JP2716790B2 - Beam direction measuring device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for measuring the traveling direction of a beam, and more particularly to an apparatus for measuring the traveling direction of a beam that cannot be directly viewed.

In a device that handles a charged particle beam, knowing where and in what direction the beam is currently traveling is information necessary for adjusting the device and the like. Knowing the exact position and direction of the beam allows the beam to be used as efficiently as possible.

[Prior Art] In the following, ions are supplied at the center of a planar gap sandwiched between magnetic poles, accelerated by a dee, which is an accelerating high-frequency electrode, and gradually move outward while forming a spiral, and are deflected to the outside. The following describes an example of a cyclotron to be extracted.

FIG. 2 schematically shows the ion trajectory in the cyclotron. In FIG. 2, a cone support tube 50 places an ion source 51 in the center. Ion beam emitted from ion source 51
Reference numeral 52 denotes a digital filter to which a high frequency voltage is applied
It is accelerated by the electric field between 55 and 56, and is given a centripetal force in a strong magnetic field formed in the front and back of the paper, forming a spiral orbit.

When the ion beam is introduced into the entrance of the deflector electrode 60 at the outermost side of the ion trajectory, the ion beam is deflected and extracted by the deflector electrode 60 to form an extracted ion beam 61.

In order to obtain a high-intensity ion beam, it is necessary to guide the beam bundle to the entrance of the deflector in the beam adjustment of the cyclotron, and to extract the beam without hitting the wall. Conventionally, adjustment of an ion beam has been performed by changing various parameters by trial and error.

[Problems to be Solved by the Invention] As described above, in the beam adjustment of the conventional cyclotron, the beam flux to be introduced into the deflector is incident even though the introduction of the beam into the deflector cannot be easily adjusted to the optimum condition. No measures were taken for measuring and controlling the angle.

In addition, even in an apparatus that handles a beam that cannot be directly viewed, the beam was identified only by forming a visible image of the beam cross section on a screen or by scanning a probe. A device for measuring not only the position of the beam but also its traveling direction has not been provided so far.

An object of the present invention is to provide a beam traveling direction measuring device for measuring the traveling direction of a beam.

It is another object of the present invention to provide a beam traveling direction measuring device capable of measuring the position of a beam along with the traveling direction of the beam.

For example, if the angle of incidence of the beam on the deflector in the cyclotron is known, the adjustment can be simplified and, consequently, can contribute to the reduction in deflector activation.

[Means for Solving the Problems] While irradiating a beam to a beam detecting means capable of detecting a beam, the beam shielding means capable of shielding the beam in front thereof is moved, and the beam shielding means for the beam detecting means is moved. Process the detection signal of the beam detection means as a function of the signal representing the relative position of.

An output signal is obtained that indicates the relative position where the beam is no longer incident on the detection means.

[Operation] FIG. 1 schematically shows the measurement principle of the present invention. In the figure, A
Represents the position of the beam detecting means, and B represents the position of the beam shielding means.

It is assumed that a beam is incident on the beam detecting means A. At this time, when the beam shielding means is moved to the position B,
It is assumed that the beam does not enter the beam detecting means A.
If the beam moves linearly, the direction connecting A and B is the incident direction of the beam. Therefore, if the relative position of the point B with respect to the point A is known, the direction of the incident beam indicated by the arrow can be known.

If the coordinates of point A are, for example, (x, y) and the coordinates of point B are, for example, (x + Δx, y + Δy),
By knowing Δx and Δy, the angle θ can be known from the law of trigonometric functions.

Detecting Δx and Δy from the position of the shielding means B and calculating the angle θ can be realized by an electric circuit.

[Embodiment] FIGS. 3A and 3B show a beam traveling direction measuring apparatus in a cyclotron apparatus according to an embodiment of the present invention. In FIG. 3A, a gap through which the beam passes is formed between the deflector electrode 10 and the septum electrode 12. It is assumed that the ion beam is incident from below in the figure.

A detection head 14 is arranged in front of a beam entrance formed by the deflector electrode 10 and the septum electrode 12. The detection head is formed of, for example, a metal electrode plate, and has a configuration in which a current corresponding to a beam current flows when an ion beam is incident.

At a predetermined position in front of the detection head 14, there is disposed a shielding head 16 that is disposed in parallel with the detection head and that can translate relatively to the detection head. Shielding head
16 is formed of, for example, graphite, and has a detection head
14 is electrically insulated.

The position of the shielding head 16 is precisely controlled by driving means such as a driving motor 18, and a relative position signal is supplied to a signal processing circuit 20. The current received by the detection head 14 is supplied to the signal processing circuit 20 as a detection signal. Detection head
The detection signal from 14 and the relative position signal from drive motor 18 are connected to CPU 23 via interface 21. In the signal processing circuit 20, the CPU 23 processes the signal and performs a logical operation. The memory 25 stores necessary information,
Retrieve the stored information as needed.

Also, the display device 29 is an interface 27 for the display device.
The operator can read necessary information on the screen of the display device 29.

The drive current for the drive motor 18 is also determined by a signal processing circuit.
Supplied from 20.

In beam adjustment, the detection head 14 is connected to the deflector electrode
It is arranged in front of a beam entrance formed by the septum electrode 10 and the septum electrode 12. First, the ion beam is adjusted so that the ion beam enters the beam entrance properly. However, if the direction of the ion beam is unknown at this time, the ion beam collides with the surface of the deflector electrode 10 or the surface of the septum electrode 12 and disappears. After adjusting the ion beam to irradiate the tip of the detection head 14, the shielding head 16 is operated to gradually shield the ion beam. When the shielding head 16 has almost completely shielded the ion beam, there is no ion beam incident on the detection head, and the current is reduced to zero.

