JPH0684854B2 - Helium refrigerator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a helium refrigerator having a binary circuit of a pre-cooling refrigeration circuit for expanding helium gas and a JT circuit (Joule Thomson circuit), and particularly The present invention relates to a measure for shortening the so-called cooldown operation time from an operation stop state (normal temperature state) to a steady operation state (generation state of extremely low temperature).

(Prior Art) Conventionally, a high-pressure helium gas compressed by a helium compressor is expanded by an expander to perform a cryostat (low temperature tank).
A pre-cooling refrigeration circuit that shields the low-temperature generation part inside from the outside by radiation, and high-pressure helium gas from the compressor is heat-exchanged in the pre-cooling refrigeration circuit to pre-cool, and the pre-cooled helium gas is further exposed to the JT valve. There is known a binary helium refrigerator provided with a JT circuit for expanding Joule-Thomson and generating an extremely low temperature in the low temperature generating portion of the cryostat by the expansion action.

(Problems to be Solved by the Invention) In a helium refrigerator having such a JT circuit, the temperature of the helium gas in the JT circuit is at room temperature (300 K )
And its density is small compared to the cryogenic temperature (about 4K) in the steady operation state. Therefore, if the opening of the JT valve is maintained at the opening (constant opening) at the steady operation level in the refrigerator, the resistance of the gas when passing through the JT valve becomes large, and as a result, The return pressure of the helium gas to the compressor may drop. Therefore, in order to avoid the reduction of the return pressure, it is necessary to change and adjust the opening of the JT valve as the cooldown operation progresses, but the cooldown operation time is extremely long and the cooldown operation time is long. There has been a problem that the opening of the JT valve has to be continuously adjusted, and its operation requires a great deal of trouble.

Therefore, the applicant of the present invention connects the high-low pressure pipes of the compressor unit of the J-T circuit with each other by a bypass circuit in order to eliminate the need to adjust the opening degree of the J-T valve during the cool-down operation. By providing a solenoid valve for opening and closing the bypass circuit and a throttle mechanism, and allowing helium gas discharged from the compressor to pass through the bypass circuit from the beginning of the cool-down operation until a predetermined time elapses. -A proposal is made that the operation of adjusting the opening of the T valve is made unnecessary.

However, in that case, J-
Since only a small amount flows into the T circuit itself, it takes time to lower the cooler of the 4K stage from 300K (normal temperature) to 150K level, and when the heat capacity of the 4K stage is large, the cool down time is drastically increased. It becomes longer and there is room for improvement.

The present invention has been made to solve the above problems,
The purpose is to use the pre-cooling refrigeration circuit and J-
In a helium refrigerator having a binary circuit consisting of a T circuit, a helium gas is added to the bypass circuit on the unit side connecting the high and low pressure pipes of the compressor unit in the JT circuit as described above, and helium gas is added to the JT valve. By providing a J-T valve side bypass circuit that bypasses and circulates and controls the opening and closing of these two bypass circuits appropriately, even if the heat capacity of the 4K stage is large, the cool down time does not become long. The purpose is to make it unnecessary to adjust the opening of the JT valve during the cool-down operation.

(Means for Solving the Problems) In order to achieve the above object, in the present invention, as shown in FIG. 1, high-pressure helium gas compressed by the compressor (3) is expanded by the expander (7). The pre-cooling refrigeration circuit (2) that expands to generate cryogenic temperature and the high-pressure helium gas from the compressors (14) and (16) are pre-cooled by heat exchange with the pre-cooling refrigeration circuit (2), and then pre-cooled. J-Thomson expansion of helium gas from J-T valve (29) to generate cryogenic temperature J-
Assume a helium refrigerator with T-circuit (1).

The compressor unit (A) of the JT circuit (1)
A unit side bypass circuit (31) for connecting the high and low pressure pipes (22) and (30) to each other, and the unit side bypass circuit (3
Unit-side electromagnetic valve for opening and closing the 1) and (SV ₁₎ and throttle mechanism (32), a J-T valve bypass circuit which helium gas is circulated by bypassing the J-T valve (29) (33),
A JT valve side solenoid valve (SV ₂ ) for opening and closing the JT valve side bypass circuit (33) and a pressure reducing mechanism (34) are provided.

