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High engineering critical current density ( J e) is demanded in high-performance large-scale applications such as power cables, high-magnetic-field magnets, accelerators, and fusion reactors. In developing high current capacity and low vulnerability under a high magnetic field, high-temperature superconducting (HTS) rare-earth barium copper oxide coated conductors (CCs) have undergone various trials, and CC tape characteristics have ultimately been greatly improved. The Korea Electrotechnology Research Institute recently developed a “multiple HTS layers on one substrate” (MHOS) conductor that can carry high critical current, I c, based on the number of superconducting layers deposited on one substrate. The superconducting layers in a MHOS conductor are much thicker than in a single-layered CC tape, possibly affecting the degradation behaviors of I c under a mechanical load. To ensure the performance and reliability of MHOS conductors, it is necessary to evaluate the strain/stress response of I c. In this study, the electromechanical properties of MHOS conductors were investigated using the uniaxial tension test method as well as the single-sided bending test at 77 K and self-field and at 0.5 T using a pair of neodymium permanent magnets.

The charge trapping characteristics of silicon (Si) substrates covered with a self-assembled monolayer (SAM) were studied using on a local biasing method with Kelvin-probe force microscopy. A hexadecyl SAM (HD-SAM) on a Si substrate, in which the molecules were covalently bonded to the Si substrate, was found to have no charge trapping sites at its monolayer/Si interface while an ocatadecylsilyl SAM (ODS-SAM) on a Si substrate, in which a thin oxide layer was inserted between the molecules and the Si substrate, showed a distinct charge trapping behavior. The alkyl monolayer directly fixed on Si is promising as a very thin insulating layer in Si microelectronics.

Cross-linking polyethylene (XLPE) power cables are widely used as an excellent insulation material for high-voltage direct current (HVDC) transmission. For the design and operation of HVDC-based power cables, the conduction properties of XLPE insulation must be obtained. This study aimed to establish a highly reliable conductivity-measurement system that can diagnose the XLPE insulation of cables before and after aging by evaluating the repeatability of their conductivity. In this study, a conductivity-measurement circuit was constructed using the polarization-and-depolarization-current technique. Conductivity was measured according to the conductor temperature by using an applied electric field, and then the repeatability of the measured conductivity was evaluated using a statistical method. The experimental results show that the minimum repeatability was 6%, thereby demonstrating the establishment of a reliable conductivity-measurement system.

XLPE (Cross Linking-Polyethylene) is widely used as an insulating material for HVDC (High Voltage Direct Current) transmission cables, and it is important to evaluate the aged state of XLPE due to long-term operation. The purpose of this paper is to evaluate the conduction characteristics of XLPE model cables before and after aging using PDC (Polarization and Depolarization Current) technique. The test sample is a model cable for research with an insulation thickness of 2.5 mm in which the inner semiconductor, XLPE insulation and outer semiconductor are incorporated. The model cable was aged at 35 kV / mm for the applied average electric field and the conductor temperature of $90^{\circ}C$ for 30 days. In order to evaluate the conduction characteristics of the test samples before and after aging, the conductivity of XLPE was measured under the conductor temperatures of $30 ^{\circ}C$, $60^{\circ}C$ and $90^{\circ}C$ and applied average electric fields of 10 kV / mm, 15 kV / mm, 20 kV / mm and 25 kV / mm respectively. After 30 days of aging, the increasing tendency of XLPE conductivity with respect to electric field turned out to be decreased compared with that of unaged model cable sample.

In order to increase the current capacity of a high-temperature superconducting REBCO-coated conductor, in this paper, a lighter aluminum alloy was employed for mechanical reinforcement. Two GdBCO tapes fabricated using the reactive coevaporation by deposition and reaction (RCE-DR) process were laminated with three Al alloy (AA-3104) tapes using a two-step process involving pretinning and bonding. It was confirmed that ultrasonic soldering using Sn-3 wt% Ag-0.5 wt% Cu was efficient at laminating the GdBCO and aluminum alloy tapes. The bonding strengths and critical currents of the laminated conductors were evaluated.

We report the fabrication of Gd films with dimples on the surface by vacuum evaporation method on Hastelloy substrate. The Gd films are structurally and morphologically studied by x-ray diffraction and field emission scanning electron microscope respectively and found to be hexagonal crystal structure. The magnetocaloric properties are studied and found to be well comparable with commercial Gd sheet. The calculated magnetic entropy change in Gd films is 9.57 J/kg K at Curie temperature (TC) of 294 K with second order magnetic phase transition under applied magnetic field 5 T.

