Diffusion pump

Abstract

A diffusion pump 1 comprises: a casing 11; a jet body 12 that is installed inside the casing 11; an intake port 13 that is installed in an upper part of the casing 11 and is connected to a vacuum container; an exhaust port 14 that is installed in a lower part of the casing 11; a working fluid storage part 15 that is installed at the bottom part of the casing 11 and stores a working fluid; a jet nozzle 17 that jets steam of the working fluid, which evaporates due to being heated by a heater, in a direction including a directional component toward the bottom part of the casing 11; and a temperature adjustment pipe 18 that is installed surrounding the casing 11. The working fluid is an alkali metal or a liquid metal having a low boiling point.

Description

Diffusion pump

[0001] The present invention relates to a diffusion pump.

[0002] A diffusion pump, which is a type of vacuum pump used in a vacuum vessel, etc., uses a high-speed jet flow emitted from a nozzle to impart momentum to gas molecules flowing in through an intake port, and then discharges the gas molecules from an exhaust port (see, for example, Patent Document 1). Such a jet flow is usually formed by the vapor of oil or fat.

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-180242 General disclosure

[0004] (Problem to be solved) A fusion reactor generates electricity by converting a fuel gas mixture containing deuterium and tritium (tritium) into plasma in a vacuum vessel, burning it, and extracting the energy produced by the fusion reaction. The exhaust gas after being used in the fusion reaction contains unconsumed radioactive tritium. Therefore, special requirements are imposed on the vacuum pump that exhausts it. In addition to exhausting the plasma, a fusion reactor also needs a vacuum pump for gas containing high concentrations of tritium, which also has similar requirements. It is difficult for existing vacuum exhaust devices to meet these conditions.

[0005] Because radioactive tritium is an isotope of hydrogen, pumps using organic materials such as oils and fats displace hydrogen in compounds, becoming a source of radioactive contamination. Furthermore, because tritium causes radiolysis of organic materials, pumps used to pump tritium must be constructed entirely of inorganic materials, such as metals and ceramics. For this reason, oil-sealed rotary pumps and Roots blowers, which use oil for bearings and lubrication, and oil-diffusion pumps, which use oil as the working fluid, cannot be used. Turbomolecular pumps induce induced currents when their conductive metal rotors move in a magnetic field. Furthermore, if metal vapor or mist is present in the exhaust gas, it will adhere to the exhaust blades. Therefore, turbomolecular pumps cannot be used near the core of a magnetic confinement fusion device. Cryopumps are not suitable for continuous pumping because the target gas condenses on the cooling surface, and they also have the problem of excessive tritium inventory.

[0006] In nuclear fusion devices, one approach is to protect the inner surface of the plasma vessel from plasma particles, neutrons, and heat by covering the inner surface of the plasma generation space with liquid metal. In this case, the gases to be pumped include metal vapor and metal mist. Mechanical pumps are known to be difficult to use because liquid and solidified metal adhere to moving parts, impeding their movement. In contrast, the use of diffusion pumps, which use mercury as the working fluid, has been considered. However, due to chemical toxicity and environmental pollution issues, the production, use, and ultimate disposal of mercury are currently prohibited. Even if mercury is used, tritium-containing exhaust gases are often subsequently treated using various catalysts. However, most of these catalysts are known to be poisoned by mercury. For these reasons, a diffusion pump that does not use oils or mercury as the working fluid is desired.

[0007] The present invention has been made in view of the above problems, and its object is to provide a diffusion pump having a working fluid that can replace oils and mercury.

[0008] In order to solve the above problems, one embodiment of the present invention provides a diffusion pump for generating a vacuum in a vacuum container, the diffusion pump comprising: a casing, a jet body disposed inside the casing, an intake port disposed at the top of the casing and connected to the vacuum container, an exhaust port disposed at the bottom of the casing, a working fluid reservoir disposed at the bottom of the casing for storing a working fluid, a jet nozzle for ejecting vapor of the working fluid heated and evaporated by a heater in a direction including a component toward the bottom of the casing, and a temperature adjustment pipe disposed surrounding the casing. The working fluid is an alkali metal or other liquid metal with a relatively low boiling point.

[0009] In one embodiment, the diffusion pump may include a base heater disposed at the bottom of the working fluid reservoir for heating the working fluid, and a side heater disposed on an outer wall of the jet body.

[0010] In some embodiments, the diffusion pump may include a thermal insulator above the jet body.

