Effect of the n value and the field inhomogeneity on thequench current of superconducting cables [magnet winding]

A model developed to obtain a relation connecting the critical current and the quench current of superconducting (S/C) cables is described. The model is based on the hypothesis that the heat produced inside the cable is only due to the ohmic dissipation, and it is only removed by thermal exchange with the liquid helium bath. The ohmic dissipation is calculated by supposing that the electrical resistance of the S/C cable at the transition to normal state is: Rαlⁿ where l is the current and n (n value) is an integer number. To calculate the function R(I), the field inhomogeneity at the conductor due to the self-field is taken into account, introducing the effective critical field     

Preparation and characterization of YBa2Cu3O7?x samples for microwave applications

We prepared several samples of YBa₂Cu₃O_7–x thick films electrophoretically deposited on metallic substrates, thin films sputtered on dielectric substrates, and bulk pellets, and we tested their microwave properties. Various preparation techniques are described in detail and the importance of appropriate thermal treatment during the fabrication process is emphasized. Experimental results show that electrophoretically deposited thick films on silver substrates reached, after heat treatment, a surface resistance at 50 K of 4×10^–2 comparable with the silver value, while the same measurement before sinterization gave a value of 0.5 . Either bulk pellets or thin films gave worse results, though a lack of sensitivity in our experimental apparatus could have influenced our data. The problem of sensitivity in the characterization of microwave properties of small samples is discussed in the appendices.     

Field Quality and Losses for the 4.5 T Superconducting Pulsed Dipole of SIS300

This paper presents the 2D design of the SIS300 synchrotron dipole of the FAIR facility at GSI. The dipole has a length of 7.8 m, a field of 4.5 T, in a 100 mm bore, and is ramped at 1 T/s. The studies are performed by INFN (Frascati, Genova and Milano-LASA) in a R&D collaboration with GSI. The program started in 2006 (DISCORAP) and has as a final goal the construction and test of a prototype. Particular emphasis is given to the study of the field quality and of the losses during the ramping of the magnet. Some calculation methods and different codes for magnet design are evaluated and compared.     

RF measurements on a TE011 YBCO cavity at 8 GHz

In the present work a cavity fully coated with an YBCO thick film was fabricated using an improved electrophoretic deposition technology with a special attempt to avoid the possible contamination of the superconducting powder during the milling process in the suspension preparation. A microwave experimental set-up was constructed to measure the rf behavior of the cavity in a wide temperature range. The loaded quality factorQ ₁ and the shift of the resonant frequency vs. the temperature at various rf magnetic fields have been measured. Furthermore, the surface resistance and the penetration depth determined from the measurements were compared with the numerical calculation in the framework of BCS theory, showing good agreement with the theoretical predictions.     

A.c. magnetic measurements on superconductors using two-channel dynamic analyser

A.c. magnetic measurements are powerful tools for characterizing superconducting materials. The a.c. susceptibility is the most used measurement and is commonly performed using a two-phase lock-in amplifier. This article describes a different method to carry out this measurement, employing a two-channel dynamic analyser. This instrument also allows us to measure further quantities, such as higher harmonics of the a.c. susceptibility, the so-called wide-band susceptibility and the magnetization loops. A remarkable feature of the dynamic analyser is its wide frequency range, from 244 μHz to 102 kHz, allowing simple, comprehensive and reliable characterization of superconductors.     

Preparation and characterization of YBa2Cu3O7−x samples for microwave applications

We prepared several samples of YBa₂Cu₃O_7?x thick films electrophoretically deposited on metallic substrates, thin films sputtered on dielectric substrates, and bulk pellets, and we tested their microwave properties. Various preparation techniques are described in detail and the importance of appropriate thermal treatment during the fabrication process is emphasized. Experimental results show that electrophoretically deposited thick films on silver substrates reached, after heat treatment, a surface resistance at 50 K of 4×10^?2 Ω comparable with the silver value, while the same measurement before sinterization gave a value of 0.5 Ω. Either bulk pellets or thin films gave worse results, though a lack of sensitivity in our experimental apparatus could have influenced our data. The problem of sensitivity in the characterization of microwave properties of small samples is discussed in the appendices.