JPS63210573A - Helium refrigerator - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a helium refrigerator having a binary circuit of a pre-cooling refrigeration circuit and a J-T circuit (Joule-Thomson circuit) for expanding helium gas, and in particular, This relates to measures to absorb fluctuations in helium gas pressure in the J-T circuit due to temperature changes between when the operation is stopped (at room temperature) and when it is in steady operation (when extremely low temperatures occur due to the completion of so-called cool-down operation). .

(Conventional technology) Conventionally, high-pressure helium gas compressed by a helium compressor is expanded before expansion to create a cryostat (cryogenic chamber).
A pre-cooling refrigeration circuit that shields the low-temperature generation part inside from radiation from the outside, and high-pressure helium gas from the compressor is heat-exchanged and pre-cooled by the pre-cooling refrigeration circuit, and the pre-cooled helium gas is roughly transferred to the J-T. 2. A J-T circuit that expands the Joule-Thomson with a valve and generates a cryogenic temperature in the low temperature generating section of the cryostat by the expansion action.
The original helium refrigerator is known.

By the way, in a helium refrigerator having such a J-T circuit, the temperature of the helium gas in the J-7 circuit drops to room temperature (300℃) during the cool-down operation from the start of operation.
K> to an extremely low temperature (approximately 4K>), the density of the gas increases as the temperature decreases, and the volume of helium gas in the J-7 circuit decreases, causing the gas pressure to drop below normal operation. Therefore, as the cool-down operation progresses, it is necessary to replenish helium gas in the circuit to eliminate the drop in gas pressure.On the other hand, if this helium gas is kept refilled, the refrigerator If the temperature rises for some reason when the unit is stopped or during operation,
Due to the increase in volume due to the decrease in density of helium gas, J-
7 Since the pressure within the circuit will rise abnormally, it is necessary to recover the replenished helium gas from within the circuit.

Normally, in order to replenish and recover such helium gas, there is a low-pressure pipe that returns the low-pressure helium gas expanded by the J-'T valve of the J-T circuit to the suction side between the compression chambers, and a compressor. A ballast tank for storing helium gas at a predetermined pressure is connected in the middle of the piping to a high-pressure piping that supplies high-pressure helium gas discharged from the J-T valve to the J-T valve, and the high-pressure piping of the ballast tank and High-pressure and low-pressure control valves are installed to automatically control communication with or cutoff of low-pressure piping, and when the gas pressure in the J-7 circuit decreases below the steady pressure due to the progress of cool-down operation, the pressure decreases. is detected and automatically opens the low pressure control valve, supplying helium gas in the ballast tank to the J-7 circuit to compensate for the pressure drop. When the gas pressure rises above the steady pressure, the pressure rise is detected and the high pressure control valve is automatically opened to recover the helium gas in the circuit into the ballast tank to suppress the pressure rise in the circuit. things are being done.

(Problem to be Solved by the Invention) However, in this case, both the low pressure and high pressure control valves that automatically open and close according to the gas pressure horn in the J-T circuit are expensive, and the cost will increase. In addition, it takes time to adjust the pressure of the pressure control valves, and the piping connection system becomes complicated due to the connection of these control valves.

The present invention has been made to solve the above problems,
Its purpose is to connect the pre-cooling refrigeration circuit and
In a helium refrigerator having a dual circuit with a T circuit,
Connecting the ballast tank and the low pressure piping via valve means,
By appropriately controlling the opening and closing of the valve means, the piping connection system is simplified, an expensive pressure control valve is not required, and an abnormal increase in operating pressure during cool-down operation is prevented. The purpose is to maintain proper operating pressure during steady operation.

(Means for Solving the Problems) In order to achieve this object, the solving means of the present invention, for example as shown in FIG. 7), a pre-cooling refrigeration circuit (2) which is expanded to generate a cryogenic temperature, and compressors (14) and (16).
) is precooled by heat exchange with the precooling refrigeration circuit (2), and the precooled helium gas is Joule-Thomson expanded to generate extremely low temperatures.
A helium refrigerator equipped with circuit (1) is assumed.

The low-pressure helium gas after being expanded by the J-T valve (29) of the J-T circuit (1) is then transferred to the compressors (14) and (16).
) A ballast tank (31) that is connected to the low pressure pipe (30) returning to the suction side of the pipe and stores helium gas at a predetermined pressure, and the ballast tank (31) is connected to or communicated with the low pressure pipe (30). Valve means (BV) such as an electromagnetic shut-off valve is provided.

