Update on Solid DT Studies John D. Sheliak, Drew A. Geller, & James K. Hoffer

1. LA-UR-04-3611 Update on Solid DT Studies John D. Sheliak, Drew A. Geller, & James K. Hoffer presented at the High Average Power Laser Workshop sponsored by The Department of Energy Defense Programs hosted by the University of California, Los Angeles Los Angeles, California, June 2-3, 2004

2. Target Injection: Target Materials Response - LANL Overall Objective…………. Response of target materials to injection stresses FY 04 Deliverables……….. 1. Finish analysis of direct heating experiments. 2. Complete final drawings for elastic modulus/yield strength experiments. 3. Measure the roughness spectrum of DT beta- layered inside a 200 micron thick layer of foam material. 4. Fabricate apparatus for elastic modulus/yield strength experiments. 5. Deposit a layer of DT inside a foam-lined heater winding and study thermal response. Relevance of Deliverables [X] Energy……………… Needed for injection into hot chamber [X] NIF…………………… Research on materials in NIF targets

3. Experimental Progress • Completed a new set of experiments with solid DT at 16 K, 17 K, 18 K, & 19 K, with a 4 hr and 18 hr equilibration at each temperature. • Completed modifications to our LabView image analysis code in order to more accurately analyze the complex image structures present in direct-heated solid DT images (effects of evolving bubble formation on layer intensity variations, and layer edge focus distortions resulting from DT crystallite formation on cell windows) • Completed a set of solid DT layering experiments inside a 4 mm dia. parylene-coated sphere-cylinder (sapphire), in preparation for follow-on experiments inside a foam-coated ‘sphylinder’. • Completed data analysis for both the direct-heating experiments, and the parylene-coated sphere-cylinder experiments. • Completed thermal modeling using use FEA (ANSYS) to estimate the heat flux into the DT layer as a function of current into the manganin coil.

4. We completed new experiments with the direct-heating of solid DT layers inside our re-entrant beta-layering cell epoxy layer coil

5. This set of experiments was performed to study the effects of equilibration temperature and equilibration time on DT solid layer roughness evolution under direct-heating • Solid layers were equilibrated at 19 K, 18 K, 17 K, and 16 K - including a 4 hr and an 18 hr equilibration at each temperature • DT was recovered after each 18 hr equilibration to remove accumulated helium, so that the solid layers equilibrated at each temperature were grown from ‘fresh’ DT • Comparisons are made between equilibration times at each temperature, and between equilibration temperatures at each equilibration time • All experiments were performed with a 100 ms heat pulse and a power density of 1 W/cm2 • The following image frames were chosen for the time of onset of layer roughness ‘runaway’ for the 4 hr equilibrations, and compared with the 18 hr equilibrations at that same time

6. Some 3He bubble formation and a DT liquid front is clearly visible in this 19 K solid layer @ 4 hrs - this is occurring 24 ms after the heat pulse initiation 19 K, 4 hrs, 0 ms 19 K, 4 hrs, 24 ms

7. Additional 3He bubble formation is observed, as well as solid DT layer ‘blowout’, in this 18 hr equilibration at 19 K - also 24 ms after the heat pulse initiation 19 K, 18 hrs, 0 ms 19 K, 18 hrs, 24 ms

8. Comparison of these two solid layers shows an earlier onset of layer roughening for the 18 hr equilibration, and increasing layer thickness due to solid layer ‘swelling’

9. Comparison of the cumulative spectra at 24 ms after heat pulse initiation, shows that roughening occurs in the mid- and low-modes under direct heating for the 18 hr run

10. Significant 3He bubble formation and a DT liquid front are visible at 28 ms into this experiment at 18 K, while the solid layer remains essentially undistorted and intact. 18 K, 4 hrs, 0 ms 18 K, 4 hrs, 28 ms

11. 3He Bubble formation has increased, and the solid layer is beginning to ‘bulge’ or distort compared with 4 hrs, for this 18 hr equilibration at 18 K 18 K, 18 hrs, 0 ms 18 K, 18 hrs, 28 ms

12. This 18 K data shows a similar pattern to the 19 K data - an earlier onset of solid layer roughening for the 18 hr equilibration, and increasing layer thickness for both

13. The 18 K cumulative spectra shows that 18 hr roughening also occurs in mid- and low-modes under direct-heating, but higher in the low-modes compared to the 19 K data

14. Significant bubble formation is observed over 2π in this 4 hr equilibration @ 17 K - but very little roughening or distortion has occurred at 32 ms after heat-pulse initiation 17 K, 4 hrs, 0 ms 17 K, 4 hrs, 32 ms

15. The layer is nearly blackened with bubbles for this 18 hr equilibration @ 17 K, with more roughening than with the 4 hr equilibration, and some layer distortion 17 K, 18 hrs, 0 ms 17 K, 18 hrs, 32 ms

16. The surface roughness deviation between the 4 and 18 hr equilibrations, is not as pronounced for this 17 K run, but the data still show earlier roughening onset at 18 hrs

