JPH0422053A - Linear filament type electron gun - Google Patents

Abstract

PURPOSE:To obtain sufficient electron beam current intensity between electron guns and restrain divergence of an electron beam at the outermost end of each electron gun by making the form of the grid of one electron gun regarding the direction of the major axis nonsymmetrical, the electron guns being located at both ends. CONSTITUTION:The outside and inside portions of each filament 2a, 2b with respect to a center position line A extending in the direction of the major axis of an electron beam opening 21a are G11, G12, respectively, and each filament 2a, 2b is formed in a non-symmetrical way. In this case, G11<G12, and each filament 2a, 2b is so formed that each length G11,G12 and the length of each filament in the direction of its major axis are in such a relation to each other as to cause a grid to generate a flat area within the area of the length G11 outside the center position line A and generate a divergence area within the area of the length G12 inside the center position line A. An electron beam emitted from each filament 3a, 3b therefore diverges on the inside portion of each filament 2a, 2b but scarcely diverges on the outside portion.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a linear filament type electron gun, and in particular, to a linear filament type electron gun that is used as a heating source for generating a rectangular metal vapor flow to increase the efficiency of generating the vapor flow. The present invention relates to a linear filament type electron gun that can perform

[Conventional technology]

Conventional linear filament type electron guns have been developed in which the length of the linear filament (or cathode) is about ten centimeters. However, no single device longer than that has currently been developed, and in order to obtain a longer electron beam, the current method is to use multiple linear filament type electron guns adjacent to each other in a straight line in the vertical direction. They need to be placed side by side.

The configuration of a typical conventional linear filament type electron gun will be explained with reference to FIGS. 6 and 7. This linear filament type electron gun has substantially the same configuration as the three-electrode type electron gun disclosed in, for example, Japanese Patent Publication No. 1-204340,
The grid has a configuration in which the grid is formed and installed in a symmetrical positional relationship with respect to the linear filament etc. as will be described later. FIG. 6 is an overall front view, and FIG. 7 is a partial plan view thereof. The details will be explained below according to the drawings.

In FIG. 6, 601 is an anode, 602 is a grid, and 603 is a filament. The anode 601 is a metal plate having a rectangular electron beam extraction hole 601a, is supported on a flange 605 by a metal support 604, and is generally held at ground potential. The grid 602 has a substantially similar shape to the anode 601 and is made of a metal plate. 602a is a rectangular electron beam extraction hole. Grid 602 is disposed over flange 605 and is held insulated and at a negative potential by support insulator 606. grid 60
The potential No. 2 is applied through the grid current introduction terminal 607 and the grid lead wire 608. Filament 603 is made of a material with high electron radiation, such as tungsten, and is supported by filament support insulator 609 and insulated from flange 605 . A voltage is applied to the filament 603 from a filament current introducing terminal 610 through a filament lead wire 611.

The linear filament type electron gun shown in FIG. 6 is called a direct heating type, and a filament 603 serves both as a cathode as an electron emission source and as a heater for heating the cathode. The filament 603 is held at a high temperature of about 2000 to 2500°C and at the same time held at a negative potential of several tens of kilovolts. Thermionic electrons emitted from the filament 603 are accelerated and pass through the electron beam extraction hole 602a of the grid 602 and the electron beam extraction hole 601 of the anode 601.
a, and is emitted from the anode 601 as an electron beam. The grid 602 is held at a potential several kilovolts more negative than the filament 603, and has the function of suppressing divergence and converging the electron beam.

[Problem to be solved by the invention]

The conventional linear filament type electron gun having the above configuration has the following characteristics with respect to operating characteristics determined depending on its shape.

In FIGS. 6 and 7, the dashed-dotted line A indicates the center position of the linear filament type electron gun, respectively. With respect to this center position line A, an opening length G and a length F are defined on the left and right sides of each of the grid 602 and the filament 603 in the long axis direction. In the configuration of the linear filament type electron gun shown in FIGS. 6 and 7, the grid 602 and the filament 603 are arranged symmetrically with respect to the center position line A. The current intensity distribution in the long axis direction of the electron beam generated by the linear filament type electron gun is determined depending on the relative relationship between the length F and the aperture length G. This will be explained based on FIGS. 8 and 9.

