Superconductivity for Magnets

The present state of development of a series of industrial superconductors is reviewed in consideration of their future applications in high field accelerator magnets, with particular attention on the material aspect. The discussion is centred on Nb3Sn and MgB2, which are industrially available in a round wire configuration in kilometre lengths and are already envisaged for use in the LHC Upgrade (HL-LHC). The two systems Bi-2212 and R.E.123 may be used in magnets with even higher fields in future accelerators: they are briefly described.Comment: 21 pages, contribution to the CAS-CERN Accelerator School: Superconductivity for Accelerators, Erice, Italy, 24 April - 4 May 2013, edited by R. Baile

Transport Properties and Exponential n-values of Fe/MgB2 Tapes With Various MgB2 Particle Sizes

Fe/MgB2 tapes have been prepared starting with pre-reacted binary MgB2 powders. As shown by resistive and inductive measurements, the reduction of particle size to a few microns by ball milling has little influence on Bc2, while the superconducting properties of the individual MgB2 grains are essentially unchanged. Reducing the particle size causes an enhancement of Birr from 14 to 16 T, while Jc has considerably increased at high fields, its slope Jc(B) being reduced. At 4.2K, values of 5.3*10^4 and 1.2*10^3 A/cm^2 were measured at 3.5 and 10 T, respectively, suggesting a dominant role of the conditions at the grain interfaces. A systematic variation of these conditions at the interfaces is undertaken in order to determine the limit of transport properties for Fe/MgB2 tapes. The addition of 5% Mg to MgB2 powder was found to affect neither Jc nor Bc2. For the tapes with the highest Jc values, very high exponential n factors were measured: n = 148, 89 and 17 at 3.5, 5 and 10T, respectively and measurements of critical current versus applied strain have been performed. The mechanism leading to high transport critical current densities of filamentary Fe/MgB2 tapes based on MgB2 particles is discussed.Comment: Presented at ICMC 2003, 25-28 May 200

Kognitive Verhaltenstherapie : Ein möglicher Behandlungsansatz des Symptoms Fatigue beim Post-Polio-Syndrom?

Hintergrund: Das Post-Polio-Syndrom (PPS) ist von geringer Bekanntheit, trotz dessen Aktualität und der beträchtlichen Anzahl Betroffener in der Schweiz. Fatigue gilt für die Mehrheit aller PPS-Erkrankten als die grösste Beeinträchtigung. Studien belegen, dass Fatigue in anderen Krankheitsbildern durch die kognitive Verhaltenstherapie (Cognitive Behavioral Therapy, CBT) verringert werden kann. Ziel: In dieser Arbeit wird aufgezeigt, ob CBT Fatigue bei neuromuskulären Erkrankungen vermindert und inwiefern diese Resultate auf das PPS übertragbar sind. Ebenfalls werden Hypothesen aufgestellt, welche Relevanz die Behandlung von Fatigue mittels CBT für die Physiotherapie hat. Methode: Von März bis November 2015 wurden in den Datenbanken CINAHL, Pubmed, Medline und PsycINFO anhand spezifischer Keywords Studien zur Beantwortung der Fragestellung gesucht. Die gefundenen Studien wurden mittels PEDro und AICA ausgewertet. Resultate: Drei Studien bestätigen, dass CBT zur Verminderung von Fatigue bei neuromuskulären Erkrankungen führt. Eine Studie widerlegt jedoch diese Annahme. Schlussfolgerung: Es bedarf sowohl im Bereich der genauen Ursachen für die Fatigue bei neuromuskulären Erkrankungen, insbesondere bei PPS, als auch bei der Effektivität von CBT weitere Forschung. Patientenedukation, strukturierte Behandlungen mit klaren Zielen und die Eigenverantwortung des Patienten sehen die Autorinnen als einen Ansatz, CBT auf Fatigue bei PPS in der Physiotherapie anzuwenden

Effects of Neutron Irradiation on Pinning Force Scaling in State-of-the-Art Nb3Sn Wires

We present an extensive irradiation study involving five state-of-the-art Nb3Sn wires which were subjected to sequential neutron irradiation up to a fast neutron fluence of 1.6 * 10^22 m^-2 (E > 0.1 MeV). The volume pinning force of short wire samples was assessed in the temperature range from 4.2 to 15 K in applied fields of up to 7 T by means of SQUID magnetometry in the unirradiated state and after each irradiation step. Pinning force scaling computations revealed that the exponents in the pinning force function differ significantly from those expected for pure grain boundary pinning, and that fast neutron irradiation causes a substantial change in the functional dependence of the volume pinning force. A model is presented, which describes the pinning force function of irradiated wires using a two-component ansatz involving a point-pinning contribution stemming from radiation induced pinning centers. The dependence of this point-pinning contribution on fast neutron fluence appears to be a universal function for all examined wire types.Comment: 8 page

