Patent Description:
A cryocooler is used in order to cool various target objects such as a superconducting device used in a cryogenic temperature environment, a measuring device, and a sample. PTL <NUM> discloses a cryopump system and a method of operating the same, and a compressor unit suitable for use in the cryopump system in which the operation frequency of the compressor is controlled based on the differential pressure between the high pressure line and the low pressure line. A storage tank is connected to the low pressure line in the high pressure mode used in cool-down operation.

To cool a target object with a cryocooler, first, it is necessary to start the cryocooler and to cool the cryocooler from an initial temperature, such as the room temperature, to a target cryogenic temperature. This is also called cooldown of the cryocooler. Since the cooldown is merely preparation for beginning the cooling of the target object, it is desirable that time taken for the cooldown is as short as possible.

An exemplary object of one aspect of the present invention is to shorten the cooldown time of the cryocooler.

According to one aspect of the present invention, there is provided a starting method for a cryocooler as defined in claim <NUM>. The cryocooler includes a compressor, a cold head, a high pressure line through which a refrigerant gas is supplied from the compressor to the cold head, and a low pressure line through which the refrigerant gas is collected from the cold head to the compressor. The method includes increasing a volume of the high pressure line when the cold head is at a room temperature, cooling the cold head from the room temperature to a cryogenic temperature while controlling an operation frequency of the compressor based on a pressure of the high pressure line or a differential pressure between the high pressure line and the low pressure line, after the volume of the high pressure line is increased, decreasing the volume of the high pressure line after the cold head is cooled to the cryogenic temperature, and maintaining the cold head at the cryogenic temperature after the volume of the high pressure line is decreased.

According to another aspect of the present invention, there is provided a cryocooler as defined in claim <NUM>. It includes a compressor, a cold head, a high pressure line through which a refrigerant gas is supplied from the compressor to the cold head, a low pressure line through which the refrigerant gas is collected from the cold head to the compressor, a pressure sensor that measures a pressure of the high pressure line or a differential pressure between the high pressure line and the low pressure line, a compressor controller that controls an operation frequency of the compressor based on the pressure measured by the pressure sensor, and a buffer volume configured to be connected to the high pressure line when the cold head is cooled from a room temperature to a cryogenic temperature and to be disconnected from the high pressure line when the cold head is maintained at the cryogenic temperature.

With the present invention, the cooldown time of the cryocooler can be shortened.

Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. In the description and drawings, the same or equivalent components, members, and processing will be assigned with the same reference symbols, and redundant description thereof will be omitted as appropriate. The scales and shapes of illustrated parts are set for convenience in order to make the description easy to understand, and are not to be understood as limiting unless stated otherwise. The embodiments are merely examples and do not limit the scope of the present invention. All characteristics and combinations to be described in the embodiments are not necessarily essential to the invention.

<FIG> and <FIG> are views schematically illustrating a cryocooler <NUM> according to a first embodiment, wherein these Figures illustrate a method according to the claims, but not a cryocooler according to the claims. <FIG> illustrates cooldown operation of the cryocooler <NUM>, and <FIG> illustrates normal cooling operation of the cryocooler <NUM>. The cryocoolers <NUM> illustrated in <FIG> and <FIG> are the same except that a high pressure side pipe of the cryocooler <NUM> is replaced and a refrigerant gas volume on a high pressure side is different.

During cooldown operation, the cryocooler <NUM> is quickly cooled from a room temperature or an initial temperature near the room temperature to a target cooling temperature. The target cooling temperature is selected from desired cryogenic temperatures for cooling a superconducting device such as a superconducting magnet or other objects to be cooled. Normal cooling operation is performed subsequent to the cooldown operation so that the cryocooler <NUM> is maintained at the target cooling temperature. When the normal cooling operation begins, an object to be cooled can be operated. As a preparatory stage, the cooldown operation is performed.

Although details will be described later, a refrigerant gas volume on the high pressure side during cooldown operation is increased compared to normal cooling operation. It can be said that the refrigerant gas volume on the high pressure side is increased during the cooldown operation compared to a low pressure side.

The cryocooler <NUM> includes a compressor <NUM> and a cold head <NUM>. The compressor <NUM> is configured to collect a working gas of the cryocooler <NUM> from the cold head <NUM>, to pressurize the collected working gas, and to supply the working gas to the cold head <NUM> again. The cold head <NUM> is also called an expander and has a room temperature section 14a and a low-temperature section 14b which is also called a cooling stage. The compressor <NUM> and the cold head <NUM> configure a refrigeration cycle of the cryocooler <NUM>, and thereby the low-temperature section 14b is cooled to a desired cryogenic temperature. The working gas is also called a refrigerant gas, and other suitable gases may be used although a helium gas is typically used. To facilitate understanding, a direction in which the working gas flows is shown with an arrow in <FIG>.

