Abstract
Estimates of random field-shape errors induced by cable mispositioning in superconducting magnets are presented and specific applications to the Large Hadron Collider (LHC) main dipoles and quadrupoles are extensively discussed. Numerical simulations obtained with Monte Carlo methods are compared to analytic estimates and are used to interpret the experimental data for the LHC dipole and quadrupole prototypes. The proposed approach can predict the effect of magnet tolerances on geometric components of random field-shape errors, and it is a useful tool to monitor the obtained tolerances during magnet production.
Highlights
The magnetic field generated by superconducting magnets used in particle accelerators [1] is affected by deviations from the ideal shape, which must be kept within a few 1024 times the main field to avoid accelerator performance limitations
Field quality is determined mainly by three contributions: namely, the geometric part given by the positioning of the conductors inside the ferromagnetic yoke [1], a persistent current effect due to cable magnetization [1,2,3], and the yoke saturation at high field [1]
In order to obtain an acceptable field quality, conductor positions must agree with the nominal design within less than 0.1 mm [4]
Summary
The magnetic field generated by superconducting magnets used in particle accelerators [1] is affected by deviations from the ideal shape, which must be kept within a few 1024 times the main field to avoid accelerator performance limitations. Field shape is expanded in a power series in the coordinates of the magnet cross section plane The coefficients of this expansion, called normal and skew multipoles, feature random variations along the longitudinal axis of the magnet. In this paper we develop a complementary approach, where all the asymmetries are considered probable, and the amplitude of the random displacement becomes the main fitting parameter This leads to the same estimate for the normal and skew components of the same order. We compare our estimates with the experimental data at room temperature, where the cable magnetization and yoke saturation are not present These data agree with the multipole decay foreseen by our scaling law, validating the way of modeling random errors. Detailed analytical computations of random errors are given in Appendix B
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