Ramping loss and mechanical response in a no-insulation high-temperature superconducting layer-wound coil and intra-layers no-insulation coil

Abstract

The layer-wound coil has a great potential in nuclear magnetic resonance and magnetic resonance imaging owing to the better spatial homogeneity of the magnetic field. However, high-temperature superconducting (HTS) coil wound by no-insulation (NI) layer-wound technique has been verified with a long field delay time. A new method named the intra-layer no-insulation (LNI) winding technique has been proposed to reduce the charging delay time of the coil. This paper is mainly to study and compare the ramping loss and mechanical characteristics of the layer-wound coil and LNI coil. The results indicate that the total ramping loss can be significantly reduced by using the LNI winding method. The effects of the ramping rate of power supply current and the contact resistivity on the ramping loss are also discussed in the paper. Furthermore, the stress distributions in the layer-wound coil and LNI coil are compared, where the cooling process and Lorentz force are both considered. It can be found that the copper sheet of the LNI coil experiences relatively higher stress than its (RE)Ba 2 Cu 3 O x (REBCO) conductor layer. Meanwhile, the magnitude of stress generated in the REBCO conductor of the LNI coil is slightly different from that of the layer-wound coil.

A modified model to estimate the screening current-induced magnetic field of a REBCO magnet

“…where M ij θ is the self-and mutual inductances [45] and the radial resistance R i r of each turn is [46] where the contact resistivity is given as ρ r = 70 µΩ cm 2 [43,47], and the dependence of the contact resistivity on the temperature, contact pressure and so on is neglected in the simulation.…”

Numerical analysis of the contact resistance in a no-insulation layer-wound coil with a simplified electromagnetic–mechanical model

“…The schematic view and equivalent circuit model are shown in figure 1, and the serial number of each turn is defined according to the direction of the transport current. In each independent circuit network, the governing equation is obtained by Kirchhoff's voltage law [34,[44][45][46]: where the subscripts k (1 ⩽ k ⩽ 152) and j (1 ⩽ j ⩽ 133) both represent the turn number. M j,k is the mutual inductance between the jth and kth turns when j and k are not equal, and the self-inductance of the jth turn when subscripts j and k are equal.…”

“…For the NI REBCO coil, the deformation and separation between adjacent turns may have an effect on contact resistance in external fields. Many studis have calculated the mechanical deformations or stresses in REBCO conductors and NI coils numerically [34][35][36][37][38]. However, few works have focused attention on the effect of separation between adjacent turns on the contact resistance of NI coils.…”

Modeling of contact resistivity and simplification of 3D homogenization strategy for the H formulation

“…As reported in [40,43], an available solution is to model the contact layer with zero thickness but requires the magnetic field to be discontinuous at the contact interface. Additionally, the distributed circuit model has been developed to calculate the responses of radial current, which is based on Kirchhoff's current and voltage laws [44][45][46][47][48].…”