Although the cryocooler <NUM> is, for example, a single-stage or two-stage Gifford-McMahon (GM) cryocooler, the cryocooler may be a pulse tube cryocooler, a Stirling cryocooler, or other types of cryocoolers. Although the cold head <NUM> has a different configuration according to the type of the cryocooler <NUM>, the compressor <NUM> can use the configuration described below regardless of the type of the cryocooler <NUM>.

In general, both of a pressure of the working gas supplied from the compressor <NUM> to the cold head <NUM> and a pressure of the working gas collected from the cold head <NUM> to the compressor <NUM> are considerably higher than the atmospheric pressure, and can be called a first high pressure and a second high pressure, respectively. For convenience of description, the first high pressure and the second high pressure are also simply called a high pressure and a low pressure, respectively. Typically, the high pressure is, for example, <NUM> to <NUM> MPa. The low pressure is, for example, <NUM> to <NUM> MPa, and is, for example, approximately <NUM> MPa.

The compressor <NUM> includes a discharge port <NUM>, a suction port <NUM>, a high pressure flow path <NUM>, a low pressure flow path <NUM>, a first pressure sensor <NUM>, a second pressure sensor <NUM>, a compressor main body <NUM>, and a compressor casing <NUM>. The discharge port <NUM> is provided in the compressor casing <NUM> as a working gas discharge port of the compressor <NUM>, and the suction port <NUM> is provided in the compressor casing <NUM> as a working gas suction port of the compressor <NUM>. The high pressure flow path <NUM> connects a discharge port of the compressor main body <NUM> to the discharge port <NUM>, and the low pressure flow path <NUM> connects the suction port <NUM> to a suction port of the compressor main body <NUM>. The compressor casing <NUM> accommodates the high pressure flow path <NUM>, the low pressure flow path <NUM>, the first pressure sensor <NUM>, the second pressure sensor <NUM>, and the compressor main body <NUM>. The compressor <NUM> is also called a compressor unit.

The compressor main body <NUM> is configured to internally compress a working gas sucked from the suction port and to discharge the working gas from the discharge port. The compressor main body <NUM> may be, for example, a scroll type pump, a rotary type pump, or other pumps that pressurize the working gas. The compressor main body <NUM> may be configured to discharge the working gas at a fixed and constant flow rate. Alternatively, the compressor main body <NUM> may be configured to change the flow rate of the working gas to be discharged. The compressor main body <NUM> is called a compression capsule in some cases.

The first pressure sensor <NUM> is disposed in the high pressure flow path <NUM> to measure the pressure of a working gas flowing in the high pressure flow path <NUM>. The first pressure sensor <NUM> is configured to output a first measured pressure signal P1 indicating the measured pressure. The second pressure sensor <NUM> is disposed in the low pressure flow path <NUM> to measure the pressure of the working gas flowing in the low pressure flow path <NUM>. The second pressure sensor <NUM> is configured to output a second measured pressure signal P2 indicating the measured pressure. Accordingly, the first pressure sensor <NUM> and the second pressure sensor <NUM> can also be called a high pressure sensor and a low pressure sensor, respectively. In addition, in the specification, any one of the first pressure sensor <NUM> and the second pressure sensor <NUM> or both of the first pressure sensor and the second pressure sensor will be collectively and simply referred to as a "pressure sensor" in some cases.

The pressure sensor may include a differential pressure sensor. The differential pressure sensor may be provided, for example, in a bypass line that connects the high pressure flow path <NUM> and the low pressure flow path <NUM> to each other to bypass the compressor main body <NUM>. The differential pressure sensor is configured to measure a differential pressure between the high pressure and the low pressure of a working gas in the cryocooler <NUM> and to output a measured differential pressure signal indicating the measured differential pressure. The differential pressure sensor may be provided instead of or in addition to the high pressure sensor and the low pressure sensor.

The compressor <NUM> can have other various components. For example, an oil separator or an adsorber may be provided in the high pressure flow path <NUM>. A storage tank and other components may be provided in the low pressure flow path <NUM>. In addition, an oil circulation system that cools the compressor main body <NUM> with an oil and a cooling system that cools the oil may be provided in the compressor <NUM>.

The cryocooler <NUM> includes a main switch <NUM>. The main switch <NUM> includes an operation tool that can be manually operated, such as an operation button and a switch. When operated, the cryocooler <NUM> is started and operation thereof begins. The main switch <NUM> may function not only as a start switch of the cryocooler <NUM> and but also serve as a stop switch of the cryocooler <NUM>. The main switch <NUM> is provided on, for example, the compressor casing <NUM>.

