A Novel Magnetic Field Active Shim Method for Air-Core High-Temperature Superconducting Quadruple Magnet

An air-core high-temperature superconducting quadruple magnet (AHQM) is composed of high-temperature superconductor (HTS) coils without an iron yoke. An AHQM exhibits magnetic field characteristics that vary linearly with respect to changes in the operating current. Further, the AHQM is more suitable for use in high heat load regions. A conventional iron-core quadruple magnet (IQM) contains an iron yoke to achieve the specific shape and magnitude of the magnetic field. In the case of IQMs, the iron yoke generates most of the magnetic field. In the case of AHQMs, the magnetic fields are generated solely by HTS coils. Thus, an AHQM requires a larger number of coils to generate a magnetic field, because the iron yoke has been removed. Consequently, the influence of manufacturing errors in the AHQM is high; these errors deteriorate the designed magnetic field. Therefore, magnetic field correction is required to reduce the deterioration in the magnetic field of an AHQM. This paper, proposes a novel active shim method to compensate for the deteriorated magnetic field of an AHQM. This method improves the uniformity, but does not affect the gradient and effective length of the quadruple magnet. The effectiveness of this method is verified by simulation.