JPS6098385A - Limiter device in nuclear fusion device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a limiter device in a nuclear fusion device used to remove impurities such as helium ions produced by a nuclear fusion reaction.

[Technical background of the invention and its problems] A tokamak-type fusion device is a typical example of a nuclear fusion device, and its main body consists of a magnetic field coil that holds and heats the plasma, and an ultra-high vacuum container that keeps the plasma region in a vacuum at its origin. By the way, in such a nuclear fusion device, impurities such as helium ions are generated by the fusion reaction of deuterium fuel and tritium. A pump limiter device is installed to prevent build-up.

FIG. 1 is a schematic cross-sectional view of a tokamak-type fusion device,
The outline of the pump limiter device will be briefly explained with reference to this figure. In the figure, 1 is a toroidal magnetic field coil, 2 is a voloidal I&I lift coil, and 3Fi vacuum vessel has a donut shape, that is, a torus shape as a whole, and plasma 4 is generated inside thereof. The superimposed magnetic field by the toroidal magnetic field coil 1 and the voloidal magnetic field coil 2 is
A torus-shaped closed magnetic surface is formed inside the reactor core to confine the reactor core plasma 4 at the pot temperature to an area as shown in FIG. j
FIG. 142 is an enlarged schematic diagram of the core plasma 4 and limiter plate 5 portions in FIG. The peripheral plasma) *7 is guided to the vicinity of the limiter plate 5 along the lines of magnetic force existing inside it, and is neutralized on its front or back surface. The neutralized particles follow the exhaust duct 6 shown in FIG. 1 and are exhausted to the outside of the Makabe container 3. Thus, the accumulation of helium ash in the reactor core resulting from the fusion reaction.

However, since the limiter plate 5 faces the high-temperature plasma directly, the following problems occur. . That is, the limiter plate 5 is
Due to the incidence of energetic charged particles such as deuterium ions flowing out from the reactor core, limiter plate atoms are subject to severe wear and tear due to sputtering.As a result, work to replace or repair limiter plates becomes frequent, and fusion device This is also a problem from the viewpoint of maintainability and availability.

Furthermore, the sputtered atoms are ionized and mixed into the core plasma as impurity ions, and if the angle of entry is large, the bremsstrahlung radiation loss of electrons due to the impurity ions increases and the core plasma 4 is cooled. As a result, the fusion reaction becomes difficult to occur, which is a problem from the economic standpoint of the fusion reactor.

In order to deal with the problems described above, several improvement plans have been proposed in the past. FIG. 3 shows a conventional example of such an improved proposal, and as is clear from this figure, the limiter plate 8 is configured to have a corner-curved shape. By configuring the limiter plate 8 in this way, it is possible to reduce the angle formed between the limiter plate 8 and the plasma surface, thereby effectively expanding the incident surface of charged particles, and as a result, the loss of the limiter material *m can be expected to decrease. That is, the amount of wear and tear on the material due to sputtering per unit time is proportional to the product of the incident particle flux (the number of incident ions per unit area) and the sputtering ratio (the number of material atoms sputtered per one incident ion). Therefore, as described above, when the limiter plate 8 is configured in a curved shape, the effective incident particle flux can be reduced, so that the amount of wear and tear on the limiter plate 8 can be reduced.

On the other hand, it is known that the bremsstrahlung radiation loss of electrons due to impurity ions increases as the number of charges on the impurity ions increases, as described above. When the bremsstrahlung radiation loss of electrons increases, problems occur in cooling the core plasma. Low atomic weight materials such as phytophytes (hereinafter referred to as
A method has been proposed in which the entire surface of the limiter plate is covered with a material called "Low 2 material". However, even if this method is used, wear and tear near the end of the limiter plate still remains. This will be explained with reference to FIG. FIG. 4 is an enlarged sectional view of the end portion 8A of the curved limiter plate 8, and in the figure, 9 indicates lines of magnetic force. Incident ions follow these magnetic field lines 9
The light enters the limiter plate 8 along the line . In this case, limiter plate 8
In the vicinity of the end 8A, the angle between the lines of magnetic force 9 and the limiter plate 8 is a right angle. Therefore, even with the curved limiter plate 8, the effect of enlarging the incident surface as described above cannot be expected. Furthermore, the lifespan of the limiter plate as a whole is determined by wear and tear on its ends. Furthermore, there is a disadvantage that the end portion of the limiter plate is heavily worn, so that the amount of impurity ions mixed in increases, and the effect of using a low 2 material cannot be achieved.

[Purpose of the Invention] This was made in view of the above-mentioned premature failure, and its purpose is to prevent wear due to sputtering at the end of the limiter plate and to reduce the amount of impurities mixed in by sputtering of the limiter material. It is an object of the present invention to provide a limiter device in a nuclear fusion device that makes possible the following.

[Summary of the Invention] In order to achieve the above object, the present invention makes the central part of the limiter plate of the limiter device in a nuclear fusion device with a low Z material such as beryllium or graphite, and the end part with a high Z material such as tungsten. This invention relates to a limiter device for a nuclear fusion device that is made of Z material to reduce material wear at the end of the limiter plate.

Next, it will be quantitatively explained below that the wear amount of the limiter plate end can be sufficiently reduced by using the Nyorori limiter device of the present invention, that is, by using a high Z material such as tungsten especially for the limiter plate end. The wear rate of the limiter plate due to sputtering is proportional to the product of the incident particle flux and the sputtering ratio, as stated above. m
In the case of the curved limiter plate 8 shown in FIG. It cannot be expected to reduce the incident particle flux at the end of the limiter plate, and therefore it cannot be expected to sufficiently reduce the wear at the end of the limiter plate.

