High-power Microwave Pulse Compression of Klystrons by Phase-Modulation of High-Q Storage Cavities

At the CERN linear electron accelerators LIL and CTF, the peak RF power from the 3GHz-klystrons was doubled by means of LIPS microwave pulse compressors. To produce constant RF power from the cavity-based pulse compressors, the klystrons were driven by a fast RF-phase modulation program. For the CLIC Test Facility CTF3, a new type of a Barrel Open Cavity (BOC) with a high quality factor Q0 has been developed. Contrary to LIPS with two resonant cavities, BOC operates with a single cavity supporting two orthogonal resonant modes TM 10,1,1 in the same cavity. For both LIPS and BOC storage cavities, it is important that the RF power reflected back to the klystron is minimal. This implies that the resonant frequencies, Q-factors and coupling factors of the two resonant modes of a pulse compressor are closely matched, and that the resonant frequencies are accurate to within a few KHz. The effects of small differences between the two orthogonal modes of the BOC cavity have been investigated. The dynamic pulse response of a klystron and LIPS pulse compressor has been measured for fast phase modulation. The high power tests have demonstrated that the compressed RF power was doubled and reached 70 MW during 1.5 μs. The power amplitude was stabilized to within ±1% by the feed-forward phase correction program, and the measured phase sag of the compressed output pulse was 8°, as predicted by the theory. At the CERN linear electron accelerators LIL and CTF, the peak RF power from the 3GHz-klystrons was doubled by means of LIPS microwave pulse compressors. To produce constant RF power from the cavity-based pulse compressors, the klystrons were driven by a fast RF-phase modulation program. For the CLIC Test Facility CTF3, a new type of a Barrel Open Cavity (BOC) with a high quality factor Q0 has been developed. Contrary to LIPS with two resonant cavities, BOC operates with a single cavity supporting two orthogonal resonant modes TM 10,1,1 in the same cavity. For both LIPS and BOC storage cavities, it is important that the RF power reflected back to the klystron is minimal. This implies that the resonant frequencies, Q-factors and coupling factors of the two resonant modes of a pulse compressor are closely matched, and that the resonant frequencies are accurate to within a few KHz. The effects of small differences between the two orthogonal modes of the BOC cavity have been investigated. The dynamic pulse response of a klystron and LIPS pulse compressor has been measured for fast phase modulation. The high power tests have demonstrated that the compressed RF power was doubled and reached 70 MW during 1.5 μs. The power amplitude was stabilized to within ±1% by the feed-forward phase correction program, and the measured phase sag of the compressed output pulse was 8°, as predicted by the theory.