Refrigeration – Gas compression – heat regeneration and expansion – e.g.,...
Reexamination Certificate
2000-02-11
2001-09-25
Doerrler, William (Department: 3744)
Refrigeration
Gas compression, heat regeneration and expansion, e.g.,...
C062S055500
Reexamination Certificate
active
06293109
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a reliable pulse tube refrigerator which can hold a cooling temperature without the use of an additional mechanism such as a heater, and a cryopump using the same.
BACKGROUND ARTS
A cryopump generally produces a high vacuum by adsorbing a gas molecule to an adsorption panel installed on a coldhead of a refrigerator. It is required in the cryopump that a cooling temperature for the adsorption panel is held in a designated range while the adsorption panel adsorbs a gas molecule.
For example, a cryopump exclusive for water requires the cooling temperature for the adsorption panel
3
(
FIG. 1
) to be held in the range of about 110K.
FIG. 1
is a general view of the cryopump exclusive for water. In
FIG. 1
, there are shown a refrigerator
1
which may be a GM (Gifford-McMahon) refrigerator, a coldhead
2
, an adsorption panel
3
installed on the coldhead
2
, a vacuum space
4
in use of the cryopump and a fixture flange
5
.
At present, a GM refrigerator is mainly employed to cool the cryopump, wherein helium gas (single gas) is used as an operating gas. During a normal operation the temperature of the adsorption panel
3
decreases to not greater than 110K (in some cases the temperature decreases to as low as 30 to 40K), and thus deviating from an original purpose to eliminate only water by freezing, other gas components may be frozen. To obviate such a problem, the cryopump exclusive for water is provided with a heater and a thermometer (both are not shown in the figure) on the coldhead
2
for holding a temperature. The adsorption panel
3
can hold its temperature by controlling the temperature of the heater.
However, the conventional cryopump has a heater wiring led out of the vacuum space
4
into the atmosphere, requiring a complicated seal with a high risk of leakage. Further, a temperature controller is necessary in order to follow heat load changes (for example, when water is excessively attached to the adsorption panel
3
or when the vacuum degree is lowered, the temperature of the adsorption panel
3
is increased, necessitating control the temperature control of the heater). Therefore, a complicated mechanism is required, resulting in a cost increase.
In Japanese Patent Publication TOKKAIHEI 6-73542, a cryopump is disclosed which includes, as temperature control means for the adsorption panel
3
, a heat exchanger, a connector connecting the heat exchanger to the adsorption panel
3
, transport means for transporting a cooling medium such as helium gas to the heat exchanger, means for regulating a flow rate of the cooling medium and the like. However, the above-disclosed cyropump also requires a complicated mechanism with a cost increase.
In view of the foregoing, it is an object of the present invention to provide a pulse tube refrigerator which can hold a cooling temperature without the use of a heater and the like and a cryopump using the pulse tube refrigerator.
DISCLOSURE OF THE INVENTION
In accordance with a first aspect of the present invention, there is provided a pulse tube refrigerator employing a working gas which has a liquefying temperature within the range of an operating temperature of the pulse tube refrigerator. In accordance with a second aspect of the present invention, there is provided a cryopump using the above pulse tube refrigerator.
The pulse tube refrigerator of the present invention employs the working gas which has a liquefying temperature within the range of the operating temperature of the pulse tube refrigerator. Therefore, during the operation of the pulse tube refrigerator, the working gas is not cooled lower than the range of the operating temperature of the pulse tube refrigerator, which is substantially equal to the liquefying temperature, and the pulse tube refrigerator keeps its temperature generally constant within the range of the operating temperature thereof. Moreover, after the working gas is cooled to the liquefying temperature, even an external heat load almost causes no temperature change of the coldhead. However, in the case that the heat intake is further increased by the external heat load, the temperature of the coldhead is rapidly increased. Accordingly, it is necessary that a designated temperature of the working gas be set in a temperature range wherein the coldhead causes almost no change in temperature by the external heat load. The temperature range can be adjusted to some extent by use of a mixture of several kinds of gas as a working gas.
More specifically, in operation of the pulse tube refrigerator employing a gas other than helium (for example nitrogen gas), as a working gas, which has a higher liquefying temperature, the working gas is liquefied at a low temperature side of the pulse tube refrigerator. However, in the pulse tube refrigerator, the working gas is compressed and expanded, or moved between the low and high temperature sides, so that the liquefied working gas may be in contact with a portion with a temperature not less than its boiling point, or so that its boiling point may be reduced due to expansion on pressure reduction. Therefore, the liquefied working gas becomes gaseous again without solidifying. Thus, the working gas is repeatedly liquefied and gasified in one cycle, so that the pulse tube refrigerator can operate without clogging a flow path by the working gas. The coldhead of the pulse tube refrigerator holds a temperature of about the liquefying temperature (boiling point) of the working gas. Where the heat load to the coldhead increases (or decreases), the volume of the liquefied gas in one cycle is decreased (or increased). Nevertheless, the coldhead holds a temperature of about the liquefying temperature of the working gas. Even if the heat intake is further increased, the coldhead holds a temperature of about the liquefying temperature of the working gas as long as the working gas is liquefied (See FIG.
2
).
As described above, the pulse tube refrigerator of the present invention make it possible to hold a cooling temperature without adjusting the temperature by use of a heater and the like as in prior art. Therefore, it is not necessary to spend electric energy for the heater and the like, resulting in reduction of energy consumption. Moreover, no control mechanism of the heater simplifies an apparatus, so that the apparatus causes less frequent failures and reduces its cost. Furthermore, no wiring into the vacuum space requires no sealing work, thereby posing no risk of leakage. The cryopump of the present invention employs the above-mentioned pulse tube refrigerator, thus providing the excellent effects described above.
Examples of the working gas in the present invention include various single gases such as nitrogen gas, argon gas and the like. In addition, usable is the air and a gas mixture of helium gas and the like with the above-mentioned single gases. Where the range of the operating temperature of the pulse tube refrigerator is readily known, it is possible to select a single gas or a mixture-ratio-adjusted gas mixture, based on the liquefying temperature thereof which is within the aforementioned range.
REFERENCES:
patent: 3892273 (1975-07-01), Nelson
patent: 5181383 (1993-01-01), Goto et al.
patent: 5269147 (1993-12-01), Ishizaki et al.
patent: 5443548 (1995-08-01), Saho et al.
patent: 03286967 (1991-12-01), None
patent: 08054151 (1996-02-01), None
Ito Daisuke
Kakimi Yasuhiro
Kunitani Shingo
Miyamoto Atsushi
Armstrong Westerman Hattori McLeland & Naughton LLP
Daido Hoxan Inc.
Doerrler William
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