Soft Iron Yoke Research Articles

Pulsed Field Magnetization of GdBaCuO Superconducting Bulks With High Magnetization Efficiency Using a Split-Type Coil With Soft Iron Yoke

Pulsed field magnetization (PFM) and field-cooled magnetization (FCM) have been carried out for GdBaCuO disk-shaped bulks fabricated by two-step buffer-assisted (BA)-top seeded infiltration growth (TSIG) technique, and the results are compared with those of bulks fabricated by conventional top seeded melt growth (TSMG) technique. In both PFM and FCM experiments, the two-step BA-TSIG bulks showed higher trapped field properties than the TSMG bulks and, in particular, the maximum trapped field by PFM was over 3.5 T at 40 K using a split-type coil with soft iron yokes. The magnetization efficiency, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sup> / <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">app</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">*</sup> , was defined to evaluate the trapped field efficiency quantitatively, where <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sup> is the maximum trapped field and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">app</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">*</sup> is the optimum applied field to achieve <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sup> at each operating temperature. A high efficiency over 80% was achieved for the two-step BA-TSIG bulks at 40 K, which was nearly 10% higher than that for the TSMG bulks. These results were due to the high critical current density, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> , and the thinness of the two-step BA-TSIG bulks, readily causing flux jumps to assist in achieving higher trapped fields.

A Numerical Evaluation of Magnetizing Characteristic of Bulk Magnet Excited by Pulsed-Field Magnetization With Different Shaped Soft-Iron Yokes

We aim to improve magnetizing efficiency while maintaining the trapped magnetic field of REBCO bulk magnet excited by pulsed-field magnetization (PFM). In PFM, a soft-iron yoke is generally used in order to exposing the bulk to as much magnetic field as possible, and we investigate an influence of the shape and size of the yoke on the trapped field performance experimentally. In this paper, we performed numerical analysis using the 3D simulation model based on our PFM experimental system, and estimated the magnetizing characteristics when using the disk-, ring- and cross-shaped yokes. The analysis results showed the same tendency as the experimental results.

Influence of Soft-Iron Yoke Thickness on the Magnetizing Characteristics of a Bulk Magnet Excited by Pulsed-Field Magnetization

Influence of Soft-Iron Yoke Thickness on the Magnetizing Characteristics of a Bulk Magnet Excited by Pulsed-Field Magnetization

Modelling higher trapped fields by pulsed field magnetisation of composite bulk MgB2 superconducting rings

The recent results of Hirano et al (2020 Supercond. Sci. Technol. 33 085002) reported a high trapped field of 1.61 T in a composite MgB2 ring comprising copper plates and and a soft iron yoke magnetised by pulsed field magnetisation (PFM). Inspired by these results, an investigation using systematic modelling methods was conducted to investigate the key parameters leading to the success of Hirano et al. Our results indicate that composite structures of MgB2 rings present a viable method of trapping high magnetic fields when magnetised with PFM. Leveraging a finite element method modelling framework with a commercial software package (COMSOL Multiphysics), we have successfully modelled the experimental data with excellent agreement. We have paid careful attention to the assumptions regarding the thermal physics, which enabled the successful and accurate modelling of the experiment. Exploiting the flexibility of computational modelling, we extend our studies to investigate the influence of the constituent elements of the composite bulk on the electromagnetic and thermal behaviour, and discuss in detail how each can enhance the trapped field performance of the bulk. Aided by the models, it is shown how the number of copper layers influences the elongation of the applied pulse, reducing the field penetration and the maximum temperature rise of the bulk. The addition of the iron yoke significantly increases the trapped field, by concentrating flux during and after the pulse.

