JPS61183862A - Gas-puff type plasma x-ray generation device - Google Patents

Abstract

PURPOSE:To stabilize a position of a spot generating X-rays by jetting a high speed air current from one electrode central part while exhausting from the other electrode central part through a cylindrical member having the flow impending hollow holes. CONSTITUTION:An electrode 2 having a nozzle 5 and a high speed piston 6, which controls air flow, and an electrode 3 supporting a cylindrical member 8, which has an exhaust hole 7 while having a hollow hole at its central part, are oppositely arranged inside a vacuum container 1 for forming an X-ray generating device. And the high pressure gas from the nozzle 5 is made to collide with the member 8 for forming an impulse wave directly in front of its end surface for generating arc discharge on an air column 13 through the voltage to be impressed between the electrodes 2 and 3 for generating X-ray as plasma gas. Accordingly, a ring-forming impulse wave can be made in a plasma gas flow so as to be able to correctly fix the position of a spot generating X-rays to the position of the impact wave for being stabilized.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a gas buff type plasma X-ray generator of the type that injects a high-speed gas flow between electrodes. This invention relates to a gas puff type plasma X-ray generator that reduces X-ray absorption.

[Background of the invention]

Plasma X-ray sources utilize X-rays emitted when high-speed electrons collide with gas atoms.

The amount of X-rays generated by a radiation source is proportional to the product of the number of target atoms and the number of high-speed electrons colliding with each other, so it is important to form a high-temperature, high-density plasma by using a magnetic pinch caused by a large current discharge. be.

As a means to achieve the above state, PHYSICAL
EVIEII LETTER5, VOL40. N(1
8, p, 515 (1978) Te T, 5hiloh et al. propose a method of injecting a high velocity gas flow between electrodes placed in a vacuum. In this method, a nozzle is provided at the center of the anode of a pair of electrodes, and a high-speed airflow is injected from there toward the cathode.

If the airflow is fast enough, gas will not have diffused to other spaces at the time the airflow reaches the cathode, so a cylinder of gas can be formed between the electrodes. If high-speed discharge is performed in this state, a cylindrical plasma is formed.

At this time, if the discharge current is large enough, the cylindrical plasma will generate a magnetic pinch and will self-contract in the radial direction. As a result of the confinement of the plasma by this magnetic pinch, the plasma density increases and X-rays are generated.

However, the X-ray source known from the above-mentioned literature has the following two problems when used as a practical device. The first is that the X-ray generation position cannot be fixed at a specific location between the electrodes. The reason for this is as follows. Generally, magnetic pinch does not occur uniformly along the axial direction of the plasma, but occurs locally. In other words, the contraction force of a magnetic pinch is proportional to the current density, so if local contraction occurs and a constriction occurs, the constriction force in that area will be greater than in other parts, while the plasma at the constriction will continue to flow toward both ends. As a result, the internal pressure decreases and the constricted area rapidly contracts, creating a magnetic pinch called a spot, which generates intense X-rays. In the above-mentioned X-ray source, since the constriction can occur anywhere, the spot formation position for each discharge is not fixed, resulting in a fluctuating light source.

The second problem is the absorption of X-rays. In the aforementioned X-ray sources, the high-speed airflow directly impinges on the cathode, causing gas to be scattered within the discharge tube. Since the generated X-rays are absorbed by the scattered gas, it cannot be used as an efficient X-ray source.

In order to improve the first of these problems, we have recently attempted an X-ray source that stabilizes the spot formation position by providing a shock wave generating rod in the center of the cathode. This is a shock wave generated when a high-speed airflow is blown onto the rod at the center of the cathode.
A minimum pressure point is created on the axis of the cylindrical airflow, thereby stabilizing the spot formation position and reducing fluctuations in the X-ray generation position. However, it has the disadvantage that the ear-pressure area downstream of the shock wave prevents the formation of a stable spot.An even bigger problem is that the airflow reversed by the shock wave generating rod diffuses into the vacuum vessel and absorbs the X-rays. Therefore, the improvement in 1 generation efficiency is significantly hindered. Therefore, this is contrary to the direction of solving the second problem.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a gas puff type plasma X-ray generation device that can stabilize the generation position of X-rays and at the same time reduce absorption of generated X-rays by gas.

