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The Pulsed Field Facility (PFF)- National High Magnetic Field Laboratory (NHMFL) in Los Alamos, New Mexico has developed and operated a several types of ultra-high field pulsed magnets, including 100 T Multi-shot, 60 T Long Pulse, and an array of small 65 T magnets for users. Separately powering (nested) coils allows to both reduce the driving voltages and have a further degree of control over the pulse duration and therefore the current carrying capacity in conductor to maximize the produced magnetic fields. Duplex design with two nested coils powered separately by two capacitors has been used at several pulsed field centers to increase the generated magnetic field. In the last year, PFF-NHMFL focused on developing such a magnet to generate maximum magnetic field up to 77 Tesla using existing 4 MJ capacitor bank. The magnet is expected to provide 75 tesla magnetic field during regular operation. A Metal Oxide Varistor (MOV) bank is used to protect the capacitor bank and its associated electrical components from the overvoltage in the case of a fault happening in the duplex magnet. This paper will outline the design, construction and operation of that magnet and the MOV bank.

Ultra-high field pulsed magnets must simultaneously satisfy a number of often competing electrical, electromagnetic, structural, thermal, and economic constraints. To produce the highest field possible, nondestructive pulsed magnets are designed to operate at the limits of mechanical strength and electrical capacity of conductors. In this presentation, we will introduce a coupled multi-engineering finite element method (FEM) implemented in COMSOL Multiphysics package for detailed and accurate calculations of the mechanical, thermal and electromagnetic performances in entire longitudinal cross-section of the pulsed magnet. These transient FEM simulations are performed for entire pulse length and take into account the temperature and magnetic field dependences of electrical conductivity and mechanical properties of all the materials to provide better accuracy. Application Programming Interface (API) feature of COMSOL was used to automate repetitive modeling steps to significantly reduce the necessary time to create FEM models for a pulsed magnet which may consists up to thousands of turns and insulation/reinforcement layers. Computational results for our signature 100T non-destructive pulsed magnet will be presented.

Extreme pressures and high magnetic fields can affect materials in profound and fascinating ways. However, large pressures and fields are often mutually incompatible; the rapidly changing fields provided by pulsed magnets induce eddy currents in the metallic components used in conventional pressure cells, causing serious heating, forces, and vibration. Here, we report a diamond-anvil-cell made mainly out of insulating composites that minimizes inductive heating while retaining sufficient strength to apply pressures of up to 8 GPa. Any residual metallic component is made of low-conductivity metals and patterned to reduce eddy currents. The simple design enables rapid sample or pressure changes, desired by pulsed-magnetic-field-facility users. The pressure cell has been used in pulsed magnetic fields of up to 65 T with no noticeable heating at cryogenic temperatures. Several measurement techniques are possible inside the cell at temperatures as low as 500 mK.

Ultra-high field the pulsed magnets are usually designed as a group of nested, concentric coils driven by separated power sources to reduce the required driving voltages and to distribute the mechanical load. Since the magnet operates in a fast transient mode, there will be strong and complicated electromagnetic couplings between the component coils. The high eddy currents generated in the reinforcement shells of the component coils during the pulses also strongly affect these couplings. Therefore, understanding the electromagnetic interaction between the component coils will allow safer, more optimized design and operation of our magnets. This paper will focus on our finite element modeling and experimental results for the electromagnetic interactions between the component coils of the 100-T nondestructive magnet and 80-T duplex magnet at our facility.

A free electron laser (FEL) can be used to produce high intensity X-rays, or other monochromatic radiation for a number of purposes. Two primary components, in terms of size and expense, of an FEL system are an electron accelerator and undulator. Reducing undulator period without reducing its magnetic field would allow a reduction in the electron beam energy and potentially reduce the total cost and complexity of FELs. In this paper, finite-element modeling and experimental approaches were used to investigate the feasibility of using high-temperature superconducting (HTS) conductor to create tunable, liquid nitrogen cooled undulators with shorter periodicity. A prototype undulator with three periods was fabricated and tested. Hiperco 50 A structures with machined grooves were used as the magnetic cores. Commercial YBCO tapes were used to wind the magnetizing coils in the grooves of the magnetic core. The undulator was tested and measured in subcooled liquid nitrogen at 65 K. Peak magnetic fields of 0.77 T with a periodicity of 14 mm were attained. Our simulations indicate that by using optimally processed magnetic core and HTS wires, fields of 1 T or higher can be achieved.

A versatile experimental facility was designed and set up to measure transport ac losses, magnetization ac losses, and total ac losses in high-temperature superconductors at variable temperatures. Several sets of measurements were carried out in the temperature range of 35 K to 100 K. Sample temperature during the measurements could be controlled within plusmn0.5 K of set temperature. Temperature dependence of transport losses reflects variation of critical current density of the tapes with temperature. Temperature dependence of magnetization losses exhibits an interesting behavior with a peak, whose position shifts to lower temperatures as the magnetic field is increased. Experimental data of ac losses at various temperatures are compared with those calculated using numerical methods. Generally, the simulated results reproduce well the experimental data.

