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 (“What limits DT layering times over foam?”) James K. Hoffer, John D. Sheliak, & Drew A. Geller presented at the High Average Power Laser Review sponsored by The Department of Energy Defense Programs hosted by the The University of Wisconsin Madison, Wisconsin, September 24-25, 2003 LA-UR

UW Sept ‘03 Overall Objective…………. Response of target materials to injection stresses FY 03 Deliverables………..1. Measure the roughness spectrum of solid DT beta-layered inside a thin (~50  m-thick) layer of foam material as a function of temperature. 2. Fabricate and assemble apparatus for measuring the response of a solid DT layer to the sudden onset of high thermal flux. 3. Deposit a layer of solid DT inside a cylindrical heater winding and observe the response to a sudden onset of high thermal flux. Relevance of Deliverables [X] Energy………………Needed for injection into hot chamber [X] NIF……………………Research on materials in NIF targets Target Injection-1: Target Materials Response - LANL

UW Sept ‘03 presented by Jim Hoffer, LANL The surface roughness of DT layers frozen inside a foam shell, “DT-in-foam” Progress report: deliverable No. 1, part A

UW Sept ‘03 A foam-lined torus has permitted clear optical observations of the DT layer: Empty torus side view (windows not shown) Filled with foam to yield a 75 micron-thick layer at the waist, then filled with liquid DT Filled with DT and beta- layered to yield a solid layer 100 microns thick.

UW Sept ‘03 The surface roughness was extremely low. Simply put, we had never seen such smooth beta-layers!! However, the thickness of the exposed DT was very low!

UW Sept ‘03 Progress report: deliverable No. 1, part B Extension of “DT–in–foam” experiments to prototypical IFE target geometries – i.e.: spherical diameter = 4 mm foam layer thickness = 200  m ‘free’ DT thickness ~  m total DT thickness ~  m The “Sphylinder”

UW Sept ‘03 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 conductor such as sapphire.

UW Sept ‘03 With no foam layer present, the surface roughness of the solid DT is ~2.5  m rms. This may be representative of native beta-layering in IFE sized targets.

UW Sept ‘03 The original sphylinders had high values of both low-mode and high-mode roughness.

UW Sept ‘03 Three sphylinders were returned to Insaco, Inc. to “true and polish” the spherical surface. Note: Images taken inside our cryostat (located inside the tritium facility) show a lower measured 1D roughness because the depth-of-field of that optical arrangement is much narrower than for our microscope in the ‘tritium- free’ laboratory.

UW Sept ‘03 3 He bubbles are still observed in the ‘polished’ sphylinders ‘Post-polish’ sphylinder with 487 µm- thick DT 5.7 hrs T = K ‘Pre-polish’ sphylinder with 430 µm- thick DT 6 hrs, T = K

UW Sept ‘03 The 450 µm DT solid layer equilbrated at just over 2 µm, then roughened to more than 5 µm during cooldown Note: equilibrium reached in just 3 hours!!

UW Sept ‘03 Plastic coated sphylinders? We hypothesized that heterogeneous 3 He 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 not yet had an opportunity to mount this parylene coated sphylinder in the tritium apparatus.

UW Sept ‘03 The sphylinders, are much rougher than most of our previous substrates have been, even after polishing. Cumulative roughnesses of the sapphire substrates are on the order of 0.5 micron, nearly as large as our best DT layers on foam! Low mode ( l < 10) substrate roughness may increase the apparent roughness of the DT solid layer. High mode ( l > 100) substrate roughness should not imprint on the DT roughness, especially as the DT layer thickness builds up. However, high mode roughness may contribute to heterogeneous 3 He bubble formation.

Because it may not be possible to prepare a sufficiently smooth sphylinder, we* have evaluated the effect of a ‘rough’ substrate on a beta-layered surface * - Drew Geller, in collaboration with Tom Asaki (Los Alamos) and with absolutely no help from JKH!

