RF-induced frequency-shift resistant design of the resonant cavity of the radio frequency quadrupole with the high average-power operation

This paper describes an effective cooling-design approach to the elimination of the RF-induced frequency-shift in the resonant cavity of the Radio Frequency Quadrupole with the high average-power operation. After the RF power is fed into the cavity, the frequency may shift due to the temperature change in the cavity. However, the RF-induced frequency shift can be diminished by the optimization of the cooling passage location and the water flow rate in the vane and wall during the design phase. The temperature of the cooling water has no effect on the RF-induced frequency shift. This approach is implemented by the coupled electromagnetic, thermal and mechanical analyses of the cavity, and has been performed on the cooling design of the CW/100 kW FRIB RFQ. The total designed flow rate is 18.2 kg/s and the RF-induced frequency shift is -0.4 kHz. During operation, the flow rate can be further adjusted within tolerance to diminish the RF-induced frequency shift as much as possible. Besides the RFQ cavity, this method is applicable to the cooling design of other room-temperature accelerators with similar structural characteristics.