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The mechanical and thermal analysis of the superconducting magnets, forming an innovative fixed-field bending section for use in a proton therapy gantry, is presented here. The design concept has a large momentum acceptance, covering the full proton energy range of 70 to 220 MeV with fixed field in the superconducting magnets, and uses a simple magnet geometry based on double-pancake high temperature superconductor coils. The main planned steps for the assembly and fabrication of the magnets are discussed. The mechanical analyses of the magnet, with emphasis on the stress state of the conductor during the powering of the magnet, is here described. The thermal analysis investigating the adequacy of the copper structure surrounding the conductor to extract the heat deposited in the conductor during powering is also discussed in detail.

The effects of soft ferromagnetic material placed nearby the high-Tc Bi-2223 coil is analyzed. Electro-magnetic simulation have been carried out to find the distributions of the magnetic field of the Bi-2223 coil. The used soft ferromagnetic material could change the distribution of the Bi-2223 coil's magnetic field, and the transport capability of the Bi-2223 coil changes consequently. According to the simulation results, the thickness of the soft ferromagnetic material plate shows a notable effect on the coil, and the position and width of the plate could present negative effects. Experimental result of a Bi-2223 coil with B30P105 silicon steel plate is consistent with the simulation conclusions, and the critical current of the developed Bi-2223 coil could achieve an improvement of 15% by using of a piece of silicon steel plate with a thickness of 0.3 mm. [ABSTRACT FROM AUTHOR]

Wireless power transfer (WPT) is of increasing interests today. High temperature superconducting (HTS) WPT has been demonstrated to be more efficient than copper WPT. In our previous work, we found that the efficiency of WPT from a copper coil to a HTS coil is lower than the efficiency of WPT from the same HTS coil to the same copper coil. Thus, the transmitter and the receiver are asymmetric and this asymmetry degrades WPT performance. In this paper, it is demonstrated theoretically and experimentally that for WPT between a HTS coil and a copper coil: asymmetry does exist and influences properties; the root of the asymmetry is the different resistances between the HTS coil and the copper coil; the effects of the asymmetry can be eliminated by optimizing the load; the proposed theoretical calculation fits the experimental results well. [ABSTRACT FROM AUTHOR]

High-temperature superconducting (HTS) magnets have several advantages for ac and pulse operation due to having a high critical temperature. However, fast magnetic field changes generate severe ac losses and eddy current losses. Therefore, loss estimation and reduction is a significant issue for HTS magnet cooling design. For future cooling design, we have measured losses of a Bi-2223 HTS magnet for beamline switching in the cyclotron facility at the Research Center of Nuclear Physics, Osaka University. The time-varying magnetic field losses for triangular wave excitation with a perpendicular magnetic field amplitude of 0.8 T in wire and a minimum period of 42 s were obtained from measured cryocooler temperatures and preliminary measured cooling capacity curve. The eddy current losses of the metal components were calculated using transient electromagnetic finite element analysis. The ac losses of the Bi-2223 wire were derived from the measured time-varying magnetic field losses and the calculated eddy current losses. The frequency dependence of their losses indicates the importance of accurate evaluation and reduction of the eddy current losses for the future magnet with higher charging speed. [ABSTRACT FROM PUBLISHER]

We have developed a manufacturing method for superconducting joints for Bi-2223/Ag tapes (DI-BSCCO Type-H, Sumitomo Electric Industries Ltd., Yokosuka, Japan). The tapes' superconducting joints were fabricated under pressure and heat treatment processes. The critical currents of these joints under relevant temperature conditions were measured to investigate their applicability to superconducting devices such as magnetic shields and superconducting magnets using current transport tests. In addition, the critical currents were investigated in a parallelmagnetic field to the tape surface up to 5 T at 4 and 20 K.We will report the results of these experiments. [ABSTRACT FROM AUTHOR]

