Laser breakdown model in the absorption mode behind a light supported detonation wave

Abstract

The light supported detonation wave (LSDW) propagation with the laser radiation absorption in a narrow layer behind wave’s front is considered in the paper alternatively to the volumetric energy source model usually used for the energy deposition simulation [1-7]. The next laser plasma flow features were revealed in [8] by methods of numerical simulation:1) laser plasma forms high-speed jet flow behind the LSDW front along the light beam propagation direction,2) jet parameters are close to an isentropic flow mode at significant distances from the LSDW front, therefor can be determined with a good approximation using the unsteady pressure solution for the point explosion model with a kinematic x-t transformation. These features allow one to determine the plasma momentum value (in the direction of a laser beam) of the optical breakdown as an additional factor of effect on gas flow, first indicated in [9]. For an argon flow, we used a comparative analysis of the results of numerical simulations obtained both accounting the absorbed energy only and the breakdown plasma momentum additionally acquired at the absorption of radiation behind the LSDW front.The experimental results of an optical discharge plasma in a subsonic argon flow are also presented. Pulse-periodic radiation with a frequency of 40 kHz and average power of 1.6 kW (peak power more than 30 kW) was generated by CO2-laser created in ITAM SB RAS. In order to obtain the LSDW mode by increasing a length of the breakdown plasma a focusing system f / d ≈ 9 was applied. A high-speed video camera with the exposure time of 1.0 μs, and the shooting speed of 200,000 frames / sec was used to record process. It has been established that the plasma dynamics has two successive stages: from the initial high-speed (of the order of 1 μs) propagation of the optical discharge to the subsequent lower-velocity gas-dynamic stage.