[Summary of the invention]

The present invention inserts an obstacle having holes into a high-speed airflow,
By making the shock wave shape hollow, a minimum point of pressure is created on the axis of the airflow.

Plasma particles around the shock wave caused by plasma contraction are allowed to move through the hollow part of the shock wave, thereby stabilizing the X-ray generation position. Also,
By exhausting air through the holes, gas diffusion is suppressed,
This reduces the absorption of generated X-rays.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. An electrode 3 facing an electrode 2 is provided inside the vacuum vessel 1, and in the center of the electrode 2 there is a nozzle 5 and a high-speed piston 6 for controlling the gas flow to the nozzle.

On the other hand, an exhaust hole 7 is provided in the center of the electrode 3, and the container 1
Exhaust the gas inside to the outside. Exhaust hole 7 in the center of the electrode 3
In the center of the member 8 having a hollow hole is an electrically insulating member 9.
It is connected to and supported by the electrode 3. The end face of the member 8 having the hollow hole is made to protrude closer to the electrode 2 than the end face of the electrode 3 . Electrode 2 and electrode 3 are connected via switch 10.

It is connected to the power supply 11. X-rays generated between the electrodes 2 and 3 are extracted to the outside through a window 12 provided on the outer wall of the container 1. The member 8 having a hollow hole is a hollow cylindrical elongated rod shown in FIG.

Next, the operation of this embodiment will be explained. When the high speed piston 6 opens, the high pressure gas inside the electrode 2 is ejected through the nozzle 5 towards the counter electrode 3. The high-speed air flow is expanded and accelerated, becomes a supersonic flow, and collides with the counter electrode 3 and the hollow cylindrical rod 8 provided at its center. At this time, a part of the flow that collided with the end face of the electrode 3 spreads into the interior of the vacuum vessel 1 due to rebound from the end face. On the other hand, the flow that collides with the hollow cylindrical rod 8 is stopped at the end surface of the rod 8 and is in a subsonic state, so that a shock wave is formed just before the end surface of the hollow cylindrical rod 8. A diagram of the hollow cylindrical rod 8 and the shock wave 14 is shown in FIG. FIG. 3 is an enlarged view of the upper half between the electrodes 2 and 3 from the center. In FIG. 3, exhaust hole 7
Among the high-speed airflow, from the holes 15 connected to the electrode 3
Airflows other than those colliding with the end face of the hollow cylindrical rod 8 pass through.

When the high-speed airflow reaches the end face of the electrode 3 and the hollow cylindrical rod, the switch 10 is closed and a large voltage is applied to the electrodes 2 and 3, and a large current flows through the air column 13, causing an arc discharge in the air column 13. As a result, it becomes plasma gas. The plasma gas becomes cylindrical. This cylindrical plasma undergoes self-contraction due to electromagnetic interaction between the magnetic field generated by the current and the current. At this time, a shock wave 14 is formed inside the air column 13. Because the pressure increases downstream of the shock wave 14,
Immediately before the shock wave 14, the pressure is at its minimum. Self-contraction of the plasma therefore precedes the location of the shock wave where the pressure is minimum, resulting in a constriction. When a constriction occurs, the current density in that part increases and the contractile force becomes greater than in other parts, while the plasma in the constricted part escapes to both ends. Since the shock waveform has an annular shape corresponding to the cross section of the hollow cylindrical rod 8, there is no shock wave in the center of the annular ring and the pressure is low, so the plasma escapes to the electrode 3 side as the constriction progresses. I can do it. As a result, the internal pressure decreases and the constriction contracts more rapidly. As a result, a spot is formed that generates X-rays.

The generated X-rays are taken out through the window 12.

Next, in explaining the effects of this embodiment, first, the generation of shock waves will be explained. The pressure distribution between electrode 2 and electrode 3 determined by the supersonic flow analysis program is shown in FIGS. 4, 5, and 6. Figure 4 shows the electrode 3
When there is no member that obstructs the flow in the center of the electrode 3, FIG. The figure shows a case where a hollow cylindrical rod 8 according to this embodiment is provided. In Fig. 4, when there is no member interfering with the flow, electrode 3 is connected from the electrode 2 side.
As the gas flows into the solid rod 16, the pressure decreases, and there is no steep pressure gradient near the electrode 3 that would indicate a shock wave.In the recently tried method shown in FIG. The generation of a shock wave 14 is shown. Immediately in front of the solid rod 16, the pressure is high. Therefore, the following problems arise. When a large current flows between the electrodes 2 and 3, the plasma-formed gas self-contracts, and the position -O is just before the shock wave, as explained above. However, as the constriction occurs and the contraction progresses, the plasma in the constricted part that is located on the opposite side of the solid rod 16 can move in that direction, contributing to a decrease in pressure. , those on the solid rod 16 side are prevented from escaping because the pressure there is high and the slope is steep. Therefore, the progress of contraction of the waist decreases.

