Thermal oscillation smoothing of DT solid layers for HAPL and NIF scale targets

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Deuterium-Tritium (D-T) solid fuel layers must meet stringent roughness specifications for both the ICF and IFE laser fusion programs and native beta-layering alone is unable to provide sufficient solid layer smoothing to meet these specifications at 18.3 K or below. Consequently, several supplemental smoothing options have been proposed to resolve this issue, including a technique called 'Thermal Breathing'. This technique consists of oscillating the temperature of the solid D-T layer about its equilibration temperature for a period of one to several hours. Recently, thermal oscillations have been used to successfully smooth rough solid D{sub 2} in spherical targets. In order ... continued below

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Sheliak, John D; Geller, Drew A & Hoffer, James K January 1, 2009.

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Deuterium-Tritium (D-T) solid fuel layers must meet stringent roughness specifications for both the ICF and IFE laser fusion programs and native beta-layering alone is unable to provide sufficient solid layer smoothing to meet these specifications at 18.3 K or below. Consequently, several supplemental smoothing options have been proposed to resolve this issue, including a technique called 'Thermal Breathing'. This technique consists of oscillating the temperature of the solid D-T layer about its equilibration temperature for a period of one to several hours. Recently, thermal oscillations have been used to successfully smooth rough solid D{sub 2} in spherical targets. In order to study this particular smoothing technique, we examined the effects of thermal oscillations on equilibrated D-T solid layers, using both ICF and IFE scale layering cells and layer thicknesses. The D-T solid layers that were Subjected to thermal breathing in these studies were equilibrated at temperatures ranging from 16.0 K to 19.25 K, followed by 1.5 to 2 hours of temperature oscillations. During the HAPL scale experiments the amplitude and period of the oscillations were both varied to examine parametric effects of these variables on final layer roughness. In both sets of experiments, once the oscillations completed we allowed the layers to 'relax' at their initial equilibration temperature for another 1 to 2 hours, to observe any 'rebounding' or re-roughening that might occur. The rCF scale experiments were performed using a 2 mm beryllium torus, for which the layer was free from optical distortions that were observed in our IFE scale cell (a 4 mm dia. sapphire sphere-cylinder). Our results showed a temperature dependent smoothing effect ofthe DT solid layer ranging from 20% to 35% over the temperature range of 17.3 K to 19.0 K for the rCF-scale, 2-mm celL The final RMS roughness for layers grown in this 2-mm Be torus was on average less than 1 /lm for modes 7 and above. Results for the rFE scale cell showed a temperature dependent smoothing effect that varied from 5% to more than 30% over a 16.0 K to 18.3 K temperature span, and which resulted in an average overall RMS roughness of3.8 /lm at 17.3 K and 3.2 /lm at 18.3 K. We discuss the configuration ofboth of these DT layering cells, the equilibration and oscillation parameters were used, and results that show thermal oscillations can make significant contributions to the smoothing of normally equilibrated beta-layered surfaces, as well as potentially reducing the time required to produce smooth solid DT surfaces.

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  • Journal Name: Fusion Science and Technology

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  • Report No.: LA-UR-09-00757
  • Report No.: LA-UR-09-757
  • Grant Number: AC52-06NA25396
  • Office of Scientific & Technical Information Report Number: 956394
  • Archival Resource Key: ark:/67531/metadc929095

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  • January 1, 2009

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  • Nov. 13, 2016, 7:26 p.m.

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  • Dec. 12, 2016, 6:47 p.m.

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Sheliak, John D; Geller, Drew A & Hoffer, James K. Thermal oscillation smoothing of DT solid layers for HAPL and NIF scale targets, article, January 1, 2009; [New Mexico]. (digital.library.unt.edu/ark:/67531/metadc929095/: accessed October 17, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.