In the stagnation stage of ICF implosion, the kinetic energy of the plasma shell layer is converted to internal energy, forming a hot spot with high density and high temperature. In this process, the energy conversion efficiency directly affects the DT ignition threshold. To understand the physical details of how the kinetic energy of the shell layer is converted to internal energy, a quasi-one-dimensional planar implosion model is adopted. Moreover, comparative simulations with the hybrid Fluid-PIC code Ascent-H and the one-dimensional hydrodynamic code MULTI-IFE are carried out. It is found that at the moment of target collision, an obvious velocity penetration phenomenon and non-Maxwell behavior in the low-density region is observed, which affects the kinetic energy conversion process significantly.

Implosion stagnation phase; Counterpenetration; Relaxation time.