JPS637655B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a neutral particle detection device that performs energy analysis and particle number detection of neutral particles emitted from plasma of, for example, a nuclear fusion device. FIG. 1 is a diagram schematically showing the configuration of a conventional neutral particle detection device. In this figure, reference numeral 1 indicates a charge exchange section, and this charge exchange section 1 is connected to the vacuum container 2.
a stripping cell 3 provided inside the vacuum container 2 for ionizing neutral particles; a gas supply device 4 for supplying charge exchange gas such as hydrogen gas to the stripping cell 3; Vacuum container 2
The stripping cell 3 is comprised of a large displacement vacuum pump 6 which exhausts gas from gas exhaust ports 5A and 5B provided on the wall of the stripping cell 3 to maintain a high vacuum state around the stripping cell 3. After the neutral particle flux 11 is converted into a charged particle flux 12 by the charge exchange unit 1, it enters the energy analyzer 10 and its energy is analyzed. The energy analyzer 10 consists of two parallel flat electrodes 7A, 7B and a power source 9 for creating an electrostatic field between the electrodes 7A, 7B.
8A to 8E are ion detectors provided corresponding to the energy analyzer 10, and are installed behind the electrode plate 7B, and the electrode plate 7B is an ion detector so that particles can enter the ion detector. A slit is provided at a position corresponding to the installation location. Further, the electrode plate 7 of the energy analyzer 10
A and 7B are installed at an angle of 45 degrees with respect to the direction of incidence of the charged particles 12. In the conventional neutral particle measuring device having the above configuration, the charged particle flux 12 enters the energy analyzer 10 and draws a parabolic trajectory due to the electrostatic field formed by the electrode plates 7A and 7B. The above-mentioned radiation trajectory draws trajectories A to E depending on the energy of the incident particle and has a spatial spread. Therefore, the emitted particle flux A'~
By measuring E′, the original neutral particle flux 11
The energy information can be obtained by the position of the spatially arranged ion detectors, and the intensity can be obtained by the magnitude of the output signal of each ion detector.
Furthermore, since the X-rays are not deflected by the energy analyzer, they are not measured by the ion detector. In conventional neutral particle measuring devices like this, the energy is converted into the spatial spread of an energy analyzer and then analyzed by an ion detector installed corresponding to the trajectory, so the energy resolution of the device is had the disadvantage that it was limited by the number of ion detectors installed. Another drawback is that when the number of ion detectors is increased in order to improve resolution, the number of measurement circuits required increases accordingly. The present invention has been made to eliminate the above-mentioned drawbacks, and an object of the present invention is to provide a neutral particle measuring device with high energy resolution and a simple device configuration. Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is a diagram schematically showing the configuration of an embodiment of the present invention. The same parts as in Figure 1 are given the same numbers. In the figure, reference numeral 20 denotes a magnetic field for deflecting the charged particle flux 12 emitted from the charge exchange section 1. Magnetic flux is applied from bottom to top in a direction perpendicular to the plane of the paper. Further, reference numeral 21 is a semiconductor detector that detects the energy of particles. Semiconductor detectors generate output signals proportional to the energy of the particles, so energy analysis and particle number detection can be accomplished simultaneously. In the present invention, by making the magnetic field 20 have a special configuration as shown in FIG.
One of the features is that the particles from the trajectory 2A to the particle 12B are focused at the position of the detector 21. The shape of the magnetic field 20 will be explained below with reference to FIG. 3. Here, we will consider the general shapes of the entrance and exit parts of the magnetic field, so we will not consider the dispersion of the incident particle flux 12, nor will we take into account the leakage magnetic field outside the magnetic field. I can't help it. Third
In the figure, the y-axis is the trajectory of the incident particle, and the incident part of the magnetic field is a plane parallel to the x-axis at the position y=b. The detector installation position, that is, the focal point 31 is located at x on the x-axis.
= position a. coordinates (o, b) along the y-axis
Particles that enter the magnetic field at an incident point 25 shown by 2 draw an arcuate trajectory due to the action of the magnetic field. The center of this arc-shaped trajectory is on the straight line y = b perpendicular to the direction of incidence from the magnetic field incidence point 25, and the radius is proportional to the momentum of the incident particle (this is called the Larmor radius).
have. That is, the Larmor radius is expressed as r=mv/eB (1). Here, m is the mass of the incident particle, v is the velocity of the incident particle, e is the charge of the incident particle, and B is the intensity of the incident magnetic field. Determining the shape of the magnetic field involves determining the shape 30 of the exit position of the particles from the magnetic field so that they reach the focusing point 31.
It is to seek. That is, a particle that enters the magnetic field at point b is deflected while drawing an arcuate trajectory 33 whose center is on the straight line of x=b with a Larmor radius 32 corresponding to the momentum of the particle itself, and the straight line of this arc The point 34 on the arc where the magnetic field is focused on the focal point 31 is set as the emission position of the magnetic field, and the emission point 34 when the Larmor radius changes from the minimum momentum to the value corresponding to the maximum momentum of the particle to be analyzed.
By finding the trajectory of the particle, the shape 30 of the emission position of the particle from the magnetic field can be found. The shape 30 of the output position of the magnetic field can be obtained analytically, and when the magnetic field input point is set to coordinates (c, b) and the focal point 31 is set to (a, o) as shown in FIG. The shape 30 is It can be expressed as The positive and negative signs of equation (2) are
It is determined by the size of the Larmor radius shown in equation (1). Larmor radius from 0

