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A recently developed prototype (Laparoscopic Differential Magnetometer, in short LapDiffMag) identifies magnetic tracer accumulated inside sentinel lymph nodes (SLNs) during clinical laparoscopic procedures. The LapDiffMag relies on excitation of superparamagnetic iron oxide nanoparticles (SPIONs) and subsequent laparoscopic detection based on a nonlinear detection principle. The prototype uses an excitation coil to generate a magnetic field needed to activate SPIONs. This study reports on the process of developing a new excitation coil by describing the design choices based upon clinical requirements, by modeling delivered magnetic field using digital twin, and by comparing the magnetic fields of modeled and manufactured prototype. Digital twin technology was used to produce relevant and reliable data to demonstrate the safety and effectiveness of the excitation coil. The magnetic field originating from manufactured prototype was validated at two different heights above the excitation coil and have shown a good concordance to the data generated by its digital twin. Clinical Relevance- Current standard-of-care for a variety of tumor types consists of minimally invasive radical resection of primary tumor and regional lymph nodes (LNs). The newly introduced excitation coil will (after full validation) enable minimally invasive harvesting of sentinel LNs by means of magnetic tracer detection.

This pilot study explored the value of localized index node removal after neoadjuvant immunotherapy in patients with stage III melanoma, for use as a response indicator to guide the extent of completion lymph node dissection. Promising technology.

Superparamagnetic iron oxide nanoparticles (SPIONs) are promising for clinical applications, because they have a characteristic nonlinear magnetic response when an external magnetic field is applied. This nonlinearity enables the distinct detection of SPIONs and makes measurements less sensitive to the human body and surgical steel instruments. In clinical applications, only a limited field strength for the magnetic detection is allowed. The signal to noise ratios (SNRs) of four nonlinear magnetic detection methods are compared. These methods include differential magnetometry and three variations of magnetic particle spectroscopy: frequency mixing, second harmonic detection and third harmonic detection. All methods were implemented on the same hardware and experimentally compared for various field strengths. To make the comparison fair, the same power was supplied to the excitation coil each time. In general, the SNR increases with increasing field strength. The SNR per drive field of all methods stabilizes or even decreases for field strengths above 6 mT. The second harmonic detection has the best SNR and the most room for improvement.

Background Low oesophageal temperatures (OTs) during cryoballoon pulmonary vein isolation (PVI) have been associated with complications. This study assessed the incidence of low OT in clinical practice during cryoballoon PVI and verified possible predictive values for low OT. Methods Consecutive patients who underwent PVI using the second-generation cryoballoon were retrospectively included. The distance from the oesophagus to the different pulmonary veins (PVs) (OP distance), body mass index (BMI), sex, age, balloon temperature and application time were studied as potential predictors of low OTs. Computed tomography was performed before the procedure to determine the OP distance. OT was measured using an oesophageal temperature probe. Applications were ended prematurely if the OT reached Results Two hundred and four patients were included. Low OT was observed in 54 patients (26%) and 27 patients (13%) reached ultralow OTs. OP distance was the only predictor of low OTs after multivariate analysis. A cut-off value of 19 mm showed 96.2% sensitivity and 37.8% specificity in predicting low OTs. No clinically relevant relation was found between low OTs and BMI, age, sex, balloon temperature or application duration. Conclusions The incidence of low OT was 26% for cryoballoon PVI. OP distance was the only predictor of low OTs. Since an OP distance

Objectives Accurate tumour localisation is essential for breast-conserving surgery of non-palpable tumours. Current localisation technologies are associated with disadvantages such as logistical challenges and migration issues (wire guided localisation) or legislative complexities and high administrative burden (radioactive localisation). We present MAgnetic MArker LOCalisation (MaMaLoc), a novel technology that aims to overcome these disadvantages using a magnetic marker and a magnetic detection probe. This feasibility study reports on the first experience with this new technology for breast cancer localisation. Materials and methods Fifteen patients with unifocal, non-palpable breast cancer were recruited. They received concurrent placement of the magnetic marker in addition to a radioactive iodine seed, which is standard of care in our clinic. In a subset of five patients, migration of the magnetic marker was studied. During surgery, a magnetic probe and gammaprobe were alternately used to localise the markers and guide surgery. The primary outcome parameter was successful transcutaneous identification of the magnetic marker. Additionally, data on radiologist and surgeon satisfaction were collected. Results Magnetic marker placement was successful in all cases. Radiologists could easily adapt to the technology in the clinical workflow. Migration of the magnetic marker was negligible. The primary endpoint of the study was met with an identification rate of 100%. Both radiologists and surgeons reflected that the technology was intuitive to use and that it was comparable to radioactive iodine seed localisation. Conclusion Magnetic marker localisation for non-palpable breast cancer is feasible and safe, and may be a viable non-radioactive alternative to current localisation technologies.

Aim: Nodal status is the most important prognostic factor in colorectal cancer (CRC). Small occult metastases may remain undetected on conventional histopathological examination, potentially resulting in undertreatment. Ex vivo sentinel lymph node mapping (SLNM) can be used to improve nodal staging accuracy, but currently used tracers suffer from drawbacks, which hampers implementation of the technique in routine clinical practice. Magnetic tracers have an optimal size for sentinel lymph node (SLN) retention and allow objective quantitative selection of SLNs and therefore have great potential for SLNM in CRC. The study evaluates the feasibility of ex vivo magnetic SLNM and compares the performance of this technique to blue dye SLNM. Method: Twenty-eight ex vivo SLNM procedures were performed in 27 histological node-negative patients with CRC using a magnetic tracer and blue dye. A magnetometer was used to select magnetic SLNs after formalin fixation of the CRC specimen. Both magnetic and blue SLNs were subjected to serial sectioning and immunohistochemical staining to reveal occult metastases. Results: At least one SLN was successfully identified in 27/28 (96%) and 25/28 (89%) of the cases with the magnetic technique and blue dye. Isolated tumour cells were detected in 10 patients. This was predicted with 100% sensitivity and accuracy using the magnetic technique, and with 91% sensitivity and 96% accuracy using the blue dye technique. Conclusion: This study demonstrates that ex vivo magnetic SLNM is a feasible technique for use in routine clinical practice, which improves nodal staging accuracy of CRC patients.

