Time-dependent impedance behavior of low-impedance REB diodes during self-pinching

The time-dependent impedance behavior of large-aspect-ratio pinched electron-beam diodes with no external magnetic field is investigated using two pulsers having 0.4–1.0 MV voltage, and the experimental results are compared to predictions from a time-dependent computer code which incorporates several important mechanisms that affect diode impedance. A discussion of these mechanisms includes experimental evidence of their existence and their effects on the observed diode impedance. A simple model for the current is used in a time-dependent analysis of the data in order to demonstrate qualitative effects. The rise time of the electric field, the cathode-plasma velocity, the time-dependent generation of ion sources from the anode, and the special diode geometries (tapered cathodes) are shown to affect the diode impedance in good agreement with theory.