JP6275602B2 - Superconducting system and current leads - Google Patents

Description

  The present invention relates to a superconducting system and a current lead for supplying current to a coil used by the superconducting system.

  In the superconducting system, the coil is cooled by a refrigerator that generates an extremely low temperature in order to place the coil in a superconducting state. As an example of a refrigerator that generates such an extremely low temperature, a Gifford-McMahon (GM) refrigerator (hereinafter referred to as “GM refrigerator”) is known. The coil of the superconducting system is supplied with a large current from the outside of the superconducting system via the current lead in a state cooled to a very low temperature. For this reason, it is desired to improve the current-carrying characteristics of the current lead.

JP 2012-28041 A

  An object of the present invention is to provide a technique for improving the current-carrying characteristics of a current lead that supplies current to a coil used in a superconducting system.

  In order to solve the above problems, a superconducting system according to an aspect of the present invention includes a multistage cryogenic refrigerator having a high temperature side cooling stage and a low temperature side cooling stage, and a coil thermally connected to the low temperature side cooling stage. A high temperature side terminal thermally connected to the high temperature side cooling stage, a low temperature side terminal thermally connected to the low temperature side cooling stage, a current lead for supplying a current to the coil, a first end portion and a first end And a heat bridge that thermally connects the multistage cryogenic refrigerator and the current lead. The current lead is a high-temperature superconductor, and the heat bridge has a first end thermally connected to the cryogenic refrigerator between the high-temperature side cooling stage and the low-temperature side cooling stage, and a second end is the high-temperature Make thermal connection with the current lead between the side terminal and the low temperature side terminal.

  Another aspect of the present invention is a current lead formed by a high temperature superconductor. This current lead includes a high temperature side terminal that can be thermally connected to a high temperature side cooling stage of a multistage cryogenic refrigerator having a high temperature side cooling stage and a low temperature side cooling stage, and a low temperature side cooling of the multistage cryogenic refrigerator. A low-temperature side terminal that is thermally connectable to the stage and that can be electrically connected to a coil that is cooled by the low-temperature side cooling stage of the multistage cryogenic refrigerator is provided. The current lead can be connected to one end of a heat bridge having two ends between the high temperature side terminal and the low temperature side terminal, and the other end of the heat bridge is a multistage cryogenic refrigerator. The multistage cryogenic refrigerator is thermally connected between the high temperature side cooling stage and the low temperature side cooling stage.

  ADVANTAGE OF THE INVENTION According to this invention, the electricity supply characteristic of the current lead which supplies an electric current to the coil used for a superconducting system can be improved.

Fig.1 (a)-(b) is a figure which shows the external appearance of the superconducting system which concerns on embodiment. It is a figure which shows typically the positional relationship of the cryogenic refrigerator, coil, and electric current lead which concern on embodiment. It is a figure explaining the cryogenic refrigerator which is one embodiment of this invention. It is a figure which expands and shows a scotch yoke mechanism. It is a disassembled perspective view which expands and shows a rotary valve. It is a figure which shows the temperature profile of the low temperature side regenerator of a cryogenic refrigerator, and the temperature profile of an electric current lead. It is a figure which shows the Ic-BT characteristic of the high temperature superconductor used for the current lead which concerns on embodiment.

  Embodiments of the present invention will be described with reference to the drawings.

  In the superconducting system according to the embodiment, the coil is cooled using a cryogenic refrigerator to bring the coil into a superconducting state. A current lead using a high-temperature superconductor is used as an introduction line for introducing a large current into the coil. Thereby, the electric resistance of the current lead is suppressed, and the heat generation of the current lead due to Joule heat is suppressed.

  Here, in general, as the temperature of the high-temperature superconductor is lower, the critical current value Ic increases, and the allowable value of the current that can be passed through the current lead increases. Therefore, in the superconducting system according to the embodiment, the current lead is thermally connected to the cryogenic refrigerator via the heat bridge, the current lead is cooled, and the current-carrying characteristics of the current lead are improved.

  Fig.1 (a)-(b) is a figure which shows the external appearance of the superconducting system 100 which concerns on embodiment. The superconducting system according to the embodiment includes a coil 70, one or more cryogenic refrigerators 10, and a cooling member 72 that thermally connects the cryogenic refrigerator 10 and the coils 70. The cryogenic refrigerator 10 is realized using, for example, a GM refrigerator. In the superconducting system 100, the portion where the cold occurs is accommodated in a vacuum container (not shown).