Sentinel lymph node biopsy has become a staple tool in the diagnosis of breast cancer. By replacing the morbidity-plagued axillary node clearance with removing only those nodes most likely to contain metastases, it has greatly improved the quality of life of many breast cancer patients. However, due to the use of ionizing radiation emitted by the technetium-based tracer material, the current sentinel lymph node biopsy has serious drawbacks. Most urgently, the reliance on radioisotopes limits the application of this procedure to small parts of the developed world, and it imposes restrictions on patient planning and hospital logistics. Magnetic alternatives have been tested in recent years, but all have their own drawbacks, mostly related to interference from metallic instruments and electromagnetic noise coming from the human body. In this paper, we demonstrate an alternative approach that utilizes the unique nonlinear magnetic properties of superparamagnetic iron oxide nanoparticles to eliminate the drawbacks of both the traditional gamma-radiation centered approach and the novel magnetic techniques pioneered by others. Contrary to many other nonlinear magnetic approaches however, field amplitudes are limited to 5 mT, which enables handheld operation without additional cooling. We show that excellent mass sensitivity can be obtained without the need for external re-balancing of the probe to negate any influences from the human body. Additionally, we show how this approach can be used to suppress artefacts resulting from the presence of metallic instruments, which are a significant dealbreaker when using conventional magnetometry-based approaches.

Background A systematic review was undertaken to assess the clinical efficacy of non-invasive high-intensity focused ultrasound (HIFU) ablation in the treatment of breast cancer. Methods MEDLINE/PubMed library databases were used to identify all studies published up to December 2013 that evaluated the role of HIFU ablation in the treatment of breast cancer. Studies were eligible if they were performed on patients with breast cancer and objectively recorded at least one clinical outcome measure of response (imaging, histopathological or cosmetic) to HIFU treatment. Results Nine studies fulfilled the inclusion criteria. The absence of tumour or residual tumour after treatment was reported for 95·8 per cent of patients (160 of 167). No residual tumour was found in 46·2 per cent (55 of 119; range 17–100 per cent), less than 10 per cent residual tumour in 29·4 per cent (35 of 119; range 0–53 per cent), and between 10 and 90 per cent residual tumour in 22·7 per cent (27 of 119; range 0–60 per cent). The most common complication associated with HIFU ablation was pain (40·1 per cent) and less frequently oedema (16·8 per cent), skin burn (4·2 per cent) and pectoralis major injury (3·6 per cent). MRI showed an absence of contrast enhancement after treatment in 82 per cent of patients (31 of 38; range 50–100 per cent), indicative of coagulative necrosis. Correlation of contrast enhancement on pretreatment and post-treatment MRI successfully predicted the presence of residual disease. Conclusion HIFU treatment can induce coagulative necrosis in breast cancers. Complete ablation has not been reported consistently on histopathology and no imaging modality has been able confidently to predict the percentage of complete ablation. Consistent tumour and margin necrosis with reliable follow-up imaging are required before HIFU ablation can be evaluated within large, prospective clinical trials.

Contains fulltext : 191246.pdf (Publisher’s version ) (Open Access) BACKGROUND: Roentgen stereophotogrammetric analysis (RSA) is used to measure early prosthetic migration and to predict future implant failure. RSA has several disadvantages, such as the need for perioperatively inserted tantalum markers. Therefore, this study evaluates low-field MRI as an alternative to RSA. The use of traditional MRI with prostheses induces disturbing metal artifacts which are reduced by low-field MRI. The purpose of this study is to assess the feasibility to use low-field (0.25 Tesla) MRI for measuring the precision of zero motion. This was assessed by calculating the virtual prosthetic motion of a zero-motion prosthetic reconstruction in multiple scanning sessions. Furthermore, the effects of different registration methods on these virtual motions were tested. RESULTS: The precision of zero motion for low-field MRI was between 0.584 mm and 1.974 mm for translation and 0.884 degrees and 3.774 degrees for rotation. The manual registration method seemed most accurate, with mu

Objectives. To assess the feasibility of a new wearable, wireless ultrasonic device, the URIKA bladder monitor (UBM), in the detection of a full bladder in children with dysfunctional voiding (DV). Methods. This observational study included 14 children with DV who were subjected to an UBM monitoring session of 1.5-2 h. Transabdominal ultrasound (TUS) images were made as reference. The UBM measured the anterior-posterior bladder dimension by an ultrasound transducer, mounted in an elastic belt around the lower abdomen. Level of agreement between both methods was estimated by Bland-Altman analysis. Receiver operating characteristics (ROC) analysis was performed to determine a full bladder threshold for the studied population. Results. In 13 out of 14 patients, the UBM measured properly. Maximum bladder dimensions detected by the UBM and TUS were 6.69 ± 1.53 cm and 4.79 ± 0.99 cm respectively. Bland-Altman analysis showed a negative bias of -0.90 cm (limits of agreement: -4.1/+2.3 cm). ROC analysis resulted in a sensitivity and specificity of 78.3% and 100%, for a bladder dimension threshold of 5.03 cm. When this threshold was implemented a priori, the full bladder detection rate would have been 71%. In children younger than 10 years, this would be 100% (n = 5). Conclusion. The UBM is able to detect a full bladder with a detection rate of 71%, if a 5.03 cm threshold would be implemented. In patients younger than 10 years, the detection rate would be 100%. Future research will focus on increasing the UBM's accuracy and investigating the effect of UBM alarm treatment in children with urinary incontinence.

