Development of Split Superconducting Magnet With Large Bore for Material Processing Applications
Yinming DaiQiuliang WangHui WangXining HuShunzhong ChenJunsheng ChengChunyan CuiYi LiLankai LiHousheng Wang
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Abstract:
A split superconducting magnet with large crossing warm bore of 150 and 50 mm is presented for material processing applications. Features of the magnet are characterized by a crossing warm bore and helium-free cryogenics. The magnet is configured in three pairs of split coils with pair separation of 85 mm to accommodate horizontal access. The magnet will be assembled after fabrications of two Nb 3 Sn and four NbTi coils. The maximum field in the inner Nb 3 Sn coils exceeds 10 T when the center magnetic field is 8 T. Magnetic structures are optimized to acquire the maximum operation margin in a dynamic temperature range around liquid helium temperature. The quench protection of the magnet is analyzed in detail to release the 1.35-MJ magnetic energy safely. Finally, magnet cryogenics is presented and discussed.Keywords:
Cryogenics
We developed a helium circulating system that re-liquefies all the evaporating helium gas and consumes far less power than conventional systems, because warm helium gas at about 40 K collected high above the surface of the liquid helium in the Dewar is used to keep the Dewar cold, and because cold helium gas just above the liquid helium surface is collected and re-liquefied while still cold. A special transfer tube with multi-concentric pipes was developed to make the system operate efficiently. The system can produce up to 35.5 l/D of liquid helium from the evaporated helium using two 1.5W@4.2K GM cryocoolers. (Translation of the article originally published in Cryogenics 48 (2008) 6-11)
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Since the discovery of high field superconductors, it has been possible to generate high magnetic fields with lightweight, compact superconducting solenoids. In most cases, these magnets are operated in conventional liquid helium Dewars which are heavy and unwieldy and usually offer only vertical access to the magnetic field, which makes them very inconvenient for many uses, such as with optical research instrumentation. A system is described in which the magnet and cryostat are integrated into a single light weight package which weighs only 13.6 kg and provides horizontal access to magnetic fields in excess of 50 kG with working bores of 3.80 cm at temperatures near 4.2°K and 2.54 cm at room temperature for periods up to 12 h between fillings. Due to its over-all configuration, the magnetic field is highly accessible and allows spectroscopic measurements to be made conveniently at 50 kG. Also, the system can be easily transported while it is filled with liquid helium.
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A helium recondenser using a 4 K pulse tube cryocooler (model PT405) has been developed as a solution to reduce liquid helium boil‐off in the existing non‐refrigerated helium dewar or helium cryostat. The condensing part of recondenser is inserted into the neck tube of the helium dewar or cryostat. The helium vapor is condensed at 4.2 K and the condensed liquid flows back to the liquid helium bath. The recondenser has been experimentally tested to condense 14 liters/day of liquid helium while consuming 4.5 kW electrical power.
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The cryogen is used in various industrial and commercial applications and the demand of the cryogens are increasing in recent years. It is necessary to measure the level of cryogen which is stored in the storage tank or dewar. It is necessary to maintain minimum cryogen level in the storage tank before filling it with a new batch of cryogen and preventing the thermal quench of superconducting equipment like superconducting magnets. Various methods are used for the measurement of cryogen. In recent years, superconducting liquid level sensor is used, however there is a drawback with this measurement unit as the sensor wire above the liquid level will be experiencing low temperature as compared to the sensor wire which is having contact with the gaseous form of cryogen. Hence, in this work, we have developed an indirect type super conducting liquid helium level sensor. The active length of the sensor developed is 40 inch and it was tested successfully. From this work, we conclude that developed sensor works effectively and will overcome the problem with super conducting level sensor.
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A large bore NbTi superconducting magnet is designed, manufactured and tested. The superconducting magnet has an inner diameter of 460 mm, outer diameter of 600 mm and height of 540 mm. The magnet is dry wound using rectangular and round superconducting wires with their dimensions of 1.3 times 2.0 mm and Oslash1.3 mm respectively. In order to improve helium cooling effect, narrow liquid helium channels are set between adjacent layers. The magnet can generate 4 T central magnetic field at the designed operating current of 305 A. The magnet has been tested in a compact cryostat. Experimental results show that the superconducting magnet reached the designed magnetic performance. Details of the magnet design, fabrication and test are described in this paper.
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