Diverter

Abstract

A diverter (1) comprises: a casing (11); a jet body (12) that is disposed inside the casing (11); an air intake port (13) that is arranged in an upper part of the casing (11); an air exhaust port (14) that is arranged in a lower part of the casing (11); a working fluid storage unit (15) that is arranged in a bottom part of the casing (11) and stores a working fluid; a jet nozzle (16) that jets, in the downward direction, vapor of the working fluid heated and evaporated with a heater; and a temperature adjustment pipe (17) arranged so as to surround the casing (11). The working fluid is an alkali metal or a low-boiling metal.

Description

Diverter

[0001] The present invention relates to a divertor for a nuclear fusion reactor.

[0002] Fusion reactors are equipped with a divertor device (hereinafter sometimes abbreviated as divertor) for discharging charged particles and the like that flow out of plasma along magnetic field lines (see, for example, Patent Document 1). The walls of the divertor are heated not only by charged particles but also by radiant heat and high-energy neutral particles, and are therefore subjected to extremely high thermal loads. [Prior Art Documents] [Patent Documents]

[0003] [Patent Document 1] Special Publication No. 2017-524928 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. Helium nuclei produced by the fusion reaction and nuclei other than deuterium and tritium that are mixed in from the vessel wall of the fusion reactor radiate energy and lower the temperature of the plasma. Therefore, these nuclei must be immediately evacuated.

[0005] A divertor is a device that solves the above problems. The divertor causes charged particles of hydrogen isotopes and impurity gases from the plasma, which enter along the magnetic field lines, to collide with a wall surface called a target, which is then exhausted using a vacuum pump. This maintains the purity of the plasma. The divertor consists of a space adjacent to the fusion plasma, where a magnetic field is generated by electromagnets installed around it, and walls made of materials such as metal and ceramic that surround the space. The divertor uses a vacuum exhaust system to exhaust and transport plasma particles as gas out of the plasma vessel, while also evacuating the energy possessed by the plasma particles using a cooling medium. The plasma particles sent to the divertor are derived from high-temperature plasma at several hundred million degrees. These particles retain approximately 20% of the energy generated by the fusion reaction, plus energy supplied from an external source for heating. This acts as a thermal load on the divertor walls.

[0006] It is known that the target surface that constitutes the divertor wall is subject to severe wear due to sputtering and thermal load when exposed to extremely high-density energy from the plasma, whether steady or instantaneous. One idea for protecting the target surface is to pour liquid metal over the surface, but the supply and discharge methods have yet to be developed and have not yet been put to practical use. Furthermore, even if liquid is applied to the target surface, there is a problem in that it evaporates due to the energy of plasma particles and reaches the downstream exhaust system and nuclear combustion plasma. There is no effective solution to this problem.

[0007] The present invention has been made in view of these problems, and its object is to provide a divertor that can exhaust heat, plasma, and impurity gases while suppressing damage caused by heat.

[0008] In order to solve the above problems, a divertor for a nuclear fusion device according to one aspect of the present invention comprises a casing, a jet body installed inside the casing, an intake port installed at the top of the casing, an exhaust port installed at the bottom of the casing, a working fluid reservoir installed at the bottom of the casing for storing a working fluid, a jet nozzle that ejects 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 control pipe installed surrounding the casing. The working fluid is an alkali metal or a low-boiling-point liquid metal.

[0009] In one embodiment, the diverter may include, as the heater, at least one of a side heater installed outside the casing and a base heater installed at the bottom of the working fluid reservoir. In one embodiment, the temperature adjustment pipe 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 heating the working fluid until at least until the working fluid starts to evaporate, and then function as the cooling pipe to start cooling the inner wall side of the casing. In one embodiment, the diverter may include a target plate in the diverter region.

[0010] In some embodiments, the divertor may include a mechanism for recovering thermal energy carried by plasma particles that enter the divertor region.

[0011] In one embodiment, the diverter may transfer energy from the plasma particles to the vapor of the working fluid by collision with the vapor of the working fluid ejected from the jet nozzle, thereby preventing or suppressing damage to components in the diverter region due to the plasma particles.

[0012] In one embodiment, the diverter may be configured such that the plasma particles collide with the vapor of the working fluid ejected from the jet nozzle, transferring energy of the plasma particles to the vapor of the working fluid, and the plasma particles are expelled from the diverter region.

[0013] In some embodiments, the diverter may prevent plasma particles from flowing back into the diverter region.

[0014] 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.

[0015] According to the present invention, it is possible to provide a divertor that can discharge impurity gases while suppressing damage caused by heat.

[0016] 1A and 1B are cross-sectional views of a diverter according to a first embodiment and a second embodiment, respectively;

[0017] 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.

