• 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.

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

The J-PARC RFQ (length 3.1m, 4-vane type, 324 MHz) accelerates a negative hydrogen beam from 0.05MeV to 3MeV toward the following DTL. As the trip rates of the practically using RFQ increased in autumn 2008, we started the preparation of a new RFQ as a backup machine. The beam dynamics design of the new RFQ is the same as the current cavity, however, the engineering and RF designs are changed. The processes of the vane machining and the surface treatments have been carefully considered to reduce the discharge problem. The vacuum brazing technique has been chosen for vane integration. In this report, the detailed design will be described with the progress of the fabrication of the new RFQ.

• K. Yoshimura, Y. Hashimoto, Y. Hori, Y. Igarashi, S. Mihara, H. Nishiguchi, Y. Sato, M. Shimamoto, Y. Takeda, M. Uota
  KEK, Ibaraki
• M. Aoki, N. Nakadozono, T. Tachimoto
  Osaka University, Osaka

Proton beam extinction, defined as a residual to primary ratio of beam intensity, is one of the most important parameters to realize the future muon electron conversion experiment (COMET) proposed at J-PARC. To achieve the required extinction level of 10^-9, we started measuring beam extinction at main ring (MR) as the first step. The newly developed beam monitor was installed into the abort beam line and the first measurement was successfully performed by using the fast-extracted MR beam. We found that empty RF buckets of RCS, in which all protons were considered to be swept away by a RF chopper before injection to RCS,, contained about 10^-5 of the main beam pulse due to chopper inefficiency. We are now developing a new beam monitor with improved performance for further studies at the abort line. In addition, we have started new measurements at the different stage of proton acceleration, i.e. at Linac, 3-50 BT line, and the main ring. In this paper, we present recent results and future prospect of beam extinction measurements.

• N. Yamamoto, M. Hosaka, H. Morimoto, K. Takami, Y. Takashima
  Nagoya University, Nagoya
• Y. Hori
  KEK, Ibaraki
• M. Katoh
  UVSOR, Okazaki
• S. Koda
  SAGA, Tosu
• S. Sasaki
  JASRI/SPring-8, Hyogo-ken

Central Japan Synchrotron Radiation (SR) Research Facility is under construction in the Aichi area, and the service will start from FY2012. Aichi Science & Technology Foundation is responsible for the operation and management, and Nagoya University SR Research Center is responsible to run the facility and support the users technically and scientifically. The accelerators consists of an injector linac, a booster synchrotron and an 1.2 GeV electron storage ring with the circumference of 72 m. To save construction expenses, the 50 MeV linac and the booster with the circumference of 48 m are built at inside of the storage ring. The beam current and natural emittance of the storage ring are 300 mA and 53 nmrad. The magnetic lattice consists of four triple bend cells and four straight sections 4 m long. The bending magnets at the centers of the cells are 5 T superbends and the critical energy of the SR is 4.8 keV. More than ten hard X-ray beam-line can be constructed. One variable polarization undulator will be installed in the first phase. The electron beam will be injected from the booster with the full energy and the top-up operation will be introduced as early as possible.

• M. Uota, Y. Hashimoto, Y. Hori, H. Matsumoto, Y. Saitoh, M. Shimamoto, M. Tomizawa, T. Toyama
  KEK, Ibaraki

In J-PARC 50GeV synchrotron ring, large vacuum pressure rises above 10^-3 Pa are found at 30GeV acceleration final stage of intensity over 10¹³ protons per pulse in the chambers of the in-vacuum electrostatic septum magnet for the slow-extraction(SX), magnetic septum for SX, and the kicker magnet for the fast-extraction. This pressure rise depends on beam intensity and peak-current, and can be reduced by continuous beam operations, such as scrubbing with proton beam, secondary emission electrons and other cations of remaining gasses or desorptions.