• K. Hasegawa, T. Kobayashi, Y. Kondo, T. Morishita, H. Oguri
  JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
• Y. Hori, C. Kubota, H. Matsumoto, F. Naito, M. Yoshioka
  KEK, Ibaraki

The J-PARC RFQ (length 3.1m, 4-vane type, 324 MHz) accelerates a beam from the ion source to the DTL. The beam test of the linac was started in November 2006 and 181 MeV beam was successfully accelerated in January 2007. Since then, the linac has been delivered beams for commissioning of the linac itself, downstream accelerators and facilities. Trip rates of the RFQ, however, unexpectedly increased in Autumn 2008, and we have been suffering from this issue for user run operation since then. We tried to recover by tender conditioning, modification of RF control, improvement of vacuum properties and so on. By taking these measures, we manage to have 2 to 3 days continuous beam operation. In this report, we describe the status of the RFQ.

• Z. Fang, S. Anami, Y. Fukui, M. Kawamura, C. Kubota, S. Michizono, F. Naito, K. Nanmo, S. Yamaguchi
  KEK, Ibaraki
• H. Asano, K. Hasegawa, T. Itou, T. Kobayashi, S. Shinozaki, N. Tsubota
  JAEA/J-PARC, Tokai-mura
• E. Chishiro, H. Suzuki
  JAEA, Ibaraki-ken

The output energy of the J-PARC LINAC will be upgraded from 181 to 400 MeV in the next two years by adding high-beta acceleration sections. The upgrade of the FPGA-based digital LLRF controller for the 400 MeV LINAC will be presented in this paper. The new LLRF control system works for both the 324 MHz low-beta and 972 MHz high-beta sections. Many functions are added into the LLRF controller, such as 1) working for different RF frequencies, 2) gradually increasing the feedback gains in the feedback loop instead of fixed ones, 3) automatic chopped-beam compensation, 4) automatically switching the beam loading compensation in accordance with the different beam operation mode, 5) input rf-frequency tuning carried out by a FPGA to match the rf cavities during the rf start-up, 6) auto-tuning of the rf cavity tuner by detecting the phase curve of the rf cavity during the field decay instead of the phase difference between the cavity input and output signals.