Introduction

Our interferometric images of radio sources reflect the synchrotron emissivity arising from their relativistic electrons and magnetic fields. These trace the underlying plasma flow, albeit imperfectly. The local dynamical evolution of the particles and fields is determined by their transport from the nuclear source, and by their in situ dynamics. This chapter presents the physics necessary for an understanding of current theories of particle acceleration and magnetic field evolution. It describes these theories and attempts to assess whether or not they provide an adequate account of the inferred particle spectra, energetics and magnetic field geometry of extragalactic jets.

It was shown in Chapter 3 that some sources have severe lifetime problems, in that the time for the electrons to be carried out to the lobes (even with a jet speed ~ c) is longer than their radiation lifetime (the upper limit of which is the lifetime to Compton losses on the 3 K background) and that the surface brightness and spectral index distributions do not decay as fast as would be expected in a constant velocity, expanding flow. These problems may be overcome by the local reacceleration of the radiating particles. Further, simple estimates of convection of flux-frozen magnetic field out from the core predict that the convected field decays significantly; however, this is probably offset by in situ amplification of the magnetic field by some dynamo process.