JPS6371689A - Pellet injector for nuclear fusion device - Google Patents

Abstract

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

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a pellet injection device for a nuclear fusion device, and in particular,
This invention relates to a pellet injection device that is suitable for injecting fuel into the center of plasma.

[Conventional technology]

As is well known, fuel supply methods for nuclear fusion devices include gas buffing and pellet injection. For example, in a tokamak type fusion device, the plasma confinement time is proportional to the plasma density (τ26Cn, 6", τE: energy confinement time, n: plasma density, a: plasma minor radius)
Moreover, the plasma density has a centrally concentrated distribution in the boloidal cross section. Alpha heating to maintain plasma combustion occurs near the plasma center on the poloidal cross section. For this reason, in the gas puff method in which combustion is supplied from the periphery of the plasma, the fuel supplied to the periphery of the plasma has a shorter confinement time than the center of the plasma, so that it is not sufficiently supplied to the center of the plasma. Also.

Since alpha heating occurs at a smaller rate around the plasma than at the plasma center, the fuel supplied around the plasma is not heated sufficiently. Alternatively, the area around the plasma may be cooled due to the supplied fuel, causing the plasma to shrink. On the other hand, when fuel is supplied to the plasma center by pellet injection, the plasma center has good confinement performance and alpha heating is large, so the supplied fuel remains in the plasma center and is heated. For this reason,
The pellet injection method is superior to the gas puff method in supplying fuel to plasma.

In conventional pellet injection devices, pellets are accelerated using a propellant gas. This method is shown in Figure 2.
Pellets are made in a pellet production device 1, passed through a pressure vessel 2 pressurized to several tens of atmospheres, opened a valve 3, and fed into a pellet acceleration section 4. The pellets accelerated in the pellet acceleration section 4 pass through a pellet-guide container 5. It passes through and is injected into the plasma 7. The propellant gas that has accelerated the pellets passes through the pellet accelerator 4 and the pellet guide container 5 and attempts to reach the plasma 7. In order to prevent this, a vacuum pump 6 was provided in the pellet guide container 5 to draw propellant gas.

[Problems to be Solved by the Invention] In the above-mentioned prior art, sufficient consideration is not given to the fact that the gas that accelerates the pellets mixes into the plasma through the pellet injection port, and the gas mixed into the plasma causes the plasma to There was a problem that the peripheral area was cooled.

An object of the present invention is to provide an apparatus that prevents a propellant gas that accelerates pellets from being mixed into plasma.

[Means for solving problems]

The above purpose is to use a pellet injection device consisting of a pellet manufacturing device and a pellet accelerator, in which a propellant gas that accelerates the pellets is mixed into the plasma, an electrode that converts the propellant gas into plasma, a gas discharge vessel that contains the plasma, and a plasma that is evacuated. This is achieved by providing a coil that creates a magnetic field to be induced toward the pump between the pellet accelerating section and the high-speed shutter. [Operation] Pellets produced by the pellet manufacturing apparatus are accelerated in the pellet accelerating section. The pellet passes through the gas discharge vessel and part of the high-speed shutter and heads toward the plasma. Electrodes are installed within the gas discharge vessel. The propellant gas that accelerates the pellets passing through the pellet guide tube is turned into plasma by the voltage applied between the electrodes. The propellant gas turned into plasma is guided toward the vacuum pump along the magnetic field created by the coil. The propellant gas that has not turned into plasma is confined by a high-speed shutter and is prevented from going to the plasma side.

From the speed of the accelerated pellet and the distance between the pellet accelerator and the high-speed shutter, the timing at which the pellet passes through the high-speed shutter is known, and the high-speed shutter is closed immediately after the pellet passes through the high-speed shutter. Another way to know when pellets pass through a high-speed shutter section is to use a device that measures pellet velocity (
For example, the velocity of the pellet is measured using a laser measuring device) and the time required for the pellet to pass through a portion of the high-speed shutter is predicted.

By exhausting the propellant gas by turning it into plasma and closing the high-speed shutter, the propellant gas that accelerates the pellets is prevented from being mixed into the plasma, so the propellant gas does not cool the surrounding area of the plasma.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. In the figure, 8 is a pellet production and pellet acceleration section, 9 is a high-speed shutter, 10 is a pellet guide tube, 6 is a connection to a vacuum pump, 7 is an entrance port for pellets into plasma, 1
1 is a propellant gas exhaust port, 14 is a coil, 15 is an electrode, 1
6 is a gas discharge vessel.

