Patent Description:
Cryostats each serving as a thermally-insulating container for keeping a cooled object at a very low temperature have been conventionally known. Technologies using such a cryostat include adoption of an NMR (Nuclear Magnet Resonance) apparatus having been widely utilized in chemical fields, medical and agrochemical fields, and industrial fields to know a bonding state between molecules. A strong magnetic field is required for measurement such NMR, and hence a superconducting magnet (cooled object) made of metal-based superconducting material, such as NbTi and Nb3Sn, is used for the NMR apparatus. The metal-based superconducting material shifts to a super conducting state only at a very low temperature. Therefore, the NMR apparatus has the aforementioned cryostat, and the superconducting magnet is immersed in liquid helium at a very low temperature in the cryostat so as to be continuously cooled. The cryostat has a helium container for storing the liquid helium and a vacuum-insulating container for accommodating the helium container. The liquid helium has a boiling point of <NUM> at an atmospheric pressure. For suppressing evaporation of the liquid helium, the helium container containing the superconducting magnet therein is accommodated in the vacuum-insulating container so as to be vacuum-insulated.

The liquid helium steadily evaporates and continues to reduce even in the cryostat. Here, Patent Literature <NUM> discloses a helium recondensation apparatus which prevents helium from reducing by recondensing vapor of the helium evaporating from a helium tank included in an NMR apparatus. The recondensation apparatus includes: a cryogenic freezer located above the NMR apparatus; a helium recondensing tank cooled by the cryogenic freezer; and a pipeline for sending out the vapor of the helium in the helium tank from the NMR apparatus to the helium recondensing tank, and returning the helium recondensed in the helium recondensing tank to the NMR apparatus.

The vapor of helium gas from the helium tank of the NMR apparatus flows into the helium recondensing tank through a flexible pipeline to be cooled by a cold head of the cryogenic freezer, and then recondensed and liquefied. The liquefied helium reflows into the helium tank of the NMR apparatus through the pipeline, and therefore a reduction in the liquid helium in the NMR apparatus is suppressible. This configuration where the pipeline connects the helium recondensing tank and the helium tank to each other suppresses propagation of vibration caused by the freezer to the NMR apparatus more effectively than a configuration where a cryogenic freezer is directly mounted on an NMR apparatus.

The present invention has been achieved in view of the aforementioned problem, and an object of the present invention is to provide a combination of a helium recondensation apparatus and a cryostat, which can stably recondense vapor of helium in the cryostat while preventing a pipeline for the recondensation from being clogged.

The above object is solved by a combination of a helium recondensation apparatus and a cryostat having the features of claim <NUM>. Further developments are subject matter of the dependent claims.

Hereinafter, a recondensation apparatus <NUM> (helium recondensation apparatus for a cryostat) according to each embodiment of the present invention will be described with reference to accompanying drawings. <FIG> is a cross-sectional view showing a state where the recondensation apparatus <NUM> according to an embodiment of the present invention is connected to an NMR apparatus <NUM>. <FIG> is a cross-sectional view of the recondensation apparatus <NUM> according to the embodiment. Here, each drawing illustrates directions "UP", "DOWN", "LEFT", and "RIGHT" for explanation, but these directions do not delimit any structure and use way of the helium recondensation apparatus for a cryostat according to the present invention.

The recondensation apparatus <NUM> is connected to the NMR apparatus <NUM> serving as an exemplary cryostat in the embodiment.

The NMR apparatus <NUM> includes: a superconducting magnet <NUM> (cooled object); a helium tank <NUM> tightly closed to store liquid helium <NUM> (coolant helium); a plurality of helium ports <NUM> each communicating with the helium tank <NUM>; a gas cooling radiation shield <NUM>; a nitrogen tank <NUM> (auxiliary coolant tank) tightly closed to store liquid nitrogen <NUM> (a thermally-insulating auxiliary coolant); a plurality of nitrogen ports <NUM> each communicating with the nitrogen tank <NUM>; and a vacuum tank <NUM>.

The superconducting magnet <NUM> generates a strong magnetic field for measurement in the NMR apparatus <NUM>. To this end, the superconducting magnet <NUM> is deeply cooled to a very low temperature and maintained in a superconducting state. The helium tank <NUM> has a cylindrical shape and stores the liquid helium <NUM> (coolant helium) therein. The superconducting magnet <NUM> is accommodated in the helium tank <NUM> in such a manner as to be immersed in the liquid helium <NUM> in the helium tank <NUM>. The helium tank <NUM> (liquid helium container) containing the superconducting magnet <NUM> in this manner is accommodated in the vacuum tank <NUM> so as to be vacuum-insulated. As a result, evaporation of the liquid helium is suppressed.

The nitrogen tank <NUM> further surrounds the helium tank <NUM> for reducing the heat which enters the helium tank <NUM>. The nitrogen tank <NUM> stores the liquid nitrogen <NUM>. The gas cooling radiation shield <NUM> having a cylindrical shape is located between the helium tank <NUM> and the nitrogen tank <NUM>. The gas cooling radiation shield <NUM> has a temperature set to around <NUM> to <NUM> with use of cold energy of vapor of the helium in the helium tank <NUM>. Such a multiple-layered thermally-insulating container is called the cryostat.

The helium still evaporates at a speed of <NUM> to <NUM> cc/h and the nitrogen evaporates at a speed of <NUM> to <NUM> cc/h in use of the NMR apparatus <NUM> even with the above-described thermally-insulating structure. Therefore, it is desirable to reduce a periodic coolant replenishment work by recondensing the vapor of the helium in the helium tank <NUM> and the vapor of the nitrogen in the nitrogen tank <NUM>. Besides, a very small electromagnetic wave is observed in the measurement in the NMR apparatus <NUM>. For improvement of the accuracy (S/N ratio) of the observation, preferably, vibration which propagates to the NMR apparatus <NUM> is maximally reduced.

The NMR apparatus <NUM> includes a nitrogen tank check valve <NUM>, a nitrogen tank pressure gauge <NUM>, a helium tank check valve <NUM>, and a helium tank pressure gauge <NUM>. Prior to the use of the NMR apparatus <NUM>, the helium tank <NUM> is filled with the liquid helium through one helium port <NUM> (a right helium port <NUM> in <FIG>) among the helium ports <NUM>. Similarly, the nitrogen tank <NUM> is filled with the liquid nitrogen through one nitrogen port <NUM> (a right nitrogen port <NUM> in <FIG>) among the nitrogen ports <NUM>. Each of the helium tank check valve <NUM> and the nitrogen tank check valve <NUM> is disposed to maintain corresponding one of the helium tank <NUM> and the nitrogen tank <NUM> at a substantially atmospheric pressure, specifically, at a pressure slightly higher than the atmospheric pressure. The helium tank pressure gauge <NUM> detects an internal pressure of the helium tank <NUM>, and the nitrogen tank pressure gauge <NUM> detects an internal pressure of the nitrogen tank <NUM>.

The recondensation apparatus <NUM> according to the embodiment can recondense each vapor of the helium and the nitrogen in the NMR apparatus <NUM>. As shown in <FIG> and <FIG>, the recondensation apparatus <NUM> includes a freezer <NUM> located away from the NMR apparatus <NUM>, a nitrogen recondensing unit A (auxiliary coolant recondensing unit), a helium recondensing unit B, a recondensation apparatus vacuum tank <NUM>, and a housing <NUM> (support mechanism).

The freezer <NUM> includes a cylinder 10P, a displacer 10Q, a motor M (drive part), and a first cooling stage <NUM> (sub-cooling part) and a second cooling stage <NUM> (main cooling part) each kept at a very low temperature. The cylinder 10P is a member having a cylindrical shape and a central axis extending in an up-down direction. The displacer 10Q is arranged in the cylinder 10P reciprocatively movable upward and downward in the up-down direction for generating cold energy by expanding coolant gas in the cylinder 10P. The motor M is located below the cylinder 10P for generating a drive force to reciprocatively move the displacer 10Q upward and downward.

