Coil End Design Research Articles

3-D Magnetic and Mechanical Design of Coil Ends for the Racetrack Model Magnet RMM

The racetrack model magnet (RMM) is a racetrack test magnet being developed at CERN. Its main goal is to demonstrate, in view of future high field accelerator magnets, that a nominal field of 16 T can be reached in a 50 mm bore, with margins and limited training. This paper presents a 3-D magnetic and mechanical study and proposes solutions to achieve a peak field in the ends lower than in the straight section, while containing the electromagnetic forces. The structure features tie rods and end-plates, which have been designed to provide an adequate support to the coil ends, in different loading configurations. In particular, the impact of different materials and the role of friction have been studied. Different solutions are compared and a final design is proposed, which offers the best compromise in terms of magnetic and mechanical criteria.

Strain Distribution in REBCO-Coated Conductors Bent With the Constant-Perimeter Geometry

Cable and magnet applications require bending REBa 2 Cu 3 O 7-δ (REBCO, RE = rare earth) tapes around a former to carry high current or generate specific magnetic fields. With a high aspect ratio, REBCO tapes favor the bending along their broad surfaces (easy way) than their thin edges (hard way). The easy-way bending forms can be effectively determined by the constant-perimeter method that was developed in the 1970s to fabricate accelerator magnets with flat thin conductors. The method, however, does not consider the strain distribution in the REBCO layer that can result from bending. Therefore, the REBCO layer can be overstrained and damaged even if it is bent in an easy way as determined by the constant-perimeter method. To address this issue, we developed a numerical approach to determine the strain in the REBCO layer using the local curvatures of the tape neutral plane. Two orthogonal strain components are determined: the axial component along the tape length and the transverse component along the tape width. These two components can be used to determine the conductor critical current after bending. The approach is demonstrated with four examples relevant for applications: a helical form for cables, forms for canted cos θ dipole and quadrupole magnets, and a form for the coil end design. The approach allows us to optimize the design of REBCO cables and magnets based on the constant-perimeter geometry and to reduce the strain-induced critical current degradation.

Discrete Differential Geometry Applied to the Coil-End Design of Superconducting Magnets

Coil-end design for superconducting accelerator magnets, based on the continuous strip theory of differential geometry, has been introduced by Cook in 1991. A similar method has later been coupled to numerical field calculation and used in an integrated design process for LHC magnets within the CERN field computation program ROXIE. In this paper we present a discrete analog on to the continuous theory of strips. Its inherent simplicity enhances the computational performance, while reproducing the accuracy of the continuous model. The method has been applied to the design of coil ends for the SIS300 dipole magnets of the FAIR project.

Coil End Design for Superconducting Magnets Applying Differential Geometry Methods

An integrated design approach is used at CERN for the design and optimization of superconducting accelerator magnets, with the ROXIE program package as the key tool. The layout of the coil ends has proven in most cases to be the limiting factor for the magnets' quench performance. The objectives for coil end design are therefore to minimize the mechanical stress on the cables, to optimize the integrated multipole content, and to limit the peak field enhancement. This paper introduces a new approach based on differential geometry methods that allows for the geometrical and mechanical optimization of cos n/spl theta/ coil ends.

New coil end design for the RHIC arc dipole

The racetrack-shaped coils for the RHIC arc dipoles are wound with 32 turns of flat cable interleaved in the curved ends with insulating material {"spacers"} of varying thickness. To simplify production, the number of spacers, about 64 in each coil end, was reduced by making some of them thicker, to about 23. A new computer program was written which gives a description of each turn closely resembling the turn as made. The output of this program is processed by newly written computer programs which change the parts descriptions into forms which are used by a computer-controlled, 5-axis milling machine. The solid spacers replace spacers assembled from laminations and improve the fit as well. The parts will be molded during production. The calculated harmonic content of the ends is compared with measurements on the first magnets built with the new ends.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Tests of Fermilab built 40 mm aperture full length SSC dipole magnets

Several 40-mm-aperture, 17-m-long dipoles have been built by Fermilab as developmental prototypes for the Superconducting Super Collider (SSC). These magnets have an external inner-outer coil splice design, a collet style end clamp assembly, a new, analytically designed minimum stress coil end design, and a new insulation system which does not employ shims or 'shoes'. In addition, the magnets were built using production-style tooling. The magnets were tested at the Fermilab Magnet Testing Facility. Quench testing and mechanical measurement results are presented and analyzed with emphasis on the new design and fabrication features of these magnets. The performance of these magnets was very good from a quench and mechanical behavior standpoint. The magnets did not exhibit excessive training behavior and only one training quench was below the nominal operating current. The coil prestress remained positive to >7 T in both magnets and most of the quenches originated in the high field region of the pole turn.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>