The main aim of the EU H2020 project EcoSwing was to demonstrate a technical readiness level of 6-7 for high-temperature superconducting (HTS) technology operating in a wind generator. To reach this goal, a full-scale synchronous HTS generator was successfully designed, built and field-tested in a 3.6 MW turbine. The generator has a rotor with 40 superconducting coils of 1.4 m long. The required >20 km of coated conductor was produced within the project's time schedule. All coils were tested prior to assembly, with >90% of them behaving as expected. The technical readiness level of HTS coils was thus increased to level 7. Simultaneously, the maturing of cryogenic cooling technology over the last decade was illustrated by the several Gifford-McMahon cold-heads that were installed on-board the rotor and connected with the stationary compressors through a rotating coupling. The cryogenic system outperformed design expectations, enabling stable coil temperatures far below the design temperature of 30 K after only 14 d of cool-down. After ground-based testing at the IWES facility in Bremerhaven, Germany, the generator was installed on an existing turbine in Thyboron, Denmark. Here, the generator reached the target power range and produced power for over 650 h of grid operation.

EuCARD-2 aims to research ReBCO superconducting magnets for future accelerator applications. The properties of ReBCO conductors are very different from low-temperature superconductors. To investigate dynamic field quality, stability, and normal zone propagation, an electrical network model for coated conductor cables was developed. To validate the model, two identical samples were prepared at CERN, after which measurements were taken at the University of Twente and Southampton University. The model predicts that for a Roebel cable, in a changing magnetic field applied in the perpendicular direction, hysteresis loss is much larger than coupling loss. In the case of a changing magnetic field applied parallel to the cable, coupling loss is dominant. In the first case, the experiment is in good agreement with the model. In the second case, the data can only be compared qualitatively because the calibration for the inductive measurement is not available.

Multifilamentary NbTi wires for ac applications are manufactured by embedding filament bundles into a metal matrix. In this stage of the manufacturing process, it is possible to affect the layout of the cross section and to choose whether to use few large or many small bundles in order to achieve a certain amount of filaments. All in all, up to 100 000 filaments are attainable for wire having the diameter of 1 mm. In this paper, ac loss measurements in external magnetic field on differently stacked NbTi samples are described. The measurements were performed in a LHe-cooled cryostat. The amplitude of the external field was varied between 250 mT and 3 T at frequencies of 0.02 and 0.12 Hz. We discuss possibilities to simulate the losses with finite element method. In particular, we concentrate on the filament bundle approximation and the possibilities to exploit it in the research and development process of new NbTi wires. In this approach, the filament bundles are considered as a homogenous mixture of matrix and superconducting filaments. According to the results, the bundle approximation greatly overestimates the losses. Furthermore, it should not be used for comparing, e.g., two wire structures where one has bundles of different size than the other. However, when considering how to situate the bundles on the cross section to achieve minimal ac loss, the bundle approximation can be a useful tool.

Measurements of the quasi-adiabatic normal zone propagation velocity and quench energies of a Superpower SCS4050 copper stabilised ReBCO superconducting tape are presented over a temperature range of 23 - 47 K; in parallel applied magnetic fields of 6, 10 and 14 T; and over a current range from 50% to 100% of I-c. The data are compared to results of analytic predictions and to one-dimensional numerical simulations. The availability of long lengths of ReBCO coated conductor makes the material interesting for many HTS applications operating well below the boiling point of liquid nitrogen, such as magnets and motors. One of the main issues in the design of such devices is quench detection and protection. At higher temperatures, the quench velocities in these materials are known to be about two orders of magnitude lower compared to low temperature superconductors, resulting in significantly smaller normal zones and the risk of higher peak temperatures. To investigate whether the same also holds for lower temperatures more extended data sets are needed, both as input and as validation for numerical design tools. (C) 2015 The Authors. Published by Elsevier B.V.

Rutherford cables with cores of E-glass and S-glass woven tape and types AISI-316 and AISI-304 stainless steel (SS) ribbon were subjected to calorimetric AC loss measurement in transverse magnetic fields of amplitude 400 mT and frequencies of up to 90 mHz applied in the face-on (FO) and edge-on (EO) orientations. The results yielded the effective interstrand con- tact resistances (ICR), Reff (to be defined), and corresponding estimates of the FO coupling magnetizations generated by fields ramping at the LHC-specified 6.5 mT/s. Detailed analysis of the results indicated: 1) a cable with a full-width 316-SS core and a satisfactory Reff value would be suitable for magnet winding; 2) a cable with an off-center partial-width core had a very low Reff and an excessively large coupling magnetization; 3) The cables with glass-tape cores although characterized by large Reffs and very small coupling magnetizations turned out to have mostly uncoupled strands with intermittent points of low resistance contact. In order to achieve the target ICR values, the level of glass insulation insert should be reduced and cable compaction adjusted.