(BiPb)SrCaCuO-(NiO) superconductor with x=0, 0.01, 0.02, 0.03, 0.04, and 0.05 wt.% was prepared using the coprecipitation technique. The average size of NiO used was 8 nm and 16 nm. The highest value of the transport critical current density, J in the bulk form was observed in the x=0.01 wt.% samples for both sizes. Based on this result, Ag sheathed superconductor tapes with starting composition (BiPb)SrCaCuO-(NiO) (with NiO particle size 8 and 16 nm) were fabricated using the powder-in-tube method. The effect of these nanoparticles addition on the microstructure, phase formation, and transport critical current density were studied. The J of the tape at 77 K in zero fields with NiO (8 nm) addition (4500 A/cm) was slightly higher than that of NiO (16 nm) added tape (4120 A/cm). The nonadded tape showed a lower J (1080 A/cm at 77 K). These results indicated that magnetic nanoparticles such as NiO could act as an effective flux pinning centers leading to the enhancement of J in the bulk and tape form. Moreover, NiO with size closer to the coherence length, ξ was more effective in enhancing J. [ABSTRACT FROM AUTHOR]

In order to quantitatively elucidate the transport characteristics of HTS conductors with large current capacities, we minutely investigated the relation between the current distributions in the sample conductor and the circuit parameters such as joint resistance and sample inductance. A high temperature superconducting current transformer (HTS-CT) was used to energize a large current in the sample conductor. No change in the joint resistance was observed with an increase of the sample current. On the other hand, the current ratio of the HTS-CT decreased with an increase in the sample current. This is considered to be equivalent to the inductance becoming large with an increase in the sample current. From the measured current distributions, we see that the current in the central area of the conductor is increased with increasing sample current. Based on these experimental results, the relation between the change of the current distributions and the increase of the sample inductance is discussed. [ABSTRACT FROM PUBLISHER]

In order to realize HTS power machines and devices with high performance, it is important to evaluate the characteristics of HTS conductors quantitatively. We developed a compact system to measure the transport characteristics of HTS conductors under various experimental conditions. This system enables us to measure the transport characteristics of straight HTS conductors up to a current capacity of 1 kA class at 77 K, 66 K, and 4.2 K. The measurement of transport current losses is done by the Poynting vector method. The distribution of Poynting vectors around the sample conductor can be obtained by using many sets of both potential leads and pickup coils. An HTS current transformer (HTS-CT) is used to feed current to the sample conductor for the measurement. A secondary current of about 1 kA at 77 K can be induced when the primary current is 40 A. The sample conductor is connected to the secondary coil of this transformer. As a sample conductor, we used a conductor consisting of 16 parallel Ag-sheathed Bi-2223 multifilamentary tapes. The joint method between the HTS-CT and sample conductors is also examined. Based on these results, the usefulness of this measurement system is discussed. [ABSTRACT FROM AUTHOR]

Abstract: The critical current property of (Bi-2223) silver-sheathed tape has been remarkably improved by application of ConTrolled Over Pressure (CT-OP) process with adjusting temperature and oxygen partial pressure. For further improvement of the property of Bi-2223 tapes, the effect of number of filaments on the critical current density J c was investigated. It was found that J c was higher and its decrease with increasing magnetic field was weaker in the tape with larger number of filaments. In addition, the irreversibility field B i increased with increasing filament number. The field-angle anisotropy J c(0°)/J c(90°) of the tape with the largest filament number was smallest, where the field-angle was measured from the a–b plane. However, the out-of-plane misorientation angle is fairly small in this tape. Hence, the low field-angle anisotropy in this tape seems to be attributed to improved superconductivity in the block layers in the superconducting region near the interface with silver matrix. [ABSTRACT FROM AUTHOR]

The flux pinning potential energy of silver (Ag) sheathed high- T c Bi-2223 tapes determined from measured current densities, J( T, H), is reported in this paper. Measurements of the transport current density, J, of the Ag sheathed Bi-2223 tapes were performed with an applied magnetic field directions parallel ( H| ab) and perpendicular ( H| c) to the tape’s board surface from 0 to 3 T, at temperatures from 23 to 77 K. To obtain the pinning potential energy of the Bi-2223 superconductor, an empirical scaling of J( T, H) is introduced in this study. Under the flux dynamics, the effective pinning energy, Ueff( T, H, J), can be formulated using the measured current density, J( T, H). Furthermore, the pinning potential energies, U( T, H), for both H| ab and H| c were quantitatively determined by the scaling of J( T, H). The two energies, U( T, H), exhibit as a function that is inversely proportional to both temperature and logarithmic magnetic field. The magnitude of U( T, H) for H|ab is three or more times larger than that for H| c under the considered conditions. The U( T, H) is sensitive to the temperature, but insensitive to the magnetic field. This characteristic of insensitiveness towards magnetic field is an advantage for applications on the conditions of high current density, high magnetic field, and low temperature. [ABSTRACT FROM AUTHOR]