FIG. 3 (B) shows an enlarged view of the measuring head portion. It is assumed that an ion beam is incident on the detection head 14 from the direction of the arrow. When the shielding head 16 moves from right to left in the drawing and reaches the position shown by the broken line, the detection head 14 is completely shielded by the beam. At this time, the detection head 14
The distance between the shielding head 16 and the shielding head 16 is w.
If the tip of the beam comes out ahead of the tip of the detection head by the length d ', the incident angle θ' of the beam is θ '= arctan (d' / w).

Since the distance w between the heads is a constant, the protruding length d 'is obtained by performing signal processing on an electric signal indicating the amount of movement of the shielding head 16 and the ion current detected by the detection head 14, and the angle θ' is determined. calculate.

FIG. 4 is a graph showing how the current of the detected ion beam changes with respect to the scanning distance of the shielding head.

As the scanning distance of the shielding head increases, the detection beam current starts to gradually decrease after passing through a certain value, and the rate of decrease gradually changes to approach zero. In the figure, a portion where the beam current decreases almost linearly is considered to be a signal while the shielding head 16 is gradually shielding the beam.

Finally, the reason why the beam current gradually decreases is that the beam bundle originally has a certain radial divergence.
This is considered to be due to the fact that components incident from directions other than the beam traveling direction indicated by arrows in FIG. Thus, the reduced portion is approximated by a straight line, and a point d 'intersecting with the x-axis is obtained, thereby obtaining a required protruding distance d' of the shielding head.

This operation for determining the position of d 'can be realized in a logic circuit.

In this way, the shielding head 16 with respect to the detection head 14
By measuring the ion beam current detected by the detection head 14 while measuring the relative position of, the incident angle of the ion beam can be measured.

Also, by knowing the position of the detection head 14 itself,
The position of the beam itself can also be known. Therefore, by knowing the position of the beam and its traveling direction, it is possible to adjust a beam handling device such as a cyclotron with high accuracy.

As described above, the embodiment in which the traveling direction of the charged beam is measured has been described by taking the cyclotron handling the ion beam in the vacuum vessel as an example, but the traveling direction of various beams that generates an electric signal by irradiation of the beam is measured. The present invention can be applied.

 FIG. 5 shows another embodiment of the present invention.

The detection head 34 has a planar detection surface, and has a number of detection elements Dij arranged in a matrix in the detection surface. That is, when the beam is incident on the detection surface of the detection head 34, it is possible to know which detection element the beam is incident on.

The shielding head 36 is still planar, and the detection head
It has sides parallel to the rows and columns of the 34 detector elements Dij. This shielding head 36 can move two-dimensionally in parallel with the plane of the detection head 34.

At least some of the detection elements Dij of the detection head 34 are irradiated with the beam, and the shielding head 36 is two-dimensionally scanned to measure how the detection current of each detection element Dij changes. Thereby, the incident direction of the incident beam can be three-dimensionally measured.

Although the embodiments have been described above, the present invention is not limited to these embodiments. For example, it will be apparent to those skilled in the art that various changes, modifications, improvements, combinations, and the like can be made.

[Effect of the Invention] As described above, the traveling direction of a beam can be measured in an apparatus that handles a beam that cannot be seen.

By knowing the direction of travel of the beam, a device utilizing the beam can be effectively adjusted and its ability can be fully demonstrated.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing the measurement principle of the present invention, FIG. 2 is a schematic plan view for explaining ion orbits in a cyclotron, and FIGS. 3 (A) and (B) show an embodiment of the present invention. FIG. 3 (A) is a block diagram of the measurement system, FIG. 3 (B) is an enlarged view of the measurement head portion, and FIG. 4 is how the detected beam current changes according to the scanning of the shielding head. FIG. 5 is a partial perspective view showing another embodiment of the present invention. In the figure, 10 ... deflector electrode 12 ... septum electrode 14 ... detection head 16 ... shielding head 18 ... drive motor 20 ... signal processing circuit 21, 27 ... interface 23 ... CPU 25 ... memory 29 ... ... Display device 34 ... Detection head 36 ... Shielding head 50 ... Cone support tube 51 ... Ion source 52 ... Ion beam 55, 56 ... D 57 ... High frequency power supply 60 ... Deflector electrode 61 ... Extracted ions beam

Claims (3)

(57) [Claims] 1. A beam detecting means capable of generating an electrical detection signal according to a beam amount by directly exposing to a beam, and a beam can be shielded, and a relative position with respect to the beam detecting means can be determined. Controllable beam shielding means, relative position signal generating means capable of generating an electrical relative position signal indicative of the relative position, and a function of said electrical relative position signal to determine the direction of beam travel. A signal processing circuit that processes the electrical detection signal. 2. A position where said signal processing circuit completely blocks the beam incident on said beam detection means for the first time from a change in said electrical detection signal as a function of said electrical relative position signal. The beam traveling direction measuring device according to claim 1, wherein the beam traveling direction is calculated by calculating the following formula. And a position measuring means for generating an electrical absolute position signal indicating an absolute position of one of the beam detecting means and the beam shielding means. The beam traveling direction measuring device according to claim 1, wherein the beam traveling direction measuring device can measure the beam traveling direction.