Summary form only given, as follows. The experiments were carried out in the AGAT accelerator, which is a microsecond diode with a magnetic insulation to study the influence of plasma on the processes of virtual cathode (VC) formation, HF-generation, and plasma ions acceleration. The accelerator produced an annular electron beam with the following parameters: E=280 keV, I=3.5 kA, t=1 ms, and the beam energy 350 J. The beam was injected into a drift chamber 4.9 cm in diameter which was filled by a gas at a pressure of 2/spl times/10/sup -5/-4/spl times/10/sup -4/ torr and placed in an external magnetic field of 4-4.5 T. It was observed that a relaxing VC with low frequency modulation of 20 MHz was formed. Due to the beam escaping to the chamber walls plasma was produced near the anode and serves as ion source. The current of the accelerated ions reached 200 A at an energy for nitrogen ions of 300 keV. Simulation confirmed the low frequency modulation of the HF-oscillations at plasma presence.