• J. Takano, T. Koseki, S. Nakamura, T. Toyama, N. Yamamoto
  J-PARC, KEK & JAEA, Ibaraki-ken
• S. Hatakeyama
  JAEA/J-PARC, Tokai-mura
• K. Niki, M. Tomizawa, S. Yamada
  KEK, Ibaraki

In the J-PARC Main Ring (MR), the bending, quadrupole, sextupole, and steering magnets can be controlled on the operating interfaces (OPI). The optics parameters for all magnets are calculated by using SAD, and are converted to BL tables (ex: 2000 points for a steering magnet) for each power supplies. The BL tables are made from the parameters of optics, pattern timing, and beam energy at flat bottom and flat top. For MR beam studies, the BL tables are adjustable with offset and factor. This system is useful for COD correction, beta function measurement, aperture survey, and slow extraction. In this proceeding, the structure of the magnet control system and OPIs for beam studies will be shown.

• K. Niki, H. Ishiyama, I. Katayama, H. Miyatake, M. Okada, Y. Watanabe
  KEK, Ibaraki
• S. Arai
  RIKEN Nishina Center, Wako
• H. Makii
  JAEA, Ibaraki-ken

The measurement of 12C(alpha,gamma) reaction is planned at TRIAC(Tokai Radioactive Ion Accelerator Complex). An intense pulsed alpha beam with the width of less 10ns and the interval between 250ns and 500ns is required for this experiment. Because the Split Coaxial RFQ (SCRFQ), which is one of the TRIAC accelerators, has a radio frequency of 26MHz, the bunch interval becomes 38.5ns. In order to make the bunch interval of 250ns or more, the pre-buncher with a frequency of 2-4MHz, is considered to be installed upstream of the SCRFQ. It is designed as the pre-buncher has two gaps with non-Pi mode. In order to make the bunching beam profile like a pseudo sawtooth-wave, the RF voltage synthesized three harmonic frequencies is applied to these gaps. Consequently, the pre-buncher has a compact size and no leakage electric field outside gaps, and can keep the RF voltage low. Recently, the beam test of this pre-buncher with a case of 2MHz-RF and SCRFQ was performed by using 16O⁴⁺ and 12C³⁺ beams. The clear bunch structure with a interval of 500ns was obtained by the SSD set downstream of the SCRFQ. The results of the beam test are almost consistent with those of the beam simulation code.

• M. Okada, H. Ishiyama, I. Katayama, H. Miyatake, K. Niki, Y. Watanabe
  KEK, Ibaraki
• S. Arai
  RIKEN Nishina Center, Wako
• H. Makii
  JAEA, Ibaraki-ken

In TRIAC (Tokai Radioactive Ion Accelerator Complex), intense bunched beams are planned for measurements of 12C(alpha, gamma) reactions. For 2-4MHz bunching to the 26MHz linac beams, sawtooth-wave pre-buncher has been developed. Since the wave applied to the pre-buncher is pseudo sawtooth shape synthesized from three sine waves, particles in out-of-bunch phase become backgrounds to the bunched beams. In order to remove them, a multilayer chopper has been newly installed upstream the pre-buncher. The multilayer chopper has 20 electrodes (40mm wide, 10mm long, and 0.1mm thick) piled up with gaps of 1.9mm in vertically to the beam direction. And a square-shape electric potential (100V maximum, 2-4 MHz) is applied to each electrodes alternately. The short gap makes it possible to realize sharp beam-chopping with relatively low electric potential and weak leakage electric field, although beam particles could be lost by 5% or more, since this chopper is set on the way of beams. As a result, the ratio of bunched particles to backgrounds has been improved from 3:1 to 99:1 by the chopper. High intensity beam test by 16O⁴⁺ beam will be also reported.

• M. Tomizawa, T. Adachi, Y. Arakaki, A. Kiyomichi, S. Murasugi, R. Muto, H. Nakagawa, K. Niki, K. Okamura, Y. Sato, S. Sawada, Y. Shirakabe, H. Someya, K.H. Tanaka, T. Toyama, E. Yanaoka
  KEK, Ibaraki
• A. Ando, Y. Hashimoto, T. Koseki, J. Takano
  J-PARC, KEK & JAEA, Ibaraki-ken
• D. Horikawa, I. Sakai
  University of Fukui, Faculty of Engineering, Fukui
• K. Mochiki, S. Onuma
  Tokyo City University, Tokyo
• H. Sato
  Tsukuba University, Ibaraki
• A. Schnase
  JAEA/J-PARC, Tokai-mura

High power protons from the J-PARC main ring is slowly extracted using the third integer resonance and delivered to the experimental hall for various nuclear and particle physics experiments. The slow extraction device comprises two electro static septa (ESS),ten magnetic septa, four bump magnets, eight resonant sextupole magnets and their power supply. One of the critical issue of the slow extraction is radiation caused by the beam loss during the slow extraction. We have developed the electrostatic and magnetic septa with thin septum thickness. A unique scheme with large step size and small angular spread of the extracted beam enables hit rate on the ESS less than 1% level. In January 2009, first 30 GeV proton beam has been successfully delivered to the fixed target. Quadrupole magnets and a DSP feedback control system to obtain a uniform beam spill structure were implemented in 2009 summer shutdown period. We will report the extraction efficiency, extracted beam profiles and spill structure obtained by the beam commissioning so far. We will also mention a upgrade plan based on some new ideas to aim a higher performance.