Showing papers by "L.J.M. van de Klundert published in 1989"

Thermally and magnetically controlled superconducting rectifiers

Abstract: The switches of a superconducting rectifier can be controlled either magnetically or thermally. The authors point out the differences between these methods of switching and discuss the consequences for the operation of the rectifier. The discussion is illustrated by the experimental results of a rectifier which was tested with magnetically as well as thermally controlled switches. It has an input current of 30 A, an output current of more than 1 kA and an operating frequency of a few Hz. A superconducting magnet connected to this rectifier can be energized at a rate exceeding 1 MJ/h and an efficiency of about 97%. >

Hysteresis losses in hollow superconductors

Abstract: Flux penetration into a hollow superconducting filament in a time-varying transverse magnetic field is determined numerically. The magnetization of the filaments is calculated for field variations below and above the penetration field of the filament. The influence of the inner radius of the superconducting filament on the magnetization and the hysteresis losses in the filament is shown. The critical current density is taken to be constant during the external field cycle and depends within the superconducting filament on the local magnetic field, which is the sum of the externally applied field and the field induced by the local screening currents. Calculations based on the theory presented here show good agreement with experimental results. >

Current distribution and AC losses in twisted multifilamentary AC superconductors

Abstract: The development of AC superconductors has led to multifilamentary wires having a highly resistive matrix material and a small twist pitch and filament diameter A numerical one-dimensional model is presented which enables the authors to calculate the current distribution as well as the magnetization and transport current loss in a current-carrying AC superconductor subjected to a transverse alternating magnetic field The impact on wire design is also discussed >

Construction of optimized superconducting spin precession magnets for neutron spectroscopy

Abstract: The design and construction of a superconducting magnet system for a high-resolution neutron spin echo spectrometer. The principal solution for the field shape of optimal precession magnets is B/sub 0/cos/sup 2/( pi z/L). In practical precession magnets, this field shape is approximated by 30 superimposed concentric solenoids with a bore of 80 mm. The required field integral of 1 Tm, providing 10/sup 4/ precession turns, is achieved in a magnet with a length of about 1.5 m. The field in the center is 1.5 T maximum. The relative line integral inhomogeneity of about 10/sup -3/ obtained with such a coil is improved to less than 10/sup -6/ by two in-beam correction coils. The advanced homogeneity level means that after 10000 precession turns the precession angle remains still well defined without using tedious correction procedures. >

Numerical solution of the transverse resistivity of superconducting cables under AC conditions

Abstract: The authors develop a numerical method for calculating the transverse resistivity of superconducting cables. A superconducting cable consists of a twisted bundle of strands with a nonconducting inner region. If such a cable is placed in an external magnetic field, the induced currents will not merely flow in the axial direction, but also around the center, in the plane of the cross section. It is shown that the transverse transport current, which is induced by external fields acting on the cable, can saturate most of the filaments of the superconducting layer. This results in a smaller maximal value of a longitudinal transport current and small coupling losses. >

The influence of transverse, compressive stress on the critical current of multifilamentary Nb/sub 3/Sn and NbTi wires

Abstract: To investigate the critical current of multifilamentary wires as a function of the applied field and transverse compressive stress, a special experimental arrangement has been developed. The repulsive Lorentz force generated by a set of magnets is used to press a sample between two parallel surfaces. From the first experimental results on a multifilamentary NbTi wire, it is concluded that this approach functions properly. >

A New Method to Calculate Conductor Magnetization in Accelerator Dipoles

Abstract: During the ramping of superconducting dipole magnets as used in particle accelerators as the proposed SSC or CERN-LHC, magnetization in the conductor will manifest itself, perturbing the field homogeneity of the dipole. A numerical method was developed that covers the calculation of magnetic field inside the conductors, keystoned cables, current redistribution due to the variation of magnetic field with time as well as the multipole distribution in the dipole. For the calculation of current redistribution in a cable a keystoned cable geometry has been assumed, although the method applies to any geometry. The model incorporates saturation in the cable. In the case of an unsaturated cable the current redistribution can be described completely analytically. Also the model allows the calculation of the interstrand coupling loss as a function of the time-varying magnetic field. Finally, field remanency due to persistent currents in the filaments is described.

On the Development of a 1 Meter “Twin Aperture” 10 T Nb3Sn Dipole Model Magnet for the CERN LHC

Abstract: The possible realization of the new 16 TeV hadron collider LHC of CERN presupposes the availability of the techniques to construct 10 tesla twin aperture dipole magnets either by using conventional NbTi magnet technology at 1.8 K or by using a Nb3Sn conductor at 4.2 K. At present both alternatives are under development at CERN in collaboration with European laboratories and industries. A new initiative to explore the Nb3Sn route was started recently in the Netherlands by the Applied Superconductivity Centre at the University of Twente and NIKHEF, the National Institute for Nuclear and High Energy Physics. A 4 years R&D program was started to design and to manufacture a 1 meter Nb3Sn dipole model magnet in collaboration with other research institutes and companies in the Netherlands. The magnet now under development will be the first one meter Nb3Sn LHC dipole model magnet with a twin aperture designed for use at a nominal field of 10 T. The paper reports on general aspects of the design of the magnet and the present state of the developments.