Superconducting Outsert Magnet Research Articles

Design and test of power supply system for 45 T hybrid magnet superconducting outsert at the CHMFL

The current work successfully designed, fabricated, installed, and tested the power supply system for the superconducting outsert magnet of the 45 T hybrid magnet in the Chinese High Magnetic Field Laboratory (CHMFL). The system has achieved a long-term current stability of 10 ppm over 4 h period with a short-term current ripple less than 0.1 ppm over a time period of one cycle after several rounds of optimization. Its dump system has functioned with 100 % reliability since its operation. This paper presents the detailed design and test results for the power supply system, with emphasis on the realization of its important specifications.

Analysis and redesign of the thermal shield for the 40-T hybrid magnet at the CHMFL

A 40 T hybrid magnet has been constructed and commissioned at the High Magnetic Field Laboratory of the Chinese Academy of Sciences (CHMFL). It consists of a 10 T superconducting outsert magnet and a 30 T resistive insert magnet. As an important component of the hybrid magnet, the 80 K thermal shield is located inside of the cryostat protecting the superconducting magnet from thermal radiation. During the commissioning phase, a trip of the water-cooled resistive magnet triggered the quench protection system of the superconducting magnet, huge induced currents resulting in expansion and rupture of the oxygen-free copper thermal shield. In this paper, the cause of thermal shield rupture was investigated via finite element simulations. And the structure design and mechanical assessment of a new alternative thermal shield adopted for the 40 T hybrid magnet is presented.

The thermal-hydraulic response of the superconducting outsert during the trip of the resistive magnet in the hybrid magnet system of the CHMFL

The hybrid magnet system has been completed the commissioning and be ready to serve users at the High Magnetic Field Laboratory of the Chinese Academy of Sciences (CHMFL) in Hefei, China. The hybrid magnet consists of a 28 MW, 34 T resistive insert coils set nested inside of a 800 mm bore 11 T superconducting outsert magnet. The outsert coils are wound with high JC Nb3Sn/Cu cable-in-conduit conductor (CICC), cooled with forced flow of supercritical helium at 4.5 K. The protection system of superconducting magnet is based on the classical approach of voltage detection with a co-wound coil. In this paper, we reviewed experimental behavior of the superconducting outsert in detail when the resistive insert magnet tripped. We also conducted a thermal-hydraulic performance analysis of the superconducting outsert for the same trip situation of the resistive insert with modified GANDALF code. The numerical simulation results of maximum inlet and outlet temperature show good agreement with the experimental data. In addition, the minimum temperature margin and maximum helium pressure in the superconducting conductor were introduced and discussed.

A CORC® cable insert solenoid: the first high-temperature superconducting insert magnet tested at currents exceeding 4 kA in 14 T background magnetic field

The results presented in this Letter describe the successful test of the first high-temperature superconducting multi-tesla insert solenoid tested at currents exceeding 4 kA while operating in a background magnetic field of a low-temperature superconducting outsert magnet. A 45-turn insert solenoid, wound from 19 meters of CORC® cable, was designed to operate at high current, high current density, and high hoop stress in high magnetic background field; a combination that is essential in the development of low-inductance, high-field magnets. The CORC® cable insert solenoid was successfully tested in liquid helium in background magnetic fields of up to 14 T, resulting in a combined central magnetic field of 15.86 T and a peak magnetic field on the conductor of 16.77 T at a critical current of 4404 A, a winding current density of 169 A mm−2, an engineering current density of 282 A mm−2, and a JBr source stress of 275 MPa. Stable operation of the CORC® cable insert magnet in its superconducting-to-normal transition was demonstrated, during charging at rates of 20–50 A s−1, without inducing a quench. The results are a clear demonstration of the major benefits of this multi-tape CORC® magnet conductor in which current sharing between tapes is possible, thereby removing some of the stringent conductor requirements of single-tape magnets. The CORC® cable insert solenoid demonstrated operation at about 86% of the expected CORC® cable performance and showed no significant degradation after 16 high-current test cycles in background fields ranging from 10 to 14 T. CORC® cables have matured into practical and reliable high-field magnet conductors, achieving important high current, high current density, stress tolerance, and quench protection milestones for high field magnet technology. They have established a straightforward path towards low-inductance magnets that operate at magnetic fields exceeding 20 T.

