The cryogenic system for ITER CC superconducting conductor test facility

This paper describes the cryogenic system of the International Thermonuclear Experimental Reactor (ITER) Correction Coils (CC) test facility, which consists of a 500 W/4.5 K helium refrigerator, a 50 kA superconducting transformer cryostat (STC) and a background field magnet cryostat (BFMC). The 500 W/4.5 K helium refrigerator synchronously produces both the liquid helium (LHe) and supercritical helium (SHe). The background field magnet and the primary coil of the superconducting transformer (PCST) are cooled down by immersing into 4.2 K LHe. The secondary Cable-In-Conduit Conductor (CICC) coil of the superconducting transformer (SCST), superconducting joints and the testing sample of ITER CC are cooled down by forced-flow supercritical helium. During the commissioning experiment, all the superconducting coils were successfully translated into superconducting state. The background field magnet was fully cooled by immersing it into 4.2 K LHe and generated a maximal background magnetic field of 6.96 T; the temperature of transformer coils and current leads was reduced to 4.3 K; the inlet temperature of SHe loop was 5.6 K, which can meet the cooling requirements of CIC-Conductor and joint boxes. It is noted that a novel heat cut-off device for High Temperature Superconducting (HTS) binary current leads was introduced to reduce the heat losses of transformer cryostat.     

Magnet Design and Analysis of a 40 Tesla Long Pulse System Energized by a Battery Bank

A 40 tesla long pulse magnet and a battery bank as the power supply have been designed. This is now under construction at the Wuhan National High Magnetic Field Center. The 22 mm bore magnet will generate smooth pulses with duration 1 s and rise time 0.5 s. The battery bank consists of 945 12V/200 Ah lead-acid battery cells. The magnet and battery bank were optimized by codes developed in-house and by ANSYS. The coil was made from soft copper with internal reinforcement by fiber-epoxy composite; it is divided into two sections connected in series. The inner section consists of helix coils with each layer reinforced by Zylon composite. The outer section will be wound from copper sheet and externally reinforced by carbon fiber composite.     

A NbTi 10T 388mm bore magnet working at 1.8K in pressurized superfluid helium

A new high field test facility has been constructed for overall property measurements of the conductors developed for the superconducting coils of the TORUS II Tokamak project proposed by the EURATOM-CEA Association. This facility features a dc background field of 10 T in a useful volume of 338 mm in diameter and super-imposed pulsed fields of various configurations.The present paper describes the design, construction and operation of the 10 T field coil system in its pressurized superfluid helium cryostat.     

A six-tesla superconducting dipole magnet design and development program for POPAE

POPAE, the proposed Proton-Proton Intersecting Storage Ring Facility at Fermi National Accelerator Laboratory, will require some 1400 superconducting 6.0 T DC dipole and quadrupole magnets. The dipoles are 6. 17 m long and consist of coils of rectangular cross section clamped directly onto the 6 cm inner diameter bore tube. Aluminum is used to support the coils, and they are wound from a rectangular monolithic 2:1 copper to NbTi filamentary conductor. An experimental program has been undertaken to test and select the size, type and internal support scheme of the conductor. Individual coils of the POPAE dipole design, foreshortened to 0.5 m but supported similarly to the full-sized magnet are being tested in the field of a 2. 0 T backing magnet modeled after the Argonne SSR magnets. We also describe the large-scale cryogenics installation needed for the facility.     

Development of a Superconducting Magnet System with Zero Liquid Helium Boil-off

A homogeneous magnetic field superconducting magnet with a cold bore of 250 mm and a central field of 4.3 T has been designed, manufactured, and tested with zero liquid helium boil-off. As a result of magnetic field homogeneity considerations, the magnet is composed of three coaxial coils: one main coil and two compensation coils. All coils are connected in series and can be charged with a single power supply. The magnetic field homogeneity is about ±3.0 % from ?200 mm to 200 mm in axial direction with 86 mm in diameter. The magnet can be operated in persistent mode with a superconducting switch. A two-stage GM cryocooler with a capacity of 1.5 W at 4.2 K was used to cool the superconducting magnet. The cryocooler prevents the liquid helium from boiling off and leads to zero helium loss during static operation. The magnet can be operated in liquid helium circumstance by cooling the gas helium with the cryocooler without additional supply of liquid helium. Under this condition, the magnet is successfully operated up to 4 T without quench. The magnet system can be generating 0.25 L/h liquid helium with the cryocooler by supplying the gas helium without loading the magnet. In this paper, the magnet design, manufacture, mechanical behavior analysis, and the performance test results of the magnet are presented.     