Superparamagnetic iron oxide nanoparticles (SPIONs) are used as a tracer material in sentinel node biopsies. The latter is a procedure to analyze if cancer cells have spread to lymph nodes, helping to personalize patient care. To predict SPION behavior in vivo, it is important to analyze their magnetic properties in biological environments. The superparamagnetic quantifier (SPaQ) is a new device to measure the dynamic magnetization curve of SPIONs. The magnetization curve was measured for two types of SPIONs: Resovist and SHP-25. We used three techniques: Vibrating Sample Magnetometry (VSM), Magnetic Particle Spectroscopy (MPS), and our new SPaQ. Furthermore, AC susceptibility (ACS) measurements were performed as part of the evaluation of the three techniques. SPaQ and VSM results were found to be similar. Measurement results were nearly identical in both directions, indicating minor hysteresis. However, in MPS measurements, a clear hysteresis loop was observed. Furthermore, the ACS measurements showed a pronounced Brownian maximum, indicating an optimal response for an AC frequency below 10 kHz for both particle systems. Both the SPaQ and MPS were found to be superior to VSM since measurements are faster, can be performed at room temperature, and are particularly sensitive to particle dynamics. The main difference between the SPaQ and MPS lies in the excitation sequence. The SPaQ combines an alternating magnetic field that has a low amplitude with a gradual DC offset, whereas MPS uses only an alternating field that has a large amplitude. In conclusion, both the SPaQ and MPS are highly suited to improve understanding SPION behavior, which will lead to the radical improvement of sentinel node biopsy accuracy.

BACKGROUND AND PURPOSE: Both hemodynamics and aneurysm wall thickness are important parameters in aneurysm pathophysiology. Our aim was to develop a method for semi-quantitative wall thickness assessment on in vivo 7T MR images of intracranial aneurysms for studying the relation between apparent aneurysm wall thickness and wall shear stress. MATERIALS AND METHODS: Wall thickness was analyzed in 11 unruptured aneurysms in 9 patients who underwent 7T MR imaging with a TSE-based vessel wall sequence (0.8-mm isotropic resolution). A custom analysis program determined the in vivo aneurysm wall intensities, which were normalized to the signal of nearby brain tissue and were used as measures of apparent wall thickness. Spatial wall thickness variation was determined as the interquartile range in apparent wall thickness (the middle 50% of the apparent wall thickness range). Wall shear stress was determined by using phase-contrast MR imaging (0.5-mm isotropic resolution). We performed visual and statistical comparisons (Pearson correlation) to study the relation between wall thickness and wall shear stress. RESULTS: 3D colored apparent wall thickness maps of the aneurysms showed spatial apparent wall thickness variation, which ranged from 0.07 to 0.53, with a mean variation of 0.22 (a variation of 1.0 roughly means a wall thickness variation of 1 voxel [0.8 mm]). In all aneurysms, apparent wall thickness was inversely related to wall shear stress (mean correlation coefficient, −0.35; P < .05). CONCLUSIONS: A method was developed to measure the wall thickness semi-quantitatively, by using 7T MR imaging. An inverse correlation between wall shear stress and apparent wall thickness was determined. In future studies, this noninvasive method can be used to assess spatial wall thickness variation in relation to pathophysiologic processes such as aneurysm growth and rupture.

Background The standard for sentinel lymph node biopsy (SLNB), the dual technique (radiolabelled tracer and blue dye), has several drawbacks. A novel magnetic technique without these drawbacks has been evaluated in a number of clinical trials. It uses a magnetic tracer and a handheld magnetometer to identify and excise sentinel lymph nodes. A systematic review and meta-analysis was performed to assess the performance and utility of the magnetic in comparison to the standard technique. Methods MEDLINE, PubMed, Embase and the Cochrane online literature databases were used to identify all original articles evaluating the magnetic technique for SLNB published up to April 2016. Studies were included if they were prospectively conducted clinical trials comparing the magnetic with the standard technique for SLNB in patients with breast cancer. Results Seven studies were included. The magnetic technique was non-inferior to the standard technique (z = 3·87, P < 0·001), at a 2 per cent non-inferiority margin. The mean identification rates for the standard and magnetic techniques were 96·8 (range 94·2–99·0) and 97·1 (94·4–98·0) per cent respectively (risk difference (RD) 0·00, 95 per cent c.i. –0·01 to 0·01; P = 0·690). The total lymph node retrieval was significantly higher with the magnetic compared with the standard technique: 2113 (1·9 per patient) versus 2000 (1·8 per patient) (RD 0·05, 0·03 to 0·06; P = 0·003). False-negative rates were 10·9 (range 6–22) per cent for the standard technique and 8·4 (2–22) per cent for the magnetic technique (RD 0·03, 0·00 to 0·06; P = 0·551). The mean discordance rate was 3·9 (range 1·7–6·9) per cent. Conclusion The magnetic technique for SLNB is non-inferior to the standard technique, with a high identification rate but with a significantly higher lymph node retrieval rate.