Electromagnetic Design of HTS Insert for Ultrahigh Field NMR Magnet

In this paper, an electromagnetic design of a 27 T nuclear magnetic resonance (NMR) magnet composed of a low-temperature superconducting outsert magnet and a high-temperature superconducting (HTS) insert magnet is carried out. An optimization code is improved according to the fabrication form of the HTS magnet. Concerns about the radial magnetic field, the hoop stress, the current margin, length of tape used, and outer diameter of the HTS insert are investigated with respect to the magnet length, inner radius, and current density. The screening current effect is taken into consideration for the sensitivity analysis. The results predict that the larger the inner radius of the HTS insert, the better the real field homogeneity can be obtained. Screening current effect can deteriorate the field homogeneity zonally by about 1 order of magnitude.

Progress in the Development of the HFML 45 T Hybrid Magnet

To extend its user's facilities, the High Field Magnet Laboratory (HFML-EMFL) at the Radboud University is in the process of building a 45-T hybrid magnet. The magnet system will consist of a 22 MW 32.7 T resistive insert and a 600-mm-bore 12.3 T superconducting outsert magnet, and the design was significantly adjusted after a thorough design revision in 2011. The HFML hybrid magnet will be operated with separate current sources for the superconducting and resistive coils (20 kA at 10 V and 40 kA at up to 550 V, respectively). The outsert coil is a solenoid layer wound with all-Nb 3 Sn/Cu cable-in-conduit conductor (CICC), cooled by a forced flow of supercritical helium and operated at 20 kA. Similar to the series-connected hybrids for the HZB (Berlin, Germany) and the NHMFL (Tallahassee, FL, USA), the HFML outsert coil contains three grades of conductor. All CICC grades are based on high-current density Nb3Sn strand produced by Oxford Superconducting Technology. The CICC production and qualification program has been completed successfully. The coil will be wound at the NHMFL and, after heat treatment and impregnation, sent to Nijmegen for integration into the cryostat. In this paper, the design choices and current status of the program are presented.

Role and Impact of the Eddy Current Shield in the LNCMI-G Hybrid Magnet

In the new 43-T LNCMI hybrid magnet, a good conducting shield is inserted between the resistive insert magnet and the superconducting outsert magnet. Its goal is to decrease the ac losses induced in the superconducting conductor during a fault of the insert, disruption of the resistive coils (i.e., fast discharge) by smoothing the flux variations, and avoidance of a quench of the superconducting coil. The induced currents within the shield are very large due to the presence of copper material, which is the drawback of a good screening effect. Such currents result in large Lorentz forces, particularly during the most severe fault scenario of the resistive insert with the burnout of half of the Bitter coils. Finally, the detection system must be specially designed to handle the effects of the shield on the induced voltages.

Quench Simulation of the Hybrid Magnet Superconducting Outsert Being Built in China

Quench simulation of the hybrid magnet superconducting outsert being built at the High Magnetic Field Laboratory, Chinese Academy of Sciences was performed. The hybrid magnet is composed of a superconducting outsert magnet and a resistive insert magnet. The superconducting outsert will produce a central magnetic field of 11.0 T at 13,410 A. An induced current of 1270 A in the superconducting outsert is generated during resistive insert magnet trip. In case of a quench occurs from an over-current condition, the superconducting outsert magnet will produce a high hot spot temperature. The positive temperature coefficient dump resistor was used for accelerating the current decay during a quench. In this paper, the quench propagation analysis of the superconducting outsert under an over-current condition was presented.