[0011] In one embodiment, a temperature adjustment pipe of a diffusion pump may be switchable between a cooling pipe and a heating pipe. In one embodiment, the temperature adjustment pipe may function as the heating pipe to heat the inner wall side of the casing from when the heater starts to heat the working fluid until at least when the working fluid starts to evaporate, and then function as the cooling pipe to start cooling the inner wall side of the casing.

[0012] In one embodiment, the diffusion pump may include a mechanism for recovering the thermal energy of the gas within the vacuum vessel.

[0013] In an embodiment, the gas in the vacuum vessel comprises liquid metal vapor or mist or powdered solid debris, and the working fluid of the diffusion pump may have an affinity for the liquid metal vapor or mist or powdered solid debris.

[0014] In some embodiments, the diffusion pump may include a gas-liquid separator that separates the liquid of the working fluid from the gas within the vacuum vessel.

[0015] In some embodiments, the working fluid of the diffusion pump may adsorb gases by chemical reaction with the gases in the vacuum vessel.

[0016] In some embodiments, the diffusion pump may be located within or adjacent to the vacuum vessel of a fusion reactor.

[0017] In addition, any combination of the above components, or mutual substitution of the components or expressions of the present invention between methods, devices, programs, temporary or non-temporary storage media on which programs are recorded, systems, etc., are also valid aspects of the present invention.

[0018] According to the present invention, it is possible to provide a diffusion pump having a working fluid that is an alternative to oil or mercury.

[0019] 1 is a cross-sectional view of a diffusion pump according to a first embodiment; 2 is a cross-sectional view of a diffusion pump according to a second embodiment; 3 is a cross-sectional view of a diffusion pump according to a third embodiment; 4 is a cross-sectional view of diffusion pumps according to fourth to eighth embodiments.

[0020] The present invention will be described below based on preferred embodiments with reference to the drawings. In the embodiments and modifications, identical or equivalent components and members are designated by the same reference numerals, and redundant descriptions will be omitted where appropriate. The dimensions of the components in the drawings are enlarged or reduced as appropriate for ease of understanding. Some components that are not important for explaining the embodiments are omitted from the drawings. Terms including ordinal numbers such as "first" and "second" are used to describe various components, but these terms are used only to distinguish one component from another and do not limit the components.

[0021] First Embodiment A preferred embodiment of the present disclosure will be described below with reference to FIGS. 1 to 3. FIG. 1 is a cross-sectional view of a diffusion pump 1 according to a first embodiment. The diffusion pump 1 generates a vacuum in a vacuum vessel. The diffusion pump 1 includes a casing 11, a jet body 12 installed inside the casing 11, an intake port 13 installed at the top of the casing 11 and connected to the vacuum vessel, an exhaust port 14 installed at the bottom of the casing 11, a working fluid reservoir 15 installed at the bottom of the casing 11, a jet nozzle 17 that ejects vapor of the working fluid L heated and evaporated by a base heater 16 installed at the bottom of the working fluid reservoir 15 downward in the figure, and a temperature adjustment pipe 18 installed surrounding the casing 11. The working fluid L is an alkali metal or a liquid metal with a relatively low boiling point. The jet flow of the diffusion pump according to this embodiment can be directed in any direction as long as it can ultimately be guided as a liquid to the working fluid reservoir 15 at the bottom of the casing.

[0022] The casing 11 is typically cylindrical, but may have any shape, such as a rectangular parallelepiped with the cross section shown in the figure. The casing 11 airtightly houses the jet body 12, the working fluid reservoir 15, and the like. An intake port 13 is provided in the upper part (typically the upper end) of the casing 11. An exhaust port 14 is provided in the lower part (typically the lower side surface of the casing 11) of the casing 11. In particular, to prevent back diffusion of the vapor of the working fluid L, which may occur during unsteady operation such as when the diffusion pump 1 is started or stopped, a baffle 21 may be optionally provided in the upper end of the casing 11 to prevent the vapor of the working fluid L from flowing back into the intake port 13.

[0023] The jet body 12, also called a chimney, is composed of nozzles such as multiple concentric cylinders or rectangular parallelepipeds having a cross section as shown in the figure. Three jet bodies 12 are shown in Figures 1 to 3. Tapered jet nozzles 17 are formed at the upper ends of the jet bodies 12. Each of these jet nozzles 17 faces downward within the casing 11. The jet nozzles 17 are configured so that the distance between each of the jet nozzles 17 and the inner wall of the casing 11 gradually narrows as it goes downward in Figures 1 to 3.

