1Managed by UT-Battelle for the Department of Energy HAPL Meeting Oct st, 2007 Review of ORNL Collaborative Materials Development Work in Support of the High Average Power Laser Program In FY-07 Work has been in five general areas: Installation of Pulsed Electron Thermofatigue System (ORNL, Duty Talk) Continuation of Tungsten Armored Ferritic thermal stability (Romanoski-ORNL) Implanted Ion Effects (Parikh-UNC, Romanoski-ORNL, Sharafat-UCLA) Thermal Fatigue Testing of Tungsten Armored Ferritic (Snead-ORNL) Irradiation of Dielectric Mirrors (Leonard-ORNL, Lahecka-PSU, Parikh-UNC) Advanced Concepts Materials (Snead-ORNL, Sawan, et al. U. Wisc.) Presented at the October HAPL Review Meeting by Lance Snead Oak Ridge National Laboratory

2Managed by UT-Battelle for the Department of Energy HAPL Meeting Oct st, 2007 Background of work He implantation Neutron irradiation Future work Irradiation Effects on Dielectric Mirrors Keith Leonard, Lance Snead, and Joel McDuffee, ORNL Tom Lahecka, PSU Summary of work coordinated by Lance Snead and presented at the October 30,31 High Average Powered Laser Program Review meeting at the Naval Research Laboratory, Washington D.C.

3Managed by UT-Battelle for the Department of Energy HAPL Meeting Oct st, 2007 Background The use of dielectric mirrors offer significantly improved transmission of reflected electromagnetic energy. However, earlier work shows differing opinions as to the use of dielectric mirrors in nuclear environments. E.H. Farnum et al. (1995) HfO 2 /SiO 2, ZrO 2 /SiO 2, and TiO 2 /SiO 2 mirrors on SiO 2 substrates. Neutron fluence: n/cm 2, ºC. Excessive damage in HfO 2 /SiO 2 and ZrO 2 /SiO 2 mirrors, including flaking and crazing of films. K. Vukolov(2005) TiO 2 /SiO 2, ZrO 2 /SiO 2 mirrors on KS-4V silica glass. Neutron fluence: up to n/cm 2, 275 ºC. Dielectric mirrors showed no significant damage. Outcomes and recommendations of their work Fewer and thinner bi-layers improve resistance to environmental effects (thermal cycling and radiation tolerance). Poor performance from SiO 2 substrates; suggested use of more damage resistant substrates: Al 2 O 3 or MgAl 2 O 4. Damage resistance is sensitive to fabrication techniques / conditions.

4Managed by UT-Battelle for the Department of Energy HAPL Meeting Oct st, 2007 Mirror Requirements Reflectivity: > 99.8% at 248 nm, (99.5% from 238 to 258 nm) Absorption: < 500 ppm measured at 248 nm Scattering: total integrated scattering < 500 ppm at 633 nm Laser Damage Threshold: ~10 J/cm 2 at 248 nm, 2 ns FWHM pulse Total neutron flux to mirror: ~1x10 13 n/cm 2 s (first mirror), ~1x10 11 n/cm 2 s (final) - Total neutron fluence in IFE in one year, assuming 80 % plant availability = 2.5x10 18 n/cm 2 (final mirror) to 2.5x10 20 n/cm 2 (first mirror) –estimates based on earlier work by M. Sawan. Total  dose rate to mirror: ~3x10 12 p/cm 2 s (first mirror), ~6x10 10 p/cm 2 s (final)

5Managed by UT-Battelle for the Department of Energy HAPL Meeting Oct st, 2007 Environment Issues and Evaluation Techniques Differences in radiation and thermally induced swelling or contraction of the film layers or strain buildup between the first layers and substrate (visual inspection, ellipsometry). Changes in surface roughness (AFM). Irradiation / thermally induced structural changes within a given layer (microscopy, x-ray, ellipsometry). Irradiation / thermally induced mixing or formation of interlayer compounds (microscopy, x-ray). Reduction in peak reflectivity and shift towards lower wavelengths (spectrophotometry). Changes in optical absorption due to radiation induced defects (spectrophotometry).

6Managed by UT-Battelle for the Department of Energy HAPL Meeting Oct st, 2007 HAPL Dielectric Mirror Samples Test samples consisted of 3 dielectric mirror designs (> 99.8% reflectivity at 248 nm) along with monolayer films to evaluate film / substrate interactions. Higher damage tolerant sapphire substrates used instead of SiO 2. Films deposited by electron beam with ion-assist; Spectrum Thin Films, Inc. SampleQuantityFilm Thickness / Description Sapphire substrates only186 mm diameter x 2 mm thickness Al 2 O 3 monolayer on sapphire18 ¼ thickness (36 nm) SiO 2 monolayer on sapphire18 ¼ thickness (40 nm) HfO 2 monolayer on sapphire18 ¼ thickness (27 nm) Al 2 O 3 / SiO 2 mirror on sapphire1826 Bi-layers, 2036 nm total thickness Al 2 O 3 / HfO 2 mirror on sapphire1814 Bi-layers, 924 nm total thickness HfO 2 / SiO 2 mirror on sapphire1811 Bi-layers, 768 nm total thickness

7Managed by UT-Battelle for the Department of Energy HAPL Meeting Oct st, 2007 HAPL Dielectric Mirror Irradiations Ion implantation Monolayer and substrate only samples Examine tolerance of film / substrate prior to neutron radiation experiments. Performed by Nalin Parikh and Shon Gilliam, UNC-Chapel Hill. Neutron irradiation Substrate, monolayer and mirror samples Examine changes in optical properties of mirrors Irradiations performed at the High Flux Isotope Reactor (HFIR) at ORNL.

