Cryogenic targets for shock ignition: Modeling of diffusion filling with a hydrogen fuel

Abstract

Currently, within the framework of the International Atomic Energy Agency (IAEA), a coordination research project (CRP) «Pathways to Energy from Inertial Fusion: Materials Research and Technology Development» has been started [1]. The P.N. Lebedev Physical Institute (LPI) takes part in this CRP under contract No. 24 154 with the aim to develop technologies for mass production of shock ignition, cryogenic fuel targets with a low initial aspect ratio because they are supposed to be more hydrodynamicaly stable during the implosion [2, 3]. A key area of research is the creation of methods and technologies with an emphasis on repetition systems [1]. For this purpose, the LPI proposes to use a unique free-standing target (FST) method [4, 5], which works with free-standing and line-moving targets. This makes it possible to economically produce a large number of fusion targets and inject them with the required rate at the focus of a powerful laser facility or an inertial fusion reactor. The preparatory stage before the formation of any targets is their filling with a hydrogen fuel, which is deuterium (D2) or deuterium-tritium mixture (D-T). In the world practice, the target shells can be filled by diffusion of the gaseous fuel through the shell wall or by injection of the liquid fuel through the fill tubes a few tens of micrometers in diameter built into the shell wall. This report at the first time presents the results of modeling the project targets filling by diffusion up to pressures of 1250 atm at 300 K for various materials of the target shell. The issues of realizing an optimal filling procedure are discussed. It is based on a ramp filling regime with a constant pressure gradient, which allows one to avoid mechanical destruction of the targets during the entire filling cycle.