Development and optimization of the relativistic klystron amplifier

The research and development of the relativistic klystron amplifier (RKA) at the Naval Research Laboratory is reviewed. The experimental and theoretical effort concentrated on the three main aspects of RKA technology development: (1) Limitation on high power RF extraction into the atmosphere (2) Reduction in beam loading effects (3) The new triaxial geometry, in which a large diameter electron beam propagates between two coaxial grounded tubes. The peak RF power generated by the RKA is limited by electron held emission in the RF converter. In the present L-band geometry, electron emission was detected at power levels above ~6 GW. Beam loading effects, which also affect power output, may be controlled by spatial and velocity inhomogeneities in the current of the electron beam driving the RKA. Finally, the new triaxial RKA, currently in the final stages of construction, promises to solve many of the existing problems and to extend the frequency domain to 10 GHz with power output in the 10´s of GW