BEAM SPACE-CHARGE MODES IN A FREE-ELECTRON LASER

Propagation of space-charge waves in a Raman free-electron laser is an alyzed. The device under consideration consists of a cylindrical metal lic waveguide filled with a relativistic electron beam which passes th rough a helical wiggler magnetic field and a uniform axial magnetic fi eld. A solution of the fluid equations and Gauss's law is developed in the form of truncated Fourier and Fourier-Bessel series. The dispersi on relation is derived and the combined effects of the waveguide bound ary and the wiggler and axial magnetic fields on cyclotron-like waves are studied numerically. In the limit of infinite waveguide radius, th e dispersion relation yields a well-known expression in which the comb ined wiggler and axial fields determine an effective plasma frequency. In the limit of zero wiggler field, it reduces to the dispersion rela tion for axisymmetric space-charge waves which, in the beam frame, are purely electrostatic. (C) 1996 American Institute of Physics.