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R. Parker, (R. Scelle), (S. Gilliam), and N. R. Parikh

Helium Retention in nano-Porous Tungsten Implanted with Helium Threat Spectrum Mimicking IFE Reactor Conditions. R. Parker, (R. Scelle), (S. Gilliam), and N. R. Parikh University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3255 R. G. Downing

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R. Parker, (R. Scelle), (S. Gilliam), and N. R. Parikh

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  1. Helium Retention in nano-Porous Tungsten Implanted with Helium Threat Spectrum Mimicking IFE Reactor Conditions R. Parker, (R. Scelle), (S. Gilliam), and N. R. Parikh University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3255 R. G. Downing National Institute of Standards and Technology, Gaithersburg, MD 20899-3460 Scott O’Dell Plasma Processes, Inc., 4914 Moores Mill Rd., Huntsville, AL 35811 G. Romanoski, T. Watkins, L. Snead Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831-6138, USA • Summary of work coordinated by Nalin Parikh (UNC) and presented by Lance Snead at the October 30,31 High Average Powered Laser Program Review meeting at the Naval Research Laboratory, Washington D.C.

  2. Outline of the Talk • Introduction – IFE conditions & He threat spectrum • Objective – Minimizing He retention • Experimental facilities – UNC-CH / NIST • Previous results – 1.3 MeV 3He implantation • He threat spectrum implantation (100 – 500 keV) • Helium retention results of nano-HfC W samples • Carbon implantation in W to form W2C • Ongoing and Proposed Research

  3. OBJECTIVE • Implant IFE helium threat spectrum in nano-porous HfC-W and study helium retention while mimicking IFE conditions. • C+ Implantation in W to Form W2C and Study 3He Diffusion Through W2C layer.

  4. Engineered Tungsten Armor Development • Vacuum Plasma Spray (VPS) forming techniques are being used to produce engineered tungsten armor. • The engineered tungsten is comprised of a primary tungsten undercoat and a nanoporous tungsten topcoat. • Nanometer tungsten feedstock powder is being used to produce the nanoporous tungsten topcoat. • The resulting nanoporous topcoat allows helium migration to the surface preventing premature failure. Nanoporous W Topcoat Primary W Layer Low Activation Ferritic Steel Schematic showing the VPSing of the engineered W armor. SEM image showing nanometer W feedstock powder produced by thermal plasma processing. Analysis has shown the average particle size is less than 100nm. This is one of two nanometer W feedstock materials used to produce the nanoporous topcoat.

  5. Engineered Tungsten Samples for Helium Implantation Experiments at UNC • To evaluate the effectiveness of the nanoporous W topcoat to prevent helium entrapment, engineered W deposits were produced with and without the nanoporous W topcoat. • For the samples without the nanoporous topcoat, two different micron size feedstock powders (-45/+20µm and -20/+15µm) were used to produce the primary W layer. • For the samples with the nanoporous topcoat, two different nanometer size feedstock powders (500 nm and 100 nm) were used. • HfC additions were made to the nanometer W feedstock powders to pin the grains and prevent grain growth.

  6. Experimental Facilities UNC – Chapel Hill, NC • 2.5 MV Van de Graaff accelerator3He implantation and helium retention measurements by nuclear reaction analysis (NRA) technique • 200 kV Eaton Ion Implanter NV-3204High fluence C+ implantation to study WCx formationHigh fluence He+ implantation to study sputtering Irradiation Damage study of multilayer dielectric mirrors NIST, Gaithersburg, MD • Nuclear reactor neutron sourceMeasure helium retention by neutron depth profiling (NDP) technique Ion Beam Laboratory University of North Carolina at Chapel Hill, NC

  7. Previous results of He retention in W • 1.3 MeV to a dose of 10203He/m2 at 850°C followed by a flash anneal at 2000°C • Same total dose was implanted in 1, 100, 500, and 1000 cycles of implantation and flash heating NRA results of 3He retention for single crystal and polycrystalline tungsten with a total dose of 1020 He/m2. Percentage of retained 3He compared to implanting and annealing in a single cycle. Ion Beam Laboratory University of North Carolina at Chapel Hill, NC

  8. Degrade the monoenergetic beam by transmission through a thin Al foil • Tilting the foil provides a range of degraded energies by varying the path length d through the foil where  = 0° is normal incidence Foil Tungsten E0 He beam E = E0 – Efoil t New work with helium threat spectrum • Al stopping power: ~330 keV/micron • 900 keV 3He beam through a 1.5 micron Al foil tilted 0 – 60° • Degraded energies: 100 – 500 keV Ion Beam Laboratory University of North Carolina at Chapel Hill, NC

  9. Threat spectrum implantation conditions • Implantation at 850°C with flash heating to 2000°C between implant steps or at the end of a single step implant. (Temp. measured by infrared thermometer.) • Total helium dose is divided by the no. of stepsPartial dose is implanted as a threat profile with the sample at 850°CSample heating 850°C  2000°C  850°C (10 s cycle) • Next implant step begins • LabVIEW automates foil tilt motions to implant correct dose at each position and controls sample temperature via power controller and infrared thermometer • NDP used to determine helium depth profiles and for comparison of total helium retention Ion Beam Laboratory University of North Carolina at Chapel Hill, NC

