High-Power RF Controls for the NBS-Los Alamos Racetrack Microtron

The high-power rf system for the National Bureau of Standards (NBS)-Los Alamos racetrack microtron (RIM)l uses waveguide power splitters2 and waveguide phase shifters to distribute rf power from a single 500-kW cw klystron to four side-coupled accelerating structures. The amplitude and phase of each structure is controlled by a feedback system that uses the waveguide variable power splitters, waveguide phase shifters, and klystron drive as the active control elements. A block diagram of this system is shown in Fig. 1. Figure 2 shows a subset of the complete system on which the measurements reported in this paper were performed. The feedback controls on the capture section use low-level rf amplitude and phase controls on the rf drive to the klystron. These controls are very fast with an open loop gain bandwidth of approximately 40 kHz. The feedback loop is identical to the feedback loop used in the chopper/buncher system described in another paper at this conference. 3