Point Contact Spectroscopy of Nb3Sn Crystals: Evidence of a CDW Gap Related to the Martensitic Transition

Two Single crystals of Nb3Sn presenting the martensitic anomaly at different temperature and shape, as observed with specific heat measurements, were used to study structural features in the electronic density of states with point contact spectroscopy. At high temperature below the martensitic anomaly, we observed different spectroscopic characteristics. One sample displaying a well marked specific heat peak, shows a clear defined structure in the differential conductance that evolves with temperature and may be associated with changes on the density of states due to the opening of a charge density wave gap. Those features are very depending on the crystallographics characteristics of the single crystal examined.Comment: 13 pages 6 figures. accepted in Solid State Communicatio

A Review of the Properties of Nb3Sn and Their Variation with A15 Composition, Morphology and Strain State

This article gives an overview of the available literature on simplified, well defined (quasi-)homogeneous laboratory samples. After more than 50 years of research on superconductivity in Nb3Sn, a significant amount of results are available, but these are scattered over a multitude of publications. Two reviews exist on the basic properties of A15 materials in general, but no specific review for Nb3Sn is available. This article is intended to provide such an overview. It starts with a basic description of the Niobium-Tin intermetallic. After this it maps the influence of Sn content on the the electron-phonon interaction strength and on the field-temperature phase boundary. The literature on the influence of Cu, Ti and Ta additions will then be briefly summarized. This is followed by a review on the effects of grain size and strain. The article is concluded with a summary of the main results.Comment: Invited Topical Review for Superconductor, Science and Technology. Provisionally scheduled for July 200

Design and Test of a Nb3Sn Subscale Dipole Magnet for Training Studies

As part of a collaboration between CEA/Saclay and the Superconducting Magnet Group at LBNL, a subscale dipole structure has been developed to study training in Nb3Sn coils under variable pre-stress conditions. This design is derived from the LBNL Subscale Magnet and relies on the use of identical Nb{sub 3}Sn racetrack coils. Whereas the original LBNL subscale magnet was in a dual bore 'common-coil' configuration, the new subscale dipole magnet (SD) is assembled as a single bore dipole made of two superposed racetrack coils. The dipole is supported by a new mechanical structure developed to withstand the horizontal and axial Lorentz forces and capable of applying variable vertical, horizontal and axial preload. The magnet was tested at LBNL as part of a series of training studies aiming at understanding of the relation between pre-stress and magnet performance. Particular attention is given to the coil ends where the magnetic field peaks and stress conditions are the least understood. After a description of SD design, assembly, cool-down and tests results are reported and compared with the computations of the OPERA3D and ANSYS magnetic and mechanical models

Flow regimes for a magnetic suspension under a rotating magnetic field

We have performed qualitative observations of both macroscopic and local motions in a ferrofluid and in a suspension of magnetic grains under a rotating magnetic field H. The individual grains rotate synchronously. We then find that : — When the macroscopic magnetization vector M is uniform over the whole sample volume, there is no bulk rotation of the liquid. — Slight departures from uniformity are enough to induce asynchronous rotations of the liquid of either sign, depending on the distribution of magnetic poles in the sample. — Large departures from uniformity and powerful bulk rotations can be imposed very easily either by inhomogeneous static fields or grain concentrations.Nous avons effectué des observations qualitatives à des échelles macroscopique et locale sur les mouvements à l'intérieur d'un ferrofluide et d'une suspension de grains magnétiques, sous l'effet d'un champ magnétique tournant H. Les grains individuels tournent de façon synchrone. Dans ces conditions, nous trouvons que : — Quand le vecteur aimantation macroscopique M est uniforme sur tout l'échantillon, il n'y a pas de rotation d'ensemble du liquide. De petits écarts à cette uniformité sont suffisants pour produire des rotations asynchrones du liquide, dans un sens ou dans l'autre, selon la distribution des pôles magnétiques à l'intérieur de l'échantillon. — On peut très facilement créer de forts écarts à cette uniformité et, par suite, d'importantes rotations d'ensemble par l'intermédiaire de champs statiques locaux ou de concentrations de grains non uniformes

Magnetic levitation

International audienc