Influence of azimuthal coil size variations on magnetic field harmonics of superconducting particle accelerator magnets

Abstract

The superconducting super collider (SSC) would have required dipole and quadrupole magnets with a very high field quality. The field quality is determined mainly by the dimensions of the magnet coils and their positions with respect to the iron yoke. It is thus very sensitive to manufacturing errors. A model is here developed to estimate the field distortions in a dipole magnet due to azimuthal coil size variations. This model is applied to the data collected during the fabrication and testing of a series of 5 cm aperture, 15 m long SSC dipole magnet prototypes. A clear correlation is observed between the predicted field distortions from the azimuthal coil sizes and the measured skew quadrupole and skew sextupole coefficients.

Measurement of AC loss and magnetic field during ramps in the LHC model dipoles

“…A reconstruction of the G c distribution in a coil is indeed possible based on the measured harmonics [5,6] but was not applied here. Secondly, both AC loss and field distortions are not only sensitive to inter-strand coupling currents, characterized by R c , but also to inter-filament coupling currents inside the strands [7,8]. While on one side the inter-filament contribution adds significantly to the total AC loss (approximately 30 % of the total loss for R c = 20 µΩ), in the case of the field distortions the inter-filament contribution is much smaller (0.7 %, 10 % and 9 % respectively for b 1 , b 3 , b 5 ) and it subtracts from the effect of inter-strand currents.…”