For small, early-stage or otherwise non-palpable breast tumors, surgeons rely on localization technologies to accurately find and remove the tumor tissue during breast conserving surgery. However, current widely accepted localization technologies either use painful and logistically challenging guidewires, or complex radioactive iodine sources. We have developed an implantable magnetic marker, intended to mark the location of a breast tumor, that can be detected during surgery using a clinical handheld magnetic susceptometry system. Here, we report on the development and optimization of this magnetic marker, focusing on the material, shape and various material assemblies. It was found that the effects of magnetic shape anisotropy may decrease localization precision. This can be circumvented by combining multiple isotropic magnetic elements separated from one another. A final optimized prototype was constructed and compared to a commercially available magnetic marker. Finally, the technology was tested in an ex vivo surgical setting on tissue to assess radiological visibility and surgical feasibility. The marker was successfully detected and removed in all ex vivo sessions, and the technology was found feasible.

Magnetic detection of sentinel lymph nodes using superparamagnetic iron oxide nanoparticles (SPIONs) is rapidly proving itself as a replacement technique for the logistically complex radioisotope-based standard of care.1 However, the SPIONs currently used in the magnetic procedure are chosen based purely on commercial availability. In this research, we evaluated three iron oxide based nanoparticles on both their magnetic characteristics and their performance in an in vivo porcine model, to illustrate that particle properties should be tailored for the application.

International audience; A European consortium has progressed towards elementary and assembled conductors viable for AC applications in the project ACropolis. The main goal was to achieve low AC losses and high critical current densities in tapes developed for AC coils, transformers and cables. In order to verify the performance of tapes an extensive characterization programme was carried out. The dependence of critical current and AC losses on the parameters of the tape manufacturing process were scrutinized. Furthermore, SEM-EDX and DTA/TG analyses were performed to study the material microstructure, and the diffusion coefficient of oxygen through different matrix metals was measured. The homogeneity of the tapes was verified with magnetic knife and Hall sensor experiments. Transport current measurements were performed at different mechanical stress conditions and also the distribution of critical current along long tapes was determined with a quasi-continuous four-point measurement. The results confirmed that the low AC loss conductors can be produced on an industrial scale and they are competitive in power engineering applications.

We have developed an instrument to study the behavior of the critical current density (Jc) in superconducting wires and tapes as a function of field (μ0H), temperature (T), and axial applied strain (ea). The apparatus is an improvement of similar devices that have been successfully used in our institute for over a decade. It encompasses specific advantages such as a simple sample layout, a well defined and homogeneous strain application, the possibility of investigating large compressive strains and the option of simple temperature variation, while improving the main drawback in our previous systems by increasing the investigated sample length by approximately a factor of 10. The increase in length is achieved via a design change from a straight beam section to an initially curved beam, placed perpendicular to the applied field axis in the limited diameter of a high field magnet bore. This article describes in detail the mechanical design of the device and its calibrations. Additionally initial Jc(ea) dat...

The large currents in the cable-in-conduit conductors (CICC) destined for the high field magnets in the International Thermonuclear Experimental Reactor (ITER), cause huge transverse forces on the strands compressing the cable against one side of the conduit. This load causes transverse compressive strain in the strands at the crossovers contacts. Moreover, the strands are also subjected to bending and contact surfaces micro-sliding, which results into friction and anomalous contact resistance versus force behavior. Three Nb/sub 3/Sn central solenoid model coil (CSMC) conductors were tested previously in the Twente Cryogenic Cable Press up to 40 cycles with a transverse peak load of 650 kN/m. This press can transmit a variable (cyclic) transverse force directly to a cable section of 400 mm length at a temperature of 4.2 K (or higher). To explore life-time cycling, we tested a CSMC Nb/sub 3/Sn conductor up to 40,000 cycles. The coupling loss and the associated interstrand resistance between various strands and strand bundles are measured at various loads. The force on the cable and the displacement are monitored in order to determine the effective cable Young's modulus and the mechanical heat generation. Some aspects of strand deformation in CICC's are discussed. The test results are discussed in view of previous press results and data extracted from the ITER model coil tests.

Scaling of the pinning force (Fp ) with temperature, field and strain for Nb 3 Sn wires is widely discussed but important issues are still unresolved, for example whether empirical engineering-oriented scaling functions can be replaced by more microscopic, physics-based models, which take account of the fact that Fp becomes zero at an irreversibility field (H*) less than the upper critical field (Hc2). In the present work we compare earlier extensive measurements of the critical current density (Jc ) of an ITER-benchmark bronze wire to new measurements of H* and Hc2 . Our study was also made in different strain states. We observe that the Kramer extrapolations, which are based on transport data taken up to 13 T, significantly overestimate the low temperature, high field behaviour and also underestimate the critical temperature (Tc ) at zero field. An attempt is made to connect measured Hc2 (T, ε) data on this practical conductor to microscopic theory. We also discuss the inevitable differences that occur between fully penetrated Jc data which average over all the A15 layers and small current-density probes of the Hc2 transition which are characteristics of the best part of the layer. We connect in this way the large-scale 'average' characteristics Jc (H, T, ε) to small current 'best' characteristics of Hc2 (T, ε).

A method to calculate the AC loss of superconducting power devices from the measured AC loss of a short sample is developed. In coils and cables the magnetic field varies spatially. The position dependent field vector is calculated assuming a homogeneous current distribution. From this field profile and the transport current, the local AC loss is calculated. Integration over the conductor length yields the AC loss of the device. The total AC loss of the device is split up in different components. Magnetization loss, transport current loss and the loss due to the combined action of field and current all contribute to the AC loss of the device. Because ways to reduce the AC loss depend on the loss mechanism it is important to know the relative contribution of each component. The method is demonstrated on a prototype transformer coil wound from Bi/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub x//Ag superconducting tape. Differences between the model assumptions and devices are pointed out. Nevertheless, within the uncertainty margins the calculated AC loss is in agreement with the measured loss of the coil.

