Update on Solid DT Studies -or-

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Update on Solid DT Studies -or- Bubble, Bubble,
Toil Trouble at Los Alamos Drew A. Geller,
John D. Sheliak, James K. Hoffer
LA-UR-04-7336

• 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

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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
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Experimental Progress (Some delay to
deliverables from engineering issues and the LANL
suspension of activities to reassess and reaffirm
our safety, security and compliance)

• 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.

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Foam-Filled Sapphire Sphere-Cylinder Experiments
Sapphire
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Bubbles were observed in both the polished and
plastic-coated sphylinders
Post-polish sphylinder with 487 µm-thick DT
solid _at_ 5.7 hrs, T 19.50 K
Parylene coated sphylinder with 500 µm-thick DT
solid _at_ 6 hrs, T 19.21 K
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Bubbles were again observed in the foam-filled
sphylinders
Post-polish sphylinder with 487 µm-thick DT
solid _at_ 5.7 hrs, T 19.50 K
DVB foam lined sphylinder with 350 µm-thick DT
solid _at_ 6 hrs, T 19.21 K
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Oh, did you think I meant 3He bubbles?
But there are two possible types of bubbles that
can exist inside solid DT

• 3He bubbles
• DT bubbles

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).
• 3He bubbles move very slowly, typically 10-20
  µm/hour.
• Large DT bubbles can move very fast, average
  layer thickness/tc, 200-400 µm/26 min 10-20
  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 3He bubbles (no mutual diffusion
  term).

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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.
DT bubble
DT bubble
liquid at 21 K
t 12 min., T 17.5 K
t 1 hour
t 3 hours
t 7 hours
t 7 days
This polycarbonate (Lexan) spherical shell is 4
x NIF size
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Short-term video of bubble propagation in the
foam-filled sphylinder
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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
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Long-term videos of bubble propagation in the
foam-filled sphylinder
show movies now(sorry - popcorn not available in
the lounge!)
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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)
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We have identified a third mechanism for
removing 3He from solid DT

• 3He 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.
• Diffusion of 3He through solid layer into DT
  vapor space
• We typically observe this mode (we see no
  bubbles) when T gt 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 lt
  T lt 19.4 K.
• Sweeping action of DT bubbles
• Fast moving DT bubbles catch up with 3He
  bubbles, coalesce, and sweep them toward the
  interior vapor space.

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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 3He bubbles will
trick our analysis software into calculating a
higher roughness than is actually present.
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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. 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.