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Reduction of Isolated Defects on Ge Doped CH Capsules to Below Ignition Specifications

K. C. Chen, Y. T. Lee, H. Huang, J. P. Gibson, A. Nikroo, M. A. Johnson, E. Mapoles

Fusion Science and Technology

Volume 51 / Number 4 / May 2007 / Pages 593-599


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The NIF Ge-doped CH capsule should be free of isolated defects on the outer surface. The allowed number and dimensions of large isolated defects over the entire capsule surface is given by the isolated feature specification.

To date NIF-thickness (146 m) capsules are plagued by a few isolated large domes on the outer surfaces that otherwise meet the atomic force microscope (AFM) spheremap modal power spectra specification. The large domes on the capsule surfaces were mostly caused by particulate contamination from the wear of an agitation tapping solenoid inside the coater. By eliminating the solenoid and using an alternate rotation agitation, most thick-walled capsules become free of large isolated defects and meet the AFM spheremap modal power spectra standard.

The number and size of the isolated defects on the outer surface were characterized with a high resolution phase-shifting diffractive spherical interferometer and checked against the NIF isolated defect specification. The results show the isolated defects on the rolled capsule are below the isolated defect specification. The growth modeling of the remaining nanometer-height domes on the capsules indicates most of these small domes come from the mandrel surface.

The rolled capsules meet the layer thickness, doping levels and wall thickness specifications and have good wall uniformity of ± m.

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