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

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

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

Fully superconducting rectifiers and fluxpumps Part 1: Realized methods for pumping flux

The magnetic and electrical properties of superconductors were a challenge for many inventors and designers to use superconducting materials in the construction of fully superconducting voltage and current sources commonly called fluxpumps. In the past twenty years a large variety of mechanically or electrically driven devices have been proposed and successfully operated.\ud \ud In this review the basic principle of operation of each class of devices is shown and specific material problems and limitations are reported. The review will be published in two parts.\ud \ud Part 1 deals with mechanical devices such as flux compressors and dynamos. Although those devices must have been of great importance for technical application, their construction and operation offered great experience with regard to the properties of superconducting materials, their joint techniques switching and mechanical and magnetic stability under ac and dc conditions.\ud \ud In this part also a start is made with the more promising class of electrically driven rectifier fluxpumps. With these rectifiers, current levels over 10 kA can be obtained with high efficiency

On fully superconducting rectifiers and fluxpumps. A review. Part 2: Commutation modes, characteristics and switches

This paper forms the second part of the review. Full and half wave superconducting transformer rectifiers are analysed. Modes of operation and loss mechanisms are detailed and a comparison between the behaviour of dynamos and rectifiers is presented. Investigations carried out to date still leave the flux pump relatively a long way from real applications. The possible use of a flux pump in a large magnet system and for the general protection of that system merits further study

Experimental Verification of the Temperature and Strain Dependence of the Critical Properties in Nb3Sn Wires

The critical current density in Nb3Sn conductors is described with an improved scaling formula for the temperature, magnetic field and strain dependence. In an earlier study, it is concluded that the largest uncertainties in this description arise from the temperature dependence that is described with various slightly different empirical relations. For the optimization of the numerical codes, used to predict the stability of large magnet systems, a more accurate description is required. Therefore, two different bronze processed conductors for the ITER CS model coil are analyzed in detail. The critical current is measured at temperatures from 4.2 K up to the critical temperature, in magnetic fields from 1 T to 13 T and with an applied axial strain from -0.6% to +0.4%. The axial strain is applied by a U-shaped bending spring and a comparison is made between brass and Ti-6Al-4V, as substrate materia

The Normal Zone Propagation in ATLAS B00 Model Coil

The B00 model coil has been successfully tested in the ATLAS Magnet Test Facility at CERN. The coil consists of two double pancakes wound with aluminum stabilized cables of the barrel- and end-cap toroids conductors for the ATLAS detector. The magnet current is applied up to 24 kA and quenches are induced by firing point heaters. The normal zone velocity is measured over a wide range of currents by using pickup coils, voltage taps and superconducting quench detectors. The signals coming from various sensors are presented and analyzed. The results extracted from the various detection methods are in good agreement. It is found that the characteristic velocities vary from 5 to 20 m/s at 15 and 24 kA respectively. In addition, the minimum quench energies at different applied magnet currents are presented

The Effect of Inter-bundle Resistive Barriers on Coupling Loss, Current Distribution and DC Performance in ITER Conductors

The role of inter-bundle resistive barriers (metal sheet wraps), introduced to reduce the inter-bundle coupling loss in multistage cabled Cable-In-Conduit Conductors (CICC) for the International Thermonuclear Experimental Reactor (ITER) is evaluated, based on results gained recently on short sample experiments in the Twente Cable Press and SULTAN. The obvious benefit of limiting the inter bundle coupling loss unavoidably goes together with impeding the redistribution of nonuniform currents in the coil winding introduced at the terminations, as well as reduction of the heat exchange between the bundles. Six-element numerical electromagnetic code simulations are presented that qualitatively explain the effect of wraps on the DC performance, strongly depending on the testing geometry. The computations illustrate that wraps can reduce the DC performance in short sample tests. At the same time simulations of the Poloidal Field Coil Insert (PFCI), with a winding length of 50 m, have shown that omitting sub-stage wraps, can even degrade the DC performance of coils due to the short current transfer length in combination with current nonuniformity causing peak voltages in the most overloaded petals

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

Field dependence of the critical current and its relation to the anisotropy of BSCCO conductors and coils

The design of HTS magnets is often based on the properties of a number of short samples that are presumed to be representative of the conductor to be used. Variability in conductor properties and inhomogeneity in the magnetic field distribution within the magnets, coupled with conductor anisotropy, provide a significant challenge to accurately predict the field dependence of the magnet critical current. This work is based on measured superconducting properties of Bi-2212 and Bi-2223 conductors at 4.2 K in parallel and perpendicular magnetic fields up to 33 T. Properties of double pancake units and stacks, from the same or similar conductor batches, are presented, based on measurements at self-field and in applied co-axial background magnetic fields up to 19 T. Modeling of this data is based on short sample properties in perpendicular field; the average grain misalignment is used as the parameter to quantify the anisotropy. Correlations and discrepancies between the measured data and models based on short sample data are discussed for Bi-2212 and Bi-2223 conductors