Encapsulation of Low Density Materials for the First Stage of Fast Ignition Realization Experiment (FIREX-I) - Control of Microstructure and Gelation Process using a Phase-Transfer Catalyst and Tailored Polymers

Development of foam capsule fabrication for cryogenically cooled fuel targets is overviewed in the present paper. The fabrication development was initiated as a part of the Fast Ignition Realization Experiment (FIREX) project at the ILE, Osaka University in the way of bilateral collaboration between Osaka University and national institute for fusion science (NIFS). For the first stage of FIREX (FIREX-1), a foam cryogenic target was designed where low-density foam shells with a conical light guide will be cooled down to the cryogenic temperature and will be fueled through a narrow pipe. The required diameter and thickness of the capsule are 500 mum and 20 mum, respectively. The material should be low-density plastics foam. We have prepared such capsules using 1) new material of (phloroglucinolcarboxylic acid)/formalin resin to control kinematic viscosity of the precursor, 2) phase-transfer-catalyzed gelation process to keep density matching of three phases of the emulsion. 3) non-volatile silicone oil as outer oil of emulsion in order to prevent hazard halogenated hydrocarbon and flammable mineral oil. The obtained foam capsule had fine structure of 180 nm (outer surface) to 220 nm (inner surface) and uniform thickness reaching to resolution limit of optical analysis (~0.5 mum). A small hole was made before the solvent exchange and the drying process to prevent distortion due to volume changes. The density of dried foam was 0.29 g/cm . After attaching the petawatt laser guiding cone and fueling glass tube, poly([2,2]paracyclophane) was coated on the foam surface and supplied for a fueling test of cryogenic hydrogen.