The development of a 25 T superconducting magnet is usually envisioned with the use of an innermost coil wound with high-temperature superconductor (HTS) material. At present, Bi2Sr2CaCu2Ox and Bi2Sr2Ca2Cu3Ox (BSCCO) conductors are the only candidate conductors available with sufficient length and current carrying capability. Unlike NbTi and Nb3Sn conductors, the BSCCO crystal structure and thus properties are strongly anisotropic. In conductor form, various degrees of anisotropy occur. It is often assumed that this anisotropy simply implies that radial field components must be minimized. We show that this assumption can be misleading. Using the average grain colony misalignment angle to parameterize the anisotropy, three regimes are distinguished in the relationship between average grain colony misalignment and critical current limiting field components. The implications of these separate regimes on the design process for 25 T superconducting magnet design are discussed.

Hysteresis loss is an important factor when the performance of superconducting electric power devices is evaluated. The non-ideal voltage–current relation in Bi2Sr2Ca2Cu3Ox/Ag conductors is one of the reasons that critical state based loss relations do not accurately predict the AC loss in these conductors. In this paper the influence of the magnetic field dependent voltage–current relation on the hysteresis loss is discussed. An analytical high-field approach is used to demonstrate the effect of the finite steepness of the voltage–current relation on the induced current. Besides, a numerical technique is used to calculate also for applied magnetic fields below the penetration field the influence of both a field dependent critical current density and a field dependent steepness of the voltage–current relation. Both the magnitude of the hysteresis loss and the field dependence of the loss are influenced by the voltage–current relation. Especially for small applied fields the field dependence of the loss deviates from the cubic dependence that is predicted by the critical state model based relations. Results of calculations are compared with measured data. An intrinsic critical current density vs. magnetic field relation is determined in order to obtain agreement between measurements and calculations.

Multi-core Bi-2223/Ag tapes with various number of filaments (21–162), different filament architecture and their changing orientation to the tape plane have been made by the tape-in-rectangular tube (TIRT) process. The transport current properties of TIRT tape samples with “parallel” and “perpendicular” filaments have been measured. The transversal Ic distribution obtained by spatially resolved transport measurements (“magnetic knife”) measurement illustrates that filament quality of TIRT tapes is better at the tape edges as in its centre. The Ic degradation due to bending shows a different behaviour for parallel and perpendicular filaments which is attributed to the difference in filament density and crack propagation.

It is well known that the critical field, -temperature and -current of Nb3Sn superconductors are very sensitive to deformations. In 1994 a new, three-dimensional (3D) model was presented, which accurately describes the behavior of the critical parameters with respect to strain, the so-called deviatoric strain description. In the following years an extensive number of Nb3Sn samples have been investigated, which resulted in a revised, unifying scaling relation for the critical current in Nb3Sn conductors as a function of field, temperature and strain, which included the 3D deformation model. Application of this scaling relation to all available data has confirmed the validity of the deviatoric strain description for various types of Nb3Sn conductors investigated in many experiments. A detailed explanatory review of the deviatoric strain description is presented and an update is provided on the latest results.

To better understand the dominant mechanisms that limit the critical current density in high temperature superconductors, the dependence of the critical current density on magnetic field and temperature of Bi2Sr2Ca2Cu3Ox tapes is measured in magnetic fields up to 8 T and temperatures between 4.2 and 100 K. The results were modeled by describing the current in the tape as two parallel current paths. The critical current density of one path is limited by weak links and that of the other path by intragranular flux pinning. The temperature dependence of the parameters used in the model indicates that the weak link contribution vanishes at a temperature of 86 K. This is an indication that the weak link behavior is dominated by a remnant Bi2Sr2CaCu2Ox phase. At higher temperatures the critical current density of the tape is limited by intragranular pinning.

The dynamic resistance loss, DC transport current combined with external AC magnetic field, in a Bi2Sr2Ca2Cu3O10/Ag superconducting tape is measured as a function of the orientation of the external AC magnetic field. We investigate the possibility of describing the AC transport current loss in an externally applied AC magnetic field from the much simpler dynamic resistance measurement. The orientation angles of the magnetic field with respect to the plane of the tape are changed from 0° (perpendicular configuration) to 90° (parallel configuration). The angular dependence of the dynamic resistance energy dissipation is described with an empirical formula. It is very similar to the angular dependence observed for the hysteresis loss. The dynamic resistance in parallel and perpendicular applied magnetic field is fairly well described with theoretical predictions based on the critical state model. The increase of the AC transport current loss due to a simultaneously applied AC magnetic field is described quite well with the dynamic resistance in the fully saturated state.

We investigated the local J/sub C/ and microstructures of Bi-2212 multilayer tapes. Multilayer tapes were prepared by wrapping four dip-coated sheets with silver foil. These tapes were fabricated with a melt-solidification method with a Pre-Annealing and Intermediate Rolling (PAIR) process. The local J/sub C/ distribution along the transverse direction of the tapes was determined in a nondestructive manner in which a magnetic field with a steep gradient was applied at 77 K, and the I/sub C/ was measured. The microstructures of the superconducting oxide layers were observed by using an optical micrograph and an SEM micrograph. Bi-2212 superconducting oxide layers existed on silver substrates homogeneously, and the silver/oxide interfaces were almost smooth along the silver substrates. From the J/sub C/-profile, J/sub C/ values at the middle region on the tape were low in comparison with the J/sub C/ values in the edge regions. The depression of the J/sub C/ values around the middle region was due to the overlapping of silver foil and, hence, the inferior microstructure.

