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.

Computation of Losses in HTS Under the Action of Varying Magnetic Fields and Currents

“…There is not wide consensus about what loss components are to be put under the term coupling loss [255]. This is because coupling losses and eddy current losses have similar nature since they both arise from currents in non-superconducting parts of the conductor [256].…”

Acceptable coupling losses in coated conductors at industrial frequencies without twisting the superconducting stripes

“…I would like to note that this function has the same form as the cosinelike distribution of the induced current in strands or round cables. [15][16][17][18][19] From Eqs. ͑11͒ and ͑12͒, one obtains then…”

“…However, any type of connection between the stripes increases the coupling losses between them. [15][16][17][18][19][20][21][22][23] The suggested full coating of the tape with normal metal 24,25 results in dramatic increase of the CLs. Therefore, twisting the stripes-like in superconducting cables-seemed to be inevitable.…”

Transient 3D Finite Element Simulations of the Field Quality in the Aperture of the SIS-100 Dipole Magnet

“…In the superconductive cables, the finite inter-strand conductivity causes losses resulting from currents induced in the superconductive filament which resistively close in a contact area between particular strands [3], [4]. As the individual strands are twisted in a certain pitch, moreover intra-strand losses arise [5]. However, the losses in the yoke, due to eddy currents as well as due to ferromagnetic hysteresis, were found to form the main contribution to the overall losses during fast ramping [6].…”