Specifications for the HAPL Shell

1. Fabrication of HAPL Sized R/F foam Shells(IFE Target Fabrication Update)Presented by Reny Paguio1D. Goodin1, J. Hund, D. Jason, A. Nikroo1, K. Saito1, K. Quan21General Atomics, Inertial Fusion Technology, San Diego, CA2UC San Diego, San Diego, CAHAPL Meeting, Madison WI, October 22-23, 2008

2. Specifications for the HAPL Shell Thin (300-1200 Å) High Z coating 10 m CH Overcoat Coating roughness of 50 nm (RMS) Foam + DT HAPL Target DT DT Vapor Foam layer: 0.18 mm thickness Divinyl Benzene (DVB) or Resorcinol-Formaldehyde (RF) ~ 2.3 mm rad • Shells need to be uniform • Wall Uniformity (Non Concentricity=NC) • NC Spec. 1-3% (Offset ~10.8m) • Sphericity-Out of Round (OOR) • OOR Spec is >1% of the shells radius (~23 m) • Gas tight pinhole free overcoat* *J. Hund, et al., HAPL Meeting, Target Fabrication, Talk 3

3. Since the last HAPL Meeting we have: • Improved the Wall uniformity & sphericity of the R/F Shells • NC of 35% to 10% • Out of Round (OOR) spec improved from 75% to 100% • Improved the surface of the foam shell • Improved the shell’s surface by 50% • (60 nm to 30 nm RMS) • Improved the solvent exchange process using Soxhlet Extractor • Faster (More efficient)

4. Used in ICF experiments on OMEGA 2 Step polycondensation reaction* Foam Is C, H, O Small Pore size (<0.10 m) -Transparent Use GDP directly as overcoat Has been shown to hold gas for HAPL size shells (15 m) New Direction from target designers has allowed the possibility to have O in the foam matrix In the Past: Foam could only be C & H Has opened the door to use materials such as R/F R/F was looked as a possible foam, because overcoated DVB shells were not gas retentive * Pekala, R.W.; et al. J. Mat. Sci., 1989, 24, 3221-3227.

5. R/F foam shells are fabricated using a triple orifice droplet generator • 3 Steps • Droplet generation • Curing • Solvent exchange & drying Supercritical CO2 dry – Resulting in a dry R/F foam shell 300-400 Cured shells Post Cure Process

6. HAPL sized R/F shells have been successfully fabricated Changed needle & collection tube size Optimized the curing step in rotobeaker More precise control of density matching between the R/F sol and the outter oil sol Lead to a high yield of intact shells (~90%) HAPL & OMEGA Sized R/F Shell 4500 m OMEGA size

7. Initial results show that the wall uniformity of HAPL R/F foam shells needs to be improved NC Spec IFT=20 dynes/cm IFT=1 dynes/cm • Looked at ways to improve the wall uniformity • Polymer Additives • Used in the OMEGA R/F shells to improve wall uniformity* • Styrene Butadiene Styrene (SBS) Co-block polymer • Raises the Interfacial Tension (IFT) & Viscosity * Paguio R.R et al., Fusion Sci & Technol, 2006,49,4

8. Modifying the O2 solution changed the viscosity of the oil and the Interfacial Tension (IFT) of the emulsion system Surfactant reduces the IFT Needed to prevent agglomeration of the shells Poly Butadiene (PBD) was investigated as a possible SBS replacement More affect on viscosity than IFT No dramatic improvement on NC Combination of the two leads to a higher IFT & viscosity

9. SBS addition has been shown to improve the wall uniformity of HAPL sized R/F foam shells NC SPEC IFT=8 dynes/cm IFT=4 dynes/cm 20 IFT=1 dynes/cm IFT=1 dynes/cm • Improved from <5% (No Additive) to ~20% with Additive • Wall uniformity not as good as DVB (75%) • Optimizing the SBS:PBD Ratio • Optimize the density matching of the O1 and R/F sol • Investigation of other possible polymer additives

10. The SBS/PBD additive blend to the O2 has also improved the OOR of the shells IFT=8 dynes/cm IFT=4 dynes/cm ( m) • Yield of shells that meet the OOR spec went from 75% to 100% • IFT increased from 4 to 8 dynes/cm when going to the SBS/PBD blend

11. Acid addition to the Post-Cure removes large isolated defects from the foam’s surface Added 0.33M of Acetic Acid to the post cure (PC) process. Foam structure unchanged Surface roughness of the bare foam improved from 60 nm to 30 nm RMS Wyko Interferometer 50X-400m scan Need to optimize the acid concentration to improve the bare foam surface No Acid Added to PC Acid Added to PC

12. Soxhlet Extractor reduced the time needed for solvent exchanging from 2-3 weeks to 3 days Traditionally: Once a day exchanged into IPA Oil still in IPA. After 2-3 weeks of solvent exchange oil oil No oil in IPA. Soxhlet Extractor After 3 days in Soxhlet This has also been extended into OMEGA & NIF R/F foam shell fabrication Soxhlet Extractor Allows a continuous exchange of IPA for the shells Using the Soxhlet Extractor is a faster more efficient way to solvent exchange larger shells

13. Soxhlet Extraction limits surface defects when shells are dried Dry shell no Soxhlet Dry shell with Soxhlet Big dents No big dents • Soxhlet extractor removes nearly all of the oil: No big dents • No Soxhlet : Left over oil which can lead to big dents

14. Successfully made improvements on the HAPL sized R/F shells & the fabrication process Improved the wall uniformity using polymer additives Avg. NC went from 35% to 10% Improved the OOR 100% of the shells meet half the HAPL Spec Improved the bare surface of the foam with acid addition to PC process Reduced the surface roughness by 50% Made the solvent exchange process more efficient using a Soxhlet Extractor Shortened Solvent exchange time from 2-3 week to 3 days

15. Investigated other organic solvent replacements for the tetrachloroethylene (TCE) Looked at two additives Bromobenzene (IFT went to 9 dynes/cm) Tri Chlorobenzene (IFT went to 12 dynes/cm) Yield of intact shells decreased (~20%) Emulsion unstable New to investigate other surfactants NC was similar to the SBS/PBD addition with TCE Bare foam roughness went up to 120 nm RMS Due to shell break up during curing process This is with the acid addition in the PC