Patent for Septum Magnet

Concept for a new accelerator component developed

a) conventional iron-dominated magnet with rectangular yoke, b) consine-theta magnet, round yoke, c) conventional septum magnet with truncated rectangular yoke, d) the new patent, cosine-theta magnet with truncated round yoke (Graphics: Kei Sugita)

GSI scientist Dr. Kei Sugita developed a novel concept for a septum magnet, which allows high magnetic-field strength in a limited region of space and a compact design. The new concept could be used in accelerators for medical purposes or for research, like the future FAIR facility. A patent for the US American market has been granted this winter; a similar patent application for Europe and Japan has been submitted and is on the verge of issuing in Europe.


In ring accelerators septum magnets are used to inject or extract the beam into or from the accelerator. This requires strong magnetic fields to force the beam onto a curved trajectory. At the same time the magnetic field must not disturb the circulating beam in the ring. Therefore a magnet with two regions divided by a thin wall (septum) is necessary, which induces a strong magnetic field on one side of the wall and a vanishing magnetic field on the other side.


Common electromagnets use a coil for the generation and a rectangular iron yoke for the forming of the magnetic field. In septum magnets the yoke is open on one side (c-shape) to reduce the field to zero on that side. Sugita's idea is based on another type of magnet: So-called cosine-theta magnets are mainly built as superconducting magnets with high magnetic-field strength. The novel concept is to equip the cosine-theta magnet with an iron yoke (in this case a round one), which is truncated on one side to reduce the field to zero. This enables the use of a cosine-theta magnet as a septum magnet.


For Sugita, who works in GSI's "SIS100/SIS18" department and comes from Japan, this work has special personal meaning. "I worked on this topic five years ago, during the time of the catastrophic earthquake in Japan. I worked very hard, because this was almost all I could do here. I was deeply impressed by my colleagues at GSI who organized a fund-raiser and supported a special programme for Japanese graduate students who could not complete their studies at Japanese accelerator facilities. Such activities at GSI truly encouraged me. I hope my patented invention will contribute to GSI and the international accelerator community."


Sugita's invention could lead to septum magnets with magnetic-field strengths of more than two Tesla, which is the limit of the conventional design. By introducing a superconducting coil, even up to eight Tesla are achieved in electromagnetic simulations. Quadrupole or higher multipole septum magnets could also be realised with the design. This new septum type might be used for accelerators in medicine or in future large-scale facilities for research such as FAIR or the Future Circular Collider (FCC) planned at CERN.

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