Investigation of the Magnetizing Performance of a REBCO Bulk Magnet Excited by Pulsed Field Magnetization Using Cross-Shaped Iron Yokes

We study to improve a trapped field of REBCO bulk excited by pulsed field magnetization (PFM). In PFM, a soft-iron yoke is used in order to expose the bulk to a large amount of magnetic flux for a long time. We paid attention to the soft-iron yoke and investigated the influence of its size and shape on the magnetizing performance. Our previous study estimated trapped-field performance when using disk-, ring-, and cross-shaped yokes and found that the cross-shaped yoke was the best. In this paper, we report our investigation of the influence of the width and arrangement of a cross-shaped yoke on magnetizing characteristics. When performing PFM experiments using yokes with 15 mm wide and 10 mm wide and arranging the growth sector region and the growth sector boundary, we obtained almost the same results. When comparing the total magnetic flux per unit weight, those values of 10 mm wide cross-shaped yoke were approximately 27% higher than those of 15 mm wide one.

A record-high trapped field of 1.61 T in MgB2 bulk comprised of copper plates and soft iron yoke cylinder using pulsed-field magnetization

A trapped field of BT = 1.61 T was experimentally achieved at the central surface of an MgB2 bulk composite (60 mm in diameter and 20 mm in height) at 20 K by double pulsed-field magnetization (PFM) using a split-type coil. The composite bulks consisted of two MgB2 ring bulks sandwiched by thin copper ring plates, which were then stacked, and a soft iron yoke cylinder was inserted in the central bore of the rings. The copper ring plates delayed the rise time and duration of the magnetic pulse due to eddy currents. The inserted soft iron yoke attracted the magnetic flux and enhanced the trapped field strength mainly due to its large permeability. As a result, the trapped field was enhanced from BT = 0.34 T for the single MgB2 ring bulk without the copper plates and soft iron yoke to BT = 1.00 T for the composite with both copper plates and the soft iron yoke. The inserted soft iron yoke can be exploited to enhance the trapped field because the intrinsic BT of the single MgB2 ring bulk was smaller than the saturation field of the yoke (∼2 T). Using an optimized second pulse application after suitable flux trapping from the first pulse application, the trapped field was enhanced considerably to BT(2nd) = 1.61 T, which is a record-high trapped field for an MgB2 bulk by PFM to date. The combination of the longer magnetic pulse application by the copper plates, the enhancement of the effective applied field by the inserted soft iron yoke, and the double pulse application using split-type coil is an effective technique to enhance the trapped field in the MgB2 bulk using PFM.

Influence of the Shape of Soft-Iron Yoke on Trapped Field Performance of HTS Bulk

We investigate the influence of soft-iron yokes on the magnetizing characteristics of HTS bulk magnet excited by pulsed field magnetization (PFM). By using the yoke, the trapped field could be improved because the bulk was exposed to the magnetic field for a long time due to hysteresis characteristic. In our previous study, a magnetizing test was performed by using the yokes with different size, resulting that the trapped field of a large yoke was higher than that of a small one. In this study, an effect of the shape of yoke on trapped field performance was evaluated quantitatively. A GdBCO bulk 60 mm in diameter and 20 mm thick was magnetized by using the disk-, ring- and cross-shaped yokes. The trapped field of the cross-shaped yoke was the highest, and that of the ring-shaped yoke was the smallest. However, when the total magnetic flux per unit weight of the yoke was compared, its value of the ring-shaped yoke was a little higher than that of the disk-shaped one. These results provided the possibility of reducing the weight of the system while maintaining the high trapped field by decreasing the volume of soft-iron yoke.

Design and realization of a sputter deposition system for the in situ and in operando use in polarized neutron reflectometry experiments: Novel capabilities

Recently, the design and realization of a sputter-deposition system for in situ and in operando polarized neutron reflectometry (PNR) was reported. The device allows magnetic thin films and heterostructures to be grown, while the sample remains aligned in the neutron beam for PNR. By now, it has been applied in experiments that investigated the magnetic and structural properties of thin Fe and Pd/Fe/Pd heterostructures as a function of the layer thickness. Here, we report on significant upgrades of the deposition system with advanced thin film growth and measurement capabilities. These include improvements to the generation of the vacuum to realize ultra-high-vacuum (UHV) conditions. A base pressure below 5 × 10−9mbar can now be obtained within less than one day of pumping time. To allow experiments over a wide range of temperatures, the system was upgraded to include a cryo-furnace. It allows the sample to be cooled or heated in the range of 10K to 1000K for both applications, sample growth and measurement. Further, a new magnetic coil setup with soft iron yoke was designed which can realize a homogeneous in-plane magnetic field of up to 300mT and electric fields at the sample position.

