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Register a new userAC loss calculation for multi pancakes of (Re)BCO coated conductor using line front
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We aim to demonstrate an efficient method to calculate the AC losses in multi-pancake coils. This method extends Yuan front-track model into several pancake application and investigates the detail parameters in comparison with established H-formula implemented in COMSOL and minimization of energy method. We use the front-track idea to analyze stacked pancakes assuming the current fronts are straight lines and using the critical state model. The current distribution is solved by two means: minimization of the perpendicular magnetic field in the subcritical region, as Clem and Yuan proposed; minimization of total magnetic energy. We also investigate the impacts of applied current and different gaps between multi pancakes on loss calculation. Our model provides a fast calculation method of AC loss in stacked (Re)BCO pancakes and is useful to HTS applications in high field magnets, energy storage devices and electric machines.
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Rare earth barium copper oxide (REBCO) coated conductor has emerged as one of the high Tc superconductors suitable for future ultrahigh field superconducting magnet applications. In the design and fabrication of such ultrahigh field REBCO magnets, it is essential to understand the behavior of REBCO coated conductor. The effect of heating on the properties of commercial REBCO coated conductors is very important for many practical reasons. Nevertheless, a comprehensive study on this effect have not yet been presented in the published literature. This work studies a commercial REBCO coated conductor heat-treated at temperatures between 175 {deg}C and 300 {deg}C for various durations. Critical current and lap joint resistivity were measured at 77 K and 4.2 K for the heat-treated samples. We found that critical current degrades with heat treatment time and temperature. This degradation can be described by a one-dimensional oxygen out-diffusion model with a diffusion coefficient of D = 2.5 x 10-6 exp (-1.17 eV/kT) m2/s. The heat treatment also causes appreciable increase in joint resistivity. Comprehensive structural and chemical analyses were performed on Cu/Ag/RECBO interfaces by transmission electron microscopy (TEM). Our electron energy loss spectroscopy (EELS) study provided direct evidence of oxygen deficiency in the heat treated REBCO samples. In addition, it is found that the oxygen diffused out of the REBCO layer forms mostly Cu2O at both Ag/REBCO and Cu/Ag interfaces. Cu2O is also observed at grain boundaries of the Ag layer. The oxygen out-diffusion model proposed in this work is used to predict REBCO thermal degradation in several engineering scenarios.
High temperature superconducting coated conductor (CC) could be practically applied in electric equipment due to its favorable mechanical properties and the critical current performance of YBCO superconducting layer. It is well known that CC could be easily delaminated because of its poor stress tolerance in thickness direction, i.e. along the c-axis of YBCO. Commonly, a stack including YBCO layer and silver stabilizer could be obtained after the delamination. It would be interesting to investigate the superconducting properties of the delaminated stack, since it could also be considered as a new type of CC with the silver stabilizer as the buffer layer, which is quite different from the oxide buffer layers in the traditional CC and might lead to new applications. In this study, a CC sample was delaminated by liquid nitrogen immersing. A Hall probe scanning system was employed to measure the critical current (IC) distribution of the original sample and the obtained stack. It was found that IC could be partially preserved after the delamination. Dense and crack-free morphologies of the delaminated surfaces were observed by scanning electron microscopy, and the potential application of the obtained stack in superconducting joint technology was discussed.
The hysteretic ac loss of a current-carrying conductor in which multiple superconducting strips are polygonally arranged around a cylindrical former is theoretically investigated as a model of superconducting cables. Using the critical state model, we analytically derive the ac loss $Q_n$ of a total of $n$ strips. The normalized loss $Q_n/Q_1$ is determined by the number of strips $n$ and the ratio of the strip width $2w$ to the diameter $2R$ of the cylindrical former. When $n>> 1$ and $w/R<< 1$, the behavior of $Q_n$ is similar to that of an infinite array of coplanar strips.
We report on microwave measurements on DyBa$_2$Cu$_3$O$_{7-rmdelta}$ monodomains grown by the top-seeded melt-textured technique. We measured the field increase of the surface resistance $R_{rm s}(H)$ in the a-b plane at 48.3 GHz. Measurements were performed at fixed temperatures in the range 70 K - $T_{rm c}$ with a static magnetic field $mu_0H<0.8$ T parallel to the c-axis. Low field steep increase of the dissipation, typical signature of the presence of weak links, is absent, thus indicating the single-domain behaviour of the sample under study. The magnetic field dependence of $R_{rm s}(H)$ is ascribed to the dissipation caused by vortex motion. The analysis of $X_{rm s}(H)$ points to a free-flow regime, thus allowing to obtain the vortex viscosity as a function of temperature. We compare the results with those obtained on RE-BCO systems. In particular, we consider strongly pinned films of YBa$_2$Cu$_3$O$_{7-rmdelta}$ with nanometric BaZrO$_3$ inclusions.
A simple analytical expression is presented for hysteretic ac loss $Q$ of a superconducting strip simultaneously exposed to an ac transport current $I_0cosomega t$ and a phase-different ac magnetic field $H_0cos(omega t+theta_0)$. On the basis of Beans critical state model, we calculate $Q$ for small current amplitude $I_0ll I_c$, for small magnetic field amplitude $H_0ll I_c/2pi a$, and for arbitrary phase difference $theta_0$, where $I_c$ is the critical current and $2a$ is the width of the strip. The resulting expression for $Q=Q(I_0,H_0,theta_0)$ is a simple biquadratic function of both $I_0$ and $H_0$, and $Q$ becomes maximum (minimum) when $theta_0=0$ or $pi$ ($theta_0=pi/2$).
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