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

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 Jc(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 Jc(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. Nb3Sn 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 application

The effect of initial and back pressures upon the water rate of a simple steam engine

Thesis (M.E.)--University of Illinois, 1916Typescrip

The critical current of Nb3Sn wires for ITER as a function of the axial tension and compression

The influence of compressive and tensile axial strains on the critical current of various Nb3Sn conductors is investigated. The investigated multifilamentary wires are especially developed for the ITER project. The critical current is determined as a function of an axial tension in a standard pull set-up. These results are compared with the results that are obtained on a bending spring-type strain device. In this second device an axial compression larger than the integral thermal shrinkage of the matrix, can be achieved. A study of the field dependence of the critical current yields the strain dependence of the extrapolated upper-critical field versus the axial strain. A good correlation is found between the two different strain devices in the tensile strain regime. There is a difference in the (limited) compressive strain regime where such a comparison can be mad

Verzet of participatie? Advies om uw huurders deel te laten nemen aan energiebesparende werkzaamheden!

In de komende jaren wil woningcorporatie Lefier Zuidoost Drenthe, hierna genoemd Lefier, 1750 woningen een energielabel C of hoger verschaffen en daarbij de klanttevredenheid waarborgen. Dit advies is geschreven voor woningcorporatie Lefier Zuidoost Drenthe. Deze woningcorporatie wil een upgrade van energielabels voor bestaande woningen in Emmen en Klazienaveen bewerkstelligen. Lefier wil dit bereiken door het uitvoeren van energiebesparende werkzaamheden. Voordat deze werkzaamheden bij de woningen doorgevoerd kunnen worden, moet 70% van de bewoners hiermee ingestemd hebben. Het probleem is echter dat in de betreffende wijken in Klazienaveen en Emmen deze 70% niet wordt gehaald en de werkzaamheden dus niet plaats kunnen vinden. De grote vraag is dan ook: ‘Welke bijdrage levert de 70% norm aan het besluit van bewoners om wel of niet deel te nemen aan energiebesparende werkzaamheden en welke rol speelt communicatie hierin?’. Om deze probleemstelling te kunnen beantwoorden hebben wij de volgende doelstelling geformuleerd: namelijk het verkrijgen van informatie door middel van een kwantitatief onderzoek om de mening van de huurders te achterhalen over de 70% regeling. Daarnaast is het onderzoek gericht op hoe de huurders het liefst benaderd worden, waardoor een zo hoog mogelijk percentage mee wil werken aan energiebesparende renovatieprojecten. Studentenonderzoek in het kader van het thema Duurzaam bouwen

To Crack or Not to Crack: Strain in High TemperatureSuperconductors

Round wire Bi 2212 is emerging as a viable successor ofNb3Sn in High Energy Physics and Nuclear Magnetic Resonance, to generatemagnetic fields that surpass the intrinsic limitations of Nb3Sn. Ratherbold claims are made on achievable magnetic fields in applications usingBi 2212, due to the materials' estimated critical magnetic field of 100 Tor higher. High transport currents in high magnetic fields, however, leadto large stress on, and resulting large strain in the superconductor. Theeffect of strain on the critical properties of Bi-2212 is far fromunderstood, and strain is, as with Nb3Sn, often treated as a secondaryparameter in the design of superconducting magnets. Reversibility of thestrain induced change of the critical surface of Nb3Sn, points to anelectronic origin of the observed strain dependence. Record breaking highfield magnets are enabled by virtue of such reversible behavior. Straineffects on the critical surface of Bi-2212, in contrast, are mainlyirreversible and suggest a non-electronic origin of the observed straindependence, which appears to be dominated by the formation of cracks inthe superconductor volumes. A review is presented of available results onthe effects of strain on the critical surface of Bi-2212, Bi-2223 andYBCO. It is shown how a generic behavior emerges for the (axial) straindependence of the critical current density, and how the irreversiblereduction of the critical current density is dominated by strain inducedcrack formation in the superconductor. From this generic model it becomesclear that magnets using high temperature superconductors will be strainlimited far before the intrinsic magnetic field limitations will beapproached, or possibly even before the magnetic field limitation ofNb3Sn can be surpassed. On a positive note, in a very promising recentresult from NIST on the axial strain dependence of the critical currentdensity in extremely well aligned YBCO, reversible behavior was observed.This result emphasizes the need for further conductor development,specifically for round wire Bi-2212, to generate a wire with a similarreversible dependence on strain. Availability of such a wire will enablethe construction of magnets that can indeed generate fields that farsurpass the limitations of Nb3Sn superconductors

