? •W is an excellent FW material. •Low sputter yield in detached plasma. •High melt](https://reader036.fdocuments.net/reader036/viewer/2022070720/5ee07e0aad6a402d666baad1/html5/thumbnails/8.jpg)
PISCES
Growth rate of Fuzz? t1/2
t (s)0 5000 10000
Laye
r thi
ckne
ss, Δ
(μm
)0
5
Ts=1120 KHe
Ts=1320 KHe
Ts=1120 KD2-0.2He
• Δ=βt1/2, where β = 1.3×10–15m2s–1 at 1120 K.
• Alarming re‐growth rate, dΔ/dt= β/(2t1/2).
• Ablation, ELMS, etc causing reduced layer thickness δ, lead to re‐growth rate:(dΔ/dt)Δ= δ = β2/(2δ) depending on whether equilibrium can be maintained.
• Experiment to test this using pulsed laser heat loads underway.
![Page 9: PISCES W fuzz experiments: A summary of work up to now. · PISCES Why do we care about fuzz? •W is an excellent FW material. •Low sputter yield in detached plasma. •High melt](https://reader036.fdocuments.net/reader036/viewer/2022070720/5ee07e0aad6a402d666baad1/html5/thumbnails/9.jpg)
PISCES
• ‘Fuzz’ layer growth after 3600 s in D2‐He and pure He plasmas shows a trend.
• Layer growthrate increasesexponentiallyfor ΓHe+ up to~7×1021 m‐2s‐1.
• Layer growthrate is optimal above this.c
Does D affect ‘fuzz’, since He is a reactor minority species? No
Γ He+ (m-2s-1)1021 1022 1023
Laye
r thi
ckne
ss (
μm)
0.01
0.1
110
Ts= 1120 Kt = 3600 s
HeD2-He
ITER (Outer strike plate)A. Kukushkin, ITER Report, [ITER_D_27TKC6] 2008
![Page 10: PISCES W fuzz experiments: A summary of work up to now. · PISCES Why do we care about fuzz? •W is an excellent FW material. •Low sputter yield in detached plasma. •High melt](https://reader036.fdocuments.net/reader036/viewer/2022070720/5ee07e0aad6a402d666baad1/html5/thumbnails/10.jpg)
PISCES
How does ‘fuzz’erode? W/ lower Y.
• Fuzz produced on W by He plasma exposure over 800 s at 1150 K, Ei ~ 90 eV.
• Switch to He/Ar plasma at t = 0 s, & measure time evolution of W I emission in front of W target.
• Ysmooth(Ar+→W) ~0.05 @ Ei ~ 110 eV, by mass loss. (Agrees w/ TRIM).
• Yfuzzy= (0.05 / WI/ArII110 eV, smooth) x WI/ArII
• Why is the sputtering yield reduced?
• Porosity? Internal bubble?
• Not well understood.
![Page 11: PISCES W fuzz experiments: A summary of work up to now. · PISCES Why do we care about fuzz? •W is an excellent FW material. •Low sputter yield in detached plasma. •High melt](https://reader036.fdocuments.net/reader036/viewer/2022070720/5ee07e0aad6a402d666baad1/html5/thumbnails/11.jpg)
PISCES
Is there a growth/erosion equilibrium. Yes
0.9 μm
2.0 μm
2.2 μm
250 eV He+
200 eV He+
60 eV He+
0.01
0.1
1
10
100 1000 104
W fuzz @ 1120K
W fuzz growth Y PA = 3.4e-4 (250 eV)Y PA = 1.5e-4 (200 eV)
W fuzz layer thickness (nm)
x
Expected fuzz thicknessin one hour with no erosion(60 eV He+)
xx
• Growth rate ‐ Baldwin et al., NF 48(2008)
• W fuzz yield ‐Nishijima et al., PSI 19
• Exploring application of method to ITER W divertor conditions
Fuzz layers after 3600 s in He plasma at 1120 K
![Page 12: PISCES W fuzz experiments: A summary of work up to now. · PISCES Why do we care about fuzz? •W is an excellent FW material. •Low sputter yield in detached plasma. •High melt](https://reader036.fdocuments.net/reader036/viewer/2022070720/5ee07e0aad6a402d666baad1/html5/thumbnails/12.jpg)
PISCES
Fuzz and gaps? LOS or NLOS?
