A method to from a rectilinear electron beam with small pulsations for free electron masers

When a solid electron beam is formed by a two-electrode axially-symmetrical gun immersed in uniform axial magnetic field, the anode aperture, cutting off the near-axis part of the beam acts as an electrostatic lens and causes unwanted pulsations of the beam. Initial oscillations of electrons are especially unfavorable for free-electron masers (FEMs), in which they lead to a too large spread in the oscillating and, correspondingly, in the translational velocities of the particles. A method for compensation of the parasitic action of the anode aperture by means of a small correcting coil and formation of an electron beam with minimum pulsations is suggested in this paper. Results of estimations and numerical simulations demonstrating the effectiveness of the method when using it in an electron-optical system of a millimeter wavelengths cyclotron autoresonance maser (CARM) are discussed.