Browsing by Subject "High power microwave (HPM)"
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Item Compact, repetitive Marx generator and HPM generation with the Vircator(Texas Tech University, 2005-12) Chen, Yeong-Jer; Neuber, Andreas A.; Mankowski, John J.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.Item Short pulse high power microwave surface flashover(2008-12) McQuage, Luke Milton; Neuber, Andreas A.; Krompholz, Hermann G.High power microwave (HPM) systems are often limited in transmitted power density and pulse length by surface flashover occurring across dielectric interfaces. This phenomenon can absorb and/or reflect the incident microwave pulse, causing transmission to cease and potentially damaging the microwave source and the dielectric interface itself. The experimental setup is designed to produce and study HPM surface flashover without the influence of a field enhancing triple point. A reflex triode virtual cathode oscillator (vircator) is fed by an 8-stage Marx generator and pulse forming line to produce a 50 MW, 50 ns pulse with an adjustable frequency from 3 to 5 GHz. This work builds on previous research using a Magnetron generated 5 MW, 4 μs pulse at 2.85 GHz, which is comparable to the current setup, but due to differences in power and pulse length the mechanisms involved have differing impacts on the flashover process. Also under investigation is the influence of factors such as gas pressure and composition. Diagnostics are designed to study the transmitted and incident power levels with sub-nanosecond resolution. Experimental results are discussed and compared with previous testing, literature, and Monte Carlo simulation models.