Enhancement of trapped field of REBCO bulk in a desktop-type magnet system

We developed a desktop-type bulk magnet system using a Stirling refrigerator and used it to study how to improve the trapped field by pulsed field magnetization (PFM). Although PFM has the advantage that the bulk is activated in a few seconds using an ordinary inexpensive equipment, the amplitude of a trapped field is low as compared with the maximum performance of the material. This paper aims to improve the trapped field by changing the size of soft-iron yoke, which are generally used to extend the pulse width. When a ϕ60-mm GdBCO bulk was magnetized using ϕ64-mm and ϕ80-mm yokes, the maximum flux density and total magnetic flux of large yoke were 13% and 23% higher than those of small one, respectively. Moreover, improvement of trapped field by multi PFM was investigated. When a magnetic field of 5.8 T was applied twice, the maximum trapped field of 1.46 T and the total magnetic flux of 1.86 mWb were achieved.

Improvement of the trapped field of REBCO bulk activated by pulsed field magnetization with a large soft-iron yoke

We study to increase the trapped magnetic field of a REBCO bulk magnet excited by pulsed field magnetization (PFM). In PFM, a soft-iron yoke is used to expose the bulk to the magnetic field for a long time. Although a small yoke 40 mm in diameter was used in our previous study, it was changed to a large yoke 64 mm in diameter in this paper. Accordingly, the pulse width was extended by 13%. When a GdBCO bulk 60 mm in diameter and 20 mm thick was magnetized by varying an amplitude of the applied field and temperature in a bulk magnet system using a two-stage GM-type refrigerator with a cooling capacity of 12 W at 20 K, the maximum trapped flux density reached 4.07 T on the center of the bulk surface and 2.56 T on the pole surface at 20 K. Moreover, the total magnetic flux was 3.28 mWb, which was about 13% larger than that of a small yoke. This result suggests that this method is useful in practice because the trapped field can be enhanced only by changing the soft-iron yoke.

Improvement of Trapped Magnetic Field of a REBCO Bulk Magnet Activated by Pulsed Field Magnetization in a High-Cooling Power Two-Stage GM-Type Refrigerator

We developed a high-cooling power bulk magnet system using a 12 K two-stage Gifford-McMahon (GM)-type refrigerator with a cooling ability of 12 W at 20 K in our previous study. When a single pulsed field was applied using a GdBCO bulk, the maximum trapped field of 3.59 T at the center of sample surface and the total magnetic flux of 2.89 mWb were achieved. In this paper, we aim to improve the trapped magnetic field by increasing the size of soft-iron yoke. When the same experiment was carried out using the same bulk, the trapped field was increased to 3.85 T. Moreover, the total magnetic flux reached a value of 3.97 mWb by a multipulsed field magnetization.

Output During Continuous Frequency Ramping of a Dynamo-Type HTS Flux Pump

Flux pumps can inject large dc currents into superconducting coils, without requiring physical connections between the cryogenic superconducting circuit and the room-temperature environment, thus significantly lowering the heat load on the cryogenic cooling system. Here, we study a dynamo-type flux pump employing a 2G ReBCO coated conductor wire at 77 K with multiple spinning Nd–Fe–B magnets and a soft ferromagnetic iron yoke, with all moving parts situated outside of the cryogenic environment. Dynamo-type flux pumps can be modeled as a dc voltage source with an internal resistance, where all output parameters are functions of the speed (frequency) of the spinning magnets. In this work, we focus on the frequency dependence of the dc output voltage. From instantaneous traces of the generated voltage waveform, we observe three distinct frequency regimes of behavior. We classify them into regions of “low,” “mid,” and “high” magnet frequency, depending on the magnitude of the dc open-circuit voltage and the shape of the voltage waveform. The voltage-generation mechanism is qualitatively understood at “low” magnet frequencies, where the dc voltage increases proportional to frequency. However, at “mid” and “high” magnet frequencies, the dynamo output deviates from this accepted model. In the “mid” frequency region, the dc output voltage is roughly constant with frequency, but is unstable. At “high” frequencies, the dc voltage drops with increasing frequency following an approximately 1/ f dependence. We have also studied the effects of ramping acceleration rate, noting a high degree of reproducibility in the low- and high-frequency regions, but complex unstable behavior in the intermediate region. We discuss our results in the context of self-heating due to EMF-driven eddy currents, leading to partial-quenching of the coated conductor wire. This becomes the dominant limiting factor in flux pump output at high frequencies, eventually suppressing the dc output altogether.

