  The paper presents the results of numerical simulation of the propagation of
a sequence of plasma knots in laboratory conditions and the astrophysical
environment. The physical and geometric parameters of the simulation have been
chosen close to the parameters of the PF-3 facility (Kurchatov Institute) and
the jet of the star RW Aur. We found that the low-density region formed after
the first knot propagation plays an important role for collimation of the
subsequent ones. Assuming only the thermal expansion of the subsequent
emissions, qualitative estimates of the time taken to fill this area with the
surrounding matter and the angle of jet scattering have been made. These
estimates are consistent with observations and results of our modeling.
