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Increased X-Ray Opacity of GDP Capsules from High Intensity X-Ray Exposure

K. L. Sequoia, H. Huang, R. B. Stephens, K. A. Moreno, K. C. Chen, A. Nikroo

Fusion Science and Technology / Volume 59 / Number 1 / January 2011 / Pages 35-38

Technical Paper / Nineteenth Target Fabrication Meeting

Inertial confinement fusion capsules must be manufactured with a high degree of azimuthal symmetry to avoid degradation by Rayleigh-Taylor instabilities. Therefore, the azimuthal fluctuations of each capsule must be characterized. We have developed a precision radiography method capable of measuring X-ray optical depth fluctuations to 1 part in 104 with a spatial resolution of 120 m. Achieving the measurement accuracy requires counting many photons.

Recent measurements of glow discharge polymer (GDP) capsules show that the high X-ray intensity required to minimize measurement time modifies the GDP shell by increasing the oxygen atomic percent. An equatorial band forms that is more optically dense than the remainder of the capsule. We believe that free radicals are formed in the GDP as a result of the X-ray exposure. These free radicals preferentially absorb oxygen from the air. We will discuss how this optically dense band forms, how it is measured, and possible solutions to this issue.

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