Magnetic field measurement of the J-PARC RCS steering magnets and sextupole magnets and comparison to the field calculation

The magnetic field of the steering magnets of the J-PARC rapid cycle synchrotron (RCS) has been measured using flip coils when the current pattern was a superposition of a direct current and an alternating current of 25 Hz. The integral of the magnetic field with respect to the beam direction, z, between -0.6 m and 0.6 m was four times as large as the requirement. The uniformity of the field integral was within ±1% for the region of |x| < 130 mm. The measurement agreed with the results from three-dimensional magnetic field calculation program OPERA3d/ELEKTRA that took eddy current effects into account. The magnetic field of the sextupole magnets has been measured using harmonic coils. The field strength was measured to have a margin of 30% from the requirement. The relative amplitude of the 18-pole component to the sextupole component was observed to by 2x10-4 that was less than the requirement of 10-3. The results were in a good agreement with the results from OPERA3d/ELEKTRA. The time shift of the 18-pole component with respect to the current pattern was observed with harmonic coils those covered the end region of the magnet. Eddy current at the stainless steel end plate and end region of the iron were the cause. (author)