Burn efficiency Φ is a key to increasing target gain in inertial fusion energy. The central ignition scheme was proposed for inertial confinement fusion (ICF) in 1960s, with the fusion peak being dominated by temperature and located in a central hot spot surrounded by a much denser and colder shell, which requires a convergence ratio Cr~35 and an implosion velocity u ~350–400 km/s to achieve Φ = 10–30%. We have proposed an ICF amplifier scheme, which also includes the implosion, stagnation, and ignition, with fusion starting from the central hot spot and serving as a spark for ignition, while it can achieve Φ = 30–50% via two cascading nuclear explosions at Cr~20 and u ~300 km/s. Our novel scheme can greatly relax the ρRT hot spot condition and the stringent requirements on engineering issues by the high-gain fusions. The primary explosion of the amplifier scheme is dominated by density and occurs in the cold shell, and the secondary explosion happens in an extremely hot and dense fireball generated by the primary explosion. Very different from the high-gain schemes of fast ignition, impact ignition, and shock ignition, the amplifier scheme does not require adding an ignitor shock separately. We discuss the principles, characteristics, and criteria of the amplifier scheme by comparing a direct-drive amplifier design that releases 1331MJ nuclear yield with Φ = 37% under a 9.84MJ laser with a central ignition design that releases a 35.5MJ yield with Φ =16.2% under a 1.6MJ laser. From 1D simulations, the yield released by the amplifier capsule after bang time is 4.88 times that before, remarkably higher than 1.25 times that of the central ignition capsule, demonstrating that the amplifier capsule can release a significant additional yield in the burn stage after ignition. Particularly, the fireball of the amplifier reaches 400 g/cm³, 580 keV, and 100 Tbar at the center with a burnt fuel radius of 350 μm when the secondary explosion happens, lasting for 33 ps between the two explosions. It leaves an important room for novel target designs toward clean fusion energy.
 

inertial confinement fusion