Nanocrystalline ZnO powders have been synthesized by co-precipitation method and investigated planetary ball milling effects on structural and optical properties. These powders were characterized using X-ray diffraction, field emission scanning electronic microscope, Infrared spectrophotometer, UV–vis spectrophotometer and Photoluminescence. It was found that prepared ZnO powders have hexagonal close packed structure which was annealed at 500 °C for 30 min. The bandgap energy of ZnO powders varied from 3.13 to 2.85 eV. The room temperature PL spectra exhibits low intensity UV emission peak at 383 nm and green emission band around 520 nm shows shifting towards higher wavelength with decrease in intensity of peak with time of planetary ball milling. Hence, it was observed that planetary ball milling can be used to tailor the optoelectronic properties of ZnO nanostructures.

Ni doped ZnO nanopowders have been synthesized by the co-precipitation route followed by planetary ball milling. The synthesized powder was characterized by X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Field Emission Scanning Electron Microscopy (FESEM), High Resolution Transmission Electron Microscopy (HR-TEM), UV–vis spectrophotometry, fluorescence spectrophotometry and Quantum Design PPMS for structural, morphological, microstructural, optical and magnetic properties measurements. All the samples show wurtzite hexagonal crystal structure. The optical absorption spectra show a shift in the position of band edge towards lower energy. The estimated band gap is found to decrease with higher nickel doping. The room temperature PL measurements illustrate UV emission centered at 390 nm (3.17 eV), which is ascribed to the near-band-edge (NBE) emissions of ZnO and broad green emission around 540 nm. Room temperature ferromagnetism in the Ni doped ZnO nanopowders has been confirmed by magnetic property measurements.

Nonuniformity of critical current, Ic is one of the most important factors to be considered for the practical applications of high-temperature superconducting (HTS) REBCO coated conductors. To investigate the variation of Ic due to mechanical strain, local critical currents were measured at various tensile strain values from 0 to 1.2% for brass-laminated GdBCO tapes at 77 K, and analyzed using the Weibull distribution function. Measured local critical currents vary and decrease significantly at strain levels above about 0.8%. The Weibull function with three parameters turned out to be applicable for describing the Ic distribution of REBCO HTS wire for the entire strain range. The statistical minimum Ic calculated from the Weibull distribution function decreased with increased tensile strain. The degree of Ic variation was observed to drastically increase when the applied tensile strain exceeded the irreversible strain of about 0.8%.

2G HTS coated conductor (CC) tapes are now used for electric device applications. The residual stress/strain induced in HTS coating films in CC tapes during cool down influences the critical current, Ic, and should be investigated. In this study, the thermal residual stress/strain induced in the REBCO coating film was calculated from deposition temperature (1073 K) to 77 K by thermo-mechanical analysis and numerical simulation. Additionally, the improvement in irreversible strain limit, eirr., with copper electroplating has been investigated.

In case of long pieces of HTS conductor, their critical current measurement is an important process for the conductor manufacturer and the customer, however, it is very time consuming process. Conventional critical current measurement is carried out by ‘four probe method’, which increase the transport current and measure the voltage between the fixed voltage taps. Therefore, it consists of conductor moving and measuring process. To speed up the measuring process, longer distance between voltage taps is required. In this case, the measured critical current is averaged and small defects, which can be very crucial for thermal stability, cannot be found. Therefore, the limitation of the voltage tap length should be carefully decided considering the cooling environment. Another non-contact or indirect method is to measure the screening effect of magnetic field and converting the field signal to the critical current, which is called as hall probe method. This process is known as a very efficient way to find local defects and estimate the distribution of the critical current, however, it contains inevitable error and noise because it should measure the small magnetic field signals. This paper describes a new critical current measurement system, which have similar hardware structure of conventional ‘four probe method’. However, it is much faster than other systems using fast feedback control of the transport current while the conductor is continuously moving with high speed. The measured results are compared with the conventional method and hall probe method.

