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IFT\P2008-088

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IFT\P2008-088

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  1. Progress on HAPL Foam Shell Overcoat FabricationPresented by Jared Hund1N. Alexander1, J. Bousquet1, Bob Cook1, D. Goodin1, D. Jasion1, R. Paguio1, K. Saito11General Atomics, Inertial Fusion Technology, San Diego, CA19th HAPL WorkshopUniversity of WisconsinMadison WIOctober 22 - 23, 2008 IFT\P2008-088

  2. Since the last HAPL meeting we have made progress on overcoats: • Improved surface defects on foam – which has resulted in fewer defects on the overcoat surface • Measured parameters important for fill cycle/tritium inventory • permeation rate at elevated temp • Built 2nd high capacity GDP(roto)coater for more experiments

  3. We are focusing on low yield steps of the foam target fabrication process ~90% DVB Droplet survival RF DVB Curing/Drying RF DVB Sphericity RF DVB at 3% NC 65% Wall uniformity (NC) DVB at 1% NC RF at 3% NC RF at 1% NC (zero yield) Foam fabrication cumulative yield (pre-coating)

  4. We are also focusing on the overcoat yield 65% Capsule fabrication cumulative yield DVB Foam Fabrication 11% RF HAPL Target DVB w/15 µm 0% Gas Retention RF w/15 µm 8% Thin High Z coating 5-10 µm CH Overcoat RF w/10 µm 0% Surface Finish DVB 0% RF 0% Foam + DT DT DT Vapor ~ 2.3 mm rad Foam layer: 0.18 mm thickness Divinyl Benzene (DVB) or Resorcinol-Formaldehyde (RF)

  5. We are working to reduce the overcoating thickness to 5-10 µm • We are continuing our parametric evaluation of GDP coating conditions on foam • Background pressure • Foam surface • Reactant flow rates • The essential function of the overcoating is to be permeable at RT yet hold the fuel at cryo • Test permeation with mass spectrometer • At 20°C • At cryo (LN2) temperature • Surface roughness • Measured with Interferometric Profiler 3” dia. chamber GDP “Rotocoater” MS Signal of Good Shell Cycled between 20°C and LN2 temperatures

  6. We can successfully make gas tight overcoatings at 15 microns thickness Improved parameters April 2008 Plot of gas retention Oct 2007 • The improvement came from tailoring the coating pressure ranges Green = pass cryo permeation test Black = fail cryo permeation test

  7. We have reduced the isolated defects appearing on the overcoated shells ~30 nm RMS RF Coated with GDP ~60 nm RMS RF Coated with GDP • Reducing defects on the foam reduced defects in the overcoating • But - the background roughness is the same Both areas ~115 nm RMS The foam surface roughness is now below the spec, but coating parameters need to be improved

  8. A number of items need to be optimized for good surface finish and gas retention • Coating pressure • Evaluated background pressures for smoothing effect • Experiments of 50 – 500 mtorr showed 250 mtorr was smoother • 250 mtorr background pressure for entire run • Sticking was a problem we were able to overcome • Stress in the coating is a problem • Use variable pressure: 250 then 50 mtorr • Current experiments: high pressure for more of the coating thickness (but not all)

  9. The tritium inventory required is set by the coating characteristics • The temperature of the fill can affect the properties of the coating (and fill rate) • Buckle strength (can decrease with T) • Permeation rate (increases with T) Plot of tritium inventory as a function of temperature for various Ea and reduction in buckle strength High temperature fill will be necessary to keep the tritium inventory low

  10. The permeation rate through GDP was measured as function of temperature • The permeation rate through GDP was measured as function of temperature Ea= 15 kJ/mole • ~4x faster permeation at 100°C • ~10x faster permeation rate at 130°C But the actual fill rate may be reduced because of a reduction in buckle strength of the shell, but that will no greatly affect tritium inventory

  11. Conclusion • Foam yields are progressing with systematic, parametric studies • We are evaluating the mechanisms to improve coatings parameters for thinner, gastight, smooth coatings • We will evaluate the needed Tritium inventory due to fill cycle • measure effect of temperature on buckle strength

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