Until [Equation], the curve is shown by the positive sign in Equation (2),

It becomes a negative sign beyond [Formula] up to r=a ² +b ² /2a. If r exceeds a ² +b ² /2a, it will not focus on the coordinates (a, o). The purpose of the present invention is to detect a particle beam at the convergence point 31, and for this purpose, since the angle of incidence of the incident particle beam is limited, the part indicated by the positive sign in equation (2) above must be There is no difference in thinking only about Now, if the trajectory corresponding to the particle with the minimum momentum to be analyzed is parallel to the y-axis and in the negative direction as shown in 12A, this particle will be deflected by 180 degrees by the magnetic field and will head toward the focusing point 31. At that time, the coordinates of the exit point from the magnetic field are as follows: In the x direction, the trajectory 12A after exit is parallel to the y axis, so the focal point 3
Since x=a is equal to the x coordinate of 1, let x=a be
By substituting into equation (2), y=b and the coordinates (a, b) become the emission point. The shape of the magnetic field from the incident point 25 to the exit point 34 corresponding to the particle with the minimum momentum to be analyzed is arbitrary since it is not originally used for analysis, but in reality, the shape of the magnetic field is determined by the coordinates (o, b) of the incident point 25. ) and the coordinates (a, b) of the emission point 32 in the shape of a straight line y=b. An example using the magnetic field of this method will be described below.
Consider hydrogen as the particle to be measured. Assuming that the detector is installed at the focal point 31 in Figure 3, a = 4 cm, b
= 20cm, the minimum Larmor radius is 2cm,
When the angle of incidence of the incident particle to the focal point is 60°,
The maximum Larmor radius is approximately 13cm. magnetic field strength
When set to 3.2 kilogauss, the particle energy corresponding to the minimum Larmor radius of 2 cm is approximately 2 KeV, and the particle energy corresponding to the maximum Larmor radius is approximately
It becomes 84KeV. That is, by using a magnetic field having the shape shown in FIG. 3, hydrogen ion particles of approximately 2 KeV to 84 KeV can be focused. Focus point 3
If the angle of incidence of the incident particles on 1 can be made larger than 60°, it is possible to focus even higher energy particles. Although the direction of the incident particle changes due to the magnetic field B, the energy is conserved, so if a particle detector capable of energy analysis, such as a silicon surface barrier type semiconductor detector, is installed at the focal point, the energy spectrum of the incident particle can be obtained. be able to. Furthermore, in the neutral particle detection device of the present invention, X-rays that are incident at the same time as the particles from the incident direction of the particles are not affected by the magnetic field and therefore do not enter the detector. Furthermore, since the energy resolution is that of the detector itself, it is possible to achieve higher resolution than in the conventional method, which is limited by the number of installed detectors. In addition, as the particle detector uses an energy analysis type particle detector that emits pulses with an output wave height corresponding to the incident energy, even if the magnetic field changes slightly and the trajectory of the particle shifts, the particle will not even enter the detector. Another advantage is that energy analysis can be performed.

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram of a conventional neutral particle measuring device; FIGS. 2 and 3 each show an embodiment of the present invention; FIG. 2 is a schematic block diagram of the entire structure; FIG. 3 is a configuration diagram showing the relationship between particle trajectories and the shape of the magnetic field. DESCRIPTION OF SYMBOLS 1... Charge exchange part, 2... Vacuum container, 3... Stripping cell, 4... Gas supply device, 6... Vacuum pump,
7A, 7B...Energy analyzer electrode, 8A-8E
...Ion detector, 9...Power source, 10...Energy analyzer, 11...Neutral particle flux, 12...Charged particle flux, 2
0...Magnetic field, 21...Semiconductor detector, 22...Amplifier,
23... Wave height analyzer, 25... Incident point, 30... Momentum analyzer shape, 31... Focusing point, 34... Outgoing point.

Claims (1)

[Scope of Claims] 1. A charge exchange unit that ionizes neutral particles while preserving their momentum; a magnetic pole that forms a uniform magnetic field in a direction perpendicular to the traveling direction of the ionized particles emitted from the charge exchange unit; and a particle detector for detecting ionized particles deflected by the magnetic pole, the direction of incidence of the ionized particles entering the magnetic field is the y-axis, the x-coordinate of the point of incidence of the ionized particles into the magnetic field is o,
The y-coordinate is b, and the installation position of the particle detector is x.
When the coordinates are a and the y coordinates are 0, the shape of the boundary on the particle exit side of the above magnetic field is What is claimed is: 1. A neutral particle detection device, characterized in that the particle detector is an energy analysis type particle detector that detects the energy of incident particles. 2. The neutral particle detection device according to claim 1, characterized in that a silicon surface barrier type semiconductor detector is used as a particle detector.