The first cooling stage <NUM> is connected to the cylinder 10P above the motor M for cooling a nitrogen recondensing chamber <NUM> (second recondensing chamber) to be described later by receiving the cold energy. Specifically, the first cooling stage <NUM> is thermally connected to the nitrogen recondensing chamber <NUM> for cooling the nitrogen recondensing chamber <NUM> to allow nitrogen gas (a heat-exchanging auxiliary coolant) to recondense in the nitrogen recondensing chamber <NUM>. The first cooling stage <NUM> has a circular pipe shape to surround the cylinder 10P.

The second cooling stage <NUM> is connected to the cylinder 10P above the first cooling stage <NUM> (at a position different from the first cooling stage <NUM>) for cooling a helium recondensing chamber <NUM> (first recondensing chamber) by receiving the cold energy. Specifically, the second cooling stage <NUM> is thermally connected to the helium recondensing chamber <NUM> for cooling the helium recondensing chamber <NUM> to allow the helium (heat-exchanging helium) to recondense in the helium recondensing chamber <NUM>. The second cooling stage <NUM> has a cylindrical shape.

As shown in <FIG>, the freezer <NUM> is surrounded by the recondensation apparatus vacuum tank <NUM> therearound and is vacuum-insulated by the recondensation apparatus radiation shield <NUM> (<FIG>) thereof. The freezer <NUM> is supported by the housing <NUM> at a predetermined height position from a floor surface (<FIG>).

The nitrogen recondensing unit A (<FIG>) recondenses the thermally-insulating nitrogen in the nitrogen tank <NUM> by receiving cold energy from the first cooling stage <NUM> of the freezer <NUM>. The nitrogen recondensing unit A includes: a nitrogen heat exchanger <NUM> (second heat exchanger); the nitrogen recondensing chamber <NUM> (second recondensing chamber); a nitrogen backward pipe <NUM> (second connection part); nitrogen forward pipe <NUM> (second connection part); a nitrogen forward-backward pipeline header <NUM>; a nitrogen transfer pipe vacuum jacket <NUM>; a nitrogen transfer pipe flexible section <NUM>; a nitrogen supply pipe <NUM>; nitrogen buffer tank <NUM>; a nitrogen supply valve <NUM>; a nitrogen buffer tank pressure gauge <NUM>; and a nitrogen recondensing chamber heater <NUM>.

The helium recondensing unit B (<FIG>) recondenses the coolant helium in the helium tank <NUM> by receiving cold energy from the second cooling stage <NUM> of the freezer <NUM>. The helium recondensing unit B includes: a helium heat exchanger <NUM> (first heat exchanger); the helium recondensing chamber <NUM> (first recondensing chamber); a helium backward pipe <NUM> (first connection part, backward section); a helium forward pipe <NUM> (first connection part, backward section); a helium forward-backward pipeline header <NUM>; a helium transfer pipe vacuum jacket <NUM>; a helium transfer pipe flexible section <NUM>; a helium supply pipe <NUM>; a helium buffer tank <NUM>; a helium supply valve <NUM>; a helium buffer tank pressure gauge <NUM>; and a helium recondensing chamber heater <NUM>. The respective components of the helium recondensing unit B sequentially correspond to the respective components of the nitrogen recondensing unit A. The nitrogen recondensing unit A has a structure similar to that of the helium recondensing unit B. From this perspective, the structure of the helium recondensing unit B will be described in detail below. Each of <FIG> is an enlarged cross-sectional view of a part of the recondensation apparatus <NUM> according to the embodiment.

The helium heat exchanger <NUM> is located above a liquid surface of the helium (coolant helium) in the helium tank <NUM> (<FIG>). The helium heat exchanger <NUM> has a circular pipe shape with an outer circumferential surface 25A (first outer peripheral surface) and an inner circumferential surface 25B (first inner peripheral surface) (<FIG>). The inner circumferential surface 25B defines an inner space S (first inner space) separated from the helium in the helium tank <NUM>. The inner space S can store liquid helium (heat-exchanging helium in liquid). The helium heat exchanger <NUM> takes heat of vaporization, which is necessary for evaporation of the heat-exchanging helium in the inner space S, from the vapor of the coolant helium in the helium tank <NUM>, thereby permitting the coolant helium to recondense through the heat exchange with the heat-exchanging helium in the inner space S. In other words, the helium heat exchanger <NUM> is exposed in the helium tank <NUM> of the NMR apparatus <NUM> to cool and liquefy helium gas around the helium heat exchanger <NUM> via a pipe wall (outer circumferential surface) of the helium heat exchanger <NUM>, thereby generating heat exchanger outer wall liquid helium <NUM>.

The helium recondensing chamber <NUM> is located away from the NMR apparatus <NUM> and has a cylindrical shape, but is thermally connected to a top surface of the second cooling stage <NUM> of the freezer <NUM>. The helium recondensing chamber <NUM> is filled with helium gas (heat-exchanging helium), and is cooled by the second cooling stage <NUM> of the freezer <NUM> to liquefy the helium in the helium recondensing chamber <NUM>. In this manner, the helium recondensing chamber <NUM> receives vapor of the helium (gaseous heat-exchanging helium) in the inner space S of the helium heat exchanger <NUM>, recondenses and liquefies the received helium by receiving the cold energy from the second cooling stage <NUM>, and discharges the recondensed and liquified helium.

The helium backward pipe <NUM> is connected to a lower portion of a side surface of the helium recondensing chamber <NUM>. The liquid helium generated in the helium recondensing chamber <NUM> is discharged from the helium recondensing chamber <NUM> through the helium backward pipe <NUM>. The helium backward pipe <NUM> has a distal end opening to the inner space S of the helium heat exchanger <NUM>, and the liquid helium having flowed out of the helium recondensing chamber <NUM> drops in the helium heat exchanger <NUM>.

Heat exchanger-inside liquid helium <NUM> contained in the helium heat exchanger <NUM> evaporates by heat having entered via the pipe wall of the helium heat exchanger <NUM> and finally refluxes to an upper portion of the helium recondensing chamber <NUM> through the helium forward pipe <NUM>. The heat exchanger-inside liquid helium <NUM> having refluxed is reliquefied in the helium recondensing chamber <NUM> and is resend to the helium heat exchanger <NUM> through the helium backward pipe <NUM>. The helium forward-backward pipeline header <NUM> is mounted to the recondensation apparatus vacuum tank <NUM> for holding the helium backward pipe <NUM> and the helium forward pipe <NUM> so that each of the helium backward pipe <NUM> and the helium forward pipe <NUM> is at a fixed position to the helium recondensing chamber <NUM>.

The helium heat exchanger <NUM> serves to execute the heat exchange inside and outside the pipe wall, and therefore the helium heat exchanger <NUM> has an internal temperature which is lower than an external temperature of the helium heat exchanger <NUM>. For instance, the internal temperature of the helium heat exchanger <NUM> is <NUM>, and the external temperature of the helium heat exchanger <NUM> (temperature of the helium tank <NUM>) is <NUM>. Therefore, the helium heat exchanger <NUM>, the helium recondensing chamber <NUM>, the helium backward pipe <NUM>, and the helium backward pipe <NUM> define an enclosed space having an internal pressure appropriately regulated, normally, to a pressure slightly lower than the atmospheric pressure. In the embodiment, the helium buffer tank <NUM> has this pressure regulating operability. The helium buffer tank <NUM> is arranged outside the freezer <NUM> at a room temperature and connected to the helium recondensing chamber <NUM> via the helium supply pipe <NUM>.