  Fig.1 (a) is a figure which shows arrangement | positioning at the time of seeing from the upper direction of the cryogenic refrigerator 10, and FIG.1 (b) shows the BB sectional drawing in Fig.1 (a). As shown in FIG. 1A, the coil 70 is an annular coil and is disposed in a vacuum container (not shown). A cooling member 72 is provided at one end of the coil 70 in the axial direction, and is cooled by the plurality of cryogenic refrigerators 10. In the example illustrated in FIGS. 1A to 1B, the superconducting system includes four cryogenic refrigerators 10. However, the number of cryogenic refrigerators 10 included in the superconducting system is not limited to four, and may be three or less or five or more.

  As shown in FIG. 1B, a heat transfer rod 74 is connected to each of the four cryogenic refrigerators 10. The cold generated by the cryogenic refrigerator 10 is transmitted to the cooling member 72 via the heat transfer rod 74. The cryogenic refrigerator 10 and the heat transfer rod 74 are provided in, for example, four equal distributions in the circumferential direction of the cooling member 72. The heat transfer rod 74 is not an essential component, and the cryogenic refrigerator 10 and the coil 70 may be in direct contact with each other.

  FIG. 2 is a diagram schematically showing a positional relationship among the cryogenic refrigerator 10, the coil 70, and the current lead 82 according to the embodiment. Although details will be described later, the cryogenic refrigerator 10 is a multistage cryogenic refrigerator including a high temperature side cooling stage 19 and a low temperature side cooling stage 20. The cryogenic refrigerator 10 also includes a motor housing 5 that houses a motor, a housing 3 that houses a rotary valve, a scotch yoke mechanism, and the like, a high temperature side cylinder 11, and a low temperature side cylinder 12.

  The high temperature side cooling stage 19 and the low temperature side cooling stage 20 cool the object to be cooled using the cold generated by the working gas expanded in the high temperature side cylinder 11 and the low temperature side cylinder 12, respectively. Although not limited, as an example, the temperature of the high temperature side cooling stage 19 is approximately 40 [K], and the temperature of the low temperature side cooling stage 20 is approximately 4 [K].

  The coil 70 is thermally connected to the low temperature side cooling stage 20 via the cooling member 72. The room current introduction lead 80 introduces a current to be supplied to the coil 70 from the outside of the vacuum vessel (not shown) into the vacuum vessel. The indoor current introduction lead 80 is electrically connected to the high temperature side terminal 82a of the current lead 82, which is a high temperature superconductor, via the high temperature side thermal conductor 84a and the high temperature side thermal stress relaxation mechanism 88a. The low temperature side terminal 82b of the current lead 82 is electrically connected to the coil 70 via the low temperature side thermal conductor 84b and the low temperature side thermal stress relaxation mechanism 88b.

  The high temperature side heat conductor 84 a thermally connects the high temperature side terminal 82 a of the current lead 82 and the high temperature side cooling stage 19 of the cryogenic refrigerator 10. The low temperature side heat conductor 84 b thermally connects the low temperature side terminal 82 b of the current lead 82 and the low temperature side cooling stage 20 of the cryogenic refrigerator 10. Thereby, the temperature of the high temperature side terminal 82 a of the current lead 82 becomes the same temperature as that of the high temperature side cooling stage 19 of the cryogenic refrigerator 10. Further, the temperature of the low temperature side terminal 82b of the current lead 82 is the same temperature as the temperature of the low temperature side cooling stage 20 of the GM refrigerator.

  As shown in FIG. 2, the current lead 82 is supported by the reinforcing member 90 via the support member 92. The reinforcing member 90 is made of, for example, a pipe or the like and is a highly rigid member. For this reason, if current lead 82 low temperature side terminal 82b or high temperature side terminal 82a is fixed, current lead 82 or reinforcing member 90 may not be able to absorb expansion and contraction due to temperature changes. In some cases, the current lead 82 or the reinforcing member 90 may be damaged.

  Therefore, the high temperature side thermal conductor 84a and the low temperature side thermal stress relaxation mechanism 88b are configured by elastic bodies (for example, plate spring-like members) that can be expanded and contracted. Thereby, the expansion and contraction due to the temperature change of the current lead 82 or the reinforcing member 90 is absorbed, the breakage of the current lead 82 can be suppressed, and the electrical connection can be maintained well.

  The heat bridge 86 includes a first end portion 86a and a second end portion 86b. The first end 86 a of the heat bridge 86 is thermally connected to the cryogenic refrigerator 10 between the high temperature side cooling stage 19 and the low temperature side cooling stage 20. The second end 86b of the heat bridge 86 is thermally connected to the current lead 82 between the high temperature side terminal 82a and the low temperature side terminal 82b. More specifically, the second end portion 86 b of the heat bridge 86 is connected to the support member 92 and is thermally connected to the current lead 82 via the support member 92. Thereby, the heat bridge 86 thermally connects the cryogenic refrigerator 10 and the current lead 82. The heat bridge 86 can be realized using, for example, a flexible heat conductor. Thereby, expansion and contraction can be absorbed by the temperature change of the heat bridge 86.

