Patent Application
20130033346
The present invention relates to a high magnetic field superconducting magnet system, and more specifically, to a high magnetic field superconducting magnet system with large crossing warm bore.
With the development of the cryogenic technology and the superconducting technology, a high magnetic field conduction-cooled superconducting magnet is convenient for system operation and has the advantage of compact size and light weight, due to its cryogenic system of a simple structure without the limitations of liquid helium or other cryogenic conditions. The critical technology of a conduction-cooled superconducting magnet system is that a cryocooler is employed to directly cool a superconducting magnet, which overcomes the conventional cooling method in which the superconducting magnet has to be cooled by using cryogenic liquid. With the development of the high temperature superconducting wire technology, Bi-based tape has a current density of Jc=104-105 A/cm2 within a temperature range of 20˜30K, even under a relatively high magnetic field. In such situation, the high temperature superconducting magnet that is cooled directly by a cryocooler has a relatively important meaning. The high temperature superconducting magnet operating at a temperature zone of 20K can make full use of the mature technology of a cryocooler of a temperature zone of 20K as well as the current carrying capacity of the high temperature superconductor and the high thermal conductivity and heat capacity of the superconducting tape, thus the high temperature superconducting magnet has a relatively high stability.
The high magnetic field superconducting magnet has important applications in the aspects of industry and scientific instrument. In situations such as multi-physical fields cooperatively act on a material under extreme conditions to study the physical characteristic, and neutron scattering, X-ray diffraction and synchronized radiation light sources are used to study the substance structure, a high magnetic field superconducting magnet with a certain size of crossing warm bore is needed to provide a background magnetic field for substance study. Such a superconducting magnet has an electromagnetic structure of relatively more complex as compared to that of an ordinary magnet, with a prominent feature of having a very large crossing warm bore so as to be suitable to access available magnetic field areas in lateral direction of the magnet. Thus, it has important applications in scientific instruments and other scientific study apparatus of extreme conditions, thereby providing innovative scientific study instrument and platform.
In this kind of superconducting magnet, due to a special crossing warm bore, the superconducting magnet will subject to a relatively strong electromagnetic force due to the interaction between superconducting coils under a high magnetic field. If the temperature is 4K, a method using combination of NbTi and Nb3Sn can generate a magnetic field of 18 T, and when the operating temperature is 2.2K, it can provide a central magnetic field up to 21 T. Recently, with the successful development of Nb3Sn superconducting wire having high current density, the superconducting magnet can provide a maximum magnetic field up to 22.3 T when the operating temperature reaches 1.8K.
In order to access the magnetic field zone in multi-dimensional directions, the superconducting magnet having super-large gap separates the superconducting coils along the direction of the magnetic field, thereby forming a relatively strong magnetic field area which can be accessed simultaneously in both the vertical and parallel directions of the superconducting magnet. Currently used low temperature superconducting magnet has a separation gap less than 20 mm, the system thereof is merely capable of providing a maximum magnetic field of 15˜17 T. In order to obtain a superconducting magnet system with coils separated by a large crossing warm bore, which has simple process and low fabrication cost, and will become an innovative superconducting magnet that can be used in combination with special material processing, X-ray, neutron scattering, other high temperature condition, high-pressure condition and associated scientific instrument, a high magnetic field magnet structure having a crossing warm bore over 100 mm is required, so as to provide a magnetic field exceeding 10 T. This magnet enables samples or other instruments to reach the relatively strong magnetic field area from different directions, thereby forming a high magnetic field magnet system that operates stably and can be applied to scientific instruments as well as scientific apparatus used for study under extreme conditions.
The present invention aims to overcome the defect that the existing separated superconducting magnet has a crossing warm bore not large enough, and proposes a high magnetic field superconducting magnet system with large crossing warm bore. The present invention proposes a conduction-cooled superconducting magnet using NbTi and high temperature superconductor, wherein the high magnetic field area of the magnet uses the high temperature superconductor, the low magnetic field area uses the NbTi, and the superconducting magnet system operates at a temperature of 4K and provides a central magnetic field strength of 10 T. Since the superconducting magnet system adopts a manner of direct cooling by a cryocooler, it significantly improves the use efficiency of the superconducting coils and reduces the distance between coils.
