An amplifier scheme for inertial confinement fusion was recently proposed to achieve burn efficiency = 30%–50% via cascading explosions, and was applied to target designs under a 10 MJ laser [Li et al 2025 Phys. Plasma32 012708; Lan et al 2025 Phys. Plasma32 082708]. In this paper, we use the amplifier scheme in a target design to obtain energy gain = 83 with = 33 under a more modest laser of 3 MJ, 490 TW and 9 W cm. We present five models under the lasers with the same main pulse but different prepulse to have different adiabat, to show the evolution from a conventional central hot-spot ignition design (CHS) of a single explosion to an amplifier design with cascading explosions, and to demonstrate how the overlap of the peak positions of density, pressure and reaction rate leads to the cascading explosions and affects the burn efficiency. Dynamics of the cascading explosions and their impact on energetics are highlighted. From simulations, the amplifier design has a larger convergence ratio with a lower adiabat than the CHS design. Nevertheless, the amplifier has a much shorter interval time between its stagnation and explosion and also a very short time between its two explosions, indicating that the development of hydrodynamic instabilities of the amplifier may not be as severe as expected. This will requires detailed simulation and experiments to demonstrate in the future.