The impact of preheating on wide-angle VISAR diagnostic in indirect-drive implosion experiments

The symmetry diagnosis of the implosion process can reflect the compression evolution, as well as laser ablation symmetry and hydrodynamic instability, which is a significant research topic for improving implosion performance in inertial confinement fusion (ICF). The wide-angle velocity interferometer system for any reflector (VISAR) has the ability to diagnose three-dimensional implosion compression. However, the preheating phenomenon limits the applicability of wide-angle VISAR. This work developed a radiation hydrodynamics simulation model of wide-angle VISAR preheating to investigate the effect of various parameters on diagnostic system performance. It specifically investigates the impact of ablator layer thickness, shielding thickness, laser energy, and M-band x-ray radiation fractions on the wide-angle VISAR. The results indicate that excessively thin ablator and shielding layers result in the preheating of the ellipsoidal mirror. The increased peak radiation temperature shifts the energy spectrum into the M-band region, causing the ellipsoidal mirror to be preheated and melted, and the wide-angle VISAR to lose its diagnostic capability. Indirect drive implosion experiments were carried out to verify the simulation results. When the peak radiation temperature is 160 eV, with insufficient thickness of the ablator layer and the shielding layer, the shock wave enters the CH layer for 0.50 ns, and the ellipsoidal Al mirror will be completely melted. However, the current wide-angle VISAR can obtain velocity information at lower drive energy. In the future work, it is planned to shield the preheating effects, which will be helpful to promote the application of wide-angle VISAR for 3D symmetry diagnostics under high radiation temperature conditions and ultimately provide an important diagnostic tool for ICF.