The injection of a nonrelativistic electron beam into a toroidal solenoid is considered. A secondary emission magnetron injection gun is proposed as a source of the electron beam. Using the drift approximation, a step value after the first turn of the beam around the solenoid is calculated. For multiturn injection, the beam must not return to the electron gun. Thus, the step value must be large enough by comparison with the gun dimension. Using this condition and the Hull cutoff magnetic field equation, the maximum electrode diameters of the magnetron injection gun are calculated. The maximum gun perveance is calculated using scale theory and experimental data from other authors. Because of the small dimensions of the gun, a concept for a multibeam gun is proposed. As an example, the total current and total power are calculated for two values of the electron beam energy and three operational facilities. In comparison with existing sources for auxiliary plasma heating, a novel approach can provide higher power. The calculated levels of the electric field strength in the gun are several times lower than those achieved in experiments. Prospects for the novel concept for plasma heating and current drive and the problem of gun cooling are discussed. Other possible applications are discussed too.