Influence of the Foucault Currents on Excitation of the Magnetic Field and Dynamics of Formation of Helical Electron Beams in Pulse Gyrotrons

We have developed a method for calculation of the pulsed magnetic field in a sophisticated system of solenoids powered by time-shifted current pulses. The method served as the basis for analysis of the temporal dynamics of magnetic-field variations both in the region of formation of the helical electron beam, and in the space of its interaction with the microwave field in a relativistic gyrotron. It is shown that at some time instants, the degree of the field nonuniformity in the operating space of the gyrotron can reach 20%. The time interval is found, during which the magnetic field in the cavity is uniform. In the experimental process, this allows one to determine the time instant at which a high-voltage pulse is fed in for generation of microwave radiation. The calculated distributions of the magnetic field are compared with the experimental data. We have also developed a method for calculation of the time evolution of the parameters of a helical electron beam formed by a magnetron-injection gun with a pulsed magnetic field, calculated the velocity distribution in the electron beam, and found the time interval, during which a beam with the parameters acceptable for generation is formed.