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Shells, Foam Non-Concentricity, Overcoats, and Characterization Methods Presented by Brian Vermillion1 G. Flint1, B. McQuillan1, R. Petzoldt1, D. Goodin1, William Holloway2, Neil Robertson2, Patrick Goodman2, Willa Maksaereekul2 1 General Atomics, Inertial Fusion Technology, San Diego, California 2 UC San Diego, San Diego, California High Average Power Laser Program LLNL June 20-21, 2005 Identified solutions for agglomeration in Summary and Highlights divinylbenzene, DVB, foam shell production process Built a Generation 2 device to better control tangential shear and improve non-concentricity, scalable to larger size Performed a detailed evaluation of the process for overcoats: yields, quality, and solutions Barry McQuillan Applied a characterization technique enabling high resolution imaging of dry, presentation opaque DVB foam shells Better than 0.8 m repeatability on > 4 mm diameter shells Haibo Huang poster We identified a solution to agglomeration... Appears ~ 5 hours into run with no early indications except Beads breed beads, once enough beads batch goes over a cliff Do the beads release solvent that Agglomeration act as a connection for agglomeration? in a rotobeaker We explored impurities and contaminants Fresh radical initiator reduces Solution we now apply: agglomeration frequency a bit Change interfacial surface tension of solution: Add surfactants at ~4 hours 5 wt% polyvinyl alcohol solution dramatically reduced agglomeration We are examining a method to improve nonconcentricity by applying tangential shear Review: As tangential shear is applied to the outer surface, fluid flows in between the inner and outer shell walls, forcing the inner sphere towards the center W2 01 W1 Hydrodynamic analogy Starting from a 3D journal bearing model to describe the centering force: F = f (density mismatch, rotation, viscous drag) Time for shell to center is much less than a second with application of ~ 10 RPM, we apply much more than this in our devices Need to vary direction and magnitude of shear The Gen 1 device had good NC, but was difficult to use we are now testing a Gen 2 device 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Frequency 2.35 Average NC Shells <5% NC ~ 100% Gen 1, 1st successful test 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 %NC Gen 1 Note: Ambiguity in definition of NC within target spec document Wallmax Wallmin 2 offset = 1% Wall Wall Withi n table Gen 2 offset 1% Wall Within the document text, and how we report our NCs Movement of the bulk fluid in the Gen 2 device is similar to swirling a wine glass Top of the fluid surface does not rotate 2 axis rotary motion, round bottom flask 70 RPM, 1 cm deep, 12 L flask Gen 2 device is based on our mathematical tangential shear model Simpler to use and more to scalable larger sizes bulk solution from the Gen 2 glass surface We calculate a helical shear wave extends ~ 8 mm with 0.1 wt% PAA(aq) Experimental observation indicates > 8 mm with 0.05 wt% 10 8 Depth (mm) 6 4 2 0 Glass surface high viscosity: PAA low viscosity: Water We had a good initial yield with the first Gen 2 test, but NC was higher 4 3 2 1 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 5 Frequency Frequency Average NC Shells <5% NC 12.50 38% 4 3 2 1 0 0 1 2 Average NC Shells <5% NC 5.00 60% 3 4 5 6 7 8 9 10 11 12 13 14 15 %NC %NC Gen 2, 1st test, 1 cm deep, 85 RPM Control We did a parametric study to pick the best conditions Tested hard DVB foam shells marked on one side, and observed parameters that best spin the shell Best observed spin was a deeper bed (3-4 cm) with the same RPM Deeper bed also reduced beaching effect We are showing improvement with the Gen 2 device using the new parameters 6 5 6 Frequency 4 3 2 1 0 0 1 2 3 4 Frequency 6.44 Average NC Shells <5% NC 35% 5 4 3 2 1 0 3.21 Average NC Shells <5% NC 86% 5 6 7 8 9 10 11 12 13 14 15 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 %NC %NC 6 5 Frequency 4 3 2 1 0 7.66 Average NC Shells <5% NC 15% Gen 2, 4 cm deep, 85 RPM Control Experimenting with greater RPMs Also going to continue with Gen 1 device 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 %NC Gen 2, 4 cm deep bed, 85 RPM, 0.1 wt% PAA(aq) Increase tangential shear by applying more velocity Height of fluid (Abs) 14 12 10 8 6 4 50 75 100 RPM 125 0.1wt% P AA 0.05 wt% P AA Water Experimental data Same amplitude, increased velocity "Beaching zone" Increased velocity, increased tangential shear on the shell Beaching zone between the two regimes, can be minimized by increased viscosity solution We are applying first of a kind high resolution characterization to opaque foam shells Divinylbenzene Shell with Full Density Overcoat 1650 1600 Radius (um) 1550 1500 1450 1400 1350 1300 1250 1200 Overcoat outer surface Foam/overcoat interface Foam inner surface Image of a dry DVB shell 0 60 120 180 240 Angle (degree) 300 360 Measurement repeatability 0.8 m on > 4 mm diameter shells, results in less than 0.5 % NC error Haibo Huang We zoom in optically for overcoat poster measurement An existing device may be adaptable to achieve two view measurement We are identifying and addressing the issues for successful target fabrication Identified solutions for agglomeration, increasing yields and successful experiments Continuing experimentation into methods to decrease non-concentricity, NC, of DVB foam shells: Parametric testing of Gen 1 and Gen 2 devices to continue We can now characterize dry opaque DVB foam shells: Better than 0.8 m repeatability on > 4 mm diameter shells

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