To produce pellets, for example, liquid hydrogen is placed in a cylindrical container, cooled and solidified, and then cut into cylindrical pellets. The produced pellets are accelerated in a pellet acceleration section. The acceleration method includes, for example, a gas gun method. In this method, pellets are accelerated with gas at tens of atmospheres. The pellets thus accelerated pass through the pellet guide tube and head toward the plasma side 7. At the same time, the propellant gas that accelerated the pellets also passes through the pellet guide tube and head toward the plasma frost.

The high-speed shutter prevents propellant gas from entering the plasma, but before doing so, reduce the amount of propellant gas going to the high-speed shutter using the method described below.

Place the electrode inside the gas discharge vessel and apply voltage. The propellant gas passing through the pellet guide tube expands within the gas discharge vessel. The pressure at which the propellant gas becomes plasma due to the voltage may be, for example, 0.1 atmosphere or less with respect to the voltage IKV.

When the diameter of the pellet guide tube is 10''δm and the distance between the pellet accelerator and the gas discharge vessel is 10''m, if the volume of the gas discharge vessel is selected to be 10''8 mJ, the pressure inside the gas discharge vessel The pressure becomes about 10-2 atmospheres, and the propellant gas is sufficiently turned into plasma.

The propellant gas turned into plasma is guided toward the vacuum pump by a magnetic field created by a coil, for example, a caps magnetic field.

Next, a case will be described in which a high-speed shutter is used as a method of preventing the propellant gas that has not turned into plasma from going to the plasma side. The time required to open and close the high-speed shutter will be evaluated by considering the severe side of designing a high-speed shutter, which does not have a mechanism to turn propellant gas into plasma.

First, in order to evaluate the time required to open the high-speed shutter, the number of particles in the pellets and the propellant gas is calculated. For example, the volume of a cylindrical hydrogen pellet with a length of 10"m and a radius of 10""8m is 3.14X 10"'m-".The density of solid hydrogen is 0.0763g/cc, so the hydrogen pellet The number of particles contained in is 7.19 X I
Ql'' pieces.

Next, calculate the number of particles in the propellant gas. Due to the conductance of the pellet guide tube, the pressure in the pellet acceleration section decreases at the high speed shutter part. High speed Co: speed of sound, r near 1
5 (hydrogen), Pa: pressure of pellet acceleration section 1M: pellet mass, A: cross-sectional area of pellet guide tube, 12 hours. FIG. 3 shows a calculation example in the case where Po=30 atm and the pellet guide pipe diameter is 10-'m and the type of gas is hydrogen. In this case, after 2 ms, the pressure becomes p(t)≦2 atm, and the velocity of the propellant gas becomes U(1)≧2) cm/s. Therefore, if the distance between the pellet accelerator and the high-speed shutter is chosen to be about 4 m, the pressure of the propellant gas near the high-speed shutter part is about 2 atm.
The speed is 2h/9.

If the time taken for the high-speed shutter to fully close from the fully open state is Δτ, under the above conditions, the number of particles N contained in the propellant gas is N = 3, 36 x 10
"Δt (pieces) (3). Therefore, in order to make the number of particles contained in the propellant gas negligibly smaller than the number of particles contained in the pellet, 3.36 x 10" Δc C! (4) From 7.19 X I O”, Δτ<0.0214 (s). Therefore,
For example, it is necessary to select approximately Δτ=10−′(s).

As a high-speed shutter that satisfies the above conditions, for example, a lens shutter or a focal point opening/closing shutter is used.

Next, another embodiment is shown in FIG. 4. In the embodiment shown in FIG. 3, the timing of the high-speed shutter was determined in advance from the gas pressure and the like. In this embodiment, the timing for opening and closing the high-speed shutter is determined by a device 12 that measures pellet speed. As a pellet velocity measuring device, for example,
A device is used to measure the scattering of laser light by pellets.

According to this embodiment, it is possible to prevent the propellant gas that accelerates the pellets from being mixed into the plasma.

[Effects of the Invention] According to the present invention, it is possible to prevent the propellant gas from being mixed into the plasma.1 For example, by selecting the opening/closing time of the high-speed shutter to be l0-8 sec, particles contained in the propellant gas can be prevented. The number can be suppressed to within 5% of the number of particles contained in the pellet.

[Brief explanation of the drawing]

Claims (1)

[Claims] 1. In a pellet injection device comprising a pellet production device and a pellet accelerating section, a high-speed shutter is provided between the pellet accelerating section and the pellet accelerating section to prevent a propellant gas that accelerates the pellets from being mixed into plasma. Provided between the plasma injection port, and
An electrode for turning the propelling gas into plasma, a gas discharge vessel for containing the plasma, and a coil for creating a magnetic field for guiding the plasma toward the vacuum pump are provided between the pellet accelerator and the high-speed shutter. Pellet injection device for a nuclear fusion device.