The cold head <NUM> includes a cold head temperature sensor <NUM> attached to the low-temperature section 14b. The cold head temperature sensor <NUM> is configured to output a measured temperature signal T1 indicating the measured temperature of the low-temperature section 14b.

In addition, the cryocooler <NUM> includes a pipe system <NUM> that allows a working gas to circulate between the compressor <NUM> and the cold head <NUM>. The pipe system <NUM> includes a high pressure line <NUM> through which the working gas is supplied from the compressor <NUM> to the cold head <NUM> and a low pressure line <NUM> through which the working gas is collected from the cold head <NUM> to the compressor <NUM>. The room temperature section 14a of the cold head <NUM> includes a high pressure port <NUM> and a low pressure port <NUM>.

The high pressure port <NUM> is connected to the discharge port <NUM> by a first high-pressure pipe 39a or a second high-pressure pipe 39b. As illustrated in <FIG>, the first high-pressure pipe 39a is used during cooldown operation. As illustrated in <FIG>, the second high-pressure pipe 39b is used during normal cooling operation. Hereinafter, the first high-pressure pipe 39a and the second high-pressure pipe 39b will be collectively called a high-pressure pipe <NUM> in some cases. The low pressure port <NUM> is connected to the suction port <NUM> by a low-pressure pipe <NUM>.

A working gas to be collected from the cold head <NUM> to the compressor <NUM> passes through the low-pressure pipe <NUM> from the low pressure port <NUM> of the cold head <NUM> to enter the suction port <NUM> of the compressor <NUM>, and further returns to the compressor main body <NUM> via the low pressure flow path <NUM> so as to be compressed and pressurized by the compressor main body <NUM>. The working gas to be supplied from the compressor <NUM> to the cold head <NUM> passes through the high pressure flow path <NUM> from the compressor main body <NUM> to exit from the discharge port <NUM> of the compressor <NUM>, and is further supplied to the cold head <NUM> via the high-pressure pipe <NUM> and the high pressure port <NUM> of the cold head <NUM>.

For example, the high-pressure pipe <NUM> and the low-pressure pipe <NUM> are configured by flexible pipes, but may be configured by rigid pipes. Detachable couplings are provided at both ends of the high-pressure pipe <NUM> and the low-pressure pipe <NUM>. Couplings that are detachable from the couplings at both ends of the high-pressure pipe <NUM> are provided at the discharge port <NUM> and the high pressure port <NUM>, and couplings that are detachable from the couplings at both ends of the low-pressure pipe <NUM> are provided at the suction port <NUM> and the low pressure port <NUM>. The detachable couplings are, for example, self-sealing couplings. Accordingly, the high-pressure pipe <NUM> and the low-pressure pipe <NUM> are removably attached to the compressor <NUM> and the cold head <NUM>.

As can be understood from comparison between <FIG> and <FIG>, the volume of the high pressure line <NUM> during cooldown operation is larger than the volume of the high pressure line <NUM> during normal cooling operation. As an exemplary configuration, the volume of the first high-pressure pipe 39a is larger than the volume of the second high-pressure pipe 39b. The first high-pressure pipe 39a is thicker than the second high-pressure pipe 39b. A nominal diameter D1 of the first high-pressure pipe 39a is larger than a nominal diameter D2 of the second high-pressure pipe 39b. For example, the first high-pressure pipe 39a may be a pipe having a nominal diameter one or two larger than that of the second high-pressure pipe 39b. Instead of or in addition to the first high-pressure pipe 39a being thicker, the first high-pressure pipe 39a may be longer than the second high-pressure pipe 39b. Although a length L1 of the first high-pressure pipe 39a is equal to a length L2 of the second high-pressure pipe 39b in <FIG> and <FIG>, for example, the length L1 of the first high-pressure pipe 39a may be within a range one to two times the length L2 of the second high-pressure pipe 39b.

In addition, as illustrated in <FIG>, during cooldown operation, the volume of the high pressure line <NUM> is larger than the volume of the low pressure line <NUM>. As an exemplary configuration, the volume of the first high-pressure pipe 39a is larger than the volume of the low-pressure pipe <NUM>. The first high-pressure pipe 39a is thicker than the low-pressure pipe <NUM>. The nominal diameter D1 of the first high-pressure pipe 39a is larger than a nominal diameter D3 of the low-pressure pipe <NUM>. For example, the first high-pressure pipe 39a may be a pipe having a nominal diameter one or two larger than that of the low-pressure pipe <NUM>. Instead of or in addition to the first high-pressure pipe 39a being thicker, the first high-pressure pipe 39a may be longer than the low-pressure pipe <NUM>. Although the first high-pressure pipe 39a and the low-pressure pipe <NUM> have lengths equal to each other in <FIG>, for example, the length L1 of the first high-pressure pipe 39a may be within a range one to two times a length L3 of the low-pressure pipe <NUM>.