Trapped Field Enhancement of a Thin, High-Jc MgB2 Bulk Without Flux Jumps Using Pulsed Field Magnetization With a Split-Type Coil With a Soft Iron Yoke

We have investigated the suppression of flux jumps and the enhancement of trapped field on a thin, high-J$_{c}$ MgB₂ bulk (30 mm in diameter and 7 mm in thickness) for the pulsed field magnetization (PFM) using a split-type coil with a soft iron yoke, and compared the results to those magnetized using the split-type coil without a yoke and a solenoid-type coil with a yoke. A maximum-trapped field, B$_{z}$, of 0.71 T at 14 K was achieved on the bulk surface without flux jumps by using the split coil with yoke. On the other hand, low B$_{z}$ values with flux jumps were observed for the cases using the split-type coil without a soft iron yoke, and the solenoid-type coil with a yoke. These results reproduce previous ones for a thick, high-J$_{c}$ MgB₂ bulk (22 mm in diameter and 15 mm in thickness), for which the trapped field was enhanced to a record high value of B$_{z}$=1.10 T at 13 K by PFM using the split-type coil with a yoke.

Pulsed-Field Magnetizing Characteristics of Rectangular-Shaped Gd–Ba–Cu–O Bulk Using Split- and Solenoid-Type Coils

We have investigated the trapped-held characteristics of a rectangular-shaped Gd-Ba-Cu-O bulk (33 × 33 × 15 mm$^3$) magnetized by pulsed-field magnetization (PFM) using split- and solenoid-type coils. A soft iron yoke was set below the bulk for the solenoid coil and two yokes are inserted in the bores of the split coil. The maximum trapped held B$_{Zmax}$ at the center of the bulk surface was 1.73 T at 40 K in the case of the solenoid coil, with a distorted profile. On the other hand B$_{Zmax}$ was enhanced to 3.05 T at 40 K for the split coil with two yokes for which a symmetric trapped-held profile was observed. The behavior of the magnetic flux motion indicated two conditions for the enhancement of the trapped held: that the magnetic flux intrudes easily into the bulk even for lower applied fields and then saturates with minimal flux creep. We have also investigated the electromagnetic and thermal properties of the bulk during PFM using a numerical simulation in which the magnetic flux tended to align along the z-axis due to the presence of the soft iron yoke. The use of the split coil with two yokes is effective in enhancing the trapped held for the rectangular-shaped bulks.

Trapped field of 1.1 T without flux jumps in an MgB2 bulk during pulsed field magnetization using a split coil with a soft iron yoke

MgB2 superconducting bulks have promising potential as trapped field magnets. We have achieved a trapped field of Bz = 1.1 T on a high-Jc MgB2 bulk at 13 K without flux jumps by pulsed field magnetization (PFM) using a split-type coil with a soft iron yoke, which is a record-high trapped field by PFM for bulk MgB2 to date. The flux jumps, which frequently took place using a solenoid-type coil during PFM, were avoided by using the split-type coil, and the Bz value was enhanced by the insertion of soft iron yoke. The flux dynamics and heat generation/propagation were analyzed during PFM using a numerical simulation, in which the magnetic flux intruded and attenuated slowly in the bulk and tended to align along the axial direction due to the presence of soft iron yoke. The advantages of the split-type coil and the simultaneous use of a soft iron yoke are discussed.

