WO2004003441A1

WO2004003441A1 - Cryovessel with gifford-mcmahon cryocooler and control method therefor

Info

Publication number: WO2004003441A1
Application number: PCT/KR2002/001339
Authority: WO
Inventors: Hong-Beom Jin; Ki-Deok Sim; Byeung-Sang Park; Hyung-Jin Kim; Suk-Jin Choi; Ho-Hwan Han; Kyung-Han Kim
Original assignee: Duksung Co., Ltd.
Priority date: 2002-06-26
Filing date: 2002-07-16
Publication date: 2004-01-08
Also published as: KR20040001073A; KR100454702B1; AU2002319932A1

Abstract

A cryovessel, in which liquid helium contained in a helium container is maintained at a constant pressure, temperature and volume by using a Gifford-McMahon cryocooler, and control method for such a cryovessel is provided. The cryovessel includes a vacuum container for heat insulation; a helium container disposed in an inner lower portion of the vacuum container in such a manner that the helium container is spaced apart from the vacuum container, the helium container accommodating a superconductive magnet dipped into a liquid helium so as to receive power through a double cable; a GM cryocooler having upper and lower cooling portions accommodated into the vacuum container and a condensing portion connected to the helium container, the GM cryocooler receiving a re-condensed helium from a condenser; a conduction cooling unit for interconnecting the upper cooling portion of the GM cryocooler and the double cable connected to the superconductive magnet, the conduction cooling unit conductively cooling a heat transferred through the double cable; a controller connected, through pipes, to the condenser, heater for heating the helium container, the helium container and the vacuum container, and which controls a pressure gauge for gauging pressure of each container; and a power supply for supplying power to each component. Thus-configured cryovessel is compact in size, inexpensive to manufacture, and capable of minimizing loss of helium. Super cooling is prevented through the use of heater and pressure, liquid level and temperature of the helium container can be maintained constant, to thereby operate the superconductive magnet in a stable manner.

Description

CRYOVESSEL WITH GIFFORD-MCMAHON CRYOCOOLER AND CONTROL METHOD THEREFOR

FIELD OF THE INVENTION The present invention relates to a cryovessel, in which liquid helium contained in a helium container is maintained at a constant pressure, temperature and volume by using a 4K two-stage Gifford-McMahon cryocooler(hereinafter, referred to as a "GM cryocooler"), and control method for such a cryovessel.

BACKGROUND OF THE INDENTION

In general, cryovessel is a device for storing cryogenic fluid or maintaining superconductive magnet at an ultra low temperature, and used for superconductive devices like MRI or NM In the cryocooler container used for the superconductive device, crygenic fluid, helium for example, is evaporated. Therefore, a recovery system for collecting and recovering the evaporated helium, and a system for liquefying the collected helium through the use of a helium liquefying device and feeding the liquefied helium to the helium container have been used.

Typically, Joule-Thomson(JT) cooler is used as a helium liquefying device. However, JT cooler has disadvantages in that it has a low efficiency as compared to a capacity, and configuration for components including pipeline arrangement is complicated because the liquefying device is mounted outside of the cryovessel. Moreover, manufacturing procedures are complicated, and manufacturing cost is high.

In a conventional cryovessel, an evaporating vapor cooling system for utilizing a helium vapor being evaporated from the helium container is adopted for cooling the cable for applying power to the superconductive magnet arranged in the helium container. This may result in the significantly large amount of helium loss, making it impossible to re- condense helium through the cooler. Further, superconductive devices using a conventional cryovessel adopting a re-condensation system can be easily used in a permanent current mode but cannot be easily used in a constant electrifying system. Therefore, it is difficult to use such superconductive devices in a single crystal growing apparatus and the like. In general, permanent current mode in operating superconductive magnet is performed in such a manner that superconductive magnet itself has a closed circuit by using the property where the electrical resistance of the superconductor is zero, after a current is fed to the superconductive magnet from an extemal source, and the superconductive magnet becomes same as a permanent magnet without having a power being supplied from an external source. The constant electrifying system allows current to be continuously supplied from an external source during operation of superconductive magnet, and differs from the permanent current mode in that the constant electrifying system generates or removes magnetic field by controlling current according to needs.

SUMMARY OF THE INVENTION

Therefore, it is an object of the present invention to overcome the above-described problems of conventional cryovessel, and provide a cryovessel with a GM cryocooler in that advantages are achieved as follows;

First, cryovessel can be manufactured into a compact size at a low cost by disposing GM cryocooler into the cryovessel.