Furthermore, the helium backward pipe <NUM> and the helium forward pipe <NUM> form a first connection part in the embodiment. The first connection part defines a flow passage for permitting the heat-exchanging helium to flow between the helium heat exchanger <NUM> and the helium recondensing chamber <NUM>. Each of the helium backward pipe <NUM> and the helium forward pipe <NUM> connects the inner space S of the helium heat exchanger <NUM> and the helium recondensing chamber <NUM> to each other for inhibiting the helium in the helium tank <NUM> from flowing out to the helium backward pipe <NUM> and the helium forward pipe <NUM>, permitting the vapor of the helium in the inner space S of the helium heat exchanger <NUM> to flow into the helium recondensing chamber <NUM>, and further permitting the helium recondensed in the helium recondensing chamber <NUM> to flow into the inner space S of the helium heat exchanger <NUM>.

As shown in <FIG>, the helium backward pipe <NUM> and the helium forward pipe <NUM> are independent of each other. In particular, the helium forward pipe <NUM> (forward section) connects the inner space S of the helium heat exchanger <NUM> and the helium recondensing chamber <NUM> to each other for permitting the vapor of the helium in the inner space S to flow into the helium recondensing chamber <NUM>. The helium backward pipe <NUM> (backward section) is independent of the helium forward pipe <NUM>, and connects the inner space S of the helium heat exchanger <NUM> and the helium recondensing chamber <NUM> to each other for permitting the helium recondensed in the helium recondensing chamber <NUM> to flow into the inner space S. As shown in <FIG>, the helium recondensing chamber <NUM> has an inlet connection port 26P opening for permitting the heat-exchanging helium to flow into the helium recondensing chamber <NUM> from the helium forward pipe <NUM>, and an outlet connection port 26Q located below the inlet connection port 26P and opening for permitting the heat-exchanging helium to flow out to the helium backward pipe <NUM> from the helium recondensing chamber <NUM>. The helium recondensing chamber <NUM> has a lower surface 26A (first lower surface) whose radially outer portion is at a lower position than its radially inner portion such that the lower surface slants downward to the helium backward pipe <NUM>, and thus results in having a structure where the recondensed liquid helium easily flows out to the helium backward pipe <NUM>.

For instance, the enclosed space (low temperature space) defined by the helium heat exchanger <NUM>, the helium recondensing chamber <NUM>, the helium backward pipe <NUM>, and the helium forward pipe <NUM> has a total capacity of around <NUM> cc. Furthermore, an amount of liquid helium existing in the enclosed space is <NUM> to <NUM> cc, and an amount of saturated gas helium existing in the enclosed space is <NUM> to <NUM> cc. When the temperature of the enclosed space reaches the room temperature in a tightly closed state, a volume expansion occurs due to the change in the temperature. As a result, the gas volume reaches <NUM> by standard-state conversion. However, when the enclosed space has the limited capacity of <NUM> cc, the internal pressure thereof reaches <NUM> atm. In the embodiment, the recondensation apparatus <NUM> includes the helium buffer tank <NUM> to increase the capacity of the enclosed space. The helium buffer tank <NUM> is connected to the helium recondensing chamber <NUM> via the helium supply pipe <NUM> and can pass and receive the helium to and from the helium recondensing chamber <NUM>. The helium buffer tank <NUM> has a capacity which is larger than a sum of a capacity of the helium recondensing chamber <NUM> and a capacity of the inner space S of the helium heat exchanger <NUM>. For instance, when the helium buffer tank <NUM> has the capacity of <NUM>, the pressure in this configuration including the enclosed space at the room temperature reaches around <NUM> atm. In other words, initially filling a system including the helium buffer tank <NUM> in addition to the enclosed space with the helium gas of around <NUM> atm at the room temperature can ensure a necessary amount of each of the liquid helium and the saturated helium gas for a steady operation after a cooling operation. The helium buffer tank <NUM> receives a supply of the helium from an unillustrated helium tank through the helium supply valve <NUM>. The helium supply valve <NUM> is closed when the helium buffer tank <NUM> receives the supply of a predetermined amount of the helium thereinto. The helium buffer tank pressure gauge <NUM> detects a pressure of the helium in the helium buffer tank <NUM>.

As shown in <FIG>, the helium (coolant) flowing between the helium recondensing chamber <NUM> and the helium heat exchanger <NUM> has a very low temperature, and hence the whole system, except for the helium heat exchanger <NUM>, needs to be vacuum-insulated. For the vacuum insulation, in the embodiment, the helium recondensing chamber <NUM> is thermally insulated therearound by the recondensation apparatus vacuum tank <NUM> as described above, and a pipeline part (including the helium backward pipe <NUM> and the helium forward pipe <NUM>) extending from the helium recondensing chamber <NUM> to the helium heat exchanger <NUM> is covered with the helium transfer pipe vacuum jacket <NUM> and thus is thermally insulated.

It is seen from <FIG> that the helium transfer pipe vacuum jacket <NUM> is provided with: a vacuum wall for thermally insulating the helium backward pipe <NUM> and the helium forward pipe <NUM> between the helium forward-backward pipeline header <NUM> and the helium heat exchanger <NUM>; and a radiation shield layer (including a first transfer pipe radiation shield <NUM>, a second transfer pipe radiation shield <NUM>, and a third transfer pipe radiation shield <NUM>) to increase the radiation reduction effect. Consequently, at maximum, a quadruple concentric pipe structure having the helium backward pipe <NUM> at the center thereof extends from the helium forward-backward pipeline header <NUM> to the helium heat exchanger <NUM>.

Furthermore, a part of each of the helium backward pipe <NUM> and the helium forward pipe <NUM> is formed with the helium transfer pipe flexible section <NUM> for reducing propagation of mechanical vibration of the freezer <NUM> and easily inserting the helium heat exchanger <NUM> into the helium port <NUM> of the NMR apparatus <NUM>. The helium transfer pipe flexible section <NUM> (first flexible section) is arranged at least between the helium heat exchanger <NUM> and the helium recondensing chamber <NUM>, has flexibility (is made of flexible member), is deformable to be suitable for a peripheral structure, and is configured to suppress the propagation of the vibration of the freezer <NUM> to the NMR apparatus <NUM> through the pipeline part (first connection part) extending from the helium recondensing chamber <NUM> to the helium heat exchanger <NUM>.

The helium recondensing chamber heater <NUM> (<FIG>) is mounted on the top surface of the helium recondensing chamber <NUM>, and generates heat in response to an input signal from an unillustrated controller. A pressure of the helium tank <NUM> is constantly maintained by regulating an output (generated heat amount) from the helium recondensing chamber heater <NUM> in correspondence to the internal pressure of the helium tank <NUM> as detected by the helium tank pressure gauge <NUM>.

As shown in <FIG> and <FIG>, the nitrogen recondensing unit A has the structure similar to the structure of the helium recondensing unit B, but the nitrogen recondensing unit A will be described below mainly for differences seen therebetween.

The nitrogen tank <NUM> included in the NMR apparatus <NUM> has a cylindrical shape surrounding the helium tank <NUM> to store the liquid nitrogen <NUM> (a thermally-insulating auxiliary coolant in liquid, thermally-insulating nitrogen in liquid). The nitrogen heat exchanger <NUM> (second heat exchanger) included in the nitrogen recondensing unit A of the recondensation apparatus <NUM> is located above a liquid surface of the liquid nitrogen <NUM> in the nitrogen tank <NUM>. The nitrogen heat exchanger <NUM> has, in the same manner as the helium heat exchanger <NUM>, an outer circumferential surface (second outer peripheral surface), and an inner circumferential surface (second inner peripheral surface) defining an inner space (second inner space) separated from the nitrogen in the nitrogen tank <NUM> for storing liquid nitrogen (heat-exchanging auxiliary coolant in liquid, heat-exchanging nitrogen in liquid). The nitrogen heat exchanger <NUM> takes heat of vaporization, which is necessary for evaporation of the liquid nitrogen in the second inner space, from vapor of the thermally-insulating nitrogen in the nitrogen tank <NUM>, thereby permitting thermally-insulating nitrogen to recondense through the heat exchange with the heat-exchanging nitrogen in the second inner space. The above-described operative action is same as the operative action of the helium heat exchanger <NUM> in the helium tank <NUM>.