Superconducting Solenoids for RF Accelerators and Electron Guns

Compact solenoids are applied at an increasing rate for beam focusing in superconducting RF accelerating structures, for instance in secondary ion beam linacs and for free electron lasers. High field solenoids with a center field of 7.9 T for the HIE-ISOLDE high-beta cryomodules at CERN are currently being designed and manufactured at Danfysik. NbTi coils and a soft iron yoke are carefully designed for operation in a LHe bath at a temperature of 4.5 K at field integral requirements of ≤ 13.5 T <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> m. The quenching characteristics of this solenoid have been studied and simulated, and a passive quench protection circuit is part of the solenoid design. The yoke outer diameter is 200 mm; the total length 312 mm. An HTS solenoid based on second-generation high-temperature superconducting technology was designed, built, tested, and delivered by Danfysik to the free electron laser project of the University of Wisconsin. The compact 136-mm-long HTS solenoid with a center field of 0.2 T operates in the temperature range between 5 and 70 K. The field integral is 3.1 T <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> mm with very small integrated field errors. Conduction cooling of the compact solenoid makes it easy to assemble and operate very close to the RF cavity.

Motion control of a large gap magnetic suspension system for microrobotic manipulation

Magnetic suspension systems have shown a great deal of promise in the field of microrobotics. This paper discusses the performance of a new large gap magnetic suspension system developed by the researchers. The magnetic drive unit consists of six electromagnets attached to a soft iron pole piece and yoke. Levitation of an 11.19 g microrobot prototype is demonstrated for step, ramp and periodic input trajectories using PID control. The working envelope of the microrobot is 30 × 22 × 20 mm3, with an RMS error on the order of 18 µm in the vertical direction and 8 µm in the horizontal direction. It is demonstrated that the levitated microrobot is able to track the desired trajectory precisely and that the system has potential application for micromanipulation.

A model of a helical high field strength short period undulator

A hybrid (superconducting + soft iron poles and yoke) short model of a helical undulator was designed, built andsuccessfully tested. The parameters of the model were chosen close to the requirements forfree electron laser undulators: 10 mm diameter clear bore, 28 mm period, 0.95 T design field.The number of full periods is 6. A NbTi composite multifilamentary strip was used in thewinding. During the tests the central magnetic field reached 1.065 T at 1215 A operatingcurrent. As far as we are aware, the combination obtained of bore-to-period ratio andmagnetic field strength can be considered one of the best achieved practically for helicalundulators.

A prototype mechanism for three-dimensional levitated movement of a small magnet

This paper deals with basic technologies for noncontact manipulation of small objects using magnets in micromachine applications. A small permanent magnet is manipulated by controlling the magnetic field applied to it. We propose a prototype mechanism to control the magnetic field for 3D levitated movement of an object. The prototype consists of eight electromagnets, pole-pieces to connect the magnetic poles, a soft iron yoke, and permanent magnets embedded in the yoke to compensate for the gravitational force of an object (a small permanent magnet). Regulation of a magnetic field and, as a result, motion of the object are strongly related to the geometric design of the pole-piece. A strategy for the pole-piece design is proposed and tested experimentally. Motion of the object in the vertical direction is realized by controlling the sum of the electromagnet currents for regulation of magnetic field gradient. Motion in the horizontal plane is realized by controlling the ratio of each electromagnet current for regulating the location of the maximum magnetic field. Results of several experiments show that the proposed prototype is effective.

Design and test of a 5 T superconducting wiggler

A description is given of a superconducting wiggler built and tested at Saclay for the Laboratoire pour l'Utilisation du Rayonnement Electromagnetique (LURE) at Orsay, France. The wiggler is being used as light source on the 1.72-GeV positron beam of the DCI storage ring at Orsay to increase the photon flux at short X-ray wavelengths. The magnet has five half-periods of field with a central amplitude of nearly 5 T, two middles with -3.6 T, and two ends with 2 T. The period length is 260 mm, the magnet gap is 67 mm, and the room-temperature beam chamber gap is 30 mm. The field is produced by ten superconducting coils embedded in a soft iron yoke which contains the magnetic forces. A correction current is applied to the end coils to ensure a zero integral field in the whole range of field. The results of three magnet training tests are briefly discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>