The paper presets the results of a study on a self-magnetically insulated ion diode with an explosive-emission potential electrode. The experiments have been carried out using the TEMP-4M accelerator, operating in a double-pulse mode: the first negative pulse (300–500 ns, 100–150 kV) followed by the second positive pulse (150 ns, 250–300 kV). The ion beam energy density was 0.3–2.5 J/cm2; the beam was composed from carbon ions (80–85%) and protons. We studied several geometries of the diode: planar and focusing strip arrangement, annular and spiral geometries. It was shown that during the second voltage pulse, a condition of magnetic insulation in the diode gap is fulfilled (B/Bcr ≥3). Using the new spiral geometry of the diode, it was possible to increase the efficiency of ion current generation due to the suppression of the electron component of the total diode current by increasing the electron transit time in the gap. We have increased the efficiency of carbon ion generation from 5–9% (in the planar strip diodes) up to 17–20% in the spiral diode. The spiral geometry of the diode makes it possible to increase the efficiency of C+ ion generation 25–30 times compared to the space-charge-limited current (Childe-Langmuir limit). This is more than two times higher than in other known geometries of self-magnetically insulated diodes. The spiral diode has a resource of more than 107 pulses.