S. P. Belov, A. N. Kuftin, V. N. Manuilov, Sh. E. Tsimring
Institute of Applied Physics RAS, N. Novgorod, Russia
The analytical theory of formation of helical electron beams in a longitudinal nonuniform magnetic field is advanced. Criteria for a required degree of nonadiabaticy of a magnetic field, sufficient for providing large enough oscillating energy of electrons in the cavity are formulated. The estimations of the basic parameters of a beam (oscillatory velocities, electron beam guiding center radius, velocity spread), using stage and bell-shaped approximations of a magnetic field are given. The factors responsible for velocity spread are considered.