The flux pinning potential energy of silver (Ag) sheathed high- T c Bi-2223 tapes determined from measured current densities, J( T, H), is reported in this paper. Measurements of the transport current density, J, of the Ag sheathed Bi-2223 tapes were performed with an applied magnetic field directions parallel ( H| ab) and perpendicular ( H| c) to the tape’s board surface from 0 to 3 T, at temperatures from 23 to 77 K. To obtain the pinning potential energy of the Bi-2223 superconductor, an empirical scaling of J( T, H) is introduced in this study. Under the flux dynamics, the effective pinning energy, Ueff( T, H, J), can be formulated using the measured current density, J( T, H). Furthermore, the pinning potential energies, U( T, H), for both H| ab and H| c were quantitatively determined by the scaling of J( T, H). The two energies, U( T, H), exhibit as a function that is inversely proportional to both temperature and logarithmic magnetic field. The magnitude of U( T, H) for H|ab is three or more times larger than that for H| c under the considered conditions. The U( T, H) is sensitive to the temperature, but insensitive to the magnetic field. This characteristic of insensitiveness towards magnetic field is an advantage for applications on the conditions of high current density, high magnetic field, and low temperature. [ABSTRACT FROM AUTHOR]

Abstract: Recently, power transmission cables made of a high temperature superconductor (HTS) are being developed, showing progress in field tests on a power network of distribution level. The HTS power cable consists of a conductor and a shield, which are composed of dozens of HTS tapes. In addition, the HTS cable with a large current capacity has a multi-layered structure in both the conductor and the shield. In such a complicated HTS cable with a multi-layered structure, the AC loss estimation is very difficult and thus not cleared yet. In this study, a hex-cable sample was prepared by arranging six Bi-2223(Bi2Sr2Ca2Cu3O10) tapes on the surface of a normal copper-rod in order to experimentally investigate the AC loss characteristics of an HTS cable. The AC loss characteristics of the Bi-2223 tape in the hex-cable were estimated in different transport modes of the tape. The AC loss characteristics of the hex-cable were also examined in different cable transport modes in order to experimentally simulate the various transport situations of the conductor and the shield in an actual HTS cable. The measured AC loss of Bi-2223 tape in the hex-cable strongly depends on the transport mode. In particular, the measured AC losses for the simultaneous mode increase as the arrangement of tapes approaches a polygonal shape. The measured AC loss when the current of the same direction flows in the hex-cable and the copper-rod is about two times larger than the transport loss. On the contrary, it is almost half of the transport loss for the current flowing in the opposite direction, especially in the region of high currents. [Copyright &y& Elsevier]

In order to evaluate the transport current loss characteristics in HTS conductors with large current capacity, we developed a new compact measurement system. This system enables us to measure the transport current losses electrically in the straight HTS conductors with the current capacity of 1 kA class by using the small capacity AC power supply of about 50 A. In this system, an HTS current transformer is used to feed current to the sample conductor for the measurement. The secondary current of this current transformer can be induced at about 1 kA at 77 K when the primary current is 40 A. The current transformer is made very compactly, and the externals size is 70mm in diameter, and 110mm in length. The sample conductor is connected with the secondary coil of this current transformer. The loss measurement is done by the Poynting vector method. The distribution of Poynting vectors around the sample conductor can be obtained by using many sets of both a potential lead and a pickup coil. To confirm the validity of this measurement system, we measured the transport current losses in an HTS conductor. As a sample conductor, we used a parallel conductor composed of 16 Ag-sheathed Bi-2223 multifilamentary tapes. The obtained results showed that this compact system was useful for measuring AC loss characteristics of large scale HTS conductors. [ABSTRACT FROM AUTHOR]

