A1261817125LUkJg

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Helium Behavior andSurface Roughening of Solid
Tungsten Q. Hu, M. Andersen, S. Sharafat, and
N. Ghoniem University of California Los
Angeles High Average Power Laser Meeting Naval
Research Laboratory Washington, DC March 3-4, 2005
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Outline

• Helium Retention and Release
• IFE
• Experiments
• Modeling Surface Roughening
• Defect-diffusion-deformation (EWG)
• Stress-induced (ATG)
• thermo-mechanical Fatigue
• Conclusions Future Directions

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IFE Local APA (He/ W-atom) per shot SRIM
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Comparison of DPA (Displacement / W-atom)
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Comparison of APA (He/W-atom)
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HEROS Temperature Profile Input
UNC
Temperature temporal Profile (uniform through
the thickness)
Temperature ?C
2000
850
Snead, Oct.04
48
60
Time sec
IEC
Temperature 940?C (constant uniform)
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HEROS Temperature Profile Input
IFE
Temperature Temporal Profile (uniform through
the thickness)
Temperature ?C
1800
1200
0.2
1?10-3
Sharafat, June04
Time sec
Efforts are under way to reach Tmax2800oC
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IEC Bubble Concentration (cm-3) Evolution
E 30 keVT 940oC7x1015 He/cm2-s
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IEC Bubble Radius Evolution
100 nm
10 nm
1 nm
E 40 keVT 940oC7x1015 He/cm2-s
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UNC (angled carbon foil) Bubble Concentration
(cm-3)
E 800 kev - 1200 keV T 850oC 2000 oC
He 3x1016 He/m2
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UNC Bubble Radius Evolution
E 800 kev - 1200 keV T 850oC 2000 oC
He 3x1016 He/m2
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IFE Bubble Concentration (cm-3) Evolution
Energy Impl. Profile Debris Burn
Tmax1800oC
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IFE Bubble Radius Evolution
Energy Impl. Profile Debris Burn
Tmax1800oC
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Comparison of Bubble Density Range During a Pulse

1016
1015
1013
1012
1014
108
Cb (1/cm3)
IFE(Burn Debris)
3 um
UNC(carbon film)
1.7 um
IEC(40 keV)
0.3 um
Peak Bubble Density
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Why do Surfaces become Rough?

1. Does roughness increase or decrease?
2. What Determines the Length Scale?
3. Will Roughness Saturate?
4. Will Cracks form from Rough Surfaces?

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X-rays, Laser, and Ions all Induce Roughness
Latkowski et.al, JNM, submitted
Kawakami Ozawa, Applied Surface Science 218
(2003)
Nd-Yag Laser 532 nm
Renk, HAPL- Feb 04, Powder Met.
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Helium Implantation Induces Roughness!!
Tokunaga, et al., JNM, 329-333 (2004)
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Mechanisms of Surface Roughening
Emelyanov-Wa1graef -Ghoniem (EWG) Defect
diffusion coupled with deformation
Asaro-Tiller-Grinfeld (ATG) Balance between
surface strain (destabilizing) and curvature
(stabilizing)
Phys.Rev.L, in pres
D. Walgraef, N.M. Ghoniem, and J. Lauzeral,
"Deformation Patterns in Thin Films Under Uniform
Laser Irradiation", Phys. Rev. B, 56, No. 23
15361-15377 (1997). PDF J. Lauzeral, D.
Walgraef, and N.M. Ghoniem, "Rose Deformation
Patterns in Thin films Irradiated By Focused
Laser Beams", Phys. Rev. Lett. 79, No. 14
2706-2709 (1997).
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Fatigue cracking is initiated at
extrusions/inclusions which are formed by
Persistent Slip Bands (PBS's)
Ma and Laird, 1989
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Asaro-Tiller-Grinfeld (ATG) Instability
ya cos(wx)
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Asaro-Tiller-Grinfeld (ATG) Instability (cont.)
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Unstable Region
Stable Region
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Unstable Region
Stable Region
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Roughness Growth for HAPL Target
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Roughness Decay for Xapper
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Conclusions Future Directions

• Both UNC and IEC cover different regions of the
  APA and DPA phase space, however
• UNC Bubble concentration are lower than IFE
  (UNC1015 /cm3 IFE 1016 /cm3 )
• IEC Bubbles densities are comparable with IFE,
  however they are very close to the surface
• Based on Experiment plus IFE simulated HEROS
  results, high helium recycling coefficients may
  be achieved for IFE Tungsten Armor
• Impact of large simultaneous damage caused by
  D, T n ?
• Qualitative understanding of surface roughening
• Role of defect-induced stresses on roughness?
• Plan full-scale modeling for thermaldefectsurfac
  e evolution for IFE Dragonfire, Xapper, and
  Rhepp experiments (Mike Andersen thesis topic).
• Does roughness saturate, or does it lead to
  cracks?
• Modeling fatigue failure internal cracking with
  Dislocation Dynamics.

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Backup Files
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Bubble Kinetics of HEROS

• The He-Bubble Release code (HEROS) now includes
  all major Bubble Kinetics phenomena.

HEROS Bubble Kinetics includes

1. Random Walk
2. Migration in Temp. Gradient
3. Bubble Volume Diffusion
4. Bubble Surface Diffusion
5. Bubble Coalescence (Brownian)
6. Bubble Coalescence (dT/dx)
7. Bubble Loss at Free Surfaces
8. Bubble Loss to Grain Boundaries

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4He Debris and Burn Spectra
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Bubble Kinetics
Reaction
By Vol Diffusion
Drift
By Surf Diffusion
By Vol Diffusion
Coalescence
By Surf Diffusion
Surface Loss
In first 0.1?m
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HEROS Spatial Model Includes
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Determine APA and DPA Profiles in W per Shot
APA He-atom / W-atom DPA Displacement /
W-atom (damage)

• SRIM Input - Ion Type, Ion Energy, Target
  MaterialOutput - DPA/ion, Ion Range, other
  damage statistics
• Threat data is only known at specific ion
  energies.
• Pick small bin-size to interpolate between known
  data points.
• Add Damage and Ion Range of all energies and
  interpolate to get DPA and APA distributions in
  target material.

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IFE Local DPA (Displacement / W-atom) SRIM
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IEC Local APA (He/ W-atom) SRIM
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IEC Local DPA (Displacement / W-atom) SRIM
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UNC (angled carbon film) Local APA (He/ W-atom)
SRIM
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UNC (angled carbon film) Local DPA (Displacement
/ W-atom) SRIM
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Baklava Structure of RHEEP Exposed W-Samples
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Self Diffusion in Tungsten
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Parameters
Parameter Value Units
g 23 N/m
E 411 GPa
Qs 3 (IFE) 5 (Xapper) eV/ atom
W 3.45 x 10-29 m3
rs 6.25 x 1018 m-2
P. Bettler and F. Charbonnier, Activation
energy for the surface migration of tungsten
atoms in the presence of a high-electric field,
Phys. Rev., Vol 119(1), p.85-93, 1960. Qs 3.14
eV without field, and 2.44 eV with field.