A method of forming a high-quality electron beam for free electron masers

A new method to form a high-quality electron beam in which electrons initially move strictly along the axis without spurious transverse velocity is discussed. A two-electrode axisymmetric gun immersed in a uniform axial magnetic field is followed by a small correcting coil which compensates the dispersing action of an anode aperture and ''straightens'' electron trajectories. Computer simulations of a magnetically insulated diode with the space-charge-limited current proved effectiveness of this method. The use of the method in a cyclotron autoresonance maser experiment provided 30% electron efficiency enhancement.