As illustrated in <FIG>, the volumes of the high pressure line <NUM> and the low pressure line <NUM> are equal to each other during normal cooling operation. The second high-pressure pipe 39b has the same volume as the low-pressure pipe <NUM>. The second high-pressure pipe 39b has the same thickness and the same length as the low-pressure pipe <NUM>.

However, in one embodiment, the volume of the high pressure line <NUM> may be larger than the volume of the low pressure line <NUM> not only during cooldown operation but also during normal cooling operation. Instead of replacing the first high-pressure pipe 39a with the second high-pressure pipe 39b, the first high-pressure pipe 39a may be used during both of the cooldown operation and the normal cooling operation.

In a typical cryocooler, the volume of the high pressure line is not changed according to an operation state. The volume of the high pressure line is equal to the volume of the low pressure line. The high pressure side pipe and a low pressure side pipe, which connect the compressor and the cold head to each other, have the same dimensions (thickness and length).

In the specification, the volume of the high pressure line <NUM> can be defined as a pipe volume from the discharge port <NUM> to the high pressure port <NUM>. The high pressure flow path <NUM> inside the compressor <NUM> and an internal flow path of the cold head <NUM> are not included in the high pressure line <NUM>. Accordingly, the volume of the high pressure line <NUM> can substantially correspond to the volume of the high-pressure pipe <NUM> (that is, any one of the first high-pressure pipe 39a and the second high-pressure pipe 39b). Similarly, the volume of the low pressure line <NUM> can be defined as a pipe volume from the suction port <NUM> to the low pressure port <NUM>. The low pressure flow path <NUM> inside the compressor <NUM> and the internal flow path of the cold head <NUM> are not included in the low pressure line <NUM>. Accordingly, the volume of the low pressure line <NUM> can substantially correspond to the volume of the low-pressure pipe <NUM>.

<FIG> is a block diagram related to the cryocooler <NUM>. The cryocooler <NUM> includes a control device <NUM> that controls the cryocooler <NUM>. The control device <NUM> includes a compressor controller <NUM> and a compressor inverter <NUM>. The control device <NUM> may be mounted on the compressor <NUM>. The compressor main body <NUM> includes a compressor motor <NUM> that drives the compressor main body <NUM>.

The first pressure sensor <NUM> and the second pressure sensor <NUM> are connected to the control device <NUM> so as to be able to communicate therewith, and output the first measured pressure signal P1 and the second measured pressure signal P2 to the control device <NUM>, respectively. The cold head temperature sensor <NUM> is respectively connected to the control device <NUM> so as to be able to communicate therewith, and outputs the measured temperature signal T1 to the control device <NUM>.

The compressor controller <NUM> controls an operation frequency of the compressor <NUM> based on a pressure measured by the first pressure sensor <NUM> or based on a differential pressure measured by the first pressure sensor <NUM> and the second pressure sensor <NUM>. Herein, for example, the operation frequency of the compressor <NUM> corresponds to a frequency of power supplied to the compressor motor <NUM>, and refers to an operation frequency or a rotation speed of the compressor motor <NUM>. The compressor controller <NUM> determines the operation frequency of the compressor <NUM>, and generates an inverter control signal S1 according to the determined operation frequency of the compressor <NUM>. In accordance with the inverter control signal S1, the compressor inverter <NUM> generates a motor drive signal S2 from power input from an external power source such as a commercial power source, and outputs the motor drive signal to the compressor motor <NUM>. The compressor motor <NUM> is driven in response to the motor drive signal S2. In this manner, the compressor motor <NUM> is driven at the operation frequency determined by the compressor controller <NUM>.

The main switch <NUM> is configured to output a starting command signal S3 to the control device <NUM> when operated. The compressor controller <NUM> receives the starting command signal S3, and begins the control of the compressor <NUM>.

The control device <NUM> is realized by an element or a circuit including a CPU and a memory of a computer as a hardware configuration and is realized by a computer program as a software configuration, but is shown in <FIG> as a functional block realized in cooperation therewith. It is clear for those skilled in the art that the functional blocks can be realized in various manners in combination with hardware and software.

