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There are very strong requirements for the magnets with very high magnetic field for experimental facilities used in the new generations of special material processing devices. A high magnetic field superconducting magnet has been designed with the center field of 8 T, warm bore of 100 mm, and warm split-gap of 100 mm. The maximum magnetic field in the superconducting winding is about 11 T. Two GM cryocoolers are employed to cool down the system. The magnet consists of two high temperature superconducting coils with commercially available Bi-2223 tapes and six NbTi superconducting coils. There is very strong attractive force between the split-pairs coils. The design, fabrication and test of the superconducting magnet are reported in this paper.

A magnetic resonance imaging (MRI) superconducting magnet with openness can reduce claustrophobia of a patient. To fabricate an open MRI magnet, a new magnet configuration with iron rings and pole plates balancing the force between the coil and the yoke, and correcting the field homogeneity has been proposed. An MRI magnet with the center field of 0.7 T generated by split-pair coils and yokes is fabricated. The coils are contained in the cryostat with separated vessels connected with two pipes. The coils are separated with a room temperature gap of 480 mm and the diameter spherical volume (DSV) of 300 mm in which the homogeneity is 3 ppm in peak-to-peak. The cryogenic system is cooled by one GM cryo-cooler to realize the zero boiling off liquid helium. In the paper, the detailed design, fabrication, and test will be reported.

A passive quench protection design of the 9.4 T whole-body magnetic resonance imaging superconducting magnet is proposed. The design of the coil subdivision with shunt resistors is introduced. The selection of the configuration of the heater network is detailed. The optimization of the geometric parameter of the heater strips and the thickness of the insulation binding outside the heater strips are discussed. A winding sequence that could accelerate the quench propagation in the compensating coil is proposed. The calculation results show that the optimized quench protection design can guarantee the safety of the magnet in the case of any coil as the quench initiation coil.

The quench protection system with the circuit subdivision and heater network for a whole-body magnetic resonance imaging superconducting magnet has been designed. A test magnet with the similar quench protection design was built. Quench experiments for the test magnet have been conducted to verify a quench simulation code that is used to optimize the quench protection design. The fabrication of the test magnet has been demonstrated. The experimental results have been analyzed. The comparison between the experimental data and the calculated results has been discussed. The quench protection method with the heater network proves to work well, and the quench simulation code is proved to be reliable.

A conduction-cooled superconducting magnet was designed, fabricated and tested. A two-stage Gifford-McMahon (GM) cryocooler with the second-stage cooling power of 1.5 W at 4.2 K is used to cool the superconducting magnet from room temperature to 4.2 K. The superconducting magnet has the operating current of 105.5 A, the effective warm bore size of 250 mm, the maximum center field of 4.5 Tesla. The superconducting magnet will be used for the material processing. In this paper, the detailed design, fabrication and test are presented.

A superconducting magnet with the center field of 9.4 T is designed and fabricated for 400 MHz Nuclear Magnetic Resonance. Superconducting coil with NbTi/Cu superconducting wire is employed and cooled by re-condensed liquid helium and the magnet system with the clear-bore of 54 mm. The pulsed tube refrigerator with separated valve is employed to cool the magnet system. The superconducting magnet has an active shield with high pure copper shield to protect during quench of the shielding coil. The paper reports the electromagnetic design, and fabrication is detailed.

Fiber Bragg grating (FBG) sensor for monitoring the electromagnetic strain in a low temperature superconducting (LTS) magnet was studied. Before used to LTS magnet strain sensing, the strain response of the sensor with 1.54- wavelength at liquid helium was experimentally studied. It was found that the wavelength shift showed good linearity with longitudinal applied loads and the strain sensitivity is constant at 4.2 K. And then, the hoop strain measurement of a LTS magnet was carried out on the basis of measured results. Furthermore, the finite element method (FEM) was used to simulate the magnet strain. The difference between the experimental and numerical analysis results is very small.

