The results of the analysis of the gigawatt-power ion-beam generation in a spiral diode in the selfmagnetic insulation mode are presented. Investigations were carried out using the TEMP-4M accelerator that operated in the double-pulse formation mode: the first pulse is negative (300–500 ns, 150–200 kV) and the second is positive (150 ns, 250–300 kV). Spiral diodes of different designs were investigated under the conditions of a closed electron drift in the anode–cathode gap without an external magnetic field. The conditions for the formation and stabilization of a virtual cathode were analyzed, and experimental studies of its configurations in diodes of different designs were performed. The influence of the gradient and centrifugal electron drifts on the stability of the virtual cathode was analyzed. Investigations showed a high correlation between the energy density and total energy of a high-power ion beam with the value of the total charge that is transferred in the diode during the beam generation. This charge is mainly determined by the duration of the first voltage pulse. To increase the duration stability of the first voltage pulse (in the double-pulse mode), the first pulse that is fed to the load of the double forming line is also used to trigger the main spark gap. This provided a high stability of the ion-beam energy density in a pulse train. The long service life of ion diodes with self-magnetic insulation and an explosive-emission cathode (more than 106 pulses) and the high beamgeneration stability in a pulse train make them promising devices for use in various technological applications.