The cryocooler of the superconducting magnet system with large crossing warm bore according to the present invention is fixed on a flange of a low temperature container, a primary cold head of the cryocooler cools a thermal shield of the low temperature container, while a secondary cold head of the cryocooler cools a low temperature superconducting coil and a high temperature superconducting coil. The low temperature superconducting coil and the high temperature superconducting coil are supported and fixed together by a drawbar. The low temperature superconducting coil and the high temperature superconducting coil are connected to the flange of the low temperature container by a supporting drawbar and the thermal shield, thus the low temperature superconducting coil and the high temperature superconducting coil as a whole are supported inside the low temperature container. A thermal switch is connected to the primary cold head and the secondary cold head of the cryocooler. The two ends of the low temperature superconducting coil and the high temperature superconducting coil are fixed by a magnet-reinforced supporting flange. The magnet-reinforced supporting flange is connected to the secondary cold head of the cryocooler by a cold conduction strip to conduct the cold energy from the cryocooler to the low temperature superconducting coil and the high temperature superconducting coil. The low temperature superconducting coil and the high temperature superconducting coil have current introduced thereto by a room temperature current lead and a high temperature superconducting current lead, respectively. The superconducting magnet conducts quench protection by a quench protection diode. The superconducting magnet system of the present invention has a room temperature bore in horizontal direction and a room temperature bore in vertical direction. A thermal shield outside the room temperature bore in horizontal direction is used for preventing thermal radiation by the room temperature bore in horizontal direction to the low temperature superconducting coil and the high temperature superconducting coil. A separation supporting frame separates the low temperature superconducting coil and the high temperature superconducting coil into two parts, such that a two-dimensional room temperature space can be included inside the superconducting magnet when the superconducting magnet is formed as a whole.
The superconducting magnet of the present invention consists of the low temperature superconducting coil and the high temperature superconducting coil, and generates a magnetic field with a range of 8˜10 T and can employ a structure in which the high temperature superconducting inside coil is internally placed and an NbTi superconducting coil is externally placed. If the central magnetic field is above 10 T, the present invention will employ a combined structure of high temperature superconductor, Nb3Sn and NbTi superconducting coils, wherein the three kinds of superconducting coils are powered separately.
The superconducting magnet coil of the present invention is separated into two parts by a gap larger than 100 mm. The high temperature superconducting coil is located inside the low temperature superconducting coil. A crossing room temperature bore having a crossing seal structure is used to form a two-dimensional room temperature space, such that inside the superconducting magnet, the high magnetic field area inside the superconducting magnet can be directly accessed in two-dimensional directions through the crossing room temperature bore.
According to the present invention, the crossing room temperature bore is placed inside the low temperature container in parallel magnetic field and vertical magnetic field directions. In order to save the space of the vertical separation gap, there is a hole of a circular structure in the middle of a separation supporting frame such that the room temperature bore can directly pass through. After the installation of the crossing room temperature bore, the separated coils are connected. The low temperature superconducting coil and the high temperature superconducting coil are separated into two parts by the separation supporting frame in horizontal direction, to form a superconducting coil structure having a crossing bore. A spacer, stainless steel supporting block for support between coils and aluminum alloy supporting block constitute the separation supporting frame. The cross room temperature bore passes through the centers of the stainless steel supporting block and the aluminum alloy supporting block. The two parts of separated coils consisting of the low temperature superconducting coil and the high temperature superconducting coil are respectively mounted to the two ends of the spacer. The separation supporting frame employs a structure in which the stainless steel supporting block and the aluminum alloy supporting block are mutually nested with the two ends fixed by the spacer. The stainless steel supporting block and the aluminum alloy supporting block are used for supporting the superconducting coils, meanwhile the aluminum alloy supporting block conducts thermal transfer between the two parts of superconducting coils.
The superconducting magnet of the present invention as a whole is directly placed inside the low temperature container, and power is supplied to the superconducting coil by connections of the high temperature superconducting current lead and the conventional current lead. A temperature control system is used for detecting operation temperature state of the superconducting coil. One or more cryocoolers are connected to the superconducting coil, for directly conducting the cold energy from the cryocooler to the superconducting coil, thereby reaching required low temperature.
The superconducting coil of the present invention adopts a manner in which power is supplied by different power sources, and the superconducting coil of each superconducting material is connected to one power source. The superconducting coil adopts a shunted protection manner. A protection diode for the low temperature superconducting coil is constituted by two parallel diodes with opposite polarities, and a plurality of protection diodes for the low temperature superconducting coil are connected in series. The number of the protection diodes for the low temperature superconducting coil depends on the voltage resistance capability of the superconducting coil. In order to decrease the highest temperature generated by the high energy density superconducting coil in the event of quench and release the energy of the superconducting coil evenly inside the magnet, a heater is mounted in the axial direction of the inner surface of the high and low temperature superconducting coils. When a local quench of the superconducting coil occurs, the energy is directly transferred to the heater, thus triggering a quench of the entire superconducting coil. The stored energy can be quickly and evenly released so as to suppress the temperature increase of the superconducting coil to the greatest extent.
The present invention adopts a technology in which a cryocooler is directly used for cooling, which can reduce the distance between coils and improve the use efficiency of the coils. In addition, since the magnet structure and the low temperature container structure are simple, the system can operate stably. Meanwhile, the use of this innovative technology can considerably reduce system operation cost and make system operation, manipulation and installation more convenient and reliable.
The present invention is further explained below in conjunction with the attached drawings and particular embodiments.
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| Number | Date | Country | Kind |
|---|---|---|---|
| 201010105262.6 | Feb 2010 | CN | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/CN10/00993 | 7/1/2010 | WO | 00 | 7/3/2012 |
