Two-photon Polymerization Printed Lattices As Support Structures in Multi-Shell ICF Targets: Platform Development and Initial Assessment

Recent interest in fielding direct drive multi-shell targets on the NIF [K. Molvig et al., Phys. Rev. Lett. 116, 255003 (2016) and S. X. Hu et al., Phys. Rev. E 100, 063204 (2019)] has highlighted the need for a low density structure to support the inner shell(s) and to avoid energy loss in the acceleration and collision process. We have developed a two-shell platform to evaluate the use of low density two-photon polymerization (2PP) printed lattices as a support structure between the shells. 2PP structures are an attractive option because they can be produced at densities as low as 5 mg/cc, which is ideal for multi-shell targets, and their 3D structure can be tailored to the user's needs. However, idealized 1D simulations of lattice strut surrogate thin shells indicate that the lattice will only isotropize before the shells collide if the strut thickness is sufficiently fine. This platform makes use of high resolution Fresnel zone plate images to evaluate the uniformity of the post-collision inner shell and provide information on how efficiently the lattice structure isotropizes. As a proof of principle, an initial experiment contrasts the case of 5 μm lattice struts that cause significant disfiguration of the inner shell with the uniform post-collision inner shell in the absence of this material. Finer lattice structures on future experiments will evaluate post-collision inner shell uniformity. This new platform and accompanying diagnostic technique can also be used to evaluate both asymmetry in capsule drive and target non-uniformities with resolution up to mode 40.