Analysis of the Magnetic Forces Generated in the Hybrid Magnet Being Built in China

A 40 T hybrid magnet is being built at the High Magnetic Field Laboratory, Chinese Academy of Sciences. The hybrid magnet consists of a superconducting outsert magnet and a resistive insert, water-cooled magnet. Both magnets are powered independently with two power supplies. A large magnetic force is generated during short circuit of the resistive insert and the misalignment installation between the superconducting outsert and the resistive insert magnet. The radial magnetic force and torque are unstable. The magnetic force of the hybrid magnet needs to be evaluated to optimize the supporting structures and the pre-compression structure. In this paper, the electromagnetic performance of the hybrid magnet was evaluated under various operating conditions.

Cold Mass Design of the Superconducting Outsert for the 40-T Hybrid Magnet

A 40-T hybrid magnet is under construction at the High Magnetic Field Laboratory, Hefei Institutes of Physical Science, Chinese Academy of Sciences (CHMFL), Hefei, China. It includes a superconducting outsert magnet that can provide a central field of 11 T and a warm bore of Ø 800 mm for the insertion of a water-cooled magnet. This superconducting magnet has three superconducting coils, all of which are wound with Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn cable-in-conduit conductors (CICCs). The structural design of the superconducting outsert's cold mass has been worked out starting from the design of the conductors and the configuration of the coils. In this paper, we present the considerations and designs for the major components of the cold mass, i.e., the winding pack, the preload structure, the CICC lead support structures, and the cooling circuit. In addition, the design of the support structure of the coils is introduced and discussed. This is a key element and a special component with the function to support the cold mass and to transfer the fault loads from the coils to the base plate of the cryostat while its heat load to the cryogenic side remains as low as possible.

Thermal-Electromagnetic Analysis for 14 kA Fast Discharge of a Model Coil

A model coil for 40-T hybrid magnet superconducting outsert magnet has been constructed and tested at the High Magnetic Field Laboratory, Chinese Academy of Sciences. The model coil was wound with Nb3Sn cable-in-conduit conductor (CICC) cabled in a 316LN jacket cooled with supercritical helium. The model coil alone can produce about 4 T maximum magnetic field with an operating current of 14 kA. The model coil, in combination with 7.57-T NbTi background coil, can produce 11.5 T central field at 14 kA. During the test campaigns, a fast discharge was triggered by a dump resistor of 3.6 mΩ to evaluate the thermal-electromagnetic behavior of the model coil. In order to avoid a quench of the background coil, no current was exerted on the background coil through a power supply during the fast discharge of the model coil. The test results show that the central magnetic field is not scaled proportionally to the current decay of the model coil. The circuit model gives excellent results compared with the measured ones for the central magnetic field evolution as a function of time in this paper. For the thermal-hydraulic behavior during the fast discharge, the maximum temperature at the inlet simulated by the 1-D Gandalf code gives excellent agreement results compared with the measured ones with the conductor coupling time constant of 63 ms.

Wide Variety of Experiments Using a Cryogen-Free 27.5 T Hybrid Magnet and a Cryogen-Free 18.1 T Superconducting Magnet

A cryogen-free hybrid magnet without liquid helium for operation, generating 27.5 T in a 32 mm room temperature bore of an 8 MW water-cooled resistive insert magnet in an 8.5 T background field of a cryogen-free superconducting outsert magnet, is being operated for basic research at low temperatures down to 17 mK in combination with a dilution refrigerator. In addition, we are developing functional materials using a differential thermal analysis DTA at high temperatures up to 1473 K in high fields up to 27 T. This cryogen-free hybrid magnet will be upgraded to generate 29 T by improving the outer superconducting magnet. A cryogen-free 18.1 T superconducting magnet with a 52 mm room temperature experimental bore, consisting of a Bi2Sr2Ca2Cu3O10 (Bi2223) insert coil, has been developed using a GM-JT cryocooler. Recently, bronze-tape-laminated Bi2223 has revealed excellent irreversible stress tolerance of 250 MPa at 77 K. In addition, the critical current properties for recent Bi2223 tapes are largely improved from 200 to 400 A/cm-width at 77 K in a self-field. Therefore, the stainless steel reinforcement tape incorporated for the previous Bi2223 insert coil is no longer needed for a new Bi2223 one. A new Bi2223 insert coil with almost the same size as the existing insert coil can generate two times higher fields at the elevated operation current from 162 to 191 A. An upgraded cryogen-free superconducting magnet can offer a long-term experiment at the constant magnetic field of 20 T for an in-field heat-treatment investigation.