Design and Performance of the First Dual-Coil Magnet at the Wuhan National High Magnetic Field Center

The first 80 T dual-coil magnet was manufactured and tested at the Wuhan National High Magnetic Field Center (WHMFC). The inner coil consists of 8 layers of 2.8 mm × 4.3 mm CuNb microcomposite wire developed in China; the bore diameter is 14 mm and the outer diameter 135 mm. The outer coil was wound directly on the inner coil with 12 layers of 3 mm × 6 mm soft copper. Each conductor layer of both coils was reinforced by Zylon/epoxy composite. The inner and outer coil were driven by a 1.6 MJ/5.12 mF capacitor bank and by eight 1 MJ/3.2 mF modules, respectively. At the voltage of 14.3 kV for the inner coil and 22 kV for the outer coil, the inner and outer coils produced peak fields of 48.5 T and 34.5 T respectively, which gave a total field of 83 T. This was the first combined operation of the new capacitor banks installed at the WHMFC. We present details of the design, manufacture and test of the dual-coil magnet and discuss crucial material properties. Based on this experience, a second dual-coil magnet will be designed; the enhanced design will be discussed. With the total energy of 12.6 MJ, peak field up to 90 T is expected.     

Two-dimensional normal zone propagation in BSCCO-2223 pancake coils

We present the results of an experimental and analytical study of two-dimensional normal zone propagation in pancake test coils, wound with silver-sheathed BSCCO-2223 tapes. Two test coils were studied in detail, one having three and the other eight layers. Each test coil was housed in an adiabatic environment whose temperature (20-70 K) was controlled and maintained by a two-stage G-M cryocooler and placed in a background field (0-6 T) generated by a Bitter magnet. With a test coil carrying a transport current (0-200 A), a local heat disturbance was applied by a heater attached to the outermost layer of the coil. The resulting electrical and thermal responses of the coil were recorded with voltage taps and thermometers attached to the coil. A normal zone propagation code was developed to accurately simulate the voltage and temperature responses of each coil for both quenching and recovering events. The code solves the nonlinear transient heat diffusion equation in two-dimensional cylindrical coordinates with a finite difference method. As an application of this code, a two-coil system, with each coil comprised of one double pancake wound with silver-sheathed BSCCO tape, was studied for its quench behaviour as one of the coils was driven normal locally. The simulation results indicate that the value of a shunt resistor connected across the terminals of each coil has a profound effect on the level of hot-spot temperature reached in the quench initiation spot.     

The 42+ T Hybrid Magnet Project at CNRS-LNCMI-Grenoble

Hybrid magnets, the combination of a resistive inner coil with a superconducting outer one, allow to generate the highest continuous magnetic fields for a given electrical power installation. A new superconducting coil outsert has been designed to be integrated in the existing infrastructure at LNCMI-Grenoble (GHMFL). Based on the specific development of a Nb–Ti Rutherford Cable On Conduit Conductor (RCOCC) cooled at 1.8 K by a bath of superfluid helium at atmospheric pressure, the superconducting coil aims to produce a continuous magnetic field of 8.5 T in a 1.1 m bore diameter. Combined with resistive insert coils, an overall continuous magnetic field of 42+ T will be produced in a 34 mm warm aperture. The main results of the conceptual study will be presented together with first developments and tests of the RCOCC.     

