Auto-tuning and Q-value monitoring of RF cavities at the J-PARC Linac

In the J-PARC proton LINAC, each klystron drives two RF cavities. The RF amplitude and phase of the cavities are controlled by an FPGA-based digital feedback control system. The tuning of each cavity is also controlled by a DSP of this control system. By adjusting the tuner position, we tune the RF cavity with a resonant frequency of 324 MHz, and register the phase difference between picked-up signal from cavity and cavity input signal, which will be used in the auto-tuning control of the RF cavity. This process is called as f0 setting of RF cavity. In this paper, three methods of f0 setting of RF cavity will be discussed. The tuning method of RF cavity with flat cavity-phase decay is adopted in the actual operation of the J-PARC LINAC. In our RF system, the tuning information including detuned frequency and phase, and Q-value of each cavity are measured in real-time and displayed in the PLC touch panel of the control system. (author)