Eddy Current Effects of the J-PARC RCS Sextupole Magnets

Sextupole magnets for the chromaticity correction of the rapid-cycling synchrotron of the Japan Proton Accelerator Research Complex have a large bore of 330 mm and a relatively short length of 320 mm. The end effect, therefore, was not negligible and a three-dimensional magnetic field calculation was necessary to achieve the required field quality of inside the radius of 141.2 mm for the designed maximum field gradient of 18.6 T/m. Eddy current effect on the field quality and temperature rise was considered because the magnets were to be excited with a current pattern of a frequency of 25 Hz. Measurement using harmonic coils confirmed that the required field quality was achieved. Measurement results of the sextupole component and 18-pole component field were reproduced with the magnetic field calculation program OPERA3d/ELEKTRA.