Continuous optical discharge stabilized by gas flow in weakly focused laser beam

Abstract

For the first time, an old experiment is described where a continuous optical discharge is maintained in a large, weakly focused beam of a gasdynamic CO 2 -laser (P = 150 kW), the discharge being stabilized by nitrogen flow at a velocity of 10 m/s opposite to the plasma propagation. This experiment, in other words, produced a large, optical plasmotron. A detailed model, developed to simulate such phenomena numerically (including the laser supported combustion wave), is described. The most important factors, two-dimensional gas flow, heat conductivity, radiation heat exchange, and refraction of the laser radiation in the plasma, are taken into account. The numerical results for the aforementioned experiment are given, the temperature and velocity fields are plotted, and the gas energy balance is analyzed. The computed gas flow velocity (9 m/s) agrees well with the experimental value. For such a velocity, the numerical model shows that the plasma exists stably in a 150-kW beam at that section of the beam (a diameter of 3.2 cm) where the plasma was observed to stop in the experiment. On the basis of the developed theory (confirmed by comparison with the experiment and the numerical model), various other laser beam/plasma phenomena can be simulated ; for example, the operation of a laser-plasma rocket thruster.