JPH0218900A - Ion damp - Google Patents

Abstract

PURPOSE:To enhance economy with a nuclear fusion reactor by reducing the amount of neutron generation in an ion damp, thereby simplifying the shelter, and lessening the frequency of regular replacement of peripheral apparatus. CONSTITUTION:An ion not neutralized by a neutralizing cell is bent in the magnetic field, penetrates a film 9, and is irradiated on an ion target plate 5 to get rid of energy. As no heavy hydrogen (D) or tritium(T) flows into an ion damp vacuum vessel 10 with the plate 5 installed from a drift pipe 3, the adsorption amount of D or T upon the plate 5 becomes smaller. The film 9 is heated by the energy loss at the time of ion penetration, so that adsorption of D or T on the film 9 is also lesser. Consequently the nuclear fusion reaction within the ion damp consists merely of D-D nuclear fusion reaction which has smaller reactional section area between ions irradiated into the plate 5 to allow only neutrons with low energy to be generated, wherein the amount of generation is also one figure smaller than conventional. Thus frequency of replacing apparatus can be decreased, and operational and maintenance cost be reduced.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a neutral particle injection device for nuclear fusion, and in particular, a method suitable for reducing the amount of neutrons generated by a nuclear fusion reaction in an ion dump. Regarding ion dump.

[Conventional technology]

When deuterium (D) is used as a neutral particle in a neutral particle injection device for nuclear fusion (hereinafter referred to as an NBI device), neutrons are generated by a DD fusion reaction within the NBI device. Regarding this phenomenon, Nuclear Technology Volume 44 (19
1979), pages 315 to 321 (Nuclear
Technology Vol, 44 (1979) P
Discussed in pages 315-321 and NBI
It is said that the ion dump section, which removes ions that have not been neutralized, generates about an order of magnitude more neutrons than other parts of the device. FIG. 2 shows a conceptual diagram of the NBI device. Deuterium ions (D+
or D″″) is deuterium gas from 10″ to 10−3
It passes through a neutralization cell 2 packed to a vacuum degree of T o r r and becomes neutral deuterium (DO). However, some ions proceed through the drift tube 3 without being neutralized. Nuclear fusion devices generally generate a strong magnetic field, so ions that have not been neutralized are bent by the magnetic field and caused to drift before they enter the plasma 7 generated in the fusion vacuum vessel 6. It collides with the inner wall of the pipe and damages the drift pipe. For this reason, in the NBI device, as shown in Fig. 2, a magnetic field is applied locally at the ion dump 8 to bend the ions that have not been neutralized and cause them to collide with the ion target plate 5, thereby removing them. ing. Ordinary hydrogen (
There is no problem if H) is used, but deuterium is often used not only in fusion reactors but also in experimental equipment. At this time, D
-D A fusion reaction occurs, resulting in the production of neutrons.

D+DnHe' (0,82MeV) + n (2,
45MeV)D+D-+T (1, OIMeV) +p
(3.03 MeV) The generated neutrons activate peripheral equipment, causing damage to the equipment or becoming a radiation source. Therefore, not only is it necessary to sufficiently shield the area around the ion dump from radiation, but also periodic replacement of peripheral equipment is required. In the case of experimental equipment, the energy of neutral particles is also several tens of KeV.
Since tritium (hereinafter referred to as T, tritium), which has a large nuclear fusion reaction cross section, is not used in the plasma, the amount of neutrons generated is not that high. but,
In a fusion reactor, the energy of neutral particles is high, several hundred KeV.
Since tritium is used in the plasma, the amount of neutrons generated at the ion target plate is an order of magnitude higher.

[Problem to be solved by the invention]

The above-described conventional NBI apparatus attempts to cope with neutron generation at the ion target plate by shielding the area around the ion dump and periodically replacing peripheral equipment. However, this method increases construction costs and operation and maintenance costs, which poses problems in improving the economic efficiency of fusion reactors.

An object of the present invention is to improve the economic efficiency of a nuclear fusion reactor by reducing the amount of neutrons generated in an ion dump, simplifying the shield and reducing the frequency of periodic replacement of peripheral equipment.

[Means to solve the problem]

The above object is achieved by installing an ion target plate in a vacuum container, attaching a thin film to the wall surface of the vacuum container on which ions are incident, and evacuating the vacuum container.

[Effect]

D and T adsorbed on the ion target plate in the ion dump shown in FIG. 2 flow in from the neutralization cell and plasma. Further, inside the ion target plate, there is D that is neutralized by the incident ions being knocked into the plate. In other words, there are three sources of D and T that cause fusion reactions with incident ions on the ion target plate: D flowing in from the neutralization cell, D and T flowing in from the plasma, and It is the incident ion itself that has become sexualized.

