High-Gain Laser-Fusion Target: Physics Design Challenges and Progress in High-Compression Implosions in China

The US National Ignition Facility (NIF) demonstrated laser fusion ignition in December 2022, achieving ten ignitions and a record target gain of 4.1 by the end of 2025, confirming the scientific feasibility of laser fusion. Transitioning to high-gain fusion, however, remains a critical challenge. Here we review the key physics challenges and progress in high-compression implosions at the SG-100 kJ facility in China. We reveal that the essential nature of high-compression implosions is the coupled growth of hydrodynamic instabilities across three interfaces: the ablative Rayleigh–Taylor instability at the outer ablation front, the classical Rayleigh–Taylor instability and perturbation feed-out at the intermediate ablator-fuel interface, and the deceleration-phase instability at the hot-spot interface. We examine the NIF’s path from the US National Ignition Campaign (NIC) setback to the High Yield Big Radius Implosion Design (HYBRID) success, distilling the central lesson that implosion design must shift from pursuing the one-dimensional theoretical optimum to achieving three-dimensional engineering robustness, and identify four intrinsic contradictions: between fusion gain and implosion stability, implosion velocity and stability, drive intensity and beam–target coupling efficiency, and implosion compression and drive asymmetry. On the original research front, we report systematic advances on the SG-100 kJ facility: identifying the intermediate interface mix as the primary bottleneck, discovering the perturbation feed-out mechanism, proposing an Atwood-number tuning strategy, and developing an innovative slowly-ramped main pulse design. These experiments have achieved controlled implosions with convergence ratios exceeding 30, demonstrating that entropy reduction and mixing control can be simultaneously realized. Our findings establish that the core of high-gain target design is the precise control of multi-interface hydrodynamic instabilities under high compression, and the innovative approach pursued in China provides essential physics support for the engineering feasibility of inertial fusion energy.