• H. Hotchi, N. Hayashi, Y. Hikichi, S. Hiroki, J. Kamiya, K. Kanazawa, M. Kawase, M. Kinsho, M. Nomura, N. Ogiwara, R. Saeki, P.K. Saha, A. Schnase, T. Shimada, Y. Shobuda, K. Suganuma, H. Suzuki, H. Takahashi, T. Takayanagi, O. Takeda, F. Tamura, N. Tani, T. Togashi, T. Ueno, M. Watanabe, Y. Watanabe, K. Yamamoto, M. Yamamoto, Y. Yamazaki, H. Yoshikawa, M. Yoshimoto
  JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
• A. Ando
  LASTI, Hyogo
• H. Harada
  Hiroshima University, Graduate School of Science, Higashi-Hiroshima
• K. Hasegawa, Y. Irie, C. Ohmori, M. Yoshii
  KEK, Ibaraki
• K. Satou, Y. Yamazaki
  J-PARC, KEK & JAEA, Ibaraki-ken

The beam commissioning of the J-PARC 3-GeV RCS started in October 2007. The initial machine parameter tuning and underlying beam studies were completed in February 2008 through various beam dynamics measurements, such as optical functions, turn-by-turn beam positions, and transverse and logitudinal beam profiles. Now the RCS is in transition from the first commissioning phase to the next challenging stage and our efforts hereafter will be focused on higher beam power operations. In this paper, we describe experimental results obtained in the high intensity demonstrations in October 2008, together with the corresponding simulation results.