Compact, repetitive Marx generator and HPM generation with the Vircator



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Texas Tech University


The electrical characteristics and design features of a low inductance, compact, 500 kV, 500 J, 10 Hz repetition rate, Marx generator for driving a high power microwave (HPM) source are described. This includes a relevant background discussion of Marx generators and HPM sources, with an emphasis on HPM generation with the virtual cathode oscillator (Vircator). The particular Compact Marx Generator design benefits from the large energy density of mica capacitors, 4 mica capacitors were utilized in parallel per stage, keeping the parasitic inductance per stage low. Including the spark-gap switches, a stage inductance of 55 nH was measured, which translates with 100 nF capacitance per stage to ~ 18.5 Ohm characteristic Marx impedance. Using solely inductors, ~ 1 mH each, as charging elements, instead of resistors, enabled charging the Marx within less than 100 ms with little charging losses. The pulse width of the Marx into a matched resistive load is about 200 ns with 50 ns rise-time. Repetitive HPM generation with the Marx directly driving a small Vircator has been verified. The Marx is fitted into a stainless steel tube with 30 cm diameter and a total length of 0.7 m. Marx operation at up to 21 kV charging voltage per stage, with repetition rates of up to 10 Hz in burst mode, primarily into resistive loads is discussed. A lumped circuit description of the Marx is also given, closely matching the experimental results. Preliminary design and testing of a low cost, all metal Vircator cathode are also discussed.