<FIG> is a flowchart showing a pressure control method for the cryocooler <NUM>. The compressor controller <NUM> of the control device <NUM> is configured to execute pressure control processing of the pipe system <NUM> to be described below. The pressure control of the pipe system <NUM> is repeatedly executed at a predetermined cycle during the operation of the cryocooler <NUM>.

The pressure of the pipe system <NUM> is measured (S10). The pressure of the pipe system <NUM> is measured using the pressure sensor. The compressor controller <NUM> acquires a measured pressure PM of the pipe system <NUM> from the first measured pressure signal P1 and/or the second measured pressure signal P2.

Next, the measured pressure PM of the pipe system <NUM> is compared to a target pressure PT (S12). The target pressure PT of the pipe system <NUM> is input to the control device <NUM> in advance by a user of the cryocooler <NUM>, or is automatically set by the control device <NUM> and is stored in the control device <NUM>. The compressor controller <NUM> compares the measured pressure PM to the target pressure PT and outputs a relationship as to which one of the measured pressure and the target pressure is larger or smaller as a comparison result. That is, the comparison result from the compressor controller <NUM> indicates any one of the following three states. (i) The measured pressure PM is larger than the target pressure PT. (ii) The measured pressure PM is smaller than the target pressure PT. (iii) The measured pressure PM is equal to the target pressure PT.

The compressor controller <NUM> determines the operation frequency of the compressor <NUM> based on the comparison result between the measured pressure PM and the target pressure PT. As described above, the compressor motor <NUM> is operated at the determined operation frequency. Accordingly, the measured pressure PM of the pipe system <NUM> is changed to become closer to the target pressure PT. In such a manner, the pressure control of the pipe system <NUM> is provided and thereby the measured pressure PM of the pipe system <NUM> can be made to follow the target pressure PT.

Specifically, (i) in a case where the measured pressure PM is larger than the target pressure PT, the compressor controller <NUM> decreases the operation frequency of the compressor <NUM> (S14). (ii) In a case where the measured pressure PM is smaller than the target pressure PT, the compressor controller <NUM> increases the operation frequency of the compressor <NUM> (S16). (iii) In a case where the measured pressure PM is equal to the target pressure PT, it is not necessary to increase or decrease the operation frequency, and thereby the operation frequency is maintained.

A changed amount (that is, an increased amount or a decreased amount) of the operation frequency of the compressor <NUM> may be determined based on a deviation between the measured pressure PM and the target pressure PT (for example, through PID control). Alternatively, the changed amount of the operation frequency of the compressor <NUM> may be an amount set in advance.

An example of the pressure control of the pipe system <NUM> is high pressure control for keeping the pressure of a working gas in the high pressure line <NUM> at a target value. In a case where the high pressure control is executed, a measured value from the first pressure sensor <NUM> is used as the measured pressure PM. In a case where the measured pressure PM is larger (smaller) than the target pressure PT, the measured pressure PM can be made smaller (larger) to become closer to the target pressure PT by decreasing (increasing) the operation frequency of the compressor <NUM>.

The value of the target pressure PT used in the high pressure control may be a relatively large value within a pressure range that is allowable. Such an allowable pressure range is typically a pressure range where the compressor <NUM> is operable, and is determined in advance as a specification of the compressor <NUM>. The value of the target pressure PT may be, for example, <NUM>% or more or <NUM>% or more of an upper limit value of the allowable pressure range, or may be equal to the upper limit value.

Another example of the pressure control of the pipe system <NUM> is differential pressure control for keeping a pressure difference between the high pressure line <NUM> and the low pressure line <NUM> at a target value. In a case where the differential pressure control is executed, a differential pressure measured value obtained by subtracting the measured value of the second pressure sensor <NUM> from the measured value of the first pressure sensor <NUM> is used as the measured pressure PM. In a case where the measured pressure PM is larger (smaller) than the target pressure PT, the measured pressure PM can be made smaller (larger) to become closer to the target pressure PT by decreasing (increasing) the operation frequency of the compressor <NUM>.

<FIG> is a flowchart showing a starting method for the cryocooler <NUM>. This method is executed by, for example, the control device <NUM> when the main switch <NUM> is operated.

As shown in <FIG>, the starting method includes increasing the volume of the high pressure line <NUM> (S20, hereinafter, also called a first step) when the cold head <NUM> is at the room temperature. The first step includes connecting the compressor <NUM> to the cold head <NUM> with the first high-pressure pipe 39a. As illustrated in <FIG>, one end of the first high-pressure pipe 39a is connected to the discharge port <NUM>, and the other end thereof is connected to the high pressure port <NUM>. In this manner, the volume of the high pressure line <NUM> is increased. The low-pressure pipe <NUM> is already connected to the compressor <NUM> and the cold head <NUM>.