[0024] The working fluid reservoir 15 stores a liquid as a working fluid. As will be described in detail later, this working fluid L is a liquid alkali metal or a metal with a low boiling point. A base heater 16 is installed at the bottom of the working fluid reservoir 15. The base heater 16 heats the working fluid L in the working fluid reservoir 15.

[0025] The temperature control pipe 18 is installed to surround the casing 11. The temperature control pipe 18 is, for example, a circular pipe that surrounds the casing 11 in a spiral shape. Normally, the temperature control pipe 18 functions as a cooling device that cools the inner wall surface of the casing 11 when the diffusion pump 1 is operating, with a refrigerant circulating inside. However, as will be described later, the boiling point of the alkali metal or liquid metal working medium is relatively higher than room temperature or the ambient temperature, so the temperature control pipe 18 is configured to also function as a heating device, especially when the diffusion pump 1 is started up.

[0026] The above is the configuration of the diffusion pump 1. Next, the operation of the diffusion pump 1 will be described. The working fluid L stored at the bottom of the working fluid reservoir 15 is heated by the base heater 16 and evaporated. The vapor of the working fluid L rises through the center of the jet body 12 and is then ejected downward (i.e., in the exhaust direction) from each jet nozzle 17. Because the casing 11 is evacuated by a low-vacuum pump (not shown) installed on the exhaust side, the vapor of the working fluid L is accelerated to the speed of sound (several hundred meters per second or more). Gas molecules in the vacuum chamber introduced into the casing 11 through the intake port 13 collide with the vapor accelerated to the speed of sound, imparting momentum in the direction of the vapor flow. As a result, the gas flows toward the exhaust side and is discharged from the exhaust port 14. During this process, the gap between each jet nozzle 17 and the inner wall of the casing 11 gradually narrows, creating a negative pressure at the intake port 13 due to the pumping action, resulting in highly efficient exhaust. In this way, residual gas in the vacuum vessel is evacuated, thereby creating a vacuum within the vacuum vessel.

[0027] On the other hand, the vapor of the working fluid L collides with the inner wall of the casing 11 and is cooled by heat exchange with the temperature control pipe 18, thereby condensing on the inner wall of the casing 11. The condensed working fluid L falls or flows down the wall surface and is recovered in the working fluid reservoir 15 as a liquid working fluid.

[0028] The diffusion pump of this embodiment uses an alkali metal or a low-boiling-point liquid metal as the working fluid. The alkali metal may be lithium, sodium, potassium, or an alloy thereof, which has a suitable melting point and vapor pressure. The diffusion pump of this embodiment is similar in structure to diffusion pumps using oil or mercury vapor, but unlike oil or mercury, which are liquid at room temperature, it has technical features in its heating method and temperature distribution control. In particular, there are various modifications possible, not only in the case of heating and evaporating the metal working fluid at high temperatures, but also in the case of setting the appropriate temperature distribution and heating / cooling design required for condensation, liquefaction, and recycling / reuse.

[0029] According to this embodiment, a diffusion pump can be realized that uses an alkali metal or a low-boiling-point liquid metal as a working fluid instead of conventional oils and mercury. This diffusion pump does not use mercury, which may poison a tritium catalyst provided in a downstream stage, when exhausting gases, and does not contain organic matter that may be decomposed by tritium radiation when exhausting gases containing radioactive materials such as tritium. This makes it possible to safely exhaust residual gases, particularly those containing tritium, from the vacuum vessel.

[0030] Second Embodiment Fig. 2 is a cross-sectional view of a diffusion pump 2 according to a second embodiment. The diffusion pump 2 includes a casing 11, a jet body 12 installed inside the casing 11, an intake port 13 installed at the top of the casing 11 and connected to a vacuum vessel, an exhaust port 14 installed at the bottom of the casing 11, a working fluid storage section 15 installed at the bottom of the casing 11, a jet nozzle 17 that ejects vapor of the working fluid L heated and evaporated by a base heater 16 installed at the bottom of the working fluid storage section 15 downward, a temperature control pipe 18 installed surrounding the casing 11, and a side heater 19 installed on the outer wall of the jet body 12. That is, the diffusion pump 2 includes the side heater 19 in addition to the components of the diffusion pump 1 shown in Fig. 1. The other components of the diffusion pump 2 are the same as those of the diffusion pump 1.

