Review of hydro-instability experiments with alternate capsule supports in indirect-drive implosions on the National Ignition Facility

Abstract

Hydrodynamic instability growth of capsule support membranes (or “tents”) has been recognized as one of the major contributors to the performance degradation in high-compression plastic capsule implosions at the National Ignition Facility (NIF) [E. M. Campbell et al., AIP Conf. Proc. 429, 3 (1998)]. The capsules were supported by tents because the nominal 10-μm diameter fill tubes were not strong enough to support capsules by themselves in indirect-drive implosions on NIF. After it was recognized that the tents had a significant impact of implosion's stability, new alternative support methods were investigated. While some of these methods completely eliminated tent, other concepts still used tents, but concentrated on mitigating their impact. The tent-less methods included “fishing pole” reinforced fill tubes, cantilevered fill tubes, and thin-wire “tetra cage” supports. In the “fishing pole” concept, a 10-μm fill tube was inserted inside 30-μm fill tube for extra support with the connection point located 300 μm away from the capsule surface. The cantilevered fill tubes were supported by 12-μm thick SiC rods, offset by up to 300 μm from the capsule surfaces. In the “tetra-cage” concept, 2.5-μm thick wires (carbon nanotube yarns) were used to support a capsule. Other concepts used “polar tents” and a “foam-shell” to mitigate the effects of the tents. The “polar tents” had significantly reduced contact area between the tents and the capsule compared to the nominal tents. In the “foam-shell” concept, a 200-μm thick, 30 mg/cc SiO2 foam layer was used to offset the tents away from the capsule surface in an attempt to mitigate their effects. These concepts were investigated in x-ray radiography experiments and compared with perturbations from standard tent support. The measured perturbations in the “fishing pole,” cantilevered fill tube, and “tetra-cage” concepts compared favorably with (were smaller than) nominal tent perturbations and were recommended for further testing for feasibility in layered DT implosions. The “polar tents” were tested in layered DT implosions with a relatively-stable “high-foot” drive showing an improvement in neutron yield in one experiment compared to companion implosions with nominal tents. This article reviews and summarizes recent experiments on these alternate capsule support concepts. In addition, the concept of magnetic levitation is also discussed.

Recent progress in quantifying hydrodynamics instabilities and turbulence in inertial confinement fusion and high-energy-density experiments

“…The fill tube is also a localized defect and even its X-ray shadow is detrimental [70,71]. Mitigation strategies of the shadow [72] reduced diameter fill tubes [71], and alternate targets supports [73] are therefore under consideration. The fill tube impact on the hot spot has been recently inferred from nuclear diagnostics [74].…”

Control of superconductivity in MgB2 by ion bombardment

“…Thin films of MgB 2 are attractive for various applications, including radiofrequency (RF) cavities [3], superconductor-based logic devices [2,4], and as a support mechanism for inertial confinement fusion fuel capsules [5]. This latter application, which is the driving force of the present study, imposes several restrictions and challenges [5,6]. One such challenge, which is common to all applications relying on magnetic flux pinning, is the optimization of superconducting properties by defect engineering.…”

Superconducting films of MgB2 via ion beam mixing of Mg/B multilayers

“…Superconducting thin films of MgB 2 are valuable for applications such as radio frequency (RF) cavities [1], superconductor-based microelectronics [2,3], and the levitation of inertial confinement fusion (ICF) fuel capsules [4,5]. For this ICF-related application [4,5], which is the focus of the present work, the MgB 2 films deposited onto spherical substrates must possess low surface roughness to limit hydrodynamic instabilities during laser-driven implosion. The growth of MgB 2 films on such non-planar substrates is inherently non-epitaxial and has proven to be challenging.…”