• S. Michizono, Z. Fang, T. Matsumoto, T. Miura, S. Yamaguchi
  KEK, Ibaraki
• T. Kobayashi
  JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
• Y. Okada
  NETS, Fuchu-shi

Upgrade of J-PARC linac has been planed using 972 MHz rf system. The rf field regulation is required to be less than ±1% in amplitude and ±1deg. in phase. The basic digital llrf concept is same as the present 324 MHz llrf system using a compact PCI crate. The main alterations are rf and clock generator (RF&CLK), mixer and IQ modulator (IQ&Mixer) and digital llrf algorithm. Since the typical decay time is faster (due to higher operational frequency than present 324 MHz cavity), chopped beam compensation is one of the main concerns. Performance of the digital feedback system using a cavity simulator is summarized.

• T. Kobayashi
  JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
• S. Anami, Z. Fang, S. Michizono, S. Yamaguchi
  KEK, Ibaraki
• H. Suzuki
  JAEA, Ibaraki-ken

In the J-PARC Linac LLRF, for the cavity warming-up, the cavity resonance is automatically tuned to be the accelerating frequency (324MHz and 972MHz) with a mechanical tuner installed on the cavity. Now we are planning to introduce a new method of the cavity-input frequency matching into the digital LLRF control system instead of the cavity resonance tuning for the cavity worming-up. For the frequency matching with the detuned cavity, the RF frequency is modulated by way of phase rotation with the I/Q modulator, while the source oscillator frequency is still fixed. The phase rotation is automatically controlled by the FPGA. The detuned frequency of the cavity is obtained from phase gradient of the cavity field decay at the RF-pulse end. No hardware modification is necessary for this frequency modulation method. The cost reduction or the high durability for the mechanical tuner is expected in the future. The results of the frequency modulation test will be reported in this presentation.