DEVELOPMENT OF 100 KW RF AMPLIFIER FOR SUPERCONDUCTING CYCLOTRON AT VECC

High power rf amplifiers (3 nos.) have been developed at our centre for feeding power to three nos. of coaxial rf cavities of the k500 Superconducting Cyclotron. Each of this amplifier can supply output power of 100 kW (max.) at 50 ohm impedance within the frequency range of 9 MHz to 27 MHz. The amplifier, based on Eimac 4CW 150,000E water-cooled tetrode, is tuned by moving the sliding short of the coaxial cavity within the said frequency range[1]. An inductive coupling loop is inserted along one side of the coaxial cavity through the sliding short and is matching the output impedance of 50 ohm. The four identical Bridge-T networks in the grid of the final amplifier are driven with equal power levels of up to 150 watts. The amplifier is operated in Class-AB mode with power gain of 22 dB. Anode Power supply of 20 KV@7.5A, Screen Power supply of 1.5 KV@1A, Grid Power supply of -500V, and Filament power supply of 15.5V@215A are applied to the terminals of the aforesaid tetrode. A PC-based stepper motor controlled sliding short movement system have been developed. The movement of the 3 transmitter cavities for tuning at different frequencies can be done from a computer located in the main RF control room through LAN. This system has been used for movement of the sliding shorts of the 3 transmitter cavities for different measurements including Q, shunt impedances etc at different resonating frequency at different length of the cavity. Limit switches are connected at the cavity for upper limit and lower limit. These limits are decided according to required cavity length at 9MHz (lowest freq) and 27 MHz (highest freq).The frequency response of the input circuit of the amplifier has been measured using Vector Network Analyzer.