Relativistic effects on magnetoresonance in free-electron lasers

Orbital motions of magnetized and relativistic electron beams in free-elect ron lasers (FEL) with electromagnetic and magnetostatic wiggler are conside red. The orbit and dispersion curves of an electromagnetic wiggler demonstr ate the magnetoresonance when the transverse motion of electrons in the wig gler field is treated nonrelativistically. Magnetoresonance is also shown i n the nonrelativistic case of the magnetostatic wiggler. It is shown that r elativistic effects, due to the transverse motion of electron in the wiggle r field, destroy the magnetoresonance in an electromagnetic wiggler and dis place it in an electrostatic wiggler. Magnetoresonance in the growth rate o f FEL in the nonrelativistic case and its destruction in the relativistic c ase are shown. (C) 2000 American Institute of Physics. [S1070-664X(00)02904 -9].