• 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.

• J. Takano, T. Koseki, S. Nakamura, T. Toyama, N. Yamamoto
  J-PARC, KEK & JAEA, Ibaraki-ken
• S. Hatakeyama
  JAEA/J-PARC, Tokai-mura
• K. Niki, M. Tomizawa, S. Yamada
  KEK, Ibaraki

In the J-PARC Main Ring (MR), the bending, quadrupole, sextupole, and steering magnets can be controlled on the operating interfaces (OPI). The optics parameters for all magnets are calculated by using SAD, and are converted to BL tables (ex: 2000 points for a steering magnet) for each power supplies. The BL tables are made from the parameters of optics, pattern timing, and beam energy at flat bottom and flat top. For MR beam studies, the BL tables are adjustable with offset and factor. This system is useful for COD correction, beta function measurement, aperture survey, and slow extraction. In this proceeding, the structure of the magnet control system and OPIs for beam studies will be shown.

• H. Someya, S. Igarashi
  KEK, Ibaraki
• S. Nakamura
  J-PARC, KEK & JAEA, Ibaraki-ken

The power supply current ripple of the quadrupole magnets of the J-PARC main ring has been measured to be the order of 10^-4. The magnetic field of the quadrupole magnets has been measured and the ripple frequency distribution of each magnet was observed to be depending on where the magnet is in the magnet chain. A transmission line model for the cable and magnets was able to explain the distribution. The field ripple made by the common mode current ripple was reduced by changing the magnet cabling to be symmetrical with respect to the N and S poles of the quadrupole magnets. The common mode ripple was drastically reduced. The normal mode ripple of 600, 1200 and 1800 Hz however remained. The field ripple was further reduced using resistors those are connected in parallel to the magnet coils and bypass the current ripple. It was effective to the higher frequency ripple of 1200 and 1800 Hz and the effect was in a good agreement with an electric circuit simulation program LTspice.