  The detection unit 94 detects a voltage between the heat bridge 86 and the current lead 82. The detection unit 94 will be described later.

  Hereinafter, the position where the first end 86a of the heat bridge 86 is connected to the cryogenic refrigerator 10 and the position where the second end 86b of the heat bridge 86 is connected to the current lead 82 will be described. The configuration of the cryogenic refrigerator 10 will be described.

  3, 4, and 5 are diagrams for explaining a cryogenic refrigerator 10 that is an embodiment of the present invention. As described above, the cryogenic refrigerator 10 is a GM refrigerator. A cryogenic refrigerator 10 according to the present embodiment includes a compressor 1, a cylinder 2, a housing 3, a motor housing 5, and the like.

  The compressor 1 collects low-pressure refrigerant gas from the intake side to which the low-pressure pipe 1a is connected, compresses this, and then supplies the high-pressure refrigerant gas to the high-pressure pipe 1b connected to the discharge side. For example, helium gas can be used as the refrigerant gas, but the refrigerant gas is not limited thereto.

  The cryogenic refrigerator 10 illustrated in FIG. 3 is a two-stage cryogenic refrigerator 10. In the two-stage cryogenic refrigerator 10, the cylinder 2 has two cylinders, a high temperature side cylinder 11 and a low temperature side cylinder 12. A high temperature side displacer 13 is inserted into the high temperature side cylinder 11. A low temperature displacer 14 is inserted into the low temperature side cylinder 12.

  The high temperature side displacer 13 and the low temperature side displacer 14 are connected to each other, and are configured to be reciprocally movable in the axial direction of the cylinder inside the high temperature side cylinder 11 and the low temperature side cylinder 12, respectively. A high temperature side internal space 15 and a low temperature side internal space 16 are formed inside the high temperature side displacer 13 and the low temperature side displacer 14, respectively. The high temperature side internal space 15 and the low temperature side internal space 16 are filled with a regenerator material, and function as a high temperature side regenerator 17 and a low temperature side regenerator 18, respectively.

  The high temperature side displacer 13 located at the upper part is connected to a drive shaft 36 extending upward (in the Z1 direction). The drive shaft 36 constitutes a part of a scotch yoke mechanism 32 described later.

  A gas flow path L1 is formed on the high temperature end side (Z1 direction side end) of the high temperature side displacer 13. Further, a gas flow path L2 that connects the high temperature side internal space 15 and the high temperature side expansion space 21 is formed on the low temperature end side (Z2 direction side end portion) of the high temperature side displacer 13.

  A high temperature side expansion space 21 is formed at the low temperature side end of the high temperature side cylinder 11 (the end on the direction indicated by the arrow Z2 in FIG. 1). Further, an upper chamber 23 is formed at the high temperature side end of the high temperature side cylinder 11 (the end on the direction indicated by the arrow Z1 in FIG. 1).

  Further, a low temperature side expansion space 22 is formed at the low temperature side end portion (the end portion on the direction side indicated by the arrow Z2 in FIG. 1) in the low temperature side cylinder 12.

  The low temperature displacer 14 is attached to the lower portion of the high temperature displacer 13 by a coupling mechanism (not shown). A gas flow path L3 that connects the high temperature side expansion space 21 and the low temperature side internal space 16 is formed at the high temperature side end of the low temperature side displacer 14 (the end on the direction indicated by the arrow Z1 in FIG. 1). Yes. Further, a gas flow path L4 that connects the low temperature side internal space 16 and the low temperature side expansion space 22 is formed at the low temperature side end of the low temperature side displacer 14 (the end on the direction indicated by the arrow Z2 in FIG. 1). ing.

  The high temperature side cooling stage 19 is disposed on the outer peripheral surface of the high temperature side cylinder 11 at a position facing the high temperature side expansion space 21. Further, the low temperature side cooling stage 20 is disposed at a position facing the low temperature side expansion space 22 on the outer peripheral surface of the low temperature side cylinder 12.

  The high temperature side displacer 13 and the low temperature side displacer 14 are moved in the vertical direction (arrows Z1 and Z2 directions) in the drawing by the scotch yoke mechanism 32 in the high temperature side cylinder 11 and the low temperature side cylinder 12, respectively.

