Low inductance, dual-feed diode development

We have tested three low inductance, sub-ohm impedance diode configurations on the SNLA SPEED pulse generator at power levels above 1 TW. SPEED is a single module, = 20 nsec FWHM accelerator with a 4 ohm triaxial power flow transmission line in the water section and a double-sided vacuum-water insulator at a radius of 53 cm. In these experiments, the dual feed was continued with a triplate disk arrangement down to a diode radius of 4 cm, resulting in a load inductance of 5 nH. The diodes were configured to operate in a Langmuir-Childe´s bipolar mode, a paravector potential mode, and a double pinched beam mode. We observed pulses with V = 900 kV, I = 1.5 MA, and pulse width = 19 nsec FWHM at the diode. Diode impedance was governed by plasma gap closure; closure velocities of ≅7 cm/µsec can be inferred from the data. In addition, a 4 nsec difference in the arrival time of the waves at the diode from the two feed lines was found to significantly perturb the expected diode performance. Diode performance improved markedly when the two feed lines were isolated from each other.