Analyzing and relieving the thermal issues caused by fabrication details of a deuterium cryogenic target

Abstract

In inertial confinement fusion experiments, fuel quality is determined mainly by the thermal environment of the capsule in the layering procedure. Owing to the absence of a radial thermal gradient, formed deuterium–deuterium (DD) ice shells in the capsule are thermally instable. To obtain a solid DD layer with good quality and long lifetime, stringent demands must be placed on the thermal performance of cryogenic targets. In DD cryogenic target preparation, two issues arise, even after the capsule’s temperature uniformity has been improved by the use of thick aluminized films. The first is the inconsistent ice shape, which is related to the capsule’s thermal field. In this article, some typical fabrication details are investigated, including adhesive penetration during assembly, the presence of the fill tube, the optical properties of the hohlraum and film surfaces, the jacket–hohlraum connection, deviations in capsule location, and asymmetrical contact at the arm–jacket interfaces. Detailed comparisons of the thermal effects of these factors provide guidance for target optimization. The second issue is the instability of seeding crystals in the fill tube due to unsteadiness of the direction of the thermal gradient in the fill tube assembly. An additional thermal controller is proposed, analyzed, and optimized to provide robust controllability of tube temperature. The analysis results and optimization methods presented in this article should not only help in dealing with thermal issues associated with DD cryogenic targets, but also provide important references for engineering design of other cryogenic targets.

Demonstration of indirectly driven implosion experiments with cryogenic pure deuterium layered capsules on the Shenguang Laser Facility

“…The capsules are further cooled below the deuterium solidification temperature when the amounts of the liquid fuel inside the capsules meet the design requirements. Following specific procedures of temperature control [21,22], it is found that a uniform D-ice layer can survive for a few minutes inside the capsule. We repeated the procedures of D-ice layering fourteen times for a single target, and by characterizing the ice layer quality with phase contrast imaging (figure 2), we found that there was a 72% chance that the amplitude of mode 1 was less than 2.8 µm, and the RMS of the power spectrum in modes 2-100 was 2.2 µm in average.…”

Properties of superconducting MgB2 spherical shells deposited on 2 mm and 1 mm diameter Si3N4 spheres

“…In this paper, we present our latest progress on the fabrication and characterization of MgB 2 spherical shells. As the diameter of the capsule in ICF may vary from about 1 to 2 mm depending on the specific design and facility [19,27], we have expanded our shell fabrication on 2 mm diameter Si 3 N 4 spheres to include that on 1 mm diameter spheres as well. For both diameters (d = 2 mm and 1 mm), the T c of the MgB 2 spherical shells has been improved to the bulk value of 39 K. Electrical transport and magnetization measurements under magnetic fields have been carried out to determine the current-carrying capability as well as various characteristic fields that define the superconducting phase diagram of the spherical shells.…”