One of the most important parameters, crucial to applications of superconductors in cryo-electrotechnique, is power loss. Measurements of losses in superconducting long sample wires require AC magnetic fields of a special geometry and appropriate high homogeneity. In the paper part of the theoretical basis for calculations and a simple design method for a race-track coil set are presented. An example of such home-made coils, with a magnetic field uniformity of about 0.2 % over the range of about 8 cm, is given. Also a simple electronic measurement system for the determination of AC magnetization loss in samples of superconducting tapes is presented.

In the work we present experimental results of ac magnetization losses measurements performed in the presence of a dc-bias magnetic field. Both ac and dc magnetic fields were coaxial and directed perpendicularly to the flat surface of sample tapes. The HTS tapes used in our experiments are commercially available composite tapes, namely a BSCCO-2223/Ag multifilamentary tape and an YBCO-123 coated conductor tape. The measurements were carried out with a sinusoidally varying magnetic fields at frequency range of about 21-113 Hz, and amplitudes up to 100 mT. The superimposed a dc-bias magnetic field was of the order of up to 50 mT. At a certain magnetic field amplitude, and at a certain dc bias magnetic field, a distinguish minimum in ac losses is observed. Occurrence of the ac loss minima differs considerably for two studied sample tapes.

In the paper we report experimental results of AC magnetization losses in a multi-filamentary BSCCO-2223 superconducting composite tape due to coaxial AC and DC magnetic fields subjected perpendicularly to the plane of the tape. Such superposition of magnetic fields usually leads to some reduction of magnetization losses. A distinguished minimum in the AC loss is observed, at a certain DC bias magnetic field and at a certain fixed magnetic field amplitude. It is shown that the minimum of the AC losses very strongly depends on magnetic history of the investigated tape, which is directly related to the magnetic flux trapping within tape's superconducting filaments region. Measurements were carried out with a sinusoidally varying magnetic fields at amplitudes up to 100 mT and a superimposed DC magnetic field up to 50 mT, at frequency range of 21-113 Hz.

We investigate conducting properties in the basal abplane before and after a long time exposure in air atmosphere of optimally oxygen doped YBa 2 Cu 3 O 7−δ single crystals. Prolonged exposure leads to an increase of the effective scattering centers of the normal carriers. The excess conductivity in a wide temperature range has exponential temperature dependence and near the critical temperature is well described within the Aslamazov-Larkin theoretical model. The prolonged exposure increases to a great extent the temperature range of the implementation of the pseudogap state, narrowing the linear section of the temperature dependence of the resistivity in the ab-plane, ρ ab (T).