Kinetic model for a collisionless ionization wave launched by a high energy-density plasma*

A high energy-density plasma embedded in a neutral gas can launch an outward-propagating nonlinear collisionless ionization wave driven by a strong sheath field [Phys. Rev. Lett. 112, 045002 (2014), Phys. Rev. E 103, 023209 (2021)]. The key feature is the trapping field structure that enables the wave to carry energetic electrons at high density. These electrons maintain a strong sheath field, ensuring long-lasting wave propagation with relativistic velocity over distances that greatly exceed the initial size of the plasma. We present an analytical solution of the kinetic equation that self-consistently describes the structure of the wave. The solution predicts a threshold for the ratio of the ambient gas density and the density of the hot trapped electrons. We also present 1D kinetic simulations supporting the analytical solution. 

This work was supported by DOE under Grants No. DE-SC0019100 and No. DE-SC0018312.