[en] Powder-in-Tube (PIT) processed Niobium-Tin wires are commercially manufactured for nearly three decades and have demonstrated a combination of very high current density (presently up to 2500 A mm^-2 non-Cu at 12 T and 4.2 K) with fine (35 (micro)m), well separated filaments. We review the developments that have led to the present state of the art PIT Niobium-Tin wires, discuss the wire manufacturing and A15 formation processes, and describe typical superconducting performance in relation to magnetic field and strain. We further highlight successful applications of PIT wires and conclude with an outlook on possibilities for further improvements in the performance of PIT Niobium-Tin wires.

[en] In the framework of the LHC magnet development program at CERN, the effect of transverse pressure on the inter-strand coupling loss of Rutherford type of cables has been investigated. For this purpose a special measuring set-up is designed to measure calorimetrically the ac loss of a stack of keystoned cable pieces for an applied transverse pressure of up to 130 MPa. An ac dipole produces a varying magnetic field with a maximum amplitude of 1 T; the stack of cable pieces can be rotated with respect to the ac dipole in order to distinguish the inter-filament coupling loss from the inter-strand coupling loss. Measurements are presented of a NbTi cable with tinned strands as envisaged to be used for the inner layer of the LHC main bending dipoles. The inter-strand coupling loss increases strongly for higher pressures. The contact resistance Rc between crossing strands, as determined using a network model for the cable, varies between about 7 and 1 μΩ for pressures between 5 and 100 MPa respectively. The small Rc value at 100 MPa corresponds well with AC loss measurements on a model magnet in which a similar cable is used

[en] 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 utilization of the high current density in the powder tube Nb₃Sn. A new field optimization 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 insulation system is applied which improves the thermal conductivity of the windings as well as the impregnation process considerably. This paper describes various design and production details of the magnet system as well as component tests

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[en] The thermal conduction of glass-mica tape, used as the insulation material for superconducting Nb₃Sn cables in fully impregnated windings for accelerator type of dipole magnets, has been investigated. Extremely low values for the thermal conductivity coefficient, ranging from 5 to 20 mWm^-1K^-1 at 4.2 K are found. The bad bonding properties of the mica flakes in the tape is the main reason for this behaviour. Moreover the temperature rise in the windings due to beam losses is studied. Beam-loss calculations show a maximum heat deposit of 10 mWcm^-3 which can lead, assuming the low thermal conductivity found, to an intolerable temperature increase of 1.5 K. Therefore, the thermal properties of the Nb₃Sn windings have to be improved

[en] We have developed and validated a straightforward and fast method to investigate the response of technological superconducting strain sensitive wires (e.g., Nb₃Sn) to a spatial periodic bending strain. In the present concept of cabled superconductors for application in nuclear fusion reactors the wires are twisted and cabled in several stages. When subjected to transverse electromagnetic forces after charging the magnet, the individual strands are subjected to spatial periodic bending with wavelengths in the order of 5-10 mm. Several apparatuses are presently under development to study the effect of bending on the transport properties, i.e., the voltage-current transition in terms of critical current (I_c) and n value. We propose a supplementary simple method to investigate the influence of bending strain by using a spatial periodic wire support on a broadly used standard I_c measurement barrel in combination with a Lorentz force. The bending force (BI) is varied by changing the applied field B. The peak bending strain in the Nb₃Sn filaments is determined by the amplitude of the bending deflection, which is deduced from the mechanical axial tensile stress-strain properties of the wire. Three different spatial periodic wavelengths are applied and the results are in good agreement with the predictions. In addition we found a good agreement with results obtained by a more advanced experiment, named TARSIS, which is described briefly. The 'barrel-with-slots' method can be applied easily and straightforward with minor effort and cost in laboratories having a standard I_c measurement facility for superconducting wire

[en] We have developed and validated a straightforward and fast method to investigate the response of technological superconducting strain sensitive wires (e.g., Nb₃Sn) to a spatial periodic bending strain. In the present concept of cabled superconductors for application in nuclear fusion reactors the wires are twisted and cabled in several stages. When subjected to transverse electromagnetic forces after charging the magnet, the individual strands are subjected to spatial periodic bending with wavelengths in the order of 5-10 mm. Several apparatuses are presently under development to study the effect of bending on the transport properties, i.e., the voltage-current transition in terms of critical current (I_c) and n value. We propose a supplementary simple method to investigate the influence of bending strain by using a spatial periodic wire support on a broadly used standard I_c measurement barrel in combination with a Lorentz force. The bending force (BI) is varied by changing the applied field B. The peak bending strain in the Nb₃Sn filaments is determined by the amplitude of the bending deflection, which is deduced from the mechanical axial tensile stress-strain properties of the wire. Three different spatial periodic wavelengths are applied and the results are in good agreement with the predictions. In addition we found a good agreement with results obtained by a more advanced experiment, named TARSIS, which is described briefly. The 'barrel-with-slots' method can be applied easily and straightforward with minor effort and cost in laboratories having a standard I_c measurement facility for superconducting wire

[en] Nuclear orientation of ¹⁸²Ta achieved by electric quadrupole interaction in TaCl₅ molecules intercalated in oriented graphite crystals has been observed. Assuming the electric field gradient V_zz along the c-axis and proper intercalation yields V_zz=+0.32(4)x10¹⁸V/cm². Other possibilities and sources of reduction of the nuclear orientation effect are considered. (orig.)

[en] A 10 cm long model of an 11.5 T Nb₃Sn accelerator dipole magnet, which will be built in the Netherlands, with a closed ring shaped collar has been constructed. Measurements of the collar deformation and the prestress at the poles have been made with a structural analysis using the Finite Element Method (FEM) of the code ANSYS. (author). 11 refs.; 18 figs.; 7 tabs

[en] Differences in the thermal contraction of the composite materials in a cable in conduit conductor (CICC) for the International Thermonuclear Experimental Reactor (ITER) in combination with electromagnetic charging cause significant axial, transverse and bending strains in the Nb₃Sn layer. These high strain loads degrade the superconducting properties of a CICC. Here we report on the influence of periodic bending load, using different bending wavelengths from 5 to 10 mm on a Nb₃Sn powder-in-tube processed strand. The strand axial tensile stress-strain curve, the critical current versus applied axial strain results, the influence of cyclic loading on the RRR and assessment of the current transfer length from AC loss measurements, required for the analysis, are presented as well. For the strand under investigation, we find an influence of bending strain on the I_c that corresponds well to the predictions obtained from the applied classical relations, distinguishing ultimate boundaries of high and low interfilament electrical resistance. The reduction versus applied bending strain is similar for all wavelengths and equivalent to the low transverse resistance model, which is consistent with the estimated current transfer length. The cyclic behaviour in terms of critical current and n-value involves a component representing a permanent reduction as well as a factor expressing reversible (elastic) behaviour as a function of the applied load. The results from the set-up enable a discrimination in performance reduction per specific load type and per strand type. In this paper, we discuss the results of the pure bending tests