Multifilamentary Bi2223 tapes are exposed to the longitudinal magnetic field as well as the transverse one in some electrical power apparatuses such as multilayer power transmission cables. Here, we define the longitudinal and transverse magnetic fields as the field components parallel and perpendicular to the tape axis, respectively. If the filament-bundle is twisted, it can couple to the AC longitudinal magnetic field to generate the longitudinal magnetization loss. Furthermore, the AC transport current flowing spirally in the twisted filament-bundle possibly influences the longitudinal magnetization. The longitudinal magnetization loss was measured in a twisted multifilamentary Bi2223 tape exposed to longitudinal magnetic field and carrying the transport current. The measured longitudinal magnetization loss in the twisted tape exposed to the longitudinal magnetic field is larger than that in another untwisted tape. Supplying the AC transport current changes the longitudinal magnetization loss in the twisted tape exposed to the AC longitudinal magnetic field. The influence of the transport current depends on the phase relation between the longitudinal magnetic field and the transport current. If their phase difference is 0°, the longitudinal magnetization loss decreases remarkably with increasing amplitude of the transport current. It means that the change in the current distribution due to the transport current results in the decrease in the power flow from the magnet power supply. But, a preliminary measurement of the transport loss shows that the total loss increases with increasing transport current.

For the optimisation of a magnet design with cable-in-conduit conductor (CICC) technology it is essential to comprehend the scaling of the critical current from the separate strand characteristics to the finally assembled cable performance in a coil. Several model coils have been tested in the framework of research for the International Thermonuclear Experimental Reactor (ITER). At present, the scaling of the critical current from the strand to the full cable performance and the apparent decrease of the n-index from strand to cable in the voltage–current curves is not understood. It is important to recognize the mechanisms behind this phenomenon in relation to the cost of the superconducting strand, which is significant in the manufacture of the magnets. Therefore, basic phenomena like the cable conductor self-field, the current unbalance introduced by the non-uniformity of the joints and a possible reversible or irreversible degradation of the voltage current characteristic of a strand during cable manufacture or electromagnetic loading of the magnet have to be considered. The voltage–current characteristic of the strand is extensively explored for the relevant range of magnetic field, temperature and axial strain space. Accordingly a numerical six-element network model is developed to simulate the conditions and behaviour of the last stage cable elements of a full-size ITER conductor. The experimental data, mainly in terms of voltage–current (VI) or -temperature (VT) characteristics, are obtained on the central solenoid insert coil (CSIC) experiment performed in Naka (Japan) in the framework of the research for ITER. The numerical model, which is briefly introduced, is used to study the cable performance by using experimentally obtained cable parameters like inter-strand (and bundle) contact resistance, strand critical current data as a function of magnetic field, temperature and applied axial strain, and external cable self-field measurements by Hall sensors for reconstruction of the current non-uniformity. The effect of a current redistribution due to the cable self-field on the voltage–temperature curve is calculated in correlation with the transverse resistance between the strands and last cabling stage bundles (petals). A realistic unbalanced current distribution is established by introducing non-uniform joints at the extremities of the CS-insert cable. It appears that the cable self-field effect hardly gives any change in the shape of the VT curve but merely a shift towards lower temperature giving a reduction of the current sharing temperature Tcs (10 μV/m) of

The magnetisation loss in multifilament HTS tape superconductors can be reduced by twisting the filaments and increasing the matrix resistivity. In this paper the influence of filament twist on the coupling current loss of the tape is studied. Magnetisation measurements on multifilament Bi2223 tape conductors with different twist pitches are performed at 77 K in magnetic field applied parallel and perpendicular to the wide face of the conductor. Both frequency and magnetic field amplitude are varied. In perpendicular magnetic field the filaments are fully coupled. In parallel magnetic field the twisted filaments are decoupled, even for twist pitches around 10 mm and a pure silver core. However, for increasing magnetic field >0.04 T, the influence of the coupling current loss increases. The transition to full coupling and the coupling current loss are analysed with an existing analytical model for a tape superconductor.

Bi2Sr2Ca2Cu3Ox/Ag tape superconductors are used in applications like power cables and transformers. In these applications the superconductor is exposed to an alternating magnetic field that has different orientations with respect to the tape surface. In this paper the angle dependency of the magnetisation loss is considered from two points of view. First the measurement technique with pickup coils is analysed theoretically. Measured magnetisation loss in uni-directional magnetic field with various orientations and rotating magnetic field are compared. When the orientation is changed from perpendicular (0°) to parallel (90°) applied magnetic fields, the contribution of the perpendicular field component to the magnetisation loss is dominant up to 60°. A new model to describe the angle dependency of the magnetisation loss, based on the measured loss in perpendicular and parallel magnetic field is developed. Deviations between models and the measured loss are explained with the help of the theoretical analysis of the measurement technique. The new model is not only applicable for the magnetisation loss but also for other AC loss components.

A model to describe the angular dependence of the critical current of a superconducting Bi-2223/Ag tape is developed. The model is based on a Gaussian distribution of the misalignment angles of the grains. With this model it is possible to calculate the standard deviation of the misalignment angle of the grains from critical current measurements in a magnetic field oriented perpendicular and parallel to the tape plane. This enables us to determine the critical current behaviour for all orientations of the magnetic field. The theory is confirmed in an experimental way. The angular dependence of the critical current of the measured tape can be described at 77 K in the region between 0 and 200 mT within 3% by using a standard deviation of 7.8° in the misalignment angle.

A high quality factor, superconducting resonator coil is developed in cooperation with the Dutch companies SMIT Transformers and SMIT DRAAD. The coil system is manufactured in industry, using industrial tooling. It has a design reactive power rating of 1 MVA at a frequency of 50 Hz and the operating temperature is 64 K. The system consists of four concentric but separate coils, made of 2 km of Bi-2223 conductors from two different manufacturers. The coils are optimized by shaping the magnetic field around the coil edges with ferro-magnetic C-cups to reach a design electrical quality factor of 1000. The system is operated in a glass-epoxy cryostat at 64 K and 77 K. The resonator coil design demonstrates all the superconducting elements that are essential for manufacturing superconducting transformers. A numerical model has been developed to predict the DC and AC behavior of the system based on measurements of short samples and test coils. A comparison is made between the experiment and model calculations.

