AC losses in superconducting cables and their expected values in magnetic systems

Abstract

After summarizing the different loss contributions in superconducting composites, some possible sources for differences in AC losses and time constants in measuring arrangements and their expected values in real magnetic systems are summarized: induced currents in end portions, field variations in time and space, mixed contributions from substructures and normal parts, longitudinal field effects and inductive coupling of current loops. Along with uncertainties in determining the effective resistivities and effective volumes for the current loops, all effects are important for evaluating the expected losses, time constants and discharging process in superconducting cables. The size effects can be calculated in most cases and incorporated into theoretical models. The spatially changing fields and coupling of current loops on the cable seem to be the most important effects causing differences in cable measurements with respect to the situation in different magnetic systems. These could be decisive for the design of large superconducting magnets with required stability and quench behaviour.