Precision Manufacturing of Inertial Confinement Fusion Double Shell Laser Targets for OMEGA

Abstract

Double shell targets have been built by Lawrence Livermore National Laboratory (LLNL) for inertial confinement fusion (ICF) experiments on the Omega laser at the University of Rochester and as a prelude to similar experiments on NIF. Of particular interest to ICF studies are high-precision double shell implosion targets for demonstrating thermonuclear ignition without the need for cryogenic preparation. Because the ignition tolerance to interface instabilities is rather low, the manufacturing requirements for smooth surface finishes and shell concentricity are particularly strict. This paper describes a deterministic approach to manufacturing and controlling error sources in each component. Included is the design philosophy of why certain manufacturing techniques were chosen to best reduce the errors within the target. The manufacturing plan developed for this effort created a deterministic process that, once proven, is repeatable. By taking this rigorous approach to controlling all error sources during the manufacture of each component and during assembly, we have achieved the overall 5 µm dimensional requirement with sub-micron surface flaws. Strengths and weaknesses of the manufacturing process will be discussed.

Experimental measurement of Au M-band flux in indirectly driven double-shell implosions

“…The fabrication of double-shell targets is considerably more difficult than their single-shell counterparts, requiring precision micromachining and accurate assembly of the various hemispherical shells. Targets employing lower density materials than those eventually required for ignition on NIF (CH vs. Au-Cu or Be) have recently been fabricated to the required precision 8 and have successfully been fielded on the Omega laser at the Laboratory for Laser Energetics, University of Rochester 9 . Several additional fabrication challenges remain, however, for the NIF-scale ignition targets.…”

Fabrication of Double Shell Targets with a Glass Inner Capsule Supported by SiO2Aerogel for Shots on the Omega Laser in 2006

“…The other aerogel hemisphere was then placed on top of the capsule. Finally, the upper ablator component was placed on top to complete the assembly [2]. Double shell targets manufactured using this assembly method performed relatively well in laser shot experiments [1], [2].…”

“…Several previous researchers have fabricated double shell targets with varying degrees of success, and a variety of different manufacturing processes have been reported in the literature [3]- [6]. The current effort used a manufacturing strategy very similar to the approach developed at Lawrence Livermore National Laboratory in recent years [2]. Schematic illustrations of the basic outline of the manufacturing plan appear in Figure 2 and Figure 3.…”

“…As a prelude to fielding ignition double shell targets on NIF, efforts are underway to field scaled ignition-like double shells on the Omega laser facility. Double shell targets shot on the Omega laser in 2003 produced encouraging results but identified several design aspects that could be changed to potentially improve performance [1], [2]. Many of these changes were incorporated into the current targets.…”

Hohlraum-Driven Ignitionlike Double-Shell Implosions on the Omega Laser Facility

“…1], and strict fabrication requirements [15] were applied to ensure repeatable target performance. Micromachined carbonized-resorcinal-formaldehyde foam hemispherical inserts of density 50mg/cc were used to support the inner shell and meet the shell concentricity specification (<5µm).…”