JPH05234698A - Accelerating tube - Google Patents

Abstract

PURPOSE:To proper suppress flashover on a dielectric vacuum surface, and to increase evacuation rate of an accelerating tube, and to absorb generated secondary ions the low stages of accelerating energy. CONSTITUTION:In an accelerating tube formed by sandwiching an insulating ring 14 by a positive electrode flat plate electrode 10 and a negative electrode flat plate electrode 12, the positive electrode flat plate electrode 10 is provided with a cylindrical electrode 10A faced to the vacuum surface 10A of the insulating ring 14 and protruded from the positive electrode flat plate electrode 10 toward the negative electrode flat plate electrode 12. In addition, in a multi-stage electrode direct current accelerating tube formed by alternately superimposing insulating rings, and accelerating tube partition electrodes for acceleration in which holes for beam transmission are punched, a hole for evacuation is punched in each accelerating partition electrode at the peripheral part of the hole for beam transmission. Each accelerating tube partition electrode is superimposed to align the hole for evacuation with the beam accelerating axial direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an accelerating tube for accelerating an ion or electron beam in a vacuum atmosphere, and in particular, a direct current for realizing a compact ion implanter and an electron beam irradiator for accelerating a large current beam in a strong electric field. Regarding the accelerator tube.

[0002]

2. Description of the Related Art Generally, an accelerating tube of this type is constructed by alternately stacking metal plate electrodes and dielectric rings (insulating rings), and a high vacuum is maintained inside the accelerating tubes. In addition, a beam passage hole is formed in the metal plate electrode coaxially with the center axis of the dielectric ring in order to accelerate the charged particle beam. The beam passage hole also serves as a vacuum exhaust hole for the acceleration tube.

In some large-sized accelerating tubes, a dedicated vacuum exhaust hole is provided around the beam passage hole. The upper limit of the potential gradient in the axis direction of the acceleration tube that can be maintained by the conventional acceleration tube is 2 MV / m (2 million volts / m). This upper limit tends to decrease as the intensity of the accelerating beam current increases, and as the accelerating tube becomes longer and the accelerating voltage becomes higher. This is because various types of loading are likely to occur in the accelerator tube depending on how it is used.

The types of loading are mainly as follows. (1) Dielectric vacuum creeping flashover (2) Electron loading (3) Paschen Breakdown (4) Positive and negative ion exchange loading [Dielectric vacuum creeping flashover] Figs. 18 to 20
FIG. 4 is a diagram showing a typical example of a plate electrode and a dielectric ring in a conventional acceleration tube. In these drawings, 1 is an anode electrode, 2 is a cathode electrode, and 3 is a dielectric ring.

In the dielectric vacuum creeping flashover, electrons are extracted by electric field emission from a triple point T where the cathode electrode 2, the dielectric ring 3 and the vacuum are in contact with each other, striking the dielectric vacuum creeping surface, and in that process Gas discharge is generated on the surface of the dielectric vacuum caused by an electron avalanche toward the anode electrode 1 while further generating secondary electrons and neutral gas from the surface of the vacuum (H. Craig Miller, "Surfac
e Flashover of Insulators ", IEEE Transactions Electr
ical Insulation, Vol. 24 No. 5, 1989, and the references cited therein).

FIG. 19 shows a conventional electron in which a shield electrode 2A protruding from the cathode electrode 2 toward the anode electrode 1 is provided near the corner of the cathode electrode 2 in order to reduce the magnitude of the external electric field acting on the triple point T. It shows avalanche deterrence measures. [Electron Loading and Paschen Breakdown] In a high voltage DC accelerating tube, the accelerating tube length must be increased in proportion to the accelerating voltage due to the relationship of the accelerating tube voltage holding ability when the accelerating voltage becomes higher. At this time, the vacuum degree in the acceleration tube is
It decreases in inverse proportion to the accelerating pipe length. When the integrated value obtained by multiplying the vacuum degree in the accelerating tube by the accelerating tube length exceeds a certain value determined by Paschen's law, avalanche multiplication of electrons occurs in the residual gas in the accelerating tube and the accelerating voltage collapse due to gas discharge in the accelerating tube. Leads to