[0031] The side heater 19 additionally heats the vapor of the working fluid L that has been heated and evaporated by the base heater 16. This makes it possible to efficiently heat the alkali metal or its liquid metal having a high boiling point to generate a jet.

[0032] (Third Embodiment) Fig. 3 is a cross-sectional view of a diffusion pump 3 according to a third embodiment. The diffusion pump 3 includes a casing 11, a jet body 12 installed inside the casing 11, an intake port 13 installed at the top of the casing 11 and connected to a vacuum vessel, an exhaust port 14 installed at the bottom of the casing 11, a working fluid storage section 15 installed at the bottom of the casing 11, a jet nozzle 17 that ejects vapor of the working fluid L heated and evaporated by a base heater 16 installed at the bottom of the working fluid storage section 15 downward, a temperature control pipe 18 installed surrounding the casing 11, a side heater 19 installed on the outer wall of the jet body 12, and a thermal insulator 20 installed above the jet body 12. That is, the diffusion pump 3 includes the thermal insulator 20 in addition to the components of the diffusion pump 2 shown in Fig. 2. The other components of the diffusion pump 3 are the same as those of the diffusion pump 2.

[0033] The thermal insulator 20 keeps the vapor of the working fluid warm, which is heated by the base heater 16 and the side heater 19. This prevents the temperature drop of the alkali metal or liquid metal, which has a higher boiling point than oil, and allows for more efficient jet generation.

[0034] The diffusion pump 3 in this example includes both the side heater 19 and the thermal insulator 20. However, the invention is not limited to this, and a configuration including only the thermal insulator 20 is also possible and useful.

[0035] (Fourth embodiment)

[0036] The diffusion pump of the fourth embodiment is any one of the diffusion pumps described above, in which the temperature adjustment pipe 18 is switchable between a cooling pipe and a heating pipe.

[0037] According to this embodiment, during operation, the device can function as a cooling device that cools the inner wall side of the casing 11 and liquefies the vapor of the working fluid, and can also function as a heating device when started up.

[0038] Another preferred embodiment of the present disclosure will be described below with reference to FIG. 4. FIG. 4 is a cross-sectional view of a diffusion pump 4 according to fifth to eighth embodiments. The diffusion pump 4 generates a vacuum in a vacuum vessel. The diffusion pump 4 includes a casing 11, a jet body 12 installed inside the casing 11, an intake port 13 installed at the top of the casing 11 and connected to the vacuum vessel, an exhaust port 14 installed at the bottom of the casing 11, a working fluid reservoir 15 installed at the bottom of the casing 11, a jet nozzle 17 that ejects vapor of the working fluid L heated and evaporated by a base heater 16 installed at the bottom of the working fluid reservoir 15 downward, and a temperature control pipe 18 installed surrounding the casing 11. The working fluid L is an alkali metal or liquid metal. The diffusion pump 4 may optionally include a side heater 19 or a gas-liquid separator 22.

[0039] The diffusion pump 4 is similar to the diffusion pumps 1 to 3 in FIGS. 1 to 3, but has a major characteristic in that it is installed inside the vacuum vessel. FIG. 4 shows a special example in which the diffusion pump 4 is installed inside (specifically, at the bottom) the vacuum vessel of a fusion reactor. Two intersecting dashed lines MFL indicate the magnetic field lines inside the fusion reactor. That is, the diffusion pump 4 is placed directly below the magnetic field lines MFL inside the fusion reactor. The casing 11 is common to part of the vacuum vessel. The other configurations and operations of the diffusion pump 4 are common to those of the diffusion pumps 1 to 3.

[0040] The working fluid L stored at the bottom of the working fluid reservoir 15 is heated and evaporated by the base heater 16 and side heater 19. The vapor of the working fluid L rises through the center of the jet body 12 and then ejects downward (i.e., toward the exhaust direction) from each jet nozzle 17. Because the casing 11 is evacuated to a low vacuum, the vapor of the working fluid L is accelerated to the speed of sound (several hundred meters per second or more). Gas molecules in the vacuum vessel introduced into the casing 11 through the intake port 13 collide with the vapor accelerated to the speed of sound, imparting momentum in the direction of the vapor flow. As a result, the gas flows toward the exhaust side and is discharged through the exhaust port 14. During this process, compression occurs between each jet nozzle 17 and the inner wall of the casing 11, creating a negative pressure at the intake port 13 due to the pumping action, resulting in highly efficient exhaust. By evacuating the residual gas in the vacuum vessel in this manner, a vacuum is created within the vessel.

