• 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.