During the acceleration of the charged particle beam, secondary electrons are produced by the collision between the residual gas in the accelerating tube and its beam particles. The secondary electrons are accelerated by the electric field in the accelerating tube, and finally collide with some electrode or the beam duct, and emit a braking X-ray from there. If the degree of vacuum in the accelerating tube is poor, the secondary electron current intensity may exceed the accelerating beam current intensity. The amount of braking X-rays generated at that time is also great, and the radiation shielding equipment for humans from the accelerator becomes large-scale. Also, braking X
In some cases, the ionization current due to the ionization of the insulating gas surrounding the accelerator high voltage terminal of the line exceeds the accelerator generated current capacity.

The above is the main mechanism that causes electron loading, and is a phenomenon that commonly appears at that time. [Positive / Negative Ion Exchange Loading] Positive / negative ion exchange loading means that when positive / negative secondary ions hit these electrodes between electrodes having a potential difference in the accelerating tube and the secondary ion emission coefficient exceeds a certain threshold, the This is a discharge phenomenon that occurs when the secondary ion current increases like an avalanche (JLMackibben,
Los Alamos Scientific Laaboratory Report LA-5376-M
S, 1973, and references therein).

Since the secondary ion emission coefficient depends on the energy of the ions striking the electrode, the positive and negative ion exchange loading suddenly occurs when the acceleration tube voltage reaches a certain value. The secondary ion species are mainly pollutants attached to the electrode surface. Therefore, if the vacuum degree in the acceleration tube is increased, the amount of contaminants attached to the electrode surface can be reduced.

[0010]

However, when the shield electrode 2A is placed as shown in FIG. 19 in order to suppress the above-mentioned dielectric vacuum creeping flashover, the insulating ring 3 has a target 2 MV / m. It was found that it could not withstand the electric potential gradient of. Further, electron loading and Paschen Breakdown can be stopped by improving the vacuum degree in the acceleration tube. The simplest way to improve the degree of vacuum in the acceleration tube is to enlarge the beam passage hole of the acceleration tube. However, in this case, the degree of freedom is increased in the positive and negative ion exchange paths between the electrodes in the accelerating tube via the beam passage hole, so that so-called micro discharge is ignited at a lower accelerating voltage.

On the other hand, in order to stop the positive and negative ion exchange loading, in the conventional accelerating tube designing method, the accelerating beam passage hole formed in the flat plate electrode is made as small as possible, and a plurality of evacuating holes are formed in the beam. It is provided around the passage hole. However, at this time, since the positive and negative ion exchange discharges are easily ignited via the vacuum exhaust hole, the position of the vacuum exhaust hole is slightly shifted in the circumferential direction of the dielectric ring about the acceleration tube axis. ing.

The larger the deviation of this angle, the less likely the electric discharge will occur, but the vacuum evacuation speed in the accelerating tube will decrease.
There is a problem that the above-mentioned electronic loading and other loadings are likely to occur. Furthermore, even if the vacuum degree in the acceleration tube is improved, contaminants cannot be completely removed by it, so that there is a limit in maintaining the potential gradient and voltage of the acceleration tube, and the potential gradient of 2 MV / m is conventionally used. It was a practical upper limit. It is also experienced that the upper limit decreases with increasing accelerating voltage and accelerating beam current intensity. It is considered that this is partly because the active gas generated by the collision between the acceleration beam and the residual gas in the acceleration tube adheres to the electrode in the acceleration tube and is not easily separated from the electrode. In particular, since the active gas is produced on the beam axis, it has a high probability of adhering to the periphery of the beam passage hole of the acceleration electrode. Further, since the place is the starting point and the ending point of the secondary charged particles at the time of positive and negative ion exchange loading, it is a place that greatly affects the difficulty of positive and negative ion exchange loading.

The present invention has been made in view of such circumstances, and it is possible to satisfactorily suppress the dielectric vacuum creeping flashover, and to increase the vacuum evacuation speed in the acceleration tube. It is an object of the present invention to provide an accelerating tube capable of absorbing secondary ions at a stage where the acceleration energy is low.