8Managed by UT-Battelle for the Department of Energy HAPL Meeting Oct st, 2007 Ion Implantation Conditions 10 keV He ions at 0º tilt, and room temperature Implanted doses of 10 18, 10 19, and He/m 2 Use of a implantation mask to maximize sample usage Monolayer and substrate only samples SRIM calculations: implantation doses produce between to 1 dpa of damage at the film / substrate interface. SiO 2 monolayer on Sapphire 6  m

9Managed by UT-Battelle for the Department of Energy HAPL Meeting Oct st, 2007 General inspection of films by optical and SEM:  No signs of delamination or blistering. A slight optical “graying” observed in the He/m 2 implanted HfO 2 monolayer sample.  May represent a significant loss of in transmission at 248 nm λ. Atomic Force Microscopy (AFM) data.  No changes in surface roughness between implanted and non-implanted regions for all samples / conditions. Possible future work: ellipsometry in determining changes in film properties following ion implantation. Ion Implantation Monolayer and substrate only samples

10Managed by UT-Battelle for the Department of Energy HAPL Meeting Oct st, 2007 Neutron Irradiation of 15 HAPL Capsules All samples tested: mirror, monolayer and substrate only samples. HFIR irradiations at 10 18, and n/cm 2, at 300ºC, samples sealed in He. Required the design of specialized holders to prevent the scratching of the optical surfaces. Samples are held only at the edges.

11Managed by UT-Battelle for the Department of Energy HAPL Meeting Oct st, 2007 Neutron Irradiation Three samples from each mirror, monolayer and substrate irradiated in the HFIR core to 10 18, and n/cm 2 (fast.) One order higher than Farnum, Two orders higher than Vukulov IFE Final Mirror 2.5 x 10 18, IFE Final Mirror 2.5 x Calculated mirror temperature 280 and 307ºC (comparable to Farnum/Vukolov work). Holders contain SiC thermometry for temperature measurement – to be determined. Temperature distribution Cross-section of holder with sample Sample Holder

12Managed by UT-Battelle for the Department of Energy HAPL Meeting Oct st, 2007 Neutron Irradiation The irradiated capsules were disassembled in the Low Activation Materials Design and Analysis (LAMDA) Laboratory. Capsule doses were between 4 and 450 contact (0.5 to 18 mrem/h at 30 cm) depending on the irradiated dose and sample type. Capsules were disassembled with remaining FY-07 funds, post-irradiation examination has been limited in the FY. The LAMDA Laboratories allow for the examination of low activation materials without the need for remote manipulation (~4500 sq ft. and over 30 different characterization tools).

13Managed by UT-Battelle for the Department of Energy HAPL Meeting Oct st, 2007 Neutron Irradiation Samples removed from aluminum holders; visually inspected. Changes in (sapphire substrate) color observed with increasing neutron exposure.  Non-irradiated controls are all clear to visible light.  Highest dose samples nearly opaque to visible light. All surfaces remain visibly smooth with no visible signs of cracking or delamination. Examples of the HfO 2 / SiO 2 mirrors are shown at right, all samples are similar.

14Managed by UT-Battelle for the Department of Energy HAPL Meeting Oct st, 2007 Future Work: Post Irradiation Examination Center for Advanced Thin-Film Solar Cells (CATS) Laboratory Newly constructed facility at ORNL Now completed and in operation Available Instrumentation Spectroscopic and transmission 2- modulator generalized ellipsometers characterize thin film thickness changes strain fields between films and substrate Perkin-Elmer Lambda Spectrophotometer 180 to 300 nm wavelength Integrating sphere (specular and non- specular reflectance and transmission) Veeco DekTak Profilometer C A T S Center for Advanced Thin-Film Solar Cells

15Managed by UT-Battelle for the Department of Energy HAPL Meeting Oct st, 2007 Future Work: Post Irradiation Examination Thermal Cycling: Tests on control materials to evaluate stability of films and optical degradation following exposure to thermal cycling conditions. Film-Structural Characterization: Cross-sectional transmission electron microscopy of irradiated mirrors. Evaluate the stability or damage sensitivity of the film layers in the dielectric mirrors, interfacial reactions, etc. Substrate-Structural Characterization and Temperature Monitors: Density change of substrate to be measured and SiC temperature monitors to be processed to determine irradiation temperature. Laser Damage Threshold Testing: Further collaboration with T. Lehecka, Penn State Electro-Optics Center. Perform initial testing on unirradiated controls, followed by irradiated samples

R. Parker, (R. Scelle), (S. Gilliam), and N. R. Parikh University of North Carolina at Chapel Hill, Chapel Hill, NC R. G. Downing National Institute of Standards and Technology, Gaithersburg, MD Scott O’Dell Plasma Processes, Inc., 4914 Moores Mill Rd., Huntsville, AL G. Romanoski, T. Watkins, L. Snead Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN , USA Helium Retention in nano-Porous Tungsten Implanted with Helium Threat Spectrum Mimicking IFE Reactor Conditions 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.