[0018] First Embodiment A preferred embodiment of the present disclosure will be described below with reference to FIG. 1 . FIG. 1 is a cross-sectional view of a divertor 1 according to a first embodiment. The divertor 1 is formed as an exhaust device in a divertor region D of a fusion reactor (typically below the magnetic field lines of the vacuum vessel of the fusion reactor). The divertor 1 includes a target plate 10, a casing 11, a jet body 12 installed inside the casing 11, an intake port 13 installed at the top of the casing 11, 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 side heater 18 installed outside the casing 11, a jet nozzle 16 that ejects vapor of the working fluid L heated and evaporated by the side heater 18 downward, and a temperature adjustment pipe 17 installed surrounding the casing 11. The working fluid L is a liquid metal with a low boiling point, such as an alkali metal.

[0019] The casing 11 is typically cylindrical, but elements of any shape, such as rectangular, trapezoidal, or sector-shaped, are combined and placed in the plasma vacuum vessel. The casing 11 airtightly houses the jet body 12, working fluid reservoir 15, and other components. An air inlet 13 is provided at the top (typically the upper end) of the casing 11. The air inlet is installed near the intersection of magnetic field lines, known as the separatrix, so as not to cross the magnetic field lines. An exhaust port 14 is provided at the bottom (typically the lower side surface of the casing 11). To prevent back-diffusion of vapor of the working fluid L, which may occur during unsteady operation, particularly during startup or shutdown of the divertor 1, a baffle may optionally be provided at the top of the casing 11 to prevent vapor of the working fluid L from flowing back into the air inlet 13.

[0020] The jet bodies 12, also called chimneys, are composed of multiple concentric cylinders or flat plates with similar cross sections. Three jet bodies 12 are shown in Figure 1. Tapered jet nozzles 16 are formed at the upper ends of the jet bodies 12. Each of these jet nozzles 16 faces downward inside the casing 11. The jet nozzles 16 are configured so that the distance between each of the jet nozzles 16 and the inner wall of the casing 11 becomes gradually narrower as it goes downward in Figure 1.

[0021] 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 low-boiling-point metal. A side heater 18 is installed on the outside of the casing 11. The side heater 18 heats the working fluid L in the working fluid reservoir 15.

[0022] The temperature control pipe 17 is installed to surround the casing 11. The temperature control pipe 17 is, for example, a circular pipe that surrounds the casing 11 in a spiral shape. Normally, a refrigerant circulates inside the temperature control pipe 17, and the temperature control pipe 17 functions as a cooling device that cools the outer wall surface of the casing 11 when the divertor 1 is in operation. However, as will be described later, since the boiling points of alkali metals or low-boiling-point metals used as working fluids are high, the temperature control pipe 17 is configured to also function as a heating device, particularly when the divertor 1 is started up, and it is necessary to constantly control the temperature of the temperature control pipe 17 to be higher than room temperature to ensure an appropriate temperature distribution.

[0023] The above is the configuration of the divertor 1. Next, the operation of the divertor 1 will be described. The working fluid L stored at the bottom of the working fluid reservoir 15 is heated and evaporated by the side heater 18. 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 16. 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). Plasma particles guided by the magnetic field lines MFL and flowing 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 plasma particles flow toward the exhaust side and are discharged from the exhaust port 14. During this process, momentum is imparted to the gas to be exhausted by the vapor between each jet nozzle 16 and the inner wall of the casing 11, and negative pressure is created at the intake port 13 by the pumping action, resulting in highly efficient exhaust. In this way, plasma particles are expelled from the divertor region.

[0024] 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 17, 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 as a liquid working fluid in the working fluid reservoir 15 and reused.

[0025] The divertor of this embodiment uses an alkali metal or low-boiling-point metal as the working fluid. The alkali metal may be lithium, sodium, potassium, or other low-melting-point alloys such as lead, tin, or indium, or their alloys. However, it must have a relatively low boiling point and a high vapor pressure upon heating. While the divertor of this embodiment is similar in structure to diffusion pumps using grease or mercury vapor, unlike grease or mercury, which are liquid at room temperature, its technical features lie in its heating method and temperature distribution control. In particular, various modifications are possible, not only for the heating and evaporation of the metal working fluid at high temperatures, but also for the appropriate temperature distribution and heating / cooling design required for condensation, liquefaction, and recycling. In particular, while the casing 11 and temperature control pipe 17 are cooled in grease or mercury diffusion pumps, the present invention requires that they be constantly maintained at a temperature higher than room temperature to prevent solidification of the liquid metal, achieve an appropriate temperature distribution, and maintain an appropriate vapor pressure.

