First Double-Shell Keyhole Target Experiment
In February 2018, a NIF experiment led by Los Alamos National Laboratory (LANL) was the first to use a double-shell keyhole target with the first high-Z (high atomic number) inner-shell capsule to study preheating of the inner capsule shell by hard x-rays generated by the hohlraum. The target was fabricated by LANL, LLNL and General Atomics. Double-shell capsules are an alternative approach to achieving indirect-drive ignition on NIF. The capsule consisted of an outer low-Z (aluminum) shell, an inner layer of foam, and a bi-layer tungsten/beryllium inner shell. The keyhole target is a diagnostic variation of the standard NIF hohlraum in which a gold conical tube is inserted through the hohlraum wall into the interior of the capsule, providing optical access to the propagating laser shocks so they can be imaged by the Velocity Interferometer System for any Reflector (VISAR), a time-resolved Doppler velocity camera. The experiment benchmarked simulations of the main shock driven through the inner capsule by the collision of the two shells.
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