In the same manner as the helium recondensing chamber <NUM>, the nitrogen recondensing chamber <NUM> is located away from the NMR apparatus <NUM> but in thermally contact with the first cooling stage <NUM>, and configured to receive vapor of nitrogen gas (a gaseous heat-exchanging auxiliary coolant) in the second inner space, recondense and liquefy the received nitrogen gas by receiving the cold energy from the first cooling stage <NUM>, and discharge the recondensed and liquefied nitrogen to the nitrogen heat exchanger <NUM>. Transfer of the nitrogen between the nitrogen heat exchanger <NUM> and the nitrogen recondensing chamber <NUM> is executed through the nitrogen backward pipe <NUM> and the nitrogen forward pipe <NUM>. The nitrogen backward pipe <NUM> and the nitrogen forward pipe <NUM> form a second connection part in the embodiment. The second connection part defines a flow passage for permitting the heat-exchanging nitrogen to flow between the nitrogen heat exchanger <NUM> and the nitrogen recondensing chamber <NUM>, and connects the second inner space of the nitrogen heat exchanger <NUM> and the nitrogen recondensing chamber <NUM> to each other for inhibiting the nitrogen in the nitrogen tank <NUM> from flowing out to the nitrogen backward pipe <NUM> and the nitrogen forward pipe <NUM>, and permitting the vapor of the nitrogen in the second inner space to flow into the nitrogen recondensing chamber <NUM>, and further permitting the nitrogen recondensed in the nitrogen recondensing chamber <NUM> to flow into the second inner space. A pipeline part (including the nitrogen backward pipe <NUM> and the nitrogen forward pipe <NUM>) extending from the nitrogen recondensing chamber <NUM> to the nitrogen heat exchanger <NUM> is covered with the nitrogen transfer pipe vacuum jacket <NUM> and is thus thermally insulated. The nitrogen transfer pipe vacuum jacket <NUM> (second flexible section) also has the nitrogen transfer pipe flexible section <NUM> (second flexible section) arranged at least between the nitrogen heat exchanger <NUM> and the nitrogen recondensing chamber <NUM> and having flexibility (made of flexible member), and thus is deformable to be suitable for a peripheral structure, and suppresses the propagation of the vibration of the freezer <NUM> to the NMR apparatus <NUM> through the pipeline part (second connection part) extending from the nitrogen recondensing chamber <NUM> to the nitrogen heat exchanger <NUM>.

As shown in <FIG>, the nitrogen recondensing chamber <NUM> surrounds the first cooling stage <NUM> having the cylindrical shape. In other words, the nitrogen recondensing chamber <NUM> has a cylindrical inner space for recondensing the nitrogen. The nitrogen recondensing chamber <NUM> has a lower surface (second lower surface), like the lower surface 26A of the helium recondensing chamber <NUM>, whose radially outer portion is at a lower position than its radially inner portion such that the lower surface slants downward to the nitrogen backward pipe <NUM>, and thus results in having a structure where the recondensed liquid nitrogen easily flows out to the nitrogen backward pipe <NUM>.

Next, the arrangement of the NMR apparatus <NUM> and the recondensation apparatus <NUM> will be further described with reference to <FIG>. In the embodiment, the housing <NUM> is adjacent to the NMR apparatus <NUM> on the floor surface. The housing <NUM> supports the helium recondensing chamber <NUM> and the nitrogen recondensing chamber <NUM> so that the helium recondensing chamber <NUM> is at a higher position than the helium tank <NUM> and that the nitrogen recondensing chamber <NUM> is at a higher position than the nitrogen tank <NUM>. The housing <NUM> further operably supports the freezer <NUM> including the first cooling stage <NUM> and the second cooling stage <NUM>. The housing <NUM> additionally supports the nitrogen buffer tank <NUM> and the helium buffer tank <NUM> below the freezer <NUM>. Here, the nitrogen buffer tank <NUM> and the helium buffer tank <NUM> may be independent of the housing <NUM>.

The NMR apparatus <NUM> has the aforementioned helium port <NUM> (inlet port) communicating with the upper end of the helium tank <NUM> for permitting the helium heat exchanger <NUM> to be inserted into the helium tank <NUM> from above. The housing <NUM> supports the helium recondensing chamber <NUM> so that the helium recondensing chamber <NUM> deviates horizontally (leftward) from the helium port <NUM> of the helium tank <NUM> above the helium port <NUM> (<FIG>).

Furthermore, the helium transfer pipe vacuum jacket <NUM> including the helium backward pipe <NUM> and the helium forward pipe <NUM> continuously extends downward from the helium recondensing chamber <NUM> to the helium heat exchanger <NUM> for permitting the liquid helium discharged from the helium recondensing chamber <NUM> to flow into the inner space S of the helium heat exchanger <NUM> by gravity. More specifically, the helium transfer pipe vacuum jacket <NUM> has a tilting section 30A tilting downward from the helium recondensing chamber <NUM> as approaching the helium port <NUM> (neck tube) and a vertical section 30B vertically extending from a distal end of the tilting section 30A to the inner space S through the helium port <NUM>. Similarly, the nitrogen transfer pipe vacuum jacket <NUM> including the nitrogen backward pipe <NUM> and the nitrogen forward pipe <NUM> extends downward (continuously downward) from the nitrogen recondensing chamber <NUM> to the nitrogen heat exchanger <NUM> for permitting the recondensed liquid nitrogen to flow by gravity. The term "continuously downward" covers a state of the pipeline partly curving or bending.

This configuration can suppress an increase in the height of the topmost portion of the recondensation apparatus <NUM> more effectively than a configuration where each of the freezer <NUM>, the nitrogen recondensing chamber <NUM>, and the helium recondensing chamber <NUM> are located right above the NMR apparatus <NUM>, and thus leads to a successful arrangement of the NMR apparatus <NUM> and the recondensation apparatus <NUM> even in an environment having a ceiling C with a height restriction.

In the embodiment, as shown in <FIG>, the motor M of the freezer <NUM> is located below the cylinder 10P, that is, the freezer <NUM> is invertedly arranged. Specifically, the first cooling stage <NUM> is connected to the cylinder 10P above the motor M for cooling the nitrogen recondensing chamber <NUM> by receiving cold energy, and the second cooling stage <NUM> is connected to the cylinder 10P above the first cooling stage <NUM> for cooling the helium recondensing chamber <NUM> at a lower temperature than a temperature of the nitrogen recondensing chamber <NUM> by receiving cold energy. As a result, each of the first cooling stage <NUM> and the second cooling stage <NUM> of the freezer <NUM> is arrangeable at a higher position than the motor M to thereby easily give a height difference therebetween for permitting the liquid helium to flow downward from the helium recondensing chamber <NUM> and permitting the liquid nitrogen to flow downward from the nitrogen recondensing chamber <NUM>.