[0014]

In order to achieve the above object, the present invention provides an acceleration tube having an insulating ring sandwiched between a positive electrode plate electrode and a negative electrode plate electrode, facing the vacuum creeping surface of the insulating ring, A cylindrical electrode protruding from the positive electrode plate electrode toward the negative electrode plate electrode is provided on the positive electrode plate electrode.

Further, in a multi-stage electrode DC accelerating tube in which an accelerating tube partition electrode for accelerating having a beam passage hole and an insulating ring are alternately stacked, a beam passage hole of each accelerating tube partition electrode is formed. It is characterized in that a hole for vacuum evacuation is formed in the peripheral portion, and the electrodes for accelerating tubes are superposed so that the holes for vacuum evacuation are aligned in the beam acceleration axis direction. Furthermore, a cylindrical electrode having an outer diameter that does not reach the vacuum exhaust hole, an inner diameter larger than the beam passage hole, and a height smaller than the gap between the acceleration tube partitioning electrodes is formed. Each acceleration tube partition electrode is provided so that its central axis coincides with the beam acceleration axis, and / or each acceleration tube partition electrode located inside the insulating ring is bent into a truncated cone shape and protrudes, and its tapered portion or flat plate It is characterized in that a hole for evacuation is formed in the portion.

[0016]

According to the present invention, the cylindrical electrode facing the vacuum surface of the insulating ring and projecting from the positive plate electrode toward the negative plate electrode is provided on the positive plate electrode. As a result, the electrons created at the triple point are attracted to the cylindrical electrode at the anode potential,
Since it accelerates toward it, electron avalanche discharge on the vacuum surface of the insulating ring is less likely to occur, and the flashover voltage on the dielectric vacuum surface is improved.

Further, a vacuum exhaust hole is formed in the peripheral portion of the beam passage hole of each acceleration tube partition electrode, and the acceleration tube partition electrodes are superposed so that the vacuum exhaust hole is aligned in the beam acceleration axis direction. I am trying. As a result, the vacuum evacuation speed in the acceleration tube can be increased. Furthermore, a cylindrical electrode having an outer diameter that does not reach the vacuum exhaust hole, an inner diameter larger than the beam passage hole, and a height smaller than the gap between the acceleration tube partitioning electrodes is formed. Provided on each acceleration tube partition electrode so that the central axis coincides with the beam acceleration axis,
And / or each accelerating tube partitioning electrode located inside the insulating ring is bent into a truncated cone shape and protruded, and a vacuum exhaust hole is formed in the tapered portion or the flat plate portion. As a result, a tilted electric field that is not parallel to the axis of the accelerating tube is formed, and the tilted electric field can cause the secondary ions to largely deviate from the beam accelerating axis direction. It can be applied to and absorbed there.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of an accelerating tube according to the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a cross-sectional view of a main part showing a first embodiment of a flat plate electrode and a dielectric ring of an accelerating tube according to the present invention. As shown in the figure, the accelerating tube is configured by sandwiching an insulating ring 14 between a positive plate electrode (anode electrode) 10 and a negative plate electrode (cathode electrode) 12, and the anode electrode 10 is insulated. A cylindrical electrode 10A that faces the vacuum surface 14A of the ring 14 and that projects from the anode electrode 10 toward the cathode electrode 12 is integrally formed.

According to the accelerating tube having the above-mentioned structure, the action of the external electric field at the location of the triple point T becomes stronger, but the electrons produced at the triple point T are attracted to the cylindrical electrode 10A at the anode potential and toward it. Because of acceleration, electron avalanche discharge on the vacuum creeping surface 14A of the insulating ring 14 is hard to be induced. Therefore, the dielectric vacuum creeping flashover voltage was improved, and according to the experiment, the improvement rate was several times that of the conventional one.

2 to 6 are sectional views showing the essential parts of the second to sixth embodiments, respectively. The same parts as those in FIG. 1 are designated by the same reference numerals, and detailed description thereof will be omitted. In the second embodiment shown in FIG. 2, the shape of the insulating ring 16 is different from that of the first embodiment. That is, the insulating ring 16 has a trapezoidal vertical cross-section and has a tapered vacuum creeping surface 16A.

