A Design Study on No-Insulation HTS Isochronous Cyclotron Magnet for Carbon Ion Therapy

Provided that a cyclotron system requires DC magnetic field, the no-insulation (NI) high temperature superconductor (HTS) magnet may be a good candidate as it may enable the cyclotron magnet to be more compact and reliable, yet operate under the liquid-helium-free environment. Here we report on a design study on an NI HTS isochronous cyclotron magnet for an acceleration of carbon ion up to an energy level of 385 MeV/u. To obtain a target beam stability, HTS coils were designed with the so-called “hill” and “valley” structure to generate a designated magnetic field profile. After the initial design on yokes and HTS coils was completed, a final design on the cyclotron magnet design was completed and its performance was analyzed using a 3D finite element method. This paper presents the magnet design and performance analyses in details that include: (1) electromagnetic design of the HTS coils and iron yokes for isochronous magnetic field; (2) mechanical stress with the use of stainless steel co-winding to limit the peak magnetic hoop stress; (3) charging and discharging scenarios with the non-linear NI characteristics considered; and (4) first-cut post-quench analysis with an estimated peak temperature and unbalanced force within the NI HTS coils.