The relative amounts of these are not clear at present, but it is estimated that the inflow and the inflow are approximately equal in half. Therefore, it is only necessary to prevent particles adsorbed onto the ion target plate, that is, D and T flowing in from the neutralization cell or plasma from being adsorbed onto the ion target plate. The inside of the vacuum chamber in which the ion target plate is installed is evacuated and sealed against the drift tube, so D and T flowing in from the neutralization cell and plasma do not reach the ion target plate. not reached. In addition, the particles of D that have been hammered into the ion target plate and flow out from the plate internal force 1 are evacuated, so that the amount of adsorption on the plate is small. If the thin film on the ion incidence surface is sufficiently thin, it will allow high-energy D+ to pass therethrough and will not prevent D+ from entering the ion target. Furthermore, during transmission, D+ imparts some energy to the thin film and loses it, so this energy heats the thin film to a high temperature. Therefore, the amount of D and T adsorbed onto the thin film from the neutralization cell or plasma becomes negligibly small. As a result, the amount of nuclear fusion reaction in the thin film becomes negligibly small. As a result, the nuclear fusion reaction in the entire ion dump is only the DD fusion reaction between the D+ bombarded into the ion target and the incident ions. Since the D-T fusion reaction with T flowing in from the plasma, which has an order of magnitude larger cross-sectional area than the D-D reaction, does not occur, the amount of particles present on the ion target plate can be reduced by half. ,
It is thought that the nuclear fusion reaction, and therefore the amount of neutrons generated, will be reduced by nearly an order of magnitude. In addition, in the DT reaction, 14 M e V
Neutrons with an energy of

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. 1st
In the figure, an ion target plate 5 is placed in an ion dump vacuum vessel 10. A thin film 9 is installed on the ion incidence surface, and the ion dump vacuum container is evacuated through vacuum exhaust bows 1 to 11.

Ions that have not been neutralized in the neutralization cell are bent by the magnetic field, pass through the thin film 9, enter the ion target plate 5, and lose energy there. In this way, D and T will not flow into the ion dump vacuum vessel 10 from the drifts 1 to 3, so the amount of D and T adsorbed on the ion target plate 5 can be made negligibly small. can. Also,
Since the thin film is heated to a high temperature due to energy loss during ion permeation, the amount of D and T adsorbed on the thin film is negligibly small, and the nuclear fusion reaction in the thin film can be ignored. As a result, the nuclear fusion reaction in the ion dump section is limited to the D-D nuclear fusion reaction, which has a small reaction cross section between the incident ions that are dumped into the ion target plate and the incident ions themselves, and is relatively Only low-energy neutrons are generated, and the amount of neutrons generated can be reduced to a value nearly an order of magnitude smaller than that of conventional methods.

In another embodiment of the present invention, the thin film material includes tungsten.
Examples include those that use thin films of high-melting metals such as tantalum, molybdenum, and rhenium. The thickness of the high-melting-point metal thin film is sufficient to be on the order of several thousand, and since the melting point of each metal is 20oO°C or higher, there is little chance of it melting even when heated by incident ions1.

Because it is durable, it has a long lifespan. Further, as another embodiment, a carbon thin film is used as the thin film.

Since carbon has a small atomic number, its interaction with incident ions is small, and even if the thickness is about 1 μm, the incident ions can pass through it. Moreover, the melting point is 3500° C. or higher, which is higher than that of high-melting point metals. On the other hand, since its strength is lower than that of metal, it is necessary to devise a method for supporting it. Carbon thin films are used as charge exchange membranes in tandem bump accelerators, and have a proven track record of transmitting high-energy ions.

FIG. 3 shows another embodiment of the invention. FIG. 3 shows only the ion dump vacuum vessel in the embodiment shown in FIG. In this embodiment, the ion target plate 5 is
It forms part of the wall of the ion dump vacuum container 5. In this way, the structure of the ion dump vacuum container can be simplified. Further, even when cooling an ion target plate, which is usually made of copper, so that the temperature thereof does not become too high, there is an advantage that the cooling pipe 12 can be easily installed as shown in FIG.

FIG. 4 shows another embodiment of the invention. Although only the ion dump vacuum vessel 1o is shown in FIG. 4, the rest is the same as the embodiment shown in FIG. In FIG. 4, the thin film 9 is attached to the ion dump vacuum vessel 10 via a ceramic insulator 14, and is electrically insulated. Both ends of the thin film are connected to an electric current g13, and the thin film can be heated by directly applying current to it. In this way, when the temperature of the thin film is insufficiently raised, the temperature of the thin film can be maintained at a high level by heating with electricity to prevent D and T from adsorbing to the thin film.

FIG. 5 shows another embodiment of the present invention. In this embodiment, a heater 15 is attached to the ion target plate 5 so that the ion target plate can be heated to a high temperature. D is injected into the ion target plate by heating it to a high temperature and diffuses out of the plate.

Since desorption can be promoted, the density of D in the ion target plate can be reduced, and as a result, the amount of neutrons generated by the nuclear fusion reaction can be reduced.