As described above, in the embodiment, the coolant helium is allowed to recondense in the helium tank <NUM> by receiving the cold energy given from the freezer <NUM> in response to the flow, accompanied by the condensation and the evaporation, of the heat-exchanging helium separated from the coolant helium. This can prevent the helium backward pipe <NUM> and the helium forward pipe <NUM> from being clogged in their respective flow passages in spite of entering of any air component of the coolant helium. More specifically, when the coolant helium evaporates in the helium tank <NUM> of the NMR apparatus <NUM>, the helium heat exchanger <NUM> takes heat from the coolant helium, thereby permitting the coolant helium to recondense and liquefy. The helium heat exchanger <NUM> is arranged in the helium tank <NUM>, and thus the coolant helium recondensed by a contact with the helium heat exchanger <NUM> is directly storable in the helium tank <NUM>. The helium recondensing chamber <NUM> is cooled by the second cooling stage <NUM> of the freezer <NUM> and thus can recondense the vapor of the heat-exchanging helium having evaporated owing to the heat taken from the coolant helium. Moreover, each of the helium backward pipe <NUM> and the helium forward pipe <NUM> connects the helium heat exchanger <NUM> separated from the coolant helium in the helium tank <NUM> and the helium recondensing chamber <NUM> located outside the NMR apparatus <NUM> to each other for circulating the heat-exchanging helium while preventing the coolant helium in the helium tank <NUM> to flow out of the NMR apparatus <NUM>. This configuration never allows the air component existing in the helium tank <NUM> to pass through the helium backward pipe <NUM> and the helium forward pipe <NUM>, and thus can prevent the air component from freezing in the flow passage defined by the helium backward pipe <NUM> and the helium forward pipe <NUM> and clogging the flow passage. The frequency of the work of replenishing the helium heat exchanger <NUM> and the helium recondensing chamber <NUM> with the heat-exchanging helium is smaller than the frequency of the work of replenishing the helium tank <NUM> with the liquid helium, and further the relevant volume for the replenishment of the heat-exchanging helium is also smaller than that for the replenishment of the liquid helium. Accordingly, the replenishing work is executable while easily preventing entering of the air component.

As described above, the helium heat exchanger <NUM> stores another liquid helium which is different from the liquid helium in the helium tank <NUM> and utilizes heat of vaporization taken from the vapor of the different liquid helium, thereby recondensing vapor of the helium in the helium tank <NUM>. This eliminates the necessity of providing an unillustrated pump for forcibly circulating the heat-exchanging helium between the helium heat exchanger <NUM> and the helium recondensing chamber <NUM>.

Moreover, in the embodiment, the vapor of the heat-exchanging helium and the recondensed heat-exchanging helium can flow respectively through the helium forward pipe <NUM> and the helium backward pipe <NUM> independent of each other. This configuration can prevent the liquid helium from impeding the flow of the gaseous helium more effectively and maintain the flows of the heat-exchanging helium in the two states more stably than a configuration where the liquid helium and the gaseous helium flow in the same connection part.

In the embodiment, the outlet connection port 26Q is located below the inlet connection port 26P in the helium recondensing chamber <NUM>. This arrangement can prevent the recondensed heat-exchanging helium from clogging the inlet connection port 26P so as not to block an inflow of the vapor of the heat-exchanging helium into the helium recondensing chamber <NUM>.

Furthermore, in the embodiment, the housing <NUM> supports the helium recondensing chamber <NUM>, and the helium transfer pipe vacuum jacket <NUM> continuously extends downward from the helium recondensing chamber <NUM> to the helium heat exchanger <NUM>. This arrangement permits the heat-exchanging helium recondensed in the helium recondensing chamber <NUM> to stably flow into the inner space S of the helium heat exchanger <NUM>.

In the embodiment, the helium buffer tank <NUM> connected to the helium recondensing chamber <NUM> can increase the capacity for accommodating the heat-exchanging helium. This configuration can decrease the pressure at the replenishment of the heat-exchanging helium necessary for the recondensation of the coolant helium to each of the helium heat exchanger <NUM> and the helium recondensing chamber <NUM> more effectively than a configuration having no helium buffer tank <NUM>.

In the embodiment, when the thermally-insulating nitrogen evaporates in the nitrogen tank <NUM> of the NMR apparatus <NUM>, the nitrogen heat exchanger <NUM> takes heat from the vapor of the thermally-insulating nitrogen, thereby permitting the thermally-insulating nitrogen to recondense. This can consequently prevent the thermally-insulating nitrogen in the nitrogen tank <NUM> included in the NMR apparatus <NUM> from evaporating and reducing, and thus can further stably cool the helium tank <NUM>. Additionally, this configuration never allows the air component existing in the nitrogen tank <NUM> to pass through the nitrogen backward pipe <NUM> and the nitrogen forward pipe <NUM>, and thus can prevent the air component from freezing in the flow passage defined by the nitrogen backward pipe <NUM> and the nitrogen forward pipe <NUM> and clogging the flow passage.

In the embodiment, the freezer <NUM> of two-stage type including the first cooling stage <NUM> and the second cooling stage <NUM> is used to thereby succeed in stable recondensation of each of the helium and the nitrogen in the NMR apparatus <NUM>. Besides, the freezer <NUM> has the motor M located below the cylinder 10P, and thus each of the first cooling stage <NUM> and the second cooling stage <NUM> is arrangeable at a higher position than the motor M. This configuration can suppress an increase in the height of the topmost portion of the recondensation apparatus <NUM> in the location thereof, and further permits the liquid helium discharged from the helium recondensing chamber <NUM> to flow into the helium heat exchanger <NUM> and permits the liquid nitrogen discharged from the nitrogen recondensing chamber <NUM> to flow into the nitrogen heat exchanger <NUM> by gravity more effectively than a configuration where the motor M is located above the cylinder 10P.

The recondensation apparatus <NUM> (helium recondensation apparatus for a cryostat) according to the embodiment of the present invention is described heretofore, but the present invention is not limited thereto, and can cover the following modified embodiments.

The pipeline for the helium recondensing chamber <NUM> and the helium backward pipe <NUM> in the form of the double-pipe structure as in the forward embodiment has a large diameter, and hence the helium port <NUM> needs a predetermined opening dimension. In contrast, in this modified embodiment, as shown in <FIG> and <FIG>, a helium backward pipe <NUM> and a helium forward pipe <NUM> are not independent of each other, but integrate into a single pipeline. Specifically, in the modified embodiment, a helium recondensing chamber <NUM> and the helium backward pipe <NUM> integrate into the single pipeline connecting an inner space S of a helium heat exchanger <NUM> and a helium recondensing chamber <NUM> to each other for permitting vapor of heat-exchanging helium in the inner space S to flow into the helium recondensing chamber <NUM> and permitting the heat-exchanging helium recondensed in the helium recondensing chamber <NUM> to flow into the inner space S. This configuration can simplify the pipeline structure for connecting the helium heat exchanger <NUM> and the helium recondensing chamber <NUM> to each other. As shown in <FIG>, the liquid helium generated in the helium recondensing chamber <NUM> is sent to the helium heat exchanger <NUM> through a lower portion of the single pipeline. In contrast, the vapor of the helium in the helium heat exchanger <NUM> flows into the helium recondensing chamber <NUM> through an upper portion of the single pipeline.

(<NUM>) Although an aspect where the recondensation apparatus <NUM> has the helium buffer tank <NUM> for supplying the helium under a predetermined pressure in connecting the recondensation apparatus <NUM> to the NMR apparatus <NUM> is described in the forward embodiment, the present invention is not limited thereto. The recondensation apparatus <NUM> may additionally include another tank.

