Indirectly Driven High Yield Implosions and Phase Contrast Imaging the N+1 Shock

Implosion designs are presented which offer the potential to significantly increase the yield of indirect drive implosions relative to the N210808 National Ignition Facility (NIF) shot, which is used as a baseline. One-dimension (1D) radiation hydrodynamic simulations are presented in which the proposed modification increases the yield by a factor of 10, this is achieved by tuning the N+1 shock to reduce the shell adiabat and as a result increase areal density by a factor of 1.5. N+1 tuning alone increases the yield in simulations from 1.2MJ to 9.4MJ, combining N+1 tuning and the shock augmented ignition scheme gives a yield of 12MJ. Although the simulations presented are 1D, they also show equivalent or reduced in-flight aspect ratio (IFAR) and implosion velocity, indicating reduced susceptibility to 2D Rayleigh-Taylor instabilities relative to the base design of the N210808 NIF shot. Further simulations with alpha heating turned off also show improved areal density and IFAR. A pulse shaping sensitivity study is also presented indicating that this design is robust against the typical pulse shaping errors of a NIF-like laser system.

A synthetic diagnostic code (GREENER) is also presented, it was written to simulate X-ray phase contrast imaging (XPCI), a particularly useful diagnostic for examining shocks and interfaces. The synthetic diagnostic code was developed within the Geant4 framework and is a Monte-Carlo based raytracer. It is shown to be able to produce synthetic images of 1D, 2D and 3D hydrodynamic simulations; importing complex geometries while preserving the required surface angles to allow refraction to be modelled accurately.

Finally, these threads are brought together by using the presented synthetic diagnostic code to design an experiment to image the N+1 shock on an indirect drive implosion, this experiment would verify the underpinning physics of the N+1 shock and pave the way for applying the N+1 tuning scheme to ignition scale experiments.