A general scaling relation for the critical current density in Nb3Sn

We review the scaling relations for the critical current density (Jc) in Nb3Sn wires and include recent findings on the variation of the upper critical field (Hc2) with temperature (T) and A15 composition. We highlight deficiencies in the Summers/Ekin relations, which are not able to account for the correct Jc(T) dependence. Available Jc(H) results indicate that the magnetic field dependence for all wires can be described with Kramer's flux shear model, if non-linearities in Kramer plots are attributed to A15 inhomogeneities. The strain (eps) dependence is introduced through a temperature and strain dependent Hc2*(T,eps) and Ginzburg- Landau parameter kappa1(T,eps) and a strain dependent critical temperature Tc(eps). This is more consistent than the usual Ekin unification, which uses two separate and different dependencies on Hc2*(T) and Hc2*(eps). Using a correct temperature dependence and accounting for the A15 inhomogeneities leads to a remarkable simple relation for Jc(H,T,eps). Finally, a new relation for s(eps) is proposed, based on the first, second and third strain invariants.Comment: Accepted Topical Review for Superconductor, Science and Technolog

An optimized BSCCO/Ag resonator coil for utility use

AC coils made with BSCCO-2223/Ag tapes and operating in liquid nitrogen have a potential for power related applications, e.g., inductors, transformers and current limiters. High-Tc tapes are available from several producers, while access to the coil building know-help is still rather limited, The relevant knowledge and technology suitable for making HTS coils for 50-60 Hz operation is being developed as a part of the current project. To verify the technology, several test solenoids and a first full-scale sub-coil have been manufactured. Electromagnetic, thermal and mechanical analysis of the coils is performed. The electromagnetic analysis focuses on the reduction of the radial magnetic field component in the windings. Voltage-current characteristics and the AC loss data obtained from relevant short sample measurements are applied. A good agreement between calculated and measured V-I curves and losses of the coils is found. A remarkable increase of the critical current and the reduction of the AC loss at the coil edges are predicted and confirmed experimentally. With the losses defined, thermal analysis and optimization of the coil structure are performed numerically followed by measurements for verification. The paper reports on the series of coils developed and explains the features of the projec

Heat treatment optimizations for Wind-and-React Bi-2212 racetrack coils

Lawrence Berkeley National Laboratory (LBNL) is developing Wind-and-React (W&R) Bi sr cacu o +δ (Bi-2212) accelerator magnet technology for insert coils, to surpass the intrinsic limitations of Nb-based magnets, and eventually develop hybrid systems that can approach 20 T dipole fields. The Bi-2212 technology is being developed in close collaboration with industry, and has been partly supported by the US Very High Field Superconducting Magnet Collaboration (VHFSMC). Steady improvements were made over the last several years, with coil HTS-SC08 reaching 2636 A, or about 85% of its witness sample critical current (Ic). Though this is still a factor 3 to 4 too low to be competitive with Nb-based materials, it is expected that the required Ic can be achieved through further conductor optimizations. Recent developments include the commissioning of infrastructure for the reaction of coils at LBNL. Earlier coils were fabricated and tested at LBNL, but were reacted at the wire manufacturer. We describe in detail the furnace calibrations and heat treatment optimizations that enable coil reactions at temperatures approaching 890 °C with a homogeneity of ± 1 °C in a pure oxygen flow. We reacted two new coils at LBNL, and tested the performance of coil HTS-SC10 at 4.2 K in self-field using a superconducting transformer system. We find that its performance is consistent with witness samples, and comparable to coil HTS-SC08, which is an identical coil that was reacted at Oxford Instruments Superconductor Technology (OST), thereby validating the in-house reaction process. 2 2 2