• K. Fan, K. Ishii, H. Matsumoto, N. Matsumoto
  KEK, Ibaraki

Injection into the J-PARC main ring is implemented by 4 kickers and 2 pulsed septa at 3 GeV in a long straight section. To accommodate the injection beam of 54 pmm.mrad, both septa have large physical acceptance of 81 pmm.mrad. However, large aperture leads to large end fringe field interfereing the circulating beam and causing beam loss, which has been observed even at low beam intensity during the beam commissioning. To provide users a proton beam with high beam power, the injection beam intensity will increase greatly in future, which creates difficulties for the present injection system. To accommodate these high intensity beams with low beam loss, the injection system needs to be upgraded. Taking account the strong space charge effects, even larger physical is needed to reduce the localized beam loss, which creates severer end fringe leakage field. This paper will discuss the problems encountered in operating the present septa, and give an optimized design for the new septa.

• K. Fan, K. Ishii, H. Matsumoto, N. Matsumoto
  KEK, Ibaraki

The J-PARC is a high intensity proton accelerator complex, which consists of a LINAC, a Rapid Cycling Synchrotron (RCS) and a Main Ring (MR). The MR injection system employs a high-field septum to deflect the incoming beam from the RCS, which has been used for the beam commissioning study with low beam intensity successfully. Relative large beam losses in the injection area have been observed, which is proportional to the injection beam intensity. In future, the beam intensity will increase about 100 times to realize high beam power (~MW) operation required from neutrino experiments. The beam loss at the injection region is expected increase greatly due to the space charge effects, which creates severe radiation problems. Since the present injection septum coil is organic insulated, which will be destroyed under such a severe irradiation quickly. To cope with this problem, a new high radiation resistant injection septum magnet is developed, which uses inorganic insulation material (Mineral Insulated Cable - MIC) to prevent the septum from radiation damage. This paper investigates different effects caused by the MIC and gives an optimization design.

• G.H. Wei
  KEK/JAEA, Ibaraki-Ken
• A. Ando, T. Koseki, J. Takano
  J-PARC, KEK & JAEA, Ibaraki-ken
• K. Fan, S. Igarashi, K. Ishii, T. Nakadaira, M. Tomizawa, M. Uota
  KEK, Ibaraki
• H. Harada, P.K. Saha
  JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken

The beam commissioning of J-PARC/MR has been started from May 2008 and is in progress*. One key purpose of MR commissioning is the 30 GeV beam fast extraction to Neutrino beam line, which reflect the overall commissioning result. In the MR, the third straight section is assigned for the fast extraction. 5 kickers and 8 septa were installed there, which can give beam a bipolar kick to inside or outside of MR. Inside kick means beam to Neutrino Oscillation Experiment, while outside kick means beam dumped to abort line. However before commissioning, the measured magnetic field distribution of each septa shows non-linear profile along the horizontal direction. In order to find the influence, a simulation with these measured field has been performed. Depends on this study and some OPI (Operation Interface) made by code SAD for orbit modification online, fast extraction of 30 GeV beam to Neutrino line has been achieved on April 23rd 2009. Beam orbit have been tuned to less than 0.5 mm and 0.1 mrad in both horizontal and vertical at the beginning of Neutrino line, which is also the end of MR fast extraction. And so far, 100 kW continual operation to neutrino line have been achieved, too.

* T. Koseki, "Challenges and Solutions for J-PARC Commissioning and Early Operation", in these proceedings

• K. Ohmi, K. Fan, S. Igarashi, Y. Sato
  KEK, Ibaraki
• H. Hotchi, Y. Shobuda
  JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken

Nonlinear space charge interaction in high intensity proton rings causes beam loss, which limits the performance. Simulations based on particle in cell method has been performed for JPARC-Rapid Cycle Synchrotron and Main Ring. Beam loss estimation during acceleration and resonances analysis are discussed with various simulations using dynamic and frozen models.