1. IFE Target Fabrication Update Presented by Jared Hund 1 N. Alexander 1, J. Bousquet 1, R. Cook 1, D. Frey 1, D. Goodin 1, J. Karnes 2, R. Luo 1, R. Paguio 1, R. Petzoldt 1, N. Petta 2, N. Ravelo 1, K. Saito 1, D. Schroen 1, J. Streit 2, A. Cheng 3, W. Holloway 3, N. Robertson 3, S. Saiedi 3, M. Weber 3 1 General Atomics, Inertial Fusion Technology, San Diego, CA 2 Schafer Corporation, Livermore, CA 3 UC San Diego, San Diego, CA HAPL Workshop Naval Research Laboratory Oct 29-30, 2007 IFT\P2007-095

2. Since the last HAPL Meeting we have: Successfully coated HAPL dimension foam shells and have shown them to be gas tight Demonstrated resorcinol formaldehyde foam shells as an option for a HAPL target –Made them as a HAPL sized capsule –Improved the wall uniformity –Successfully overcoated with GDP –Shown them to be gas tight –Approaching surface finish specifications We are beginning to characterize the capsule beyond the basics –The foam density uniformity across the shell wall has been measured for DVB and RF Begun a collaboration with U of Rochester and UCLA to investigate additional control of shell fabrication (Dielectrophoresis)

3. The current high-gain HAPL target design is a 4.6 mm diameter foam capsule DT Vapor Foam + DT Thin (300-1200 Å) High Z coating ~ 2.3 mm rad 10  m CH Overcoat DT Foam layer: 0.18 mm thickness Divinyl Benzene (DVB) or Resorcinol-Formaldehyde (RF) Important Specifications Foam shell: –Out of round –Wall uniformity Plastic Overcoating: –Gas tight –Smooth (50 nm RMS) High Z coating

4. The specifications of the NRL/HAPL target have dramatically evolved Foam capsule 20 mg/cc DVB → 100 mg/cc DVB → 100 mg/cc DVB or R/F Coatings 1 μm overcoating → 5 μm → 10 μm today

5. The specifications of the NRL/HAPL target have dramatically evolved Foam capsule 20 mg/cc DVB → 100 mg/cc DVB → 100 mg/cc DVB or R/F very fragile foam → more robust foam → smaller pore size R/F foam diameter increased slightly in the evolution of physics design Elemental composition – DVB (CH) initially preferred because does not contain oxygen like RF (CHO) Coatings 1μm overcoating → 5 μm → 10 μm today

6. The specifications of the NRL/HAPL target have dramatically evolved Foam capsule 20 mg/cc DVB → 100 mg/cc DVB → 100 mg/cc DVB or R/F very fragile foam → more robust foam → smaller pore size R/F foam diameter has increased slightly in the evolution of the physics design Elemental composition – DVB (CH) initially preferred because does not contain oxygen like RF (CHO) Coatings 1μm overcoating → 5 μm → 10 μm today increased thickness in order to survive fabrication and filling initial design depended on primary strength from the foam layer

7. Do we meet foam capsule requirements? AttributeValue Tolerance DVBRFComments O, N content0?Pass (0 at%) Pass (12 at%) Diameter4.6 mm  0.2 Pass 0.025 mm range Pass ± 0.06 mm range Wall thickness 180  m  20 Pass (± 20 um) In progress Density20-120 mg/cc [25%]Pass (97± 5 mg/cc) Pass Pore size <3  m Pass (~1 um) Pass (~0.01 um) Based on SEM for DVB. RF measured with SEM and N2 adsorption Out of round<1 % of radius --Pass (<0.3 %) Borderline (1% average) Measured by single view on dry foam shells. Non- concentricity < 1-3% of wall th. --Pass (~60% of shells <3% NC) In Progress (10% of shells <3% NC Areal density< 0.3%Modes 100 to 500 Contact radiography to determine radial density variation.

