Development of a 5-Axis Winding Method for Saddle-Shaped Coils Using Coated ReBCO High Temperature Superconductors

Saddle-shaped superconducting coils are efficient in terms of generating an ideal multipole field inside a cylindrical bobbin which is the typical shape used in particle accelerators, electric motors, nuclear magnetic resonance (NMR), magnetic resonance imaging (MRI), and other application. Compared to low-temperature superconductors, rare earth barium copper oxide (ReBCO) high-temperature superconductor (HTS) wires exhibit excellent electromechanical behavior, high current carrying capacity to generate high magnetic fields and high thermal stability to reduce cooling costs. Despite such advantages, attempts to wind a saddle-shaped coil by using the coated HTS conductor have been rarely reported due to a hard-way bending characteristics of the thin tape-shaped HTS conductor. Here, we introduce the concept of a dedicated winding machine capable of winding saddle-shaped coils including the numerical modelling and visualization. To simplify the implementation of the winding machine, we utilized one universal joint and two 2D linear stages. We also derived control variables that can be directly applied in practical operations.

I. Introduction

Saddle-shaped coils are advantageous for creating ideal multipole magnetic fields in the magnet with a cylindrical bobbin when the magnet current is azimuthally distributed as [1], [2], [3], [4], [5]. From a practical implementation point of view, the saddle-shaped structure is not only a proper structure for placing such cosine-theta current distribution but it is also convenient for implementing high-field magnetic multipole especially when iron yoke cannot be used to tune multipole field shape due to a full saturation. Thanks to these advantages, saddle-shaped coils are widely used in applications such as NMR, MRI, and high-field large-scale particle accelerators, that require a homogeneous and strong magnetic field [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17].