Furthermore, during the cool-down operation, the JT valve side solenoid valve (SV ₂ ) is opened and the unit side solenoid valve (SV ₁ ) is closed at the initial stage, and the cooler (27) moves to the compressors (14), (16). When the return pressure of helium gas returning to) rises above a predetermined pressure or when the temperature of the cooler (7) drops below a predetermined temperature, J- after opening the unit side solenoid valve (SV ₁ ) A control means (50) is provided to control so that the T valve side solenoid valve (SV ₂ ) is closed and the unit side solenoid valve (SV ₁ ) is also closed at the end.

(Operation) With this configuration, in the present invention, during the cool-down operation of the helium refrigerator, the operation of the control means (50) causes
The temperature level of the cooler (27), which is a 4K stage, is at room temperature (30
Initially (0K), the JT valve side solenoid valve (SV ₂ ) is opened and the unit side solenoid valve (SV ₁ ) is closed. In this state, the helium gas discharged from the compressors (14) and (16) hardly flows through the J-T valve (29), and most of the J-T valve (2).
9) bypass the JT valve side bypass circuit (3
3) flow. Therefore, even if the temperature of the helium gas in the 4K stage is high and the density thereof is low, the return pressure returning to the compressors (14) and (16) is prevented from decreasing.

Thereafter, as the cool-down operation progresses, when the return pressure of the helium gas returning from the cooler (27) to the compressors (14) and (16) rises above a predetermined pressure, or the cooler (27). When the temperature falls below a predetermined temperature, the unit side solenoid valve (SV ₁ ) is opened, and then the JT valve side solenoid valve (SV ₂ ) is closed. Then, at the end of the cool-down operation, the solenoid valve (SV ₁ ) on the unit side is closed, and finally the operation goes to the steady operation state.

In this case, during the cool down operation as described above, when the JT valve side solenoid valve (SV ₂ ) is open (the unit side solenoid valve (SV ₁ ) is closed), the helium gas is J-
Helium gas flows through the T-valve (29) by bypass, and then the unit side solenoid valve (SV ₁ ) is opened (J-T valve side solenoid valve (SV ₂ ) is closed). , (30)
Since the two flow short-circuiting each other, the opening of the J-T valve (29) can be maintained at the steady opening during steady operation of the refrigerator throughout the cool down operation, and thus J during the cool down operation can be maintained. -The operation of adjusting the opening of the T valve (29) can be eliminated.

At the beginning of the cool-down operation, J
-By flowing through the JT circuit (1) itself while bypassing the T valve (29), the cooling capacity of the JT circuit (1) is ensured, so even if the heat capacity of the 4K stage is large, it is cool. The downtime can be greatly reduced.

(Example) Hereinafter, the Example of this invention is described based on drawing.

FIG. 1 shows the overall structure of a helium refrigerator of a two-stage two-stage compression cycle according to an embodiment of the present invention. (1) is a J-Thomson expansion for compressing helium gas to generate a cryogenic temperature. A T circuit, (2) is a precooling refrigeration circuit for compressing and expanding the helium gas in order to precool the helium gas in the JT circuit (1) to generate an extremely low temperature. The JT circuit (1) Between the JT side compressor unit (A) and the cryostat (C) (low temperature tank) having the low temperature generation part (C ₁ ) for holding the cooled object (not shown) in a cooled state, Pre-cooling refrigeration circuit (2)
Are arranged in parallel with each other across the precooling compressor unit (B) and the cryostat (C).

The pre-cooling compressor unit (B) separates and removes the pre-cooling compressor (3) for compressing helium gas, and the lubricating oil for the compressor (3) from the high-pressure helium gas compressed by the compressor (3). And an adsorber (5) for adsorbing and removing impurities such as water and impure gas in the helium gas that has passed through the oil separator (4). It is connected to the high pressure side inlet (8a) of the casing (8) in the expander (7) fitted in the cryostat (C) through the high pressure pipe (6).