Furthermore, when starting up the helium refrigerator, the valve means (BV)
is closed prior to starting the compressors (14) and (16), and the compressor (14).

(16) after a certain period of time has elapsed or after the high pressure piping (16) supplies the high pressure helium gas discharged from the compressors (14) and (16) to the J-T valve (29).
22) is provided with a control means (51) that is controlled to open when the gas pressure in the container falls below a predetermined pressure.

(Function) With the above configuration, in the present invention, when the helium refrigerator is started, the control means (51) is activated to first activate the valve means (
BV) is closed. By this closing operation of the valve means (BV), communication between the ballast tank (31) and the low pressure pipe (30) of the J-7 circuit (1) is cut off, and the ballast tank (3
Helium gas in 1) is not supplied into the J-7 circuit (1). After this, the compressors (14) and (16) are started and shift to a cool-down operation state, but due to the continuation of this cool-down operation, the volume of 1 cm gas in the J-7 circuit (1) decreases in temperature. The pressure inside the J-T circuit (1) decreases due to the increase in density associated with it. The decrease in gas pressure in the J-7 circuit (1) occurs when a certain period of time has elapsed since the start of the compression 8N (14), (16) or when the gas is discharged from the compression IN (14), (16). This is indirectly detected when the pressure in the high-pressure pipe (22) that supplies helium gas to the J-T valve (29) drops below a predetermined pressure, and at that point the control means (51)
), the valve means (BV) is opened, and the helium gas in the ballast tank (31) flows into the J-7 circuit (1).
The insufficient amount of gas in the J-7 circuit (1) is replenished, and the gas pressure in the J-7 circuit (1) is maintained at a steady pressure by this replenishment.

In addition, the valve means (BV) is kept open during steady operation after the cool-down operation, and as a result, the helium volume in the J-7 circuit (1) increases due to the temperature rise, and the gas pressure increases. Even if the helium gas rises, the increased helium gas is recovered into the ballast tank (31) through the valve means (BV) and reaches an equilibrium state, thereby preventing an abnormal increase in the gas pressure in the J-7 circuit (1). Avoided.

Furthermore, when the operation of the helium refrigerator is stopped, the valve means (
BV) is opened, which causes the J-7
Helium gas in the circuit (1) is recovered into the ballast tank (31) through the valve means (BV) to avoid an abnormal increase in gas pressure in the J-T circuit (1).

Therefore, in this case, without using an expensive pressure control valve as in the past, it is possible to maintain the operating pressure at an appropriate level during steady operation and prevent the transition to abnormally high pressure during cool-down operation, simplifying piping, It is possible to reduce costs and eliminate the need for pressure adjustment.

(Example) Embodiments of the present invention will be described below based on the drawings.

FIG. 1 shows the overall configuration of a binary two-stage compression cycle helium refrigerator according to an embodiment of the present invention. 7 circuits, (2) is the above J-T circuit (1
), the J-T circuit (1) includes a J-T side compressor unit (A), A cryostat (C) that includes a low temperature generation part (C1) that maintains a cooled object (not shown) in a cooled state.
(low temperature tank), and the precooling refrigeration circuit (2) is connected to the precooling compressor unit (B) and the cryostat (C).
are arranged in parallel to each other.

The pre-cooling compressor unit (B) includes a pre-cooling compressor (3) that compresses helium gas, and separates lubricating oil for the compressor (3) from the high-pressure helium gas compressed by the compressor (3). The adsorber (5) is equipped with an oil separator (4) for removing oil, and an adsorber (5) for adsorbing and removing impurities such as moisture and impure gas in the helium gas that has passed through the oil separator (4). are sent to the cryostat (C) via the high pressure piping (6).
It is connected to the high-pressure side inlet (8a) of the casing (8) in the expanded expander (7).