In order to increase energy dumping speed, IGBT (insulated gate bipolar transistor) is used in quench protection of a 2 MJ superconducting magnet. 88 resistors, each connects in series with an IGBT, are connected in series-parallel connection to form a controllable varistor. On/off of the IGBTs are controlled by two single chip processors. Energy dumping with nearly constant magnet terminal voltage is realized in training quenches of the magnet. The necessary breaking capacity of the circuit breaker is also lowered. Details of quench protection electric circuit design and experimental results are presented.

For the goal of superconducting magnet applications in the advanced testing device for high temperature superconducting (HTS) wire and sample coils, a wide bore conduction-cooled superconducting magnet with available warm bore of phi 186 mm and center field of 5 T for the background magnetic field applications was designed and fabricated and tested. A sample cryostat with two GM cryocoolers is inserted in the background magnet. The system allows measurements to be performed in a repeatable and reliable fashion. The detailed design, fabrication and thermal analysis are presented in the paper.

We are carrying out a project to develop a conduction-cooled high temperature superconducting magnet system with an energy storage of 25 kJ. This magnet system will be used to investigate fast discharging performances. The magnet is constructed with 20 double pancakes. Each pancake is wound with Bi2223 tape. The magnet has an outer diameter of 212 mm and a clear bore of 108 mm. Cryogenics for the magnet system is designed to cool the coils with a GM cryocooler together with solid nitrogen. It is expected to operate the magnet system stand-alone. The operating current is designed as 110 A. It can generate a central magnetic field of 3.8 T at a temperature of 20 K. In this paper, the magnet design, coil fabrication and cryogenic system are presented.

A 6 T conduction-cooled superconducting magnet was designed, fabricated and tested. The magnet is composed of two coaxial NbTi solenoid coils with identical axial length. Clear bore of the magnet is phi 226 mm. The magnet is installed in a vacuum cryostat with a phi 100 mm room temperature bore. The cryostat is designed in a support frame to be rotatable in a horizontal or vertical direction. A two-stage 4 K Gifford-McMahon (GM) cryocooler is used to cool down the superconducting magnet from room temperature to 4 K. The cooling power of the 4 K cold head is 1 W. A pair of Bi-2223 high temperature superconducting current leads was employed to reduce heat leakage into 4 K cold mass. Total cold mass of the superconducting magnet is about 115 kg. It takes 82 hours to cool down the magnet from 300 K to 4 K directly through the cryocooler. The superconducting magnet reached the designed central magnetic field of 6 T in the warm bore when a 115 A energizing current is applied. The superconducting magnet was stably operating more than 275 hours continuously in full field. Further, a Nb3Sn coil insert to be installed, the magnet can provide the maximum center field of 10 T with effective warm bore of phi 100 mm. In this paper, the detailed design, fabrication and test are presented

The genetic algorithm (GA) is an efficient method in the optimization of superconducting magnets, but there are some limitations of the GA applied to practice design of superconducting magnet, such as poor local search ability, premature convergence, etc. An improved hybrid genetic algorithm is developed by combination of the sequential quadratic programming (SQP). A high temperature superconducting (HTS) magnet by Bi-2223/Ag tape is designed through the improved hybrid GA. A new configuration of the HTS magnet which can reduce the winding volume and become more convenient to construct is suggested with consideration of the constraints, such as central magnetic filed, critical current characteristic, storage energy, and so on.

Superconducting magnets cooled by cryocooler, without liquid helium, have been developed in recent years. This kind of magnet system is very easy and convenient to operate. The stability of the magnet depends on the balance between the cryocooler refrigeration capacity and the thermal loads. Based on thermal analysis for the magnet, study has been carried out on the stability of cryocooler-cooled superconducting magnet during current excitation.

A superconducting magnet system for MHD propulsion research is being constructed at the IEE CAS. The magnet is a large bore dipole with an inner diameter of 205 mm, the winding is a layer wound 60/spl deg/ circular saddle with a design central field of 4 T and a length of 830 mm. The outer diameter, the total length and height of the cryostat are 650 mm, 1300 mm and 1390 mm respectively. Equipped with a removable current lead and a superconducting switch, the system will be operated for 5 days with available liquid helium of 50 liters. The magnet system will be used for a MHD propulsion model ship.