  As shown in FIG. 3, the housing 3 has a rotary valve 40 and the like, and the motor accommodating portion 5 accommodates the motor 31.

  The motor 31, the drive rotating shaft 31a, and the Scotch yoke mechanism 32 constitute a drive device. The motor 31 generates a rotational driving force, and a rotating shaft connected to the motor 31 (hereinafter referred to as “driving rotating shaft 31 a”) transmits the rotational motion of the motor 31 to the scotch yoke mechanism 32. The drive rotating shaft 31a is supported by a bearing 60.

  FIG. 4 is an enlarged view showing the scotch yoke mechanism 32. The scotch yoke mechanism 32 includes a crank 33, a scotch yoke 34, and the like. The scotch yoke mechanism 32 can be driven by driving means such as a motor 31.

  The crank 33 is fixed to the drive rotating shaft 31a. The crank 33 is configured such that a crank pin 33b is provided at a position eccentric from the mounting position of the drive rotating shaft 31a. Therefore, when the crank 33 is attached to the drive rotation shaft 31a, the crank pin 33b is eccentric with respect to the drive rotation shaft 31a. In this sense, the crank pin 33b functions as an eccentric rotating body. Note that the drive rotary shaft 31a may be rotatably supported at a plurality of locations in the longitudinal direction.

  The scotch yoke 34 includes a drive shaft 36a, a drive shaft 36b, a yoke plate 35, a roller bearing 37, and the like. A housing space is formed in the housing 3. This accommodation space is an airtight container having airtightness for accommodating the scotch yoke 34 and a rotor valve 42 of the rotary valve 40 described later. Therefore, hereinafter, the accommodation space in the housing 3 is referred to as an “airtight container 4” in the present specification. The airtight container 4 communicates with the intake port of the compressor 1 through the low pressure pipe 1a. Therefore, the airtight container 4 is always maintained at a low pressure.

  The drive shaft 36a extends upward (Z1 direction) from the yoke plate 35. The drive shaft 36 a is supported by a sliding bearing 38 a provided in the housing 3. Therefore, the drive shaft 36a is configured to be movable in the vertical direction in the figure (the directions of arrows Z1 and Z2 in the figure).

  The drive shaft 36b extends downward (Z2 direction) from the yoke plate 35. The drive shaft 36 b is supported by a sliding bearing 38 b provided in the housing 3. Therefore, the drive shaft 36 is also configured to be movable in the vertical direction in the figure (the directions of arrows Z1 and Z2 in the figure).

  The drive shaft 36a and the drive shaft 36b are supported by the slide bearing 38a and the slide bearing 38b, respectively, so that the scotch yoke 34 can move in the vertical direction (the directions of arrows Z1 and Z2 in the figure) within the housing 3. It has become.

  In the present embodiment, the term “axial direction” is sometimes used to express the positional relationship of the components of the cryogenic refrigerator in an easily understandable manner. The axial direction represents the direction in which the drive shaft 36a and the drive shaft 36b extend, and also coincides with the direction in which the high temperature side displacer 13 and the low temperature side displacer 14 move. For the sake of convenience, the relative proximity to the expansion space or the cooling stage in the axial direction may be referred to as “lower” and the relative distance from the expansion space or the cooling stage may be referred to as “upper”. That is, it is sometimes called “upper” when it is relatively far from the end on the low temperature side and “lower” when it is relatively close. Such expressions are not related to the arrangement when the cryogenic refrigerator 10 is attached. For example, the cryogenic refrigerator 10 may be attached with the expansion space facing upward in the vertical direction.

  The yoke plate 35 has a horizontally long window 35a. The horizontally long window 35a extends in a direction intersecting with the extending direction of the drive shaft 36a and the drive shaft 36b, for example, a direction orthogonal to each other (directions of arrows X1 and X2 in FIG. 4).

  The roller bearing 37 is disposed in the horizontally long window 35a. The roller bearing 37 is configured to be able to roll within the horizontally long window 35a. A hole 37 a that engages with the crank pin 33 b is formed at the center position of the roller bearing 37. The laterally long window 35a allows lateral movement of the crank pin 33b and the roller bearing 37. The horizontally long window 35a includes an upper frame portion and a lower frame portion extending in the horizontal direction, and extending in the axial direction or the vertical direction at the horizontal ends of the upper frame portion and the lower frame portion, and the upper frame portion and the lower frame. A first side frame part and a second side frame part that join the parts.