  10. NDP Neutron Depth Profiling • Technique: Neutron Depth Profiling (NDP) measures elemental concentration profiles up to a few micrometers in depth for elements that emit a charged particle following neutron capture. (R.G. Downing, et al., NIST J. Res. 98 (1993)109.) • Elements Analyzed: boron, lithium, helium, nitrogen and several additional light elements with less sensitivity. • Sample Environment: In an evacuated chamber, samples are irradiated with a beam of low energy neutrons. A small percentage of the emitted reaction particles are analyzed by surface barrier detectors to determine their number and individual energies. • Principles: The emission intensity is compared to a known standard to quantitatively determine the elemental concentration. The emitted particles lose energy at a predicable rate as they pass through the film; the total energy loss correlates to the depth of the reacting nucleus. • Advantage: NDP is non-destructive - allowing repeated determinations of the sample volume following different treatment processes. • Neutron beam flux at sample: ~7.5x108 n/cm2-s • Beam area: from a few mm2 to ~110 mm2 • Reaction: NDP utilizes the 3He(n,p)T reaction (5333 barns) and produces 572 keV protons and 191 keV recoil tritons. Si detectors Neutron monitor Neutron q Sample beam NDP Experimental Arrangement NDP of boron in silicon Depth range: 15 nm – 3.8 µm 1e22 1e20 1e18 1e16 1e14 1e12 XRF FTIR RBS NDP Detection limit (at/cm3) TOF-SIMS TXRF Dynamic SIMS 1000 Å 1µm 10 µm 100 µm 1 mm 1 cm Sample Dimension

  11. He retention for 1020 He/m2 in nano-W(<100nm Particles) Ion Beam Laboratory University of North Carolina at Chapel Hill, NC

  12. He retention comparisons for 1020 He/m2nano-porous (>500nm particles) W with HfC Ion Beam Laboratory University of North Carolina at Chapel Hill, NC

  13. Results of He3 Retention in nano-porous W Implanted with Helium Threat Spectrum Nano- porous W (<100 nm) samples showed very dramatic decrease in retention of He when high dose (1E20/m2) implanted sample was heated to 2000 C, 5 min. - Results confirm diffusion data of Wagner and Seidman- Phys Rev Lett 42, 515 (1979) Nano-cavity W (>500 nm) samples behaved very much like poly crystalline W. - nano particle size too big to have effective diffusion. Ion Beam Laboratory University of North Carolina at Chapel Hill, NC

  14. Carbon implantation in W to form WCx Shon Gilliam, Zane Beckwith, Richard Parker, Nalin Parikh (UNC-Chapel Hill) Greg Downing (NIST) Glenn Romanoski, Lance Snead (ORNL) Shahram Sharafat, Nsar Ghoniem (UCLA) Why are we interested? • Carbon ion irradiation and high temperatures in the first wall may lead to tungsten carbide formation • The presence of WCx may affect helium retention characteristics Objectives • Try to form W2C in W samples through high fluence implantation of C and high temperature annealing • Study how W2C effects hydrogen and helium retention/diffusion Ion Beam Laboratory University of North Carolina at Chapel Hill, NC

  15. XRD Spectra of C+ implantation into W to form W2C under various implantation conditions GM2 W2C Formation • GM2 100 keV 1.4e19 C/cm2 at RT 2000C/5min. • GM3 1.5 MeV 3.5e17 C/cm2 at RT 2000C/5min. • P04637 (threat spectrum) 1e18 C/cm2 at RT 2000C/5min.

  16. Summary of W2C formation study • 100 keV C implantation shows new XRD peaks compared to unimplanted W • Need to establish conditions for W2C formation for samples implanted with C threat-spectrum • Need to confirm that new peaks indicate W2C formation • XTEM to observe microstructure of new phase • After the phase is identified, implant H and He threat spectra to study retention

  17. Proposed Research • Reproduce He3 retention in nano-porous W • In cooperation with Plasma processes, Inc. (Scott O’Dell) and NIST (G. Downing) • Formation of Tungsten Carbide • UNC (Parikh,et al), ORNL (G. Romanoski) and UCLA (S. Sharafat, N. Ghoniem) • Accrual of carbon in near surface volumes of tungsten. • Damage phenomena associated with the implantation of Carbon • Mobility of carbon to the W/steel interface by grain boundaries and splat boundaries (for plasma sprayed tungsten).  This route should be at least 10X faster than bulk diffusion through tungsten. • Effect of Carbide on Diffusion and Surface Integrity • Implantation and carbide formation, UNC (Parikh, et al) • Thermal Fatigue and Thermal Stability (Romanoski, et al ORNL) • Modeling of diffusion and release of helium

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