[0041] Fifth Embodiment The diffusion pump 4 of the fifth embodiment includes a mechanism for recovering the thermal energy of the gas in the vacuum vessel. The thermal energy may be recovered using a temperature control pipe or by providing a dedicated thermal energy recovery device outside the vacuum vessel.

[0042] The plasma exhaust is initially in an ultra-high temperature state of tens of thousands to hundreds of millions of degrees. The plasma particles gradually lose energy through collisions with gas particles and a series of excitation phenomena known as atomic and molecular processes, and are ultimately exhausted as a gas at room temperature. During this process, the thermal energy of the plasma is transferred from the alkali metal vapor, which is the working fluid of the diffusion pump, to the heat medium in the casing 11 and the temperature control pipe 18.

[0043] If the temperature of the working fluid L ejected from the jet nozzle 17 is approximately 100°C or less, the heat can be discarded to the external environment without being used as waste heat. However, the alkali metal working fluid L in this embodiment retains heat upon cooling, reaching 100°C or higher in the case of sodium and 300°C or higher in the case of lithium. This heat can be utilized as thermal energy for power generation, etc. Much of the energy generated in the fusion reaction is transferred to the blanket as neutron kinetic energy. However, 20 to 40% of this kinetic energy is lost as alpha particles of helium, which is the plasma exhaust. Furthermore, the plasma particles retain the energy required to heat and maintain the plasma. Therefore, recovering this energy significantly contributes to improving the energy balance of the fusion reactor, increasing the amount of power generated through energy utilization, and ultimately improving the energy conversion efficiency and reducing power generation costs throughout the plant.

[0044] Sixth Embodiment In a sixth embodiment, the gas in the vacuum vessel contains liquid metal vapor or mist or powdered solid debris, and the working fluid L has an affinity for the liquid metal vapor or mist or powdered solid debris.

[0045] In magnetic confinement fusion devices, one approach is to place liquid metal on the divertor surface to avoid the inevitable loss of material in the solid material blanket. In this case, the exhaust gas from the plasma, as shown in Figure 4, contains liquid metal vapor and condensed mist. Furthermore, the target chambers of inertial confinement fusion devices using lasers or particle beams generally have liquid metal on their inner surfaces. Furthermore, in reactors such as magnetized target compression fusion devices and collisional fusion devices, the plasma is also surrounded by liquid metal.

[0046] According to this embodiment, the liquid metal vapor or mist or powdered solid debris is exhausted by the diffusion pump 4 and does not return to the vacuum vessel. Furthermore, since the working fluid L has an affinity for the liquid metal vapor or mist or powdered solid debris, it is incorporated into the working fluid L. By appropriately extracting this from the working fluid loop, the entire device can be operated stably. In particular, in an inertial confinement device, where the frequency of pulsed operation is important from an economical standpoint, rapid exhaust from the plasma chamber is possible.

[0047] A portion of the working fluid L leaks to the exhaust port 14. Therefore, by using a gas-liquid separator 22 to separate the liquid of the working fluid L from the exhaust gas, the device can be operated more stably.

[0048] Seventh Embodiment The working fluid L of the diffusion pump 4 of the seventh embodiment adsorbs the gas in the vacuum vessel by chemical reaction with the gas.

[0049] The exhaust gases from the plasma are thought to contain water vapor, hydrocarbons, ammonia, and other tritiated compounds. Because alkali metals are chemically active, they undergo chemical reactions when they collide with these compound gases. For example, by reducing water vapor, they can return these to hydrogen isotopes (deuterium and tritium), and the resulting gases can also be adsorbed.

[0050] According to this embodiment, the exhaust effect can be improved by chemical interaction between the alkali metal or liquid metal working fluid and the gas to be exhausted.

[0051] (Eighth embodiment) The diffusion pump 4 of the eighth embodiment is installed inside a vacuum vessel or in a space adjacent thereto. In particular, the diffusion pump 4 is installed inside (specifically, the lower part of) a vacuum vessel of a fusion reactor or in a space adjacent thereto. The casing 11 may be common to a part of the vacuum vessel of the fusion reactor.

[0052] According to this embodiment, the degree of freedom in the configuration of the vacuum vessel equipped with the diffusion pump can be increased.