The expander (7) includes the casing (8) arranged outside the cryostat (C) and a cylinder (9) connected to a lower portion of the casing (8). The cylinder (9) First and second heat stations (10) and (11) which are inserted into the cryostat (C) are provided on the outer circumference of the. Although not shown, the helium gas, which is opened at every rotation of the casing (8) and flows from the high pressure side inlet (8a), is introduced into the cylinder (9).
A rotary valve to be supplied to the inside and a valve motor to drive the rotary valves are fitted, while a slack piston that reciprocates according to opening and closing of the rotary valve in the cylinder (9) and the slack piston. A displacer that is integrally driven to reciprocate and reciprocates in the cylinder (9) to expand the helium gas by Simon is inserted. The first heat station (10) of the cylinder (9) is in thermal contact with the radiation shield part (C ₂ ) arranged so as to surround the low temperature generation part (C ₁ ) in the cryostat (C), By opening the rotary valve of the expander (7), high-pressure helium gas is expanded in the cylinder (9) to generate a low temperature state, and the low temperature state is generated in the first and second heat stations ( The radiation shield part (C ₂ ) which is held in 10) and (11) and is in thermal contact with the first heat station (10) is cooled to a low temperature, and the low temperature generating part (C ₁ ) inside thereof is cooled.
Is configured to shield the radiation from the outside.

In addition, the casing (8) of the expander (7) is provided with a low pressure side outlet (8b) for discharging the expanded low pressure helium gas, and the low pressure side outlet (8b) is passed through a low pressure pipe (12). Is connected to a surge bottle (13) provided in the precooling compressor unit (B), the surge bottle (13) is connected to the suction side of the precooling compressor (3), and the expander (7) is connected. The pressure fluctuation of the low-pressure helium gas discharged from (1) is absorbed by the surge bottle (13) and sucked into the compressor (3). As described above, the high-pressure helium gas discharged from the precooling compressor (3) is supplied to the expander (7) via the oil separator (4) and the adsorber (5), and the expander (7) is supplied. The temperature of the heat stations (10) and (11) is lowered by adiabatic expansion at the temperature to shield the low temperature generation part (C ₁ ) in the cryostat (C) from radiation and pre-cooled later in the JT circuit (1). Bowl (2
4) and (25) are pre-cooled, and the expanded low-pressure helium gas is returned to the compressor (3) via the surge bottle (13) and re-compressed.

On the other hand, in the JT side compressor unit (A), a low-stage compressor (14) that compresses helium gas to a predetermined pressure, and a compressor (from a high-pressure helium gas discharged from the compressor (14) ( 14) An oil separator (15) for separating and removing lubricating oil, and a high-stage compression for compressing the high pressure helium gas discharged from the oil separator (15) and passing through the intermediate pressure pipe (35) to a higher pressure. Machine (16), an oil separator (17) for separating and removing lubricating oil for the compressor (16) from the high-pressure helium gas discharged from the compressor (16), and the oil separator (17) And an adsorber (18) for adsorbing and removing impurities in the high-pressure helium gas.