The expander (7) includes the casing (8) disposed outside the cryostat (C), and a cylinder (9) connected to the lower part of the casing (8). First and second heat stations (10) and (11) inserted into the cryostat (C) are provided on the outer periphery of the cryostat (C).
) is provided. Although not shown, inside the casing (8) is a rotary valve that opens each time it rotates and supplies helium gas flowing from the high-pressure side inlet (8a) into the cylinder (9), and A valve motor that drives the valve is fitted in the cylinder (9), while a slack piston that reciprocates in response to the opening and closing of the rotary valve and a slack piston that is integrally driven and engaged with the slack piston is fitted inside the cylinder (9). A displacer that reciprocates within the cylinder (9) and causes Simon expansion of the hem ram gas is fitted. And the first cylinder (9)
The heat station (10) is a cryostat (C
) is in thermal contact with the radiation shield part (C2) arranged to surround the low temperature generation part (C1) in the expander (7).
The first and second heat stations (10) and (11) expand high-pressure helium gas in the cylinder (9) by opening the rotary valve to generate a low temperature state, and create the low temperature state in the cylinder (9). ), the radiation shield part (C2) in thermal contact with the first heat station (10) is cooled to a low temperature, and the low temperature generating part (C1) inside thereof is radiation shielded from the outside. has been done.

Further, the casing (8) of the expander (7) has a low pressure side outlet (8b) for discharging low pressure helium gas after expansion.
is opened, and the low pressure side outlet (8b) is connected to the low pressure pipe (12).
The surge bottle (13) is connected to the surge bottle (13) provided in the pre-cooling compressor unit (B) through the
The above pre-cooling compression is connected to the suction side of (3),
The pressure fluctuations of the low-pressure helium gas discharged from the expander (7) are absorbed by the surge bottle (13), and the pressure fluctuations are absorbed by the compressor (3).
). As described above, the high pressure helium gas discharged from the pre-cooling compressor (3) is sent to the expander (7) via the oil separator (4) and the adsorber (5).
and lowering the temperature of the heat stations (10) and (11) by adiabatic expansion in the expander (7),
In addition to shielding the low temperature generation part (C1) in the cryostat (C) from radiation, precooling the precoolers (24>, (26), which will be described later) in the J-T circuit (1), and discharging the expanded low-pressure helium gas into a surge bottle ( 13) through the compressor (3
) and recompress it.

On the other hand, the J-T side compressor unit (A>) includes a low-stage compressor (14) that compresses helium gas to a predetermined pressure, and a compressor (14) that compresses the high-pressure helium gas discharged from the compressor (14). Oil separator (15) that separates and removes lubricating oil for
), a high-stage compressor (16) that compresses the high-pressure helium gas that has passed through the oil separator (15) to an even higher pressure, and a compressor (
16) an oil separator (17) for separating and removing lubricating oil;
An adsorber (18) is provided for adsorbing and removing impurities in the high-pressure helium gas that has passed through the oil separator (17).

In addition, the cryostat (C) has a primary side and a secondary side.
- First to third J-T heat exchangers (19) to (21) that exchange heat with each other between helium gases passing through the next side, respectively.
) are fitted, and these J-T heat exchangers (19) to (21
), the second and third J-T heat exchangers (20>, (
21> is the radiation shield part (C) of the cryostat (C).
2) is located within. The first J-T heat exchanger (1
9) is connected to the adsorber (18) of the J-T side compressor unit (A>) via the high-pressure pipe (22). Heat exchanger (19
) and (20) are connected to each other via an adsorption device (23) and a first precooler (24) disposed around the outer periphery of the first heat station (10) of the expander (7). and the second and third J-T heat exchangers (20>, (2
1), the adsorber (25) and the expander (25) are connected to each other in the same way.
7) is connected via a second precooler (26) disposed on the outer periphery of the second heat station (11). Roughly speaking, 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 connected to the low temperature generating part (21).
The adsorber (28) is located in the cooler (27) located in the
) and the J-T valve (29). The J-T valve (29) is for Joule-Thomson expansion of high-pressure helium gas, and its opening is controlled by a motor (M) such as a stepping motor from the outside of the cryostat (C) via an operating lever (29a). adjusted by. The cooler (27) is connected to the third and second coolers.
J-T heat exchanger (21>.

(20) through each secondary side of the first J-T heat exchanger (19)
The secondary side of the first J-T heat exchanger (19) is connected to the low-stage compressor ( 14).Thus, the two compressors (14) and (16) connected in series in the two stages compress helium gas to high pressure and supply it to the cryostat (C) side. ,
It is heat exchanged with the low-temperature, low-pressure helium gas that returns to the J-T side compressor unit (A>) in the first to third J-T heat exchangers (19) to (21) of the cryostat (C), and First and second precoolers (24), (26)
The first and second heat stations (
After cooling by heat exchange with 10) and (11), J-T
The valve (29) inflates the Joule Thomson and the cooler (27)
) during steady operation, the helium is at a pressure of 1 atm and about 4 liters, and then the low pressure helium gas is transferred to the first to third J.
-J through each secondary side of the T heat exchanger (19) to (21)
- It is configured to be sucked into the low-stage compressor (14) of the T-side compressor unit (A>) and recompressed.