  When the motor 31 is driven and the drive rotary shaft 31a rotates, the crank pin 33b rotates to draw an arc. As a result, the scotch yoke 34 reciprocates in the directions of arrows Z1 and Z2 in the figure. At this time, the roller bearing 37 reciprocates in the horizontal window 35a in the directions indicated by arrows X1 and X2.

  The high temperature side displacer 13 is connected to a drive shaft 36 b disposed under the scotch yoke 34. Therefore, when the scotch yoke 34 reciprocates in the directions of arrows Z1 and Z2 in the drawing, the high temperature side displacer 13 and the low temperature side displacer 14 connected thereto also move within the high temperature side cylinder 11 and the low temperature side cylinder 12 with the arrows Z1 and Z2. Move back and forth in the direction.

  Next, the valve mechanism will be described. The cryogenic refrigerator 10 according to the embodiment uses a rotary valve 40 as a valve mechanism.

  The rotary valve 40 switches the flow path of the refrigerant gas. The rotary valve 40 functions as a supply valve that guides the high-pressure refrigerant gas discharged from the discharge side of the compressor 1 to the upper chamber 23 of the high-temperature side displacer 13 and also supplies the refrigerant gas from the upper chamber 23 to the compressor 1. It functions as an exhaust valve that leads to the intake side.

  As shown in FIG. 5 in addition to FIG. 3, the rotary valve 40 includes a stator valve 41 and a rotor valve 42. The stator valve 41 has a flat stator side sliding surface 45, and the rotor valve 42 has a flat rotor side sliding surface 50. The stator-side sliding surface 45 and the rotor-side sliding surface 50 are in surface contact with each other, thereby preventing refrigerant gas from leaking.

  The stator valve 41 is fixed in the housing 3 with a fixing pin 43. By fixing with the fixing pin 43, the rotation of the stator valve 41 is restricted.

  The rotor valve 42 is rotatably supported by a rotor valve bearing 62. An engagement hole (not shown) that engages with the crank pin 33b is formed in the opposite end surface 52 that is located on the opposite side of the rotor-side sliding surface 50 of the rotor valve 42. When the crank pin 33b is inserted into the roller bearing 37, the tip of the crank pin 33b projects from the roller bearing 37 in the direction of the arrow Y1 (see FIG. 1).

  The tip of the crank pin 33 b protruding from the roller bearing 37 is engaged with an engagement hole formed in the rotor valve 42. Therefore, when the crank pin 33b rotates (eccentric rotation), the rotor valve 42 rotates in synchronization with the scotch yoke mechanism 32.

  The stator valve 41 has a refrigerant gas supply hole 44, an arc-shaped groove 46, and a gas flow path 49. The refrigerant gas supply hole 44 is connected to the high-pressure pipe 1 b of the compressor 1 and is formed so as to penetrate the central portion of the stator valve 41.

  The arc-shaped groove 46 is formed in the stator side sliding surface 45. The arc-shaped groove 46 has an arc shape centered on the refrigerant gas supply hole 44.

  The gas flow path 49 is formed across the stator valve 41 and the housing 3. One end of the gas flow path 49 on the valve side opens into the arc-shaped groove 46 to form an opening 48. Further, in the gas flow path 49, a discharge port 47 is opened on the side surface of the stator valve 41. The discharge port 47 communicates with the gas flow path 49 in the housing. The other end of the gas flow path 49 in the housing is connected to the high temperature side expansion space 21 via the upper chamber 23, the gas flow path L1, the high temperature side regenerator 17, and the like.

  On the other hand, the rotor valve 42 has an oval groove 51 and an arc-shaped hole 53.

  The oval groove 51 is formed on the rotor side sliding surface 50 so as to extend in the radial direction from the center thereof. The arc-shaped hole 53 penetrates from the rotor-side sliding surface 50 of the rotor valve 42 to the opposite end surface 52 and is connected to the airtight container 4. The arc-shaped hole 53 is formed on the same circumference as the arc-shaped groove 46 of the stator valve 41.

  The refrigerant gas supply hole 44, the oval groove 51, the arc-shaped groove 46, and the opening 48 constitute a supply valve. The opening 48, the arc-shaped groove 46, and the arc-shaped hole 53 constitute an exhaust valve. In the present embodiment, the spaces existing inside the valve such as the oval groove 51 and the arc-shaped groove 46 may be collectively referred to as a valve internal space.

  In the cryogenic refrigerator 10 having the above-described configuration, when the rotational driving force of the motor 31 is transmitted to the Scotch yoke mechanism 32 via the drive rotating shaft 31a and the Scotch yoke mechanism 32 is driven, the Scotch yoke 34 is Z1, Reciprocates in the Z2 direction. By the operation of the scotch yoke 34, the high temperature side displacer 13 and the low temperature side displacer 14 reciprocate in the high temperature side cylinder 11 and the low temperature side cylinder 12 between the bottom dead center LP and the top dead center UP.

