Unsteady Nonequilibrium Model of a Laser-Induced Blast Wave

Abstract

As laser propulsion can be one of the interesting next-generation space propulsion systems, it is important to analyze the mechanism of LSD (Laser-Supported Detonation) waves caused by laser absorption. The performance of laser propulsion is determined mainly by the laser absorption efficiency. To raise the efficiency, it is necessary to generate sufficient free electrons in the laser absorption zone; they are generated by the vaporization of solid propellant due to laser irradiation. These free electrons start absorbing the incident laser, and produce the high temperature and pressure in the form of a blast/shock wave. This in turn generates an increased number of free electrons; ignition occurs. This grows eventually into a detonation wave. We find that four physico-chemical processes take place in a LSD wave: (i) Laser energy is absorbed by free electrons though inverse Bremsstrahlung. (ii) This energy is distributed to heavy particles (atoms and ions) through elastic and (iii) inelastic collisions, (iv) although it is partly lost as radiation emission by Bremsstrahlung. Based on such backgrounds, we simulate this LSD wave and clarify the mechanism on the ignition phenomenon in a laser-sustained plasma. Radiation and ionization occurring in a LSD impose some stiffness to the numerical analysis. To remove the stiffness, we have used a modified Harten-Yee-type TVD scheme which takes into account real gas effects.