1. Strong X-rays cannot be obtained because the contraction weakens, and the pressure on the solid rod 16 side also increases with the contraction.

Therefore, there is a problem in that the constriction is pushed back toward the electrode 2 side, causing the position of the spot where X-rays are generated to fluctuate.

FIG. 6 shows the pressure distribution in this embodiment using the hollow cylindrical rod 8. There is a steep pressure gradient just in front of the hollow cylindrical rod 8, indicating the generation of a shock wave 14. The shape of the shock wave 14 is different from that shown in FIG. 5, and is shaped so as to surround the end face of the hollow rod 8, forming an annular shape.

In the case of an annular shock wave, the effect of determining the position of the constriction generated in the plasma is the same as when the solid rod 16 is provided, but as the constriction progresses, the hollow rod 8 of the plasma in the constricted part The plasma on the sides can escape through the hole in the center of the nine-ring shock wave. This is because since the shock wave is annular, the high-pressure part downstream of the shock wave is also annular, and there is a low-pressure part in the center.

Therefore, the pressure in the area where the constriction occurs is reduced and contraction is promoted. Moreover, since the central part of the annular shock wave is at low pressure, the pressure on the hollow cylindrical rod 8 side will not increase due to contraction of the plasma, and the spot generation position will not be pushed back toward the electrode 2 side. Therefore, there is an effect of stabilizing the position of the spot that generates X-rays at the position of the shock wave 14.

A further significant effect is that the amount of gas diffused into the container 1 is reduced, the amount of generated X@ absorbed is reduced, and the intensity of the extracted X-rays is increased. Figure 7 shows
The density distribution of high-speed airflow was analyzed using the supersonic flow analysis program mentioned above. The figure shows the density (0, l x 10 bow kg/m3) showing the airflow boundary among the density distribution immediately after the high-speed airflow ejected from the nozzle 5 collides with the electrode 3.
This figure shows contour lines 17 of . Among the gases that have spread in this way, those included in the range shown by B are gases that self-contract when a large current is passed through them, and are unrelated to the absorption of xm. Gases in the range indicated by A absorb X-rays. The density of the airflow ejected from the nozzle 5 is greatest at the central axis and decreases toward the periphery. In the recently tried method using the solid rod 16, there is a problem that the flow in the high-density region at the center of the airflow is reflected by the solid rod 16 and flows out to the outer edge of the container 1, contributing to X-ray absorption. . On the other hand, according to this embodiment, since the rod 8 has a hollow structure and is connected to the exhaust hole, the flow in the high-density region at the center of the airflow is not reflected, so that the outflow to the outer edge of the container 1 is reduced. , has the effect of reducing X-ray absorption. X-ray generation position in Figure 7 (
FIG. 8 shows the density distribution along the two-dot chain line). In FIG. 8, the horizontal axis indicates the positions on the two-dot chain line, and particularly shows position A where X-ray absorption is large. The vertical axis shows the density, and the electrode 3
When there is no obstruction in the middle part of the voice, we will compare the recently tried case of using the solid rod 16 and the case of this embodiment using the hollow rod 8. In the X-ray absorption region A, the density distribution according to the present invention is approximately the same as in the case of no obstruction, indicating that the diffusion of high-velocity gas is small. Also, compared to the recently tried method using solid rods 16, the maximum density is 35%.
It can be seen that it is decreasing. As described above, the method using the hollow rod 8 according to this embodiment has the effect of reducing the density of the gas that absorbs X-rays by 35% at the maximum. FIG. 9 shows the relationship between the density reduction amount converted to X-ray absorption and the hollow diameter inside the cylinder 8. The horizontal axis in the figure shows the value obtained by dividing the hollow diameter d of the cylindrical rod 8 by the outer diameter of the cylinder, and when d/D=O, this corresponds to the case of the recently tried solid rod 16, and when d/D=1. When it is 0, it corresponds to the case where there is no obstacle. The vertical axis shows the amount of X-ray absorption as a relative value, and the value when d/D=O is 1
It was set as 00%. If the hollow hole is opened even slightly, the high-density central part of the high-speed airflow ejected from the nozzle 5 will flow from the hollow hole 15 to the exhaust hole 7, and gas diffusion to the outer edge of the container 1 will be reduced. However, the amount of X-ray absorption is also reduced accordingly. In particular, the density distribution of the high-speed airflow has a higher density toward the center, so a large amount of airflow flows to the exhaust hole 7 with a small hollow diameter, and diffusion into the container 1 is reduced. Therefore, the amount of X-ray absorption decreases rapidly as d/D increases. When d/D=1.0, only the airflow reflected from the end face of the electrode 3 flows out to the outer edge of the container 1.