On the other hand, the sputtering ratio S of paulownia wood is given by the following zMI according to the experimental formula, assuming that the energy of incident ions is E (eV).
E −Eth S(,,J” Z?ZL M, ((H−Eth)+5
0”.21]z(Btam/1on)O and Uo...Binding energy of limiter material (eV
) Zl, z,...Number of charges of each incident ion and limiter material MI, ML...Atomic weight of each incident ion and limiter material Eth...Threshold of incident ion energy for sputtering Here, The threshold value Eth of the incident ion energy for sputtering is determined by the relationship between the atomic weights Ml and ML of each incident ion and the limiter material, respectively, as follows: Hth = (
Ml +M,,) ”Uo /4MIML (Mr <
ML), Hth=MLUo/M Engineering (Ml>ML
) is given by

Figure 5 shows ■ Beryllium B when hydrogen ions are incident.
2 is a diagram showing an example of calculation of the incident ion energy dependence of the Snow Ivy ratio for e and tungsten W.

By the way, the energy of incident ions varies depending on the position on the limiter plate surface, and ranges from i keV to several ke at the center of the limiter plate.
V, and the incident energy gradually decreases toward the end. In particular, the end of the limiter plate is located in the outer region of the peripheral plasma layer and is away from the core plasma, so the plasma temperature is low, and therefore the incident energy is also low, ranging from tens to hundreds of eV. In this energy range, as shown in the example of beryllium in Figure 5, it is generally low
The material has a very high sputtering ratio. Furthermore, as mentioned above, the incident particle flux cannot be expected to be reduced at the end of the limiter plate.

Therefore, when low-Z paulownia wood is used for the entire limiter plate including the end portions, the synergistic effect of these two causes extremely serious wear and tear on the end portions of the limiter. As a result, the amount of impurities mixed into the core ends up increasing, making it difficult to fully utilize the effects of using low-2 materials.

On the other hand, in the case of high 2 material, tungsten (W) in Figure 5
As shown in the example, sputtering hardly occurs in the energy range of several tens to one hundred eV. Therefore, by using the AZ material at the end of the limiter plate, it is possible to sufficiently reduce the wear and tear at the end. In addition, as a result, it is possible to sufficiently reduce the amount of impurities mixed in, M.
The effect of using a low Z material in other parts including the central part can also be fully exhibited.

[Embodiments of the invention] An example of the present invention will be described with reference to the drawings.

FIG. 6 is an enlarged sectional view of one embodiment of the present invention.

As shown in the figure, the limiter plate of the present invention has a curved shape as a whole, and the limiter plate supporting portion 110 has a curved shape similar to the curved shape described above. The end portions 12, 12 are provided, and a central portion 13 made of a low-grade material is provided in the central portion thereof. In addition, 4 is core plasma,
7 is a peripheral plasma layer.

When the limiter plate 10 is configured as described above, the incident energy at the center of the limiter plate made of low Z material is 1 keV to several keV as described above, but the incident energy at the edge of the limiter plate made of high Z material is 1 keV to several keV. is several tens to 100 eV, J\, so in this energy range, sputtering I
rJ-1 Note: This hardly occurs, and the loss hhi at the end of the limiter plate can be sufficiently reduced. Therefore, the amount of impurities mixed in at the end of the limiter plate can be sufficiently reduced, and the effect of using the low-Z material in other parts other than the end including the center of the limiter plate can also be fully demonstrated. be able to.

[Effects of the Invention] As explained above, according to the present invention, it is possible to sufficiently reduce the wear and tear on the limiter plate, especially at its ends, thereby improving the maintainability and operating rate of the fusion device. do. The amount of limiter material that is sputtered into the reactor core is reduced, and the decrease in core power due to bremsstrahlung radiation loss is also sufficiently suppressed, so the economic effects of the fusion reactor are extremely large.

[Brief explanation of drawings]

Figure 1 is a schematic cross-sectional view of a conventional tokamak-type fusion device, Figure 2 is an enlarged fc schematic diagram of the core plasma and limiter plate portions in id' 1v1, and Figure 3 is a schematic cross-section of a conventional curved limiter plate. 4 is an enlarged view of the end of the limiter plate in FIG. 3, FIG. 5 is a diagram showing the incident ion energy dependence of the limiter material sputtering ratio, and FIG. 6 is a schematic cross section showing an embodiment of the present invention. O in the figure 1... Toroidal magnetic field coil 2... Voloidal magnetic field coil 3... Vacuum vessel 4... Core plasma 5.8.10
...Limiter plate 6...Exhaust duct 7...Peripheral plasma layer Agent Patent attorney Yoshiaki Inomata (1 person) 1st
Figure 2 Figure 33

Claims (2)

[Claims] (1) In a limiter device in a nuclear fusion device equipped with a limiter plate disposed inside a torus-shaped vacuum vessel, the center portion of the cross section in the voloidal direction of the limiter plate is made of a low atomic weight material, and the end portion is made of a high atomic weight material. 1. A limiter device in a nuclear fusion device, characterized in that the limiter device is made of a material to reduce wear due to sputtering at the end of the limiter plate. (2) Low atomic weight materials are beryllium or graphite,
Claim 1: The island atomic leaf material is tungsten.
A limiter device in the nuclear fusion device described in .