Bartek A. Glowacki

The effect of potential contact position on AC loss measurements in superconducting BSCCO tape

Abstract AC losses in (Bi, Pb) 2 Sr 2 Ca 2 Cu 3 O x silver-sheathed tape were measured as a function of frequency and amplitude of a sinusoidall y varying transport current. Experimental results show that energy losses are purely hysteretic in nature in the range of applied frequencies for transport currents below the critical value I c . The lossy component of the measured voltage is very dependent on the position of the potential taps placed onto the surface of the tape. This can be explained using the theory of Norris [J. Phys. D 3 (1970) 489] for ellipsoidal conductors. It means that neither voltage gives an accurate measurement of the loss. The error is least for the side contacts but still varies from 40% at I c to a factor of four at 0.1 I c .

Current status of high-Tc wire

This paper is the result of the work of a SCENET (The European Network for Superconductivity) material working groups efforts on giving values for present and future expected performance of high-temperature superconducting (HTS) wires and tapes. The purpose of the work is to give input to the design of HTS applications like power cables, motors, current leads, magnets, transformers and generators. The current status performance values are supposed to be used in the design of todays prototypes and the future values for the design of fully commercial HTS applications of the future. We focus on what is expected to be the relevant parameters for HTS application design. The most successful technique by far for making HTS tapes has been on the (Bi, Pb)2Sr2Ca2Cu3Ox (Bi-2223) material by the powder-in-tube (PIT) technique and this paper therefore focuses on giving the current status and expected future performance for Bi-2223 tapes.

AC losses in striated YBCO coated conductors

We measured AC losses in RABiTS nonstriated as well as striated coated conductors provided by the US Air Force Research Laboratory. In addition, samples with different kinds of well defined inter-filament bridging have been measured and their losses compared with those of samples with unbridged filaments and with mono-layer samples. This bridging is designed to aid current sharing between filaments, which is advantageous, but it is necessary to determine if the effect on AC losses is detrimental. It was found that AC losses of striated samples with multiple bridges are higher than those of the samples with no bridges due to significant filament coupling but even so the losses are still substantially lower than those of a monolayer sample.

Resources: Stop squandering helium.

Establish a global agency to build a sustainable market for this precious commodity, say William J. Nuttall, Richard H. Clarke and Bartek A. Glowacki.

Trapped fields greater than 7 T in a 12 mm square stack of commercial high-temperature superconducting tape

Superconducting bulks can be magnetized to act as powerful permanent magnets; however, for high trapped fields at temperatures below 77 K, bulks have poor thermal stability and are limited by low mechanical strength. The trapped fields reported in this paper are between two stacks of commercial high-temperature superconducting tape each with 120 layers, magnetized by field cooling. 7.34 T was trapped at approximately 4.2 K, the highest field ever achieved for such a sample. The trapped field also continued to increase below 20 K showing high thermal stability, largely due to the silver over-layer which effectively dissipates heat.

Trapped fields up to 2 T in a 12?mm square stack of commercial superconducting tape using pulsed field magnetization

The ability of superconductors to sustain persistent currents has been well exploited with (RE)BCO superconducting bulks, which can be magnetized to form a compact source of high magnetic field. However, thin films can also sustain persistent currents, which can be utilized by stacking them in layers to create a type of composite bulk. Such a stack is capable of trapping higher fields than a bulk, as reported in this paper. 12 mm wide, 55 m thick commercial (RE)BCO tape from Superpower Inc was cut into 12 mm by 12 mm squares, stacked together and magnetized at temperatures between 10 and 77.4 K using a sequence of pulsed magnetic fields. The results are compared to a commercial 14 mm diameter YBCO bulk, showing that the stack of tapes outperformed the bulk at temperatures below approximately 60 K. Particularly high trapped fields were achieved below 50 K, with a maximum of 2.0 T at 10 K measured 0.8 mm from the stack surface. The maximum trapped field possible for a stack of tapes increases significantly with decreasing temperature down to 10 K, rather than saturating at a higher temperature as in the case of a bulk, due to superior thermal stability. The Jc, thermal and mechanical properties of commercial (RE)BCO tapes give them great potential for use as trapped field magnets activated by pulsed magnetic fields. (Some figures may appear in colour only in the online journal)

Deposition of photocatalytically active TiO2 films by inkjet printing of TiO2 nanoparticle suspensions obtained from microwave-assisted hydrothermal synthesis

In this paper, we present an inkjet printing approach suited for the deposition of photocatalytically active, transparent titanium oxide coatings from an aqueous, colloidal suspension. We used a bottom-up approach in which a microwave-assisted hydrothermal treatment of titanium propoxide aqueous solutions in the presence of ethylenediaminetetraacetic acid and triethanolamine was used to create suspensions containing titania nanoparticles. Different inkjet printing set-ups, electromagnetic and piezoelectric driven, were tested to deposit the inks on glass substrates. The presence of preformed titania nanoparticles was expected to make it possible to reduce the heating temperature necessary to obtain the functionality of photocatalysis which can widen the application range of the approach to heat-sensitive substrates. We investigated the crystallinity and size of the obtained nanoparticles by electron microscopy and dynamic light scattering. The rheological properties of the suspensions were evaluated against the relevant criteria for inkjet printing and the jettability was analyzed. The photocatalytic activity of the obtained layers was analyzed by following the decomposition of a methylene blue solution under UV illumination. The influence of the heat treatment temperature on the film roughness, thickness and photocatalytic activity was studied. Good photocatalytic performance was achieved for heat treatments at temperatures as low as 150 °C, introducing the possibility of using this approach for heat-sensitive substrates.

Chemical solution deposition using ink-jet printing for YBCO coated conductors

This paper reports the successful application of ink-jet printing to the deposition of both continuous coatings and multi-filamentary structures of YBCO. Stable inks have been prepared using both the established TFA-MOD route and novel fluorine-free precursors with appropriate rheological properties for ink-jet printing. Continuous and well textured coatings with lengths exceeding 100?m and a thickness of 0.5??m have been deposited by electromagnetic ink-jet printing from TFA precursors on LZO-buffered Ni?W substrates and samples have achieved a Jc around 1.5?MA?cm?2 (self-field, 77?K). On single crystal substrates, continuous coatings and multi-filamentary structures have been deposited using piezoelectric ink-jet printing both from TFA-?and water-based precursors, achieving Jc values up to 3?MA?cm?2.

Superconducting Nb3Sn intermetallics made by electrochemical reduction of Nb2O5–SnO2 oxides

Abstract The article is focused on low temperature superconducting Nb 3 Sn material manufactured by novel electrodeoxidizing method developed in Cambridge whereby the range of alloys and intermetallics are produced cheaply making potential superconducting wires more cost effective. The process of direct electrochemical reduction of Nb 2 O 5 –SnO 2 mixtures and in situ formation of the Nb 3 Sn is discussed in details.

Oxidation thermodynamics of metal substrates during the deposition of buffer layer oxides

Abstract The oxidation state of a metal surface during the initial stages of deposition of an epitaxial oxide buffer layer is discussed from a thermodynamic viewpoint. The basic problem is one of minimizing oxidation of the surface of the metal while ensuring that the buffer layer oxide is able to form in the desired phase. Particular attention is paid to the deposition of CeO 2 , SrTiO 3 and Y 2 O 3 –ZrO 2 (YSZ) onto nickel. Such materials are candidates for use in the production of high- T c coated conductors. Calculation of the Gibbs free energy changes for the oxidation reactions, under various regimes of vacuum and gas supply, suggest conditions which are reducing for the metal oxide but under which the buffer layer oxide remains stable.