Superconducting magnets for the CBA project

The superconducting magnets that were designed and tested for the BNL colliding beam accelerator are described, including dipoles, quadrupoles and trim coils. The dipoles had an effective length of 436 cm, a good field aperture of 8.8 cm diameter, and were designed for an operating field of 5.28 T in a temperature range between 2.6 K and 3.8 K (provided by supercritical helium). The quadrupoles had the same aperture, an effective length of 138.5 cm, and were designed to operate in series with the dipoles, with a gradient of 70.8 T/m. The dipoles incorporated internal sextupole, octupole, and decapole trim coil windings; the quadrupole trim coils consisted of dipole, quadrupole, and dodecapole windings. The design, construction, and performance (training, field quality, quench protection characteristics) of prototype magnets are discussed in considerable detail.     

Conductor and joint test results of JT-60SA CS and EF coils using the NIFS test facility

In 2007, JAEA and NIFS launched the test project to evaluate the performance of cable-in-conduit (CIC) conductors and conductor joints for the JT-60SA CS and EF coils. In this project, conductor tests for four types of coil conductor and joint tests for seven types of conductor joint have been conducted for the past eight years using the NIFS test facility. As a result, the test project indicated that the CIC conductors and conductor joints fulfill the design requirement for the CS and EF coils. In addition, the NIFS test facility is expected to be utilized as the test facility for the development of a conductor and conductor joint for the purpose of the DEMO nuclear fusion power plant, provided that the required magnetic field strength is within 9 T.     

A multiple purpose 7TNbTi split coil superconducting magnet system for Mössbauer spectroscopy and susceptibility measurements at various temperatures

The design, construction and test results of a compact NbTi coil system are described. The dimensions are: 198 mm outside diameter, 290 mm total length, 52 mm vertical central bore, 20 mm horizontal bore. The system consists of two assistant coils in addition to the main split pair. A total of ten wire sections is involved. Each part of the system can be separately charged or several other modes of operation are possible. So the main split pair can be used alone. In the screening mode operation one or both of the assistant coils keep the magnetic induction below 0.1 T, within certain ranges on and near the axis. Finally, in the gradient mode operation, the assistant coils are charged in the opposite direction so that a linear gradient field is superposed onto the main field. The versatility of this coil system implies the use of three independent superconducting switches.The coil system is mounted in a stainless steel dewar which has horizontal and vertical access for Mössbauer spectroscopy at various temperatures. An additional insert allows susceptibility measurements in the temperature range from 2 K up to 300 K. Details on the cryostat (designed by L. Bogner, F. Parak and W. Wiedemann) will be published later.     

Fabrication experiences and performance tests of the coal-fired flow facility superconducting dipole magnet

The Argonne National Laboratory has designed, constructed and tested a large aperture superconducting MHD magnet for use in the coal-fired flow facility at Tullahoma, Tennessee. The magnet generates a peak on-axis field of 6 T in a MHD warm bore of 80 cm diameter at inlet, 100 cm diameter at outlet, and 300 cm effective length. The stored energy of the magnet is 210 MJ, the cold mass (4.2 K) is 131 metric tons and the ampere-turns, 13.7 × 10⁶. The final design of the magnet will be briefly introduced. Described in detail are the experiences of coil winding and coil assembly, the assembly of force-containment superstructure, assembly of magnet cryostat and results of magnet performance tests.     

Cluster test facility for superconducting tokamak toroidal magnet system development

As the step of development of superconducting tokamak toroidal magnet system, a Cluster Test system is being constructed. The test facility has two coils, called cluster test coil (CTC), in a sector position, which provides back-ground field to a test module coil (TMC). The oval-shaped TMC has a mean width of 1.5 m and a mean height of 2.0 m. And it is designed to operate at a peak field of 8 T and an average current density of 3 KA/cm²on the winding space when CTC, operated with rated current, has 7 T as a peak field with current density of 3 KA/cm². Experience on the Cluster Test will provide fabrication techniques and verifications of computer codes for future toroidal coil design principles.     

