Author: Tamura, F.
Paper Title Page
MOPC019 Condition of MA Cut Cores in the RF Cavities of J-PARC Main Ring after Several Years of Operation 107
 
  • M. Nomura, A. Schnase, T. Shimada, F. Tamura, M. Yamamoto
    JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken, Japan
  • E. Ezura, K. Hasegawa, K. Takata
    KEK, Tokai, Ibaraki, Japan
  • K. Hara, C. Ohmori, M. Toda, M. Yoshii
    KEK/JAEA, Ibaraki-Ken, Japan
  • T. Sato, M. Yamamoto
    JAEA, Ibaraki-ken, Japan
 
  J-PARC 3 GeV RCS and 50 GeV Synchrotron (MR) employ RF cavities loaded with Magnetic Alloy (MA) cores to generate a high field gradient. The RF cavities in RCS use MA un-cut cores. On the other hand, the RF cavities in MR employ MA cut cores to increase the Q-value from 0.6 to 26. We observed the impedance reductions of all MR RF cavities during several years operation. Opening the RF cavities, we found that the impedance reductions were resulting from corrosion on the cut and polished surfaces of MA cores. Before installation of the RF cavities, we had 1000 and 2000 hours long tests at a test stand. We didn't observe the impedance reduction related to the corrosion on the MA core cut surfaces at the test stand. The only difference between the test stand and MR is the quality of cooling water. The MR cooling water contains copper ions for example from copper hollow conductors of the main magnets. We report the influence of the copper ions to the corrosion on the MA core cut surface. We also show plans how to solve the issue of MA core cut surface corrosion.  
 
WEPS097 Performance of Multi-harmonic RF Feedforward System for Beam Loading Compensation in the J-PARC RCS 2733
 
  • F. Tamura, M. Nomura, A. Schnase, T. Shimada, M. Yamamoto
    JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken, Japan
  • K. Hara, C. Ohmori, M. Toda, M. Yoshii
    KEK/JAEA, Ibaraki-Ken, Japan
  • K. Hasegawa
    KEK, Tokai, Ibaraki, Japan
 
  The beam loading compensation is a key part for acceleration of high intensity proton beams in the J-PARC RCS. In the wide-band MA-loaded RF cavity, the wake voltage consists of not only the accelerating harmonic component but also the higher harmonics. The higher harmonic components cause the RF bucket distortion. We employ the RF feedforward method to compensate the multi-harmonic beam loading. The full-digital feedforward system is developed, which compensates the first three harmonic components of the beam loading. We present the results of the beam test with a high intensity proton beam (2.5·1013 ppp). The impedance seen by the beam is greatly reduced, the impedance of the fundamental accelerating harmonic is reduced to less than 25 ohms in a full accelerating cycle, while the shunt resistance of the cavity is in the order of 800 ohms. The performance of the feedforward system is promising for achievement of the design beam power, 1 MW, in the future.  
 
MOPS008 Simulation of Longitudinal Emittance Control in J-PARC RCS for 400 MeV Injection 607
 
  • M. Yamamoto, M. Nomura, A. Schnase, T. Shimada, F. Tamura
    JAEA/J-PARC, Tokai-mura, Japan
  • E. Ezura, K. Hara, K. Hasegawa, C. Ohmori, A. Takagi, K. Takata, M. Toda, M. Yoshii
    KEK, Tokai, Ibaraki, Japan
 
  The injection energy upgrade of the J-PARC RCS from 181 MeV to 400 MeV is scheduled, this is necessary to achieve the design beam intensity. The high intensity beam is delivered to the MR, and the space charge effect at the MR injection should be alleviated by optimizing the longitudinal beam emittance at RCS extraction. This is realized by matching the shape of the beam emittance between the RCS and the MR. We describe the results of particle tracking simulation with the longitudinal emittance control during the whole acceleration period of the RCS.  
 
WEPS010 Acceleration of High Intensity Proton Beams in the J-PARC Synchrotrons 2502
 
  • M. Yoshii
    KEK/JAEA, Ibaraki-Ken, Japan
  • E. Ezura, K. Hara, K. Hasegawa, C. Ohmori, K. Takata, M. Toda
    KEK, Tokai, Ibaraki, Japan
  • T. Minamikawa
    University of Fukui, Fukui, Japan
  • M. Nomura, A. Schnase, T. Shimada, F. Tamura, M. Yamamoto
    JAEA/J-PARC, Tokai-mura, Japan
 
  The J-PARC accelerator complex consists of the linac, the 3GeV rapid cycling synchrotron (RCS) and the 50GeV main synchrotron (MR). These synchrotrons are the first MW-class proton accelerators which employ the high electric field gradient magnetic alloy (MA) loaded RF cavities. The beam commissioning was started in October 2007 for RCS and in May 2008 for MR. High intensity beam operation studies and user runs have been performed, while carefully controlling and minimizing the beam loss. The cycle to cycle beam operation is reproducible and quite stable, because of the stable linac beam energy and the reproducible bending field in both synchrotrons. The MA loaded RF systems and the full digital LLRF also guarantee the stable longitudinal particle motion and precise beam transfer synchronization from RCS to the MLF user facility as well as to the MR. A high intensity proton beam of 2.5·1013 ppp is accelerated in RCS. And in MR, a beam intensity up to ~100 Tera ppp was obtained. We summarize the RF systems and the longitudinal parameters in both rings.  
 
THOBB02 High Gradient Magnetic Alloy Cavities for J-PARC Upgrade 2885
 
  • C. Ohmori, O. Araoka, E. Ezura, K. Hara, K. Hasegawa, A. Koda, Y. Makida, Y. Miyake, R. Muto, K. Nishiyama, T. Ogitsu, H. Ohhata, K. Shimomura, A. Takagi, K. Takata, K.H. Tanaka, M. Toda, M. Yoshii
    KEK, Tokai, Ibaraki, Japan
  • T. Minamikawa
    University of Fukui, Fukui, Japan
  • M. Nomura, A. Schnase, T. Shimada, F. Tamura, M. Yamamoto
    JAEA/J-PARC, Tokai-mura, Japan
 
  Magnetic alloy cavities are used for both MR and RCS synchrotrons. Both cavity systems operate successfully and they generate a higher voltage than could be achieved by an ordinary ferrite cavity system. For the future upgrade of J-PARC, a higher RF voltage is needed. A new RF cavity system using the material, FT3L, is designed to achieve this higher field gradient. A large production system using an old cyclotron magnet was constructed to anneal 85-cm size FT3L cores in the J-PARC Hadron Experiment Hall. The muSR (Muon Spin Rotation/Relaxation/Resonance) Experiments were also carried out to study the magnetic alloy. The status of development on the J-PARC site and a new RF system design will be reported.  
slides icon Slides THOBB02 [2.729 MB]  
 
MOPS004 Mitigation of Beam Instability due to Space Charge Effects at 3 GeV RCS in J-PARC 595
 
  • Y. Shobuda, M. Yamamoto
    JAEA/J-PARC, Tokai-mura, Japan
  • Y.H. Chin
    KEK, Ibaraki, Japan
  • F. Tamura
    KEK/JAEA, Ibaraki-Ken, Japan
 
  In order to accomplish high intensity proton beams, it is important to identify the impedance source in accelerators. At 3 GeV rapid cycling synchrotron (RCS) in Japan Proton Research Complex (J-PARC), the kicker impedance is the most dominant among such impedance sources. Beam instability can be observed by correcting chromaticity during the acceleration. Growth rate due to the beam instability can be reduced by making peak current larger (bunching factor smaller). In other words, it is experimentally found that space charge effects mitigate the beam instability.