[0053] In the above, an example has been described in which the base heater 16 or the side heater 19 provided on the outer wall of the lower part of the casing 11 heats and evaporates the working fluid L stored in the working fluid storage section 15. However, the working fluid L stored in the working fluid storage section 15 may be heated by a heater other than the base heater 16 or the side heater 19 provided on the outer wall of the lower part of the casing 11. In other words, the heater that heats the working fluid L may be installed at a position relative to the casing 11 other than the position where the base heater 16 or the side heater 19 provided on the outer wall of the lower part of the casing 11 is installed.

[0054] To operate the diffusion pump in a high-pressure environment, the working fluid L is preferably a liquid metal with a high vapor pressure and a low boiling point. The working fluid L may be, for example, an alkali metal, an alkali metal alloy, or another liquid metal with a relatively low boiling point and a high vapor pressure (e.g., 100 Pa or higher). A liquid metal with a low boiling point, i.e., a low-boiling-point metal, may be, for example, a metal having a boiling point at 1 atmosphere (101.325 kPa) of less than 2950°C, preferably less than 2650°C, more preferably less than 1700°C, and even more preferably less than 1400°C. Furthermore, a low-boiling-point metal is preferably, for example, a metal having a boiling point at 1 atmosphere of 400°C or higher. The alkali metal is preferably a metal having a boiling point at 1 atmosphere of less than 1700°C, more preferably less than 1400°C.

[0055] The low-boiling metal may be, for example, a metal having a boiling point of less than 1850°C, preferably less than 1500°C, more preferably less than 1100°C, and even more preferably less than 750°C at a vapor pressure of 100 Pa. The low-boiling metal is preferably, for example, a metal having a boiling point of 150°C or higher at a vapor pressure of 100 Pa. The alkali metal is preferably a metal having a boiling point of less than 1100°C, more preferably less than 750°C at a vapor pressure of 100 Pa.

[0056] The low-boiling metal may be, for example, a metal having a boiling point at a vapor pressure of 1 Torr (133.332 Pa) of less than 1850°C, preferably less than 1500°C, more preferably less than 1100°C, and even more preferably less than 750°C. The low-boiling metal is preferably, for example, a metal having a boiling point of 150°C or higher at a vapor pressure of 1 Torr (133.332 Pa). The alkali metal is preferably a metal having a boiling point at 1 Torr (133.332 Pa) of less than 1100°C, more preferably less than 750°C.

[0057] The alkali metal that can be used as the working fluid L may be lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), or an alloy thereof. The low-boiling point metal other than the alkali metal that can be used as the working fluid L is preferably a metal other than mercury, and may be, for example, lead (Pb), indium (In), gallium (Ga), tin (Sn), or an alloy thereof.

[0058] In the fourth embodiment, the temperature adjustment pipe 18 can be switched between a cooling pipe and a heating pipe. This allows the device to function as a cooling device that cools the inner wall surface of the casing 11 and liquefies the vapor of the working fluid during operation, and also as a heating device during startup. Here, startup refers to the period from when at least one of the base heater 16 and the side heater 19 provided on the outer wall of the lower part of the casing 11 starts heating the working fluid L until the working fluid L stored in the working fluid reservoir 15 starts evaporating. Operation refers to the period during which gas molecules in the vacuum vessel are introduced into the casing 11 through the intake port 13.

[0059] The temperature adjustment pipe 18 may function as a cooling pipe by flowing a cooling fluid through the pipe. The temperature adjustment pipe 18 may function as a heating pipe by flowing a heating fluid through the pipe. The temperature adjustment pipe 18 may function as a heating pipe to heat the inner wall surface of the casing 11 from the time when at least one of the base heater 16 and the side heater 19 provided on the outer wall of the lower part of the casing 11 starts heating the working fluid L until at least the working fluid L starts to evaporate, and then function as a cooling pipe to cool the inner wall surface of the casing 11. The temperature adjustment pipe 18 may function as a heating pipe to heat the inner wall surface of the casing 11 from the time when at least one of the base heater 16 and the side heater 19 provided on the outer wall of the lower part of the casing 11 starts heating the working fluid L until at least the working fluid L starts to evaporate, and then function as a cooling pipe to cool the inner wall surface of the casing 11 in response to the start of evaporation of the working fluid L. The temperature control pipe 18 functions as a heating pipe to heat the inner wall side of the casing 11 from the time when at least one of the base heater 16 and the side heater 19 provided on the outer wall of the lower part of the casing 11 starts heating the working fluid L until at least the time when the working fluid L starts to evaporate, and then functions as a cooling pipe to cool the inner wall side of the casing 11 in response to the start of introduction of gas molecules from the vacuum container into the casing 11 through the intake port 13.