FIG. 6 shows another embodiment of the invention. In FIG. 6, the thin film 9 is attached to a mesh of high melting point metal such as tungsten or tantalum. In a reactor-scale NBI device, the cross-sectional size of the ion beam is approximately several tens of diameters. When the size becomes this size, it is impossible to support it with just a thin film. Therefore, by attaching a thin film to a high-melting point metal mesh and attaching it to an ion dump vacuum vessel, reliability is improved and the life of the thin film is extended.

FIG. 7 shows another embodiment of the present invention. In Figure 7,
Storage box 20 for unused thin films and storage box 1 for used thin films
9 is installed adjacent to the ion dump vacuum vessel 10. Inside each is a GT membrane and its support supported by a spring 17. After a certain amount of time has passed using the thin film,
A linear feeder 18 forces the unused membrane toward the ion dump vacuum vessel 10 . At the same time, the thin film 9 installed in the ion dump vacuum container is pushed out to the used thin film storage box 19 and replaced with a new one. In this way, the thin film can be replaced while the drift tube is evacuated, so the NBI equipment can be operated efficiently.

Moreover, by periodically replacing the thin film, it is possible to prevent an accident in which a large amount of D and T flows into the ion dump vacuum vessel due to breakage of the thin film, causing a nuclear fusion reaction and generating neutrons.

FIG. 8 shows another embodiment of the present invention, in which the electrode 21 is a thin film 9.
and the ion target plate 5, the ion target plate 5
installed parallel to the

A high voltage power source 24 is connected to the electrode 21 through a voltage introduction terminal 22.
An appropriate voltage is applied by the voltage dividing resistor 23 to decelerate the incident ions. In this way, ions that have entered the ion dump vacuum vessel 10 through the thin film 9 are decelerated by the deceleration voltage applied to the electrode 21. If the energy of the ions decreases, the cross section of the fusion reaction decreases rapidly, so the amount of neutrons generated can be significantly reduced without completely slowing down the ions. The idea of decelerating ions has been around for a long time, but because the electrodes were previously installed in a drift tube with poor vacuum, the higher the energy of the neutral particles, the more the discharge at the electrodes and voltage introduction terminals. Destruction occurs;
It was difficult to apply voltage stably.

According to this embodiment, since the electrodes are installed in the ion dump vacuum vessel 10, which is independently evacuated and maintained at a vacuum several orders of magnitude better than that of a drift tube, discharge breakdown is less likely to occur. , voltage can be applied stably.

Moreover, since the radiation shielding body around the ion dump part can be made smaller, the equipment construction cost can also be reduced.

〔Effect of the invention〕

According to the present invention, the amount of neutrons generated by the nuclear fusion reaction in the ion dump section of the NBI device can be reduced by nearly an order of magnitude or more, the frequency of equipment replacement can be reduced, and operation and maintenance costs can be reduced. Can be reduced.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of one embodiment of the present invention, FIG. 2 is an explanatory diagram showing an outline of an NBI device, and FIGS. 3 to 8 are explanatory diagrams of other embodiments of the present invention. 3... Drift tube, 5... Ion target plate, 9
... Thin film, 10... Ion dump vacuum container, 11.
...Vacuum exhaust port. Figure 2 Figure 7

Claims (1)

[Claims] 1. In an ion dump of a neutral particle injection device for nuclear fusion, an ion target plate that absorbs ion energy is installed in a vacuum container, and at least one surface of the vacuum container is an ion incidence surface. An ion dump comprising a thin film and capable of evacuating the vacuum container. 2. The ion dump according to claim 1, wherein the ion target plate constitutes a part of the wall of the vacuum container. 3. The ion dump according to claim 1, wherein the thin film on the ion incidence surface is carbon. 4. The ion dump according to claim 1, wherein the thin film on the ion incidence surface is made of a high melting point metal such as tungsten, tantalum, molybdenum, rhenium, or the like. 5. The ion dump according to claim 1, characterized in that the thin film on the ion incidence surface can be heated. 6. The ion dump according to claim 5, wherein the thin film is heated by directly applying electricity to it. 7. The ion dump according to claim 1, wherein the thin film is attached to a mesh made of a high melting point metal such as tungsten, tantalum, or molybdenum. 8. In claim 1. An ion dump characterized in that a heater is attached to the ion target plate. 9. In claim 1, containers for storing unused and used thin films and their supporting materials are installed separately outside the vacuum container, without breaking the vacuum of the neutral particle injection device. An ion dump characterized in that a mechanism is provided for attaching and detaching the thin film and its supporting material to and from the ion incidence surface of the vacuum container from outside the vacuum. 10. In claim 1, within the vacuum vessel, on a line connecting the ion target plate and the thin film on the ion incidence surface, parallel to the ion target plate and insulated from the vacuum vessel. An ion dump characterized by the installation of electrodes.