Design of racetrack coils for high-field dipole magnets

The magnet group at LBNL is in the process of developing high-field accelerator magnets for use in future colliders. One of the primary challenges is to provide a design which is cost-effective and simple to manufacture, at the same time resulting in good training performance and field quality adequate for accelerator operation. Studies have focused on a racetrack geometry that has the virtues of simplicity and conductor compatibility. The results have been applied to the design of a series of prototype high-field magnets based on Nb/sub 3/Sn conductor.

I. Introduction

A program to develop high-field accelerator magnets for future colliders is underway at several U.S. laborato-ries. After completion of the 13.5 dipole D-20 [1], the LBNL magnet group has started to investigate the “common coil” configuration for two-aperture dipoles, using racetrack coils shared between both magnet apertures [2], [3]. The first test involved a 6 T short model (RD-2) built using ITER-type Nb₃ Sn conductor. The magnet reached short sample field with no training in a variety of pre-load configurations [4]. The following magnet in this series (RD-3) uses high-performance Nb₃ Sn conductor with critical current density above 2 kA/mm² at 12 T, 4.2 K, and is designed to reach 14 T [5]. The coil structure is composed of two outer modules and one inner module. The two outer modules have been pre-tested in back-to-back configuration (RT-l) and have achieved a field of 12 T [6]. The complete structure is now assembled and testing is underway.