Experimental study of efficiency optimization in a three-cavity gyroklystron amplifier

An experimental study quantifying the effects of both penultimate cavity tuning and magnetic field profiling on the saturated efficiency of a three-cavity gyroklystron amplifier has been performed at a frequency of 4.5 GHz. As predicted by theory, it is observed that the penultimate cavity detuning in the gyroklystron is in the opposite direction from a conventional klystron for enhanced efficiency operation. This is a result of the opposite energy dependence of the bunching mechanism for the two interactions. Magnetic field profiling has also been shown to have a very strong effect on the amplifier efficiency, both through beam loading effects in detuning the penultimate cavity and through enhanced energy extraction in the output cavity. The measured efficiency of the gyroklystron is observed to improve from 5% to 21% by profiling the magnetic field along the device, and then from 21% to 29% by penultimate cavity detuning with an optimized magnetic field profile.<
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