Temporal behaviour of multipole components of the magnetic field in a small dipole magnet wound with coated conductors

Abstract

To study the influence of coated-conductor magnetization on the field quality of accelerator magnets, we made a small dipole magnet consisting of four racetrack coils wound with GdBCO coated conductors and measured its magnetic field in liquid nitrogen by using rotating pick-up coils. We focused on the dipole and sextupole components (coefficients) of the magnetic field, which vary with time owing to the decay of the magnetization of the coated conductors. About 50 min (3055 s) after the current was ramped up to 50 A, the dipole coefficient normalized by the design value of the dipole component, i.e., the value calculated with the designed coil shape and the uniform current distribution in the coated conductors, increased by 7.4 × 10 −4 , and the sextupole coefficient normalized by the design value of the dipole component increased by 1.8 × 10 −4 . The magnitudes of the dipole and sextupole components depended on the excitation history of the magnet. Electromagnetic field analyses were carried out to calculate the current distributions in coated conductors, considering their superconducting properties; the dipole and sextupole coefficients were then determined from the calculated current distributions. Although the analyses were based on the two-dimensional approximation of the cross-section of the magnet, the temporal behaviours as well as the hysteretic characteristics of the calculated dipole and sextupole coefficients agree qualitatively with those of the dipole and sextupole coefficients measured in the magnet.

Test of an 8.66-T REBCO Insert Coil With Overbanding Radial Build for a 1.3-GHz LTS/HTS NMR Magnet

“…However, the error field introduced by the SC field within the ±15-mm region is around several hundred ppm, which may be reduced by the “field-shaking” technique [2], [23]. The temporal behavior of the SC field is also a big issue, which strongly depends on the excitation history [24]. …”

Magnetic Field Drifts of Small HTS Dipole Magnet Under Repeated Excitation

“…Moreover, numerical electromagnetic field analyses were conducted to visualize the electromagnetic field distribution in the coated conductors during repeated excitation. [11] We conducted multipole magnetic field measurements using the rotating pickup coil method. In this method, the pickup coil is rotated at a constant speed in the magnetic field at the center of the magnet, and the induced voltage generated by the change in the interlinkage magnetic flux is measured.…”

Optimized Magnetic Design of Superconducting Magnets for Heavy Ion Rotating Gantries

“…In order to achieve this objective, the use of high temperature superconductors (HTS) in the design of combined function magnets have been studied and modelled in this paper. Compared to the characteristics of LTS, HTS possesses several advantages including: the generation of higher magnetic fields due to their high critical current densities; easy and efficient cooling through the use of a cryocooler; as well as improved thermal stability [3] - [4]. Another consideration which was taken into account throughout the design process was to design a HTS combined function magnet with an economical amount of HTS tape, due to the costs associated with superconducting tape [5] and losses even carrying DC current [6] - [10].…”