Revisiting Spiral Generator Operation

A spiral generator (SG) is a pulsed power source introduced in the middle of the previous century as a generator whose operation is based on transient processes in transmission strip lines, a so-called “vector inversion generator” (VIG). SGs are favored for their simplicity and are widely used in research and applications that require high-voltage (HV) pulses of several kilovolt and pulse duration of $10^{-9}$ – $10^{-7}$ s. In this study, we present the results of experiments on three different SGs of varying sizes and geometries, loads, spark gap triggering switches, and with or without ferrites. The output voltage, switch current, magnetic field, and other various measurable quantities are monitored. It is found that the output voltage and magnetic field inside and outside the SG appear virtually simultaneously with the discharge current through the primary switch. Based on these observations and on input and output impedance measurements, a model of the SG as a transformer is derived and tested against output voltage and switch current waveforms obtained in experiments. The proposed model shows good agreement with the experimental results. Finally, analytic expressions for the circuit elements of the model are devised, and design considerations of the SG for maximal voltage multiplication are shown.