Pe. Hardee et al., DYNAMICS AND STRUCTURE OF 3-DIMENSIONAL POLOIDALLY MAGNETIZED SUPERMAGNETOSONIC JETS, The Astrophysical journal, 485(2), 1997, pp. 533
A set of three-dimensional magnetohydrodynamical simulations of superm
agnetosonic magnetized jets has been performed. The jets contain an eq
uipartition primarily poloidal magnetic field, and the effect of jet d
ensity on jet dynamics and structure is evaluated. The jet is precesse
d at the origin to break the symmetry and to excite Kelvin-Helmholtz-u
nstable helical modes. In the linear limit, observed structures are si
milar in all simulations and can be produced by structures predicted t
o arise as a result of instability. The amplitude of various unstable
modes is evaluated. Most unstable modes do not reach the maximum ampli
tudes estimated from the linear theory by computing displacement surfa
ces associated with the modes. Surprisingly, even these large-amplitud
e distortions are fitted reasonably well by displacement surfaces comp
uted from the linear theory. Large-amplitude helical and elliptical di
stortions lead to significant differences in the nonlinear development
of the jets as a function of the jet density. Jets less dense than th
e surrounding medium entrain material, lose energy through shock heati
ng, and slow down relatively rapidly once large-amplitude distortions
develop as a result of instability. Jets more dense than the surroundi
ng medium lose much less energy as they entrain and accelerate the sur
rounding medium. The dense jet maintains a high-speed spine that exhib
its large-amplitude helical twisting and elliptical distortion over co
nsiderable distance without disruption of internal jet structures as h
appens for the less dense jets. This dense high-speed spine is surroun
ded by a less dense sheath consisting of slower moving jet fluid and m
agnetic field mixed with the external medium. Simulated synchrotron in
tensity and fractional polarization images from these calculations pro
vide a considerably improved connection between simulation results and
jet observations than do images made using the fluid variables alone.
Intensity structure in the dense jet simulation appears remarkably si
milar to structure observed in the Cygnus A jet. These simulations sug
gest that the extended jets in high-power radio sources propagate to s
uch large distances without disruption by entrainment because they are
surrounded by a lobe or cocoon whose density is less than the jet den
sity.