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

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 W 2 C and Study 3 He Diffusion Through W 2 C layer.

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. Low Activation Ferritic Steel Primary W Layer Nanoporous W Topcoat 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.

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.

Experimental Facilities UNC – Chapel Hill, NC 2.5 MV Van de Graaff accelerator 3 He implantation and helium retention measurements by nuclear reaction analysis (NRA) technique 200 kV Eaton Ion Implanter NV-3204 High fluence C + implantation to study WC x formation High fluence He + implantation to study sputtering Irradiation Damage study of multilayer dielectric mirrors NIST, Gaithersburg, MD Nuclear reactor neutron source Measure helium retention by neutron depth profiling (NDP) technique Ion Beam Laboratory University of North Carolina at Chapel Hill, NC

Previous results of He retention in W NRA results of 3 He retention for single crystal and polycrystalline tungsten with a total dose of He/m 2. Percentage of retained 3 He compared to implanting and annealing in a single cycle. 1.3 MeV to a dose of He/m 2 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 Ion Beam Laboratory University of North Carolina at Chapel Hill, NC

New work with helium threat spectrum E 0 He beam FoilTungsten E = E 0 –  E foil t 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 Al stopping power: ~330 keV/micron 900 keV 3 He 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

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 steps Partial dose is implanted as a threat profile with the sample at 850°C Sample 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

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: ~7.5x10 8 n/cm 2 -s Beam area: from a few mm 2 to ~110 mm 2 Reaction: NDP utilizes the 3He(n,p)T reaction (5333 barns) and produces 572 keV protons and 191 keV recoil tritons. Neutron Sample  beam NDP Experimental Arrangement NDP NDP of boron in silicon Depth range: 15 nm – 3.8 µm Sample Dimension TXRF NDP XRF RBS Detection limit (at/cm 3 ) TOF-SIMS Dynamic SIMS FTIR 1000 Å 1µm 10 µm 100 µm 1 mm 1 cm 1e22 1e20 1e18 1e16 1e14 1e12 Neutron monitor

He retention for He/m 2 in nano-W(<100nm Particles) Ion Beam Laboratory University of North Carolina at Chapel Hill, NC

He retention comparisons for He/m 2 nano-porous (>500nm particles) W with HfC Ion Beam Laboratory University of North Carolina at Chapel Hill, NC

Results of He 3 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/m 2 ) 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

Carbon implantation in W to form WC x 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 WC x may affect helium retention characteristics Objectives Try to form W 2 C in W samples through high fluence implantation of C and high temperature annealing Study how W 2 C effects hydrogen and helium retention/diffusion Ion Beam Laboratory University of North Carolina at Chapel Hill, NC

30Managed by UT-Battelle for the Department of Energy HAPL Meeting Oct st, 2007 XRD Spectra of C + implantation into W to form W 2 C under various implantation conditions 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. W 2 C Formation GM2

Summary of W 2 C formation study 100 keV C implantation shows new XRD peaks compared to unimplanted W Need to establish conditions for W 2 C formation for samples implanted with C threat-spectrum Need to confirm that new peaks indicate W 2 C formation XTEM to observe microstructure of new phase After the phase is identified, implant H and He threat spectra to study retention

Proposed Research Reproduce He 3 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

Acknowledgement This research is supported under the US Department of Energy, High Average Power Laser Program managed by the Naval Reactor Laboratory through subcontract with the Oak Ridge National Laboratory. Publications S. Gilliam, S. Gidcumb, D. Forsythe, N. Parikh, J. Hunn, L. Snead, G. Lamaze, Helium retention and surface blistering characteristics of tungsten with regard to first wall conditions in an inertial fusion energy reactor, Nuclear Instruments and Methods B, 241 (2005) S. Gilliam, N. Parikh, S. Gidcumb, B. Patnaik, J. Hunn, L. Snead, G. Lamaze, Retention and surface blistering of helium irradiated tungsten as a first wall material, Journal of Nuclear Materials, 347 (2005) R. G. Downing, R. Parker, R. Scelle and N. Parikh, Helium Retention in Nano- Cavity Tungsten Implanted with Helium Threat Spectrum Mimicking IFE Reactor Conditions, American Nuclear Society (Nov. 2007) Ion Beam Laboratory University of North Carolina at Chapel Hill, NC