A facile and rapid glycine-assisted combustion method was developed to synthesize polycrystalline La0.8Ca0.2MnO3 (LCMO) powder by dissolving lanthanum nitrate, calcium nitrate, manganese nitrate (oxidant) and glycine (fuel) as the starting materials and water as solvent and then heating the resulting solution on a heating plate. The X-ray diffraction and FTIR analyses confirmed the orthorhombic crystal structure, and a morphological study showed the polycrystalline form of the LCMO powder. The calculated lattice constants a = 5.46, b = 7.73, and c = 5.49 A agreed well with the standard values. The magnetic measurements showed a paramagnetic behavior of LCMO at room temperature. The maximum change in entropy observed for the LCMO sample was −1.95 J/kgK at an applied magnetic field of 2 T at the Curie temperature of 165 K.

In this study, in order to investigate the strain effect in the critical current, I c of coated conductor (CC) tapes under magnetic field a newly devised measurement system using a pair of permanent magnets was constructed. The level of magnetic field applied could be controlled by the distance between magnets located in parallel. The distribution of magnetic field between the permanent magnets was checked using a hall probe sensor. External magnetic field was applied perpendicular to the CC tapes surface. Uniaxial tensile strain was applied to the tape by using devised loading frame mounted on a universal testing machine and the strain induced was measured by using a Nyilas type extensometer. I c /I c0 –e t relation of the CC tape was first measured at self field. External magnetic field was then varied to investigate the dependency of critical current, I c , and its effect on the reversible strain limit under uniaxial tension. Finally, the transport property characteristic of SmBCO CC tapes under magnetic field with uniaxial tension using permanent magnet is compared to the case using superconducting magnet.

Sm 1+xBa 2Cu 3+y O 7−d coated conductors were fabricated by reactive co-evaporation method in the evaporation using drum in dual chambers (EDDC) deposition chamber. The effect of substrate temperature on the superconducting properties was investigated. Three samples were prepared with different substrate temperatures of 740, 780, and 800 °C. In plane and out-of-plane texture were confirmed by X-ray patterns of 2 theta and phi scan and turned out to be almost the same. Angular dependences of critical currents of those samples were measured at 0.5 and 1 T. The magnetic field dependence of critical current with the magnetic field direction parallel to the c-axis of SmBCO film was measured in the range of 0.01–1.5 T. The critical current of the sample prepared at 740 °C was slightly lower than that of other samples in the range of 0.5–1.5 T. Also we investigated the effect of thickness of superconducting layer on the magnetic field dependence. Two samples with different SmBCO film thicknesses of 0.8 and 5 μm were prepared. The magnetic field dependence of critical current in the direction parallel to the c-axis of SmBCO film was measured in the range of 0.01–1.5 T. We found that the normalized critical current of a 5 μm thick sample was higher than that of 0.8 μm thick sample possibly due to the higher pinning force of thick film than that of thin film.

Long-length (Sm1+xB2-xC3O7-y) coated conductor was fabricated using ion beam assisted deposition (IBAD)-MgO template (LaMnO3/IBAD - MgO/Y2O3/Al2O3/Hastelloy) by the reactive co-evaporation method for electric power applications. SmBCO superconducting layers with thicknesses from 1 to 3 ?m were deposited to investigate the effect of SmBCO thickness on the in-plane texture, surface morphology and superconducting properties. In this study, the optimal deposition conditions were examined to make thick SmBCO coated conductor without degradation of critical current density. The oxygen partial pressure and temperature were controlled in the range of 1~20 mTorr and 600 ~ 800°C, respectively. SmBCO/IBAD-MgO coated conductors showed high critical current densities over 2.0 MA/cm2 with small amount of degradation by increasing the thickness of superconducting layer up to 3 ?m. The critical current of 637.5 A/cm-w (JC = 2.12 MA/cm2) at 77 K in self- field was obtained in 3 ?m-thick and 1 m long coated conductor. This is the highest critical current reported so far of the coated conductor with SmBCO superconducting layer deposited by co-evaporation.

The Hall probe measurement system was used to measure the critical current distribution of superconducting coated conductor. The system consists of reel to reel moving apparatus, 7 array Hall probe, a rotary encoder and permanent magnet. The magnetic field profile across the width of superconducting coated conductor using Bean's critical state model was calculated. The effect of various parameters of the formulas on the magnetic field distribution and the effect of shape and size of artificial defects, which were formed on the surface of SmBa2Cu3O7-d(SmBCO) coated conductor using laser marking system, on the Hall probe magnetic field signal of the Hall probe measurement system was investigated.