The starting method includes, after the volume of the high pressure line <NUM> is increased, cooling the cold head <NUM> from the room temperature to the cryogenic temperature while controlling the operation frequency of the compressor <NUM> based on the pressure of the high pressure line <NUM> or a differential pressure between the high pressure line <NUM> and the low pressure line <NUM> (S22, hereinafter also called a second step). The second step includes cooling the cold head <NUM> from the room temperature to the cryogenic temperature and controlling the operation frequency of the compressor <NUM> such that the pressure of the high pressure line <NUM> follows a pressure target value.

The starting method includes, after the cold head <NUM> is cooled to the cryogenic temperature, decreasing the volume of the high pressure line <NUM> (S24, hereinafter, also called a third step). The third step includes connecting the compressor <NUM> to the cold head <NUM> with the second high-pressure pipe 39b. The first high-pressure pipe 39a is removed, and the second high-pressure pipe 39b is connected to the discharge port <NUM> and the high pressure port <NUM> instead. Since the volume of the first high-pressure pipe 39a is larger than the volume of the second high-pressure pipe 39b as described above, the volume of the high pressure line <NUM> is decreased.

The starting method includes, after the volume of the high pressure line <NUM> is decreased, maintaining the cold head <NUM> at the cryogenic temperature (S26, hereinafter, also called a fourth step). The fourth step includes controlling the operation frequency of the compressor <NUM> such that a differential pressure between the high pressure line <NUM> and the low pressure line <NUM> follows a differential pressure target value. After the fourth step, the normal cooling operation of the cryocooler <NUM> is performed.

In the second step, it is also possible to automatically transition from cooldown operation to normal cooling operation based on the measured temperature of the low-temperature section 14b of the cold head <NUM>. Such an example will be described.

<FIG> is a flowchart showing an example of the second step of the starting method. As shown, the compressor controller <NUM> compares the measured temperature of the low-temperature section 14b to a temperature threshold value based on the measured temperature signal T1 from the cold head temperature sensor <NUM> (S30). The temperature threshold value is, for example, the target cooling temperature (for example, approximately <NUM> to approximately <NUM>) of the cold head <NUM>.

In a case where the measured temperature exceeds the temperature threshold value (Y of S30), high pressure control is executed (S32). When the cold head <NUM> is cooled from the room temperature to the cryogenic temperature, the compressor controller <NUM> controls the operation frequency of the compressor <NUM> such that the pressure of the high pressure line <NUM> measured by the pressure sensor follows the pressure target value, based on the temperature measured by the cold head temperature sensor <NUM>.

In a case where the measured temperature is equal to or lower than the temperature threshold value (N of S30), differential pressure control is executed (S34). When the cold head <NUM> is maintained at the cryogenic temperature, the compressor controller <NUM> controls the operation frequency of the compressor <NUM> such that a differential pressure between the high pressure line <NUM> and the low pressure line <NUM>, which is measured by the pressure sensor, follows the differential pressure target value, based on the temperature measured by the cold head temperature sensor <NUM>.

In this manner, high pressure control is executed during cooldown operation, and differential pressure control is executed during normal cooling operation. After transition to the normal cooling operation, the third step can be performed. Alternatively, after transition to the normal cooling operation, it is possible not to perform the third step.

The configuration of the cryocooler <NUM> according to the embodiment has been described hereinbefore. Next, the operation thereof will be described. When the main switch <NUM> is operated, the cryocooler <NUM> begins cooldown operation. In this case, high pressure control is performed in the compressor <NUM>. Since the pressure target value of the high pressure control is set to a relatively large value, the pressure of the high pressure line <NUM> does not satisfy the target value in general. Accordingly, the operation frequency of the compressor <NUM> is increased and the rotation speed of the compressor motor <NUM> is increased such that the pressure of the high pressure line <NUM> is increased to become the target value. In addition, since the volume of the high pressure line <NUM> is increased, the high pressure line <NUM> is unlikely to be pressurized. This also works to increase the operation frequency of the compressor <NUM>.

Then, the flow rate of a working gas supplied from the compressor <NUM> to the cold head <NUM> through the high pressure line <NUM> increases, and also the flow rate of the working gas collected from the cold head <NUM> to the compressor <NUM> through the low pressure line <NUM> increases. For this reason, a differential pressure between the high pressure line <NUM> and the low pressure line <NUM> becomes large. In theory, the cooling capacity of the cryocooler <NUM> is proportional to the differential pressure. Accordingly, when the differential pressure increases, the cooling capacity of the cryocooler <NUM> improves. The cooling speed of the cold head <NUM> is increased.