[0060] In the above, an example was described in which the jet nozzle 17 sprays the vapor of the working fluid L heated and evaporated by at least one of the base heater 16 and the side heater 19 provided on the outer wall of the lower part of the casing 11 downward, but the downward direction may be a direction that includes a component toward the bottom of the casing 11.

[0061] The present invention has been described above based on several embodiments. These embodiments are merely examples, and it will be understood by those skilled in the art that various modifications and changes are possible within the scope of the claims of the present invention, and that such modifications and changes also fall within the scope of the claims of the present invention. Therefore, the descriptions and drawings in this specification should be treated as illustrative rather than restrictive.

[0062] In the above-described embodiment, a nuclear fusion reactor is mainly used as the vacuum vessel, and the gas to be pumped is the gas exhausted from plasma. However, the diffusion pump of the present disclosure is not limited to this, and can be suitably applied to a wide range of fields, such as aeronautical engineering, space engineering, particle accelerators, medical equipment, and precision machinery manufacturing.

[0063] Any combination of the above-described embodiments and modifications is also useful as an embodiment of the present invention. A new embodiment resulting from the combination has the combined effects of each of the combined embodiments and modifications.

[0064] When understanding the abstract technical ideas of the embodiments and modifications, the technical ideas should not be interpreted as being limited to the contents of the embodiments and modifications. The above-described embodiments and modifications are merely illustrative examples, and many design modifications, such as changes, additions, and deletions of components, are possible. In the embodiments, the contents in which such design modifications are possible are emphasized by adding the notation "embodiment." However, it goes without saying that design modifications are also permitted even in contents not so notated.

[0065] 1. Diffusion pump 2. Diffusion pump 3. Diffusion pump 4. Diffusion pump 11. Casing 12. Jet body 13. Inlet port 14. Outlet port 15. Working fluid reservoir 16. Base heater 17. Jet nozzle 18. Temperature adjustment pipe 19. Side heater 20. Thermal insulator 21. Baffle 22. Gas-liquid separator MFL. Magnetic field lines L. Working fluid

Claims

1. A diffusion pump for generating a vacuum in a vacuum container comprising: a casing; a jet body installed inside the casing; an intake port installed in the upper part of the casing and connected to the vacuum container; an exhaust port installed in the lower part of the casing; a working fluid storage section installed in the bottom of the casing for storing a working fluid; a jet nozzle that sprays vapor of the working fluid heated and evaporated by a heater in a direction including a component of a direction toward the bottom of the casing; and a temperature adjustment pipe installed surrounding the casing, wherein the working fluid is an alkali metal or a low-boiling point liquid metal.

2. The diffusion pump according to claim 1, further comprising a base heater disposed at the bottom of the working fluid reservoir for heating the working fluid.

3. The diffusion pump of claim 2, further comprising a side heater on an outer wall of said jet body.

4. A diffusion pump as claimed in claim 2 or 3, further comprising a thermal insulator on the upper side of said jet body.

5. The diffusion pump of claim 1, wherein the temperature adjustment pipe is switchable between a cooling pipe and a heating pipe.

6. A diffusion pump as described in claim 5, wherein the temperature adjustment pipe functions as the heating pipe to heat the inner wall side of the casing from the time when the heater starts to heat the working fluid until at least the time when the working fluid starts to evaporate, and then functions as the cooling pipe to start cooling the inner wall side of the casing.

7. The diffusion pump according to claim 1, further comprising a mechanism for recovering thermal energy contained in the gas within said vacuum vessel.

8. A diffusion pump as described in claim 1, wherein the gas in the vacuum vessel contains liquid metal vapor or mist or powdered solid debris, and the working fluid has an affinity with the liquid metal vapor or mist or powdered solid debris.

9. The diffusion pump of claim 8, further comprising a gas-liquid separator for separating the liquid of said working fluid from the gas within said vacuum vessel.

10. The diffusion pump of claim 1, wherein said working fluid adsorbs said gas within said vacuum vessel by chemical reaction with said gas.

11. The diffusion pump according to claim 1, which is installed inside a vacuum vessel of a nuclear fusion reactor or in a space adjacent thereto.

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