The third embodiment shown in FIG. 3 is a cathode electrode 1.
The shape of 8 is different from that of the first embodiment. That is, the cathode electrode 18 has a step at the cathode corner electrode in the direction opposite to the anode electrode 10. According to the cathode electrode 18 having this structure, an external electric field stronger than that in the first and second embodiments acts to attract electrons generated from the triple point T to the cylindrical electrode 10A. Therefore, the dielectric vacuum creeping flashover voltage is higher than that of the first and second embodiments.

In the fourth embodiment shown in FIG. 4, an insulating ring 16 having a trapezoidal vertical cross section is used, and only the shape of this insulating ring 16 is different from the third embodiment. Figure 5
Also, the fifth and sixth embodiments shown in FIG. 6 differ from the third and fourth embodiments in the shape of the anode electrode 20, especially the shape of the cylindrical electrode 20A fixed to the anode electrode 20. There is. That is, the tip of each of the cylindrical electrodes 20A is formed in a knife edge shape.

FIG. 7 and FIG. 8 are enlarged views of a main part including each cylindrical electrode, and schematically show the difference in the shape of each cylindrical electrode and the feature of the trajectory of secondary ions. Cylindrical electrode 10A
20A, when the distance between the cylindrical electrode tip and the cathode electrode is fixed, in the cylindrical electrode 10A having a rounded tip, the positive and negative ion exchange occurrence probabilities between the electrode tip and the cathode electrode 18 are both Since the facing area of the electrodes is larger than that in the case of the knife edge-to-plate electrode and the effect of removing secondary ions from the outside of the electrode gap is small, an inter-electrode exchange discharge is likely to occur. Therefore, the vacuum insulation ability between the flat plate and the rounded cylindrical electrode 10A at the tip is lower than that in the case where the tip is a knife electrode 20A.

Although the tip of the cylindrical electrode 20A is a single-edged blade, the tip may be double-edged as in the cylindrical electrode 20B as shown in FIG. FIG. 10 is a plane view showing a seventh embodiment of the acceleration tube according to the present invention, and FIG.
It is sectional drawing which follows the 11th line. This accelerating tube is a multi-stage electrode DC accelerating tube in which accelerating tube partitioning electrodes 30 and insulating rings 32 are alternately stacked, and each accelerating tube partitioning electrode 30
The beam passage hole 30B for accelerating the charged particle beam 34 is formed in the central portion thereof, and four vacuum exhaust holes 30C are formed in the peripheral portion of the beam passage hole 30B.

Further, the accelerating tube partitioning electrodes 30 in each stage are overlapped so that the vacuum exhaust holes 30C are aligned in the beam accelerating axis direction, that is, no angular deviation in the circumferential direction occurs. Further, the cylindrical electrode 30A as described above is fixed to the acceleration tube partitioning electrode 30. According to the accelerating tube configured as described above, the cylindrical electrode 30A distorts the ambient electric field, and an axisymmetric tilted electric field that is not parallel to the accelerating tube axis is created around the vacuum exhaust hole 30C.

When an inclined electric field is applied to the periphery of the vacuum exhaust hole 30C in this manner, loading through the vacuum exhaust hole 30C, which tends to occur when the vacuum exhaust holes 30C are superposed in phase, is unlikely to occur. Become. This is because the orbits of secondary electrons and positive and negative ions that have passed through the vacuum evacuation hole 30C and are accelerated between the accelerating tube electrodes having a positive and negative potential difference are largely bent from the axis direction of the accelerating tube due to the action of the inclined electric field. This is because the inter-electrode range of particles is reduced. If the average range becomes smaller, the collision energy of ions on the electrode surface becomes smaller, and the efficiency of generating secondary ions and electrons decreases, so that various types of loading are less likely to occur. Incidentally, FIG. 11 schematically shows the equipotential lines and the trajectories of the secondary charged particles starting from a certain electrode.

