The insulation and ion generation characteristics of coaxial magnetically insulated diodes were tested using microsecond voltage pulses from a Marx generator with magnetic fields ranging up to 20 kG, voltages of 150–300 kV, and gap widths of 0.3–0.9 cm. Voltage standoff was observed for up to 4 &mgr;sec when using graphite or metallic electrodes. With plasma‐producing nylon filament anodes, high‐energy ion beam pulse lengths of up to 2 &mgr;sec and total charge generation densities of up to 7.5 &mgr;A sec/cm2were obtained.