8. How well are we meeting the overcoat specs…? AttributeValueToleranceDVBRFComments Coating composition CHNO PVP/G DP (CHO) GDP (CH) Coating Thickness 10  m +/- (30 – 300) nm +/- 2um GDP process - Δwall set by areal density specification Power spectrum (surface finish) <50 nm-- > 500 nm Getting close (50 - 200 nm) Permeability (gas tight) and yield TBD-- Fail at 10 um Fail at 10um, some good at > 20 um For current techniques require ~20 um thickness, working to minimize Strength (for filling) TBD-- > 2 atm For a >20 um thick coating These specs are evolving as more simulations are done by the designers

9. The DVB capsule meets the sphericity specification, but RF still requires work The yield of RF shells that meet the 1% of radius Out- of-Round (OOR) specification is 70% RF Shell DataDVB Shell Data A possible fix for this is to increase the interfacial tension of the RF system before curing OOR = (max radius – min radius) 100% Yield 70% Yield max radius min radius

10. Currently DVB shells have a better yield of shells that meet the wall uniformity specification DVB is better for the NC specification (at the moment) Uniformity defined in terms Nonconcentricity (NC) Offset = distance between centers of inner and outer wall Percentile Plot of Foam Wall Uniformity

11. Density Uniformity of shells Procedure –The shell is placed in contact with glass supported film and exposed to x-rays –Film is developed and digitized –Image analyzed by “unwrapping” shell and comparing attenuation to known standard Capabilities –+/- 10% Absolute error, +/- < 1% relative error within shell RF GDP Radiograph of sector of Coated Foam shell Interior of shell Interface positions on a poor NC shell Grayscale between interfaces provides density information

12. Many of the DVB shells tested have a density variation along the thickness of the foam wall

13. RF shells also have a density variation along the thickness of the foam wall Is this a problem for the target physics?

14. The next steps in characterization of areal density 2D Areal density: –Contact radiography Measure density vs. angle Wallmapping is being used to get the overcoating thickness around the shell –Interferometric technique developed for ICF 3D Areal density: –3D X-ray Tomography –Precision radiography Directly measure x-ray attenuation of shell

15. Overcoating Currently evaluating GDP coatings Could be complemented by RF skin technique Other alternative described in previous HAPL workshops –Interfacial polymerization –Interfacial polymerization/GDP

16. Measured buckle strength of GDP coated foam shells Tritium inventory implication : ~1 kg for 100° C fill of a capsule with 25 um GDP coating (dominated by layering time) High temperature fill needs to be tested

17. A number of GDP/RF shells have been shown to be leak tight Shells filled with D 2 and the leak rate measured with mass spectrometer Leak rate measured at room and liquid nitrogen temperatures –To distinguish between pinhole and permeation flow Test developed at GA for LLE cryo work and validated based on success of cryo foam targets at LLE Specs: 4 mm diameter 25 um of GDP on RF The shells are tested to be “gas tight” and can survive cryo cooling and warming cycle

18. Gas testing results: 4-4.6 mm diameter GDP/RF (HAPL size foam shell) Pinhole free Leak Mechanisms:

19. Coated R/F foam shells are smoother than over-coated DVB shells Optical Profiler (WYKO) measurements acquired at 20x, with a 300 x 200 um area Surface Roughness of HAPL Coated Foam Shells (> 4 mm diameter) Shell/Coating Type: DVB/PVPDVB/PVP/ GDP RF/GDP

20. Spheremapping of GDP coated, 3 mm diameter foam shell with 10 um GDP wall Spheremap – AFM technique for measuring roughness of spherical capsules OOR of shells must be better for routine spheremapping Meets roughness specification: 42 nm RMS for modes 50-1000 Power Spectrum of Surface Roughness AFM Traces Around Shell

21. Changing the background pressure during the GDP coating run affects the final surface Background pressure: 500 mtorr250 mtorr75 mtorr This may be a technique for improving surface finish of a GDP overcoating Standard condition “Coral” DLA structure Dome growth Smooth surface

22. We have begun a collaboration with U of Rochester and UCLA to investigate additional control of shell fabrication We can manipulate the shells using electric fields through dielectrophoresis (DEP) 1,2 The electric field also has a centering effect on the inner droplet Currently work is being done for OMEGA direct drive – HAPL size capsules will be done in parallel Possibility for HAPL scale up 1.H. Pohl, Dielectrophoresis : the behavior of neutral matter in nonuniform electric fields, 1978 2.T. Jones, Electromechanics of particles, 2005 cusped E field cap electrode ring electrode DEP Levitation Concept capsule

23. Conclusions HAPL specifications have evolved into 1.DVB foam option: –Good NC (yield: 60% < 3% NC) –DVB with PVP/GDP – still have pinholes at >10 um –Poor roughness of coated DVB shells 2.RF option: –NC is worse, but improving (yield: 10% < 3% NC) –RF gas tight shells at 20 um (no pinholes) –The surface roughness is most promising