EFFECTS OF WIGGLER AND AXIAL-GUIDE FIELDS ON WAVE-PROPAGATION IN A FREE-ELECTRON LASER

An analysis of the propagation of space-charge and electromagnetic wav es through combined helical wiggler and axial guide magnetic fields is presented. A convenient method using complex basis vectors is used to derive a dispersion relation for coupled electrostatic and electromag netic waves. Numerical results for space-charge waves differ markedly from the conventional approximation. For example, the effective electr on-density factor Phi is double valued, becomes complex in some parame ter regimes and large in others, and does not become singular near the stability limit for group I orbits. A numerical study of right circul arly polarized electromagnetic waves also shows interesting effects of the combined wiggler and guide fields on the dispersion. (C) 1998 Ame rican Institute of Physics. [S1070-664X(98)02811-0].