Improved Method for Determining the n-Value of HTS Bulks

International audienceThe complete penetration magnetic field Bp is the main feature of a superconducting pellet submitted to an axial applied magnetic field. The electric E-J characteristics of HTS bulk is generally described by a power law E(J) = Ec(J/Jc)^n. The influence of the n-value and applied magnetic field rise rate Vb on the Bp of a HTS cylindrical pellet has been presented in a previous paper. The numerical results presented come from numerical resolution of a non linear diffusion problem. With the help of these simulations a linear relationship between Bp, ln Vb and n-value has been deduced. This comparison allows determining the critical current density Jc and the n-value of the power law based on direct measurement of Bp in the gap between two bulk HTS pellets. In this paper, an improvement of this method is presented. The influence of geometric parameters R and L is studied to give generality to the relationship between Bp, Vb and n-value. Previous Bp formula is confirmed by these new simulations. To correctly connect simulation and experimental results, the influence of spacing e between bulks is studied and presented. A relationship between Bp and measured complete penetration magnetic field Bpm is determined

Proposal of a novel design for linear superconducting motor using 2G tape stacks

This paper presents a new design for a su- perconducting linear motor (SLM). This SLM uses stacks of second-generation (2G) superconducting tapes, which are responsible for replacing yttrium barium copper oxide bulks. The proposed SLM may operate as a synchronous motor or as a hysteresis motor, depending on the load force magnitude. A small-scale linear machine prototype with 2G stacks was constructed and tested to investigate the proposed SLM topology. The stator traveling magnetic field wave was represented by several Nd-Fe-B permanent magnets. A relative movement was produced between the stator and the stack, and the force was measured along the displacement. This system was also simulated by the finite element method, in order to calculate the induced currents in the stack and determine the electromagnetic force. The H-formulation was used to solve the problem, and a power law relation was applied to take into account the intrin- sically nonlinearity of the superconductor. The simulated and measured results were in accordance. Simulated re- sults were extrapolated, proving to be an interesting tool to scale up the motor in future projects. The proposed motor presented an estimated force density of almost 500 N/kg, which is much higher than any linear motor.This work was supported in part by the following agencies: CNPq/CAPES/INERGE, CNPq—Ci ˆ encias sem Fronteiras, FAPERJ, Catalan Government 2014- SGR-753, CONSOLIDER Excellence Network MAT2014-56063-C2-1-R and MAT2015-68994-REDC, Eurofusion EU COST ACTIONS MP1201/ MP1014/PPPT-WPMAG 2014, EUROTAPES FP7-NMP-Large-2011- 280432, FORTISSIMO FP7-2013-ICT-609029, and Spanish Govern- ment Agencies—Severo Ochoa Programme Centres of Excellence in R&D. (Corresponding author: Guilherme G. Sotelo.