Niobium-tin Conductors Research Articles

Niobium Tin Conductors for High Energy Physics, Fusion, MRI and NMR Applications Made by Different Techniques

Niobium tin was one of the first superconductors to be made into relatively small high field magnets forty-six years ago. Conductors made from it are widely used for a range of different applications and development efforts are still being carried out to improve properties and reduce costs. The paper describes some of the work being carried out by the authors to make such improved conductors for fusion, high-energy physics and other applications. Three different types of niobium-tin conductors are described: 1. Low loss material with modest current density for fusion magnets. 2. High current density, higher loss material for high field high energy physics magnets. 3. Tubular type, low cost material with intermediate current density and small subelement size that could have application in a wide range of different magnets. Some of the advantages and drawbacks of each type of conductor are described together with illustrative properties.

RCA’s Role in Early Superconducting Magnet Research

We would like to add a note concerning some of the historical information published in our article “Superconducting Magnets Above 20 Tesla” (Physics Today, August 2002, page 37). During the 1960s, the RCA Laboratories in Harrison, New Jersey, also made significant contributions to the early development of niobium tin conductors and magnets, based on the chemical vapor deposition process. In particular, by 1968, RCA had developed a 14-T magnet using their Nb 3Sn tape conductor. The company discontinued development of superconducting magnet technology in 1970. We thank J. J. Hanak for bringing to our attention the details of RCA’s activities.Our article was not intended as a rigorous review, and the history was intentionally kept short to highlight the progress in the early days of development. Rather, our aim was to give some perspective for later large-magnet development at extreme magnetic fields, development that includes the use of the new high-temperature superconductors. © 2003 American Institute of Physics.

Toward an accurate scaling relation for the critical current in niobium-tin conductors

Until a few years ago, a set of equations commonly referred to as the Summers relations gave the most accurate description of the critical current in Nb/sub 3/Sn conductors as a function of applied field, temperature and axial strain. Although highly empirical, they describe reasonably well the critical current data of past Nb/sub 3/Sn conductors. New data from various types of Nb/sub 3/Sn conductors, as well as recent analysis of the ITER CS model coil results reveal however, that this description lacks the precision, required to correlate the conductor data to the model coil results. This discrepancy, attributed to the highly empirical background for the relations, manifests itself mainly in the strain- and temperature dependence. The development of an alternative, more accurate description of the behavior of the critical current, starting from a more fundamental description of the strain dependence, has been initiated. At the moment, the development concentrates around the improvement of the temperature dependency relations to achieve a better accuracy of the overall descriptions, especially in the high temperature region.

Investigation of critical current distribution in composite superconductors

For the design of superconducting magnets, the E-field vs. current curve (E(I)-curve) of the composite superconductor is an important property. We studied a model which describes the E(I)-curve by means of a Gaussian distribution of local critical currents. Therefore, resistive measurements in magnetic fields up to B=15 T were performed on several niobium-titanium, niobium-tin conductors and Bi-2223-conductors. We calculated the critical current distribution by differentiating E(I) twice with respect to the current. For metallic superconductors we got only the lower portion of the distribution because of sample quenches. That means, no complete distribution could be seen, but only a fraction of the curve. We developed a new numerical method to estimate the parameters of these fragmented critical current distributions. The knowledge of the parameters enabled us to calculate the whole curves and to compare them with the results of the measurements. This comparison clearly showed that for NbTi and Nb/sub 3/Sn composite superconductors, which are not additionally stabilised, the quench of the sample occurs far below the mean critical current.

Scaling of the critical current in ITER type niobium-tin superconductors in relation to the applied field, temperature and uni-axial applied strain

The three dimensional surface of the critical current density versus field and temperature J/sub c/(B,T) of niobium-tin is a function of the strain state of the superconductor. A brief review of literature on this subject is presented. The J/sub c/(B) function is described by the relations for flux pinning. The temperature and strain dependencies are added to this relation, This results in a unifying scaling law for A15 materials, which is verified for different niobium-tin conductors with respect to all the relevant variables, i.e. field, temperature and uni-axial strain. Nb/sub 3/Sn conductors from 9 manufacturers are measured in the frame work of the third ITER benchmark tests on critical current. The investigated ranges are: applied field from 7 to 13 T, temperature from 4.2 to 8 K and applied strain from -0.4 to +0.8%. Special attention is paid to the region of compressive axial strain, which is the most relevant state of strain for superconductors under thermal compression in practical applications.

Large-bore, superconducting magnets for high-energy density propellant storage

A study has been conducted on the design of large-bore, superconducting solenoid magnets in an effort to determine how weight and cost scales with field and size. The fields considered ranged from 0.5 to 20 T and bore sizes from 3 to 10 m. The designs are based on light-weight, high-performance superconducting magnet designs using cable-in-conduit niobium-titanium and niobium-tin conductors. All methods to reduce the weight of the magnets are used, and both aluminum and stainless steel are considered for the structure, With the length of the magnets fixed at 10 m, the amount and cost of the conductor is determined for each field and bore size. The largest magnets are determined for each field value that have weights under 10/sup 4/, 10/sup 5/, and 10/sup 6/ kg. The cost scales as the square root of stored energy and in millions of dollars is twice the product of field (T) and bore (m).

Fully bonded internal-tin, niobium-tin (Nb/sub 3/Sn) conductor development at Oxford Superconducting Technology

Niobium-tin conductors are the class of conductors which allow the fabrication of superconducting magnets that generate over 9 T at 4.2 K and 12 T at 1.8 K, Oxford Superconducting Technology makes a wide range of niobium-tin conductors. One such conductor is a fully bonded internal tin, Nb/sub 3/Sn composite. The process for the manufacture of the fully bonded Nb/sub 3/Sn conductor is described. The process is applicable to conductors for high current applications and applications requiring low AC losses. Results for both classes of conductors are reported.

Development of niobiumtin conductors at SLE

Superconductors Lips ECN is a recently formed company which produces NbTi and Nb 3Sn multifilament wires as well as superconducting cables. Multifilamentary Nb 3Sn wire, produced by the powder route, is developed commercially. About 30 km of strand material has been produced for the SULTAN 12 T project. These wires showed good performance. Developments are underway to reduce gradually the filament diameter at the same current performance to meet the full requirements for the NET and LHC conductors.