Voidless fuel solidification within a foam material is attempted for the development of a Fast Ignition Realization EXperiment (FIREX) target. A typical target consists of a foam shell with a thin solid fuel layer, a gold cone guide and a glass fill tube. The foam layer is formed with aggregations of tiny cells. The porous foam material has the advantage of forming a uniform layer in a liquid state by the effect of capillarity. Random liquid–solid transitions of fuel, however, would cause void spaces in each cell because of their different densities. To form a voidless solid fuel layer in the FIREX target, we propose a layering method, which includes the process of controlled solidification and simultaneous liquid fuel supply to the liquid/solid interface. Normal H2 is used as a surrogate fuel for our experiments. By applying a resorcinol/formalin aerogel, which has been developed in the Institute of Laser Engineering, Osaka University, instead of a foam material, formation of a solid H2 layer with reduced void spaces is preliminarily demonstrated. Related solid H2 refractive indices are measured to estimate the void fraction. Eventually, its filling factor reaches ∼99%. Furthermore, the application of the proved method is numerically simulated on the FIREX target. The method is confirmed to be applicable in it with a cone guide heating technique.
泡沫材料内无空隙燃料凝固的研究，是为了开发快速点火实现实验（FIREX）靶而进行的。典型靶由带有薄固体燃料层的泡沫壳、金锥导向器和玻璃充气管组成。泡沫层由微小细胞的聚集体形成。多孔泡沫材料具有通过毛细作用形成均匀液态层的优势。然而，燃料的随机液-固转变会因密度差异而在每个细胞中产生空隙。为了在FIREX靶中形成无空隙的固体燃料层，我们提出了一种分层方法，该方法包括受控凝固过程和同时向液-固界面供应液态燃料的过程。在我们的实验中，使用普通氢（H2）作为替代燃料。通过使用大阪大学激光工程研究所开发的间苯二酚-甲醛气凝胶代替泡沫材料，初步展示了减少空隙的固体H2层的形成。测量了相关固体H2的折射率以估算空隙率。最终，其填充率达到了约99%。此外，对该方法在FIREX靶上的应用进行了数值模拟。结果表明，该方法结合锥形导向加热技术是可行的。