Abstract: A practical Bi-2223 superconducting magnet, working in liquid nitrogen (L.N), was designed and fabricated. Bi-2223 tape with a critical current of 147A was prepared by a controlled overpressure (CT-OP) process at 77.3K in self-field. Ten double-pancake coils were resistively connected by copper terminals. The bore diameter was 54mm, the magnet outer diameter was 122mm, the height of the magnet was 124mm, and the weight of the magnet was about 3kg. The maximum magnetic field at the center of the bore was 0.48T with an operating current of 50A. The experimental results agree well with design predictions calculated by finite element method. AC operation was also performed, and no distortion of the voltage waveform was observed. Therefore, this Bi-2223 superconducting magnet is a suitable replacement for copper magnets designed for applications in science and technology. [Copyright &y& Elsevier]

Abstract: The critical current property of Bi-2223 silver sheathed tape has been significantly improved by application of ConTrolled Over Pressure (CT-OP) process with adjusting temperature and oxygen partial pressure at the final heat treatment. In this paper, the field-angle dependence of the critical current density was measured at 77.3K and the crystalline misorientation angle was estimated for four specimens with different critical current densities. It is found that in a parallel magnetic field, the critical current density of the latest Bi-2223 tape of 190A class is remarkably higher than the other specimens over a wide region of magnetic field. On the other hand, although the critical current density of the latest tape in a normal magnetic field is higher than the other specimens, the difference is relatively small especially at high magnetic fields. Thus, the field-angle anisotropy of the latest tape is higher than the other specimen. The observed results can be explained by the improved condensation energy density and the better c-axis alignment in the latest tape. [Copyright &y& Elsevier]

Due to strong magnetization currents induced in HTS coils wound with wide superconducting tapes the distribution of the magnetic field and currents inside the winding is difficult to calculate. We prepared an experimental coil wound with 4.2 mm wide multifilamentary BSCCO tape and measured the radial component of the magnetic field inside the winding using a thin Hall probe. At first, we calculated the radial component assuming a uniform current distribution and compared it with the data measured at room temperature. Then, the coil was cooled to 77 K and the evolution of the radial field distribution during the increase and decrease of the coil current was measured and compared with the calculations. The field map inside the winding is important for the calculation of AC losses, which are controlled by the radial field component. [ABSTRACT FROM AUTHOR]

In order to realize HTS power devices with high performances, it is important to evaluate the characteristics of HTS conductors theoretically and experimentally. In the experimental evaluation, an ac power supply with a large current capacity and few ripples is necessary. lo this end, we developed a compact HTS current transformer for evaluating the characteristics of HTS conductors. This transformer is wound in an elliptical shape with using Bi-2223 tape. The secondary current of the current transformer can be induced at about 1 kA at 77 K when the primary current is 40 A. The transformer was fabricated very compactly, and the externals size is 70 mm in the diameter, and 110 mm in length. To confirm the practicality of the transformer, the current was actually energized to an HTS conductor composed of 16 Bi-2223 tapes. The results of the performance test of the current transformer and the method of increasing the current capacity of the current transformer are also discussed. [ABSTRACT FROM AUTHOR]

Abstract: A conduction-cooled high-temperature superconducting (HTS) coil consisting of two double pancake coils was fabricated. The current–voltage (I–V) characteristics of HTS coil were obtained at different temperatures by using GM cryocooler. Using OPERA 2D, magnetic field (B r ) perpendicular to the surface of the tape at each layer of HTS coil was obtained. In order to compare with the measured values, I–V curve of the HTS coil was simulated, in the basis of the magnetic field dependence of the critical current (I c) in Bi-2223 tapes and index of n-value. Results showed pretty good agreement between the simulated and the measured critical currents at 77.3K and 40K, with a bit difference under simple assumption of index of n value. [Copyright &y& Elsevier]

Abstract: Investigation is done on the effect of ConTrolled Over Pressure (CT-OP) processes on the critical current properties in multifilamentary Bi-2223 tapes. It is found that the critical current density at low magnetic fields is remarkably improved by the new CT-OP process. This result with those on irreversibility field and n-value are compared with the numerical calculation based on the flux creep and flow model. The analysis reveals that the most probable value is increased, although the statistical distribution width is increased for the flux pinning strength. This result indicates that the critical current density at high magnetic fields is deteriorated by the widened distribution. If such an inhomogeneity can be reduced to the level of previous tapes by improving the CT-OP process, the high field performance is shown to be significantly improved. [Copyright &y& Elsevier]

