L. N. Pyatnitskii

Resonant and hollow beam generation of plasma channels

We report two variations on plasma channel generation using the propagation of intense Bessel beams. In the first experiment, the propagation of a high intensity Bessel beam in neutral gas is observed to give rise to resonantly enhanced plasma channel generation, resulting from resonant self-trapping of the beam and enhanced laser-plasma heating. In the second experiment, a high power, hollow Bessel beam (J5) is produced and the optical breakdown of a gas target and the generation of a tubular plasma channel with such a beam is realized for the first time. Hydrodynamic simulations of the laser-plasma interaction of are in good agreement with the results of both experiments.

On the nature of turbulence

A concept of turbulence is presented that is based on the results of an investigation of the structure of a gas flow in a tube with a square cross section in front of a nonsteady-state moving flame front. It is shown that a region of elevated pressure, consisting of alternating condensations, is formed in the gas flow near the tube walls. These condensations are the sources of waves which form a distribution of velocity fluctuations in the gas flow over a wide range of amplitudes, frequencies and directions. The dynamics of the perturbations at the walls and the configuration of the wave in the gap make it possible to consider the fluctuations in the flow as pseudochaotic and to use statistical methods to describe them.