17. These cumulative roughness spectra for the 17 K runs actually show more mid-mode roughening for the 4 hr equilibration, as well as more mode 6 roughness

18. The onset of roughening for the 4 hr equilibration at 16 K, occurs around 52 ms with significant bubble formation 16 K, 4 hrs, 0 ms 16 K, 4 hrs, 52 ms

19. The solid layer appears less translucent for the 18 hr equilibration @ 16 K, due to He bubble formation and increased solubility at this temperature 16 K, 18 hrs, 0 ms 16 K, 18 hrs, 52 ms

20. The DT roughness deviation between 4 and 18 hrs for the 16 K data, begins at nearly the same time after heat-pulse initiation, but the 18 hr roughness increases at a faster rate

21. The cumulative spectra for the 16 K runs show roughness increasing in some mid- and most low-modes for the 18 hr data, and decreasing or nearly unchanged for the 4 hr data

22. The data for this set of experiments do show a temperature dependence of solid surface roughness evolution under direct-heating, but statistical studies should be done as well

23. Adding sapphire/glass inserts to our current cell design, may provide a clearer view of the DT solid layer structure and liquid front under direct-heating Insertion of windows at the ends of the coil will provide a clearer view through the layer and will confine the material at the ends. Thickness of windows must be carefully chosen to leave only small gaps at ends of the cell.

24. Conclusions • Lowering equilibration temperature and/or shortening equilibration time delays the onset of DT solid layer roughening under direct heating • The shortening of layer roughening time with 18 hr equilibrations is evidence that the bubble formation is in fact 3He, due to 3He buildup inside the DT solid layer • Short (4 hr) equilibrations and/or lower equilibration temperatures generally result in roughening of the low modes; long (18 hr) equilibrations at higher temperatures (18 K and above) result in mid- and low-mode roughening • Increasing layer thickness over time is likely due to thermal expansion and volume change due to melting.

25. Foam-Coated Sapphire Sphere-Cylinder Experiments

26. It is possible to measure the surface roughness of DT beta-layered onto a true spherical surface, using only flat optics: This material must be optically clear and be a good thermal conductorsuch as sapphire.

27. 3He bubbles are still observed in the ‘polished’ sphylinders ‘Pre-polish’ sphylinder with 430 µm-thick DT solid @ 6 hrs, T = 19.60 K ‘Post-polish’ sphylinder with 487 µm-thick DT solid @ 5.7 hrs, T = 19.50 K

28. Plastic coated sphylinders? • We hypothesized that heterogeneous 3He nucleation might not occur if the ‘polished’ surface were coated with a few microns of polymer, by filling in or smoothing over the nucleation sites in the sapphire. • Diana Schroen, at Schafer, Inc. arranged to have one of the remaining two polished sphylinders coated with 2 microns of parylene “N”. • There is clearly a cleaning issue, but any remaining plastic debris should not affect the beta-layering. • We have finally(!) had an opportunity to mount this parylene coated sphylinder in the tritium apparatus.

29. 3He bubbles are again observed in the coated sphylinders ‘Post-polish’ sphylinder with 487 µm-thick DT solid @ 5.7 hrs, T = 19.50 K Parylene coated sphylinder with ~500 µm-thick DT solid @ 6 hrs, T = 19.21 K

30. Sphere-Cylinder comparison data shows very little variation in DT solid layer roughness vs. equilibration temperature, for each of the cells that we studied

31. 3He bubbles are again observed in the foam-filled sphylinders ‘Post-polish’ sphylinder with 487 µm-thick DT solid @ 5.7 hrs, T = 19.50 K DVB foam lined sphylinder with ~550 µm-thick DT solid @ 6 hrs, T = 19.21 K

32. The foam layer appears to buckle or de-laminate over time. DVB foam lined sphylinder with ~350 µm-thick DT solid @ 6 hrs, T = 19.21 K First 10-hour cycle (ser. ‘b’). DVB foam lined sphylinder with ~350 µm-thick DT solid @ 6 hrs, T = 19.21 K Second 10-hour cycle.

33. Current and upcoming experimental work • Complete experiments in foam-coated sphere-cylinder and compare bubble formation and roughness data with data from previous sphere-cylinder experiments. • Perform a new set of solid DT direct-heating experiments with modified cell (sapphire inserts) in an effort to provide a better view of the solid layer (i.e. 3He bubble and DT liquid front formation and evolution) and a better measurement of solid layer roughness at late times. • Conduct direct-heating experiments in a foam-lined cell • Complete assembly of strength cell and new strength cell cryostat. Conduct test experiments with D2.

34. These cumulative spectra are solid DT roughness data for three sapphire sphere-cylinders, averaged over each equilibration temperature shown in the graph

35. Comparison of cumulative roughness spectra for DT solid layers that were equilibrated in three sphere-cylinders at 19.2 K, and an empty unpolished sphere-cylinder

36. This graph compares the total RMS roughness for all four empty sphere-cylinders used in our experiments

37. Additional roughness observed for plastic- and foam-coated ‘sphylinders’ is the likely effect ‘light piping’ which produces image intensity variations at the edge of interest