Experimental Study On The Efficient Operation Of 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 multi-cavity gyroklystron amplifier has been performed using the three cavity C-band amplifier at NRL. 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, through both 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 16% by penultimate cavity detuning employing a uniform magnetic field profile, and from 20% to 28% by profiling the magnetic field along the device. Comparison with theory will be presented.