Improvement of the homogeneity of magnetic field by the attenuation of a selected component with an open superconducting shield made of commercial tapes

Abstract

Homogeneous magnetic fields are needed in many applications. The resolution of medical imaging techniques depends on the quality of the magnetic field, as does the efficiency of electron cooling systems used at particle accelerators. Current methods of improving homogeneity require complex arrangements of magnet windings. In this work, the application of commercial superconducting tapes for this purpose is analyzed experimentally and numerically. The shielding effect exhibited by the superconductors can be used to control the shape of the magnetic field. An open magnetic shield made of superconducting tapes is able to nullify the radial component of a solenoidal magnetic field, forming the long region of the homogeneous magnetic field. To form a shield, the superconducting tapes are wound on a former. Then, it is positioned coaxially inside an electromagnet. The measurements are performed in the DC magnetic field and at zero-field cooling conditions. A numerical model is developed to further analyze the magnetic field. New simplifications and proper constraints allow the use of an axial symmetry despite relatively complex geometry of the shields. Results from the simplified model and obtained experimentally are consistent. The decrease of radial component of the magnetic field and the significant improvement of its homogeneity are observed in a shielded region. The decrease of shielding quality with the increase of an applied magnetic field is observed. Empirical formulas describing the dependence of shielding quality on the geometry and the critical current of the shield are developed.

Distribution of Trapped Magnetic Flux in Superconducting Stacks Magnetised by Angled Field

“…The results can help understand the behaviour of tilted stacks, which were observed to provide good homogeneity and strength of the field [19]. Similar patterns of currents are observed in magnetic shields, which can be used to decrease demagnetisation [20], especially open magnetic shields made of short pieces of tapes [21].…”

Modelling and Performance Analysis of MgB2 and Hybrid Magnetic Shields

“…Recently, tested solutions have included both active (i.e., a set of coils fed with appropriate currents [6]) and passive layouts (i.e., a simple superconducting cavity [7][8][9]). The latter ones, which exploit the intrinsic property of the SC materials, can be assembled using SC bulks [10][11][12] and/or SC coated conductors/tapes [13][14][15][16][17]. Furthermore, promising improvements of the shielding ability have been achieved by superimposing SC and ferromagnetic (FM) materials [18][19][20][21][22][23][24], including the possibility to cloak static (DC) and alternating (AC) magnetic fields in suitably shaped SC/FM heterostructures [25][26][27][28][29][30].…”

Proof of Concept of High-Temperature Superconducting Screens for Magnetic Field-Error Cancellation in Accelerator Magnets

“…Previous work for mitigating magnetic field imperfections led to magnetic cloaks for sensors [9,10], shim coils for magnetic resonance imaging [11] and nuclear magnetic resonance [12] applications, selective shields for field homogenization in solenoids [13]. Recently, persistent-current shims coils were introduced as a conceptual solution for improving the field quality in accelerator magnets [14,15].…”