FIG. 12 is a plan view showing an eighth embodiment of the accelerating tube according to the present invention, and FIG. 13 is a sectional view taken along line 13-13 of FIG. The same parts as those of the seventh embodiment are designated by the same reference numerals, and detailed description thereof will be omitted. The eighth embodiment shown in FIGS. 12 and 13 differs from the seventh embodiment in the shape of the acceleration tube partitioning electrode 36. That is, the accelerating tube partitioning electrode 36 is formed in a concave shape by bending the electrode portion inside the insulating ring 32 into a truncated cone shape. still,
The vacuum exhaust hole 36C is provided outside the tapered portion 36D of the acceleration tube partitioning electrode 36.

By bending the accelerating tube partitioning electrode 36 in a concave shape in this way, an axisymmetric tilted electric field can be created in the peripheral portion of the vacuum exhaust hole 36C, and the same effect as when the cylindrical electrode 30A is provided is obtained. can get. 14 to 15
Are the ninth to eleventh embodiments of the accelerating tube according to the present invention.
It is a section surface showing an example. The same parts as those in the above-described embodiment are designated by the same reference numerals, and detailed description thereof will be omitted.

The ninth embodiment shown in FIG. 14 is different from the seventh embodiment shown in FIG. 11 in the position of the cylindrical electrode 38A fixed to the acceleration tube partitioning electrode 38. That is, the cylindrical electrode 38A fixed to the accelerating tube partitioning electrode 38 is provided with the vacuum exhaust hole 30.
Beam passing hole 30 having an outer diameter not reaching C
It has an inner diameter larger than B. The cylindrical electrode 38A provided at this position can create an axisymmetric tilted electric field not only in the peripheral portion of the vacuum exhaust hole 30C but also in the peripheral portion of the beam passing hole 30B.

As shown in FIG. 14, the cylindrical electrode 38A distorts the ambient electric field and attracts the electrons and negative ions formed around the vacuum exhaust hole 30C and the beam passage hole 30B to the opposing anode, where they are absorbed. To do. By doing so, of the positive and negative ion current loops that support the positive and negative ion exchange loadings, the negative ion current loops are cut off, so the positive and negative ion exchange loadings do not continue. Note that FIG. 17 has the same structure as FIG. 14, and is drawn by a computer by using the electron orbit calculation result as a locus. Also, in the figure, the secondary electrons that started from a certain electrode part of the vacuum exhaust hole are also accelerated in the acceleration tube by the action of the gradient electric field acting on the vacuum exhaust hole before being accelerated to high energy in the acceleration tube. It is shown that it can be received by the electrode.

In the tenth embodiment shown in FIG. 15, the electrode portion inside the insulating ring 32 of the accelerating tube partitioning electrode 40 is bent into a truncated cone shape to form a concave shape, and the eighth embodiment shown in FIG. Although similar to the embodiment, the acceleration tube partitioning electrode 4
The difference is that a vacuum exhaust hole 40C is formed in the taper portion 40D of 0. In the eleventh embodiment shown in FIG. 16, the electrode portion inside the insulating ring 32 of the acceleration tube partitioning electrode 42 is bent into a truncated cone shape to form a concave shape.
Further, a cylindrical electrode 42A similar to that of the ninth embodiment shown in FIG. 14 is provided so that the action of the gradient electric field is further strengthened.

According to the electrode structure of the accelerating tube partitioning electrode 42, the insulating ring 32 is blocked by the electrodes and is not visible at all from the accelerating beam. This is important in protecting the insulating ring 32 under a high potential gradient from ultraviolet rays and soft X-rays associated with the acceleration beam. Now, with respect to the acceleration tube shown in FIG. 1 and the conventional acceleration tube shown in FIG. 18, the applied voltage between the electrodes was gradually increased, and the initial spark voltage was examined.

The insulating ring used is inner diameter × height = 140
The borosilicate glass was 100 mm × 100 mm, and the cylindrical electrode was made of SUS304 having an outer diameter × height = 110 × 90 mm. The portion of the cylindrical electrode facing the cathode was sharpened to form a knife edge. The degree of vacuum in the insulating ring was on the order of 10 ⁻⁶ Torr. The initial dielectric vacuum creeping discharge voltage was 35 to 40 KV without the cylindrical electrode, but increased to 300 KV when the cylindrical electrode was attached.