A superconducting High Gradient Magnetic Separation (HGMS) sample test facility has been constructed at the IEE CAS. In order to shorten the magnet charging time, it is necessary not only to reduce the magnet inductance, but also to increase the cryogenic stability. Based on our experience, narrow LHe channel cooling inside the high current density magnet is a good solution. In this paper, design, construction and test results are described. The solenoid is wound with 1.46 mm/spl times/2.4 mm and 1.26 mm/spl times/2.4 mm rectangular NbTi-Cu composite, the filament diameter is about 25 /spl mu/m, and the length, the inner and outer diameter are 420 mm, 176 mm and 232 mm, respectively. The channel between two layers is formed by 0.5 mm/spl times/4 mm epoxy fibreglass strip along the axis. The central field of 5.45 T has been reached and the charging speed of 9 T/min has been achieved.

The ultra-high-field superconducting magnets have been widely applied in scientific instruments for condensed matter physics. A superconducting magnet with the center field of 25 T in a warm bore-size of 32 mm in diameter has been designed for the Extreme Condition Experimental Science Facility (ExCES). The superconducting magnet consists of NbTi, Nb3Sn superconducting coils and YBCO high-temperature superconducting (HTS) insert operated at the 4.2 K. In order to prove the technical feasibility to achieve the target of 25 T, high-temperature superconductor YBCO and Bi2223 inserts have been designed, fabricated and tested in the operating temperature of 4.2 K. Inner diameter, outer diameter, and height for the YBCO insert are 40 mm, 68.9 mm, and 253 mm, respectively. The larger Bi2223 insert has the inner diameter, outer diameter, and height of 120 mm, 212 mm, and 268.8 mm, respectively. Tests at liquid helium temperature show that the YBCO and Bi2223 inserts can generate the center field of 5 T and 5.05 T, respectively. The assembly of the Bi2223 and YBCO insert coils can generate a center magnetic field of 7.6 T when tested at the liquid helium temperature. In this paper, the design, fabrication, and test of the HTS insert and the 25 T magnet are reported.

The nuclear magnetic resonance superconducting magnet technology is being developed in our laboratory. Because the upper critical magnetic field of NbTi alloy is not high enough, an Nb3Sn superconductor has to be used in the manufacture of magnets for 500 MHz and above. In this paper, an experimental Nb3Sn superconducting coil was manufactured to study the fabrication technology. The bobbin with Al2O3 ceramic coating is made of stainless steel. A vertical tube type vacuum heat treatment furnace was established for Nb3Sn formation. Heat treatment parameters for the Nb3Sn coil were done at 670°C in vacuum. Vacuum pressure impregnation was done to strengthen the assembly. The Nb3Sn coil, the switch, and the current leads were joined together using superconducting solder matrix replacement method. In the test the maximum current of the Nb3Sn coil was 263 A, corresponding to a central magnetic field of 3.47 T. Persistent current mode operation was also successfully performed.

A project to develop a 9.4 T magnetic resonance imaging system is proposed for bioscience research applications. A whole body superconducting magnet system will be manufactured and test in the Institute of Electrical Engineering, Chinese Academy of Sciences (IEE, CAS). This magnet system features a room temperature bore of 800 mm in diameter, helium bath cooing, 9.4 T center magnetic field and passive iron shielding. The magnet is designed with radial layer-winding method. Five coaxial coils will be wound independently and assembled together as the main magnet. Coil length of the magnet is 3000 mm. In the magnet design, current density grading is performed to optimize the magnetic field distribution and stress level in the coil windings. The maximum magnetic field is 9.505 T, corresponding to an operating current of 224.515 A. The total magnetic energy storage is 138 MJ. Detailed magnetic and mechanic structure design as well as structure stress analysis are presented in this paper.