Papers by Author: Janos Kósa

Abstract: The paper presents the results of our experiments with novel devices, which may open a new path for advanced applications by using continuous, perfectly closed superconducting YBCO loops. With this solution we wanted to examine whether it is possible to create novel fault current limiter, 3-phase self-limiting transformer. We considered the significance and efficiency of the perfect closed loop made from YBCO wire. The used superconducting wire was produced at SuperPower, Inc. in New York, USA. Type: SF 12050.

Abstract: This paper presents the results of my experiments that may open a new path for advanced applications by using continuous closed superconducting YBCO loops. I examined a novel arrangement of a perfectly closed superconducting loop made of HTS wire in DC and AC flux transformer. I designed a self-limiting transformer with this solution. At the same time I also tested the operation of the continuous YBCO loop developed with my own technology. In the first experiment I used YBCO superconducting rings made from a bulk. Later I used superconducting wire. I could carry out these experiments because earlier I had elaborated the machining of the YBCO bulk and wire.

Abstract: In this work we present a solution for testing the quality of YBCO rings made from bulk and 100% YBCO wire loops. We used the transformation of the DC magnetic field [1]. Nowadays there are more and more solutions for checking the quality [2]. In this article we show a new method for testing applying the transformation of the DC magnetic field between two independent iron cores inductively.

Abstract: MgB2-based nanostructural materials with rather high oxygen concentration (5-14 wt.%) and dispersed grains of higher borides (MgB12, MgB7) high-pressure (2 GPa or 30 MPa) synthesized (in-situ) or sintered (ex-situ) demonstrated high superconducting characteristics (critical current density, jc, up to 1.8-1.0106 A/cm2 in the self magnetic field and 103 in 8 T field at 20 K, 3-1.5105 A/cm2 in the self field at 35 K, upper critical field up to HC2 = 15 T at 22 K, field of irreversibility Hirr =13 T at 20 K). The additives (Ti, SiC) and synthesis or sintering temperature can affect the segregation of oxygen and formation of oxygen-enriched Mg-B-O inclusions in the material structure, thus reducing the amount of oxygen in the material matrix as well as the formation of higher borides grains, which affects an increase of the critical current density. The record high HC2 and Hirr have been registered for the material high-pressure (2 GPa) synthesized from Mg and B at 600 oC having 17% porosity and more than 7 wt.% of oxygen. The attained values of the critical current, AC losses and thermal conductivity make the materials promising for application for fault current limiters and electromotors. The structural and superconducting (SC) characteristics of the material with matrix close to MgB12 in stoichiometry has been studied and the SC transition Tc=37 K as well as jc= 5×104 A/cm2 at 20 K in the self field were registered, its Raman spectrum demonstrated metal-like behavior.