The experiment on the multi-stage electrode accelerating tube is shown in FIG.
Use the structure shown in, and set the helium beam 3 μA to 6
The number of sparks per day was measured while accelerating at 00 KV for a long time. When the cylindrical electrode was removed, the number of sparks was several to 10 times per day, but when the cylindrical electrode was attached, it was 0. The insulating ring used in the experiment had an inner diameter × height of 60 × 9 mm and an accelerating tube length of 250 mm. The remarkable effect of this cylindrical electrode insertion is that it produces a tilted electric field around the vacuum exhaust hole and an axisymmetric electric field that scatters the electrons and negative ions generated from the periphery of the beam passage hole from the accelerating tube axis. The result of this experiment suggests that it can be attributed to.

[0035]

As described above, according to the acceleration tube of the present invention, the cylindrical electrode facing the vacuum surface of the insulating ring is provided on the positive plate electrode, so that the dielectric vacuum surface flashover is satisfactorily achieved. Can be deterred. Further, since an axisymmetric tilted electric field which is not parallel to the axis of the accelerating tube is formed, the tilted electric field can cause the secondary ions to largely deviate from the beam accelerating axis direction. Can be applied to the electrode in the acceleration tube and absorbed there. This makes it possible to suppress the appearance of positive and negative ion exchange loadings through the evacuation hole, and it becomes possible to arrange the evacuation holes in the same phase in the circumferential direction. In this case, the vacuum evacuation speed can be significantly improved compared to other accelerating tubes that use insulating rings with the same inner diameter, and the acceleration beam generated by the residual gas collision, which has been a problem with the conventional implanter accelerating tube, is accelerated. It is possible to reduce the ratio of the coarse ion beam and the main ion beam that are generated. Furthermore, the improvement of the evacuation speed allows the use of an accelerating tube longer than before, and the accelerating voltage can be increased accordingly. Incidentally, the strong electric field accelerating tube has a simple beam accelerating optical system, and a beam with little distortion can be produced.

[Brief description of drawings]

FIG. 1 is a sectional view of an essential part showing a first embodiment of a plate electrode and a dielectric ring of an accelerating tube according to the present invention.

FIG. 2 is a cross-sectional view of essential parts showing a second embodiment of the plate electrode and the dielectric ring of the accelerating tube according to the present invention.

FIG. 3 is a cross-sectional view of the essential parts showing a third embodiment of the plate electrode and the dielectric ring of the accelerating tube according to the present invention.

FIG. 4 is a cross-sectional view of an essential part showing a fourth embodiment of the plate electrode and the dielectric ring of the accelerating tube according to the present invention.

FIG. 5 is a cross-sectional view of an essential part showing a fifth embodiment of a flat plate electrode and a dielectric ring of an accelerating tube according to the present invention.

FIG. 6 is a cross-sectional view of an essential part showing a sixth embodiment of the plate electrode and the dielectric ring of the accelerating tube according to the present invention.

FIG. 7 is an enlarged view of a main part including the cylindrical electrode shown in FIGS. 1 to 4.

FIG. 8 is an enlarged view of a main part including the cylindrical electrode shown in FIGS. 5 and 6;

9 is an enlarged view of an essential part showing another embodiment of the cylindrical electrode shown in FIG.

FIG. 10 is a plan view showing a seventh embodiment of the acceleration tube according to the present invention.

11 is a cross-sectional view taken along line 11-11 of FIG.

FIG. 12 is a plan view showing an eighth embodiment of the acceleration tube according to the present invention.

13 is a sectional view taken along line 13-13 of FIG.

FIG. 14 is a sectional view showing a ninth embodiment of the accelerating tube according to the present invention.

FIG. 15 is a sectional view showing a tenth embodiment of the accelerating tube according to the present invention.

FIG. 16 is a sectional view showing an eleventh embodiment of the acceleration tube according to the present invention.

FIG. 17 is a drawing in which a computer draws the acceleration tube schematically shown in FIG. 14 and the electron trajectory in the acceleration tube.

