Non-uniform ramping losses and thermal optimization with turn-to-turn resistivity grading in a (RE)Ba2Cu3Ox magnet consisting of multiple no-insulation pancake coils

Abstract

This paper presents a study on the ramping losses of a high temperature superconductor (HTS) magnet consisting of multiple no-insulation (NI) (RE)Ba2Cu3Ox coils. The (RE)Ba2Cu3Ox (REBCO) conductor is the second generation HTS thin tape where RE stands for rare-earth. During a ramping operation of the NI HTS magnet, Losses are generated both across turn-to-turn resistances and inside superconducting layers. The former comes with radial current, which is called 'turn-to-turn loss'; the latter one is induced by flux creep and jump, called 'magnetization loss'. The modeling and experimental studies on the ramping losses have been reported on a single NI pancake coils in the previous part. In a HTS magnet consisting of multiple NI coils, the electromagnetic coupling between coils have a considerable influence on the distribution of ramping losses. Here the experimentally validated model is used to investigate a HTS magnet consisting of 14 single pancake (SP) REBCO coils. Results show that both the turn-to-turn loss and magnetization loss present a significant non-uniform distribution among coils. The highest turn-to-turn loss occurs to the middle coils of the magnet, while the highest magnetization loss happens on the end coils. The non-uniform distribution of ramping losses can result in a considerable temperature difference among coils in the NI HTS magnet. It leads to an additional quench risk on the magnet and requires more attentions in design. The distribution of the turn-to-to-turn loss can be optimized by adjusting the turn-to-turn resistivity. A much more uniform turn-to-turn loss distribution among coils is achieved by applying a graded turn-to-turn resistivity on the multiple coils.

Electromagnetic modelling using T‐A formulation for high‐temperature superconductor (RE)Ba 2 Cu 3 O x high field magnets

“…Magnetisation loss is generated in superconducting layers during the ramping operation of HTS magnet, due to flux creep and jump [52]. This is the main part of ramping loss of HTS magnet below critical current, which may lead to a potential quench and ramp failure [33, 53]. In T‐A models, this magnetisation loss can be calculated by where W m and Q m are the magnetisation loss power and energy, respectively.…”

“…However, these methods cannot do a comprehensive electromagnetic analysis on the HTS, and are also not suitable for complex electromagnetic environments and operations. Finite-element method (FEM) based on H-formulation has been widely applied on the electromagnetic modelling of HTS applications [30][31][32][33], and homogenous Hformulation model has been developed to reduce the computation cost [34,35]. Its governing equation uses magnetic intensity H as solution variable, and the whole model can be built and solved in commercial FEM software Comsol Multi-physics.…”

Development and Test of One Commercial Megawatt Superconducting DC Induction Heater With Extra High Energy Efficiency

“…The ramp rate of HTS coils has two limitations: voltage of power supply and ramping loss in coils. The ramp operation of HTS coils generates magnetization loss on the superconducting layers, which is called ramping loss [34], [35]. The ramping loss can lead to heat accumulation as well as temperature rise on the HTS coils, which is main reason of most ramp failures.…”

Magnetization of the joint-free high temperature superconductor (RE)Ba2Cu3Ox coil by field cooling

“…Therefore, an approximate 2D axisymmetric model is built for the joint-free coil. The model is based on H-formulation of HTS, whose governing equation is as: [31][32][33][34][35][36][37][38] …”