DOE DP This work was performed under the auspices of the U. S. Department of Energy by the Los Alamos National Laboratory under contract No. W-7405-Eng-36. ESA-TSE Engineering Sciences and Applications Division Tritium Science & Engineering Update on Solid DT Studies -or- “Bubble, Bubble, Toil & Trouble at Los Alamos” Drew A. Geller, John D. Sheliak, & James K. Hoffer presented at the High Average Power Laser Workshop sponsored by The Department of Energy Defense Programs hosted by the Princeton Plasma Physics Laboratory Princeton, New Jersey, October 27-28, 2004 LA-UR

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 Target Injection: Target Materials Response - LANL

Experimental Progress: (Some delay to deliverables from engineering issues and the LANL suspension of activities to reassess and reaffirm our safety, security and compliance) 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. Complete experiments in foam-coated sphere-cylinder and compare bubble formation and roughness data with data from previous sphere- cylinder experiments.

Foam-Filled Sapphire Sphere-Cylinder Experiments Sapphire Foam

Bubbles were observed in both the polished and plastic-coated sphylinders ‘Post-polish’ sphylinder with 487 µm- thick DT 5.7 hrs, T = K Parylene coated sphylinder with ~500 µm-thick DT 6 hrs, T = K

Bubbles were again observed in the foam-filled sphylinders ‘Post-polish’ sphylinder with 487 µm- thick DT 5.7 hrs, T = K DVB foam lined sphylinder with ~350 µm-thick DT 6 hrs, T = K

Oh, did you think I meant 3 He bubbles? 3 He bubbles DT bubbles But there are two possible types of bubbles that can exist inside solid DT: The trick is to know which is which! Any bubble inside the self-heated solid DT tends to move inwards, just like the ‘big one’ (i.e., the DT vapor space in the center). 3 He bubbles move very slowly, typically ~10-20 μm/hour. Large DT bubbles can move very fast, ~[average layer thickness]/t c, = μm/26 min = μm/min. Small DT bubbles may move more slowly because of the smaller thermal gradient across the bubble. For comparable sizes, DT bubbles should move much faster than 3 He bubbles (no mutual diffusion term).

In our large Lexan sphere, we observed a DT vapor bubble (spawned in the fill tube) which moved through the solid at ~ 10 μm/min. liquid at 21 Kt = 12 min., T = 17.5 Kt = 1 hour t = 3 hours This polycarbonate (Lexan) spherical shell is ~ 4 x NIF size t = 7 hourst = 7 days DT bubble

Short-term video of bubble propagation in the foam-filled sphylinder

The drive for bubble propagation is the thermal gradient in the self-heated DT solid. Thus we expect the bubble velocity will slow down as it nears the vapor space:

Long-term videos of bubble propagation in the foam-filled sphylinder show movies now (sorry - popcorn not available in the lounge!)

If DT bubbles are leaving the foam, then DT solid must be filling in the voids. We should observe the DT thickness to slowly decrease (or the inner radius to increase):

We have identified a third mechanism for removing 3 He from solid DT 1. 3 He bubble formation in the solid DT layer: Beta-layering s l o w l y moves the bubbles into the DT vapor space. Typically, this mode is observed about 5 hours after the initial beta-layering equilibration, but only when T  ~18 K. 2.Diffusion of 3 He through solid layer into DT vapor space: We typically observe this mode (we see no bubbles) when T > ~18 K. But in our recent experiments in the sphylinders, where we can see clearly through the solid DT at the edge of the vapor space, we have observed bubbles when 18 K < T < 19.4 K. 3.Sweeping action of DT bubbles: Fast moving DT bubbles catch up with 3 He bubbles, coalesce, and sweep them toward the interior vapor space.

So far, we have been silent concerning the roughness of a ~300 μm-thick pure DT solid layer nucleated in foam. Caveat - the presence of DT & 3 He bubbles will trick our analysis software into calculating a higher roughness than is actually present.

Current and upcoming experimental work Fabricate new set of sphylinders with improved surface finish in an attempt to remove defects that trap and later release DT bubbles. (On hand as of 10/3/04 !) Run DT experiments. Add filling of enhanced open-celled foam (Vycor-like). Repeat DT experiments. Perform a 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. 3 He 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 D 2.