• S. Igarashi, T. Oogoe, H. Someya, S. Yamada
  KEK, Ibaraki
• Y. Kuniyasu
  MELCO SC, Tsukuba
• S. Nakamura
  J-PARC, KEK & JAEA, Ibaraki-ken

Efforts have been made to reduce the magnetic field ripple of the bending, quadrupole and sextupole magnets of the J-PARC main ring using the trim coils of the magnets. The quadrupole magnet has 24 turn main coil and 11 turn trim coil per pole those can be considered as a primary winding and a secondary winding of a transformer. When the trim coil is shorted, the induced trim coil current cancels the field ripple. The field ripple of the quadrupole magnet was reduced by a factor of 6 by shorting trim coil. The trim coil current, however, deforms the acceleration field pattern if the coil is shorted all the time of the current pattern of flat bottom, acceleration, flat top and recovery. The MOSFET relay was used to short the coil and to reduce the field ripple during the flat bottom and flat top. The circuits were built for the quadrupole and sextupole magnets. The plan has been made to wind optimized trim coils for the bending magnets.

• M.J. Shirakata, T. Oogoe
  KEK, Ibaraki

The beam transport line between 3 GeV Rapid Cycling Synchrotron and Main Ring has a beam collimator system in order to improve the quality of injected beam in the main ring. The beam power deposited into the collimators is required to be increased for high intensity beam operation. The tolerance of existing radiation shield becomes insufficient, even though there is no heat problem. The gate-type shield system has been preparing in order to satisfy both the radiation shielding and feasibility of maintenance. The development of movable gate-type shield system is reported here, which fully covers more than 20 meters long collimator section.