Relativistic electron beam equilibrium in the presence of a gas channel

A pre-formed density channel or weak conductivity channel can modify the equilibrium of a propagating beam in a non-trivial way, since electrostatic image forces dominate the beam-channel interaction at the beam head, while magnetic image forces dominate further back. To study questions such as these, we have developed a code called DYNASTY that solves the field equations fully implicitly, in three dimensions without linearizing about cylindrical symmetry. The code uses fast Fourier transform in the azimuthal dimension and finite differences with nonuniform mesh in the radial direction. In the presence of a channel we have found two distinct types of equilibria, with the beam either on-axis or displaced from the axis by a precribed amount. A variety of other results will be discussed as well.