Surface Effects and Retention of Steady State 3 He + 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

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 3 He + to fluences of 5x10 16 cm -2 at ~850 °C and 4x10 17 and 5x10 18 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 3 He(d,p) 4 He nuclear reaction analysis (NRA) Retained He fluence, retention ratios and depth profiles were measured by 3 He(n,p)T neutron depth profiling (NDP) 2

UW 1.7 MeV Tandem Accelerator UW Ion Beam Assisted Analysis Techniques: Elastic Recoil Detection (ERD) & Nuclear Reaction Analysis (NRA) 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 He + /cm 2 O 4+ beam only penetrated 130 nm Tungsten Sample 2 MeV D + beam α-particle p (14.7 MeV) Solid-State Detector 500 μm Al foil NRA uses the 3 He(d,p) 4 He nuclear reaction D + beam easily penetrates the He implanted region He retention data was acquired for tungsten samples at implant fluences between 5x10 16 – 5x10 18 He + /cm 2 3

NIST Cold Neutron Facility and the Neutron Depth Profiling (NDP) Analysis Technique NDP uses a cold neutron source and the 3 He(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

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

Polycrystalline Tungsten Irradiated to 5x He + /cm 2 at ~850 ºC 1 μm Unirradiated 1 μm 5x10 16 cm -2 6

1 μm 5x10 18 cm -2 1 μm 4x10 17 cm -2 Polycrystalline Tungsten Irradiated with 3 He + to 4x10 17 and 5x10 18 cm -2 at ~1000 ºC 7

Single Crystalline Tungsten Irradiated to 5x He + /cm 2 at ~850 ºC 1 μm Unirradiated 1 μm 5x10 16 cm -2 8

1 μm 5x10 18 cm -2 Single Crystalline Tungsten Implanted with 3 He + to 4x10 17 and 5x10 18 cm -2 at ~1000 ºC 1 μm 4x10 17 cm -2 Pores 9

Comparison of Single & Polycrystalline Tungsten Implanted with 3 He + to 5x10 16 cm -2 at ~850 ºC 1 μm Single-crystallinePolycrystalline 10

Comparison of Single & Polycrystalline Tungsten Implanted with 3 He + to 4x10 17 cm -2 at ~1000 ºC 1 μm Single-crystallinePolycrystalline 11

1 μm Single-crystallinePolycrystalline Comparison of Single & Polycrystalline Tungsten Implanted with 3 He + to 5x10 18 cm -2 at ~1000 ºC 12

NRA and NDP Show Retained He Fluence Saturates at ~4x10 17 cm -2 in Tungsten NRA = Nuclear Reaction Analysis NDP = Neutron Depth Profiling 13

Comparing ERD with NRA & NDP Techniques Confirms Retained He Fluence Does Not Exceed ~4x10 17 cm -2 in Tungsten *R.F. Radel and G.L. Kulcinski (2007) * NRA = Nuclear Reaction Analysis NDP = Neutron Depth Profiling ERD = Elastic Recoil Detection 14

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 4x10 17 cm -2 15

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

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

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

Fluence to Full Power Day Equivalent (FPD) in the Reference HAPL Chamber 2.0 FPD8.5 FPD223 FPD10 19 cm FPD0.9 FPD22.3 FPD10 18 cm FPD 0.1 FPD 2.2 FPD10 17 cm -2 Full He + Spectrum 10 – 100 keV 10 – 30 keV *Reference HAPL chamber with 10.5 m radius and 5 Hz duty cycle 19

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

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

Future Work Carbon Velvet Spikes Length ~ 1 mm Diameter (base) ~ 35 μm 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 22 Photo courtesy of Thad Heltemes - UW

Conclusions The threshold for pore formation after 3 He + implantation in both SCW and PCW is observed between 5x x10 17 cm -2, becoming extensive by 5x10 18 cm -2 The retained helium fluence in tungsten saturates at ~4x10 17 He/cm 2 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

Questions Samuel Zenobia University of Wisconsin-Madison 1500 Engineering Drive Madison, WI (608)