The I-V curves of Bi-Sr-Ca-Cu-O superconductors were measured in DC magnetic fields, oriented both parallel and perpendicular to the tape surface, up to 33 T, 4.2 K, in resistive magnets at the National High Magnetic Field Laboratory. This paper presents the experimental set-up, results of critical current measurements, and an analysis of the obtained I/sub c/(B) curves in terms of strongly and weakly linked current paths. A distinct double-step behavior is observed for field perpendicular to the tape surface. The scaling behavior of the applied field with its component perpendicular to the ab-plane, and the implied average grain-misalignment angle, is investigated.

The quality of the magnetic field in superconducting accelerator magnets is associated with the properties of the superconducting cable. Current imbalances due to coupling currents /spl Delta/I, as large as 100 A, are induced by spatial variations of the field sweep rate and contact resistances. During injection at a constant field all magnetic field components show a decay behavior. The decay is caused by a diffusion of coupling currents into the whole magnet. This results in a redistribution of the transport current among the strands and causes a demagnetization of the superconducting cable. As soon as the field is ramped up again after the end of injection, the magnetization rapidly recovers from the decay and follows the course of the original hysteresis curve. In order to clarify the interactions between the changes in current and magnetization during injection the authors performed a number of experiments. A magnetic field with a spatially periodic pattern was applied to a superconducting wire in order to simulate the coupling behavior in a magnet. This model system was placed into a stand for magnetization measurements and the influence of different powering conditions was analyzed.

Potentially, coils made with BSCCO-2223/Ag tape and operating in liquid nitrogen at 50-60 Hz are interesting for power related applications. The electrical characteristics of such a coil depend on the radial magnetic field in the windings. One way to suppress the radial field is by placing small iron pieces around coil edges. V-I curves of the 100 kVA coil are calculated and measured for two cases: coil edges without and with iron pieces. The coil is a solenoid with inner and outer diameters and a height of 470, 474 and 614 mm respectively. A numerical model adapted to the coil geometry is used to calculate the conductor losses. The loss voltage is also evaluated by measuring the coil temperature. The total loss of the coil is measured electromagnetically. Calculated and measured losses are in agreement. Finally, the loss V-I curves of the coil are simulated in the frequency range of 0 to 400 Hz. The results are applied to the design of a 1 MVA resonator coil.

In order to improve the understanding of the dominant mechanisms that limit the critical current in high temperature superconductors, the dependence of the critical current on magnetic field and temperature of a Bi/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub x/ tape has been investigated in detail. The critical current is measured in magnetic fields up to 8 T, at temperatures ranging from 4.2 K to 70 K. The results are compared with existing models that describe the current path as two parallel systems, one depending on weak links and the other on flux pinning. The critical current at low magnetic fields is reduced drastically by the self-field of the superconductor. At intermediate magnetic fields, the field dependence of the critical current is mainly dominated by weak links, while at higher fields it is dominated by the strong-links current path, and depends on flux pinning. To clarify the models used to describe the measurements, the temperature dependence of the parameters used in the models is studied. The temperature dependence of the parameters used to describe the weak-links current path points out that the weak links are formed by remnant Bi/sub 2/Sr/sub 2/Ca/sub 1/Cu/sub 2/O/sub x/ phase at the grain boundaries.

An engineering function to describe the AC loss of BSCCO/Ag tape conductors is developed. For a wide range of transport currents and magnetic fields (with different orientation) the loss is described with an uncertainty of 10%. The equation is based on the analytical expressions available, BSCCO/Ag tapes used in power applications at liquid nitrogen temperature are fed with an AC transport current and exposed to an AC magnetic field. The magnetic field in a device has different orientations with respect to the position of the conductor in the device. In this contribution, AC loss measurements for simultaneously applied magnetic field (with different orientation) and transport current are presented for a high quality tape conductor that is used in a transformer coil. The results are separated into a magnetic and a transport current loss component.

Magnetisation loss is an important factor in the design of superconducting transformers and motors. In these devices the tapes are usually placed face-to-face. Then the magnetisation loss is influenced by the mutual magnetic shielding between adjacent tapes. The shielding is investigated by measuring the magnetisation loss in stacks with various numbers of Bi-2223 tapes, exposed to a 48-Hz perpendicular magnetic field at 77 K. In a stack the penetration field is increased and the magnetisation loss below penetration is greatly decreased, compared to the behaviour of a single tape. The loss at high magnetic-field amplitudes is unaffected. The measured loss is compared to the loss calculated with two different models. The effect of shielding is qualitatively well described with an analytical model. However, predictions made with a numerical model display a better quantitative agreement with the measurement results.

We focus on a react and wind Bi-2223 conductor with a pure silver matrix. The stress–strain–critical current relation is determined for coils with a uniform stress distribution, at 4.2 K and 19 T. Somewhat surprisingly, the coils fail at a Lorentz force induced strain value close to the value for uni-axially loaded straight samples. This implies that bending strain is only partially retained due to the plastic nature of the pure silver matrix. Also, a double-pancake coil with a 15 mm winding thickness, resulting in a non-uniform stress distribution, is tested at 4.2 K and 19 T. The coil current is cycled with increasing peak values and the onset and evolution of critical current degradation in the coil is shown.

