Solid DT Studies Update

1
Solid DT Studies - Update
LA-UR-06-8489

• presented by
• John Sheliak - GA
• Drew A. Geller, James K. Hoffer - LANL
• presented at the
• 16th High Average Power Laser Workshop
• sponsored by
• The Department of Energy Defense Programs
• hosted by
• Princeton Plasma Physics Laboratory
• Princeton, NJ Dec 12-13, 2006

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FY-06 HAPL Uncompleted Milestones
6/5/06 Relocation commenced
6/30/07 DT strengthapparatuscomplete
June July August September October
November December January February March
April May June
12/31/06 Relocationcompleted
3
We have fielded an improved direct-heating cell

• Insertion of sapphire windows at the ends of the
  coil provides a clearer view through the solid DT
  layer and confines the material at the ends.

The thickness of the internal windows was chosen
to leave only small gaps at ends of the cell.
4
Target lifetimes are now more than triple those
measured in the previous unconfined cell

• There is now no apparent displacement of solid
  ice along the cylindrical axis when the heater is
  energized.
• The 'lifetime of the ice layer is now
  appreciably (3 X) longer than what we measured
  previously in the unconfined cell. 
• _at_ 1 W/cm2 and 19 K, we see no distortions for
  70 /- 10 ms. 
• At 18 K, 'lifetime' is gt 125 ms. 
• At 17 K, gt 160 ms.
• At 16 K, gt 190 ms.
• The first 'event' we see now, even before we see
  a liquid layer form at the outer perimeter of the
  solid, is a 'crack' radially through the solid. 
  This is probably a result of the whole ice layer
  starting to buckle from external pressure.
• lifetime for these measurements is defined
  as the 2 db point, or at the time of 25
  roughening above the normalized initial layer
  roughness value, as measured at the inner DT
  solid layer edge

X position error (mm)
Target leaves conducting tube
5
Solid DT layers showing 4 hr equilibrated layers
at 16 K, 17 K, 18 K, with later direct-heating
effects
16 K _at_ 4 hrs 0 ms
17 K _at_ 4 hrs 0 ms
18 K _at_ 4 hrs 0 ms
17 K _at_ 4 hrs 200 ms
18 K _at_ 4 hrs 160 ms
16 K _at_ 4 hrs 200 ms
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Comparison of our current direct-heating data
with previous data shows survival time more than
tripling
Direct heating with old cell
Direct heating with newer improved cell
7
Solid DT layer thickness increases about 2 for
new cell v.s. 4 for old cell, over the survival
period - at 18 K

Direct heating with old cell
Direct heating with newer improved cell
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Comparison of current and previous experiments
showing direct-heated roughening of 4 hr old
layers
Direct heating with old cell
Direct heating with newer improved cell
9
Comparison of current and previous experiments
showing direct-heated roughening of 16-18 hr old
layers
Direct heating with old cell
Direct heating with newer improved cell
10
Survival time is an inverse function of
equilibration temperature higher temperature
shorter survival
Direct heating with old cell
Direct heating with newer improved cell
11
Using 1 dB (12) roughening as the survival
benchmark lowers survival time, but not
substantially
Direct heating with old cell
Direct heating with newer improved cell
12
Survival time is also an inverse function of
equilibration time longer equilibration time
shorter survival
Direct heating with old cell
Direct heating with newer improved cell
13
Update on DT strength cell construction
It is not obvious here, but the upper Macor
spacer is slightly canted and must be re-machined
before the lower-layering-post assembly may
proceed.
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Update on DT strength cell construction (cont.)
The cryostat for testing the functioning of the
strength cell (operation of electro-strictive
strain actuator, calibration of piezoelectric
stress sensor, etc.) is nearly complete! During
these tests, a simple spring will take the place
of the upper layering post.
15
We are nearly ready to resume experiments at our
new DT layering laboratory - early Jan 2007
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Progress summary for solid DT studies

• Our most recent direct-heating experiments using
  an improved cell have shown survival time for
  solid DT layers to be more than 3x that of
  previous experiments ( 90 ms _at_ 19 K to 190 ms _at_
  16K for 2 dB roughening benchmark)
• The cryostat for testing the functioning of the
  strength cell is nearly complete and nearly ready
  for calibration
• We have completed our laboratory relocation and
  set-up, with DT delivery expected by mid
  December and new experiments beginning in early
  Jan 2007