1,721,037 research outputs found
Study of the protection system for Nb3Sn "slot" design NED dipole
No full textThe Next European Dipole (NED) Collaboration has the scope to promote the study and development of a high magnetic field (about 15 T on the conductor) and large aperture dipole magnet aimed at LHC upgrade and at the next generation colliders. Among different configurations, a novel solution has been considered. This magnet will be based on a high current density Nb3Sn superconductor (Jc around 1500 A/mm(2) @ 15 T, 4.2 K in the non-copper section), and will have a large stored magnetic energy (4.0 MJ/m, i.e. 18 times higher than for one LHC dipole), that makes the magnet protection extremely critical. In this paper we have investigated the quench propagation assuming different dump resistance values and operating conditions (quench heaters efficiency, delay time for the Quench Detection System), in order to optimize the protection system in terms of peak temperatures in the coils and maximum voltage drops. The study has been performed by using the quench propagation code QLASA, which has been developed at LASA Lab, Milan
Critical current statistical distribution and voltage–current characteristics in superconducting wires
No full textType II superconductors, like Nb–Ti and Nb3Sn, play a central role in the design of magnets for fusion and particle accelerators. These materials show experimentally a longitudinal electric field which depends in a nonlinear way on the current. Different models have been developed to analyse this phenomenon, mainly based on the role of defects and inhomogeneities in the superconducting sample. Some of these models are based on a statistical description of the critical current distribution along the wire, that can explain the presence of a curvature in the volt–ampere characteristic (VAC). In the work we have studied the impact of different critical current statistical distributions on the VAC and their implications, and compared some experimental data with our theoretical results
Magnetization measurements and analyses on thin filament Nb-Ti wires for SIS300 synchrotron superconducting dipoles
No full textIn order to minimise the heat generation in the fast cycled superconducting dipoles foreseen for the synchrotron SIS300 at FAIR, thin filaments NbTi wires must be developed (see presentation of G. Volpini). Following the previous efforts earned out many years ago in SSC developments, we have analyzed some thin filament NbTi wires obtained either from laboratories or industry. These wires give us the opportunity to set up suitable metodology for studying the wire needed to the manufacturing of SIS300 dipoles. We use a magnetic characterization, by means of vibrating sample magnetometer, to get important informations in the wire performances. Rather than the usual critical current density computation, this presentation will deal with typical aspects of thin filaments NbTi wires which can be experimentally derived: The transverse resistivity, the presence of magnetic materials, and the proximity effect
Thermal and electrical behaviour of a resistive joint in the ATLAS toroids
No full textATLAS air core toroids exploit aluminum-clad NbTi/Cu superconducting cables. Several joints along the conductor are presently foreseen, e.g, between pancakes and between coils. The operating current (20.5 kA) is about 4 times larger than in the previous comparable magnets, and so the power dissipated in a similar joint is substantially higher, making the resistance value critical. In this work we have developed some analytical models describing the temperature profile along the conductor given a localized or distributed heat source. By means of these models we found the highest resistance permissible in order not to exceed a given local temperature rise, Later we have calculated through a 2-D finite elements program the specific resistance that can be expected when the joint is performed by TIG-welding the aluminum matrices. Such a value depends strongly on the aluminum-copper interface resistance and on the aluminum RRR in the welding region. We have shown that with reasonable assumptions specific resistances lower than 10(-9) Ohm m should be achieved, The results from the first measurements, confirming such a value, are reported and discussed
Study of the protection system for Nb3Sn cos-theta NED dipole
No full textThe Next European Dipole (NED) Collaboration has the scope to promote the study and development of a high magnetic field (15 T conductor peak field) and large aperture (88 mm) dipole magnet aimed at LHC upgrade and at the next generation colliders. Among different configurations, a classical cosine-theta solution is considered. This magnet will be based on a high current density (Jc around 1500 A/mm2 @ 15 T, 4.2 K in the noncopper section) Nb3 Sn superconductor, and will have a high stored magnetic energy (1.8 MJ/m, i.e. 8 times higher than for one LHC dipole), that makes the magnet protection extremely critical. In this paper we have investigated the quench propagation assuming different dump resistance values and operating conditions (quench heaters efficiency, delay time for the Quench Detector System), in order to optimize the protection system in terms of peak temperatures in the coils and maximum voltage drops. The study is performed by using two quench propagation codes, which exploit different approaches, in order to further validate our conclusion
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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