Development of Fast High-Power Rf Vector Modulator Employing Tem Ferrite Phase Shifters

Recent charged-particle accelerator projects employ high power RF distribution systems to power superconducting radio frequency (SRF) accelerating cavities. Each cavity usually requires several hundred killowatts of pulsed power at relatively high duty cycle (roughly up to 10% in high-power proton linear accelerators) in low UHF bands for production of the particle beam. So far, one amplifier to one cavity configuration is common, since precise vector control of RF is done at the low power inputs of the amplifiers. If a fan-out configuration that feeds many cavities with a single very high-power amplifier klystron is realized, significant cost savings can be achieved in construction and installation. The fan-out configuration, however, requires independent control of RF amplitudes and phases to the cavities at high power level. A prototype high-power RF vector modulator for such applications has been built and tested. The vector modulator employs a quadrature hybrid and two fast ferrite phase shifters in square coaxial transverse electromagnetic (TEM) transmission lines. The square coaxial format can provide the power-handling capability and thermal stability. RF properties of the design and results of high power system testing of the design are presented.