<FIG> is a cross-sectional view showing a state where a recondensation apparatus <NUM> (helium recondensation apparatus for a cryostat) according to a second modified embodiment of the present invention is connected to an NMR apparatus <NUM>. In this modified embodiment, differences from the forward embodiment (<FIG>) will be mainly described (hereinafter, the same description way is applied to the subsequent modified embodiments to be described later). As shown in <FIG>, the recondensation apparatus <NUM> further includes a nitrogen reservoir tank <NUM>, a nitrogen pump <NUM>, a nitrogen pump discharge three-way switch valve <NUM>, and a nitrogen pump intake three-way switch valve <NUM> each constituting a part of a nitrogen recondensing unit A, and includes a helium reservoir tank <NUM>, a helium pump <NUM> arranged between a helium buffer tank <NUM> and the helium reservoir tank <NUM>, a helium pump discharge three-way switch valve <NUM>, and a helium pump intake three-way switch valve <NUM> each constituting a part of a helium recondensing unit B. Hereinafter, the structure of the helium recondensing unit B in this modified embodiment will be exemplarily described.

The helium reservoir tank <NUM> is independent of a helium recondensing chamber <NUM>, and is connected to the helium buffer tank <NUM> via the helium pump <NUM>. As a result, the helium reservoir tank <NUM> and the helium buffer tank <NUM> can supply and pass helium (heat-exchanging helium) therebetween. Besides, the helium pump discharge three-way switch valve <NUM> (discharge-side switch valve) is disposed between the helium buffer tank <NUM> and the helium pump <NUM>, and the helium pump intake three-way switch valve <NUM> (intake-side switch valve) is disposed between the helium reservoir tank <NUM> and the helium pump <NUM>. The helium pump intake three-way switch valve <NUM> is disposed on an intake side of the helium pump <NUM> for switching a supply source of supplying heat-exchanging helium to the helium pump <NUM> between the helium buffer tank <NUM> and the helium reservoir tank <NUM>. The helium pump discharge three-way switch valve <NUM> is disposed on a discharge side of the helium pump <NUM> for switching a discharge destination to which the heat-exchanging helium is discharged from the helium pump <NUM> between the helium buffer tank <NUM> and the helium reservoir tank <NUM>. The helium pump discharge three-way switch valve <NUM> and the helium pump intake three-way switch valve <NUM> respectively change the supply source of the helium for the helium pump <NUM> and the discharge destination of the helium from the helium pump <NUM> between the helium buffer tank <NUM> and the helium reservoir tank <NUM> in response to an instruction signal from an unillustrated controller. The helium pump <NUM>, the helium pump discharge three-way switch valve <NUM>, and the helium pump intake three-way switch valve <NUM> form a pressure regulation mechanism of the present invention. The pressure regulation mechanism regulates a transfer amount of the heat-exchanging helium between the helium buffer tank <NUM> and the helium reservoir tank <NUM> so that a pressure of the helium buffer tank <NUM> falls within a predetermined range.

In a case where the pressure of the helium buffer tank <NUM> detected by a helium buffer tank pressure gauge <NUM> is higher than a predetermined pressure (deviates from an appropriate range) after the recondensation apparatus <NUM> shifts to a steady operation in the same manner as in the forward embodiment, an unillustrated controller controls the helium pump discharge three-way switch valve <NUM> and the helium pump intake three-way switch valve <NUM> for switching so that the intake side of the helium pump <NUM> is connected to the helium buffer tank <NUM> and the discharge side of the helium pump <NUM> is connected to the helium reservoir tank <NUM>. As a result, the helium reservoir tank <NUM> is replenished with the helium from the helium buffer tank <NUM> and the helium buffer tank <NUM> is regulated to a redetermined pressure. Conversely, in a case where the pressure of the helium buffer tank <NUM> detected by the helium buffer tank pressure gauge <NUM> is lower than the predetermined pressure, the helium pump discharge three-way switch valve <NUM> and the helium pump intake three-way switch valve <NUM> are switched so that the intake side of the helium pump <NUM> is connected to the helium reservoir tank <NUM> and the discharge side of the helium pump <NUM> is connected to the helium buffer tank <NUM>. As a result, the helium is discharged from the helium reservoir tank <NUM> to the helium buffer tank <NUM>, and the helium buffer tank <NUM> is regulated to the predetermined pressure. Completion of the regulation of the pressure may be determined depending on the pressure of the helium buffer tank <NUM> detected by the helium buffer tank pressure gauge <NUM>. Similarly, in the nitrogen recondensing unit A, the nitrogen pump discharge three-way switch valve <NUM> and the nitrogen pump intake three-way switch valve <NUM> can switch a discharge destination from the nitrogen pump <NUM> between the nitrogen buffer tank <NUM> and the nitrogen reservoir tank <NUM>, and a pressure of the nitrogen buffer tank <NUM> detected by a nitrogen buffer tank pressure gauge <NUM> is set to fall within an appropriate range.

Even when a pressure in each of a nitrogen heat exchanger <NUM> and a helium heat exchanger <NUM> changes depending on the characteristics (thermal-insulation capability), an operation state (room temperature, room pressure), a change in the operation state (power outage) of the NMR apparatus <NUM>, or individuality (freezing capability) and maintenance condition (replacement) of a freezer <NUM>, this configuration can automatically regulate the pressure and stably maintain the recondensation of each of the nitrogen and the helium.

<FIG> is a cross-sectional view showing a state where a recondensation apparatus <NUM> (helium recondensation apparatus for a cryostat) according to a third modified embodiment of the present invention is connected to an NMR apparatus <NUM>. In the modified embodiment, two reservoir tanks, i.e., a helium high-pressure reservoir tank <NUM> (high-pressure reservoir tank part) and a helium low-pressure reservoir tank <NUM> (low-pressure reservoir tank part), are connected to a helium buffer tank <NUM> in parallel to each other. The helium low-pressure reservoir tank <NUM> has a lower pressure than the helium buffer tank <NUM>, and the pressure is set to a value equal to or lower than the atmospheric pressure. In contrast, the helium high-pressure reservoir tank <NUM> has a higher pressure than the helium buffer tank <NUM>, and the pressure is set to a value equal to or higher than the atmospheric pressure. A helium pump <NUM> is arranged between the helium high-pressure reservoir tank <NUM> and the helium low-pressure reservoir tank <NUM>. A helium low-pressure valve <NUM> is disposed between the helium pump <NUM> and the helium low-pressure reservoir tank <NUM>, and openable to permit heat-exchanging helium to flow out to the helium low-pressure reservoir tank <NUM> from the helium buffer tank <NUM> in response to an operation of the helium pump <NUM>. A helium high-pressure valve <NUM> is disposed between the helium pump <NUM> and the helium high-pressure reservoir tank <NUM>, and openable to permit the heat-exchanging helium to flow into the helium buffer tank <NUM> from the helium high-pressure reservoir tank <NUM> in response to an operation of the helium pump <NUM>. In this manner, the helium high-pressure valve <NUM> opens in an operation state of the helium pump <NUM> to supply the helium from the helium high-pressure reservoir tank <NUM> to the helium buffer tank <NUM>. In contrast, the helium low-pressure valve <NUM> opens to discharge the helium from the helium buffer tank <NUM> to the helium low-pressure reservoir tank <NUM>. As described above, an unillustrated controller controls the helium high-pressure valve <NUM> or the helium low-pressure valve <NUM> in response to a detection result from a helium buffer tank pressure gauge <NUM> so that a pressure of the helium buffer tank <NUM> falls within an appropriate range after each of the recondensation apparatus <NUM> and the NMR apparatus <NUM> shifts to a steady operation in this modified embodiment as well. Consequently, the modified embodiment can exert the same advantageous effect as the first modified embodiment. In addition to the helium pump <NUM>, the helium high-pressure reservoir tank <NUM>, the helium low-pressure reservoir tank <NUM>, the helium high-pressure valve <NUM>, and the helium low-pressure valve <NUM> form the pressure regulation mechanism of the present invention. Here, a nitrogen high-pressure reservoir tank <NUM>, a nitrogen low-pressure reservoir tank <NUM>, a nitrogen high-pressure valve <NUM>, and a nitrogen low-pressure reservoir valve <NUM> also have similar operability.