Design of the Outsert Coil of the 45 T Hybrid Magnet at the Nijmegen High Field Magnet Laboratory

The Nijmegen High Field Magnet Laboratory (Nijmegen HFML) is developing a 45 T hybrid magnet consisting of a 12 T CICC <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">${\rm Nb}_{3}{\rm Sn}$</tex></formula> superconducting outsert magnet and a 33 T Florida-Bitter resistive insert magnet. After a thorough review last year of the conceptual design of the superconducting outsert magnet in particular, the conductor and coil design for the outsert magnet have been adapted to create a larger performance margin so as to meet more adequately the possible uncertainties especially in CICC performance.

Investigation of 15 to 24 MW Resistive Insert Magnets Built Into a 20 T $\varnothing$440 mm Room-Temperature Bore Superconducting Outsert Magnet

The Tsukuba Magnet Laboratory and the High Field Laboratory for Superconducting Materials collaborated on developing the next-generation 50 T-class hybrid magnet. One of the properties to be incorporated into this next-generation hybrid magnet is energy-saving operation in generating a high-strength magnetic field. This report presents the estimated performance of this hybrid magnet, on the basis of a 20 T O440 mm room temperature bore for the superconducting outsert magnet, DC power of 15-24 MW for a three-layered Bitter resistive insert magnet, and a O32 mm room-temperature bore for the resistive insert magnet. Cu-Zr (Cu-Ag) alloy is assumed material to be used for the outermost layer (inner two layers) of the Bitter magnet. The estimation indicates that the hybrid magnet generates magnetic fields beyond 47.9 T (49.1 T) for a resistive insert magnet operation power of 15 MW (24 MW) in a 20 T background magnetic field, where the upper-limit design stress on the innermost Bitter coils is tentatively assumed to be 800 MPa. An ultimate tensile strength exceeding 1140 MPa with a conductivity of 72% International Annealed Copper Standard (IACS) for a Cu-Ag alloy plate would be necessary to meet the design stress of 800 MPa. Using this material, we could make the 15 MW water-cooled resistive insert magnet (WM) for this energy-saving, compact hybrid magnet that generates magnetic fields of 47 T and beyond. For a moderated upper-limit design stress of 760 MPa, the corresponding magnetic fields of the hybrid magnet are 47.5 and 48.5 T.

Protection System for the Superconducting Outsert Coils of the HFML 45 T Hybrid Magnet

The High Field Magnet Laboratory of the Radboud University Nijmegen is developing a 45 T hybrid magnet consisting of a 33 T resistive insert magnet and a 12 T, all Nb3Sn-Cu Cable-In-Conduit Conductor (CICC) based superconducting outsert magnet. Standard quench protection of the outsert coils is achieved with a permanently connected external dump resistor parallel to the coils. A major challenge is to prevent a quench of the outsert magnet during spurious trips of the insert circuit that may occur. Such an event is characterized by a fast decay of the insert current generating field changes at the windings of the outsert coils of a few T/s. Without precautions, the resulting AC losses in the superconducting strands would quench the inner windings. Here we present a model to analyse the effectiveness of an adapted protection scheme in terms of system and component characteristics and the required AC loss properties of the proposed CICC design.