The graph in FIG. 9 approaches this value. According to the analysis results of the supersonic flow analysis program, when d/D=0.5,
This has the effect of reducing the amount of line absorption by about 75%.

FIG. 10 shows another embodiment of the invention. The difference from the previous embodiment is that instead of the flat hollow cylindrical rod 8 shown in FIG.
This is because a hollow cylindrical rod 19 is provided. By providing this edge 18, it is possible to reduce the spread of the airflow that is scattered by hitting the tip of the rod, which has the effect of reducing the absorption of X-rays.

FIG. 11 shows still another embodiment of the present invention.
10 is that a hollow cylindrical rod 21 with an edge 20 is provided inside the tip. this edge 2
By providing 0, the high density gas at the shock wave generation position is
The gas can be easily evacuated through the exhaust hole 15 at the center of the rod, preventing gas from diffusing into the vacuum container and reducing X-ray absorption.

FIG. 12 shows still another embodiment of the present invention.
10 and 11 is that a hollow cylindrical rod 23 having not only one hole 22 but a large number of holes 22 is provided. By providing a large number of holes 22, the effective cross-sectional area that contributes to evacuation increases, so that the evacuation efficiency of high-density gas increases. Moreover, unlike the method of simply increasing the diameter of the hole to increase the effective cross-sectional area that contributes to exhaust, stable generation of shock waves is maintained as is. As a result, a radiation source with less fluctuation and less absorption of X-rays can be obtained.

〔Effect of the invention〕

According to the present invention, it is possible to create an annular shock wave within the plasma gas flow, which has the effect of accurately fixing the position of the spot where X-rays are generated at the position of the shock wave. In addition, since the dense fluid in the center of the gas flow is guided to the exhaust port, the amount of gas that diffuses to the outer edge of the container is reduced.
It has the effect of reducing the amount of linear absorption. The effect is a 75% reduction in X-ray absorption when a solid rod is placed at the center of the flow, which is equivalent to when there is no obstruction at the center of the flow.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of one embodiment of the present invention, and FIG. 2 is a sectional view of an embodiment of the present invention.
An enlarged view of member 8 in Fig. 1, Fig. 3 is a conceptual diagram of shock waves generated in a gas flow, and Figs. 4, 5, and 6 are contour diagrams of the pressure distribution within the gas flow determined by numerical analysis. , Fig. 7 is a contour map of the density determined by numerical analysis, Fig. 8 is a cross-sectional view taken along line 8-A' in Fig. 7, and Fig. 9 is a contour diagram of the density determined by numerical analysis. Graphs showing the amount of absorption, FIG. 10, FIG. 11, and FIG. 12 are sketches of the member 8 in other embodiments. 2... Electrode, 3... Electrode, 5... Nozzle, 7...
- Exhaust port, 8... Member having a hollow hole, 9... Electrical insulation member.

Claims (1)

[Claims] 1. A gas puff type plasma X-ray generator having a pair of opposing electrodes, in which a high-speed airflow is ejected from the center of one electrode and exhausted from a hole provided in the center of the other electrode,
An X-ray generator characterized in that a member that obstructs the flow is provided at a position off-axis of the exhaust hole. 2. The X-ray generating device according to claim 1, characterized in that a cylindrical member having a hollow hole is provided as the member that obstructs the flow.