A Simple Model for Pre-Breakdown Over-Voltage and Methods for Analysis of Switching Diagnosis on Early Stages of PFMA1 Discharge

Summary form only given. The PFMA-1 (plasma focus for medical applications 1) is a device conceived to deliver the 150 kJ energy stored in the capacitor bank to the plasma load, at a repetition rate of 1 Hz. Its goal will be the production of short lived radio isotopes for medical PET-TAC applications. A representative lumped circuit model has been already developed and its results validated during short circuit tests aimed at comparing the real machine total inductance with the design value. Analytical solutions of a new extended model and comparisons with numerical simulations are now presented to predict the behavior of voltage and current ramps and their typical oscillations during the early stages of the capacitors discharge, just before the full development of gas breakdown between the electrodes (Mather-type configuration). This analysis is particularly important for the design of the collector of the kind of devices such as PFMA-1, especiallv for the optimization of dielectrics. By extending the model to the post-breakdown phase, it is also possible to characterize the frequency shifting on the waveforms collected. Then a technique of time-frequency multi-resolution analysis based on wavelet transforms is proposed for the detection of breakdown delay or of spark gap misfirings based on the observation of the higher harmonics shifting in the signal.