Refrigeration – Storage of solidified or liquified gas – With measuring
Reexamination Certificate
2003-02-14
2004-11-02
Doerrler, William C. (Department: 3744)
Refrigeration
Storage of solidified or liquified gas
With measuring
C062S050200
Reexamination Certificate
active
06810679
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to apparatus for cooling samples made of various devices and materials (such as various semiconductor devices, semiconductor materials, magnetic materials, superconducting materials, other metal materials or inorganic materials) and maintaining the samples at low temperatures when measurements, observations, or operations are performed regarding such samples at low temperatures reaching the boiling points of liquefied gases.
2. Description of the Related Art
Recently, high-sensitivity magnetometers having spatial resolutions on the order of micrometers and known as SQUIDs (Superconducting Quantum Interference Devices) have been put into practical use, and measurements using SQUID microscopes have been increasingly performed on various devices and materials. Since SQUIDs use superconductivity, it is necessary to cool them at temperatures lower than the temperature of liquid nitrogen (from several K to 77 K). Furthermore, the sample also needs to be retained at low temperatures in many cases. In addition, where samples are observed by tunneling microscopes or atomic force microscopes as well as by SQUIDs, samples are maintained at low temperatures in some cases.
FIG. 2
is a schematic view showing one example of cooling apparatus of related art for cooling a sensor side. A three-axis scanning stage
20
, a cooling head
30
, a coolant introduction port
42
, a sensor
50
, a sample
60
, etc. are installed inside a vacuum chamber
10
. A vacuum pump
70
, a liquefied gas storage tank
40
, and a transfer tube
90
are installed outside the vacuum chamber
10
.
The vacuum chamber
10
is made of stainless steel and maintained in a vacuum state to make provide thermal isolation from the outside.
The three-axis scanning stage
20
is used to place the sample
60
and to control the relative position between the sensor
50
and the sample
60
.
The cooling head
30
is a hermetically closed container made from oxygen-free copper to improve the thermal conduction. A first pipe
31
and a second pipe
32
forming an inlet and an outlet for the coolant are connected with the cooling head
30
. The flow rate of the coolant flowing into the cooling head
30
is adjusted by a needle valve
33
.
The storage vessel is a liquefied gas storage tank
40
which is a vacuum isolation container for storing a liquefied gas
41
. Liquid helium is used as the liquefied gas
41
.
The coolant introduction port
42
is used to introduce the liquid helium into the cooling head
30
installed inside a vacuum chamber. The coolant introduction port
42
and liquefied gas storage tank
40
are connected by the transfer tube
90
, and the coolant stored in the liquefied gas storage tank
40
is introduced into the cooling head
30
.
A SQUID having a detection coil about 10 &mgr;m in diameter is used as the sensor
50
. Niobium operating near the boiling point of liquid helium is used as a superconducting material for fabricating the SQUID. The sensor
50
is made stationary while placed in thermal contact with the cooling head
30
.
The vacuum pump
70
is used to lower the pressure inside the second pipe
32
, cooling head
30
, first pipe
31
, and transfer tube
90
and to transfer the liquid helium in the liquefied gas storage tank
40
.
The procedure for cooling the cooling head
30
is as follows. The coolant introduction port
42
and liquefied gas storage tank
40
are connected by the transfer tube
90
. The vacuum pump
70
is operated and thus the liquid helium stored in the liquefied gas storage tank
40
is passed through the cooling head
30
. In this way, the temperature of the cooling head
30
is cooled close to the boiling point of liquid helium.
After cooling of the cooling head
30
, the sensor
50
is operated, and the relative position between the sensor
50
and the sample
60
is controlled using the three-axis scanning stage
20
. A signal owing to the sensor
50
is recorded. Thus, the magnetic distribution of the sample
60
is measured.
With the above-described cooling apparatus of the related art, where stored liquefied gas is directly used as means for cooling a sensor or a sample to a low temperature, the liquefied gas is often transported into a location to be cooled while using a thin pipe as a medium, or the liquefied gas is transported through a minute space such as a needle valve to adjust the flow rate of the liquefied gas. The stored liquefied gas often contains impurities such as solidified carbon dioxide, oxygen, nitrogen, and water, as well as foreign substances such as microscopic dust and metal fragments. Therefore, foreign substances and impurities sometimes clog up the pipe or needle valve that is a transportation medium for the liquefied gas. Consequently, there is a problem in that the apparatus ceases to function as cooling apparatus. Furthermore, where impurities adhere to the interface portion between the vacuum thermal isolation pipe and coolant introduction port, the interface portion becomes an adhesively bonded state. The vacuum thermal isolation pipe cannot be removed unless an operation for dissolving away the impurities is performed. Hence, the ending operation for the cooling apparatus cannot be performed. Thus, there is a problem in that the workability is poor.
SUMMARY OF THE INVENTION
(First Means)
In accordance with the present invention, a gas collection port is provided in a liquefied gas storage tank of a cooling apparatus. Gas produced by evaporation of the liquefied gas is collected and used as a coolant for a cooling head.
(Second Means)
In addition to the first means, a mechanism for measuring the liquid level of the liquefied gas is provided. The gas collection port is made movable vertically.
(Third Means)
In addition to the first means, a gas-cooling mechanism is provided.
(Fourth Means)
In addition to the first means, a structure is provided in which the liquefied gas storage tank is provided with a gas introduction port.
(Fifth Means)
In addition to the first means, a structure is provided in which a refrigerator and a gas introduction port are used instead of the liquefied gas storage tank.
According to the structure of the cooling apparatus owing to the first means, gas evaporated from the liquefied gas is used as a coolant for the cooling head and so even where impurities are mixed in the liquefied gas stored in the liquefied gas storage tank, a high-purity gas can be used as a coolant. Consequently, the pipe or needle valve for transporting the coolant is not clogged up. The cooling apparatus can be run stably.
Owing to the second means, the liquid level of the liquefied gas can be known. Therefore, the gas collection port can be placed close to the liquid level. Gas of lower temperature can be collected and used as a coolant. In consequence, the cooling head can be cooled to a lower temperature.
Owing to the third means, the collected gas becoming the coolant can be cooled to a lower temperature. As a result, the cooling head can be cooled to a lower temperature.
Owing to the fourth means, the pressure inside the liquefied gas storage tank can be adjusted. Therefore, the pressure inside the liquefied gas storage tank can be prevented from becoming a negative pressure. That the gas becoming the coolant cannot be transported can be prevented. Hence, the cooling apparatus can be run stably.
Owing to the fifth means, a high-purity gas can be used as a coolant without using a liquefied gas. Therefore, intrusion of foreign substances into the cooling apparatus can be prevented. The cooling apparatus can be run stably.
REFERENCES:
patent: 3092974 (1963-06-01), Haumann et al.
patent: 5101636 (1992-04-01), Lee et al.
patent: 5506200 (1996-04-01), Hirschkoff et al.
patent: 5834938 (1998-11-01), Odawara et al.
patent: 6332324 (2001-12-01), Saho et al.
patent: 6583619 (2003-06-01), Zimmermann et al.
Adams & Wilks
Doerrler William C.
SII NanoTechnology Inc.
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