Computation of the diocotron spectrum of a cylindrical non-neutral plasma

A finite difference method is developed and used to compute the diocotron spectrum (discrete plus continuum) of a non-neutral plasma column with an arbitrary profile of the number density. For step function density profiles the results agree with the analytical dispersion relation. In contrast to earlier results, it is found that for a continuously varying hollow density profile the mode with azimuthal mode number l=2 has a growth rate comparable to that for a step function hollow density profile. The results obtained have been verified using an alternative numerical method in which the density is assumed to be constant over small intervals in the radius. (C) 1999 American Institute of Physics. [S1070-664X(99)00909-X].