Investigation of a microwave pulse compressor with a Magic-tee-based plasma interference switch

摘要

A microwave pulse compressor with a Magic-tee as an interference switch was investigated in numerical simulations and experimentally. If the compressor cavity is connected to the H- or E-arm of the Magic-tee with shorted side-arms, the necessary condition for the microwave energy storage is the identity of the shorted arms regardless of the frequency. It means that the compressor operation in different cavity eigenfrequencies is possible without mechanical tuning. We have studied the two-frequency S-band compressor. Using the 3-D version of the code MAGIC1, different regimes of the microwave energy accumulation and release were found. For energy storage, regimes are characterized by the ratio between the electric field amplitude in the side-arms and that in the antinodes of the standing wave in the cavity. For energy release, a characteristic is the transmission coefficient, i.e., the ratio of the output power to the input one, when the shorted arms lengths differ from each other by quarter guide wavelength. The full transmission was found to be possible only for one frequency. The release of microwave energy was simulated by setting variable ionization rates for the plasma formation in the layer crossing the side-arm waveguide at the location of the electric field maximum. Experiments with the compressor charging by the magnetron (200–400 kW, 2.4 μs) at a variable frequency (2.8 to 2.9 GHz) confirmed the simulation results concerning the stage of energy storage. Output pulses at two resonant frequencies were obtained in the self-breakdown mode initiated by either Cu- or W-made cones. Two configurations, with higher and lower electric fields in the location of the plasma discharge, were tested. The efficiency of microwave extraction was limited either by an insufficient coupling to the output arm (high-field case) or by a non-uniformity of the plasma discharge (low-field case). The operation can be improved by introducing special matching- elements into the Magic-tee and/or by using a laser to initiate a plasma discharge.