Numerous manufacturers and different strand processing techniques are involved with the production of the Nb3Sn strand material required for ITER. The superconducting transport properties of brittle Nb3Sn layers strongly depend on their strain state. Hence, the thermal compression and the substantial transverse load in combination with the key choice for the cabling pattern of the CICCs, will determine their performance. Knowledge of the influence of axial strain, periodic bending, and contact stress on the critical current (I-c) of the used Nb3Sn strands is inevitable to gain sufficient confidence in an economic design and a stable operation of ITER. We have measured the I-c and n-value of Nb3Sn strands from various manufacturers in the TARSIS facility, when subjected to spatial periodic bending and contact stress. The I-c and n-values have been determined for applied axial compressive and tensile strain varying from -0.8% up to +0.5%, between T = 4.2 K and 10 K and B = 6 T to 14 T. The strain sensitivity varies appreciably for different strand types. We present a selection of the results obtained so far.

Measurements have been made of the critical current on an Nb3Sn superconducting strand destined for the ITER (International Thermonuclear Experimental Reactor) prototype cable-in-conduit conductors. Characterization of the strand was performed on a recently developed spring device, named Pacman, allowing measurements of the voltage–current characteristic of an Nb3Sn strand over a wide range of applied axial strain, magnetic field, temperature and currents up to at least 700 A. The strand was measured in a magnetic field between 4 and 11 T, temperatures of 4.2–10 K and applied axial strain ranged from −0.9% (compressive) to +0.3% (tensile). The critical currents were then used to derive the superconducting and the deformation-related parameters for the scaling of measured results, based on the so-called ‘improved’ deviatoric strain model. We also demonstrate that the same values can be derived from a partial critical-current data set without spoiling the overall scaling accuracy. This indicates that the proposed scaling relation can be used not only as a fitting tool, but is promising for reliable extrapolation as well, providing substantial savings in cost and time for the experimental routine.

Last year a record central field of 11 T at first excitation at 4.4 K has been achieved with the experimental LHC model dipole magnet MSUT by utilising a high J/sub c/ powder-in-tube Nb/sub 3/Sn conductor. This is the first real breakthrough towards fields well above 10 T at 4 K. The clear influence of magnetisation and coupling currents on the field quality, the quench behaviour and the temperature development in the coils has been measured and is discussed. For application in high-field accelerator magnets (10-15 T dipoles, 300-400 T/m quadrupoles) these experimental results clearly reveal the potential, the present limitations and the necessary improvements of Nb/sub 3/Sn technology with respect to strand, cable and coil design and manufacturing. A brief review of developments in this field is presented. The focus is on accelerator dipole magnets but the key issues for quadrupole magnets are quite similar.

As part of the magnet development program for the LHC an experimental 1 m long 11.5 T single aperture Nb3Sn dipole magnet has been designed and is now under construction. The design is focused on full utilisation of the high current density in the powder tube Nb3Sn. A new field optimisation has led to a different winding layout and cable sizes as compared to the reference LHC design. Another important feature of the design is the implementation of a shrink fit ring collar system. An extensive study of the critical current of the Nb3Sn cables as a function of the transverse stress on the cables shows a permanent degradation by the cabling process of about 20 %, still leaving a safety margin at the operation field of 11.5 T of 15 %. A revised glass/mica glass insulation system is applied which improves the thermal conductivity of the windings as well as the impregnation pro-cess considerably. This paper describes various design and production details of the magnet system as well as component tests.

In the frame work of the VAMAS intercomparison activities the second critical field B-c2 of the standard NIST NbTi/Cu superconductor was investigated in several laboratories in the world. In this paper the specific results obtained in the UT laboratory are reported. On a single piece of wire of 1.5 meter length the voltage is measured across 10 straight (crossing the magnet axis) and 10 bend sections (on radius 25 mm in the magnet bore). A detailed analysis of all possible errors in field, temperature and voltage is presented. The bend sections provide the best results. As a characteristic result we mention a B-c2 (at 50%) at 4.2 K of 11.31 T with an error of 10 mT only. The variation in B-c2 over the sections is about the same as the variation found for various runs of the same section. The B-c2- homogeneity of the wire over a length of 1.5 meter is extremely good (<10(-3)). This accuracy is such that the B-c2 of the standard wire could be used as a field calibrating method.