JP2002022870A - Neutral particle injection unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To generate deuterium plasma having a high degree of ionization efficiently while lowering the working pressure of a neutralization cell 50. SOLUTION: Target particles, e.g. hydrogen gas or deuterium gas, is introduced into a neutralization cell 50 and mixed gas of cesium metal having ionization energy lower than that of the target particles. The gas of cesium metal is contained in a vaporizer 54 and vaporized by heating at 200-300 deg.C before being fed to the neutralization cell 50 by opening/closing a valve 55 intermittently. Subsequently, the target particles are irradiated with microwave from a microwave generator 51 to generate plasma efficiently under a low working pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a neutral particle injector capable of efficiently generating neutral particles used in a tokamak fusion reactor or the like.

[0002]

2. Description of the Related Art In tokamak-type fusion reactors and the like, high-speed (high-energy) neutral particles are generated, incident on the fusion reactor, and used for heating plasma.

[0003] Hydrogen and deuterium are used as such neutral particles. It should be noted that there is no difference in basic principle between using hydrogen and deuterium, so the following description will be made using deuterium as an example.

[0004] As shown in FIG.
An ion that is connected to a tokamak-type fusion reactor or the like (hereinafter simply referred to as a fusion reactor) and injects generated neutral particles into the fusion reactor, and generates deuterium negative ions. A source chamber 110, a neutralization cell 150 that neutralizes the negative ions by causing a collision reaction with the negative ions that have been introduced and injected with the target particles, between the ion source chamber 110 and the neutralization cell 150, and It is constituted by vacuum chambers 130 and 140 provided between the neutralization cell 150 and the fusion reactor.

[0005] The ion source chamber 110 is provided with a tungsten filament (not shown), a plurality of extraction electrodes 112, and the like. The inside of the ion source chamber 110 is about 1 Pa
Deuterium gas is introduced so that the operating pressure becomes approximately the same as before and after, and negative ions (D ⁻ ) of deuterium are generated by DC discharge by the tungsten filament.

[0006] The generated negative ions are accelerated by a plurality of extraction electrodes 112 electrically insulated by an insulating material 113 to become high-speed ions, which are extracted from extraction holes (not shown) formed in the extraction electrodes 112 and are evacuated to a vacuum chamber. The light enters the neutralization cell 150 via 130.

[0007] An exhaust pump (not shown) is connected to the vacuum chambers 130 and 140 to exhaust gas flowing out of the ion source chamber 110 and the neutralization cell 150.

In general, deuterium gas is introduced into the neutralization cell 150 as target particles, and the incoming negative ions cause a collision reaction with the target particles to strip off the electrons of the negative ions. It becomes high-speed neutral particles (D ⁰ ).
Then, the light enters the fusion reactor through the vacuum chamber 140.

In the following description, a case where the deuterium gas introduced into the neutralization cell 150 acts as a target particle is referred to as a gas cell, and as described later, the deuterium gas is turned into plasma and the deuterium plasma is generated. The case where it acts as a target gas is called a plasma cell.

FIG. 5 is a graph showing the composition ratio of the deuterium gas to the linear density when negative ions of 750 keV are incident on the gas cell. It can be understood that neutralization efficiency can be obtained.

Under these circumstances, there has been a demand for further improving the efficiency of generating neutral particles with the progress of the development of the nuclear fusion reactor system.

In response to such a demand, a configuration has been proposed in which deuterium is converted into plasma and used as target particles as shown in FIG. Such a configuration is called a plasma cell.

The microwave cell 151 includes a plurality of waveguides 15 in the plasma cell of the neutralizing particle injector.
2 to convert the introduced deuterium gas into plasma.

As described above, the reason that the neutralization efficiency is improved when the plasma cell is used is that the reaction cross section when negative ions react with plasma is several tens of times larger than the reaction cross section when reacting with deuterium molecules. This is because the negative ions and the target particles efficiently cause a collision reaction.

FIG. 7 shows the composition ratio of the deuterium plasma to the linear density when negative ions of 750 keV are incident on such a plasma cell (the degree of ionization of the plasma is 20%). It corresponds to.

The ratio of neutralization at the optimum linear density is 75
% Of the gas cell (about 6% in the case of a gas cell).
(Was 0%).

Note that the neutralization efficiency when this plasma cell is used depends on the degree of ionization in the plasma cell as shown in FIG.

FIG. 8 shows the ionization degree of the plasma on the horizontal axis and the neutralization efficiency and the linear density on the vertical axis. The ionization degree is around 40% and the neutralization efficiency is 80% or more.

[0019]

However, even if the conventional gas cell is simply replaced with a plasma cell, the above-described effects cannot be obtained.

That is, the linear density of the plasma cell required for neutralization is a value determined by the plasma density and the plasma cell length. If the operating pressure of the plasma cell is set to be high, high-density plasma is easily selected. Easy to obtain linear density.

However, when the operating pressure of the plasma cell increases, the amount of plasma flowing into the vacuum chambers 130 and 140 increases accordingly, and the load on the exhaust system increases. There is a case where the effect of adopting is canceled.