FIG. 18 is a sectional view showing a first example of a plate electrode and a dielectric ring of a conventional accelerating tube.

FIG. 19 is a sectional view showing a second example of the plate electrode and the dielectric ring of the conventional accelerating tube.

FIG. 20 is a cross-sectional view showing a third example of the plate electrode and the dielectric ring of the conventional accelerating tube.

[Explanation of symbols]

10, 20 ... Positive plate electrode (anode electrode) 12, 18 ... Negative plate electrode (cathode electrode) 10A, 20A, 20B, 30A, 38A, 42A ... Cylindrical electrode 14, 16, 32 ... Insulating ring 14A, 16A ... Vacuum surface 30, 36, 38, 40, 42 ... Accelerator tube partitioning electrode 30B ... Beam passage hole 30C, 36C, 40C ... Vacuum exhaust hole 34 ... Charged particle beam 36D, 40D ... Tapered portion

Claims (8)

[Claims] 1. An accelerating tube formed by sandwiching an insulating ring between a positive electrode plate electrode and a negative electrode plate electrode, facing a vacuum creeping surface of the insulating ring and from the positive electrode plate electrode toward the negative electrode plate electrode. An accelerating tube characterized in that a protruding cylindrical electrode is provided on the positive plate electrode. 2. The accelerating tube according to claim 1, wherein the cylindrical electrode has a knife edge-shaped tip portion projecting toward the negative plate electrode. 3. A multi-stage direct current accelerating tube comprising an accelerating tube partition electrode for accelerating and a ring for accelerating the beam, and an insulating ring, which are alternately stacked. An accelerating tube, characterized in that a vacuum exhaust hole is provided in the peripheral portion, and the respective acceleration tube partition electrodes are superposed so that the vacuum exhaust hole is aligned in the beam acceleration axis direction. 4. A multi-stage electrode DC accelerating tube in which an accelerating tube partitioning electrode for accelerating a beam passage hole and insulating rings are alternately stacked, having an outer diameter smaller than that of the insulating ring. A cylindrical electrode having an inner diameter larger than that of the beam passage hole and having a height smaller than the gap between the acceleration tube partitioning electrodes is arranged so that the central axis of the cylindrical electrode coincides with the beam acceleration axis. An acceleration tube characterized by being fixed to a partition electrode. 5. A multi-stage direct current accelerating tube in which an accelerating tube partitioning electrode for accelerating a beam passing hole and insulating rings are alternately stacked, wherein a beam passing hole of each accelerating tube partitioning electrode is formed. A vacuum exhaust hole is formed in the peripheral portion, and each accelerating tube partitioning electrode is overlapped so that the vacuum exhaust hole is aligned with the beam accelerating axis direction and has an outer diameter smaller than that of the insulating ring and allows the beam to pass therethrough. A cylindrical electrode having an inner diameter larger than that of the working hole and a height smaller than the gap between the respective acceleration tube partitioning electrodes is attached to each acceleration tube partitioning electrode so that the central axis of the cylindrical electrode coincides with the beam acceleration axis. Accelerator tube characterized by being fixed. 6. The accelerating tube according to claim 4, wherein the cylindrical electrode projects toward the accelerating tube partitioning electrode on the negative potential side, and the projecting tip portion is formed in a knife edge shape. .. 7. A multi-stage electrode DC accelerating tube in which an accelerating tube partition electrode for accelerating having a beam passage hole and an insulating ring are alternately stacked, wherein each accelerating member positioned inside the insulating ring. Bend the tube partition electrode into a truncated cone shape and project it, and make a hole for vacuum exhaust in the tapered part or flat plate part, and superimpose each acceleration tube partition electrode so that the hole for vacuum exhaust is aligned with the beam acceleration axis direction. Accelerator tube characterized by. 8. A cylindrical electrode having an outer diameter that does not reach the vacuum exhaust hole, an inner diameter that is larger than the beam passage hole, and a height that is smaller than the gap between the acceleration tube partition electrodes. The accelerating tube according to claim 7, which is fixed to each accelerating tube partitioning electrode so that the central axis of the cylindrical electrode coincides with the beam accelerating axis.