Briefly, as shown in FIG. 2, the features of the present invention are as follows:
The J-T side compression of the above J-T circuit (1) is performed by the unit (A>
, a low pressure pipe (
30) is connected to a ballast tank (31) that stores helium gas at a predetermined pressure via a connecting pipe (32). Further, this connecting pipe (32) is provided with a normally open solenoid valve (BV) as a valve means for communicating or cutting off communication between the ballast tank (31) and the low pressure pipe (30).
) are provided. The solenoid valve (BV) is configured such that its opening/closing is controlled by a gas pressure control section (51) of a controller (50) as a control means, and the gas pressure control section (51) includes the above-mentioned J - Gas pressure in the high-pressure pipe (22) that supplies high-pressure helium gas discharged from the high-stage compressor 1 (16) of the T-side compressor unit (A>) to the J-T valve (29) of the cryostat (C). The signal of the pressure switch (PS) which operates ON/OFF according to
6) is input, and the gas pressure control section (51) of this controller (50) starts the solenoid valve (
BV) is closed when starting up the helium refrigeration chamber, prior to starting up the low stage and high stage compressors (14) and (16), and after starting up the compressors ta (14) and (16), the high pressure It is controlled to open based on the ON signal of the pressure switch (PS) when the gas pressure in the pipe (22) drops below a predetermined pressure.

In addition, as shown in FIG. 1, in the J-T circuit (1), the cooler (27> and the third
The upstream end of a bypass pipe (33) is branched to the pipe connecting the secondary side of the J-T heat exchanger (21), and the downstream end of the bypass pipe (33) is connected to the first and second two pipes. The first J-T heat exchanger (19) and the second J-T heat exchanger (20) are branched into two branch pipes (33a) and (33b), respectively.
) and the piping between each secondary side and the second J-T heat exchanger (
20) and the third J-T heat exchanger (21).

Further, the first and second branch pipes (33a>, (33b)) of the bypass pipe (33) each have first and second solenoid valves for opening and closing the respective branch pipes (33a>, (33b)). (BV+>, (BV2>) are provided.These solenoid valves (BVl) and (BV2) are connected to the bypass solenoid valve control unit (CV2) which is connected to the coat roller (50).
52), and this control section (52) includes the bypass control section in the piping between the cooler (27) and the secondary side of the third J-T heat exchanger (21). The temperature on the upstream side of the upstream end branch of the pipe (33),
In other words, the output signal of the temperature sensor (34) that detects the return temperature of the helium gas returning from the cooler (27) reaching level 4 is input, and the bypass solenoid valve control section (52) controls the helium refrigerator. At the beginning of the cool-down operation, the return gas from the cooler (27) is transferred to the second and third J-T by listening to the first solenoid valve (BV+) and closing the second solenoid valve (BV2).
The heat exchangers (21) and (20> are bypassed, and as soon as the return temperature of helium gas detected by the temperature sensor (34) drops to the first set temperature (for example, 50K>) as the cool-down operation progresses, is, contrary to the above, the first
Close the solenoid valve (BV+) and close the second solenoid valve (BV2>
By opening the opening, the return gas from the cooler (27) bypasses only the third J-T heat exchanger (21), and the second J-T heat exchanger (21), whose return temperature is roughly lower than the first set temperature, is
When the temperature drops to a set temperature (for example, 20K), both the first and second solenoid valves (BV+) and (BV2) are closed, thereby allowing J-T heat exchange of the return helium gas from the cooler (27). The device is configured to release the bypass for the devices (20) and (21>).

Roughly speaking, the motor (M) which is drivingly connected to the J-T valve (29) and adjusts its opening degree is connected to the controller (5).
The J-T valve control section (53) has the J-T valve control section (53).
- A pressure sensor (
The detection signal of 35) is inputted, and this J-T valve control section (53) causes the above-mentioned bypass solenoid valve control section (52)
While the helium gas return path is being adjusted in accordance with the operation of the J-T valve (2), the helium gas return path detected by the pressure sensor (35) is kept approximately constant.
9) is configured to variably adjust the opening degree.

