Power amplifier for RIKEN ring cyclotron

The power amplifier for RIKEN ring cyclotron can generate an output power of 300 kW in a frequency range of 17 to 45 MHz. The final tube RS2042SK is used in grounded grid configuration. Load resistance matching is made by a variable capacitor inserted in series at its output port. The tuning element of the plate circuit is an adjustable quarter wave length coaxial stub whose stroke is 1.2 m. The cathode circuit consists of a quarter wave length coaxial stub and a variable tuning capacitor by which tuning and impedance matching are simultaneously carried out. The filament current is supplied through the stub from a power source at ground potential without a choke coil. All the systems were installed at the cyclotron vault in August 1986 and its performance studied. The SIEMENS RS2042, whose maximum plate dissipitation is 300 kW, is used as the final tubes. Its specification is shown. A schematic diagram of the power amplifier is given and the plate circuit used is described. The structure, tuning characteristics and input impedance of the cathode tuning circuit are outlined. Some results of a power test carried out are also described. (Nogami, K.)