In addition, the cryostat (C) has a primary side and a secondary side.
First to third JT heat exchangers (19) to (21) for exchanging heat with each other between the helium gases passing through the next sides are fitted, and these JT heat exchangers (19) to (). 21) out of
The second and third J-T heat exchangers (20), (21) are arranged in the radiation shield part (C ₂ ) of the cryostat (C). The primary side of the first J-T heat exchanger (19) is connected to the adsorber (18) of the J-T side compressor unit (A) via a high pressure pipe (22). The primary sides of the first and second JT heat exchangers (19) and (21) are connected to the adsorber (23) and the outer periphery of the first heat station (10) of the expander (7). Is connected via the first precooler (24) arranged in the same manner, and the primary sides of the second and third J-T heat exchangers (20), (21) are similarly adsorbed by the adsorber (25 ) And a second precooler (26) arranged on the outer periphery of the second heat station (11) of the expander (7). Further, the primary side of the third J-T heat exchanger (21) is supported by the lower end of the cylinder (9) of the expander (7) and is cooled as a 4K stage located in the low temperature generating part (C ₁ ). It is connected to the container (27) through an adsorber (28) and a JT valve (29). The JT valve (29) expands high-pressure helium gas by Joule-Thomson, and its opening is fixed to a steady opening during steady operation of the helium refrigerator. The cooler (27) passes through the secondary sides of the third and second J-T heat exchangers (21) and (20) to the first JJ.
The secondary side of the -T heat exchanger (19) is connected to the secondary side of the first J-T heat exchanger (19) through the low pressure pipe (30).
-Low side compressor (14) in T side compressor unit (A)
Is connected to the suction side of. Therefore, the two compressors (14) and (16) connected in series in two stages compress the helium gas to a high pressure and supply the helium gas to the cryostat (C) side. Third J-
In the T heat exchangers (19) to (21), heat is exchanged with the low temperature and low pressure helium gas returning to the JT side compressor unit (A), and at the first and second precoolers (24) and (26). The first and second heat stations (1) of the expander (7)
After cooling by heat exchange with (0) and (11), the JT valve (2
At 9), the Joule-Thomson was expanded, and the cooler (27) produced helium at 1 atm and about 4K during steady operation. Then, the low pressure helium gas was passed through the first to third JT heat exchangers (19). Through (21) through the respective secondary sides, the low-stage compressor (14) of the JT side compressor unit (A) is sucked and recompressed.

Further, as a feature of the present invention, the compressor unit (A) of the JT circuit (1) is connected to the low pressure pipe (30) of the high pressure arrangement (22) by a unit side bypass circuit (31), The unit side bypass circuit (31) is provided with a unit side solenoid valve (SV ₁ ) for opening and closing the bypass circuit (31) and a capillary tube (32) as a throttle mechanism. The flow rate of helium gas determined by the capillary tube (32) of (31) is
The return pressure of the helium gas returning to the compressors (14) and (16) is set to be the normal return pressure even at room temperature (300K), which is the start of the cooldown operation of the refrigerator.

On the other hand, in the JT circuit (1) in the cryostat (C), a JT valve side bypass circuit (33) that allows helium gas to flow by bypassing the JT valve (29).
Is branched and connected to the JT valve side bypass circuit (33) to open and close the JT valve side solenoid valve (SV).
₂ ) and a capillary tube (34) as a pressure reducing mechanism are arranged.

The solenoid valves (SV ₁ ) and (SV ₂ ) are configured so that their opening and closing are controlled by a controller (50) as a control means, and the controller (50) includes a cooling unit as the 4K stage. From vessel (27) to compressor (14), (16)
The output signal of the pressure sensor (51) for detecting the return pressure of the helium gas returned to is input to the solenoid valve of the JT valve side at the initial stage of the cool-down operation under the control of this controller (50). SV ₂ ) is opened and unit side solenoid valve (SV ₁ ) is closed, while cooler (27)
When the compressor (14), the return pressure of the helium gas back to (16) rises above a predetermined pressure from the unit-side electromagnetic valve (SV ₁₎ is J-T valve side electromagnetic valve after opening (SV ₂ )
Is closed and finally the unit side solenoid valve (SV ₁ ) is controlled to be closed.

Further, as shown in FIG. 2, in the JT side compressor unit (A) of the JT circuit (1), the oil separator (1
The intermediate pressure pipe (35) connected to the discharge side of 5) (the suction side of the high-stage compressor (16)) and the high-pressure pipe (22) connected to the discharge side of the adsorber (23) are connection pipes. A ballast tank (37) for storing helium gas at a predetermined pressure and a high-pressure pipe (2) connected in the middle of the connection pipe (36).
2) A high pressure control valve (38) that automatically opens when the helium gas pressure in the rises above a predetermined pressure and allows the high pressure helium gas in the high pressure pipe (22) to flow into the ballast tank (37). When the helium gas pressure in the pressure pipe (35) becomes lower than the gas pressure in the ballast tank (37), the helium gas in the ballast tank (37) corresponding to the difference in pressure is fed into the intermediate pressure pipe (35). And a capillary tube (39) for flowing into the chamber. Further, a solenoid valve (SV ₃ ) is connected to the connection pipe (36) in parallel with the high pressure control valve (38).