Alternating current (ac) loss and quench behavior measurements were performed on a YBa2Cu3Ox coated conductor at 45 K. The minimum quench energies (MQEs) and the quench propagation velocities were measured as a function of transport current and frequency. AC losses were measured at the corresponding temperature and frequencies to quantify the internal thermal load during ac quench measurements. It was found that the direct current (dc) and ac quench behavior are similar, but that the MQE for dc experiments is higher than the corresponding ac cases. This difference is not seen in the normal zone propagation velocity data, indicating that the difference in MQE is minimal if the ac losses are included in the energy calculation. The ac experiments show that the MQE and propagation velocity varies weakly with frequency.

The design of a versatile ac loss and stability characterization facility for high temperature superconducting materials suitable for variable temperature measurements is described. A non-metallic vessel inside a transverse field double-helix magnet acts as the measurement chamber. A cryocooler cools the samples to a target measurement temperature between 35 and 80 K. The facility is suitable for measurements on samples as long as 15 cm with ac transport current and ac background magnetic field, both at variable frequency. The facility allows for sample rotation to vary its orientation with respect to the magnetic field. Initial temperature measurements showed that the sample could be maintained at uniform temperature to plusmn0.5 K. AC loss measurements performed on a precursor setup, identical in concept, confirmed the suitability of the double-helix magnet design and cryocooler based cooling arrangement.

Total AC losses in multi-filamentary, silver-sheathed Bi/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub y/ (Bi-2223) tape were measured as functions of transport current, applied magnetic field and frequency by electromagnetic and calorimetric methods. Results of both methods agree well with each other. The calorimetric method was employed to investigate the effect of the phase difference between transport current and applied field, /spl Delta//spl phi/, on total AC loss. Total loss changes significantly with /spl Delta//spl phi/ when applied magnetic field is perpendicular to the surface of the sample. The effect of /spl Delta//spl phi/ on total loss in parallel magnetic applied field is smaller.

Practical applications of HTS tapes cannot avoid various stresses and strains, including tension, bending and/or torsion. These loads directly affect the critical current and AC losses of HTS tapes. Thus the investigation of the effect of stress/strain on HTS tapes is important for practical applications. Here, the critical currents and AC losses are measured at 77 K for different Bi2223/Ag composite tapes under different room temperature stress/strain. The strain dependence of the critical currents and AC losses of Bi2223/Ag composite superconducting tapes are studied. A comparison is given for the measured results and the values calculated from the formulae developed from the Norris formula and critical current-strain relationship.

Numerical modeling of superconductors is widely recognized as a powerful tool for interpreting experimental results, understanding physical mechanisms and predicting the performance of high-temperature superconductor (HTS) tapes, wires and devices. This is especially true for ac loss calculation, since a sufficiently low ac loss value is imperative to make these materials attractive for commercialization. In recent years, a large variety of numerical models, based on different techniques and implementations, have been proposed by researchers around the world, with the purpose of being able to estimate ac losses in HTSs quickly and accurately. This article presents a literature review of the methods for computing ac losses in HTS tapes, wires and devices. Technical superconductors have a relatively complex geometry (filaments, which might be twisted or transposed, or layers) and consist of different materials. As a result, different loss contributions exist. In this paper, we describe the ways of computing such loss contributions, which include hysteresis losses, eddy current losses, coupling losses, and losses in ferromagnetic materials. We also provide an estimation of the losses occurring in a variety of power applications., IEEE Transactions on Applied Superconductivity, 2013

PURPOSE To assess the efficacy of percutaneous insertion of n-butyl cyanoacrylate (NBCA) in the ablation of bile ducts in patients with persistent postsurgical bile leaks in which traditional means of treatment have failed. MATERIALS AND METHODS Ablation of bile ducts with NBCA was performed in six patients (two men and four women). The average length of follow-up was 27 months (range, 13–46 months). Four patients presented after hepatic lobectomy with a persistent bile leak, one patient presented after cholecystectomy with a chronically obstructed bile duct, and one patient presented after cholecystectomy from intraoperative bile duct injury. After access to the biliary system was obtained, a cholangiogram was obtained. After the desired duct was isolated, it was copiously irrigated with saline solution. A glue solution containing NBCA glue, Ethiodol, and tantalum powder was delivered into the duct through a polyethylene catheter that had been irrigated with dextrose solution. RESULTS Four patients had problems arising from isolated segmental ductal systems that had no communication with the normal biliary ductal system and were treated successfully on the first attempt. In two patients, there was communication to the main biliary ductal system and a persistent bile leak occurred that required placement of a coil and a second final gluing procedure. The only complication observed was unintentional spillage of glue into the main biliary system in one patient, which was ultimately clinically insignificant. CONCLUSION The use of NBCA glue in obliteration of bile ducts is a safe procedure with excellent results in patients with complications from isolated segmental ducts. Although a repeat procedure may be necessary if the duct communicates with the main biliary tree, the procedure can decrease the morbidity associated with chronic external biliary drainage.