Second, loss of helium is prevented by directly re-condensing helium gas in the cryovessel through the GM cryocooler.

Third, phenomenon where the internal pressure of helium container is lowered by a super cooling exceeding the amount of evaporation of helium from helium container, is prevented through the use of heating means.

Fourth, cryovessel can be used in a constant electrifying system through the use of means for directly conductively cooling, by using a cooler under a vacuum, the cable for applying power to the superconductive magnet.

Fifth, superconductive magnet can be operated in a stable manner by maintaining pressure, liquid helium level and temperature in the helium container constant through the control of each component of cryovessel, thereby obtaining a high efficiency cryovessel.

To accomplish the above-described objects of the present invention, there is provided a cryovessel with GM cryocooler, including a vacuum container for heat insulation; a helium container disposed in the inner lower portion of the vacuum container in such a manner that the helium container is spaced apart from the vacuum container, the helium container accommodating a superconductive magnet dipped into a liquid helium so as to receive power through a double cable; a GM cryocooler having upper and lower cooling portions accommodated into the vacuum container and a condensing portion connected to the helium container, the GM cryocooler receiving a re-condensed helium from a condenser; a conduction cooling unit for interconnecting the upper cooling portion of the GM cryocooler and the double cable connected to the superconductive magnet, the conduction cooling unit conductively cooling the heat transferred through the double cable; a controller connected, through pipes, to the condenser, heater for heating the helium container, helium container and the vacuum container, and which controls a pressure gauge for gauging pressure of each container; and a power supply for supplying power to each component. Preferably, the double cable connected to the superconductive magnet is constituted by a metal coil and a high temperature superconducting (HTS) coil which are interconnected through a connection member, and the metal coil is formed of a sheet metal, laminated in such a manner that the sheet metal, insulating sheet, and an end of the conduction cooling unit are stacked in sequence from the connection member and fixed through the connection member like a bolt.

The helium container and the condensing unit are connected through a connection portion constituted by a corrugated pipe so as to prevent damage caused due to a vibration.

A method for controlling a cryovessel with a GM cryocooler according to the present invention comprises the steps of turning on and operating a heater for compulsorily evaporating a helium until the GM cryocooler operates and the pressure of the helium container reaches a predetermined pressure level; tiirning off the heater when the pressure reaches a predetermined level, and condensing the helium by the GM cryocooler so as to maintain the pressure at a constant level; and controlling, through a container, a condenser, heater and a pressure gauge in such a manner that the GM cryocooler is turned off by turning off the condenser at a pressure lower than a predetermined pressure level, and tuned on again when the pressure of the helium container is higher than 0.0 bar so as to prevent the pressure of the helium container from becoming lower than 0.0 bar due to the incomplete operation of the heater.

DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic view illustrating a cryovessel with a GM cryocooler adopting a helium re-condensing system in accordance with the present invention;

Fig. 2 is an enlarged schematic view illustrating a coupling relation between the GM cryocooler and helium condensing portion;

Fig. 3 is an enlarged schematic view illustrating a coupling relation between the GM cryocooler and conduction cooling unit; and

Fig. 4 is an enlarged schematic view illustrating a coupling relation between the double cable and conduction cooling unit.

DETAILED DESCRIPTION OF THE PRESENT -INVENTION A cryovessel with GM cryocooler according to the present invention will be explained in more detail with reference to the attached drawings.

Fig. 1, is a schematic view illustrating a cryovessel with a GM cryocooler adopting a helium re-condensing system in accordance with the present invention, wherein a solid line denotes a cable, a dot line denotes a control relationship and a one-dot chain line denotes a gas feed relationship. Referring to Fig. 1, a vacuum container 3 for heat insulation accommodates a helium container 20 disposed in the lower portion thereof in such a manner that the helium container 20 is spaced apart from the vacuum container 3. The helium container 20 is filled with a liquid helium 5 into a predetermined height, and a superconductive magnet 7 for receiving power from a power supply 13 through a double cable, is dipped into the liquid helium 5.