  Before the high temperature side displacer 13 and the low temperature side displacer 14 reach the bottom dead center LP, the exhaust valve is closed, and then the supply valve is opened. That is, a refrigerant gas flow path is formed between the refrigerant gas supply hole 44, the oval groove 51, the arc-shaped groove 46, and the gas flow path 49.

  Therefore, the high-pressure refrigerant gas begins to be filled from the compressor 1 into the upper chamber 23. Thereafter, the high temperature side displacer 13 and the low temperature side displacer 14 start to rise past the bottom dead center LP, and the refrigerant gas passes from the top to the bottom through the high temperature side regenerator 17 and the low temperature side regenerator 18, and the high temperature side expansion space 21. And the low temperature side expansion space 22 is filled.

  When the high temperature displacer 13 and the low temperature displacer 14 reach the top dead center UP, the supply valve is closed. At the same time or after that, the exhaust valve opens. That is, a refrigerant gas flow path is formed between the gas flow path 49, the arc-shaped groove 46, and the arc-shaped hole 53.

  Thus, the high-pressure refrigerant gas expands in the high temperature side expansion space 21 and the low temperature side expansion space 22 to generate cold, and cools the high temperature side cooling stage 19 and the low temperature side cooling stage 20. The low-temperature refrigerant gas that has generated cold flows from the bottom to the top while cooling the regenerator material in the high-temperature side regenerator 17 and the low-temperature side regenerator 18, and then returns to the low-pressure pipe 1 a of the compressor 1. .

  Thereafter, before the high temperature side displacer 13 and the low temperature side displacer 14 reach the bottom dead center LP, the exhaust valve is closed, and then the supply valve is opened to complete one cycle. Thus, by repeating the cycle of compression and expansion of the refrigerant gas, the high temperature side cooling stage 19 and the low temperature side cooling stage 20 of the cryogenic refrigerator 10 are cooled to a cryogenic temperature. The high temperature side cooling stage 19 and the low temperature side cooling stage 20 of the cryogenic refrigerator 10 respectively convert the cold generated by expanding the refrigerant gas in the high temperature side expansion space 21 and the low temperature side expansion space 22 into the high temperature side cylinder 11 and Conducted to the outside of the low temperature side cylinder 12.

  As described above, in the cryogenic refrigerator 10 according to the embodiment, cold is generated by converting the driving force of the driving device such as the motor 31 into the reciprocating movement of the high temperature side displacer 13 and the low temperature side displacer 14. . Thereby, the temperature of the high temperature side cooling stage is about 40K, and the temperature of the low temperature side cooling stage 20 is an extremely low temperature of about 4K. The temperature of the high temperature side terminal 82a of the current lead 82 thermally connected to the high temperature side cooling stage 19 is about 40 [K]. The temperature of the low temperature side terminal 82b of the current lead 82 thermally connected to the low temperature side cooling stage 20 is about 4 [K].

  FIG. 6 is a diagram showing a temperature profile of the low temperature side regenerator 18 of the cryogenic refrigerator 10 and a temperature profile of the current lead 82. More specifically, the graph shown by the solid line in FIG. 6 shows the low temperature side regenerator 18 when the position of the high temperature side cooling stage 19 of the cryogenic refrigerator 10 is 0 and the position of the low temperature side cooling stage 20 is 1. A temperature profile is shown. 6 shows a temperature profile of the current lead 82 when the position of the high temperature side terminal 82a of the current lead 82 is 0 and the position of the low temperature side terminal 82b of the current lead 82 is 1.

  As indicated by a broken line in FIG. 6, the temperature profile of the current lead 82 decreases linearly from the high temperature side terminal 82a toward the low temperature side terminal 82b. On the other hand, as shown by the solid line in FIG. 6, the low temperature side regenerator 18 has a temperature decrease rate on the high temperature side cooling stage 19 side, that is, on the high temperature end side. Greater than rate. That is, the temperature profile of the low temperature side regenerator 18 becomes a non-linear graph convex downward. Thus, the temperature of both ends of the current lead 82 and the low temperature side regenerator 18 are substantially equal. However, when the temperature of the intermediate part between the current lead 82 and the low temperature side regenerator 18 is measured at a position where the distance from the high temperature end is equal, the low temperature side regenerator 18 is lower than the current lead 82.