In addition, the compressor (3) of the pre-cooling compressor unit (B) and the two compressors (1) of the J-T side compressor unit (A>
The structures of 4) and (16) and their peripheral equipment are similar, and in Fig. 1, (36) is the structure of each compressor (3).
, (14), (16) from the discharge side of the oil separator (4), (
15) and (17), the discharge gas coil (36) is connected to the casing (not shown) of each compressor (3), (14), and (16). ) It is wrapped around the upper half of the outer circumference. In addition, a cooling water coil (37) through which cooling water flows is wound around the entire outer peripheral surface of the casing of each compressor (3), (14), and (16) approximately parallel to the discharge gas coil (36). Due to the cooling water flowing through the cooling water coil (37),
Compressor (3).

(14), (16) and the discharge gas coil (3
6) It is designed to cool the high-temperature, high-pressure helium gas flowing inside.

Moreover, (38) is each compressor (3), (14).

(16) Cooling water coil (3
7) is an oil coil wound approximately parallel to the
The upstream end of the nuclear oil coil (38) is connected to each compressor (3), (14
) and (16), the downstream end is connected to the suction side of the compressors (3), (14), and (16) through an injection pipe (40) with an oil filter (39) interposed therein. are connected to the compressors (3) and (1), respectively.
4>.

The lubricating oil in the casing discharged from (16) together with helium gas is fed to the oil coil (38) and cooled by the cooling water in the cooling water coil (37), and this cooled lubricating oil is transferred to the injection pipe. (40), the helium gas is injected into the suction helium gas.

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

When the helium refrigerator starts up, first, the pre-cooling refrigeration circuit (2
) and the two low-stage and high-stage compression UNs (14) and (16) of the J-T circuit (1) are activated to perform a cool-down operation. In this cool-down operation state, the cryostat (
High-pressure helium gas supplied from the compressor (3) is expanded in the expander (7) on the C) side, and as the gas expands, each heat station (10), (11) of the cylinder (9) is heated.
) and the first heat station (10), the temperature of the radiation shield part (C2) which is in thermal contact with the first heat station (10) decreases, and the low temperature generating part (C]) in the cryostat (C) is radiation shielded from the outside.

Meanwhile, at the same time, helium gas returning from the cryostat (C) via the J-T circuit (1) is sucked and compressed by the low stage compressor (14) and cooled by the cooling water coil (37) around it. The helium gas is cooled to room temperature 300K with water, and after the oil component is separated in an oil separator (15), it is sucked and compressed by a high-stage compressor (16). Furthermore, the discharged gas from the compressor (16) is cooled again to room temperature 300K by cooling water in the cooling water coil (37) around the compressor (16), and then sent to the oil separator (17).
After the oil is separated in the adsorber (18), impurities are adsorbed in the adsorber (18), and the thus obtained clean high-pressure helium gas 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),
The first heat is cooled from room temperature 300K by heat exchange with the low pressure helium gas on the secondary side returning to the J-T side compressor unit (A>), and then cooled to 50 to 60K in the expander (7). The first precooler (
24> where it is further cooled to a lower temperature. This cooled gas enters the primary side of the second J-T heat exchanger (20) and undergoes heat exchange with the low-pressure helium gas on the secondary side that returns to the J-T side compressor unit (A>). After being cooled, it enters the second precooler (26) on the outer periphery of the second heat station (11), which is cooled to 15-20K in the expander (7), and is cooled to a low temperature. enters the primary side of the third J-T heat exchanger (21), is cooled by heat exchange with the low-pressure helium gas on the secondary side, and passes to the J-T side compressor unit (A>). The high-pressure helium gas is throttled by the J-T valve (29) and expanded into Joule-Thomson gas, and then supplied to the cooler (27).Then, the cooler (27) is The low-pressure return helium gas that comes out is transferred to the third to first J-T heat exchangers (21) to (19).
), and after passing through the secondary side of at least the first J-T heat exchanger (19) and increasing the temperature to approximately 300 K by heat exchange with the high pressure helium gas on the primary side, the low pressure piping (30)
through and return to the J-T side compressor unit (A>).

Thereafter, a similar cycle is repeated and cool-down operation is performed for a predetermined period of time.