In addition, the two compressors (1) of the compressor (3) of the precooling compressor unit (B) and the JT side compressor unit (A)
The structure of 4) and (16) and its peripheral devices are constructed in the same structure. In FIG. 1, (40) is each compressor (3),
Oil separators (4), (15), from the discharge side of (14), (16)
A discharge gas coil (40) provided in the middle of a flow path reaching (17), wherein the discharge gas coil (40) is provided for each compressor (3),
It is wound around the upper half of the outer circumference of the casing (not shown) of (14) and (16). Further, a cooling water coil (41) through which cooling water flows is wound around the entire outer peripheral surface of each compressor (3), (14), (16) substantially in parallel with the discharge gas coil (40). The cooling water flowing through the cooling water coil (41) causes the compressors (3), (1
The high temperature and high pressure helium gas discharged from 4) and (16) and flowing in the discharge gas coil (40) is cooled.

Reference numeral (42) is an oil coil wound around the lower half of the outer peripheral surface of the casing of each compressor (3), (14), (16) substantially parallel to the cooling water coil (41). Coil (42)
Of the compressor (3), (14), (16) has an oil reservoir at the bottom of the casing, and a downstream end of the compressor (3), (14), (16) via an injection pipe (44) provided with an oil filter (43). 3), (14) and (16) are respectively connected to the suction side, and the lubricating oil in the casing discharged from the compressors (3), (14) and (16) together with the helium gas is transferred to the oil coil (42). ) To cool the cooling water in the cooling water coil (41) and inject the cooled lubricating oil into the suction helium gas through the injection pipe (44).

Next, the operation of the helium refrigerator of the above embodiment will be described in detail.

With the start-up of the helium refrigerator, first, the compressor (3) of the pre-cooling refrigeration circuit (2) and the two low-stage and high-stage compressors (14), (16) of the JT circuit (1) are connected. Is activated and the cool-down operation is performed. In this cool-down operation state, basically, the high-pressure helium gas supplied from the compressor (3) is expanded by the expander (7) on the cryostat (C) side in the pre-cooling refrigeration circuit (2), and this gas is expanded. As the cylinders (9) expand, the heat stations (1
0), (11) and the temperature of the radiation shield part (C ₂ ) that is in thermal contact with the first heat station (10),
The low temperature generation part (C ₁ ) in the cryostat (C) is shielded against the outside.

Meanwhile, at the same time, the helium gas returning from the cryostat (C) through the JT circuit (1) is sucked and compressed by the low-stage compressor (14) and cooled by the cooling water coil (41) around it. Cooled to 300K at room temperature with water,
This helium gas is sucked and compressed by the high-stage compressor (16) after the oil component is separated by the oil separator (15). Further, the discharge gas from the compressor (16) is cooled again to room temperature 300K by the cooling water in the cooling water coil (41) around the compressor (16), and is separated by the oil separator (17) and then adsorbed. Impurities are adsorbed in the vessel (18), and the clean high-pressure helium gas thus obtained is supplied to the cryostat (C).

