SPACE-CHARGE WAVES IN THE WIGGLER FIELD OF A RAMAN FREE-ELECTRON LASER

A waveguide filled with a relativistic electron beam that passes throu gh a helical wiggler magnetic held and a uniform axial magnetic field is considered. The propagation of two types of space-charge waves in t his device is analyzed. An electrostatic approximation is employed tha t is based on Gauss's law and the requirements that the magnetic field of the wave and the curl of the electric field of the wave both be ze ro in the electron-beam reference frame. These equations transformed i nto the laboratory reference frame are shown to be more accurate than a system of equations that includes Gauss's law in conventional form. A dispersion relation is derived with the combined effects of the wigg ler and axial magnetic fields and the waveguide boundary included. Som e numerical results are presented for both plasma and cyclotron types of space-charge waves.