  FIG. 7 is a diagram illustrating Ic-BT characteristics of the high-temperature superconductor used for the current lead 82 according to the embodiment. FIG. 7 is a graph with the empirical magnetic field [T] of the high-temperature superconductor as the horizontal axis and the critical current [A] of the high-temperature superconductor as the vertical axis. When the temperature of the high-temperature superconductor is 4 [K] (solid line) And 40 [K] (broken line).

  As shown in FIG. 7, the critical current Ic of the high-temperature superconductor is smaller as the empirical magnetic field of the high-temperature superconductor is larger. Moreover, the empirical magnetic field becomes larger as it is closer to the coil. Therefore, in order to stabilize the high-temperature superconductor, it is preferable to cool the position close to the coil 70. Although not limited, as an example, the coil 70 used by the superconducting system 100 according to the embodiment generates a magnetic field of 5 [T] or more. Suppose that the empirical magnetic field of a high-temperature superconductor is 2 [T]. From FIG. 7, when the temperature of the high-temperature superconductor is 4 [K], the critical current Ic is about twice or more than the critical current Ic when the temperature is 40 [K]. The critical current Ic is a current of about several hundred [A] to several thousand [A].

  When the current flowing through the high-temperature superconductor exceeds the critical current Ic, the high-temperature superconductor is transferred to a normal conductor. In general, it is preferable that the value of the critical current Ic of the high-temperature superconductor constituting the current lead 82 is large because more current can be supplied to the coil 70 more safely.

  Therefore, in the superconducting system 100 according to the embodiment, the low temperature side regenerator 18 and the current lead 82 are thermally connected via the heat bridge 86. As described above, when the temperature of the intermediate portion between the current lead 82 and the low temperature side regenerator 18 is measured at the same distance from the high temperature end, the low temperature side regenerator 18 is lower than the current lead 82. . For this reason, when the low temperature side regenerator 18 and the current lead 82 are thermally connected, heat is transferred from the current lead 82 toward the low temperature side regenerator 18, and the temperature of the current lead 82 can be lowered.

  Here, in order to increase the value of the critical current Ic of the current lead 82, the temperature of the current lead 82 should be as low as possible. For this reason, the second end portion 86b of the heat bridge 86 is thermally connected on the high temperature side terminal 82a side with respect to the intermediate portion between the high temperature side terminal 82a and the low temperature side terminal 82b of the current lead 82. As a result, the temperature can be lowered from a location close to the high temperature side terminal 82a of the current lead 82.

  On the other hand, the low temperature side end of the low temperature side regenerator 18 is thermally connected to the low temperature side cooling stage 20, and the low temperature side cooling stage 20 cools the coil 70. For this reason, the temperature of the low temperature side cooling stage 20 may rise. Therefore, the first end portion 86 a of the heat bridge 86 is thermally connected to the low temperature side regenerator 18 on the high temperature side cooling stage 19 side rather than the intermediate portion between the high temperature side cooling stage 19 and the low temperature side cooling stage 20. Thereby, the temperature of the current lead 82 can be lowered while suppressing an increase in the temperature of the low temperature side cooling stage 20.

  Moreover, when the heat of the current lead 82 moves to the low temperature side regenerator 18, the temperature profile of the low temperature side regenerator 18 approaches a straight line. It is known that the refrigeration performance of the cryogenic refrigerator 10 improves as the temperature profile of the low temperature side regenerator 18 becomes closer to a straight line. In this regard, thermally connecting the low temperature side regenerator 18 and the current lead 82 can improve the refrigeration performance of the cryogenic refrigerator 10.

  Thus, the critical current Ic of the current lead 82 can be increased by lowering the temperature of the current lead 82. When the current lead 82 is in the superconducting state, the electric resistance of the current lead 82 is 0. Therefore, all the current that has reached the high-temperature side terminal 82 a from the indoor current introduction lead 80 to the current lead 82 flows to the current lead 82. However, if for some reason at least a portion of the current lead 82 transitions to a normal conductor, the current lead 82 will have an electrical resistance.

  Therefore, the detection unit 94 measures the voltage between the heat bridge 86 and the high-temperature side terminal 82 a of the current lead 82. If the current lead 82 is in a superconducting state, there will be no voltage drop even if a current flows through the current lead 82. However, if the current lead 82 transitions to a normal conductor, the heat bridge 86 and the high-temperature side terminal of the current lead 82 will have resistance. A potential difference is generated between the terminal 82a and the terminal 82a. By detecting the voltage between the heat bridge 86 and the current lead 82 by the detection unit 94, it is possible to detect whether the current lead 82 is in a superconducting state or a normal conductor.

  As described above, according to the superconducting system 100 according to the embodiment, the energization characteristics of the current lead 82 can be improved.