Conceptual Design of the 45 T Hybrid Magnet at the Nijmegen High Field Magnet Laboratory

A 45 T Hybrid Magnet System is being developed at the Nijmegen High Field Magnet Laboratory as part of the Nijmegen Center for Advanced Spectroscopy. The 45 T Hybrid Magnet System will be used in combination with far-infra-red light produced by a Free Electron Laser under construction directly adjacent to the High Field Magnet Laboratory. The superconducting outsert magnet will consist of three CICC coils wound on a single coil form, using strands. A test program for strand and cable qualification is underway. The CICC will carry 13 kA and the coils will produce 12 T on axis field in a 600 mm warm bore. The nominal operating temperature will be 4.5 K maintained with forced-flow supercritical helium. The insert magnet will produce 33 T at 40 kA in a 32 mm bore consuming 20 MW, and will consist of four coils. The insert magnet will be galvanically and mechanically isolated from the outsert magnet. Complete system availability for users is expected in 2014. In this paper we will report on the conceptual design of the 45 T Hybrid Magnet System.

A 40 T Hybrid Magnet Under Construction in China

The Chinese National Project to develop new high magnetic field facilities began in 2008. It includes the construction of a 40 T hybrid magnet. The magnet will be built at the Chinese High Magnetic Field Laboratory (CHMFL) of the Chinese Academy of Sciences. It consists of a superconducting outsert magnet and a resistive insert magnet. The outsert magnet with a bore diameter of 580 mm at room temperature is expected to provide 11 T. It is composed of two coils: the inner coil is made of cable-in-conduit-conductor (CICC), the outer coil of NbTi CICC. The insert magnet, which will be a 20 MW Florida-Bitter-type resistive magnet with a clear bore diameter of 32 mm, will produce 29 T. The construction of the hybrid magnet is scheduled to be completed in 2013.

Tohoku High Magnetic Field Research Activities Using Cryogen-Free Superconducting Magnets

In order to realize a hybrid magnet with no need of liquid helium for operation, we have designed a 28 T cryogen-free hybrid magnet with a 32 mm room temperature experimental bore, and actually tested to generate the peak field of 27.5 T. An easy-to-operate cryogen-free hybrid magnet is now operating for basic research in high fields up to 27 T at low temperatures down to 40 mK, using a dilution refrigerator. In addition, we are intending to develop a 100 mm wide bore water-cooled resistive insert magnet combined with a cryogen-free superconducting outsert magnet for X-ray diffraction measurements in steady magnetic fields up to 20 T.

A 13.4 MW Bitter Insert for a 37.9 T Hybrid Magnet

The water-cooled insert magnet of the TML hybrid magnet successfully generated 37.9 T in a 32-mm room- temperature bore with a 14.02 T buckup field generated by a superconducting outsert magnet. At that magnetic field, the maximum electric power for the insert magnet was 13.35 MW. This Bitter-type insert magnet is divided into three coaxial coils, and the innermost coil consists of two coaxial coils. The inner coil is connected in series with the outer two coils connected in parallel. The Bitter plates for the outermost coil were made of GlidCop AL-25, and those for the other coils were made of hard-worked Cu-Ag plates. The thickness of the Cu-Ag plates was 0.40 mm, and the average 0.2% yield strength was about 810 MPa at 373 K

AC loss measurement of the 45-T hybrid/CIC conductor

The results of calorimetric measurements of the AC loss in a cable-in-conduit (CIC) conductor under development for the a 45T hybrid superconducting outsert magnet are reported. The technique is unique in that the absorbed energy is determined by measurement of the temperature rise in the He II contained in the conductor. The sample is located in a separate cryostat and placed in the bore of a 7 T superconducting dipole magnet. A change in transverse field results in heating which produces an easily measurable temperature increase of the helium surrounding the conductor. Samples of Nb/sub 3/Sn CIC conductor developed for the high field portion of the 45 T hybrid magnet system have been measured. The time constant measured for this sample is compared to analysis based on a combination of hysteresis and eddy current losses.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>