Abstract: The hot topics of the critical current properties in YBCO coated conductors and Bi-2223 silver-sheathed tapes are discussed. The dependence of the critical current density in YBCO coated conductors on the superconducting layer thickness is partly associated with the defects nucleated in thicker films and is also caused by the thickness dependent influence of the flux creep. Experimental results on PLD processed conductors with different thicknesses are compared with the theoretical analysis based on the flux creep-flow model. A discussion will also be given for the optimum layer thickness for applications. In Bi-2223 tapes introduction of CT-OP (ConTrolled Over Pressure) process has significantly improved the critical current properties. This progress can be attributed to the improvement of the mean value of the flux pinning strength and the decrease in its distribution width. The possibility of further improvement of the critical current properties is discussed using the flux creep-flow model. [Copyright &y& Elsevier]

We have developed a measurement method to evaluate the current distributions in several HTS tapes arranged in parallel. In this method, the current distributions are indirectly found from the results of the field distributions measured by a pickup coil located around the upper surface of the sample tapes. To confirm the accuracy and sensitivity of this method, current distributions in a test conductor made of three copper tapes are measured. Numerical and measured current distributions are compared, and it is found that our method is accurate enough to measure the current distributions in HTS tapes. Using this method, we measured the current distributions in Bi-2223 tapes arranged in parallel at room temperature and 77 K. The comparison between the experimental and numerical results shows a good agreement. On the basis of the obtained results, the characteristics of the AC current distributions in the HTS tapes are discussed. [ABSTRACT FROM AUTHOR]

A cylindrical high temperature superconductor (HTS) is often used in power applications such as power transmission cables and matrix fault current limiters. In commercialization of these apparatuses, AC loss is a critical factor but not elucidated completely because of complexities in its measurement, e.g. non-uniform current distribution and phase difference between currents flowing in an individual HTS tape. We have prepared two cylindrical conductors composed of a Bi-2223 tape with different critical current density and one hollow conductor made of Bi-2212 bulk material. In this paper, the AC loss characteristics of the conductors have been experimentally investigated and numerically analysed. The results show that the measured losses for all the conductors are not dependent on both arrangements and contact positions of a voltage lead. This implies that most of loss flux is only in the conductors. The loss for the Bi-2223 conductor with high critical current density is in good agreement with the numerically calculated one based on the polygon model, whereas the loss measured for the Bi-2223 conductor with low critical current density coincides with the calculated loss from the monoblock model. [ABSTRACT FROM AUTHOR]

Abstract: Bi-2223 tape is a low-cost, long-length high temperature superconducting material. The new application of Bi-2223 tape for gradient coils for magnetic resonance imaging (MRI) is studied in this paper. Because Bi-2223 tape has a much higher critical current density and a much lower power loss than copper, a Bi-2223 high temperature superconductor (HTS) gradient coil shows great advantages in high gradient strengths, long continuous gradient rating, and free of cooling system over a copper gradient coil. The power losses of Bi-2223 tapes at working frequencies of gradient coils are compared to copper. The critical current degradation of tapes is also discussed. A prototype of HTS tape gradient coil is fabricated and its gradient field distributions are measured. Technical issues of resistance, gradient strength, continuous gradient rating, and cryostat are also discussed. [Copyright &y& Elsevier]

Abstract: The critical current properties of a superconducting Bi-2223 tape produced by the over pressure processing at the final heat treatment were investigated. The critical current density increased more than the factor of densification of the superconducting region. In addition, the irreversibility field also increased. This means that the quality of flux pinning is improved by the new process. From the numerical calculation based on the flux creep and flow model, it is speculated that the fraction of weakly pinning regions decreases due to the improved connectivity of grains. [Copyright &y& Elsevier]

