This invention relates to a method for cooling an article using a cryocooler and the cryocooler.
In a superconducting filter of IT communication field, a superconducting MRI of medical field, or in fundamental scientific field, it is required to cool a high precise electron microscope or a high performance precise instrument such as a high sensitivity submillimeter wave detector or an infrared ray detector to eliminate thermal disturbances therefrom. In cooling such a high performance precise instrument as mentioned above, as of now, a liquefied gas or a cryocooler is employed. Recently, the cooling temperature range of the cryocooler is improved down to 4K, which can be easily operated by pushing a button and in the past, can be realized only by using an extremely low temperature cryogen.
Fig. 1 is a structural view schematically illustrating a conventional GM (Gifford McMahon) type cryocooler. The cryocooler 10 illustrated in Fig. 1 includes a compressor 11 and a cryocooler cold head 12. In the cryocooler cold head 12 are provided a regenerator 13 and a displacer 14, and at the bottom in the cryocooler cold head 12 is provided a cold end 16. The combination of the regenerator 13 and the displacer 14 is called as a cooling cylinder. A high pressure gas and a low pressure gas are supplied to the cryocooler cold head 12 from the compressor 11 through the flexible hoses 15 and via the switching valve 17, compressed and expanded at the cryocooler cold head 12.
At the displacer 14, cooling power is created through the expansion of the gas to be synchronized with the expansion of the gas at the next stage by operating the motor 18. The coolant is repeatedly created through a plurality of expansions of the gas, and the thus obtained cooling power is are stored in the regenerator 13. As a result, the cold end 16 is cooled down to an extremely low temperature. An article is contacted with the cold end 16 to be cooled.
Fig. 2 is a structural view schematically illustrating a pulse tube type cryocooler. The cryocooler illustrated in Fig. 2 includes a compressor 21 and a cryocooler cold head 22. In the cryocooler cold head 22 are provided a regenerator 23 and a pulse tube 24, and at the bottom in the cryocooler cold head 22 is provided a cold end 26. The combination of the regenerator 23 and the pulse tube 24 is called as a cooling cylinder. A high pressure gas and a low pressure gas are supplied to the cryocooler cold head 22 from the compressor 21 through the flexible hoses 25 and via the switching valve 27, compressed and expanded at the cryocooler cold head 22.
At the pulse tube 24, cooling power is created through the expansion of the gas to be synchronized with the expansion of the gas at the next stage by operating the switching valve. The gas expansion is carried out by controlling the introduction timing of the gas into a buffer tank 28, which is successive to the pulse tube 24, via an orifice 29. The cooling power is repeatedly created through a plurality of expansions of the gas, and the thus obtained cooling power is stored in the regenerator 23. As a result, the cold end 26 is cooled down to an extremely low temperature. An article is contacted with the cold end 26 to be cooled.
In both of the GM type cryocooler and the pulse tube type cryocooler, since the high pressure gas and the low pressure gas, which are supplied from the compressors 11 and 21, are circulated in the cryocooler cold heads 12 and 22, the cold ends 16 and 26 are vibrated inevitably by an amplitude of about 10 µm in the axial directions thereof. The allowable limit in vibration of the high performance precise instrument is within a range of submicro-meter, so that if a relatively large vibration is applied to the precise instrument, the inner structure and the controllability of the precise instrument may be destroyed, so that the precise instrument may malfunction.
It is an object of the present invention to cool an article such as a high performance precise instrument up to an extremely low temperature without the application of vibration to the article.
In order to achieve the above object, this invention relates to a method according to claim 1 for cooling an article using a cryocooler , and a cryocooler according to claim 5.
The inventors had intensely studied to achieve the above-mentioned object. As a result, they found out the following fact.
The cold end is formed in circular shape, and two pairs of cooling cylinders are arranged on the main surface of the cold end so that the diagonal line connecting one pair of cooling cylinders is orthogonal to the diagonal line connecting the other pair of cooling cylinders. Then, a high pressure gas is supplied to the one pair of cooling cylinders, and a low pressure gas is supplied to the other pair of cooling cylinders. In this case, the shape of the cold end is deformed as shown in Fig. 3. As is apparent from Fig. 3, although the shape of the cold end is changed with time, the portion substantially near and along the diameter of the cold end, particularly the almost center portion of the cold end is not deformed and remain stationary.
Therefore, if a stationary point is set onto the stationary area of the cold end, and a given article is cooled by utilizing the stationary point, the article can be cooled up to an extremely low temperature with isolation of vibration to the article.
For better understanding of the present invention, reference is made to the attached drawings, wherein
This invention will be described in detail with reference to the accompanying drawings. Fig. 4 is a structural view illustrating a cold end of a cryocooler according to the present invention, and Fig. 5 is a structural view illustrating the connection of the cooling cylinder of the cryocooler illustrated in Fig. 4 to the cold end thereof. In Fig. 4, a compressor is omitted and only the cryocooler cold head is drawn.
The cryocooler cold head 30 illustrated in Fig. 4 includes two pairs of cooling cylinders 31, 32 and a cold end 36 which is provided at the bottoms of the cooling cylinders 31 and 32 so as to be connected with the cooling cylinders 31 and 32.
As illustrated in Fig. 5, the cooling cylinders 31 and 32 are connected with the cold end 36 so that the diagonal line X connecting the cooling cylinders 31 is orthogonal to the diagonal line Y connecting the cooling cylinders 32.
A high pressure gas is supplied to the cooling cylinders 31, and a low pressure gas is supplied to the cooling cylinders 32. In this case, the portion of the cold end 36 to which the high pressure gas is applied is deformed downward, and the portion of the cold end 36 to which the low pressure gas is applied is deformed upward.
However, the area near and along the diameter Z between the upward and the downward deformed portions of the cold end 36 is not almost deformed, and particularly, the center O of the cold end 36 is not almost deformed. Therefore, a stationary point can be set onto the area near and along the diameter Z.
In the cryocooler 30 illustrated in Fig. 4, a mounting slot 39 is formed at the center O of the cold end 36 as the stationary point. Therefore, if a given article is mounted on the mounting slot 39, the article can be cooled almost with isolation of vibration to the article.
If the gas supply cycle to the cooling cylinders 31 is shifted from the gas supply cycle of the cooling cylinders 32 by a phase shift of 180 degrees and the cold end 36 is made by thick and rigid material such as tungsten carbide, the cold end 36 itself can not be vibrated. In this case, the stationary point can be set onto any portion of the cold end 36.
Although the present invention was described in detail with reference to the above examples, this invention is not limited to the above disclosure and every kind of variation and modification may be made without departing from the scope of the present invention.
According to the present invention can be cooled an article such as a high performance precise instrument up to an extremely low temperature with isolation of vibration to the article.
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