The propagation of the resistive region in high current density superconducting coils

A method is given describing the propagation phenomenon of the resistive region within the winding of superconducting coils wound from semi-stabilized filamentary conductors. The method permits the approximate calculation of the velocities of propagation of the normal conducting front in superconducting coils of high current density. The calculation is carried out assuming that the parameters of the conductor materials, the short sample data, and the heat transfer coefficient from the conductor into the ambient medium are given. The propagation velocities of the normal front have been measured in insulated wires freely immersed in liquid helium, in test samples using conventional interleaving material, and in a compact multilayer coil wound from the same wire. The calculated results are compared with experimental data.     

A superconducting coil indirectly cooled by forced helium flow

A small superconducting coil is indirectly cooled by a forced flow of helium. The coil, wound from Nb-Ti-Zr multifilament superconducting composite, is 15 mm id, 24 mm od and 30 mm long. The maximum central field is 30.3 kG at 4.2 K. Contact between the cooling tube and the coil is achieved using grease.The experimental results are expressed by a relation of critical current and energizing rate. Typical transient temperatures of the coil and coolant during energizing and after quenching are presented.The analysis shows the design of coils of this type is possible using hysteresis loss and heat conduction analysis.     

Hydraulic behavior of forced-flow cooled superconducting coils for the large helical device

The large helical device (LHD) has been operated since 1998 and the 13th experimental campaign was conducted in 2009. Before final assembling, cool-down and excitation tests for the Inner Vertical (IV) field coil, which is one of the LHD poloidal field coils, were carried out in 1995. This coil, which consists of a cable-in-conduit conductor, (CICC) is cooled by the forced-flow of supercritical helium. During the tests of the IV coil, hydraulic characteristics, such as flow distribution among cooling channels and friction factors, were measured. In this paper, the consistency of the behavior of the IV coil will be presented and comparison with other fusion devices using superconducting coils will also be made at not only cryogenic temperatures but also at room temperature.     

A high homogeneous field superconducting magnet for Argonne polarized proton target

We have designed and built a superconducting magnet for a large polarized proton target. The magnet consists of a pair of thick Helmholtz coils. Each Helmholtz coil consists of 9 step-subcoils balancing the ampere-turns around the Helmholtz line, thus providing an optimum for field uniformity without the help of Correction coils. This magnet generates 25 kilogausses with field uniformity one part in 10,000 over more than 5 cm diameter spherical target volume. It was designed to allow a large warm bore of 34.5 cm with axial aperture of 96° and between the Helmholtz pair, a wide warm separation of 12.7 cm with transverse aperture of 23°, thus allowing large accessibility to the proton target and for the scattering detectors in high energy scattering experiments.     

AC Loss Analysis of a Model Coil for a 40 T Hybrid Magnet

A model coil for a 40 T hybrid magnet was designed and manufactured at the High Magnetic Field Laboratory of the Chinese Academy of Sciences (CHMFL); the model coil was wound with Nb₃Sn cable-in-conduit-conductors (CICC) and cooled with 4.5 K supercritical helium. The performance of the model coil was tested, and the performance tests included a DC charging test, AC losses test, temperature margin test, cyclic load test, and fast discharge test. The AC losses produced in the different operation scenarios of the tests were simulated and analyzed by a modified Gandalf code. The simulated AC losses will be presented and compared with the test results in this paper.     

Development of a cryogenic test bed for high amperage critical current measurement on high temperature superconductor wire

Many areas of research have benefited from the application of conduction-cooled superconducting magnet technology. The middle and small-scale magnets immersed in the liquid helium will be replaced by the easy-operating conduction-cooled superconducting magnet due to convenient operation, lower operating cost and easy for user. For the goal of superconducting magnet applications in the advanced testing for high temperature superconducting (HTS) wire and sample coils, a wide bore conduction-cooled superconducting magnet with available warm bore of ?186 mm and center field of 5-6 T for background magnetic field applications was designed, fabricated and tested. The system allows measurements to be performed in a repeatable and reliable fashion. In order to support the high stress in magnet, the detailed finite element (FE) analysis with electro-plastic model is proposed. The sample cryostat is designed with cryofree. It includes two GM cryocoolers. The detailed design, fabrication and thermal analysis are presented in the paper.     

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.