A study of the degradation of the critical current of Bi-2223 tapes under AC magnetic fields is of great importance for HTS power applications. In particular, in a common AC coil design, the field component parallel to plane of the tape is much stronger than the perpendicular component. In this work we present the results of electric field measurements of Bi-2223 tape exposed to AC magnetic field parallel to the broad side of the tape with various frequencies and amplitudes. The observed E-I curves can be described as an additional voltage to the E-I curve superimposed on the zero-field curve. This additional voltage increases with amplitude and frequency of the AC magnetic field and grows almost linearly with DC current, peaks close to the zero-field critical current and decreases thereafter. We analyzed the correlation of the electric field with indicated parameters on the base of the theoretical predictions of H. Brandt and G Mikitik and found a striking agreement of the calculated and observed values. Measurements of the time dependent electric field exhibit double-frequency features and strong dependence of the electric field on the amplitude and frequency of the AC magnetic field. [ABSTRACT FROM AUTHOR]

We have experimentally studied relation between mechanical losses and thermal expansion properties in super- conducting coils. For the experiments, three kinds of structural materials (GFRP, DGFRP, and ZFRP) were used. A glass fiber reinforced plastic (GFRP) contracts with decreasing temperature; on the contrary, a Dyneema and grass fiber reinforced plastic (DGFRP) and a Zylon fiber reinforced plastic (ZFRP) expand with the decrease of temperature. We used sample holders made of those plastics and measured AC current losses of a Bi-2223 tape in liquid nitrogen. Even if the magnetic field applied to the tape and an AC transport current of the tape were same, the loss depended on the sample holder materials. When the sample holder is the GFRP, the loss was largest in the three kinds of plastics, and in case of the ZFRP, the loss was smallest. The ZFRP has the largest expansion property of the three materials, that is, the loss decreased with expansion of the sample holder's materials. [ABSTRACT FROM AUTHOR]

Abstract: The magnetic field angle dependence of J c was measured by four probe method and DC magnetization method. The latter measurement was used for the specimen before and after bending to break the intergrain current in order to investigate only the intragrain current. It was found that the intragrain critical current density could be increased by a factor 2.7 in a parallel magnetic field when the c-axis misorientation could be improved. From the field angle dependence of the intragrain critical current density, the anisotropy parameter was estimated as 20.4. [Copyright &y& Elsevier]

Abstract: The use of Bi-2223 tapes as the material for gradient coils in Magnetic Resonance Imaging (MRI) is promising because Bi-2223 tapes have very high critical current and very low power loss. Frequency dependent AC loss in Bi-2223 tapes was measured at the operating frequencies of gradient coil from 200Hz up to 2000Hz. It is found that AC loss decreases with frequency below 800Hz and then increases from 800Hz to 2000Hz. The contribution of hysteresis loss, eddy current loss and resistive loss to the total AC loss are investigated individually. The power-law E–J characteristic of tapes and position dependent current distribution are considered as the major reasons for the frequency dependence below 800Hz. Eddy current loss should account for the increasing power loss with frequency above 800Hz. [Copyright &y& Elsevier]

A study of the DC I-V curves of BSCCO tapes exposed to AC perpendicular and parallel magnetic fields is presented. AC magnetic fields with amplitudes up to 700 G and frequencies from 1 to 430 Hz have been applied perpendicular and parallel to tapes carrying DC currents at T = 77 K. Both field orientations result in a significant DC electric field increase, in comparison to applying DC magnetic fields of the same intensity. However, the observed I-V curves behavior is different for the perpendicular and parallel cases. In the perpendicular case, we distinguish between two frequency regimes: for frequencies above 40 Hz, the observed I-V curves obey the empirical power law dependence with current density, J c, and power index, n, that strongly depend on the field amplitude. For frequencies below 20 Hz, the observed I-V curves deviate from power law description. In the parallel field case, the I-V curve can be regarded as a superposition of an additional DC voltage over the no field I-V curve. This additional voltage increases with increasing current, peaks near the critical current and decreases thereafter. The results are discussed assuming a narrowing down of the DC current path under the application of a perpendicular AC field. Shaking of the pinned vortices under the application of a parallel AC field is assumed for explaining the results in this case. [ABSTRACT FROM AUTHOR]

The critical current property of a superconducting Bi-2223 tape produced by the over pressure processing at the final heat treatment was investigated. The critical current density increased by a factor of 1.6-1.8 at 77.3 K in comparison with the tape produced by the usual process. Thus, the critical current increased in spite of a reduction in the filament thickness. It was also found that the irreversibility field increased by a factor of 1.34 at 77.3 K by the new process. As a result, the enhancement of the critical current density at higher fields is remarkable. These results suggest that the over pressure process not only enriches the mass concentration of the superconducting phase but also contributes to the c-axis alignment. This is supported directly by the reduction of FWHM of rocking curve and indirectly by an enhancement the n value. The critical current property at lower temperatures is also investigated and the possibility of the further improvement of the property is discussed. [ABSTRACT FROM AUTHOR]