UW Sept ‘03 A perturbative analysis was constructed... … and solved for both the cylindrical and spherical cases...

UW Sept ‘03 … with appropriate boundary conditions. Boundary conditions: Outer surface of solid is isothermal, Inner surface of solid is isothermal, Temperatures of solid and vapor match at the solid-vapor interface, No sources of heat at the interface,

UW Sept ‘03 We can now calculate the imprint of substrate roughness on the inner DT layer: Cylinder: Sphere: [Conversion of 1D power spectrum to 2D can be done per S.M. Pollaine, S.P. Hatchett, and S.H. Langer, LLNL ICF Quarterly Rept. 4, pp (1994).]

UW Sept ‘03 But our layers in the sphylinder are currently too rough for this to matter, due to bubbles

UW Sept ‘03 The next step still remains to add a foam layer:

UW Sept ‘03 But because the foam-filled sphylinder is a later deliverable, we have decided to concentrate our efforts on the ‘heater cell’: 1March 2, 2003, Measure the roughness spectrum of solid DT beta-layered inside a thin (~50  m-thick) layer of foam material as a function of temperature. 2May 30, 2003, Fabricate and assemble apparatus for measuring the response of a solid DT layer to the sudden onset of high thermal flux. 3August 31, 2003, Deposit a layer of solid DT inside a cylindrical heater winding and observe the response to a sudden onset of high thermal flux. 4November 30, 2003, Prepare a modified heater winding incorporating an intermediate layer of fine-pore-sized foam (as in a high-gain direct-drive target) 5February 29, 2004, Complete final design drawings for apparatus to measure the elastic modulus and yield strength of solid DT at temperatures near 19 K. 6May 30, 2004, Measure the roughness spectrum of solid DT beta-layered inside a prototypical (~200  m-thick) layer of foam material. 7August 31, 2004, Fabricate apparatus for measuring the elastic modulus and yield strength of solid DT at temperatures near 19 K. 8November 30, 2004, Deposit a layer of solid DT inside a foam-lined cylindrical heater winding and observe the response to a sudden onset of high thermal flux. 9February 28, 2005, Measure the elastic modulus and yield strength of solid DT at temperatures near 19 K. 10May 30, 2005, Modify apparatus for measuring the elastic modulus and yield strength of solid DT to incorporate a fine-pore-sized foam. 11August 31, 2005, Measure the elastic modulus and yield strength of foam-reinforced solid DT. 12November 30, 2005, Modify the LANL CPL apparatus to incorporate IR irradiation of the layering sphere. 13February 28, 2006, Observe response of a DT-filled spherical prototypical high-gain direct-drive target to the sudden onset of IR heating.

UW Sept ‘03 The effect of a rapid temperature transient on a solid DT layer- The Heater Cell Progress report: deliverable No. 2 & 3,

UW Sept ‘03 A new beta-layering cell has been designed, fabricated, assembled and tested.

UW Sept ‘03 The entire heater cell has been meticulously assembled

UW Sept ‘03 John Sheliak has designed (and is building) new electronics to provide cw or pulsed power input and rapid temperature readout capabilities.

UW Sept ‘03 The heater cell has been installed in the cryostat Remaining tasks: -Complete the electronics -Acquire a fast data logger -Calibrate the Cernox thermometer -Test with D 2, then fill with DT! -We are verrrry close to meeting our milestone ( but already one month late ).

UW Sept ‘03 presented by Jim Hoffer, LANL DT/foam modulus and yield Target Survival Workshop

UW Sept ‘03 LANL is preparing a stress-strian cell to directly measure the yield strength of solid DT. The design and drawings are complete; machining of parts have begun.

UW Sept ‘03 What the camera will see: Camera resolution field: 2mm x 2mm 1024 x 1024 pixels, 12 bit dynamic range, DT edges determined to < 1  m.

