  We extend investigations of mass entrainment by jets, which previously have
focused on cylindrical supermagnetosonic jets and expanding trans-Alfv\'enic
jets, to a set of expanding supermagnetosonic jets. We precess these jets at
the origin to excite the helical mode of the Kelvin-Helmholtz (or KH)
instability, in order to compare the results with predictions from linear
stability analysis. We analyze this simulation set for the spatial development
of magnetized mass, which we interpret as jet plus entrained, initially
unmagnetized external mass. As with the previous simulation sets, we find that
the growth of magnetized mass is associated with the growth of the KH
instability through linear, nonlinear, and saturated stages and with the
expansion of magnetized material in simulated observations of the jet. From
comparison of measured wavelengths and wave speeds with the predictions from
linear stability analysis, we see evidence that the KH instability is the
primary cause for mass entrainment in these simulations, and that the expansion
reduces the rate of mass entrainment. This reduced rate can be observed as a
somewhat greater distance between the two transition points separating the
three stages of expansion.
