Abstract
We present a series of numerical simulations which explore different aspects of the formation of working surfaces in HH jets. These working surfaces can be at the head of the jet (resulting from a ``turning on'' of the ejection) or within the body of the jet (resulting from a time-variability of the ejection). We explore the effect of having a conical outflow of different opening angles and the effect of having a non-top hat ejection velocity cross section. We also illustrate the differences that are obtained by varying the resolution of the simulations, and by changing from 2D (axisymmetric) to 3D descriptions of the flow. Finally, we describe the effect of a toroidal magnetic field on the working surfaces of the jet.