[0026] The plasma particles flowing into the divertor region are locally several tens to several hundreds MW / m ２ , which has a high energy density reaching 1000 keV. Therefore, if this were to collide directly with the solid walls that make up the divertor, it would cause significant damage to the entire divertor. On the other hand, the above energy flux is concentrated in an extremely narrow range of a few millimeters. The vapor flow of alkali metal or low-boiling-point metal according to the present disclosure receives high-energy plasma particles within the divertor space. Furthermore, the working fluid of alkali metal or low-boiling-point metal can become liquid even on the solid walls of the divertor and receive plasma particles. This makes it possible to prevent damage to the solid walls of the divertor. As described above, according to this embodiment, a divertor that can receive plasma particles while suppressing damage caused by heat can be realized.

[0027] Second Embodiment A divertor according to a second embodiment includes a target plate 10 in the divertor region D. The target plate 10 may be made of a carbon composite material, tungsten, or the like. According to this embodiment, the presence of the target plate 10 can prevent damage to components in the divertor region D and the divertor vessel wall caused by plasma particles, and can minimize the risk of leakage from the temperature control pipe 17.

[0028] (Third embodiment) The divertor of the third embodiment includes a mechanism for recovering the thermal energy of the plasma particles that have flowed into the divertor region D. The thermal energy recovery may be performed using a temperature control pipe 17, or a dedicated thermal energy recovery device may be provided externally.

[0029] As mentioned above, the plasma particles flowing into the divertor region have a localized energy density of several tens to several hundreds MW / m ２ This energy accounts for 20-30% of the total output of a fusion reactor. Recovering and reusing this energy will improve the energy balance of the fusion reactor, increase the amount of power generated through energy utilization, and ultimately contribute greatly to improving the energy conversion efficiency of the entire plant and reducing power generation costs.

[0030] (Fourth embodiment) In a divertor of the fourth embodiment, the vapor of the working fluid L ejected from the jet nozzle 16 collides with the plasma particles, and the energy of the plasma particles is transferred to the vapor of the working fluid L. This prevents or suppresses wear of components in the divertor region D due to the plasma particles.

[0031] As mentioned above, the plasma particles flowing into the divertor region have a localized energy density of several tens to several hundreds MW / m ２The plasma has a high energy density ranging from 1000 to 10000 rpm. Therefore, if this energy flux were to collide directly with components in the divertor region D, it would cause significant damage to the components. The above energy flux is concentrated in an extremely narrow area of ​​a few mm. The vapor flow of alkali metal or low-boiling-point metal according to the present disclosure intercepts the high-energy plasma particles in the divertor space. Furthermore, the working fluid of alkali metal or low-boiling-point metal can become liquid even on the solid walls of the divertor and intercept the plasma particles. This prevents damage to the components in the divertor region D.

[0032] Fifth Embodiment In a divertor according to a fifth embodiment, the vapor of the working fluid L ejected from the jet nozzle 16 collides with the plasma particles, and the energy of the plasma particles is transferred to the vapor of the working fluid L. As a result, the plasma particles are expelled from the divertor region D.

[0033] The plasma particles flowing into the divertor region D contain helium produced by the fusion reaction and impurities released from the reactor wall surfaces, etc. Therefore, these must be exhausted. In this embodiment, the vapor flow of the working fluid L imparts unidirectional momentum to the plasma particles, thereby transporting the plasma particles to the exhaust port 14. In other words, the divertor of this embodiment functions as a pump. This function does not suffer from the problems associated with other exhaust devices such as turbomolecular pumps and cryopumps, such as the difficulty of mechanical movement in a magnetic field and a large tritium inventory. Therefore, this embodiment makes it possible to effectively and continuously exhaust plasma particles containing impurities present in a fusion reactor.

[0034] Sixth Embodiment In a divertor according to a sixth embodiment, plasma particles are prevented from flowing back from the divertor region D into the plasma.

[0035] As mentioned above, the divertor is a device for removing impurities from the fusion plasma and maintaining its purity. Therefore, backflow into the fusion plasma must be prevented, including that of alkali metals or low-boiling-point metals, which are the working fluid. In particular, the atomic number of impurities in fusion plasma must be kept as low as possible, because the higher the atomic number, the greater the heat they radiate. In this embodiment, backflow of alkali metal vapor, such as lithium, which is the working vapor, is undesirable, but the unidirectional molecular flow of vapor from the nozzle prevents this. Furthermore, lithium, with its atomic number of 3, is the third smallest after hydrogen and helium, making it ideal for use in the divertor.

[0036] Seventh Embodiment FIG. 2 is a cross-sectional view of a divertor 1 according to a seventh embodiment. The divertor 1 according to the seventh embodiment differs from the divertor 1 according to the first embodiment in that a base heater 20 is installed at the bottom of the working fluid reservoir 15. The base heater 20 heats the working fluid L in the same manner as the side heater 18 installed on the outer wall of the casing 11 around the working fluid reservoir 15, i.e., on the outer wall of the lower part of the casing 11. The side heater 18 and the base heater 20 are examples of heaters that heat the working fluid L, and the divertor 1 may include at least one of the side heater 18 and the base heater 20. The divertor 1 may also include another heater that heats the working fluid L, which is installed at a position other than the side heater 18 and the base heater 20.