Considering the expansion of application field of coated conductor (CC) tapes, it is preferred to adopt IBAD substrate which has high yield strength to resolve the strength problem. The electro-mechanical characteristics of the CC tapes will be influenced by the superconductor type and the deposition process adopted during manufacturing. In this study, the Ic degradation behavior of jointed IBAD processed CC tapes under uniaxial tension has been investigated. The Ic degradation behavior of the jointed CC tapes under uniaxial tension has also been compared with those in single tapes. Differently processed YBCO and SmBCO CC tapes with IBAD substrate have been used as samples. The CC tapes jointed by mechanical controlled method were subjected to uniaxial loading. Joint resistances and critical current of lap-jointed specimens have been derived from the I - V curves obtained at each tensile load at 77 K under self-field. In the case of YBCO CC tapes, lap-jointed tape showed a comparable irreversible strain limit with the single tape.

It is environmentally important to recycle the wastewater, since paper factories use a large amount of water and equivalent amount of wastewater is generated. Conventional water treatment facilities like precipitation process need large-scale equipment and wide space to purify the wastewater of paper factory. In case of massive waste water, high gradient magnetic separation (HGMS) parts are more effective to purify it rapidly and to occupy relatively small space, since large voids at filter with HGMS are adopted. In this respect, we prepared two types of superconducting magnets in order to apply HGMS parts for wastewater purification process. We made cryo-cooled Bi-2223 (HTS) superconducting magnet parts with room temperature bore in diameter of 70 mm and 200 mm in height. Also, cryo-cooled Nb-Ti superconducting magnet with room temperature bore in diameter of 100 mm and 600 mm in height was used for magnetic separator. Magnetic filters were designed by the analysis of magnetic field distribution at superconducting magnets. The faster wastewater's flow rate was, the worse the degree of clarity in treated water was. The ability of wastewater treatment in the case of magnetic separation used with 10 of magnetite particles was better than that in the case of 5 of magnetite particles.

We report a successful fabrication of GdBa2Cu3O7-delta (GdBCO) coated conductor on the ion-beam assisted deposition (IBAD) MgO template with a new buffer layer of BaZrO3 (BZO). The BZO films were deposited on the IBAD-MgO template at various substrate temperatures (T S) and oxygen partial pressures (PO2) by pulsed laser deposition (PLD). In the broad ranges of T S and PO2, all BZO layers showed almost uniform in-plane texture (Deltaphi of ~ 6deg ), implying that BZO is an attractive buffer layer. The surface roughness of BZO layer was sensitive to PO2 but not to T S. On the optimally processed BZO buffer layer with 5.1 nm RMS roughness, GdBCO coated conductor deposited at T S of 750degC and PO2 of 400 mTorr exhibited Deltaphi of 4.4deg , T c,zero of 90.3 K, and J c of 1.35 MA/cm2 (77 K, self-field).

We measured the magnetic hysteresis loops (M-H loop) of SmBCO coated conductor (CC) and YBCO-CC by using SQUID-magnetometer. These samples were fabricated by RABiTS method and IBAD method. We found the peak shifts of their M-B loops were qualitatively different. To understand this, we measured the magnetic field profiles, H(x), of SmBCO-CC and YBCO-CC by using scanning Hall probe method and calculated their current profiles, J(x). We found that the contrasting difference of M-B loops of the two types of CC was partly due to the inhomogeneous distributions of field and current, which depend on the sample shapes.

The evaporation and sputtering simultaneous deposition (ESSD) system was developed for in-situ deposition of MgB2 thin films. Mg was evaporated from the nozzle of cylinder crucible which is heated by high frequency induction heating, while B was sputtered by RF-magnetron sputtering. The nozzle-substrate distance was small enough to keep high vapor pressure of Mg on the substrate. The Mg-flux coming out of the nozzle was controlled by means of regulating the temperature of Mg source, was monitored and was calculated in detail with the variation of the distance from its nozzle. The optimal deposition condition with the variations of substrate temperature, the temperature of Mg source and the power of RF-magnetron sputtering, was investigated. MgB2 films with onset Tc of 14 K was obtained. The Tc of the film is lower than the bulk value of 39 K. Further works are in progress to improve the quality of MgB2 films by further optimization of deposition parameters and improvement of the ESSD system.

