Title: Design, Fabrication, and Test of a Superconducting Dipole Magnet Based on Tilted Solenoids
Abstract: Design, Fabrication, and Test of a Superconducting Dipole Magnet Based on Tilted Solenoids S. Caspi, D.R. Dietderich, P. Ferracin, N.R. Finney, M.J. Fuery, S.A. Gourlay and A.R. Hafalia Abstract— It can be shown that, by superposing two solenoid-like thin windings that are oppositely skewed (tilted) with respect to the bore axis, the combined current density on the surface is “cos- theta” like and the resulting magnetic field in the bore is a pure dipole. As a proof of principle, such a magnet was designed, built and tested as part of a summer undergraduate intern project. The measured field in the 25mm bore, 4 single strand layers using NbTi superconductor, exceeded 1 T. The simplicity of this high field quality design, void of typical wedges end-spacers and coil assembly, is especially suitable for insert-coils using High Temperature Superconducting wire as well as for low cost superconducting accelerator magnets for High Energy Physics. Details of the design, construction and test are reported. Index Terms— Superconducting magnet, pure dipole, insert magnet, tilted solenoid. I. I NTRODUCTION n a published paper by D.I. Meyer and R. Flasck in 1970 [1] the authors discussed the magnetic field resulting from the superposition of two oppositely skewed (tilted) solenoids with respect to the bore axis (Fig. 1). The resulting superimposed current density cancels the azimuthal component of the magnetic field and enhances its axial component in proportion to J 0 cos θ . The idea reappeared in a series of publications presently building a similar quadrupole magnet. Advantages of this concept are as follows: 1) high field quality in an extended dynamic range, 2) no field optimization required, 3) small number of components - wedges and spacers not needed, 4) coil assembly not needed (all poles are wound together around a single bore), 5) small bore sizes not limiting “cos-theta” windings, 6) continuous windings and ease of magnet “grading”. There are also other open issues such as magnet protection and pre-stress that will need to be addressed in the future. The concept can work well for “stand alone” accelerator magnet as well as insert coils to existing magnets. The technology is particularly suitable for Nb 3 Sn conductor as well as high temperature superconducting wires. In section II we give a short mathematical proof addressing the perfect dipole quality followed, in section III, with details on the magnet design and construction. In section IV we report test results and draw final conclusions. I [2]-[5] that, by not crediting the 1970’s publication, may have been unaware of it. With renewed interest in high field Nb 3 Sn magnets at LBNL and CERN [6], [7] the idea gained interest leading to the construction a small dipole magnet. As part of LBNL summer student program in 2005, we have designed, built and tested a superconducting dipole that is based on the concept of tilted solenoid windings. The design and analysis was done with the program MathCad® and carried out by two undergraduate students over a period of three weeks. Impressed by the simplicity of the design and low construction cost (in full agreement with all previously published conclusions) we have extended the concept and are Manuscript received August 27, 2006. This work was supported by the Director, Office of Energy Research, Office of High Energy and Nuclear Physics, High Energy Physics Division, U. S. Department of Energy, under Contract No. DE-AC02-05CH11231. Authors are with Lawrence Berkeley National Laboratory, Berkeley, CA 94720 USA (e-mail: [email protected]). N.R. Finney and MJ. Furry are undergraduate students at UCB an USD. Fig. 1. Superposition of two alternating skewed solenoids generating a perfect dipole field. A. Mathematical Model A simplified mathematical proof is used to show that skewed windings on the surface of a cylindrical correspond to an axial current-density distribution that is cos ϑ like, and therefore produce a “pure” dipole field. The current density flow lines that are distributed on the surface of the cylinder are elliptical (inclination angle α with respect to the cylinder axis) with flow lines coordinates expressed as (see Fig. 1-2)
Publication Year: 2009
Publication Date: 2009-03-13
Language: en
Type: article
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