[0037] 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. 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.

[0038] 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.

[0039] 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.

[0040] The temperature adjustment pipe 18 may have a function that can be switched between a cooling pipe and a heating pipe. 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. This allows the temperature adjustment pipe 18 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 may refer to the period from when at least one of the base heater 20 and the side heater 18 starts heating the working fluid L to when evaporation of the working fluid L stored in the working fluid reservoir 15 begins. Operation may refer to the period during which gas molecules in the vacuum vessel are introduced into the casing 11 through the intake port 13.

[0041] The temperature adjustment pipe 18 may function as a heating pipe to heat the inner wall side surface of the casing 11 from the time when at least one of the base heater 20 and the side heater 18 starts heating the working fluid L until at least the time when evaporation of the working fluid L starts, and then function as a cooling pipe to cool the inner wall side surface of the casing 11. The temperature adjustment pipe 18 may function as a heating pipe to heat the inner wall side surface of the casing 11 from the time when at least one of the base heater 20 and the side heater 18 starts heating the working fluid L until at least the time when evaporation of the working fluid L starts, and then function as a cooling pipe to cool the inner wall side surface of the casing 11 in response to the start of evaporation of the working fluid L. The temperature control pipe 18 may function 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 20 and the side heater 18 starts heating the working fluid L until at least the time when the working fluid L starts to evaporate, and then function as a cooling pipe to cool the inner wall side of the casing 11 in response to the start of gas molecules in the vacuum container being introduced into the casing 11 through the intake port 13.

[0042] 1 shows an example in which the target plate 10 is provided on the inner wall side surface of the connection portion between the exhaust port 14 and the casing 11, which is near the exhaust port 14. However, the target plate 10 may be provided at any location within the divertor region D. The target plate 10 may also be provided on the entire inner wall side surface that constitutes the divertor region D of the casing 11.

[0043] In the above, an example has been described in which the jet nozzle 16 sprays the vapor of the working fluid L heated and evaporated by at least one of the side heater 18 and the base heater 20 downward, but the downward direction may be a direction that includes a component toward the bottom of the casing 11.

[0044] A portion of the working fluid L leaks to the exhaust port 14. For this reason, the diverter 1 shown in Figures 1 and 2 may be provided with a liquid separator 19. By using the gas-liquid separator 19 to separate the liquid of the working fluid L from the exhaust gas, the device can be operated more stably.

[0045] 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.

[0046] The divertor of the present disclosure includes a diffusion pump type divertor mechanism instead of or in addition to a conventional divertor plate. This new type of divertor can be suitably applied to various types of fusion reactors, such as tokamak, helical, and RFP types.

[0047] 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.

[0048] 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.

[0049] 1. Diverter 10. Target plate 11. Casing 12. Jet body 13. Inlet port 14. Outlet port 15. Working fluid reservoir 16. Jet nozzle 17. Temperature control pipe 18. Side heater 19. Gas-liquid separator 20. Base heater MFL. Magnetic field lines L. Working fluid D. Diverter region

Claims

1. A divertor for a nuclear fusion device comprising: a casing; a jet body installed inside the casing; an intake port installed at the top of the casing; an exhaust port installed at the bottom of the casing; a working fluid storage section installed at 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 that includes a component toward the bottom of the casing; and a temperature control pipe installed surrounding the casing, wherein the working fluid is an alkali metal or a low-boiling point metal.

2. A diverter as described in claim 1, comprising as the heater at least one of a side heater installed on the outside of the casing and a base heater installed at the bottom of the working fluid storage section.

3. The diverter of claim 1, wherein the temperature adjustment pipe is switchable between a cooling pipe and a heating pipe.

4. A diverter as described in claim 3, wherein the temperature control 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.

5. The diverter of claim 1, further comprising a target plate in the diverter region.

6. A divertor according to any one of claims 1 to 5, including a mechanism for recovering thermal energy of plasma particles that have flowed into the divertor region.

7. A divertor as described in any one of claims 1 to 5, wherein the energy of the plasma particles is transferred to the vapor of the working fluid by collision between the vapor of the working fluid ejected from the jet nozzle and plasma particles, thereby preventing or suppressing damage to components in the divertor region due to the plasma particles.

8. A divertor as described in any one of claims 1 to 5, wherein the plasma particles collide with the vapor of the working fluid ejected from the jet nozzle, transferring energy of the plasma particles to the vapor of the working fluid, and the plasma particles are expelled from the divertor region.

9. The divertor of claim 8, wherein the plasma particles are prevented from flowing back into the divertor region.

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