Development of Perdeuterated Polymer Foams for Inertial Confinement Fusion Targets in China

Abstract

In this paper, we report the progress made in fabrication of perdeuterated polymer foam materials such as deuterated polystyrene (d-PS), deuterated polyethene (d-PE), and deuterated divinylbenzene (d-DVB) based on the inertial confinement fusion (ICF) research in China. Perdeuterated DVB foams were fabricated using the high internal phase emulsion (HIPE) technique, and perdeuterated PS and PE foams were prepared via the thermally-induced phase separation (TIPS) of polymer solution and freeze-drying. As a result, foams with a deuterium/hydrogen (D/H) ratio of more than 95%, density of 10-200 mg/cm 3 , and average porous sizes of 1-20 µm were obtained. Deuterated polymer foams as a type of target material can be widely used in high-gain, high-density compression fusion targets, for example, as supporting materials in multilayer targets, as holders of liquid or solid DT layers in cryogenic targets, and so on. They are more essential than other protonated polymer foams because of the following advantages [1]: they are more chemically and physically stable, are nonradioactive, and have a very high proportion of D/H (more than 98%). Therefore, not only can they increase the fusion fuel density of fusion targets but can also improve the wettability of liquid deuterium-tritium (DT).It is well known that in mild conditions the exchange of deuterium and hydrogen is very difficult. Therefore, the method of fabrication of deuterated polymer foams is similar to that for protonated polymers such as HIPE, TIPS, and Sol-Gel. However, there are few deuterated polymers for the fabrication of low-density foams at present.Steckle et al.[2] first reported a method to synthesize deuterated DVB (d-DVB). Moreover, they prepared perdeuterated polymer foams with d-DVB by means of the HIPE technique. The synthesis method is quite complex and includes a D/H exchange reaction using the high temperature and dilute acid (HTDA) technique. In our work, partially replaced deuterium foams were prepared from deuterated styrene (d-St) and protonated divinylbenzene (DVB) [3] using the HIPE technique. However, the deuterated ratio values of those foams were less than 90%.As an alterative technique, TIPS could be a competent method for fabricating perdeuterated polymer foams. Combined with freeze-drying, it can be used to prepare many low-density polymer foams such as polystyrene, PE, poly(4-methyl-1-pentene) (PMP), and cellulose. The author's e-mail: zhlmy@sina.com structure and density of the fabricated foams can be controlled by controlling the concentration of the polymer solution and the freezing rate of the solution. Using these two techniques, PMP, PS, and PE foams were prepared in our laboratory. They had a density of 10-200 mg/cm 3 and an average porous size of 1-10 µm. Meanwhile, d-PS and d-PE were also prepared; they had D/H ratios and purities of more than 98%.Because of different demands of ICF experiments in terms of density, porous size, deuterium content, etc, different foams need to be developed. In this paper, the fabrication methods...