Progress Since Last Meeting

1. Surface Effects and Retention of Steady State 3He+ Implantation in Single and Polycrystalline Tungsten S.J. Zenobia, G.L. Kulcinski, E. Alderson, G. Becerra, B. Cipiti, R. Radel, J. Shea, G. Downing, R. Cao, L. Snead, R. Noll, and D. Savage HAPL Meeting-LANL April 8th, 2008 Fusion Technology Institute University of Wisconsin-Madison

2. Progress Since Last Meeting • Three single-crystalline (SCW) and three polycrystalline (PCW) tungsten specimens were acquired from Dr. Lance Snead and ORNL • Both SCW and PCW were implanted in the UW IEC device with 30 keV 3He+ to fluences of 5x1016 cm-2 at ~850 °C and 4x1017 and 5x1018 cm-2 at ~1000 °C • Pre and post-irradiation SEM analysis was done on each sample to diagnose surface morphology changes • Helium retention fluences and retention ratios were measured in all specimens using 3He(d,p)4He nuclear reaction analysis (NRA) • Retained He fluence, retention ratios and depth profiles were measured by 3He(n,p)T neutron depth profiling (NDP) 2

3. 500 μm Al foil 2 MeV D+ beam Solid-State Detector p (14.7 MeV) Tungsten Sample α-particle UW Ion Beam Assisted Analysis Techniques: Elastic Recoil Detection (ERD) & Nuclear Reaction Analysis (NRA) • NRA uses the 3He(d,p)4He nuclear reaction • D+ beam easily penetrates the He implanted region • He retention data was acquired for tungsten samples at implant fluences between 5x1016 – 5x1018 He+/cm2 • Previous work by Radel used the ion beam for ERD analysis of HAPL samples • Helium retention and depth profile was determined for polycrystalline W between 1018 - 1019 He+/cm2 • O4+ beam only penetrated 130 nm UW 1.7 MeV Tandem Accelerator 3

4. NIST Cold Neutron Facility and the Neutron Depth Profiling (NDP) Analysis Technique • NDP uses a cold neutron source and the 3He(n,p)T nuclear reaction • Neutrons are ideal for depth profiling and measuring concentration (negligible energy loss) • He retention for tungsten samples was acquired from Greg Downing at the NIST facility 4

5. Results • Morphology changes (SEM) • Helium retention (NRA, NDP, & ERD) • Materials viability assessment 5

6. 5x1016 cm-2 1 μm 1 μm Polycrystalline Tungsten Irradiated to 5x10163He+/cm2 at ~850 ºC Unirradiated 6

7. 5x1018 cm-2 4x1017 cm-2 1 μm 1 μm 1 μm Polycrystalline Tungsten Irradiated with 3He+ to 4x1017 and 5x1018 cm-2 at ~1000 ºC 7

8. 5x1016 cm-2 1 μm Single Crystalline Tungsten Irradiated to 5x10163He+/cm2 at ~850 ºC Unirradiated 1 μm 8

9. 5x1018 cm-2 Pores 1 μm 1 μm Single Crystalline Tungsten Implanted with 3He+ to 4x1017 and 5x1018 cm-2 at ~1000 ºC 4x1017 cm-2 9

10. 1 μm 1 μm Comparison of Single & Polycrystalline Tungsten Implanted with 3He+ to 5x1016 cm-2 at ~850 ºC Single-crystalline Polycrystalline 10

11. 1 μm 1 μm Comparison of Single & Polycrystalline Tungsten Implanted with 3He+ to 4x1017 cm-2 at ~1000 ºC Single-crystalline Polycrystalline 11

12. 1 μm 1 μm Comparison of Single & Polycrystalline Tungsten Implanted with 3He+ to 5x1018 cm-2 at ~1000 ºC Single-crystalline Polycrystalline 12

13. NRA and NDP Show Retained He Fluence Saturates at ~4x1017 cm-2 in Tungsten NRA = Nuclear Reaction Analysis NDP = Neutron Depth Profiling 13

14. Comparing ERD with NRA & NDP Techniques Confirms Retained He Fluence Does Not Exceed ~4x1017 cm-2 in Tungsten * NRA = Nuclear Reaction Analysis NDP = Neutron Depth Profiling ERD = Elastic Recoil Detection 14 *R.F. Radel and G.L. Kulcinski (2007)

15. Observations on Retained He Fluence in Single and Polycrystalline Tungsten • Saturation of retained He fluence occurs prior to extensive surface morphology change • Maximum retained He fluence is observed near 4x1017 cm-2 15

16. Tungsten’s Helium Retention Ratio Decreases with Increasing Implant Fluences NRA = Nuclear Reaction Analysis NDP = Neutron Depth Profiling 16

17. All Techniques Indicate an Increased Retention Ratio of He in W with Decreasing Implant Fluence * NRA = Nuclear Reaction Analysis NDP = Neutron Depth Profiling ERD = Elastic Recoil Detection 17 *R.F. Radel and G.L. Kulcinski (2007)

18. Observations on the He Retention Ratio in Single and Polycrystalline Tungsten • Surface damage increases despite a decreasing He retention ratio 18

19. Fluence to Full Power Day Equivalent (FPD) in the Reference HAPL Chamber 10 – 30 keV 10 – 100 keV Full He+ Spectrum 0.1 FPD 1017 cm-2 2.2 FPD 0.02 FPD 1018 cm-2 22.3 FPD 0.9 FPD 0.2 FPD 1019 cm-2 223 FPD 8.5 FPD 2.0 FPD *Reference HAPL chamber with 10.5 m radius and 5 Hz duty cycle 19

20. Extensive Surface Damage Relatively Unaffected Summary of Examined Materials Viability (Cipiti, Radel, and Zenobia) SiC PCW PCW CCV SiC CCV 20

21. Observations on FW Candidate Materials for the HAPL Chamber • SCW, W-coated TaC foams, and PCW appear to be the most robust materials • SiC, velvet materials (examined to date), and W-Re alloys respond poorly to ion implantation • Abatement of the ion threat spectra is necessary to extend the lifetime of any of the examined materials to practical lifetimes 21

22. Carbon Velvet Spikes Length ~ 1 mm Diameter (base) ~ 35 μm Future Work Future Work Cont. ? • Depth profiling analysis for SCW and PCW specimens is currently underway • Focused ion beam (FIB) milling will be used to determine the penetration depth of pores below the tungsten surface • Surface erosion and roughness will be measured using optical profilometry to give mass loss estimates Photo courtesy of Thad Heltemes - UW 22

23. Conclusions • The threshold for pore formation after 3He+ implantation in both SCW and PCW is observed between 5x1016 - 4x1017 cm-2, becoming extensive by 5x1018 cm-2 • The retained helium fluence in tungsten saturates at ~4x1017 He/cm2 • The He retention ratio in tungsten decreases with increasing implant fluence, showing strong He trapping efficiency at low fluences • He+ abatement is required to extend the lifetimes of any of the IEC examined materials 23

24. Samuel Zenobia University of Wisconsin-Madison1500 Engineering DriveMadison, WI 53706(608) 265-8699zenobia@wisc.edu Questions