Early-stage diagnosis of shock wave in indirect-drive implosions with wide-angle VISAR

Implosion symmetry represents a critical parameter governing compression efficiency and is closely linked to radiation-driven asymmetry, laser-plasma instabilities, and hydrodynamic instabilities. The evolution of asymmetry during early implosion phases impacts compression performance yet remains experimentally challenging to quantify. In this work, a wide-angle velocity interferometer system for any reflector (VISAR) was employed to diagnose the compression dynamics during the initial stage of indirect-drive implosions. Two experimental configurations—focused on total laser energy control and laser energy distribution control—were implemented to validate the diagnostic capabilities of the wide-angle VISAR. At 3 kJ drive energy, the wide-angle VISAR successfully resolved early shock transmission within the carbon hydrogen (CH) layer, with measured shock velocities of ~ 13 km/s. Under asymmetric drive conditions, the asymmetric evolution process of the capsule (P₂) exhibited negative, near-linear growth within 0.5 ns, ultimately reaching ~ 30%. For higher drive energies (6.4 kJ), preheating effects induced a significant reduction in normalized reflectivity prior to shock arrival in the CH layer, resulting in irreversible fringe degradation within < 0.5 ns. These findings confirm the efficacy of wide-angle VISAR for diagnosing early-stage indirect-drive implosions. To extend its applicability, future development should focus on radiation-shielding architectures that enhance imaging robustness while mitigating preheating effects. Such advancements will enable operation at ignition-relevant energies, establishing wide-angle VISAR as a pivotal diagnostic tool for inertial confinement fusion research.