Lattice deformation in an axially strained BiSrCaCuO/Ag tape conductor investigated by X-ray diffraction

The lattice deformation of a Bi-2212/Ag tape conductor is investigated as a function of an externally applied strain at 300 K. This macroscopic strain is applied in the same direction (¿axial¿) as where the current is normally passed through the conductor. A small but significant shift is observed in the position of the diffraction peak. In a limited strain regime this shift is proportional to the applied strain. The deformation of the c-axis that corresponds to the observed peak shift can be described well with an elastic grain deformation. For tensile axial strains above 0.2% and below ¿0.1% strain, the c-axis deformation is limited to an almost constant value. These two limits in the elastic behaviour divide the axial strain range into three regimes. A good correlation with the axial strain dependence of the critical current at 77 K, is obtained when the thermal contraction is taken into account. In the central strain range, where an elastic lattice deformation is observed, the critical current remains almost constant. Any tensile or compressive deformation that exceeds the elastic limits causes a more severe and irreversible reduction of the critical current

Analysis of AC loss in superconducting power devices calculated from short sample data

A method to calculate the AC loss of superconducting power devices from the measured AC loss of a short sample is developed. In coils and cables the magnetic field varies spatially. The position dependent field vector is calculated assuming a homogeneous current distribution. From this field profile and the transport current, the local AC loss is calculated. Integration over the conductor length yields the AC loss of the device. The total AC loss of the device is split up in different components. Magnetization loss, transport current loss and the loss due to the combined action of field and current all contribute to the AC loss of the device. Because ways to reduce the AC loss depend on the loss mechanism it is important to know the relative contribution of each component. The method is demonstrated on a prototype transformer coil wound from Bi/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub x//Ag superconducting tape. Differences between the model assumptions and devices are pointed out. Nevertheless, within the uncertainty margins the calculated AC loss is in agreement with the measured loss of the coil

Compressive and tensile axial strain reduced critical currents in Bi-2212 conductors

Mono and multifilamentary wires of BSCCO-2212 in Ag matrix are investigated in an axial strain experiment. The superconducting samples are soldered to a substrate that is bend in order to achieve a compressive or tensile axial strain. The I/sub c/-strain dependence is measured in magnetic fields up to 16 T at 4.2 K and the strain is varied from -2% to +1.2%. In these Bi-2122 samples any strain-induced I/sub c/ reduction is irreversible. Moreover a significant rise in I/sub c/ was never observed after changing the strain. Special attention is paid to the tensile axial strain regime (0 to 0.4%). A small but significant reduction in I/sub c/ is found in this case. The strain behaviour of these wires indicates that the I/sub c/ reduction is due to fractures in the superconducting filament

Study of the Effect of Transport Current and Combined Transverse and Longitudinal Fields on the AC Loss in NET Prototype Conductors

AC losses in cables carrying DC as well as AC transport currents at different DC background fields up to 2T have been measured on three types of Nb3Sn subcables in a new test facility. In this facility it is possible to apply sinusoidal transverse AC fields up to dB/dt=5T/s and longitudinal AC fields up to dB/dt=30T/s separately and simultaneously. The AC loss is measured with a calorimetric method. Simultaneously applied transverse and longitudinal fields can result in a loss which exceeds the added contributions of the separate applied AC fields. Within the measured range it is about correct (within 10%) to add the loss components due to DC transport current up to 10 kA and both applied transverse and longitudinal AC fields. The measured total loss is always above the sum of the loss component

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

Tightness of lead times

This paper introduces a general, formal treatment of dynamic constraints, i.e., constraints on the state changes that are allowed in a given state space. Such dynamic constraints can be seen as representations of "real world" constraints in a managerial context. The notions of transition, reversible and irreversible transition, and transition relation will be introduced. The link with Kripke models (for modal logics) is also made explicit. Several (subtle) examples of dynamic constraints will be given. Some important classes of dynamic constraints in a database context will be identified, e.g. various forms of cumulativity, non-decreasing values, constraints on initial and final values, life cycles, changing life cycles, and transition and constant dependencies. Several properties of these dependencies will be treated. For instance, it turns out that functional dependencies can be considered as "degenerated" transition dependencies. Also, the distinction between primary keys and alternate keys is reexamined, from a dynamic point of view.

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

Calculation of the Critical Current Reduction in a Brittle Round Multifilamentary Wire due to External Forces

A simple model is presented that can describe the electro-mechanical state of a multifilamentary wire. An elastic cylinder model is used to derive the strain state analytically. Axial and transverse forces came a position dependent critical current density in the wire. The integral critical current of such a wire is calculated. The effect of two different parameters, the hydrostatic and the deviatoric strain, on the critical current is compared. The critical current reduction of a model wire due to various external loads in a Nb 3Sn wire is analysed. Finally the position of the superconducting filaments is considere

Small and repetitive axial strain reducing the critical current in BSCCO/Ag superconductors

The critical current in two types of axially deformed BSCCO/Ag tape conductors is investigated. An Ic reduction is observed for small axial strains (ranging from 0 to 0.3%) with a characteristic slope dic/d&epsiv;=-5±1 (relative Ic, change per relative change in length). In the case of an axial compression there is a more pronounced Ic reduction. For small axial strains (<0.3%) a certain reversible change in Ic is observed. This reversible behaviour occurs in combination with an irreversible reduction that increases when the number of strain cycles is increased. The reversible part of the Ic change remains for a large number of strain cycles (>10000) and has a similar negative slope for both compressive and tensile strains. It is proposed that the reversible Ic change is correlated to a non-hydrostatic lattice deformation. The Ic versus strain behaviour is in good agreement with an earlier proposed mode

An engineering formula to describe the AC loss of BSCCO/Ag tape

An engineering function to describe the AC loss of BSCCO/Ag tape conductors is developed. For a wide range of transport currents and magnetic fields (with different orientation) the loss is described with an uncertainty of 10%. The equation is based on the analytical expressions available, BSCCO/Ag tapes used in power applications at liquid nitrogen temperature are fed with an AC transport current and exposed to an AC magnetic field. The magnetic field in a device has different orientations with respect to the position of the conductor in the device. In this contribution, AC loss measurements for simultaneously applied magnetic field (with different orientation) and transport current are presented for a high quality tape conductor that is used in a transformer coil. The results are separated into a magnetic and a transport current loss componen