Abstract
Field quality in superconducting magnets strongly depends on the geometry of the coil. Fiberglass spacers (shims) placed between the coil and the collars have been used to optimize magnetic and mechanical performances of superconducting magnets in large accelerators. A change in the shim thickness affects both the geometry of the coil and its state of compression (prestress) under operational conditions. In this paper we develop a coupled magnetomechanical model of the main Large Hadron Collider dipole. This model allows us to evaluate the prestress dependence on the shim thickness and the map of deformations of the coil and the collars. Results of the model are compared to experimental measurements carried out in a dedicated experiment, where a magnet model has been reassembled 5 times with different shims. A good agreement is found between simulations and experimental data both on the mechanical behavior and on the field quality. We show that this approach allows us to improve this agreement with respect to models previously used in the literature. We finally evaluate the range of tunability that will be provided by shims during the production of the Large Hadron Collider main dipoles.
Highlights
In superconducting magnets used for particle accelerators, the magnetic field strongly depends on the position of the conductors [1]
In a production phase one has a mix of both cases, where an acceptable range has been defined for the prestress, and shims are used both to stay in this range and to reach the optimal coil size for field quality
In this paper we analyzed how the field quality of the main Large Hadron Collider (LHC) dipole can be tuned by changing the coil geometry with fiberglass spacers placed on the coil pole faces
Summary
In superconducting magnets used for particle accelerators, the magnetic field strongly depends on the position of the conductors [1]. In the case of the superconducting dipoles of the Large Hadron Collider (LHC) [2], under construction at the European Organization for Nuclear Research (CERN), the beam dynamics constraints require a control of field homogeneity up to 1025 for some components [3] This implies that the standard deviation of the cable positioning is around 0.03 mm [4], leading to global tolerances of the coil layout of less than 0.1 mm. Adjustable shims have been used in magnets for the Tevatron [5], for the High Electron Ring Accelerator (HERA) [6], in the Superconducting Super Collider (SSC) magnet prototypes [7], and for the Relativistic Heavy Ion Collider (RHIC) [8,9] They aim at optimizing either the mechanical or the magnetic performance. In a production phase one has a mix of both cases, where an acceptable range has been defined for the prestress, and shims are used both to stay in this range and to reach the optimal coil size for field quality (see for instance the experience of Tevatron [5], HERA [6], and RHIC [8,9])
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
