Top: density plot of one jet of case D at time t = 0.25. Bottom: pressure plot of one jet of case D at time t = 0.25. Formation of a structured beam for the jet by pushing material from the ISM by the head of the jet, as by a piston. Because of adiabatic expansion, the density in that outer layer is low, whereas density and pressure build up in front of the head of the jet. Formation of standing recollimation shocks along the path of the jet.