• F. Tamura, K. Hasegawa, M. Nomura, A. Schnase, T. Shimada, H. Suzuki, M. Yamamoto
  JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
• K. Hara, C. Ohmori, M. Tada, M. Yoshii
  KEK/JAEA, Ibaraki-Ken

In the J-PARC RCS, we employ the longitudinal painting methods, the momentum offset injection method and applying the second harmonic RF voltages, to increase the bunching factor so that the space-charge tune shift is reduced. By the dual-harmonic operation with wide-band MA loaded cavities, in which each single cavity is driven by a superposition of the fundamental and the second harmonic RF signals, we can generate a large amplitude second harmonic RF voltage without extra cavities for the second harmonic RF. We present the results of the beam tests for the longitudinal painting in the J-PARC RCS. Also, we present the beam behavior at very high beam power.

• M. Nomura, K. Hasegawa, A. Schnase, T. Shimada, H. Suzuki, F. Tamura, M. Yamamoto
  JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
• E. Ezura, K. Hara, C. Ohmori, M. Tada, M. Yoshii
  KEK, Ibaraki
• A. Takagi
  KEK/JAEA, Ibaraki-Ken

J-PARC consists of a 181 MeV linac, a 3GeV Rapid Cycling Synchrotron (RCS) and a 50 GeV Synchrotron (MR). The RCS is designed to accelerate a high intensity proton beam. One of the key issues of the RCS RF system is how to achieve the very high accelerating field gradient of more than 20kV/m. This is impossible with conventional ferrite-loaded cavities. We reach this goal by the development of Magnetic Alloy (MA) core loaded RF cavities. We installed 10 RF cavities in the RCS tunnel on May 2007. The RCS beam commissioning was started on September 2007 and we successfully accelerated a proton beam up to 3GeV on October 2007. We also employed MA cores for MR RF cavities and use a cut core configuration to adjust the Q-value. The MR beam commissioning was started on May 2008. We didn't have any trouble caused by the MA cores during operation. We measured the impedance of the RF cavities several times at the shutdown periods. We show the results of impedance measurements. From these results, we can make an assumption about the core condition.

• C. Ohmori, E. Ezura, K. Hara, A. Koda, Y. Miyake, K. Nishiyama, K. Shimomura, M. Tada, A. Takagi, S. Takeshita, M. Yoshii
  KEK, Ibaraki
• K. Hasegawa, M. Nomura, A. Schnase, T. Shimada, H. Suzuki, F. Tamura, M. Yamamoto
  JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
• M. Miyazaki
  GUAS, Kanagawa

J-PARC RCS accelerates a high intensity beam using 11 sets of Magnetic Alloy loaded cavities. It supplies the proton beam to the MLF (Material Life Science Facility) for the neutron and muon experiments. For very high resolution muon experiments, a short proton beam bunch of few ten ns is necessary. To reduce the bunch width to several ten ns, a bunch rotation scheme before extraction will be useful. For the bunch width of few ten ns, a much higher RF voltage is also required. Based on a new magnetic alloy core technology, a design of a new RF cavity to increase the maximum RF voltage by a factor of two will be described in this paper.

• 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.

• M. Yamamoto, K. Hasegawa, M. Nomura, A. Schnase, T. Shimada, H. Suzuki, F. Tamura
  JAEA/J-PARC, Tokai-mura
• E. Ezura, K. Hara, C. Ohmori, M. Tada, A. Takagi, M. Yoshii
  KEK, Ibaraki
• K. Horino
  Nippon Advanced Technology Co. Ltd., Ibaraki-prefecture

J-PARC RCS is in the beam commissioning period. Some longitudinal beam gymnastics and the acceleration has been successfully perfomed under the high intensity operation. We have developed a longitudinal particle tracking code, which includes beam loading and space charge effects. The comparison between the beam test result and the particle tracking simulation is described.

• A. Schnase, M. Nomura, F. Tamura, M. Yamamoto
  JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
• E. Ezura
  KEK, Ibaraki
• K. Hara, K. Hasegawa, C. Ohmori, T. Shimada, H. Suzuki, M. Tada, M. Yoshii
  KEK/JAEA, Ibaraki-Ken

The J-PARC Rapid Cycling Synchrotron (RCS) uses broadband magnetic alloy loaded cavities to create the acceleration voltages needed for rapid cycling at 25 Hz rate. Besides the desired second harmonic of the acceleration frequency, which is employed in the painting process of RCS injection, also unwanted harmonics can be found at the acceleration gaps of the cavities. Here, the effect of the vector sums of undesired harmonics during the acceleration process is estimated.