Defense PhD Thesis

Ing. Marek Búran

IEE SAS, February 9, 2024,  10,00 a.m.

Title: Thermal stability of composite MgB2 superconductors at high current densities

Abstract:
Although magnesium diboride (MgB2) is well-known since 1954, it took almost 50 years later to discover the superconductivity at temperature close to 40 K. The combination of cheap production with excellent transport properties and high critical temperature predestines their use in a variety of commercial applications. This thesis investigates the thermal stability of MgB2 composite conductor at various current densities. In addition to providing a comprehensive introduction to the field of superconductivity, the theoretical section of this work delves into characterizing the fundamental properties of MgB2 superconductors and elucidates the methods employed in manufacturing composite wires tailored for practical applications. The study encompasses an exhaustive exploration of factors that exert influence on stability, accompanied by a detailed description of the superconductor’s behaviour when subjected to current levels surpassing critical values. This intricate analysis is underpinned by a set of complex equations, which serve to elucidate the intricate interplay between generated and dissipated power. The assessment of thermal stability hinges upon transport measurements of the V-A characteristics. These measurements are conducted until the superconductor undergoes a transition to its normal state, commonly referred to as “quenching.” These experiments are carried out under the stringent conditions of liquid helium cooling at 4.2 K while subjecting the system to an external magnetic field ranging from 0 to 8 T. Furthermore, a cryogen-free system is employed to investigate the transport properties and stability of composite superconductors across a broad temperature spectrum, with a lower limit of 10 K. This investigation is carried out in the presence of various cooling media, including water ice, nitrogen ice, and helium gas, contributing to a comprehensive understanding of the material’s performance under diverse cooling conditions.