Showing papers by "L.J.M. van de Klundert published in 1990"

Effects of Transverse Stress on the Current Carrying Capacity of Multifilamentary Wires

Abstract: The influence of transverse compressive stress on the current carrying capacity of multifilamentary Nb3Sn wires has been investigated on three short samples with a copper, bronze and mixed matrix. A 10 % current reduction has been observed at stresses ranging from 50 to 100 MPa for the three wires. In the test arrangement both applied force and deformation of the wires have been determined during the experiments. It has been found, that the critical current degradation can be described more unambiguously as a function of the deformation of the wire than as a function of applied load. This is caused by hysteresis effects in the stress-strain relation of the matrix material. There are indications that the length over which a compressive stress is applied is important for the observed current reduction. It has been found that degradation effects are more severe when small compression lengths are used.

On the Inductive Method for Maximum Current Testing of Superconducting Cables

Abstract: In order to test superconducting cables at high currents it is convenient to generate the required transport current inductively, i.e. by means of a superconducting transformer. The paper gives a survey of the devices in different laboratories that apply this technique to test cables above 20 kA. An existing test facility at the University of Twente, suitable for 50 to 200 kA, is treated in more detail. Specific aspects of such a facility are discussed, for example the design of the transformer, the methods to measure the current in the superconducting secondary circuit and the fabrication of joints with a sufficiently low electrical resistance.

A Study of Quench Current and Stability of High-Current Multi-Strand Cables Having a Cu or a CuNi Matrix

Abstract: This paper discusses the experimental results concerning maximum current and stability of two braided superconducting cables. The expected critical current of both conductors is 95 kA under self field conditions, at 4. 2 K. An essential difference is that one of these conductors has a pure CuNi matrix, the other a Cu matrix. The maximum current of the cables was measured as a function of the temperature and the ramp rate of the current. We observed a remarkable decrease of the current-carrying capacity with increasing current rate in both cables, independent of the matrix material. Furthermore, the stability of the cables was investigated.

A Convenient Method for Testing High-Current Superconducting Cables

Abstract: Superconducting cables with critical currents in the range of 50 kA to 200 kA are presently under investigation in Twente. Therefore, a low-cost test facility has been developed in which the required current is generated inductively, allowing cables to be tested up to at least 200 kA. A superconducting transformer induces the current through the sample and provides the background magnetic field. The secondary part of the transformer consists of one turn of the test cable. A part of it can be varied in temperature by means of a heater. The data aquisition, analysis and storage is accomplished by means of a microcomputer system. So far, two cables having critical currents in the order of 100 kA have been successfully tested concerning their maximum current, stability and quench behaviour. The paper describes the test set-up and presents some first results.

Development of a 10 T Nb3Sn “Twin Aperture” Model Dipole Magnet for the CERN LHC

Abstract: A colliding energy of 16 TeV as requested for the proposed new hadron collider LHC of CERN can only be attained if the techniques to construct 10 T dipole magnets are available since LHC should be installed in the existing LEP tunnel. At the moment a development programme is carried out at CERN in collaboration with European laboratories and industries to construct several 10 tesla model magnets following either the NbTi/2 K or the Nb3Sn/4 K routes. Here we present a new initiative to explore the Nb3Sn route. a 4 years R&D programme was started in 1988, in the framework of a cooperation agreement with CERN, by the Applied Superconductivity Centre at the University of Twente and NIKHEF, the National Institute for Nuclear and High Energy Physics in collaboration with ECN, HOLEC and SMIT WIRE. The paper reports on various design aspects and the present state of development.

AC losses in a prototype NbTi cable for LHC dipole magnets

Abstract: In this paper loss measurements on a prototype NbTi cable for the Large Hadron Collider dipole magnets are presented The cable is meant to be used for the outer layer of the magnets It is a trapezium-shaped (key-stoned) Rutherford cable The experimental results were obtained in a Twente test facility Magnetization loss measurements as well as transport current loss measurements were performed The results are compared with classical loss models From the magnetization experiments the coupling time constant of the cable at different magnetic fields can be obtained It is also possible to estimate the critical current density from these measurements The critical current and the effective transverse resistivity are important for calculations concerning the loss during ramping the magnetic field and the field disturbance due to shielding currents in the filaments and to the coupling currents

Superconducting Magnets for Disk-Shaped MHD Generators Review and Predesign

Abstract: In this paper possible magnet systems that can be used in combination with disk-shaped MHD generators are reviewed. The main coil configurations are the single solenoidal magnet and the split-pair magnet. Advantages and disadvantages of these magnet systems are discussed. After an enumeration of a few basic design considerations, a predesign of a split-pair magnet for a compact open disk demonstration unit with a thermal input power of 10 MW is presented. Furthermore, the use of Nb3Sn technology is envisaged to obtain a compact magnet with 9 T in the centre of the MHD channel. The preliminary design configuration consists of a NbTi and a Nb3Sn section. The distribution of winding volume among both sections is based upon minimum conductor costs.

AC Loss Measurements on Superconductors Using a (Low-Inductive) Coil Geometry

Abstract: In this paper loss measurements on various superconductors are presented. The measurements were performed on samples in a coil configuration. Most of the results will be used in the VAMAS Round Robin Test, in the course of which the experimental data of several laboratories throughout the world are compared. The characteristic loss parameters of the conductors are extracted from the experimental results, when possible, using classical loss theories.

A Mechanically Driven Switch for Decoupling Cryocoolers

Abstract: A superconductive magnet system solely cooled by thermal conduction and two Gifford-McMahon cryocoolers has been developed at our institute. One cooler is redundant to obtain reliable and serviceable operation. The magnet operates at a temperature of 12 K. In order to reduce the heat flux into the system when one cooler is out of service, two thermal switches were developed with the following features. In both cases thermal contact is made by pressing two or more pieces of metal against each other. The first switch is a lathe-chuck type and consists of three metal pieces symmetrically arranged around a metal bar. They are simultaneously pushed in a radial direction thus making mechanical and thermal contact. The switch is closed by an external force applied via a Bowden cable. The second is a bench-vise type. A metal bar is clamped between two metal jaws by means of the action of a screw driven by an external torque. In both cases relatively fast switching is possible. Thermal resistances were measured as a function of the contact force and with various surface materials. The thermal resistance obtained in the on-state was better than 0.5 W/K, and in the off-state at least a factor of 1000 less. Thermal and mechanical cycling appeared to have no large influence on the switch performance.

The influence of additives on the current carrying capacity of bulk YBa2Cu3OX

Abstract: We studied the influence of using different powders and several additives on the shaping process and critical current density of sintered bulk YBa2Cu3OX. It was found that all additives used facilitated the shaping process. Silver and most organic additives influenced the critical current density only little, Zinc reduced it to zero, but an ethylenebisstearoylamide compound doubled the critical current density as compared to samples without additives.

Numerical analysis of the voltage current transition in superconducting cables

Abstract: A new method is presented to calculate the voltage current transition in a superconducting cable using any E(J) relation for the superconductor in the cable. The method gives the possibility of comparing the voltage current transition in a superconducting wire with the transition in a cable composed of a number of these wires. Results are presented using a distribution function g(J) to describe the relation E(J). Differences in the transition of wires and cables will be shown as a function of a number of parameters.