Surface impedance measurements on Nb3_{3}Sn at high magnetic fields

Nb$_{3}$Sn is a superconductor of great relevance for perspective RF applications. We present for the first time surface impedance $Z_s$ measurements at 15 GHz and low RF field amplitude on Nb$_{3}$Sn in high magnetic fields up to 12 T, with the aim of increasing the knowledge of Nb$_{3}$Sn behavior in such conditions. $Z_s$ is a fundamental material parameter that directly gives useful information about the dissipative and reactive phenomena when the superconductor is subjected to high-frequency excitations. Therefore, we present an analysis of the measured $Z_s$ with the aim of extracting interesting data about pinning in Nb$_{3}$Sn at high frequencies. From $Z_s$ we extract the vortex motion complex resistivity to obtain the $r$-parameter and the depinning frequency $\nu_p$ in high magnetic fields. The comparison of the results with the literature shows that the measured $\nu_p$ on bulk Nb$_{3}$Sn is several times greater than that of pure Nb. This demonstrates how Nb$_{3}$Sn can be a good candidate for RF technological applications, also in high magnetic fields.Comment: ASC 2018 conference, accepted in IEEE Trans Appl Supercon

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

Phase coexistence and critical temperatures of the (Bi, Pb)2Sr2Ca2Cu3Ox phase under partial pressures of oxygen between 10−3 and 0.21 bar with and without additions of silver

We have investigated the stability of the (Bi, Pb)2Sr2Ca2Cu3Ox phase for the stoichiometry (Bi: Pb: Sr:Ca: Cu = 1.72: 0.34: 1.83: 1.97: 3.13), subjecting it to temperatures between 700 and 850 °C under various oxygen partial pressures. A narrow region was found in which Bi, Pb(2223) was the only superconducting phase. This region follows closely the thermal decomposition line. X-ray pure Bi, Pb(2223) will partially decompose if treated outside of the stability region. For a given oxygen partial pressure, the Bi, Pb(2223) phase tends to coexist with the 2201 phase for temperatures above, and the 2212 phase for temperatures below this region. At even lower temperatures an additional lead-rich phase appears. Critical temperatures Tc vary little with treatment and range between 108.5 K and 110.8 K. If 10% silver is added to the starting powder, the phase coexistence regions shift. Silver does not seem to have a significant effect on the absolute values of the critical temperature. The Bi, Pb(2223) thermal decomposition temperature for a given oxygen pressure is lowered by at least 10 K by the presence of A

Bewegungsalltag im Homeoffice vs. Arbeit im Betrieb : eine Mixed-Methods-Studie während der Covid-19- Pandemie

Ausgangslage: Personen, die Schreibtischarbeit im Büro, insbesondere auch im Homeoffice verrichten, verbringen einen Grossteil ihres Alltags sitzend und bewegen sich zu wenig. Dadurch stellen sie eine Risikopopulation für ein erhöhtes Mass an nicht übertragbaren Krankheiten dar. Die Arbeit von zu Hause verringert einerseits die Alltagsbewegung, andererseits kann die im Homeoffice gewonnene Zeit für mehr körperliche Aktivität genutzt werden. Ziel: Diese Bachelorarbeit hat das Ziel, den Bewegungsalltag im Homeoffice mit dem im Betrieb zu vergleichen und darzulegen, welche Faktoren zum Bewegungsverhalten im Homeoffice beitragen und welche Bedürfnisse die Erwerbstätigen haben. Methode: Für die Datenerhebung wurde ein exploratives Mixed-Method-Design angewendet. Zuerst wurde eine quantitative Befragung mit 65 Erwerbstätigen durchgeführt. Anhand der Ergebnisse konnten sechs Erwerbstätige für qualitative Interviews rekrutiert werden. Ergebnisse: 50 % der Befragten bewegen sich im Homeoffice allgemein weniger als im Büro, ein Viertel bewegt sich mehr. Wiederum macht die Mehrheit im Homeoffice mehr Sport, längere Unterbrüche und ist mehr in der Natur im Gegensatz zum Betrieb. Das soziale Umfeld, das Wohlbefinden und der Workload sind wichtige Einflussfaktoren auf die Bewegung. Schlussfolgerung: Der Bewegungsalltag ist sehr individuell. Aufgrund der Eigenverantwortung im Homeoffice muss die Bewegung bewusst in den Alltag integriert werden. Die Unterstützung von gesundheitsförderlichen Verhaltensweisen erfordert das Verständnis der verschiedenen Faktoren, welche die körperliche Aktivität beeinflussen

The upper critical field of filamentary Nb3Sn conductors

We have examined the upper critical field of a large and representative set of present multi-filamentary Nb3Sn wires and one bulk sample over a temperature range from 1.4 K up to the zero field critical temperature. Since all present wires use a solid-state diffusion reaction to form the A15 layers, inhomogeneities with respect to Sn content are inevitable, in contrast to some previously studied homogeneous samples. Our study emphasizes the effects that these inevitable inhomogeneities have on the field-temperature phase boundary. The property inhomogeneities are extracted from field-dependent resistive transitions which we find broaden with increasing inhomogeneity. The upper 90-99 % of the transitions clearly separates alloyed and binary wires but a pure, Cu-free binary bulk sample also exhibits a zero temperature critical field that is comparable to the ternary wires. The highest mu0Hc2 detected in the ternary wires are remarkably constant: The highest zero temperature upper critical fields and zero field critical temperatures fall within 29.5 +/- 0.3 T and 17.8 +/- 0.3 K respectively, independent of the wire layout. The complete field-temperature phase boundary can be described very well with the relatively simple Maki-DeGennes model using a two parameter fit, independent of composition, strain state, sample layout or applied critical state criterion.Comment: Accepted Journal of Applied Physics Few changes to shorten document, replaced eq. 7-