In AC regime, the peak current, Ip, in a superconducting tape can surpass the critical current, Ic, so that the circuit is superconducting only part of the time and normal the rest. Up to the limit Ip=Ic, the losses in the tape are the typical AC superconducting losses. But for Ip>Ic part of the losses are from the Joule heat in the normal tape resistance. Analysis of the plot of loss per cycle against peak current gives Ic as the point of change of the trend. [Copyright &y& Elsevier]

The critical current reduction caused by the self-field of the current is measurable on modern HTS tapes. The current density reduction is strongest near the tape edges due to tape geometry and strong anisotropy. In voltage (V)–current (I) measurement the self-field also increases with rising current. In this paper V(I) measurements are simulated with Finite Element Method to study the evolution of the current density distribution in increasing self-field. The computations are based on local magnetic flux density dependent current density-electric field characteristics, which have been derived from V(I) characteristics measured at external magnetic fields. Current densities determined with least squares method from measured magnetic flux density profiles are compared to the computed ones. The results show good correlation between the power law model calculations and measurements, but only with current amplitudes bigger than half of the critical current. [Copyright &y& Elsevier]

We present results on DC current carrying capability and AC transport current losses of cabled conductors assembled from multifilamentary (PbBi)2Sr2Ca2Cu3O10+x tapes. The DC critical current of cabled conductors lies systematically below the sum of critical currents of the tapes. By considering the self field a model for the critical current of cabled conductors is derived which reproduces also the dependence of critical currents on external magnetic fields. For the AC self field transport current losses an empirical description based on the Norris model is derived leading to a scaling of the normalised loss. [Copyright &y& Elsevier]

To improve on present critical current ( Jc) performance, multifilamentary Ag/Bi-2223 tapes with a large range of reduction rates were manufactured. The relative core mass density D was calculated, dependent on the measured geometric dimensions of the tapes. Experimental results, D vs. Jc, D vs. maximum pinning force density F max, and D vs. irreversible magnetic field Birr, are quantitatively formatted. In particular, the magnetic field dependence of Jc is critically dependent on its core density. If the core density increases by 10%, Jc of the tapes in this experiment is enhanced by as much as 100%. Therefore, in the present state of the technological process for manufacturing Ag/Bi-2223 tape, increasing the core density is clearly a significant strategy in improving the electronic and magnetic properties of the tapes and enhancing the capacity for carrying current at high magnetic fields. The limit of the bulk self-field- Jc can be calculated by the relationships of Jc vs. D. The limit is estimated to be on the order of 200 kA/cm2 for multifilamentary Bi-2223 tapes, which was supported by magneto-optical (MO) magnetization measurements results. It is a hard task to approach this limit with the present state of the art in manufacturing Ag/Bi-2223 tape, and it is the time to suggest some new ideals for Bi-2223 tapes to promote large-scale applications. [ABSTRACT FROM AUTHOR]

The author’s recent studies on the critical current properties in Bi-2223 multifilamentary tapes as well as YBCO coated IBAD tapes have been reviewed. Extended electric field vs. current density (E–J) characteristics were studied over wide range of temperature, T, magnetic field, B, and angle, θ. Based on the analysis of statistic Jc distribution and scaling, we derived an analytical expression for J as a function of E, T, B, and θ. This method allows us to describe and extrapolate the nonlinear E–J characteristics even in extremely low E region and/or high B region based on rather simple measurements. [Copyright &y& Elsevier]

By dc magnetic measurements, we have confirmed the significant enhancement of vortex pinning by the fission-induced randomly oriented tracks in Ag–(BiPb)2Sr2Ca2Cu3O10 tapes. The flux motion is found to be quite different for the samples with and without fission tracks. A two dimensional vortex glass model is suggested to explain the nonexistence of “plateau” or “peak” in the temperature dependence of creep rate for the sample with fission tracks. This scenario is attributed to the combination of the crossing-track induced zigzag excitations and the high anisotropy of Bi-2223, and is proved to be reasonable by a good scaling considering a finite pinning correlation length. [Copyright &y& Elsevier]

