Theory of beam channel hydrodynamics

We report on recent theoretical studies and numerical simulations of hot channels produced in a gaseous medium by a beam. Experiments at NRL have demonstrated that similar channels produced by electric discharges and/or laser pulses in air or nitrogen undergo rapid, turbulent cooling. We explain this phenomenon on the basis of vorticity generation by “zero order” misalignment of pressure and density gradients as the hot channel expands to pressure equilibrium. We derive equations describing the residual vortex strength and mixing time scale for fundamental classes of asymmetry. Comparisons of theoretical calculations to numerical simulations and to experimental data on laser and discharge channels provide a calibration of the theory and permit the identification of the most important sources of turbulence in beam channels.