We investigated the ex-situ conversion process of amorphous precursor films for SmBa2Cu3O7-delta (SmBCO) coated conductors (CC). Amorphous precursor films were first deposited on the LaMnO3/homoepi-MgO/ IBAD-MgO/Y2O3/Al2O3/Hastelloy substrate by e-beam co-evaporation and subsequently crystallized to the superconducting phase at various post-annealing temperatures in two different reduced oxygen pressures. In 100 ppm of O2 in Ar, c-axis oriented SmBCO grains with minor a-axis oriented grains were grown at 825degC whereas polycrystalline SmBCO film with some a -axis oriented grains was formed at 800degC. In the temperature region of 825 ~ 850degC, protruded spots were observed on the sample surface. In 6 ppm of O2 in Ar, SmBCO film composed of a-axis oriented SmBCO grains with partial c-axis oriented grains were obtained at 700degC but other phases were formed above 725degC. The SmBCO sample grown at 700degC exhibited Tc ,zero value of 90.2 K. However, its Jc value at 77 K was negligibly small due to the formation of a-axis oriented grains.

In order to investigate the possibility of using mixed rare earth (Nd1/3Eu1/3Gd1/3)Ba2Cu3O7-x (NEG123) as the superconducting layer of the HTS coated conductor, the NEG123 thin film was deposited epitaxially on LAO(100) single crystal and IBAD_YSZ metal templates by pulsed laser deposition. Systematic studies were carried out to investigate the influences of deposition parameters of PLD on the microstructure, texture and superconducting properties of NEG-123 coated conductor. Deposition at oxygen partial pressure of 600 mTorr was needed to routinely obtain high quality NEG123 films with JC's (77 K) over 2 MA/cm2 and Tc's over 90 K (DeltaT ~ 2 K) . We verified from magnetization study that the NEG123 has an improved in-field Jc as the field increases at temperatures between 10 K and 77 K compared with Gd123. The JC (77 K, self field) and the value of onset TC of NEG123 thin film on LAO substrate was 4.0 MA/cm2 and 92 K, respectively. This is the first report, to the best of our knowledge, of coated conductors with NEG123 film as the superconducting layer which have Ic and Jc over 40 A/cm-width and 1.6 MA/cm2 at 77 K, self field. This study shows the possibility of using NEG123 film as the superconducting layer of the HTS coated conductor which can be used in high magnetic field power electric devices.

The electro-mechanical properties of lap-jointed ReBCO coated conductor (CC) tapes have been investigated. Different contact configurations considering its geometry were adopted in this study. The configuration where the YBCO layer is in close proximity showed much less joint resistance. In all joint configurations, the electrical resistance decreased as the joint length increased. For HTS tapes, the joint resistance-joint length behavior could be explained by parallel circuit analysis. In easy and hard bending modes, the Ic degradation behaviors in lap-jointed HTS tapes were examined. The critical radius for 95% Ic retention in each bending mode were determined.

Bi2212/Ag round wire can be used as large current capacity conductor fabricated in the shape of Rutherford cable. We have fabricated 110 m long Bi2212 Rutherford cable of 20 strand and 10 m long Bi2212 Rutherford cable of 30 strand and 8 strand by using our own Rutherford cabling machine. The critical current (I c) of the reacted Rutherford cables have been measured at 4.2 K and 65 K, respectively. The magnetization (M) versus. magnetic field (H) and magnetic irreversibility (DeltaM) versus. magnetic field (H) have been measured at 5-40 K in background magnetic field up to 8 T using PPMS instrument. It is estimated from DeltaM that critical current density (J c) of 20 strand Rutherford cable is higher than that of 30 strand Rutherford cable.

The important merit of Bi-2212/Ag high Tc superconducting wire is to apply cable as round wire geometry. Bi-2212/Ag wires were fabricated in order to develop Rutherford cable for SMES near the future. Various Ag ratio and various numbers of filaments for PIT (Powder-In-Tube) process were applied to investigate the workability during drawing and to improve critical current property of the wires. Rutherford cabling machine for B-2212/Ag strands was designed and manufactured. We designed and manufactured Rutherford cabling machine with 32 bobbins which had 2 km length of wire. This machine was constituted with Turks head, caterpillar tread and take-up facility. In order to obtain uniform working conditions without defects, Turks head's rolling system and Ag ratio of Bi-2212/Ag strands were modified. We tried to fabricate Rutherford cables with 20 and 30 Bi-2212 strands. Proper working conditions for without breakage strand in cable were investigated. We made successfully Bi-2212 Rutherford cable. The critical current of Bi-2212 Rutherford cable with 30 strands showed 420 A at 64 K and 4008 A at 4.2 K. The critical current of Bi-2212/Ag wire with 847 filaments was 398 A at 4.2 K and self field.