UW Sept ‘03 Adding a block of foam to the anvils is a later task: 1March 2, 2003, Measure the roughness spectrum of solid DT beta-layered inside a thin (~50  m-thick) layer of foam material as a function of temperature. 2May 30, 2003, Fabricate and assemble apparatus for measuring the response of a solid DT layer to the sudden onset of high thermal flux. 3August 31, 2003, Deposit a layer of solid DT inside a cylindrical heater winding and observe the response to a sudden onset of high thermal flux. 4November 30, 2003, Prepare a modified heater winding incorporating an intermediate layer of fine-pore-sized foam (as in a high-gain direct-drive target) 5February 29, 2004, Complete final design drawings for apparatus to measure the elastic modulus and yield strength of solid DT at temperatures near 19 K. 6May 30, 2004, Measure the roughness spectrum of solid DT beta-layered inside a prototypical (~200  m-thick) layer of foam material. 7August 31, 2004, Fabricate apparatus for measuring the elastic modulus and yield strength of solid DT at temperatures near 19 K. 8November 30, 2004, Deposit a layer of solid DT inside a foam-lined cylindrical heater winding and observe the response to a sudden onset of high thermal flux. 9February 28, 2005, Measure the elastic modulus and yield strength of solid DT at temperatures near 19 K. 10May 30, 2005, Modify apparatus for measuring the elastic modulus and yield strength of solid DT to incorporate a fine-pore-sized foam. 11August 31, 2005, Measure the elastic modulus and yield strength of foam-reinforced solid DT. 12November 30, 2005, Modify the LANL CPL apparatus to incorporate IR irradiation of the layering sphere. 13February 28, 2006, Observe response of a DT-filled spherical prototypical high-gain direct-drive target to the sudden onset of IR heating.

UW Sept ‘03 presented by Jim Hoffer, LANL Low temperature layering Target Survival Workshop

UW Sept ‘03 Cooling to 16 K increased the surface roughness by about 50%, but it is still ≤ 1.4 µm

UW Sept ‘03 The ‘reverse sum’ of the l-mode roughness shows the DT-in-foam roughening process

UW Sept ‘03 Roughening observed during the cooling process recovers only partially as the temperature is raised

UW Sept ‘03 Roughening appears to be dominated by modes 10 to 50 & mode 2

UW Sept ‘03 We have measured the effect on the layer roughness of cooling from above K down to 15 K Cooling an equilibrated DT-in-foam layer from K to 16 K increased the average surface roughness 50-75%, but on average the layers remain as smooth as, or smoother than those from our previous experiments formed above 19 K without foam. (Re-crystallization might be occurring during cooling???) Warming the cooled DT solid layer back to K does not reverse the roughening that was observed during the cooling process, although some smoothing is observed (~15%). Roughening appears to be dominated by l-mode 2 and modes By in large, these same modes remain degraded during re-warming.

UW Sept ‘03 The question ‘in limbo’: How low can we go?” (and still have a smooth DT layer) Cracking phenomenon will almost certainly depend on the morphology of the DT solid. Polycrystalline DT may better withstand cracking. The final answer depends on cell geometry, total layer thickness, solid morphology, and the yield strength of solid DT as a function of rate and temperature. We previously studied beta-layering in a 2 mm-diameter hemispherical geometry. During a rapid cool-down, a 318  -thick, pure DT layer formed cracks at temperatures below ~16 K. When the cell was warmed back up 4 hours later, fine 3 He bubbles appeared uniformly throughout the solid layer, but the cracks completely disappeared. t = 0, T = Kt = 1 min., T = Kt = 2 min., T = Kt = 3 min., T = 9.52 Kt = 255 min., T = 18.8 K

UW Sept ‘03 Solid DT-in-Sphylinder Cooling Sequence from 19K to 16K 19K : 6 hrs17.4K : +8min16K : +16min 16K : +38min16K : +78min16K : +138min

UW Sept ‘03 The 450 µm DT solid layer equilbrated at just over 2 µm, then roughened to more than 5 µm during cooldown

UW Sept ‘03 Low modes (l~8) appear to dominate the roughening process during cooldown to 16 K