In AC loss measurements of superconductors using the four‐terminal method, the voltage measured consists of two components. The loss voltage component is in phase with transport current while the inductive voltage is out of phase with transport current. Here we report on the use of a compensation coil to nearly cancel the inductive voltage. The loss voltage was amplified by a transformer amplifier and observed on a digital oscilloscope. The waveform of the measured voltage was compared with that of a calculated signal. The loss voltage was analytically calculated for a round wire using the critical state model. The effects of frequency on the waveform of the loss voltage are also studied. Finally, a comparison between waveforms of loss voltages obtained with sine‐wave and triangle‐wave transport currents are presented.

The critical current of (Bi,Pb)2Sr2Ca2Cu3Ox (Bi‐2223) was varied between 2 A and 120 A using three different approaches: field angle with respect to the wide face of the tape, mechanical strain, and heat treatments. The results of transport loss measurements carried out on the three sets of samples showed that reduced critical current density caused an increase in AC loss as expected from Norris’s model. Comparison of the data among the three sets, however, showed some interesting features in the dependence of the AC loss behavior on the method used to vary critical current density. The results are explained based on the type of defects, localized or distributed, caused by the particular approach used in lowering the critical current.

Sandia has successfully integrated the capability to apply uniform, high magnetic fields (10-30 T) to high energy density experiments on the Z facility. This system uses an 8-mF, 15-kV capacitor bank to drive large-bore (5 cm diameter), high-inductance (1-3 mH) multi-turn, multi-layer electromagnets that slowly magnetize the conductive targets used on Z over several milliseconds (time to peak field of 2-7 ms). This system was commissioned in February 2013 and has been used successfully to magnetize more than 30 experiments up to 10 T that have produced exciting and surprising physics results. These experiments used split-magnet topologies to maintain diagnostic lines of sight to the target. We describe the design, integration, and operation of the pulsed coil system into the challenging and harsh environment of the Z Machine. We also describe our plans and designs for achieving fields up to 20 T with a reduced-gap split-magnet configuration, and up to 30 T with a solid magnet configuration in pursuit of the Magnetized Liner Inertial Fusion concept.

The combination of noninductive winding and the two-in-hand tape configuration has been found to be very effective in reducing the AC loss of coils of RABiTS™ YBCO coated conductor for fault current limiting (FCL) applications. In this study, a noninductive coil composed of 11 turns of two-in-hand RABiTS™ YBCO tape was designed and constructed for characterizing and investigating the AC loss, critical current and inductance. The AC losses in this coil were also calculated by finite element modeling (FEM) using the COMSOL Multiphysics package. With the magnetic field dependent permeability and ferromagnetic loss of the substrate material taken into account, the simulation results are in good agreement with the experimental data. The simulations therefore were employed to study the effect on the AC loss behavior of the coil of the width of YBCO tape and of the spatial separation between the coil turns to suggest a more effective coil design.

This paper presents a study of the total ac loss characteristics of a rolling-assisted biaxially textured substrate (RABiTS) YBa2Cu3O7 (YBCO) sample exposed to a parallel ac magnetic field. The results have shown that, for a given applied magnetic field and transport current, a RABiTS YBCO tape can generate very different magnitudes of ac loss, depending on whether the transport current and applied field have the same phase or opposite phase. The results of this study are very important for the optimization of the design of a RABiTS YBCO cable because they can suggest an appropriate arrangement of RABiTS tapes in a cable to minimize the cable ac loss. In this study, both experimental and finite-element method simulation approaches were employed. A modeling model that takes the magnetic field dependent permeability and ferromagnetic loss of the substrate into account reproduced well the experimental data for both self-field and total ac losses.

A numerical model is developed to calculate the total alternating-current (ac) loss of Cu-stabilized YBa2Cu3O7−δ (YBCO) coated conductors with a ferromagnetic substrate when carrying an alternating transport current in an ac background magnetic field. The time evolutions of current and magnetic field distributions along the width of the conductor are calculated by solving the one-dimensional Poisson equation for the magnetic vector potential. In addition to the ac loss dissipated in the superconducting layer, the ferromagnetic loss in the substrate and eddy current loss in the Cu stabilizer are also modeled. In the calculations, the superconducting voltage-current behavior is assumed to follow a power law. The model is capable of addressing other practical aspects of YBCO conductors, including the field dependence of the critical current density, and n value, and nonuniformities in the conductor. The magnetic shielding of the ferromagnetic substrate, however, was ignored in the calculations. Numerical results are compared with analytical and experimental results for some special cases.