On the other hand, the negative ions emitted from the ion source chamber 110 are supplied to the vacuum chamber 13 before entering the plasma cell.
Collides with deuterium in zero.

The target particles flowing from the neutralization cell 150 into the vacuum chamber 130 are deuterium gas in the case of a gas cell and deuterium plasma in the case of a plasma cell.

At this time, when the neutralization cell 150 is a gas cell, the electron stripping reaction of the negative ions due to the collision between the negative ions and the deuterium gas is small, but in the case of the deuterium plasma, it is large. Become.

FIG. 9 shows the ion source chamber 110 and the neutralization cell 1.
FIG. 4 is a diagram showing the neutralization efficiency when a reaction between negative ions and deuterium plasma generated in a vacuum chamber 130 between 50 and 50 is considered.

As can be seen from this figure, even if the linear density of the plasma cell is maintained optimally, when there are many reactions in the vacuum chamber 130 between the ion source chamber 110 and the neutralization cell 150, On the contrary, the neutralization efficiency decreases, and the neutralization cell 15
In some cases, the effect of converting 0 into a plasma cell is lost.

Therefore, it is difficult to improve the desired neutralization efficiency only by replacing the gas cell with the plasma cell.

Accordingly, an object of the present invention is to provide a neutral particle injector capable of efficiently improving neutralization efficiency while lowering the operating pressure of a plasma cell.

[0029]

According to a first aspect of the present invention, an ion particle accelerated by an electric field is guided to a neutralization cell, and a target introduced into the neutralization cell is provided. In a neutral particle injector that reacts with particles to form high-speed neutral particles, a gas having a lower ionization energy than the target particles introduced into the neutralization cell is mixed into the neutralization cell, It is characterized in that the operating pressure of the gasification cell is lowered so that neutral particles can be generated efficiently.

[0030] The invention according to claim 2 is characterized in that the target particles are hydrogen or deuterium, and the gas mixed into the neutralization cell is an alkali metal gas.

According to a third aspect of the present invention, the gas mixed into the neutralization cell is at least one of cesium and xenon.
It is characterized by including.

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of a neutral particle injector applied to the description of the present embodiment.

The neutral particle injector is provided in the ion source chamber 1
0, vacuum chambers 30, 40, neutralization cell 50, vacuum chamber 30,
The neutralizing particles are incident on a tokamak-type fusion reactor or the like via a drift tube 60.

In the following description, the neutralization cell may be referred to as a gas cell or a plasma cell. In such a case, the gas cell 50 or the plasma cell 50 will be described.

The ion source chamber 10 is provided with a tungsten filament (not shown), an extraction electrode 12, etc.
Deuterium gas is introduced so as to have an operating pressure around a,
Negative ions deuterium by DC discharge by a tungsten filament (D ^-) is generated.

The negative ions generated in this manner are accelerated by the electric field generated by the plurality of extraction electrodes 12 electrically insulated by the insulating material 13 to become high-speed ions, and formed on the extraction electrodes 12. It is taken out from a drawing hole (not shown) and enters the neutralization cell 50 via the vacuum chamber 30.

An exhaust pump (not shown) is connected to the vacuum chambers 30 and 40, and the ion source chamber 10 and the neutralization cell 50 are connected.
It is designed to exhaust gas flowing out of the system.

In general, deuterium gas is introduced as target particles into the neutralization cell 50, and the deuterium gas is excited by the microwave oscillator 51 to generate plasma.

This deuterium gas is supplied from a gas supply port 53 and is supplied from a microwave oscillator 51 at 2.45 GHz.
The microwave of z is transmitted through the waveguide 52 to excite the deuterium gas.

Then, the incoming negative ions collide with the deuterium plasma to cause the electrons of the negative ions to be stripped off, thereby generating high-speed neutral particles (D ⁰ ) and passing through the vacuum chamber 40. Injects into a fusion reactor such as a tokamak fusion path.

Needless to say, in the neutralization cell 50, the re-ionization reaction of the neutralized neutral particles (D ⁰ ) is generated in competition with the electron stripping reaction of the negative ions (D ⁻ ). Ions are bent by an electric or magnetic field to form a vacuum chamber 40
Is guided to a beam dump 41 installed in the apparatus and is subjected to thermal treatment.

The deuterium gas in the plasma cell 50 is ionized by microwaves and turned into plasma. At this time, the use of a magnetic field facilitates the ionization.

For this reason, in the present invention, a magnet 59 such as a permanent magnet or an electromagnet is arranged around the neutralization cell 50 to promote the generation of plasma to reduce the operating pressure. The magnetic field also contributes to confinement of plasma.

In particular, the magnet 59 is set so that the magnetic flux density near the wall of the neutralization cell 50 becomes 875 gauss. As a result, electron cyclotron resonance is generated by the combination of the magnetic flux density of 875 gauss and the microwave of 2.45 GHz, and the electrons resonately absorb the energy of the microwave to efficiently generate the plasma. I have.

