In FY-07 Work has been in five general areas:

1 Managed by UT-Battellefor the Department of Energy HAPL Meeting Oct 30 -31st, 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 30-31 HAPL Review Meeting by Lance Snead

Oak Ridge National Laboratory


• 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.


BackgroundThe 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)• HfO2/SiO2, ZrO2/SiO2, and TiO2/SiO2 mirrors on SiO2 substrates.

• Neutron fluence: 1019 n/cm2, 270-300ºC.

• Excessive damage in HfO2/SiO2 and ZrO2/SiO2 mirrors, including flaking and crazing of films.

K. Vukolov(2005)

• TiO2/SiO2, ZrO2/SiO2 mirrors on KS-4V silica glass.

• Neutron fluence: up to 1019 n/cm2, 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 SiO2 substrates; suggested use of more damage resistant substrates: Al2O3 or MgAl2O4.

• Damage resistance is sensitive to fabrication techniques / conditions.


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/cm2 at 248 nm, 2 ns FWHM pulse

• Total neutron flux to mirror: ~1x1013 n/cm2s (first mirror) , ~1x1011n/cm2s (final)

- Total neutron fluence in IFE in one year, assuming 80 % plant availability = 2.5x1018 n/cm2 (final mirror) to 2.5x1020 n/cm2 (first mirror) –estimates based on earlier work by M. Sawan.

• Total dose rate to mirror: ~3x1012 p/cm2s (first mirror), ~6x1010 p/cm2s (final)


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).


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 SiO2.

• Films deposited by electron beam with ion-assist; Spectrum Thin Films, Inc.

Sample Quantity Film Thickness / Description

Sapphire substrates only 18 6 mm diameter x 2 mm thickness

Al2O3 monolayer on sapphire 18 ¼ thickness (36 nm)

SiO2 monolayer on sapphire 18 ¼ thickness (40 nm)

HfO2 monolayer on sapphire 18 ¼ thickness (27 nm)

Al2O3 / SiO2 mirror on sapphire 18 26 Bi-layers, 2036 nm total thickness

Al2O3 / HfO2 mirror on sapphire 18 14 Bi-layers, 924 nm total thickness

HfO2 / SiO2 mirror on sapphire 18 11 Bi-layers, 768 nm total thickness


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.


Ion ImplantationConditions

• 10 keV He ions at 0º tilt, and room temperature

• Implanted doses of 1018, 1019, 1020 and 1021 He/m2

• Use of a implantation mask to maximize sample usage

Monolayer and substrate only samples

SRIM calculations: implantation doses produce between 0.001 to 1 dpa of damage at the film / substrate interface.

SiO2 monolayer on Sapphire

6 m


• General inspection of films by optical and SEM:

No signs of delamination or blistering.

• A slight optical “graying” observed in the

1021 He/m2 implanted HfO2 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


Neutron Irradiation of 15 HAPL Capsules• All samples tested: mirror, monolayer and substrate only samples.

• HFIR irradiations at 1018, 1019 and 1020 n/cm2, 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.


Neutron Irradiation• Three samples from each mirror, monolayer and substrate irradiated in the HFIR core

to 1018, 1019 and 1020 n/cm2 (fast.)

• One order higher than Farnum, Two orders higher than Vukulov

• IFE Final Mirror 2.5 x 1018, IFE Final Mirror 2.5 x 1020

• 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


Neutron Irradiation

• The irradiated capsules were disassembled in the Low Activation Materials Design and Analysis (LAMDA) Laboratory.

• Capsule doses were between 4 and 450 mrem/h @ 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).


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 HfO2 / SiO2 mirrors are shown at right, all samples are similar.


Future Work: Post Irradiation ExaminationCenter 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 SC A T S Center for

Advanced

Thin-Film

Solar Cells


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

QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.

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

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 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

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.

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 ActivationFerritic 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.

Primary W Layer Nanoporous W TopcoatW(-45/+20µm)

Thickness: ~0.6mmW(-20/+15µm)

Thickness: ~0.6mmW(-45/+20µm) W(100nm) - HfC

Thickness: ~0.5mm Thickness: ~75µmW(-45/+20µm) W(500nm) - HfC

Thickness: ~0.5mm Thickness: ~50µm

V2-06-355 8

V2-06-450 8

None

Feedstock Powders Used to Produce the Engineered W ArmorID Number

No. of Samples

V2-06-443 8

V2-06-349 None 8

Experimental Facilities

UNC – Chapel Hill, NC• 2.5 MV Van de Graaff accelerator

3He 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 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 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.

• 1.3 MeV to a dose of 1020 3He/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

Ion Beam Laboratory


0.00

0.20

0.40

0.60

0.80

1.00

1.00E+17 1.00E+18 1.00E+19 1.00E+203He dose per cycle (m-2)

Relative

3 He retention Mono He in SCW

Threat Spec in PolyW

New work with helium threat spectrum

E0 He beam

Foil Tungsten

E = E0 – Efoil

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 incidenceè cos

t d =

• 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


Threat spectrum implantation conditionsIFE Helium Threat Spectrum

0 200 400 600 800 1000 1200 1400

Energy (keV)

Relative He fluence

• 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


• 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.

Neutro

n

Sample

bea

m

NDP Experimental Arrangement

NDNDPP

NDP of boron in siliconNDP of boron in siliconDepth range: 15 nm – 3.8 µmDepth range: 15 nm – 3.8 µm

Sample Dimension

TXRF

NDP

XRF

RBS

Det

ectio

n lim

it (a

t/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 1020 He/m2 in nano-W(<100nm Particles)

Ion Beam Laboratory


He retention comparisons for 1020 He/m2

nano-porous (>500nm particles) W with HfC

Ion Beam Laboratory


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


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



XRD Spectra of C+ implantation into W to form W2C 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.

W2C

Formation

GM2

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

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

AcknowledgementThis 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) 491-495.

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) 289-297.

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


In FY-07 Work has been in five general areas:

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