J. Le Bars

Bio: J. Le Bars is an academic researcher. The author has contributed to research in topics: Solenoid & Electrical conductor. The author has an hindex of 4, co-authored 6 publications receiving 39 citations.

Construction and Test of the Cello Thin-Wall Solenoid

Abstract: A large thin-wall superconducting solenoid has been constructed at Saclay and mounted on a large detector CELLO. This is one of the experiments installed on the e+e- colliding beam facility PETRA at DESY (Hamburg).

An aluminium stabilized conductor for the ALEPH solenoid

Abstract: Continuous controls during the production and results of short sample tests are the subject of this report. The conductor, made of a Cu:Nb-Ti cable inside a pure aluminium matrix is obtained by a coextrusion process. A knowledge of the quality of bonding between these two parts was important an a set of controls using classical sample tests and new continuous controls has been developed at Saclay.

Long term experience on the superconducting magnet system for the CELLO detector

Abstract: A large superconducting magnet system has been installed and is currently operated at the PETRA storage ring (Desy/Hamburg) for the CELLO detector. This system has been carried out as a joint collaboration of CEN/, Saclay and ITP/Karlsruhe and includes as main components a large "thin wall" solenoid cooled by force flow in a pipe bonded to the winding, two bath-cooled compensating solenoids, a 450 W liquifier-refrigerator unit and all connecting lines and appropriate control equipment designed for long-term automatic operation. The system has been in operation for nearly two years with continuous runs exceeding three months and has provided considerable technical experience.

A control line for the qualification of large quantities of superconducting wires

Abstract: The fabrication of the coils for the toroidal field of Tore Supra has now been ordered. The first lengths of conductors are expected in February 1983. A special line has been developed, in order to control at room temperature the overall production of the 320 kms of conductor in a continuous process. Special attention is drawn on the shape, the mechanical integrity and homogeneity of the conductor. The geometrical sizes are measured by two special devices. One uses Hall probes moving in the bore of permanent magnets, the other explores the outer surfaces with diamonds attached to electric sensors. The resistance of each meter of conductor can be directly related to the local amount of Niobium-Titanium, and provides a very good information on the homogeneity of the composite. A device developed by the CEA using induced eddy currents is able to detect very local changes in the amount of copper, and the presence of voids, bad bonding, inclusions and surface defects.

Evaluation of the scattering in critical current and Niobium-Titanium volume fraction along a length of conductor

Abstract: The knowledge of critical current at any point of a length of a conductor has always been a wish for a coil designer. It is now possible to contemplate this matter without running the whole length at helium bath temperature. From the local resistance per metre of composite measured at room temperature it is possible to derive the cross sectional area of the Niobium-Titanium. We show from samples taken along lengths of different conductors that the cross sectional areas derived from weighing the Niobium-Titanium and from the resistance per metre measurements are in very good agreement and that the current density is constant along a given length. As a result the critical current can be estimated from three measurements: critical current, weight of the Niobium-Titanium in a sample taken at one end and the measurement on line of the resistance per metre.

Self-heating in normal metals and superconductors

Abstract: This review is devoted to the physics of current-carrying superconductors and normal metals having two or more stable states sustained by Joule self-heating. The creation, propagation, and localization of electrothermal domains and switching waves leading to the transition from one stable state to another in uniform and nonuniform samples are treated in detail. The connection between thermal bistability and hysteresis, dropping and stepped current-voltage characteristics, self-induced oscillations of current and voltage, selfreplication of electrothermal domains, and the formation of periodic and stochastic resistive structures are considered.

Superconducting Materials and Conductors:. Fabrication and Limiting Parameters

Abstract: Superconductivity is the technology that enabled the construction of the most recent generation of high-energy particle accelerators, the largest scientific instruments ever built. In this review we trace the evolution of superconducting materials for particle accelerator magnets, from the first steps in the late 1960s, through the rise and glory of Nb–Ti in the 1970s, till the 2010s, and the promises of Nb3Sn for the 2020s. We conclude with a perspective on the opportunities for high-temperature superconductors (HTSs). Many such reviews have been written in the past, as witnessed by the long list of references provided. In this review we put particular emphasis on the practical aspects of wire and tape manufacturing, cabling, engineering performance, and potential for use in accelerator magnets, while leaving in the background matters such as the physics of superconductivity and fundamental material issues.

Design, construction and test of the large superconducting solenoid ALEPH

Abstract: A large superconducting solenoid (5-m bore, 7-m length) has been designed and constructed at the CEN/Saclay for the ALEPH detector, to be installed on the LEP collider at CERN. Special features of this solenoid are described such as the Al-stabilized superconducting cable, bobbinless internal winding, vacuum impregnation, indirect cooling, thermosyphon refrigeration mode, cryostat assembly. Preliminary tests without the iron carried out successfully in April 1987, and a complete test with the iron calorimeter at CERN in September 1987 are briefly reviewed. >

Superconducting magnets and their applications

Abstract: Since the discovery of superconductivity almost a century ago, there has been a steady increase in the variety of superconducting magnet applications. Progress in superconducting magnet technology has resulted in applications in areas of basic science, medicine, separation, and levitation. Performance improvements in a variety of materials, from low-temperature to high-temperature superconductors, are the foundation of recent rapid development. In addition, large increases in affordable computing power, along with steady refinement of three-dimensional analytical tools and improved materials characterization, have allowed many more advanced magnet concepts to be realized directly in hardware without scale prototype testing than was previously possible. This in turn has broadened opportunities for new science and technology results in many fields including the basic sciences, medical imaging, fusion, environmental remediation, and transportation. In this paper, a few examples of these applications will be discussed, representing a range in magnetic field, current density, and overall size, from the practical to the developmental.