  Moreover, the temperature profile of the low temperature side regenerator 18 can be made closer to a linear shape, and the refrigeration performance of the cryogenic refrigerator 10 can be improved.

  As mentioned above, although this invention was demonstrated based on embodiment, embodiment only shows the principle and application of this invention. In the embodiment, many modifications and arrangements can be made without departing from the spirit of the present invention defined in the claims.

  DESCRIPTION OF SYMBOLS 1 Compressor, 1a Low pressure piping, 1b High pressure piping, 2 Cylinder, 3 Housing, 4 Airtight container, 5 Motor accommodating part, 10 Cryogenic refrigerator, 11 High temperature side cylinder, 12 Low temperature side cylinder, 13 High temperature side displacer, 14 Low temperature Side displacer, 15 High temperature side internal space, 16 Low temperature side internal space, 17 High temperature side regenerator, 18 Low temperature side regenerator, 19 High temperature side cooling stage, 20 Low temperature side cooling stage, 21 High temperature side expansion space, 22 Low temperature side expansion space , 23 upper chamber, 30 drive device, 31 motor, 31a drive rotary shaft, 32 scotch yoke mechanism, 33 crank, 33b crank pin, 34 scotch yoke, 35 yoke plate, 35a lateral window, 36 drive shaft, 37 bearing, 37a hole 38a, 38b Bearing, 40 Rotary valve, 41 Stator valve, 42 Rotor valve, 43 Fixing pin, 44 Refrigerant gas supply hole, 45 Stator side sliding surface, 46 Arc-shaped groove, 47 Discharge port, 48 opening, 49 Gas flow path, 50 Rotor-side sliding surface, 51 Oval groove, 52 Opposite end surface, 53 Arc-shaped hole, 62 Rotor valve bearing, 70 Coil, 72 Cooling member, 74 Heat transfer rod, 80 Indoor current introduction lead, 82 Current lead, 82a High temperature side terminal, 82b Low temperature side terminal, 84a High temperature side thermal conductor, 84b Low temperature side thermal conductor, 86 Heat bridge, 86a First end, 86b Second end, 88a High temperature side thermal stress relaxation mechanism, 88b Low temperature side Thermal stress relaxation mechanism, 90 reinforcement member, 92 support member, 94 detector, more than 100 Conduction system.

Claims (6)

A multi-stage cryogenic refrigerator having a high temperature side cooling stage and a low temperature side cooling stage;
A coil thermally connected to the low temperature side cooling stage;
A high temperature side terminal thermally connected to the high temperature side cooling stage, a low temperature side terminal thermally connected to the low temperature side cooling stage, and a current lead for supplying current to the coil;
A heat bridge having a first end and a second end, and thermally connecting the multistage cryogenic refrigerator and the current lead;
The current lead is a high temperature superconductor;
The heat bridge is
The first end is thermally connected to the cryogenic refrigerator between the high temperature side cooling stage and the low temperature side cooling stage;
The superconducting system, wherein the second end portion is thermally connected to the current lead between the high temperature side terminal and the low temperature side terminal. Further comprising a support member thermally connected to the current lead and supporting the current lead,
The superconducting system according to claim 1, wherein the second end portion of the heat bridge is connected to the support member.   The superconducting system according to claim 1, wherein the heat bridge is a flexible heat conductor.   The superconducting system according to any one of claims 1 to 3, further comprising a detection unit that detects a voltage between the heat bridge and the current lead. The heat bridge is
The first end portion is thermally connected to the cryogenic refrigerator on the high temperature side cooling stage side than an intermediate portion between the high temperature side cooling stage and the low temperature side cooling stage,
The said 2nd end part is thermally connected with the said current lead in the high temperature terminal side rather than the intermediate part of the said high temperature side terminal and the said low temperature side terminal. Superconducting system. A current lead formed by a high temperature superconductor,
A high temperature side terminal thermally connectable to a high temperature side cooling stage of a multistage cryogenic refrigerator having a high temperature side cooling stage and a low temperature side cooling stage;
A low temperature side terminal that is thermally connectable to a low temperature side cooling stage of the multistage cryogenic refrigerator and is electrically connected to a coil that is cooled by the low temperature cooling stage of the multistage cryogenic refrigerator. Prepared,
The current lead can be connected to one end of a heat bridge having two ends between the high temperature side terminal and the low temperature side terminal, and the other end of the heat bridge is connected to the multi-stage. A current lead that is thermally connected to the multistage cryogenic refrigerator between a high temperature side cooling stage and a low temperature side cooling stage of the type cryogenic refrigerator.

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