The high-pressure helium gas supplied to the cryostat (C) side enters the primary side of the first J-T heat exchanger (19), and J-
Returning to the T-side compressor unit (A), heat is exchanged with the low-pressure helium gas on the secondary side to cool from room temperature 300K, and then the first heat station (50) to 60K of the expander (7). 10) It enters the first precooler (4) on the outer periphery and is further cooled to a low temperature. This cooled gas is the 2nd J
After entering the primary side of the −T heat exchanger (20) and returning to the JT side compressor unit (A), the expander (7) is cooled by heat exchange with the low pressure helium gas on the secondary side. No. 2 on the outer periphery of the No. 2 heat station (11) cooled to 15 to 20K
It enters the precooler (26) and is cooled to a low temperature. further,
The gas enters the primary side of the 3rd J-T heat exchanger (21) and
It is cooled by heat exchange with the low pressure helium gas on the secondary side over the T side compressor unit (A), and reaches the JT valve (29). The high-pressure helium gas is throttled by the JT valve (29) and expanded by Joule-Thomson, and then supplied to the cooler (27). Thereafter, the low-pressure return helium gas that has exited the cooler (27) is supplied to the third to first J-T heat exchangers (21) to
After passing through each secondary side of (19) and raising the temperature to about 300K by heat exchange with the high pressure helium gas on the primary side, it passes through the low pressure pipe (30) and the JT side compressor unit (A ) Return to. After that, the same cycle is repeated and the cool down operation is performed for a predetermined time.

When such a cool-down operation is completed, the refrigerator shifts to a steady operation state, and in this steady operation state, the above J-T
Due to Joule-Thomson expansion in the valve (29), the high-pressure helium gas becomes helium in a gas-liquid mixed state of 1 atm and 4.2K, and then the latent heat of vaporization of the liquid portion in the helium in the gas-liquid mixed state in the cooler (27). Is used for the liquefaction and recondensation of other helium gas or for cooling the cooled object. Also,
Low-pressure helium gas from the cooler (27) is about 4.2K.
After becoming saturated gas of JT side compressor unit (A)
Return to and continue this cycle.

Then, in this embodiment, at the same time when the helium refrigerator is activated, the controller (50) is actuated so that the unit side electromagnetic wave in the compressor unit (A) of the JT circuit (1) is changed as shown in FIG. The valve (SV ₁ ) is closed to close the unit side bypass circuit (31), and the JT valve side solenoid valve (SV ₂ ) is opened to open the JT valve side bypass circuit (3).
3) is opened, and by opening the JT valve side bypass circuit (33), the compressor (14) of the compressor unit (A),
Most of the high pressure helium gas supplied from (16) bypasses the JT valve (29) and passes through the JT valve side bypass circuit (33) to the compressors (14), (16). Return to.
This ensures a large return pressure of the helium gas returning to the compressors (14) and (16).

After this, J-
The gas temperature in the cooler (27) of the T circuit (1) is lowered to near cryogenic temperature, and the density of the helium gas is increased accordingly, so that the volume of the helium gas in the JT circuit (1) is reduced and When the return pressure decreases, the unit side solenoid valve (SV ₁ ) is opened by the controller (50) which receives the output signal of the pressure sensor (51), and then the JT valve side solenoid valve (SV ₂ ) is opened. These solenoid valves (SV ₁ ), (S
The high pressure helium gas supplied from the compressors (14) and (16) flows through the JT valve (29) by switching the V ₂ ), and the Joule-Thomson expansion is performed by the JT valve (29). After that, it returns to the compressor (14), (16). Then, finally, the unit side solenoid valve (SV ₁ ) is also closed to shift to the steady operation state.

In this case, in the cool-down operation state of the refrigerator, helium gas flows by-passing the JT valve (29), so that the opening degree of the JT valve (29) is constant, that is, the refrigerator is stationary. Even if it is fixed to the steady opening during operation, the return pressure of the helium gas returning to the compressors (14) and (16) can be secured to a large extent, and the JT valve (2
You can simplify the work by eliminating the opening adjustment operation of 9),
Therefore, the cooldown operation of the helium refrigerator can be automated.

Also, during such a cool-down operation, helium gas bypasses the JT valve (29), but the JT circuit (1)
Since it flows through itself, even if the heat capacity of the cooler (27) as a 4K stage is large, especially when the cooler (27) is kept at room temperature (30
It is possible to cool from 0K) to 150K level in a short time, so that the cooldown time until the steady operation state of the refrigerator is reached can be greatly shortened.

