Promising effects of a new hat structure and double metal ring for mechanical reinforcement of a REBaCuO ring-shaped bulk during field-cooled magnetisation at 10 T without fracture

Abstract

PAPERPromising effects of a new hat structure and double metal ring for mechanical reinforcement of a REBaCuO ring-shaped bulk during fieldcooled magnetisation at 10 T without fracture AbstractWe have investigated a new reinforcement hat structure for a RE-Ba-Cu-O (REBaCuO, RE: rare earth element or Y) ring-shaped bulk superconductor (ring bulk) shrink-fitted with a double Al alloy ring and set on the cold stage of a cryogenic refrigerator prior to field-cooled magnetisation (FCM). With the hat structure, a ring bulk having an outer diameter of 64 mm, inner diameter of 40 mm, and height of 20.5 mm achieved a trapped field as high as 6.8 T at 50 K during FCM with an applied magnetic field at B app =10 T without fracture; a similar ring bulk without the hat structure broke during FCM at B app =8.8 T. Using a numerical simulation for electromagnetic and mechanical properties, the potential benefit of the hat structure was confirmed. The magnetic field dependence of the average critical current density J c (B) of the ring bulk used in the simulation was determined by experimental results of time step dependence of the trapped field B z at the bulk centre. As a result, the total hoop stress σ θ total in the ring bulk including the resulting stress of cooling from 300 K to 50 K and subsequent FCM at B app =10 T is lower than the fracture strength of a typical Ag-doped REBaCuO bulk material. The effect of double Al alloy ring reinforcement was also analysed using a numerical simulation and compared with that of the conventional single Al alloy ring reinforcement. These results suggest that the double ring provides only a limited benefit, whereas the hat structure is fairly effective in reducing the electromagnetic hoop stress during FCM at B app =10 T. Using this reinforcement method, a 400 MHz (9.4 T) nuclear magnetic resonance bulk magnet system could be realised.

R-z plane spatial critical current inhomogeneity-induced mechanical response of GdBCO superconducting bulks during field cooling magnetization

“…In this way, a stack of two 24 mm diameter GdBCO disc bulk could trap a magnetic field of 17.6 T in the center without being damaged [2]. Much research [7,24] have been conducted to investigate the influence of the reinforcement of stainless steel ring, yet a significant limitation remains in their use of a homogeneous J c distribution. This section will introduce the impact of stainless steel ring reinforcement on the mechanical response of GdBCO bulks with r-z plane J c inhomogeneity.…”

“…Most notably, the above methods all adopted a spatial homogeneous J c distribution to estimate the average and macroscopic J c (B) characteristics of the HTS bulk [24,25] which may not completely reflect the real mechanical response distribution during FCM. According to the simulation of Takahashi [26], the simulated strain of homogeneous J c model was approximately 50% higher than that of the absolute value of the experimental one.…”

Simulation study for magnetic levitation in pure water exploiting the ultra-high magnetic field gradient product of a hybrid trapped field magnet lens (HTFML)

“…To obtain the  value at each temperature, we refer to our experimental FCM result for the GdBaCuO bulk ring. Figure 2 presents the temperature dependence of the trapped field, BT, in the ring-shaped GdBaCuO bulk (40 mm in inner diameter, 64 mm in outer diameter and 20 mm in height), which was magnetized by FCM from an applied field of 10 T at 50 K and then measured in the heating run as the temperature is increased to 93 K, i.e., above its Tc [41]. The experimental BT(T) curve would have a tendency to saturate under 50 K due to the full magnetization of the bulk within its Jc capability.…”

Numerical modelling and simulations on the mechanical failure of bulk superconductors during magnetization: based on the phase-field method

“…Ainslie et al [8,26] developed a modelling framework couples electromagnetic, thermal and structural mechanics to analyze the mechanical stresses in bulk superconductor magnets during field-cooled magnetization with and without mechanical reinforcement using stainless steel ring. In addition, the prediction of crack initiation and propagation through computational models is of significant importance for the application of bulk superconductors [20,27]. Research group lead by Zhou has made significant contributions to modeling the mechanical behaviors of bulk superconductors, and has systematically investigated the flux-pinning-induced magnetostriction [28], singular stress field and current density distribution in front of cracks within bulk superconductors [29,30].…”