LOSSES IN COMPOSITE SUPERCONDUCTORS FOR HIGH-SPEED GROUND TRANSPORTATION SYSTEMS

Abstract

The paper discusses losses in composite superconducting systems which are intended to provide electrodynamic levitation in high-speed ground transport (HSGT) systems. The existing suspension types are given, on which the selection of the linear motor used depends. A brief overview of the linear motors used in the HSGT using electromagnetic and electrodynamic levitation is given. Composite superconductors based on niobium-titanium (NbTi), which are widely used in practice and are low-temperature superconductors (LTSC) are discussed. NbTi superconductors are composites consisting of many thin NbTi filaments, the number of which can reach several hundred thousand. The filaments are distributed in a stabilizing sheath made of copper or aluminum, as well as other elements such as diffusion barriers and resistive matrices. The types of losses that occur in technological composite superconductors are studied. The main and additional losses in composite superconductors are considered. The main losses are hysteresis losses in the superconducting material and losses in the matrix. Additional losses include the ones in the matrix due to eddy currents. Formulas that are used to determine energy losses both for filaments with a diameter d≤10 µm and for filaments with a larger diameter obtained using the Bean and Kim-Anderson models for the critical state are given.