Abstract
The paper describes a semi-analytical hysteresis model for hard superconductors. The model is based on the critical state model considering the dependency of the critical current density on the varying local field in the superconducting filaments. By combining this hysteresis model with numerical field computation methods, it is possible to calculate the persistent current multipole errors in the magnet taking local saturation effects in the magnetic iron parts into consideration. As an application of the method, the use of soft magnetic iron sheets (coil protection sheets mounted between the coils and the collars) for the part compensation of the multipole errors during the ramping of the magnets is investigated.
Highlights
The Large Hadron Collider (LHC) [1], a proton-proton superconducting accelerator, will consist of about 8400 superconducting magnet units of different types, all operating in superfluid helium at a temperature of 1.9 K
The persistent current distribution has been modeled by means of the critical state model [2], taking into account their dependency on the magnetic induction by use of a current fit [3]
In the LHC main dipole magnet, which is used as an example, the local field in the coil varies depending on the excitation current and changing yoke saturation during the ramping of the magnets
Summary
The Large Hadron Collider (LHC) [1], a proton-proton superconducting accelerator, will consist of about 8400 superconducting magnet units of different types, all operating in superfluid helium at a temperature of 1.9 K. Field variations in the LHC superconducting magnets, e.g., during the ramping of the magnets, induce magnetization currents in the superconducting filaments. In the LHC main dipole magnet, which is used as an example, the local field in the coil varies depending on the excitation current and changing yoke saturation during the ramping of the magnets. The magnetization model is combined with the coupled boundary elementfinite element method (BEM-FEM method) [4] for the computation of the local field in the coil. The discretization errors due to the finite-element part in the BEM-FEM formulation are limited to the iron magnetization arising from the surrounding yoke structure, which accounts for about 20% of the total field. With a sheet of suitable thickness the nonlinearities in the multipole errors during the upramp cycle of the dipoles can be significantly reduced
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