When this down-down operation is completed, the refrigerator shifts to a steady operating state, and in this steady operating state, the 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 4.2, and then the liquid portion is poured into the gas-liquid mixed helium in the cooler (27). The latent heat of vaporization is used to liquefy or recondense other helium gases or to cool objects to be cooled.

Furthermore, after the low pressure helium gas discharged from the cooler (27) becomes a saturated gas of about 4.2 liters, it returns to the J-T side compressor unit (A>, and this cycle is continued.

In this embodiment, when the helium refrigerator is started, the two compressors (14) and (16) of the J-T circuit (1)
is activated, the solenoid valve (BV) connected to the low pressure piping (30) of the J-T circuit (1) is activated by the operation of the gas pressure control section (51) in the controller (50). It is closed from the open state, and communication between the low pressure pipe (30) and the ballast tank (31) is cut off. After that, as the cool-down operation of the refrigerator progresses, the gas temperature in the cooler (27) of the J-T circuit (1) decreases to near cryogenic temperatures, and the density of helium gas increases accordingly.
- When the volume of helium gas in the T circuit (1) decreases and the gas pressure drops below the steady state, the high pressure pipe (22
) The pressure switch (PS) is turned on due to the pressure drop in the pressure switch (PS), and the solenoid valve (BV) is opened by the gas pressure control section (51) of the controller (50) that receives the ON operation signal of the pressure switch (PS). By opening this solenoid valve (BV), the helium gas in the ballast tank (31) flows into the low pressure pipe (30), and the insufficient helium gas is replenished into the J-T circuit (1). This replenishment maintains the gas pressure in the J-T circuit (1) in a steady state.

The solenoid valve (BV) is maintained in an open state even during steady operation of the refrigerator. For this reason, the gas temperature in the cooler (27) rises due to some reason, and the density of the helium gas decreases, causing the volume of gas in the J-T circuit (1) to increase and the gas pressure to become steady. Even if the helium gas in the J-T circuit (1) attempts to increase more than the current state, the helium gas in the J-T circuit (1) will flow into the ballast tank (31) through the solenoid valve (BV) spaced apart by the amount of increase in volume. The pressure absorption effect of the ballast tank (31) can prevent the gas pressure in the J-T circuit (1) from rising abnormally. Further, when the operation of the refrigerator is stopped, the gas pressure control section (51) of the controller (50) stops operating, and the solenoid valve (BV) enters the normal closed state.
This confines helium gas at a predetermined pressure within the ballast tank (31).

In addition, in parallel with such control, in the cool-down operation state of the refrigerator, the J-T circuit (
1) Two solenoid valves (BV+) in the bypass piping (33)
>, (BV,! > is controlled to open and close, and at the start of the cool-down operation, first, the first solenoid valve (BV+) is opened and the second solenoid valve (BV2) is closed, and the return air is returned from the cooler (27). The helium gas bypasses the second and third J-D circuits (21>, (20>),
The compressor unit (
A> is returned.゛Then, the return temperature of the helium gas from the cooler (27) is detected by the temperature sensor (34), and this return temperature is set as the first set temperature (50K).
), the first solenoid valve (BV+) is closed and the second solenoid valve (BV2) is opened. Therefore, the helium gas from the cooler (27) bypasses only the third J-T circuit (21) and passes through the other two J-T heat exchangers (20) and (19) to the compressor unit (A >.Furthermore, the return temperature is returned to the second set temperature (20
K>, both the first and second solenoid valves (BV+) and (BV2) are closed, and the cooler (
Helium gas from 27) is supplied to the 3rd to 1st J-T circuits (2
1) to (19) and is returned to the compressor unit (A), thereby achieving a steady operating state.

In this way, during the cool-down operation, the return helium gas is transferred to the third J-T heat exchanger (21) or the third and second
By flowing by bypassing the J-T heat exchanger (2'l) and (20), the returning helium gas flows through the J-T
The helium gas on the primary side of the heat exchanger (21>, (20>) does not raise the temperature to a high temperature, and as a result,
The cool-down time required for the helium refrigerator to reach a steady operating state can be significantly shortened.

Further, during the cool-down operation of the refrigerator, the motor (M) is operated and controlled by the operation of the J-T valve control section (53) of the controller (50), and the gas pressure in the low pressure pipe (30) is controlled. The opening degree of the J-T valve (29) is adjusted to be approximately constant.

This eliminates the need to adjust the opening of the J-T valve (29) during cool-down operation, and it is possible to automate the cool-down operation of the helium refrigerator.

