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Fabrication Improvements of the Aluminum Unconverted Light Shields for the National Ignition Campaign

J. F. Hund, J. W. Crippen, K. Clark, N. Martinez, D. J. Jasion, M. P. Farrell, D. T. Frey

Fusion Science and Technology / Volume 63 / Number 2 / March 2013 / Pages 252-256

Technical Paper / Selected papers from 20th Target Fabrication Meeting, May 20-24, 2012, Santa Fe, NM, Guest Editor: Robert C. Cook

The National Ignition Campaign (NIC) target consists of precisely machined and assembled components. A subset of the components of this target is the aluminum shielding around the silicon support and cooling arms, which is designed to alleviate harmful unconverted light reflecting from the arms into the laser optics. This NIC target shielding consists of two external shields and four inner shields located between the arms. Recently, we have developed a process to add a plastic coating to the shields with precisely defined edges that can survive pressing the part into a three-dimensional shape. After this process was demonstrated on prototypes, it was further refined to improve yield and is currently being used to fabricate and deliver parts for NIC experiments on a regular basis. The final process that we developed consists of seven steps to fabricate these shields: (1) applying a photolithographed plastic layer to electrically isolate the shields from the electrical traces on the cooling arms, (2) plasma etching to improve adhesion during the subsequent aluminum coating, (3) large-batch electron-beam aluminum coating, (4) laser cutting and custom die cutting to various shapes and specified patterns, (5) utilizing heat pressing techniques that soften the plastic coating enough to be coined into a three-dimensional shape, (6) accurate positioning and bonding of Mylar liners under the tops of the shields, and (7) final characterization. Through these process steps high process yields were achieved against the rigorous NIC requirements.

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