AC losses in Bi,Pb(2223) multifilamentary wires with square cross-section

We have fabricated prototype Bi,Pb(2223)/Ag superconduting multifilamentary wires with a square cross-section. The AC losses of these wires were measured, compared with those of tapes and also compared with the theory. Wires show largely reduced AC magnetic field losses at 47 Hz, compared to those of tapes in a perpendicular magnetic field. The effects of the twist pitch and of the use of the high resisitive barriers were also investigated. The results show that the use of a twist pitch of about 10 mm is sufficient for decoupling the filaments, and that the use of very short twist pitches does not further reduce the absolute value of the AC losses. The losses in the wires are still higher than those of tapes in a parallel magnetic field, but the results show that the square or round configurations are interesting for applications where a perpendicular component of the magnetic field cannot be avoided, or for applications in rotating magnetic fields.Comment: 8 pages, 11 figures, submitted to Physica

Study of coupling loss on bi-columnar BSCCO/Ag tapes by a.c. susceptibility measurements

Coupling losses were studied in composite tapes containing superconducting material in the form of two separate stacks of densely packed filaments embedded in a metallic matrix of Ag or Ag alloy. This kind of sample geometry is quite favorable for studying the coupling currents and in particular the role of superconducting bridges between filaments. By using a.c. susceptibility technique, the electromagnetic losses as function of a.c. magnetic field amplitude and frequency were measured at the temperature T = 77 K for two tapes with different matrix composition. The length of samples was varied by subsequent cutting in order to investigate its influence on the dynamics of magnetic flux penetration. The geometrical factor $\chi_0$ which takes into account the demagnetizing effects was established from a.c. susceptibility data at low amplitudes. Losses vs frequency dependencies have been found to agree nicely with the theoretical model developed for round multifilamentary wires. Applying this model, the effective resistivity of the matrix was determined for each tape, by using only measured quantities. For the tape with pure silver matrix its value was found to be larger than what predicted by the theory for given metal resistivity and filamentary architecture. On the contrary, in the sample with a Ag/Mg alloy matrix, an effective resistivity much lower than expected was determined. We explain these discrepancies by taking into account the properties of the electrical contact of the interface between the superconducting filaments and the normal matrix. In the case of soft matrix of pure Ag, this is of poor quality, while the properties of alloy matrix seem to provoke an extensive creation of intergrowths which can be actually observed in this kind of samples.Comment: 20 pages 11 figure, submitted to Superconductor Science and Technolog

Higgs-mass predictions in the MSSM and beyond

Predictions for the Higgs masses are a distinctive feature of supersymmetric extensions of the Standard Model, where they play a crucial role in constraining the parameter space. The discovery of a Higgs boson and the remarkably precise measurement of its mass at the LHC have spurred new efforts aimed at improving the accuracy of the theoretical predictions for the Higgs masses in supersymmetric models. The "Precision SUSY Higgs Mass Calculation Initiative" (KUTS) was launched in 2014 to provide a forum for discussions between the different groups involved in these efforts. This report aims to present a comprehensive overview of the current status of Higgs-mass calculations in supersymmetric models, to document the many advances that were achieved in recent years and were discussed during the KUTS meetings, and to outline the prospects for future improvements in these calculations

TWO NEW METALLIC MATERIALS WITH HIGH SPECIFIC HEAT FOR SUPERCONDUCTOR STABILIZATION

Nous avons mesuré la chaleur spécifique de deux composés métalliques à basse température. En raison de transitions de phase de types différents, ces composés de terres rares montrent des anomalies très importantes dans leur capacite calorifique, ce qui les rend très interessants pour la stabilisation de supraconducteurs techniques. Les premiers essais d'application sont présentés.We report our measurement of the low temperature specific heat of two metallic rare earth compounds in magnetic fields up to 7 Tesla. Due to different types of phase transitions, these compounds exhibit very large peaks in the heat capacity which makes them attractive for stabilization of technical superconductors. First attempts for applications are presented

DEPENDENCE OF THE AC LOSSES OF Nb3Sn MULTIFILAMENT SUPERCONDUCTORS ON THEIR STRUCTURAL PROPERTIES

Les pertes par hystérésis et les pertes par couplage de différents types de conducteurs multifilamentaires à base de Nb3Sn ont été mesurées pour des cycles de champs magnétiques de zéro à 6 Tesla et pour des fréquences allant jusqu'à 100 Hz. Les deux types de pertes dépendent largement des conditions de traitement thermique. Les couches de Nb3Sn ont été caractérisées par des analyses au microscope électronique et par des mesures de Tc.Hysteresis and coupling losses have been measured on different types of Nb3Sn multifilament superconductors at magnetic field cycles from zero up to 6 Tesla respectively at frequencies up to 100 Hz. Both types of losses depend strongly on the conditions of the diffusion heat treatment. The Nb3Sn layers were characterized by electron microscopy and by Tc measurements

SCALING LAW FOR FILAMENTARY SUPERCONDUCTOR HYSTERESIS LOSSES IN SUPERIMPOSED dc AND ac MAGNETIC FIELDS

On a examiné les pertes par hystérésis de supraconducteurs filamentaires dans un champ magnétique surimposé ac et dc, perpendiculaire à l'axe du conducteur. On a vérifié qu'on peut décrire les pertes par une loi où seulement le rapport entre le champ appliqué ac et le champ de pénétration du filament joue un rôle, sans aucune influence des paramètres du conducteur. Les avantages et les limites d'une telle loi d'échelle sont discutés.Hyteresis losses of multifilament superconductors have been considered in transverse, superimposed ac and dc magnetic fields. These losses scale following a law in which the ratio of the ac field to the penetration field is the only important parameter. The advantages and the limits of such a scaling law are discussed

Alternating magnetic field losses in high-Tc superconducting multifilament tapes with a mixed matrix of Ag and BaZrO₃

Alternating magnetic field losses for the new (Bi, Pb)2Sr2Ca2Cu3O10 multifilament tapes with a mixed Ag–BaZrO3 matrix for coupling loss reduction have been measured at 77 K and at frequencies up to 100 Hz. Due to the presence of oxide barriers around the filaments, the effective transverse electrical resistivity in the matrix is increased by a factor of eight, with a corresponding modification of the frequency dependence of the coupling losses. This result is a very promising step in the development of low loss high-Tc superconductors for 50 Hz applications. For larger ΔB values, it seems feasible to reduce the coupling losses at 50 Hz to a tolerable level by both, applying high-resistive barriers and changing the conductor dimensions, away from the extremely flat tape geometry. A saturation loss criterion is derived for twisted flat multifilament tapes