(Other Embodiments) FIG. 3 shows another embodiment of the present invention. The same parts as in FIG. A capillary tube (41) as a pressure reducing mechanism is disposed in the connecting pipe (32) connecting the low pressure pipe (30) and the ballast tank (31) of 1). In this case, the helium gas in the ballast tank (31) is gradually supplied to the low pressure pipe (30) as the solenoid valve (BV) opens, so that the gas pressure in the J-1 circuit (1) suddenly increases. This has the advantage of suppressing fluctuations.

In each of the above embodiments, when the helium refrigerator is started and after the compressors (14) and (16) are started, the solenoid valve (BV) is operated so that the gas pressure in the high pressure pipe (22) drops below a predetermined pressure. However, when a certain period of time has passed since the start of the compressors (14) and (16), the J-1 circuit (1)
Roughly assuming that the gas pressure inside has decreased, the solenoid valve (B
V) may be opened ``, and the same effects as in each of the above embodiments can be achieved.

(Effects of the Invention) As explained above, according to the present invention, in a helium refrigerator having a binary circuit of a pre-cooling refrigeration circuit and a J-1 circuit, the low pressure reaching the suction side of the compressor of the J-1 circuit A ballast tank for helium gas storage is connected to the piping, and a valve means is provided for communicating or cutting off communication between the ballast tank and the low pressure piping, and when the helium refrigerator is started, the valve means is connected to the compressor. The compressor is controlled to close before startup, and to open after a certain period of time has passed after startup or when the gas pressure in the high-pressure piping from the compressor drops below a predetermined pressure. By doing so, it is possible to omit the conventionally expensive pressure control valve, maintain the operating pressure of the helium refrigerator at an appropriate level during steady operation, and prevent the pressure from shifting to abnormally high pressure during cool-down operation. This makes it possible to simplify the piping of the refrigerator, reduce costs, and eliminate the need for pressure adjustment.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention, and FIG. 1 is an overall configuration diagram of a helium refrigerator, and FIG. 2 is a piping system diagram showing the main parts. FIG. 3 is a diagram corresponding to FIG. 2 showing another embodiment. (A)... J-T side compressor unit, (B)... Pre-cooling compressor unit, (C)... Taliostat,
(1)...J-1 circuit, (2)...Pre-cooling refrigeration circuit,
(3)... Pre-cooling compressor, (7)... Expansion machine, (1
4)...Low stage compressor, (16)...High stage compressor, (
22)...High pressure piping, (19) to (21)...J-
T heat exchanger, (29)...J-T valve, (30)...
Low pressure piping, (31)...Ballast tank, (BV)
・・Solenoid valve, (PS) ・・Pressure switch, (33)・
...Bypass piping, (BV+>, (BV2)", solenoid valve, (34)...Temperature sensor, (35)...Pressure sensor, (50)...Controller, (51)...
Gas pressure control section, (53)...J-T valve control section. Patent applicant: Daikin Industries, Ltd. 1”’)l
””2 Jin. Representative 1) Hiroshi JIJJi-
'・Figure 2 3 [

Claims (1)

[Claims] (1) A pre-cooling refrigeration circuit (2) in which the high-pressure helium gas compressed by the compressor (3) is expanded in the expander (7) to generate a cryogenic temperature, and the high pressure from the compressors (14) and (16) Helium gas is precooled by heat exchange with the precooling refrigeration circuit (2), and the precooled helium gas is transferred to the J-T valve (29).
In a helium refrigerator equipped with a J-T circuit (1) that generates a cryogenic temperature by expanding Joule-Thomson,
It is connected to a low-pressure pipe (30) that returns the low-pressure helium gas expanded by the J-T valve (29) of the J-T circuit (1) to the suction side of the compressors (14) and (16), and is connected to a predetermined pressure. a ballast tank (31) for storing helium gas; a valve means (BV) for communicating or cutting off the communication between the ballast tank (31) and the low pressure piping (30); The valve means (BV) is connected to the compressor (
14) and (16) are closed, and after the compressors (14) and (16) are started, a certain period of time has elapsed since the start of the compressors (14) and (16), or when the compressors are discharged from the compressors (14) and (16). It is characterized by being provided with a control means (51) that controls the opening when the gas pressure in the high-pressure pipe (22) that supplies high-pressure helium gas to the J-T valve (29) drops below a predetermined pressure. A helium refrigerator.