The radiofrequency system of the RIKEN ring cyclotron

Abstract

A new type of variable-frequency resonator is developed for the RIKEN ring cyclotron ( K = 540). The resonator is of a compact, half-wavelength coaxial type (2.1 m ( H) × 3.5 m ( W) × 1.6 m ( D)) in which a delta-shaped dee of 2.7 m in radial length is supported in the median plane by vertical stems from both sides. It is tuned in a frequency range of 20 to 45 MHz by moving a pair of boxes which surround the stems and are in contact only with the outer conductor. The dee voltage has a radially increasing distribution that is desirable for phase compression of a beam, and the maximum power loss in generating the required dee voltage is 220 kW. Each of two resonators is powered by a separate rf amplifier capable of delivering a power of 300 kW through a 50 Ω coaxial feeder line (2 m in length), which is coupled with the resonator in good impedance matching by means of a tunable capacitive coupler. The whole system was installed at RIKEN in September 1986 and has been working successfully.