1. Helium Behavior and Surface 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

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

3. IFE: Local APA (He/ W-atom) per shot SRIM:

4. Comparison of DPA (Displacement / W-atom):

5. Comparison of APA (He/W-atom):

6. 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)

7. HEROS: Temperature Profile Input
IFE
Temperature Temporal Profile: (uniform through the thickness)
current
goal
Temperature C
1800
1200
Sharafat, June’04
110-3
0.2
Time sec
Efforts are under way to reach Tmax=2800oC

8. IEC: Bubble Concentration (cm-3) Evolution
6x1017 He/cm °C
1 mm
Helium
E = 30 keV T = 940oC 7x1015 He/cm2-s

9. IEC: Bubble Radius Evolution
100 nm
10 nm
1 nm
E = 40 keV T = 940oC 7x1015 He/cm2-s

10. UNC (angled carbon foil): Bubble Concentration (cm-3)
Snead, Oct. ‘04
Helium
E = 800 kev keV; T = 850oC – 2000 oC ; He = 3x1016 He/m2

11. UNC: Bubble Radius Evolution
10 nm
100 nm
1 nm
E = 800 kev keV; T = 850oC – 2000 oC ; He = 3x1016 He/m2

12. IFE: Bubble Concentration (cm-3) Evolution
current
planned
Helium
Energy & Impl. Profile: Debris + Burn; Tmax=1800oC

13. IFE: Bubble Radius Evolution
10 nm
1 nm
Energy & Impl. Profile: Debris + Burn; Tmax=1800oC

14. Comparison of Bubble Density Range During a Pulse :
108
1012
1013
1014
1015
1016
Cb (1/cm3)
IFE (Burn + Debris)
~ 3 um
UNC (carbon film)
~ 1.7 um
IEC (40 keV)
~ 0.3 um
Peak Bubble Density

15. Why do Surfaces become Rough?
Does roughness increase or decrease?
What Determines the Length Scale?
Will Roughness Saturate?
Will Cracks form from Rough Surfaces?

16. 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.

17. Helium Implantation Induces Roughness!!
Tokunaga, et al., JNM, (2004)

18. 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: (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: (1997).

19. Fatigue cracking is initiated at extrusions/inclusions which are formed by Persistent Slip Bands (PBS's)
Ma and Laird, 1989
Surface roughness due to PSB/surface interaction in a copper crystal fatigue tested. Strain amplitude of 2 x10-3, cycles [12, p.328].

20. Asaro-Tiller-Grinfeld (ATG) Instability
y=a cos(wx)

21. Asaro-Tiller-Grinfeld (ATG) Instability (cont.)

22. Unstable
Region
Stable
Region

23. Unstable Region
Stable Region

24. Roughness Growth for HAPL Target

25. Roughness Decay for Xapper

26. 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 (UNC~1015 /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 thermal+defect+surface 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.

27. Backup Files

28. Bubble Kinetics of HEROS
The He-Bubble Release code (HEROS) now includes all major Bubble Kinetics phenomena. T1
T1 < T2 T2
Temperature
Distance
Volume
Diffusion
Surface
Bubble
HEROS Bubble Kinetics includes:
Random Walk
Migration in Temp. Gradient
Bubble Volume Diffusion
Bubble Surface Diffusion
Bubble Coalescence (Brownian)
Bubble Coalescence (dT/dx)
Bubble Loss at Free Surfaces
Bubble Loss to Grain Boundaries

29. 4He Debris and Burn Spectra
FIRST the “Burns”: start ~ 0.1ms; end ~1ms
FOLLOWED by Debris: start ~1ms; end ~ 2ms ?
Range in Solid Tungsten (mm)

30. Bubble Kinetics Reaction + Drift + Coalescence + Surface Loss
By Vol Diffusion:
+ Drift
By Surf Diffusion:
By Vol Diffusion:
+ Coalescence
By Surf Diffusion:
+ Surface Loss
In first 0.1m:

31. HEROS: Spatial Model Includes
Tungsten
Helium
100 mm
Precipitates
Grain Boundaries
Dislocation Lines

32. 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 Material Output - 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.

33. IFE: Local DPA (Displacement / W-atom) SRIM:

34. IEC: Local APA (He/ W-atom) SRIM:

35. IEC: Local DPA (Displacement / W-atom) SRIM:

36. UNC (angled carbon film): Local APA (He/ W-atom) SRIM:
Snead, Oct. ‘04

37. UNC (angled carbon film): Local DPA (Displacement / W-atom) SRIM:

38. Baklava Structure of RHEEP Exposed W-Samples
Renk, Oct’04
Dummer, 1998: as received Tungsten

39. Self Diffusion in Tungsten
Mostly along GB
Diffusion
much faster
along GB

40. Parameters Parameter Value Units g 23 N/m E 411 GPa Q*s 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.