PISCES-A He plasma on W (0.5, 1.0, 1.5 mm) gap target
Ts = 1100 KTexp = 3600 sEion ~ 70 eVΓHe+ = 1019 cm-2s-1
25 mm
SEM section
‘fuzz’
bulk
11 m
m
0.5 mm 1.0 mm 1.5 mm
(in gaps)FUZZ
(on surface)
(non LOS)
• Benchmark gap target produced in PA.
• Currently collaborating with D Boridin of Forschungszentrum Jülich to model observations.
![Page 13: PISCES W fuzz experiments: A summary of work up to now. · PISCES Why do we care about fuzz? •W is an excellent FW material. •Low sputter yield in detached plasma. •High melt](https://reader036.fdocuments.net/reader036/viewer/2022070720/5ee07e0aad6a402d666baad1/html5/thumbnails/13.jpg)
PISCES
D Retention in fuzz? Very low!HELIUM
Time (s)
500 1000 1500 2000
m/e
= 4
par
tial p
ress
ure
(x
10-9
Tor
r)
01
23
45
Temperature (K)400 600 800 1000 1200
D2 on W w/ 'fuzz' layer
D2 -He(10%) on W
D2 on W
He - V binding(bubbleprecursers)
DEUTERIUM
Time (s)
500 1000 1500 2000m/e
= 4
par
tial p
ress
ure
(x
10-9
Tor
r)-9
Tor
r)
05
1015
20
Temperature (K)400 600 800 1000 1200
D2 on W 'fuzz' [-.- x10-- D /m2]
D2 -He(10%) on W [1.1 x1020 D /m2]
D2 on W [5.0 x1020 D /m2]
Fluence[D+] ~5 x1025 m-2, Ts ~420 K, Ei ~30 eVHELIUM
Time (s)
1000 2000 3000
m/e
= 4
par
tial p
ress
ure
( x
10-9
Tor
r)
05
1015
20
Temperature (K)500 1000 1500
D2 only [no fuzz]
D2 -He(10%) [fuzz]
He only [fuzz]
He 2
-10 -
V
DEUTERIUM
Time (s)
1000 2000 3000m/e
= 4
par
tial p
ress
ure
( x
10-9
Tor
r)-9 T
orr)
01
23
45
Temperature (K)500 1000 1500
D2 only [no fuzz]
D2 -He(10%) [fuzz]
He only [fuzz]
Fluence ~2 x1026 m-2, Ts ~1120 K, Ei ~50 eV
He n
>10 -
V
He
inte
rstit
ial ?
• Little or no D is detected during TDS when He is used as a pretreatment or admixture to/in D plasma.
• D inventory below detection limit (~1018 D/m2) in cases where ‘fuzz’ was exposed to D or D:He plasma.
• Fuzz seems to be a remarkable permeation barrier.
![Page 14: PISCES W fuzz experiments: A summary of work up to now. · PISCES Why do we care about fuzz? •W is an excellent FW material. •Low sputter yield in detached plasma. •High melt](https://reader036.fdocuments.net/reader036/viewer/2022070720/5ee07e0aad6a402d666baad1/html5/thumbnails/14.jpg)
PISCES
• Selected W samples exposed to the Magnetized Co‐axial Plasma Gun (MCPG) at Univ. of Hyogo, Japan.
• Energy density: ~0.3‐0.7 MJ/m2
• Pulse width: ~0.5 ms
• Ion energy for D+: ~30 eV
• ne ~1021 m‐3, Γi ~ 1‐2x1025 m‐2 s‐1
• Comparable to type I ELMs in ITER
How does fuzz take power loads?Initial tests encouraging.
![Page 15: PISCES W fuzz experiments: A summary of work up to now. · PISCES Why do we care about fuzz? •W is an excellent FW material. •Low sputter yield in detached plasma. •High melt](https://reader036.fdocuments.net/reader036/viewer/2022070720/5ee07e0aad6a402d666baad1/html5/thumbnails/15.jpg)
PISCES
Summary of fuzz PMI experiments.Pros Cons What Next?
• Self limited t1/2
growth at surface.
• Erodes with low sputter yield w.r.tbulk W.
• Very low hydrogen isotope retention.
• Good permeation barrier.
• Seemingly resilient to power loads.
• Fuzz will manifest in long pulse high T reactors w/ FW W.
• Unknown surface properties w.r.t W.
• Potential for enhanced material loss during transients.
• Surface and potential deep GB destruction.
• Found in gaps.
• HIGH Z dust?
• Materials modeling to understand growth mechanisms.
• Resilience/erosion under continuous transient loads
• Develop mitigation strategies (T control, heavy alloying etc … ? ?)
• Can we live with fuzz: Do the Pros outweigh Cons?