Further, after the JT valve side solenoid valve (SV ₂ ) is closed along with the release of the helium gas bypass to the JT valve (29), the bypass side solenoid valve (SV ₁ ) is kept open. Since the return pressure of the helium gas can be secured to a large extent, the adverse effect does not occur so much even if the closing timing of the JT valve side solenoid valve (SV ₂ ) is roughly set.

In parallel with such control, helium gas is automatically exchanged between the ballast tank (37) and the JT circuit (1) during the cooldown operation of the refrigerator. That is, the gas temperature in the cooler (27) of the JT circuit (1) decreases to near cryogenic temperature, and the density of the helium gas increases accordingly, so that the volume of the helium gas in the JT circuit (1) is reduced. When the gas pressure in the intermediate pressure pipe (35) decreases and becomes lower than the gas pressure in the ballast tank (37) below the steady state, the gas pressure in the intermediate pressure pipe (35) and the ballast tank (37) decreases. Tank due to the difference in gas pressure (37)
The helium gas in the inside automatically flows into the intermediate pressure pipe (35) through the capillary tube (39), whereby the insufficient helium gas is replenished in the JT circuit (1), and J -The gas pressure in the T circuit (1) is kept in a steady state.

Then, during steady operation of the refrigerator, the gas temperature in the cooler (27) rises for some reason, and the density of the helium gas decreases, so that the volume of gas in the JT circuit (1) increases. Then, when the gas pressure tries to increase above the steady state, the high pressure control valve (38) automatically opens at that point, and J
-The helium gas in the T circuit (1) flows into the ballast tank (37) through the open high pressure control valve (38) by the amount of increase in the volume, and the helium gas is generated by the ballast tank (37). JT circuit (1) due to pressure absorption
It is possible to suppress an abnormal rise in the gas pressure inside.
Also, when the operation of the refrigerator is stopped, the solenoid valve (SV ₃ ) is immediately opened accordingly, which causes the high pressure pipe (2
The high-pressure helium gas in 2) flows into the ballast tank (37), and the helium gas having a predetermined pressure is stored in the ballast tank (37).

In this case, the ballast tank (37) and the intermediate pressure pipe (35) are connected by the capillary tube (39), and the capillary tube (39) allows the helium in the ballast tank (37) during the cooldown operation of the refrigerator. Since the gas is automatically supplied into the JT circuit (1),
Compared to the conventional case where a low pressure control valve is used (see FIG. 4), the expensive low pressure control valve can be omitted, and the cost can be reduced accordingly.

(Other Embodiments) FIG. 4 shows another embodiment of the present invention (note that the same parts as those in FIG. 2 are designated by the same reference numerals and detailed description thereof will be omitted), JT circuit. The intermediate pressure pipe (30) of (1) and the ballast tank (37) are connected by the low pressure control valve (45), while the high pressure control valve (38) in the above embodiment is omitted and the solenoid valve (SV ′ _{3) is used.} ) Only, this solenoid valve (SV ' ₃ )
The open / close control is performed according to the ON / OFF signal of the pressure switch (PS) that detects the gas pressure in the high-pressure pipe (22).

Therefore, in this embodiment, when the gas pressure in the intermediate pressure pipe (35) drops below a predetermined pressure due to the progress of the cooldown operation of the refrigerator, the low pressure control valve (45) automatically opens and the ballast tank ( The helium gas in 37) is supplied into the intermediate pressure pipe (35). On the other hand, when the gas pressure in the high-pressure pipe (22) rises above the predetermined pressure due to the temperature rise, the pressure switch (PS) turns ON, and this pressure switch (PS)
The solenoid valve (SV ′ ₃ ) is opened in response to the ON signal, and the helium gas in the high-pressure pipe (22) is stored in the ballast tank (37). Therefore, in the case of this embodiment, the expensive high pressure control valve is omitted, and the cost can be reduced accordingly.

In each of the above embodiments, when the return pressure of helium gas rises above a predetermined pressure during the cool down operation of the helium refrigerator, the unit side solenoid valve (SV ₁ ) is opened and the JT valve side solenoid valve is opened. I'm trying to close (SV ₂ ),
The solenoid valves (SV ₁ ) and (SV ₂ ) are opened and closed by switching to the cooler (2
It may be performed when the temperature of 7) drops below a predetermined temperature, and the same operational effect as each of the above-described embodiments can be obtained.

