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Properties of Silicon-Doped GDP Shells Used for Cryogenic Implosions at OMEGA

R. W. Luo, A. L. Greenwood, A. Nikroo, C. Chen

Fusion Science and Technology / Volume 55 / Number 4 / May 2009 / Pages 456-460

Technical Paper / Eighteenth Target Fabrication Specialists' Meeting /

One suggested approach to decreasing preheat of Laboratory for Laser Energetics cryotargets is to add a silicon dopant ~4 to 6 at.% to normal plasma polymer. As in the case of pure CH and CD shells used previously, the physical properties of these shells are of utmost importance to allow proper fielding for cryogenic shots. We have fabricated and characterized two types of Si-doped glow discharge polymer (GDP) capsules: single-layer Si-doped GDP shells (SiGDP) and double-layer Si-doped GDP/SCD shells (SiGDP/SCD).

The Si-doped GDP shells with an ~870-m diameter and 5-m-thick walls were fabricated to meet the cryogenic direct laser fusion experiment requirements. Si-doped GDP shells with <0.25-m wall variation and 5% silicon dopant level were delivered. These cryogenic shells can survive a 1000-atm D2 or deuterium-tritium fill and cryogenic cooling without bursting or buckling. With an average buckle strength of 70 psi, a half-life of 12 s, and a D2 permeability at 20°C of 2.4 × 10-14 (mol × m/m2 × Pa × s), Si-doped GDP shells meet the criteria for cryogenic experiments. A possible drawback of the SiGDP layer is its rapid OH pickup due to exposure to air, which can increase the amount of infrared light absorbed in the shell wall as compared to D2 ice and possibly result in a poor ice uniformity during the cryogenic layering process. The absorption coefficient of the SiGDP at 3160 cm-1 measured by Fourier transform infrared spectroscopy is ~48 cm-1 at 0.1 h to ~130 cm-1 at 167 h of air exposure.

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