Ionizing Shock Structure in a Monatomic Gas

The structure of an ionizing shock front in a monatomic gas is described. Both atom‐atom and electron‐atom collisional ionization are considered. The ionization rates for either of these processes is assumed to be controlled by the rate of excitation from the ground state to the first excited level. In the front part of the shock, called the atom‐atom shock, atom collisional dissipative mechanisms (viscosity and thermal conductivity) determine the shock structure. A bimodal Mott‐Smith velocity distribution function is assumed for the atoms in this region, which has a thickness of the order of the atom‐atom viscosity mean free path. In the rear part of the shock front, called the relaxation zone, the collisional ionization processes determine the structure. For this region, which has a thickness proportional to the electron‐atom ionization mean free path, Maxwellian velocity distributions are assumed for the electrons, ions, and atoms. It was found that for Mach numbers of 30 or more the atom‐atom shock is of comparable thickness to the relaxation zone and the degree of ionization behind the atom‐atom shock is the order of ${10}^{\text{−1}}$ .