Numerical simulation of nonstationary processes in intense helical electron beams of gyrotrons

Experiments with helical electron beams (HEB) of powerful gyrotrons displayed the existence of intense nonstationary processes in HEB. A version of numerical simulation of HEB's is proposed, which is based on the method of large particles. Some results of the analysis are given with account of the electrons reflected from the magnetic mirror and locked in the adiabatic trap. One of the effects detected is intense bombardment of the cathode by the trapped electrons. Besides, formation of quasi-stationary states whose parameters (velocity spread, pitch-factor) differ significantly from those given by the static theory was observed. In the absence of the reflected particles, the solution acquires a stable state. The HEB parameters in this case are almost the same as the static parameters.