Lubomir Frolek

AC Loss in Pancake Coil Made From 12 mm Wide REBCO Tape

The design of a superconducting coil from high-performance REBCO coated conductors is often complicated because of complex anisotropy of the critical current density Jc . It is important to understand how much detail of this feature must be taken into consideration in the prediction of maximum achievable current and the expected ac loss. We present the results of investigation performed with a small (ten turns, 60 mm inner diameter) coil made from SuperPower tape of 12 mm width. The knowledge of Jc(B,θ) determined on short sample allowed prediction of the maximum achievable current of the coil and the ac loss behavior. We have also investigated the effect of the tape nonuniformity. Our results confirm that the lateral nonuniformity when Jc at tape edges is lower than in its center leads to significant increase of ac loss. A longitudinal nonuniformity, in particular a reduction of critical current in some portion along the tape length, is hardly observable in the ac loss result. On the other hand, using a piece of tape with lower Jc in the innermost coil turn would significantly reduce the maximum current. We also present calculations showing the change in current-voltage curve and redistribution of ac dissipation in the case of nonuniform tape quality.

Electromagnetic modelling of superconductors with a smooth current–voltage relation: variational principle and coils from a few turns to large magnets

Many large-scale applications require electromagnetic modelling with extensive numerical computations, such as magnets or 3-dimensional (3D) objects like transposed conductors or motors and generators. Therefore, it is necessary to develop computationally time-efficient but still accurate numerical methods. This article develops a general variational formalism for any

Partitioning of transport AC loss in a superconducting tape into magnetic and resistive components

{\bf E}({\bf J})

Non-uniform current distribution as the cause of false voltage signals in the ac loss measurement on a superconducting cable

relation and applies it to model coated-conductor coils containing up to thousands of turns, taking magnetization currents fully into account. The variational principle, valid for any 3D situation, restricts the computations to the sample volume, reducing the computation time. However, no additional magnetic materials interacting with the superconductor are taken directly into account. Regarding the coil modelling, we use a power law

AC Loss Measurement of YBCO Cable Model

E(J)

Measurement of AC profiles of magnetic field above HTSc tape using Hall probe technique with help of DAQ cards and triggering

relation with magnetic field-dependent critical current density,

Numerical Study on Magnetization Characteristics of Superconducting Conductor on Round Core Cables

J_c

Phase shifts of parallel currents in a single-Layer model of Superconducting cables

, and power law exponent,

Measurement of DC critical current in superconducting cable with non-uniformities

n

Spark-Discharge Plasma as a Method to Produce Low AC Loss Multifilamentary (RE)Ba2Cu3 O7 Coated Conductors

. We test the numerical model by comparing the results to analytical formulas for thin strips and experiments for stacks of pancake coils, finding a very good agreement. Afterwards, we model a magnet-size coil of 4000 turns (stack of 20 pancake coils of 200 turns each). We found that the AC loss is mainly due to magnetization currents. We also found that for an