The initial stage of forming the electron sheath and electron beam generation in magnetron guns for the case when the secondary emission process is triggered by nanosecond pulses is considered. In the guns with small transverse sizes, tubular electron beams with an outer diameter of 4-6 mm and a current of 1-2 A are produced at a cathode voltage of 5-10 kV. It is shown that the formation of the electron cloud and beam current pulse front for a time of ≥2 ns is a possibility. [ABSTRACT FROM AUTHOR]