(Effects of the Invention) As described above, according to the present invention, the helium refrigerator having the pre-cooling refrigeration circuit and the binary circuit of the JT circuit is used, as opposed to the high / low pressure pipe of the compressor unit of the JT circuit. A unit-side bypass circuit that connects the two to each other and a J-T valve side bypass circuit that allows helium gas to flow by bypassing the J-T valve are provided, and the J-T valve described above is initially provided during the cool-down operation of the refrigerator. After opening the side bypass circuit and closing the unit side bypass, after opening the unit side bypass circuit when the return pressure of the helium gas rises above a predetermined pressure or when the temperature of the cooling stage drops below a predetermined temperature. By closing the J-T valve side bypass circuit and finally closing the unit side bypass circuit as well, it is possible to adjust the opening degree of the J-T valve during the cool down operation. It is possible to secure a large return pressure of the helium gas and shorten the cooldown time without requiring any operation for automating the cooling down operation of the helium refrigerator having the JT circuit, and to shorten the cooldown operation. it can.

[Brief description of drawings]

The drawings show an embodiment of the present invention. Fig. 1 is an overall configuration diagram of a helium refrigerator, Fig. 2 is a piping system diagram around a ballast tank, and Fig. 3 is a JT circuit during cooldown operation.
It is a characteristic view showing each characteristic of the temperature change of the 4K stage and the return pressure change of helium gas. FIG. 4 is a view corresponding to FIG. 2 showing another embodiment. (A) ... JT side compressor unit, (B) ... precooling compressor unit, (C) ... cryostat, (1)
…… JT circuit, (2) …… Pre-cooling refrigeration circuit, (3) ……
Pre-cooling compressor, (7) …… expander, (14) …… low stage compressor, (16) …… high stage compressor, (22) …… high pressure piping, (2
9) …… JT valve, (30) …… Low pressure piping, (31) …… Unit side bypass circuit, (SV ₁ ) …… Unit side solenoid valve, (32) …… Capillary tube, (33)… ... JT
Valve side bypass circuit, (SV ₂ ) …… JT valve side solenoid valve, (3
4) …… Capillary tube, (35) …… Intermediate pressure piping,
(37) …… Ballast tank, (50) …… Controller.

Claims (1)

[Claims] 1. A precooling refrigeration circuit (2) for expanding a high pressure helium gas compressed by a compressor (3) to generate an extremely low temperature by an expander (7), and a compressor (14), (16). Of the high pressure helium gas is pre-cooled by heat exchange with the pre-cooling refrigeration circuit (2), and the pre-cooled helium gas is cooled by the JT valve (29).
And a JT circuit (1) for expanding the Joule-Thomson to generate a cryogenic temperature.
The unit side bypass circuit (31) connecting the high and low pressure pipes (22) and (30) of the compressor unit (A) of the JT circuit (1) and the unit side bypass circuit (31) are opened and closed. Unit side solenoid valve (SV ₁ ) and throttle mechanism (32)
And a JT valve side bypass circuit (33) that allows helium gas to flow by bypassing the JT valve (29), and
The J-T valve side solenoid valve (SV ₂ ) that opens and closes the T valve side bypass circuit (33) and the pressure reducing mechanism (34), and the above J-T valve side solenoid valve (SV ₂ ) at the initial stage of cool-down operation. Open and close the solenoid valve (SV ₁ ) on the unit side, and when the return pressure of the helium gas returning from the cooler (27) to the compressors (14), (16) rises above a predetermined pressure or the cooler (2
When the temperature of 7) drops below the specified temperature, open the unit side solenoid valve (SV ₁ ) and then open the JT valve side solenoid valve (SV1).
A helium refrigerator comprising: a control means (50) for closing V ₂ ) and closing the unit side solenoid valve (SV ₁ ) at the end.