Refractive channeling of heating wave driven by laser beam interaction with plasma of subcritical density

The phenomenon of laser-driven heating wave propagation in a plasma with a density less than the critical density is considered for the case of a finite radius of the laser beam. Based on computational and theoretical studies, the effect of channeling the heating wave propagation in the central axial region of plasma due to the reflection of laser radiation on density gradient, formed by plasma motion, at the tuning point was found. Unlike the self-focusing phenomenon, where the laser flux is concentrated without ray intersection, in refractive channeling, this occurs due to ray intersection. This is similar to the creation of a high flux density during multi-beam irradiation of the laser target. It is shown that the longitudinal velocity of heating wave in the channeling region is significantly larger compared with that in the peripheral plasma regions located at a distance of about laser beam radius.