Therefore, with the cryocooler <NUM> according to the embodiment, cooldown time can be shortened.

In cooling an object to be cooled, such as a superconducting device, with the cryocooler <NUM>, there are two methods in general. That is, there are a so-called conduction cooling method of cooling the object to be cooled by bringing the object to be cooled into contact with the low-temperature section 14b of the cold head <NUM> and a method of cooling a refrigerant such as liquid helium with the low-temperature section 14b and cooling the object to be cooled with the use of the refrigerant. In the refrigerant method, when the refrigerant is stored, the object to be cooled can be cooled even during non-operation (for example, maintenance) or cooldown of the cryocooler <NUM>. However, in the conduction cooling method, the object to be cooled cannot be cooled during the non-operation or cooldown of the cryocooler <NUM> or cooling is insufficient. Therefore, the cryocooler <NUM> according to the embodiment is particularly suitable for a cryogenic system under the conduction cooling method in that cooldown time can be shortened.

With the cryocooler <NUM> according to the embodiment, high pressure control can be combined with cooldown operation. In the high pressure control, by setting the pressure target value of the high pressure line <NUM> to the upper limit value of the allowable pressure range or a value close thereto, the pressure of the high pressure line <NUM> can be controlled such that the pressure becomes such a relatively large value, and the cooling capacity of the cryocooler <NUM> during the cooldown operation can be easily maintained at a high level.

On the other hand, in a case of combining cooldown operation with differential pressure control, the differential pressure target value can be increased in order to improve the cooling capacity of the cryocooler <NUM>. In this case, it is not clear if the pressure of the high pressure line <NUM> obtained as a result thereof is maintained within the allowable pressure range. The same applies to the pressure of the low pressure line <NUM>. When the pressure of any one of the high pressure line <NUM> and the low pressure line <NUM> deviates from the allowable pressure range, the compressor <NUM> can output a warning or automatically stop the operation. It may be necessary to restart the compressor <NUM>. It is not preferable when time taken for the cooldown operation is extended.

In addition, with the cryocooler <NUM> according to the embodiment, normal cooling operation is combined with differential pressure control. Since the operation frequency of the compressor <NUM> can be appropriately adjusted according to the load of the cold head <NUM>, the differential pressure control is useful in reducing power consumption of the cryocooler <NUM>.

<FIG> is a view schematically illustrating the cryocooler <NUM> according to a second embodiment. The cryocooler <NUM> according to the second embodiment is different from the cryocooler <NUM> according to the first embodiment in terms of a configuration where it is possible to change the volume of the high pressure line <NUM>, but the rest is mostly the same. Hereinafter, different configurations will be mainly described, and common configurations will be briefly described or description thereof will be omitted.

The pipe system <NUM> includes a buffer volume <NUM> configured to be connected to the high pressure line <NUM> when the cold head <NUM> is cooled from the room temperature to the cryogenic temperature and to be disconnected from the high pressure line <NUM> when the cold head <NUM> is maintained at the cryogenic temperature. The first step shown in <FIG> includes connecting the buffer volume <NUM> to the high pressure line <NUM>. The third step includes disconnecting the buffer volume <NUM> from the high pressure line <NUM>.

The buffer volume <NUM> includes a buffer tank <NUM>, a connecting pipe <NUM> that connects the buffer tank <NUM> to the high pressure line <NUM>, and a valve <NUM> that is provided on the connecting pipe <NUM>. The connecting pipe <NUM> branches from the high-pressure pipe <NUM>.

The valve <NUM> is configured to control the flow of a working gas in the connecting pipe <NUM>. The valve <NUM> is controlled in accordance with a valve control signal V input from the control device <NUM>. That is, the valve <NUM> is opened and closed or an opening degree thereof is adjusted in accordance with the valve control signal V. The valve <NUM> is connected to the control device <NUM> so as to be able to communicate therewith such that the valve receives the valve control signal V.

When the valve <NUM> is opened, the buffer tank <NUM> communicates with the high pressure line <NUM> through the connecting pipe <NUM>, allowing the flow of a working gas between the buffer tank <NUM> and the high pressure line <NUM>. In this manner, the volume of the high pressure line <NUM> is increased. When the valve <NUM> is closed, the buffer tank <NUM> is disconnected from the high pressure line <NUM>, blocking the flow of the working gas between the buffer tank <NUM> and the high pressure line <NUM>. In this manner, the volume of the high pressure line <NUM> is decreased.

The control device <NUM> controls the valve <NUM> based on a temperature measured by the cold head temperature sensor <NUM>, and accordingly changes the volume of the high pressure line <NUM>.