Referring to Fig. 2, a GM cryocooler 30 has a condensing portion 35 connected to the top of the helium container 20. The GM cryocooler 30 includes a head portion exposed to outside of the vacuum container 3, and upper and lower cooling portion 31 and 33 and the condensing portion 35 accommodated into the vacuum container 3. The condensing portion is a cylinder formed of a copper material. Fig. 3 illustrates a schematic configuration of upper and lower cooling portions 31 and 33 excluding the head portion and condensing portion of the GM cryocooler 30. As shown in Fig. 2, it is preferable that the GM cryocooler 30, condensing portion 35 and the helium container 20 are connected through a connection portion 21 which is constituted by a corrugated pipe so as to prevent damage caused due to a vibration. The connection portion 21 can be formed of a stainless material. The lower cooling portion 33 and the condensing portion 35 have connection portions 33a and 35a connected through soldering. The connection through soldering improves contact and achieves sealing preventing leakage of helium from the condensing portion 35. As shown in Fig. 1, the GM cryocooler 30 is fed with the re-condensed helium from a condenser 15. Thus-configurated GM cryocooler 30 conductively cools the helium condensing portion 35 contacting the lower cooling portion 33, thus condensing the helium vapor from the helium container 20 when the helium vapor contacts the condensing portion 35.

As shown in Fig. 3 where the coupling relation between the GM cryocooler and the conduction cooling unit are illustrated, the double cable for applying power to the upper cooling portion 31 of the GM cryocooler 30 and to the superconductive magnet 7, is connected through a conductive cooling unit 45. The conductive cooling unit 45 can be formed of a sheet metal, namely sheet copper, and minimizes inflow of heat to the helium container 20 by conductively cooling, through the upper cooling portion 31 of the GM cryocooler 30, the heat transferred through the double cable when the superconductive magnet 7 is electrified.

As shown in Fig. 4 where the coupling relation between the double cable and conduction cooling portion is illustrated in detail, the double cable connected to the superconductive magnet 7 is constituted by a metal coil 41 and an HTS coil 43(shown in Fig.l) which are interconnected through a connection member B like a bolt or rivet. Preferably, the metal coil 41 is formed of a metal sheet, and configured in such a manner that the metal sheet, an insulating sheet 47, and an end of the conduction cooling unit 45 opposite to the connection portion of the upper cooling portion 3 are stacked in sequence from the connection member and fixed through the bolt B. For the convenience of explanation, the laminated structure including the double cable, conduction cooling unit and the insulating sheet is shown in Fig. 4 as if they are protruded; however, they are laminated in an even manner without no protrusion in a practical application. The bolt B is used as a connection member for achieving a tight connection and smooth heat transfer. The insulating sheet 47 is employed for insulation from the conduction cooling unit 45 since the double cable has a high current flowing thereon. The metal coil and HTS coil are directly conductively cooled through the conduction cooling unit 45 in the vacuum state within the vacuum container 3, thus making it possible to use the cryovessel 1 adopting a helium re-condensing system, in a constant electrifying mode, which is otherwise permitted to be used only in the permanent current mode. The constant electrifying mode is needed because the conventional cryovessel adopting a permanent current mode cannot be used in cases where the current switching at a constant interval is required for devices like a single crystal growing device. Referring back to Fig. 1, a controller 11 controls the condenser 15, a heater 9 for heating the helium container 20, and a pressure gauge 17 connected to the helium container 20 and the vacuum container 3 through pipes PI and P2 so as to gauge pressure of containers 20 and 3. The control relationship is shown in a dot line. As shown in Fig. 1, the pipe PI is protruded from the top of the vacuum container 3, and the pipe P2 having a diameter smaller than diameter of the pipe PI is arranged within the vacuum container 3 from the helium container 20 such that the pipe P2 is spaced part from the pipe PI. A safety disc 19 and a pressure gauge 17 are installed at ends of pipes PI and P2. The safety disk 19 prevents the risk of explosion caused due to the excessive pressure of the vacuum container 3 when the internal pressure of the vacuum container 3 and the helium container 20 is higher than a predetermined level, for example, 0.5 bar.

The components shown in Fig. 1 are fed with a power supplied from a power supply 13. For simplicity, the power supply 13 and the double cable are interconnected through a solid line.