As a result, the operating pressure of the neutralization cell 50 can be reduced, and plasma can be easily generated even at 0.1 Pa or less.

In the present invention, a predetermined amount of gas having a lower ionization energy than that of the deuterium is mixed with the deuterium gas introduced into the neutralization cell 50 in such a configuration.

This is because when a gas having a low ionization energy is mixed, discharge is more likely to occur than in the case of using deuterium or hydrogen alone, and a deuterium plasma having a high ionization degree can be generated at a lower operating pressure.

As the gas to be mixed as described above, an alkali metal having a low ionization energy (eg, sodium, potassium, cesium, etc.) is preferable. Incidentally, the ionization energy of hydrogen is 13.6 eV, and sodium is 5.1
eV, potassium are 4.3 eV, and cesium is 3.9 eV.

Then, the metal is vaporized by heating in a vaporizer 54 containing such a metal, and the neutralized cell 50 is heated.
To be introduced. The introduction amount is set by adjusting the degree of opening and closing of the valve 55.

For example, when cesium is used, the vaporizer 54 is vaporized at a temperature of 200 to 300 ° C., and the gas is supplied to the neutralization cell 50 by opening and closing the valve 55 intermittently.

Thus, the operating pressure of the neutralization cell 50 can be set to about 0.01 Pa.

When cesium was used as the gas to be mixed into the neutralization cell 50, the cesium was vaporized using the vaporizer 54 as described above. However, when xenon was used, the vaporizer 54 was used. There is an advantage that the configuration becomes simple because it becomes unnecessary.

In the above description, microwaves have been described as an example of a method for exciting the target particles of the neutralization cell 50. However, the present invention is not limited to this. For example, as shown in FIG. Alternatively, a direct current discharge by the filament 58 may be used, or a discharge method using an electromagnetic wave in the MHz band by the RF oscillator 57 may be used as shown in FIG.

The DC discharge method shown in FIG. 2 has the advantage that it is suitable for upsizing based on past results, etc., and its operating pressure is slightly higher than that of microwaves. However, the discharge pressure can be reduced by mixing a small amount of cesium. Can be reduced to 0.1 Pa or less, and the degree of ionization also improves as in the case of microwaves.

When a gas having a low ionization energy is mixed as described above, discharge is more likely to occur than in the case of using deuterium alone, and a deuterium plasma having a high ionization degree can be generated at a lower operating pressure. become.

In the case of the discharge method using the RF oscillator 57, since it is a non-polar discharge without using a cathode similarly to the case of the microwave, there is an advantage that the maintainability is excellent. Note that the frequency is preferably 13.56 MHz.

Then, RF power is supplied to a solenoid-like antenna 56 installed inside the neutralization cell 50 to excite target particles.

In this case, although the operating pressure is higher than in the case of microwaves, the discharge pressure is reduced by mixing a small amount of cesium, the operation can be performed even at 0.1 Pa or less, and the degree of ionization is improved.

[0059]

As described above, according to the present invention,
Since hydrogen or deuterium gas introduced into the neutralization cell is mixed with an alkali metal gas such as cesium or xenon gas, the operating pressure of the neutralization cell can be reduced, and the target particles can be reduced. And the neutralization of particles can be efficiently generated.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a neutral particle injector applied to the description of an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a neutral particle injector that heats deuterium gas by a filament.

FIG. 3 is a schematic configuration diagram of a neutral particle injector that heats deuterium gas by high frequency.

FIG. 4 is a schematic configuration diagram of a neutral particle injector using a gas cell applied to the description of a conventional technique.

FIG. 5 is a diagram showing a composition ratio with respect to a linear density when a gas cell is used.

FIG. 6 is a schematic configuration diagram of a neutral particle injector using a plasma cell applied to the description of a conventional technique.

FIG. 7 is a diagram showing a composition ratio with respect to a linear density when a plasma cell is used.

FIG. 8 is a diagram showing neutralization efficiency and linear density with respect to the degree of ionization of deuterium plasma.

FIG. 9 is a diagram showing a linear density and a neutralization efficiency in a vacuum chamber.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Ion source chamber 12 Extraction electrode 13 Insulation material 30, 40 Vacuum chamber 41 Beam dump 50 Neutralization cell (gas cell, plasma cell) 51 Microwave oscillator 54 Vaporizer 55 Valve 57 RF oscillator 58 Filament

Claims (3)

[Claims] 1. A neutral particle injector that guides ion particles accelerated by an electric field to a neutralization cell and reacts with target particles introduced into the neutralization cell to form high-speed neutral particles. A neutral particle injector, wherein a gas having a lower ionization energy than target particles introduced into the neutralization cell is mixed into the neutralization cell. 2. The target particle is hydrogen or deuterium,
The neutral particle injector according to claim 1, wherein the gas mixed into the neutralization cell is an alkali metal gas. 3. The neutral particle injector according to claim 1, wherein the gas mixed into the neutralization cell contains at least one of cesium and xenon.