TUNGSTEN FOAM: 1 Transient Thermal Analysis 2 Helium Management

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TUNGSTEN FOAM(1) Transient Thermal
Analysis(2) Helium Management
Shahram Sharafat and Nasr M. Ghoniem Contributors
Qyuiang Hu and Tony Tan University of California,
Los Angeles (UCLA) High Average Power Laser
Program Workshop E-Meeting June 6, 2003
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Outline

• W-Foam
• Getting the right Foam by Materials Design?
• Thermal Conductivity ?
• Transient and Steady State Thermal Response
• Helium Management
• Effective He-Diffusion
• He-Recycling Coefficient of W-Foam

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Current-Technology W-Foam Samples
ULTRAMET shipped the following foam samples to
LLNL and Sandia in May
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W-Foam Samples
Cross Section of a Foam Ligament (ULTRAMET)

• Why Test Other Materials ?
• W-Foam has carbom-core
• Forms carbides at high T
• Enough C to carburize all W
• The XAPPER and RHEEP tests will also evaluate
  other non carbide forming materials.
• Later ULTRAMET is to investigate high T
  (gt2300oC) hydrogen atmosphere to remove carbon
  from W-foam

RVC Carbon-Core (1-2 um)
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W-Foam Thermal Conductivity Estimates
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FEM-Based Thermal Conductivity Estimates
These estimates do not include 1) Large-scale
3-D effects (-) 2) Photon scattering
inside foam ()
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FEM-Based Thermal Diffusivity Estimates
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W-Foam Material Design Parameters
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Make Use of the C-Core in W-Foam?
Klett has used a process of graphitization
process to raise the thermal conductivity of the
carbonized foams from 12 W/m K to 50 - 150 W/m K.
James Klett, et al., High-thermal-conductivity,
mesophase-pitch-derived carbon foams effect of
precursor on structure and properties, Carbon
38 (2000) 953973.
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High k W-Foams ?

• Graphitize the RVC prior to building up
  W-ligaments.
• Deposit an Ir or Re coating on the graphitized
  foam skeleton as a diffusion barrier to prevent
  WC formation
• Build the ligaments on the high conductivity
  graphitized skeleton.
• ISSUES Neutron damage, Tritium retention

W-Ligament
Ir or Re Diffusion Barrier
Graphitized RVC Carbon-Core (1-2 um)
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Transient Thermal Response of Foam

• Need a 3-D Foam Model
• Homogenization in 1-D models can be
  misleading!
• Start with a simple Cubic Cell Structure

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Modeling Foam Transient Thermal Response

• FIRST Benchmarking 3-D with 1-D Analysis

Jake Blanchard, UWM, HAPL-Meeting Dec. 2002
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Foam Model forTransient Thermal Response
(SLoad areas Cube Footprint)
Loaded Volumes
W-Foam

• Requires 3-D Model
• Foam ModelCubic-Cell 200 ppi 25 dense
• Use temperature dependent solid W properties

0.5 mm
ODS Steel
25 um
1 mm
LAFS Steel
2 mm
125 um
Solid Model for FEM
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W-Foam Transient Thermal Response
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Temperature History of the Top W-Ligament
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Steady StateTemperatures

• Loading
• 41 MJ / shot? 0.39 MW/m2 average surface heat
  load for a 6.5 m chamber
• hcoef 10,000 W/m2-K
• Tcool 400oC
• Tungsten
• (1) kf k (W)
• (2) kf 0.5 k (W)
• Steady state
• (1) Tmax 493oC
• (2) Tmax 518oC

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Helium Management

• Use Threat Spectra/SRIM for helium distributions
• Use 3-D transient temperature profiles in
  W-Ligaments
• Use steady state radiation damage model based
  effective diffusion coefficient during
  implantation (lt3.75e-6 s)
• Estimate helium recycling coefficient

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Effective He-Diffusion Coefficients in
WSteady-State Radiation Theory (Ref. 1 )
1 Ghoniem, Sharafat, Williams, and Mansur (JNM
117 1983 96-105). 2 Wilson, Bisson (Radiat.
Eff. 19 1973 53/8). 3 Takamura (Radiation
Eff. Letters 43 No.2 1979 69/73). 4
Smedskjaer, Loper, Chaseo, Siegel (Mater. Res.
Soc. Symp. Proc. 41 1985 57/62).
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Effective He-Diffusion Coefficients in
WSteady-state theory (Ref. 1 )
EHe 0.2 migration Do 10-3 cm2/s Tlt848 K
EHe-eff-m EHe-interstial (0.2 eV)
848ltTlt1700 K EHe-eff-m EV-m (1.9 eV) Tgt1700
K EHe-eff-m EHeV-B EHe-m EV-F (0.49 eV)
1 Ghoniem, Sharafat, Williams, Mansur, JNM,
117(1983)96-105
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Effect of Temperature on Effective He-Diffusion
Coefficients in W (Steady-state theory)
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He-Diffusion in Top W-Ligament
He-Diffusion in Top W-Ligament
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He-Diffusion Length in Top W-Ligament
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Helium Diffusion

• Helium Diffusion Profiles

Implantation Zone (0 5 um) D-He 10-14 to
10-13 cm2/s
Damage Free Zone (5 25 um) D-He 10-4 cm2/s
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Helium Diffusion Profiles

• Helium Diffusion Profile of Implanted Zone on
  log-scale

Implantation Zone (0 5 um) D-He 10-14 to
10-13 cm2/s
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Helium Fluxes from Front Back Ligament
Surfaces

• Ligament Back Side
• 9.6x1016 per shot

• Ligament Front Side
• 1.2x1015 per shot

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Helium Fluxes out of Front Back Ligament
Surfaces

• Recycling coefficient for the back side is about
  66
• Estimates are based on 1D need to account for
  Helium loss through the 2 side-walls.

Front
25 um
Back
He out

• More detailed calculations are needed to
  establish total recycling coefficient.

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Conclusions

• W-Foam samples supplied to LLNL and Sandia.
• W-foams have low k (5-15 W/m-K)
• May be enhanced by foam design
• Thermal diffusivity determines transient
  response.
• 3D Thermal transient analysis of W-foam shows
  promising results
• Surface loads are distributed onto several layers
• Maximum temperatures are not much different from
  1-D bulk-W.
• Steady-state analysis with foam indicates maximum
  average temperature rise of 100oC compared to
  35oC for bulk-W coatings.
• Diffusion of Helium during irradiation pulse
  (3.75x10-6 s) is slow, however, during the off
  time diffusion is rapid (assumes no bubble
  formation, no radiation damage, etc.).
• Release rates of Helium from the side-walls and
  the back side of the ligament show high
  He-recycling coefficients (more detailed analysis
  to be done).

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W-Foam Detail
Future FEM analysis should include details such
as shown below