(<NUM>) Although an aspect where the nitrogen tank <NUM> surrounds the helium tank <NUM> is described in the embodiment, an argon layer may be arranged in place of the nitrogen tank <NUM> to suppress entering of the heat into the helium tank <NUM> by liquid argon. In this case, the argon layer is desirably provided with a heat exchanger similar to the nitrogen heat exchanger <NUM>. Furthermore, in another aspect, the nitrogen heat exchanger <NUM> may not be arranged in the nitrogen tank <NUM> under the condition that the helium heat exchanger <NUM> is arranged in the helium tank <NUM> to encourage recondensation of the helium in the helium tank <NUM>.

A helium recondensation apparatus for a cryostat according to one aspect of the present invention is a helium recondensation apparatus for a cryostat which includes a helium tank tightly closed to store coolant helium in liquid and accommodates a cooled object immersed in the coolant helium, the apparatus being connectable to the cryostat for recondensing vapor of the coolant helium in the helium tank. The helium recondensation apparatus for a cryostat includes: a freezer located away from the cryostat and including a main cooling part kept at a very low temperature; and a helium recondensing unit which recondenses the coolant helium in the helium tank by receiving cold energy from the main cooling part of the freezer. The helium recondensing unit includes: a first heat exchanger located above a liquid surface of the coolant helium in the helium tank, and having a first inner space separated from the coolant helium in the helium tank for storing heat-exchanging helium in liquid, the first heat exchanger taking heat of vaporization for evaporation of the heat-exchanging helium in the inner space, from the vapor of the coolant helium in the helium tank; a first recondensing chamber located away from the cryostat but in thermally contact with the main cooling part, and configured to receive vapor of the heat-exchanging helium in the first inner space, recondense and liquefy the received vapor of the heat-exchanging helium by receiving the cold energy from the main cooling part, and discharge the recondensed and liquefied heat-exchanging helium; a support mechanism which supports the first recondensing chamber so that the first recondensing chamber is at a higher position than the helium tank; and a first connection part continuously extending downward from the first recondensing chamber to the first heat exchanger located in the cryostat to define a flow passage for permitting the heat-exchanging helium to flow between the first recondensing chamber and the first heat exchanger so that the heat-exchanging helium discharged from the first recondensing chamber flows to the first inner space of the first heat exchanger by gravity.

According to this configuration, the coolant helium is allowed to recondense in the helium tank by receiving the cold energy given from the freezer in response to the flow, accompanied by the condensation and the evaporation, of the heat-exchanging helium separated from the coolant helium. This can prevent the first connection part from being clogged in the flow passage thereof despite entering of any air component of the coolant helium. More specifically, when the coolant helium evaporates in the helium tank of the cryostat, the first heat exchanger takes heat from the coolant helium, thereby permitting the coolant helium to recondense. The first heat exchanger is arranged in the helium tank, and thus the coolant helium recondensed by a contact with the first heat exchanger is directly storable in the helium tank. The first recondensing chamber is cooled by the main cooling part of the freezer and thus can recondense the vapor of the heat-exchanging helium owing to the heat taken from the coolant helium. Moreover, the first connection part connects the first heat exchanger separated from the coolant helium in the helium tank and the first recondensing chamber located outside the cryostat to each other for circulating the heat-exchanging helium while preventing the coolant helium in the helium tank to flow out of the cryostat. In this case, the relative positional relationship between the first recondensing chamber and the first heat exchanger achieves a stable inflow of the heat-exchanging helium recondensed in the first recondensing chamber into the first inner space of the first heat exchanger. This configuration never allows an air component pass through the first connection part even when the air component happens to enter the helium tank at the supply of the liquid helium into the helium tank, and thus can prevent the air component from freezing in a flow passage defined by the first connection part and clogging the flow passage.

In the configuration, the first connection part preferably includes: a forward section which connects the first inner space of the first heat exchanger and the first recondensing chamber to each other for permitting the vapor of the heat-exchanging helium in the first inner space to flow into the first recondensing chamber; and a backward section which is independent of the forward section and connects the first inner space of the first heat exchanger and the first recondensing chamber to each other for permitting the heat-exchanging helium recondensed in the first recondensing chamber to flow into the first inner space.

In this continuation, the vapor of the heat-exchanging helium and the recondensed heat-exchanging helium can flow respectively through the forward section and the backward section independent of each other. This configuration can prevent the liquid helium from impeding the flow of the gaseous helium more effectively and maintain the flows of the heat-exchanging helium in the two states more stably than a configuration where the liquid helium and the gaseous helium flow in the same connection part.

In the configuration, the first recondensing chamber desirably has: an inlet connection port for permitting the heat-exchanging helium to flow into the first recondensing chamber from the forward section; and an outlet connection port located below the inlet connection port for permitting the heat-exchanging helium to flow out to the forward section from the first recondensing chamber.

According to this configuration, the outlet connection port is located below the inlet connection port in the first recondensing chamber. This arrangement can prevent the recondensed heat-exchanging helium from clogging the inlet connection port so as not to block an inflow of the vapor of the heat-exchanging helium into the first recondensing chamber.

In the configuration, the first connection part desirably includes a single pipeline connecting the first inner space of the first heat exchanger and the first recondensing chamber to each other for permitting the vapor of the heat-exchanging helium in the first inner space to flow into the first recondensing chamber, and permitting the heat exchanging helium recondensed in the first recondensing chamber to flow into the first inner space.

This configuration can simplify the pipeline structure for connecting the first heat exchanger and the first recondensing chamber to each other.

In the configuration, the first recondensing chamber desirably has a first lower surface slanting downward to the first connection part.

This configuration achieves a stable inflow of the heat-exchanging helium recondensed in the first recondensing chamber into the first connection part.

In the configuration, the first connection part desirably has a first flexible section made of flexible member and arranged at least between the first heat exchanger and the first recondensing chamber.

This configuration can suppress propagation of the vibration of the freezer to the cryostat through the first connection part.

The configuration desirably further includes a helium buffer tank connected to the first recondensing chamber for transferring the heat-exchanging helium between the helium buffer tank and the first recondensing chamber, and having a capacity which is larger than a sum of a capacity of the first recondensing chamber and a capacity of the first inner space.

This configuration where the helium buffer tank connected to the first recondensing chamber can increase the capacity for storing the heat-exchanging helium can reduce the pressure at the replenishment of the heat-exchanging helium to each of the first recondensing chamber and the first heat exchanger more effectively than a configuration having no helium buffer tank.

The configuration desirably further includes: a helium reservoir tank which is independent of the first recondensing chamber and connected to the helium buffer tank for transferring the heat-exchanging helium between the helium reservoir tank and the helium buffer tank; and a pressure regulation mechanism which regulates a transfer amount of the heat-exchanging helium between the helium buffer tank and the helium reservoir tank so that the pressure in the helium buffer tank falls within a predetermined range.

According to this configuration, the pressure regulation mechanism can regulate the pressure of the helium buffer tank even when the pressure of the heat-exchanging helium fluctuates in use of the cryostat. This consequently achieves stable condensation of the cooling helium in the helium tank.

In the configuration, the pressure regulation mechanism desirably includes: a helium pump arranged between the helium buffer tank and the helium reservoir tank; an intake-side switch valve disposed on an intake side of the helium pump for switching a supply source of supplying the heat-exchanging helium to the helium pump between the helium buffer tank and the helium reservoir tank; and a discharge-side switch valve disposed on a discharge side of the helium pump for changing a discharge destination to which the heat-exchanging helium is discharged between the helium buffer tank and the helium reservoir tank.

