Melt-textured bulk samples of YBa
2Cu
3O
7−
δ
which have a high potential for magnetic applications are usually characterized by trapped field measurements. In this paper we present a fitting ...procedure which allows to eliminate the influence of different geometric parameters of the sample and the set-up and to calculate an effective value of the critical current density. A more general fitting procedure allows to calculate the spatial distribution of the critical current density
j
c.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The formation of superconducting junctions between MT-YBCO using TmBa2Cu3O7-delta powder as a solder has been studied. The method proposed excludes the step of a very slow cooling (at a rate of ...several degrees per hour) during seam formation. The heating and cooling rate for joining parts produced from single-domain material without visible cracks (macrocracks) can be rather high (500-1000 K h-1) and a holding time at the highest temperature (1010 deg C) of several minutes (0.05 h) is enough to form a reliable junction. Reasonable rates of heating and cooling are however around 100 K h-1 if crack propagation is to be avoided in joined blocks used for practical application. Modelling experiments on rings and studies of the ring properties by vibrating sample magnetometer (VSM), field mapping with a Hall probe and magneto-optical microscopy have shown that superconducting properties of the junction were not lower than that of the joined material (jc of about 30 kA cm-2 was observed in zero field at 77 K) and that the proposed process of joining did not adversely affect the properties of the material. The structure of the resulting junction was in good agreement with the structure of MT-YBCO.
The Tm–Ba–Cu–O solder can be successfully used to produce a superconductive joint between melt-textured YBa
2Cu
3O
7−
δ
(MT-YBCO) parts. The peculiarities of solidification, phase formation, ...structure transformations and electromagnetic properties of MT-YBCO soldered with TmBa
2Cu
3O
7−
δ
are discussed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Recently developed manufacturing technologies use high pressure and various doping additions to prepare bulk MgB sub(2)-based materials with a high critical current density measured by the ...magnetization method. We use a contactless transformer method, which is based on studying the superconductor response to an induced transport current, to measure AC losses in bulk MgB sub(2) rings synthesized under high pressure. The obtained dependence of the losses on the primary current (applied magnetic field) is fitted by a power law with an exponent of ~2.1 instead of the cubic dependence predicted by Bean's model and power law electric field-current density (E-J) characteristics with a large exponent. An unusually strong dependence of the AC losses on the frequency is also observed. It is shown that the E-J characteristic of bulk MgB sub(2) is well fitted by the dependence used in the extended critical state model based on account of the viscous vortex motion in the flux flow regime. Numerical simulation using this E-J characteristic gives current and frequency AC loss dependences that agree well with the experimental results.
The homogeneity of a large YBa
2Cu
3O
7−
δ
(YBCO) sample fabricated by top-seeded melt-growth has been studied in details. It was particularly shown how structural imperfections and superconducting ...properties are distributed along the growth front. These distributions are hard to explain within the flat a-growth front suggestion. These are better fitted by the growth scenario when the a-growth fronts seem concave and consist of small growth steps.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
A fast method of characterizing HTSC bulk material Zeisberger, M.; Habisreuther, T.; Litzkendorf, D. ...
IEEE transactions on applied superconductivity,
06/2003, Volume:
13, Issue:
2
Journal Article, Conference Proceeding
Peer reviewed
HTSC bulk material which has been developed during the last ten years is now prepared in increasing quantities and used in demonstrators or prototypes of several applications, e.g., flywheels and ...motors. The quality control of large amounts of samples requires a method which is fast and provides essential information about the sample quality. In particular, the critical current density and its inhomogeneity should be determined. In this contribution we report about a trapped field measurement technique using pulsed field magnetization and field detection by a Hall-array. With this arrangement the required time of measurement is in the order of a few minutes per sample. The software which controls the devices contains also an analyzing procedure for the calculation of an effective critical current density as well as parameters describing the homogeneity of the samples.
Two new types of HTS electric machines are considered. The first type is hysteresis motors and generators with cylindrical and disk rotors containing bulk HTS elements. The second type is reluctance ...motors with compound HTS-ferromagnetic rotors. The compound HTS-ferromagnetic rotors, consisting of joined alternating bulk HTS (YBCO) and ferromagnetic (iron) plates, provide a new active material for electromechanical purposes. Such rotors have anisotropic properties (ferromagnetic in one direction and diamagnetic in perpendicular one). Theoretical and experimental results for HTS hysteresis and reluctance motors are presented. A series of hysteresis HTS motors with output power rating from 1 kW (50 Hz) up 4 kW (400 Hz) and a series of reluctance HTS motors with output power 2-9 kW (50 Hz) was constructed and successfully tested by the cooperation of MAI (Moscow, Russia) and IPHT (Jena, Germany). It was shown that HTS reluctance motors could reach 2-5 times higher specific output than conventional asynchronous motors of the same size and will have higher values of power factor (cos/spl phi//spl ges/0.7-0.8).
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