Search

An initial experimental study of a vircator where a feedback mechanism is used to premodulate the electron beam has been performed. The anode-cathode gap distance and the applied voltage were varied and their influence on the frequency content and field strength of the generated microwave pulse are investigated and compared with particle in cell simulations. The frequency content of the microwave radiation was in good agreement between experiments and simulations. The vircator was very narrow banded at 2 GHz., QC 20121116

Experiments on an axial virtual-cathode oscillator (vircator) with a resonance cavity enclosing the virtual cathode are reported. The vircator is driven by a repetitive Marx generator operating in a single-shot mode. To be able to separate different radiation mechanisms, the design of the vircator allows adjustment of the cavity depth as well as the way microwave radiation is extracted. The microwave radiation is measured with a pair of free-field B-dot sensors. The maximum field strengths were registered when the bandwidth was very narrow., QC 20110616

One method to characterize the radiated microwave field from a high-power microwave (HPM) source is to measure the radiated high-level electromagnetic field in several locations at a high sampling rate registering the frequency time dependence, thus being able to determine the radiated pattern and mode. A complete free-field measurement system for measuring the magnetic field component in high-level electromagnetic fields has been developed at FOI. The system consists of a B-dot sensor and a balun, both designed and constructed at FOI. The B-dot sensor is designed as two cylindrical loop sensors with differential output. The balun is a microstrip design etched on a dual sided PTFE circuit board. Complete systems have been calibrated at SP Technical Research Institute of Sweden. A method to analyze the data from the free-field systems has been developed., QC 20110616

Repetitive use of a high-power microwave (HPM) radiation source implies strong erosion on cathode and anode materials. Electrode material endurance has been studied in a series of experiments with an axial vircator powered by a compact Marx generator. The Marx generator operated in a 10 Hz repetitive mode with a burst of ten pulses. Velvet and graphite was used as electron-emitting materials, and they showed markedly different pulse characteristics. Three different anode materials were used; stainless steel mesh, stainless steel wires and molybdenum wires, which all had different influence on the pulse characteristics., QC 20110616

Studies of the concept of direct excitation of the TE11 mode in a coaxial vircator using three-dimensional particle-in-cell simulations is presented. The excitation of the TE11 mode is made possible by sectioning the emitting surface of the cathode, thus creating two interacting virtual cathodes. It is shown that the two virtual cathodes formed oscillate in push-pull mode as previously has been described for a planar geometry., QC 20121116

A research activity involving the detailed consideration of novel high-voltage transformers for pulsed-power applications has recently begun at Loughborough University. Although the main goal is the demonstration of a compact and lightweight unit employing magnetic insulation under vacuum conditions, the initial stage of the work is directed toward the development of a conventional air-cored transformer as a main component in a compact power supply for high power microwave sources. In cooperation with the Swedish Defence Research Agency (FOI), the power supply has been tested with a microwave source of the vircator type. The power generator for the system uses a 70-kJ/25-kV capacitor bank and an exploding wire array to generate a 150-kV voltage pulse in the primary circuit of a transformer. A pressurized SF6 spark gap in the secondary circuit sharpens the high-voltage output so that pulses approaching 500 kV and with a rise time well below 100 ns are generated on a 20-Omega high-power resistors With the peak power in excess of 10 GW. Experimental results are presented from final testing of the system, where a reflex triode vircator replaces the 20-Omega resistor. Measurements of the microwave emission using free-field sensors are presented, and comments are made with the microwave emission from the same vircator when powered by a Marx generator at FOI., QC 20110429

QC 20121115