The control device <NUM> includes a temperature comparison unit <NUM> and a valve control unit <NUM>. The temperature comparison unit <NUM> is configured to compare the measured temperature of the low-temperature section 14b to a temperature threshold value T0 based on the measured temperature signal T1. The temperature comparison unit <NUM> is configured to output the result of temperature comparison to the valve control unit <NUM>. The valve control unit <NUM> is configured to generate the valve control signal V in accordance with the input from the temperature comparison unit <NUM>. The valve control unit <NUM> opens the valve <NUM> when the measured temperature is higher than the temperature threshold value T0, and closes the valve <NUM> when the measured temperature is equal to or lower than the temperature threshold value T0. The temperature threshold value T0 may be, for example, the target cooling temperature of the cold head <NUM>, or may be determined in advance from, for example, a temperature range of approximately <NUM> to approximately <NUM>. The control device <NUM> may include a storage unit <NUM> that stores the temperature threshold value T0.

Accordingly, the valve <NUM> is opened during cooldown operation, and the valve <NUM> is closed during normal cooling operation.

As in the first embodiment, the control device <NUM> may include the compressor controller <NUM>, and execute control processing shown in <FIG>. Accordingly, when the measured temperature is higher than the temperature threshold value T0, the valve <NUM> is opened to increase the volume of the high pressure line <NUM>, and high pressure control is executed. When the measured temperature is equal to or lower than the temperature threshold value T0, the valve <NUM> is closed to decrease the volume of the high pressure line <NUM>, and differential pressure control is executed.

Therefore, with the cryocooler <NUM> according to the second embodiment, cooldown time can be shortened as in the first embodiment.

<FIG> illustrate other examples of the buffer volume <NUM>. As illustrated in <FIG>, the buffer tank <NUM> may be connected not only to the high pressure line <NUM> but also to the low pressure line <NUM>. The valve <NUM> is provided on the connecting pipe <NUM> on the high pressure side, which connects the buffer tank <NUM> to the low pressure line <NUM>. Another valve <NUM> is provided on a connecting pipe on the low pressure side, which connects the buffer tank <NUM> to the low pressure line <NUM>. For example, by opening the valve <NUM> in a timely manner during normal cooling operation, the pressure of the buffer tank <NUM> can return to an initial pressure, which is convenient.

It is not essential for the buffer volume <NUM> to take the form of a tank. As illustrated in <FIG>, the buffer volume <NUM> may include a buffer pipe <NUM> that is connected in parallel to the high pressure line <NUM> and valves <NUM> and <NUM> that are provided at an inlet and an outlet of the buffer pipe <NUM>. The buffer pipe <NUM> is connected to the high pressure line <NUM> by the valves <NUM> and <NUM>. The volume of the high pressure line <NUM> is increased by opening the valves <NUM> and <NUM>, and the volume of the high pressure line <NUM> is decreased by closing the valves <NUM> and <NUM>.

The present invention has been described hereinbefore based on the examples. It is clear for those skilled in the art that the present invention is not limited to the embodiments, various design changes are possible, various modification examples are possible, and such modification examples are also within the scope of the present invention. Various characteristics described in relation to one embodiment are also applicable to other embodiments. A new embodiment generated through combination also has the effects of each of the combined embodiments.

Although cooldown operation is combined with high pressure control in the embodiment described above, if circumstances permit, the cooldown operation may be combined with differential pressure control in the cryocooler <NUM> according to the embodiment.

Although the present invention has been described using specific phrases based on the embodiments, the embodiments merely show one aspect of the principles and applications of the present invention, which is defined in the claims.

Claim 1:
A starting method for a cryocooler (<NUM>), the cryocooler (<NUM>) including a compressor (<NUM>), a cold head (<NUM>), a high pressure line (<NUM>) through which a refrigerant gas is supplied from the compressor (<NUM>) to the cold head (<NUM>), and a low pressure line (<NUM>) through which the refrigerant gas is collected from the cold head (<NUM>) to the compressor (<NUM>), the method comprising:
increasing a volume of the high pressure line (<NUM>) when the cold head (<NUM>) is at a room temperature;
cooling the cold head (<NUM>) from the room temperature to a cryogenic temperature while controlling an operation frequency of the compressor (<NUM>) based on a pressure of the high pressure line (<NUM>) or a differential pressure between the high pressure line (<NUM>) and the low pressure line (<NUM>), after the volume of the high pressure line (<NUM>) is increased;
decreasing the volume of the high pressure line (<NUM>) after the cold head (<NUM>) is cooled to the cryogenic temperature; and
maintaining the cold head (<NUM>) at the cryogenic temperature after the volume of the high pressure line (<NUM>) is decreased.