Critical aspects in the development of a curved fast ramped superconducting dipole for FAIR SIS300 synchrotron

Abstract

The FAIR facility, under development at GSI, includes a large synchrotron for heavy ions acceleration: the SIS300, so called for having a magnetic rigidity of 300 Tm. The dipoles of this synchrotron shall be pulsed at the rate of 1 T/s up to 4.5 T maximum field in a bore of 100 mm. The magnets have a magnetic length ranging from 3.94m to 7.89 m with a cos-theta configuration. The coils with have the particular characteristic to be curved (the sagitta is 114 mm for the long dipoles). Design activities, coupled with conductor R&D and model coil construction, are under way for developing a curved fastcycled superconducting dipole, suitable for operations of the SIS300. The main goal is the construction, before the end of 2009, of a prototype magnet, including cold mass, fully integrated into a horizontal cryostat. An important intermediate milestone is the industrial feasibility assessment of the winding technology developed for a curve cos-theta dipole, through the construction of cured curved magnet poles, actually under way. The paper covers the critical aspects of this development, with particular emphasis on the constructive problems. INTRODUCTION This paper deals with R&D activities in progress at Italian Institute for Nuclear Physics aimed at developing the high field rapidly-cycling super-conducting dipoles needed for SIS300 [1]. In order to have the maximum possible acceptance at a minimum field volume, a curved design with a radius of 66.67 m was proposed for the bending dipoles by FAIR team. The present lattice design includes 48 long dipoles with magnetic length 7.89 m and 12 short dipoles with magnetic length 3.94 m. The coils have two main features: they is curved with a sagitta of 114 mm for long dipoles), and they are fast ramped. Both these characteristics demanded for a challenging R&D, aimed at the development of the required low loss conductor, a robust design with respect fatigue issues and a suitable winding technology. The Italian National Institute of Nuclear Physics (INFN) proposed to perform this R&D in a larger framework aimed to construct a model magnet. A project, called DISCORAP (“Dipoli SuperCOnduttori RApidamente Pulsati”), started in 2006 according a specific INFN-FAIR Memorandum of Understanding signed by both institutions in December 2006. The aim is to have a complete cold mass prototype of the short dipole ready in the summer of 2009. After a preliminary test of the cold mass in a vertical cryostat, it will be integrated in a horizontal cryostat for a test campaign at GSI. BASIC DESIGN CONCEPTS Table 1 shows the main characteristics of the model coil. The basic assumption for the design was that the coil should be wound curved, because in this way one can avoid the problem of spring back effects during all manufacturing stages and coil operation. At an initial stage the choice of a curved winding led the design to a layout based on a single layer coil mechanically supported only by the collars. This basic choice was due to the envisaged manufacturing difficulties related to the mechanical coupling between two curved layers or between a curved collared coil and a curved yoke. Nevertheless later on we realized that the iron yoke must have a role in limiting the mechanical deformations of the collared coil. If not, we could have fatigue failures in some locations of the collar. Table 1: Characteristics of the model coil Nominal Field (T) : 4.5