Transformers, motors and magnets based on Bi-2223 tapes have an optimum working temperature where the sum of investment and exploitation costs has a minimum. The investment cost is lower at temperatures below 77 K due to the higher critical current of the superconductor. The exploitation cost is mainly determined by the ac loss, which is dominated by the magnetization loss. The magnetization loss of a Bi-2223 tape at 48 Hz is measured for various temperatures between 65 and 77 K. The temperature dependence of the magnetization loss is fully explained by the change in critical current and agrees with the critical-state model. At high magnetic-field amplitudes the magnetization loss normalized with the critical current is independent of the temperature. Nevertheless, at lower temperatures the exploitation cost is higher due to the higher cooling penalty factor. A relation for the optimum temperature is developed, based on realistic expressions for the cooling penalty factor and the critical current as a function of the temperature. The influence of the other relevant parameters is summarized into a single dimensionless number. It is concluded that the optimum temperature of a power device based on Bi-2223 tapes is in the range 65-75 K.

Testbeds for quality measurements on superconducting materials and cables have been developed in collaboration between industry and research institutes. The work is focused on the latest generation of BiSrCaCuO (Bi-2223) powder-in-tube superconductors, which is the only material that is utilized in various demonstrator cable projects around the world. The results of the project are separated into three parts: an in-process critical current testbed, the development of an ac-loss testbed for single tapes and ac-loss measurement systems for cables. Based on the design studies and the experimental results that were obtained with these demonstrators, conclusions are drawn and formulated as recommendations for the development of written standards on measuring methods for superconducting materials and cables.

When a multi-filamentary superconductor is exposed to an alternating external magnetic field, coupling-current loss is a significant part of the magnetization loss. The coupling-current loss at low magnetic-field frequencies is determined by the effective transverse resistivity of the inner filamentary region. The effective resistivity is calculated for various shapes and structures of the inner filaments. Bi-2223/Ag tapes typically have filaments with a high aspect ratio, causing an anisotropic transverse resistivity. When there is no contact resistance between the filaments and the matrix material, the presence of the filaments decreases the effective resistivity. The decrease is greatest for overlapping filaments whose wide sides are oriented parallel to the external magnetic field. Good insulating barriers result in a high contact resistance from the filaments to the matrix. Then the effective resistivity is greatly increased, especially for overlapping filaments that are oriented perpendicularly to the magnetic field. The results are relevant for the calculation of the coupling-current loss in Bi-2223 tapes with twisted filaments.

AC coils made with BSCCO-2223/Ag tapes and operating in liquid nitrogen have a potential for power related applications, e.g., inductors, transformers and current limiters. High-T/sub c/ tapes are available from several producers, while access to the coil building know-help is still rather limited, The relevant knowledge and technology suitable for making HTS coils for 50-60 Hz operation is being developed as a part of the current project. To verify the technology, several test solenoids and a first full-scale sub-coil have been manufactured. Electromagnetic, thermal and mechanical analysis of the coils is performed. The electromagnetic analysis focuses on the reduction of the radial magnetic field component in the windings. Voltage-current characteristics and the AC loss data obtained from relevant short sample measurements are applied. A good agreement between calculated and measured V-I curves and losses of the coils is found. A remarkable increase of the critical current and the reduction of the AC loss at the coil edges are predicted and confirmed experimentally. With the losses defined, thermal analysis and optimization of the coil structure are performed numerically followed by measurements for verification. The paper reports on the series of coils developed and explains the features of the project.

At high amplitudes and frequencies of the external magnetic field, the superconducting filaments in a composite conductor are fully coupled. This causes a high magnetisation loss. Methods to decouple the filaments are well known for the low-Tc superconductors and have recently been applied also to high-Tc composites. In this paper, expressions are derived for the magnetic-field amplitude and frequency where full coupling sets in, as well as for the twist length required for decoupling the filaments in a general rectangular composite. A comparison is made with other expressions found in the literature. The filaments in a typical Bi-2223/Ag tape in parallel magnetic fields are decoupled just by twisting. In perpendicular fields a high transverse resistivity is required to decouple the filaments and decrease the magnetisation loss.

The transport properties of superconductors are commonly characterized by means of a 4-probe measuring technique and the critical current is determined on a certain criterion for the electrical field. An alternative method to investigate the transport properties is to measure the magnetic response of a superconductor in a changing magnetic field. This magnetic technique has the interesting advantage that it can be used to investigate long lengths of (insulated) conductor. A detailed analysis is made to develop a reliable measuring procedure for this new test facility. The magnetic response of a superconductor is modeled in a description for an infinitely long tape with a rectangular cross-section and an arbitrary voltage-current relation. The calculated magnetic profiles, in space and time, are compared with experimental results at 77 K. It is demonstrated that the magnetic signal can be used to monitor the quality of a long length of tape (>500 m) with a high accuracy. Additionally it is shown that the shape of the voltage-current relation can be reconstructed based on the frequency dependence of the magnetic response.

The three dimensional surface of the critical current density versus field and temperature J/sub c/(B,T) of niobium-tin is a function of the strain state of the superconductor. A brief review of literature on this subject is presented. The J/sub c/(B) function is described by the relations for flux pinning. The temperature and strain dependencies are added to this relation, This results in a unifying scaling law for A15 materials, which is verified for different niobium-tin conductors with respect to all the relevant variables, i.e. field, temperature and uni-axial strain. Nb/sub 3/Sn conductors from 9 manufacturers are measured in the frame work of the third ITER benchmark tests on critical current. The investigated ranges are: applied field from 7 to 13 T, temperature from 4.2 to 8 K and applied strain from -0.4 to +0.8%. Special attention is paid to the region of compressive axial strain, which is the most relevant state of strain for superconductors under thermal compression in practical applications.