Even when the pressure in the first heat exchanger changes depending on the characteristics, an operation state, and a change in the operation state of the cryostat, or individuality and a maintenance condition of the freezer, this configuration can automatically regulate the pressure and stably maintain the recondensation of the heat-exchanging helium.

In the configuration, the helium reservoir tank desirably has: a low-pressure reservoir tank part having a lower pressure than the helium buffer tank; and a high-pressure reservoir tank part having a higher pressure than the helium buffer tank. The pressure regulation mechanism desirably includes: a helium pump arranged between the low-pressure reservoir tank part and the high-pressure reservoir tank part; a helium low-pressure valve disposed between the helium pump and the low-pressure reservoir tank part, and openable to permit the heat-exchanging helium to flow out to the low-pressure reservoir tank part from the helium buffer tank in response to an operation of the helium pump; and a helium high-pressure valve disposed between the helium pump and the high-pressure reservoir tank part, and openable to permit the heat-exchanging helium to flow into the helium buffer tank from the high-pressure reservoir tank part in response to an operation of the helium pump.

In this configuration, it is desirable that: the cryostat further includes an auxiliary coolant tank surrounding the helium tank and tightly closed to store a thermally-insulating auxiliary coolant in liquid, and the freezer further includes a sub-cooling part arranged at a position different from the main cooling part and kept at a very low temperature. The configuration desirably further includes an auxiliary coolant recondensing unit which recondenses the thermally-insulating auxiliary coolant in the auxiliary coolant tank by receiving cold energy from the sub-cooling part of the freezer. The auxiliary coolant recondensing unit desirably further includes: a second heat exchanger located above a liquid surface of the thermally-insulating auxiliary coolant in the auxiliary coolant tank, and having a second inner space separated from the thermally-insulating auxiliary coolant in the auxiliary coolant tank for storing a heat-exchanging auxiliary coolant in liquid, the second heat exchanger taking heat of vaporization for evaporation of the heat-exchanging auxiliary coolant in the second inner space, from the vapor of the thermally-insulating auxiliary coolant in the auxiliary coolant tank; a second recondensing chamber located away from the cryostat but in thermally contact with the sub-cooling part, supported by the support mechanism at a higher position than the auxiliary coolant tank, and configured to receive vapor of the heat-exchanging auxiliary coolant in the second inner space, recondense and liquefy the received vapor of the heat-exchanging auxiliary coolant by receiving the cold energy from the sub-cooling part, and discharge the recondensed and liquefied heat-exchanging auxiliary coolant; and a second connection part continuously extending downward from the second recondensing chamber to the second heat exchanger located in the cryostat to define a flow passage for permitting the heat-exchanging auxiliary coolant to flow between the second recondensing chamber and the second heat exchanger so that the thermally-insulating auxiliary coolant discharged from the second recondensing chamber flows to the second inner space of the second heat exchanger by gravity.

According to this configuration, when the thermally-insulating auxiliary coolant evaporates in the auxiliary coolant tank of the cryostat, the second heat exchanger takes the heat from the thermally-insulating auxiliary coolant, thereby permitting the heat-exchanging auxiliary coolant to recondense. This can consequently prevent the thermally-insulating auxiliary coolant in the auxiliary coolant tank from evaporating and reducing, and thus can further stably cool the helium tank. This configuration where an air component existing in the auxiliary coolant tank never passes through the second connection part can prevent the air component from freezing in a flow passage defined by the second connection part and clogging the flow passage.

In the configuration, the second recondensing chamber desirably has a second lower surface slanting downward to the second connection part.

This configuration achieves a stable inflow of the heat-exchanging auxiliary coolant recondensed in the second recondensing chamber into the second connection part.

In the configuration, the second connection part desirably has a second flexible section made of flexible member and arranged at least between the second heat exchanger and the second recondensing chamber.

This configuration can suppress propagation of the vibration of the freezer to the cryostat through the second connection part.

In the configuration, the freezer desirably includes: a cylinder having a cylindrical shape and a central axis extending in an up-down direction; a displacer arranged in the cylinder reciprocatively movable upward and downward in the up-down direction for generating cold energy by expanding coolant gas in the cylinder; and a drive part located below the cylinder for generating a drive force to reciprocatively move the displacer upward and downward. The sub-cooling part is desirably connected to the cylinder above the drive part for cooling the second recondensing chamber by receiving the cold energy. The main cooling part is desirably connected to the cylinder above the sub-cooling part for cooling the first recondensing chamber at a lower temperature than a temperature of the second recondensing chamber by receiving the cold energy.

According to this configuration, the freezer of two-stage type including the main cooling part and the sub-cooling part is used to thereby succeed in stable recondensation of the coolant helium and the thermally-insulating auxiliary coolant in the cryostat. Besides, the freezer has the drive part located below the cylinder, and thus each of the main cooling part and the sub-cooling part is arrangeable at a higher position than the drive part. This configuration can suppress an increase in the height of the topmost portion of the helium recondensation apparatus for a cryostat in the location thereof, and further permits the heat-exchanging helium discharged from the first recondensing chamber to flow into the first heat exchanger and permits the heat-exchanging auxiliary coolant discharged from the second recondensing chamber to flow into the second heat exchanger by gravity more effectively than a configuration where the drive part is located above the cylinder.

Claim 1:
A combination of a helium recondensation apparatus (<NUM>) and a cryostat (<NUM>) which includes a helium tank (<NUM>) tightly closed to store coolant helium (<NUM>) in liquid and accommodates a cooled object (<NUM>) immersed in the coolant helium (<NUM>), the helium recondensation apparatus (<NUM>) being connected to the cryostat (<NUM>) for recondensing vapor of the coolant helium (<NUM>) in the helium tank (<NUM>), and comprising:
a freezer (<NUM>) located away from the cryostat (<NUM>) and including a main cooling part (<NUM>) kept at a very low temperature; and
a helium recondensing unit (B) for recondensing the coolant helium (<NUM>) in the helium tank (<NUM>) by receiving cold energy from the main cooling part (<NUM>) of the freezer (<NUM>), wherein
the helium recondensing unit (B) includes:
a first heat exchanger (<NUM>) located above a liquid surface of the coolant helium (<NUM>) in the helium tank (<NUM>), and having a first inner space (S) separated from the coolant helium in the helium tank (<NUM>) for storing heat-exchanging helium (<NUM>) in liquid, the first heat exchanger (<NUM>) taking heat of vaporization for evaporation of the heat-exchanging helium (<NUM>) in the inner space, from the vapor of the coolant helium (<NUM>) in the helium tank (<NUM>);
a first recondensing chamber (<NUM>) located away from the cryostat (<NUM>) but in thermally contact with the main cooling part (<NUM>), and configured to receive vapor of the heat-exchanging helium (<NUM>) in the first inner space (S), recondense and liquefy the received vapor of the heat-exchanging helium (<NUM>) by receiving the cold energy from the main cooling part (<NUM>), and discharge the recondensed and liquefied heat-exchanging helium (<NUM>);
a support mechanism (<NUM>) which supports the first recondensing chamber (<NUM>) so that the first recondensing chamber (<NUM>) is at a higher position than the helium tank (<NUM>); and
a first connection part (<NUM>, <NUM>) continuously extending downward from the first recondensing chamber (<NUM>) to the first heat exchanger (<NUM>) located in the cryostat (<NUM>) to define a flow passage for permitting the heat-exchanging helium (<NUM>) to flow between the first recondensing chamber (<NUM>) and the first heat exchanger (<NUM>) so that the heat-exchanging helium (<NUM>) discharged from the first recondensing chamber (<NUM>) flows to the first inner space (S) of the first heat exchanger (<NUM>) by gravity.