The homogeneity of HTS tapes can be studied by measuring magnetic flux density maps with the Hall sensor magnetometer. The measurements are usually performed above samples carrying either the DC transport current or the remanence currents after switching off the transport current. In this paper time dependent maps above samples carrying AC transport current at 50 Hz are presented together with the DC and remanence maps. Several current amplitudes are used and measurements are repeated after drilling a hole into each sample. Finally, the applicability of the different types of maps to the homogeneity studies is discussed. [Copyright &y& Elsevier]

The measurement results of AC transport current losses in BSCCO/Ag tapes caused by AC transport currents and the simultaneously presented AC magnetic fields were reported. The measurements were carried out at 77 K and power frequency (50 Hz) for AC applied magnetic fields of 48, 80 and 120 mT, respectively. The angle between the direction of the magnetic field and the wide side of the tape varied from 0° to 90° with a step of 10°. Analyses on the angular dependency of the AC losses for BSCCO/Ag tapes were given. A theoretical model to describe the angular dependency of AC losses was proposed and compared with the experimental results. [Copyright &y& Elsevier]

Tokyo Electric Power Company and Sumitomo Electric Industries, Ltd. have been jointly developing elementary technologies for an high temperature superconducting (HTSC) cable system, such as conductor wound with HTSC wires, thermal insulation pipes, terminations and so on. Verification tests of a 100 m HTSC cable system integrating these elementary technologies have been conducted in collaboration with Central Research Institute of Electric Power Industry (CRIEPI) to verify its long term electric and cryogenic properties.The cable conductor is composed of four layers of Bi-2223 wires wound spirally around a former. Polypropylene laminated paper impregnated with liquid nitrogen is adopted as cable insulation for its properties of high insulation strength and low dielectric loss. HTSC wires are also wound around the electrical insulation to form an electrical and magnetic shield. To reduce heat invasion from ambient temperature part, multi-layer insulation is wound between the co-axial stainless corrugated pipes where high vacuum is maintained. The cable was partially installed into a ∅ 150 mm duct and formed in a U-shape. Each end has a splitter box and three terminations. The cable and the terminations are cooled using two separate sets of a pressurized and sub-cooled liquid nitrogen cooling system.The cable has been developed and laid at CRIEPI''s test site and long-term tests have been under way since June, 2001. This paper presents the design of the cable and some results of the first cooling tests. [Copyright &y& Elsevier]

We have started a project to develop a 100 m 3-core 66 kV/1 kA/114 MVA high temperature superconducting (HTSC) cable system to certify the manufacturing capability and the practicability of an HTSC cable system for use as actual power system equipment. The cable is designed based on the results of a 30 m, 3-core test cable. The cable is composed of a conductor and a shield wound with Ag–Mn sheathed Bi-2223 tapes, electrical insulation with polypropylene laminated paper impregnated with liquid nitrogen and thermal insulation with co-axial corrugated pipes. The three cores are housed in this thermally insulated pipe. The cable has been developed and laid at CRIEPIs test site and long-term tests have been under way since June. [Copyright &y& Elsevier]

A high temperature superconducting (HTSC) cable is expected to transport large electric power with a compact size because of its high critical current density. We have been developing a 3-core 66 kV class HTSC cable, which is applied to the ∅150 mm duct, and is composed of a conductor and a shield wound with Ag–Mn sheathed Bi-2223 tapes, electrical insulation with polypropylene laminated paper impregnated with liquid nitrogen and thermal insulation with co-axial corrugated pipes.A 30 m, 3-core cable system has been constructed to verify the 3-core performance after its production, laying and cooling. The cable had good performance to mechanical stress in the factory process. The critical current of the cable was more than 2.4 kA at 77 K. The AC loss of the conductor part was 0.5 W/m/phase at 1 kA rms, which agreed well with the calculated value of the spiral pitch adjustment technique. A 130 kV rms AC was successfully applied without any change in tanδ and capacitance. As a next step, a 100 m HTSC cable has been designed and developed based on these experimental results. [Copyright &y& Elsevier]