Nikolay Mineev

Pinning Properties of PLD-Obtained GdBa2Cu3O7-x Coated Conductors Doped With BaSnO3

This work is devoted to high-rate pulsed laser deposition of BaSnO₃-doped superconducting films on long buffered metal tape substrates with the use of pilot-scale equipment and common deposition conditions typical for commercial 2G high-temperature superconducting wire production at SuperOx Japan. BaSnO₃ inclusions were found to grow as nanocolumns elongated along the vertical direction and having biaxial texture. With BaSnO₃ doping, the angular dependence of critical current measured at 77 K became much more isotropic. At 77 K, the lift-factor (<italic>I_c/I_c^s^f)</italic> values in BaSnO₃ -doped samples increased almost twice in 0.5–3 T magnetic field in perpendicular orientation; at the same time, the absolute critical current increased only by 10%. At 4.2 K, in 0.5–3 T perpendicular field, the absolute critical current in doped samples increased 1.8 times.

Measurements and Numerical Simulations of Trapped Field in a Stack of HTS Tapes

Trapped field magnets are usually constructed on the base of bulk YBCO superconductors. However, recent achievements in the production of long-size coated conductors have opened the opportunity of using a tape stack for these applications. Better thermal conductivity, mechanical stability in high fields, and high critical current densities make such systems favorable. Moreover, the tape form of the conductor allows for organizing different spatial structures and optimizing device design. Trapped field was measured on the stack of high-temperature superconducting tapes in this work. An industrially stabilized (with copper shield) tape, which was produced by SuperOx company with GdBa2Cu3O7-x superconductor inside, was used in experiments. The stack was made of 12-mm-diameter disk-shaped tapes, and the height was 20 layers. Magnetization was carried out by an 8-T superconducting magnet on the temperature of 77 K. To calculate the trapped field of a stack, field dependence and angular field dependence of critical current were measured on these tapes. The finite-element method was used for numerical simulations. It is shown that taking into account the magnetic field orientation in different areas of the stack leads to better agreement with the experimental measured trapped field values.

Contactless measurements of local transport characteristics of coated conductors under the bending strain

The influences of bending strain on the critical current density Jc in coated conductor (CC) tapes were investigated at 77 K by contactless method based on scanning Hall probe magnetometry (SHPM). In order to clarify the reasons of variations in critical current for different bending radius we carried out local studies of critical currents in CC tapes before and after bending strain. By using SHPM we defined two-dimensional maps of critical current distribution at various bending radiuses. It was demonstrated that the superconducting layer in CC tape cracked at critical bending radius into periodical regions with unchanged and decreased transport properties. Appearance of local cracks with reduced value of the critical current leads to degradation of the critical current of the whole tape. It is found that the both critical bending radius and kind of tape cracking depend on the type of metallic substrates. The results of contactless studies are in good agreement with direct transport measurements.

Investigation of the hysteresis losses in CC tapes after laser filamentation

Study of AC loss has been conducted on the 4 mm wide CC-tapes manufactured by SuperOx. Filamentation was carried out by laser cutting of the commercially available tapes with a copper coating. Also for comparison, original tapes and commercial multifilament tapes (manufactured by SuperOx by using chemical etching method) were studied. Losses were obtained from the magnetization curves measured on a vibration sample magnetometer in the temperature range from 4 K to 77 K. In addition, the current carrying characteristics of tapes were studied, and the effect of filamentation on the critical current value were examined. We present an analysis of the experimental results, as well as a comparison of data for different types of samples. The possibility of decreasing the energy losses due to filamentation tapes was demonstrated.

Magnetic and transport properties of HTS MgB2 wires

Critical current Ic and magnetization M of industrial MgB2 tape and wire were measured in order to estimate their suitability for production of liquid helium free cryomagnetic system. Samples were subjected to bending with different diameters Db and critical current was measured at temperature T = 4.2 K in magnetic fields up to 10 T. The dependences of the critical current on the diameter of the bend Ic (Db) were found and used for optimization of liquid helium free cryomagnetic system. The magnetization of the wire was measured by a vibrating sample magnetometer at temperatures T = 4.2,10, 15, 20, 25 K in magnetic fields up to 14 T. It was found that the magnetization curve M (H) is influenced by ferromagnetic response of the metal matrix. Ferromagnetic contribution had been taken into account and magnetization loops caused by the diamagnetic contribution of the superconducting phase were extracted. Dependencies Ic(T) and Ic(H) were obtained from the data.