Phase-locked radial klystron oscillators

Summary form only given, as follows. The advantages of the radial klystron over the conventional klystron, and in particular, the radial klystron oscillator over the radial klystron amplifier has been reported by Arman et al. (1995). Briefly, the radial structure of this design allows for much smaller impedances and thus higher powers, the beam-cavity coupling is stronger because the beam travels inside the cavity; and the source is much more compact because there is no need for external magnetic fields. The radial klystron oscillator is particularly interesting because it is more compact, and being a transit-time oscillator, it is more stable and more efficient. The amount of power extracted from a single source, however, is limited in many ways, the most important being the low efficiencies associated with high power single sources. Overall high efficiency is crucial for sustained (longer than 100 ns) operation. Phase locking of several sources has been suggested as an alternative means of achieving higher powers for longer durations. Phase-locking however, although relatively successful for amplifiers, has proven difficult for oscillators. I report on the phase-locking of two radial klystron oscillators and present the results of the numerical simulations, carried out using the PIC codes MAGIC and SOS. The method devised here can be easily extended to many identical sources of this kind, making coherent radiation of RF energy in the tens of kilojoules, a possibility.