The cryovessel of the present invention is configured in such a manner that the helium container 20 is filled with a liquid helium through the pipe P2 at the state where the cryovessel is maintained at a vacuum, and the helium container 20 is sealed when the superconductive magnet is completely dipped into the liquid helium and reaches the temperature of 4.2K. When the GM cryocooler 30 operates, the heater 9 is repeatedly turned on or off by the control of the controller 11, thereby maintaining the internal pressure of the helium container 20 constant. When the superconductive magnet 7 is fed with a direct current, the superconductive magnet generates a magnetic field. Here, amount of evaporation of helium increases due to the fine heat produced from the superconductive magnet 7. The GM cryocooler 30 is configured such that the cycle is repeated where the high pressure helium gas produced from the condenser 15 performs cooling operation in each part of the GM cryocooler 30, independently of the liquid helium contained in the helium container 20, and the helium gas returns to the condenser 15. The cryovessel with thus-configured GM cryocooler is organically controlled through the controller 11, and such a control relationship turns on the heater 9 so as to compulsorily evaporate the helium until the pressure of the helium container 20 reaches a predetermined level, for example 0.05 bar, when the GM cryocooler 30 operates and the helium is condensed in the condensing portion 35. When the pressure of the helium container 20 has reached 0.05 bar by the operation of the heater 9, the heater 9 is turned off and the GM cryocooler 30 is operated, if necessary, so as to condense the helium such that the pressure reaches a predetermined level, for example, 0.01 bar. The GM cryocooler 30 is turned off by turning off the condenser 15 at a pressure lower than a predetermined level, for example -0.03 bar, and the GM cryocooler 30 is turned on again when the pressure is higher than 0.0 bar, so as to prevent the pressure of the hehum container 20 from becoming lower than 0.0 bar due to the incomplete operation of the heater 9. The detection of pressure is performed through the pressure gauge 17.

As described above, the cryovessel according to the present invention has advantages as follows.

First, GM cryocooler is arranged within the cryovessel so as to thereby achieve a compact cryovessel inexpensive to manufacture.

Second, hehum gas is directly re-condensed within the cryovessel through the GM cryocooler so as to thereby miriimize loss of hehum and maintain the initial charged amount. Third, suitable amount of helium is compulsorily evaporated through the heater, such that the internal pressure of the hehum container is prevented from being lowered due to the super cooling exceeding the amount of helium being evaporated from the hehum container. Thus, the pressure of the helium container and the level and temperature of liquid helium are maintained constant, to thereby operate the superconductive magnet in a stable manner. Fourth, double cable for applying power to the superconductive magnet is directly conductively cooled through the GM cryocooler under the vacuum state, to thereby permit the cryovessel to be used in a constant electrifying mode.

Fifth, each component of the cryovessel is controlled organically through the controller, to thereby obtain a high efficiency cryovessel.

Claims

WHAT IS CLAIMED IS:

1. A cryovessel with GM cryocooler, comprising: a vacuum container(3) for heat insulation; a hehum container(20) disposed in an inner lower portion of said vacuum container in such a manner that the helium container is spaced apart from said vacuum container, said hehum container accommodating a superconductive magnet dipped into a liquid hehum so as to receive power through a double cable; a GM cryocooler(30) having upper and lower cooling portions(31,33) accommodated into said vacuum container and a condensing portion(35) connected to said hehum container, said GM cryocooler receiving a re-condensed helium from a condenser^ 15); a conduction cooling unit(45) for interconnecting said upper cooling portion of said GM cryocooler and said double cable connected to said superconductive magnet, said conduction cooling unit conductively cooling a heat transferred through said double cable; a controller^ 11) connected, through pipes(Pl,P2), to said condenser, heater for heating said helium container, said hehum container and said vacuum container, and which controls a pressure gauge(17) for gauging pressure of each container(20,30); and a power supply(13) for supplying power to each component.

2. A cryovessel with GM cryocooler according to claim 1, wherein said double cable connected to said superconductive magnet is constituted by a metal coil(41) and a high temperature superconducting(HTS) coil(43) which are interconnected through a connection member, and said metal coil is formed of a sheet metal, laminated in such a manner that said sheet metal, insulating sheet, and an end of said conduction cooling unit are stacked in sequence from a connection member and fixed through the connection member such as a bolt.

3. A cryovessel with GM cryocooler according to claim 1, wherein said hehum container and said condensing portion are interconnected through a connection portion(21) constituted by a corrugated pipe so as to prevent damage caused due to a vibration.

4. A method for controlling a cryovessel with GM cryocooler according to one of claim 1 to claim 3, said method comprising the steps of: turning on and operating a heater(9) for compulsorily evaporating hehum until said GM cryocooler(30) operates and the pressure of a helium container(20) reaches a predeteπnined pressure level; turning off said heater when the pressure reaches a predetermined level, and condensing the helium by said GM cryocooler so as to maintain a pressure at a constant level; and controlling, through a container, a condenser(15), a heater(9) and a pressure gauge(17) in such a manner that said GM cryocooler is turned off by tiirning off said condenser at a pressure lower than a predetermined pressure level, and tuned on again when the pressure of the hehum container is higher than 0.0 bar so as to prevent the pressure of said helium container from becoming lower than 0.0 bar due to the incomplete operation of said heater.