• Y. Arakaki, S. Murasugi, R. Muto, K. Okamura, Y. Shirakabe, M. Tomizawa
  KEK, Ibaraki
• D. Horikawa, I. Sakai
  University of Fukui, Faculty of Engineering, Fukui
• M. Nishikawa
  Nippon Advanced Technology Co. Ltd., Ibaraki-prefecture

The two electrostatic septa are one of the most important device for the slow extraction in 50GeV proton synchrotron. We have developed the thin ribbon type septum in order to reduce the beam loss. If alignment of ribbons is poor, the effective thickness seen from the beam become large, and it would increase the beam-hitting rate. The alignment of ribbon over 1.5m long septa was measured by a laser-focus displacement meter. The achieved effective thickness of septa is estimated to be 0.075mm and 0.080mm respectively. We will report a high voltage conditioning and a performance under beam commissioning.

• 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.