THE STRONGEST PERMANENT DIPOLE MAGNET - Proceedings of the 2003 Particle Accelerator Conference

Aug 29, 2026

Authors present the development of exceptionally strong permanent magnets, describing progress from a 4.45 T dipole field toward much higher strengths using a specially designed magnetic circuit. The work introduces a hybrid flux-compression approach combined with an extended Halbach concept and detailed materials and gap considerations. Latest measurements are reported for the strongest permanent dipole magnet built, emphasizing field strength limits, practical design constraints, and record-setting performance relative to prior permanent-magnet and hybrid-magnet efforts.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages3

Reading Time8 min

AccessFree to download

Abstract

Introduction

Six Tesla Permanent Magnet Dipole

Design approach and materials

Field measurements and performance context

Proceedings of the 2003 Particle Accelerator Conference THE STRONGEST PERMANENT DIPOLE MAGNET M. Kumada, NIRS/JST/Lviv Polytechnic, Chiba, Japan Y. Iwashita, Kyoto University, Kyoto, Japan M. Aoki, E. Sugiyama, Sumitomo Special Metals, Osaka, Japan Abstract The authors have been developing very strong permanent magnets. In the past, our magnets could generate a 4.45 Tesla dipole field. We are now in a process of reaching much higher fields by a special magnetic circuit. We will present our latest results of the strongest permanent dipole magnet ever built. INTRODUCTION An everlasting desire of magnet builder is to pursue to produce a magnetic field strength as high as possible. The strongest manmade magnetic field must be the one made by Terawatt level of Laser. It is an equivalent magnetic field. Duration of the field is short as the laser pulse. Oneof the author(Kumada) proposed the magnetic field can be used as a Laser wiggler for a compact X ray Laser FEL but has not been constructed. A very strong magnetic field is generated by flux compression mechanism by theta pinch plasma or metallic cylinder by implosion but they are single shot and destructive. A rather practical strongest field must be the one by hybrid magnet where it is made of a combination of a superconducting magnet and a pulsed magnet. Again the duration of pulse is not very long as the pulsed magnet is made of copper conductor. The field strength of permanent magnet is rather modest compared with those magnets. Residual field strength of the strongest permanent magnet material is ata level of 1.3 Tesla. And in most cases, the magnetic field strength made by these materials is half of the residual field. But using the permanent magnet is still attractive as it provides us almost eternal field without energy consumption. The permanent magnet is especially attractive to the application of small gap size magnet or magnet having short period. Successful applications to a wiggler or undulator are widely accepted. Extensive efforts to get higher field with wiggler of undulator with permanent magnet have been made. By using permendur, which is a material of high saturation field, 3 Tesla field was achieved at SPRING 8 by a group of University of Tokyo. The working mechanism of the undulator is due to Halbach. The field strength of this magnet is stronger than the residual field. Halbach had invented a novel magnetic circuit of Rare Earth Cobalt(REC) magnet where the maximum increase can be factor of 2 for the case of his REC quadrupole magnet. Then a motivation of designing a medical accelerator as compact as possible one of the authors (Kumada) then invented an extended Halbach dipole magnet. A concept of saturated iron and flux compression is developed. Dipole magnet is designed and constructed. A method of increasing the field by cooling the magnet is also shown to work. World record of 4.45 T in 8 mm gap was reached in this way[1,2,3,4] . The increase of the field can also be applied to the permanent multipole magnets. Straight application is to a final focus quadrupole of the linear collider[5,6] . Encouraged by the result of the 4.45 T dipole the authors proposed a project of permanent magnet based cyclotron and got a grant from Japan Science Technology. The magnet consists of hill and valley. The maximum field of the hill is about 2.2 T and the average field is 1.4 T. A new concept of flux compression is invented in it. The details with full of new ideas will be presented in a forthcoming 18-th Magnet technology conference (MT18) in Japan this fall. Cugart and Block of ESRF of Grenoble broke this record shortly. They recorded a 5 Tesla inside a tiny gap of 0 . 15mm[7] . Applying similar magnetic compression scheme of the cyclotron magnet, we have designed and manufactured a 6 T dipole magnet. While we broke the new record again, we only reached 5.16 T with a gap height of 2mm where a Grenoble group reached 5 T with a gap height o

FAQs

What magnetic-field strengths do the authors aim to achieve, and how did their earlier magnet perform?

They aim to reach much higher fields than their previous permanent dipole, which generated a 4.45 Tesla dipole field. The paper describes a process toward higher fields using a special magnetic circuit.

Why do the authors consider permanent magnets attractive despite their lower residual-field strength?

Permanent magnets offer almost eternal field without energy consumption. They are especially attractive for small-gap applications and magnets with short periods, and practical wiggler/undulator uses are widely accepted.

What design changes were made to develop a six-tesla permanent dipole magnet?

To go beyond 5 T, the authors adopt a small-gap approach combined with a flux-compression-type circuit, using permendur as the central pole and arranging permanent magnet blocks to direct flux toward the center. They then present measured results for the 6 T dipole.

Aug 29, 2026

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