In FIG. 9, the horizontal axis shows the ratio Gt/Ft, and the vertical axis shows the longitudinal intensity distribution (peak/average) of the electron beam current. In FIG. 9, when the ratio reaches a value of about 1.5 or more, a diverging region is formed at the end of the electron beam in the long axis direction. This state is shown in FIG. 8(a). In FIG. 8, the horizontal axis represents the position in the long axis direction of the electron beam, and the vertical axis represents the electron beam current intensity. In Figure 9, the ratio is approximately 1.1 to 1.5.
When the electron beam current intensity takes a value between the two, a flat region is formed in which the top portion is flat and both end portions rise, as shown in FIG. 8(b). When the ratio takes a value of about 1.1 or less, a peaking region is formed where both ends rise sharply and a peak occurs, as shown in FIG. 8(c).

In addition, data obtained by actually measuring the distribution characteristics of the divergent region, the distribution characteristics of the flat region, and the distribution characteristics of the peaking region shown in FIG. 9 are shown in FIG. 10 (a).

Shown in (b) and (c). In this measurement, the accelerating voltage was set to 50
KV, the electron beam output is approximately several hundred kilowatts.

Therefore, when a long linear filament type electron gun is manufactured by arranging a plurality of linear filament type electron guns adjacent to each other in the long axis direction, when using a conventional linear filament type electron gun, The following problems occur due to the shape.

When linear filament type electron guns having the electron beam current intensity characteristics shown in FIG. 8(a) are arranged in series, the electron beam becomes divergent at both outermost ends of the lined up linear filament type electron guns. There is a problem that the efficiency of using the electron beam decreases. There is also a risk of damaging containers such as crucibles. Furthermore, if linear filament type electron guns having the electron beam current characteristics shown in FIG. A problem occurs in that the electron beam current intensity between the two is significantly reduced.

An object of the present invention is to obtain sufficient electron beam current intensity between the electron guns when a long linear filament type electron gun is manufactured by connecting a plurality of linear filament type electron guns in the longitudinal direction. The object of the present invention is to provide a long linear filament type electron gun that can suppress the divergence of the electron beam at the outermost end and satisfy these conflicting technical requirements.

[Means to solve the problem]

A first linear filament type electron gun according to the present invention is a linear filament type electron gun in which a plurality of three-electrode type electron guns each having an anode, a grid, and a filament are arranged in series in the longitudinal direction to increase the length. , is characterized in that the shape of at least one of the grids in the long axis direction of the electron guns located at both ends is asymmetrical.

In the second linear filament electron gun according to the present invention, in the first configuration, the asymmetric shape of the grid of the electron gun located at the end is a grid with respect to the generation state of the current intensity distribution of the electron beam emitted from the filament. The feature is that the inner side forms a divergent area and the outer side of the grid forms a flat area.

[Effect]

In the first and second linear filament type electron guns according to the present invention, the grid length of the conventional linear filament type electron gun is By eliminating the axially symmetrical shape and creating an asymmetrical shape, it has become possible to generate an electron beam current distribution that suits the purpose. In particular, in the second linear filament electron gun, for example, the electron guns located at both ends of a plurality of linear filament electron guns installed in series are arranged so that divergence occurs on the inside and flat distribution characteristics occur on the outside. It is possible to generate electron beam current distribution characteristics that are optimal for a long linear filament type electron gun.

〔Example〕

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a front view showing a first embodiment of a linear filament type electron gun according to the present invention, in which two sets of filaments and grids are arranged in series in the longitudinal direction. 1
One basic linear filament type electron gun is composed of a set of filaments and a grid. 1 is the anode,
2a and 2b are grids, and 3a and 3b are filaments. Grid 2a and filament 3 a % grid 2
b and filament 3b each constitute a linear filament type electron gun, and the anode 1 is disposed in common to these electron guns. The anode 1 is supported by an anode support 4 erected on a flange 5, and has an electron beam extraction hole 1a. grid 2a
, 2b are supported by support insulators 6a and 6b respectively erected on the flange 5, and are connected to the electron beam extraction hole 21.
a, 21b. The filaments 3a and 3b are supported by filament support insulators 7a and 7b respectively erected on the flange 5. 8a and 8b are grid current introduction terminals for applying a required voltage to the grids 2a and 2b, respectively, and 9a and 9b are filament current introduction terminals. Further, 10a and 10b are filament lead wires, respectively.

A voltage is applied from a separately installed filament power source through the filament current introduction terminal to the elongated linear filament type electron gun having the above configuration and having two linear filament type electron guns installed in series as described above, and the filament 3a , 3b independently to about 2300°C, and about -30°C to the flange 5 which is at ground potential.
Hold at KV. Also, for grids 2a and 2b,
Grid current introduction terminal 8 from a separately installed grid power supply
filaments 3a and 8b respectively independently.
A negative potential approximately 1KV lower than 3b is applied. Since the anode 1 is electrically connected to the flange 5 via the anode support 4, it has a positive potential of about 30 KV with respect to the filaments 3a and 3b.

When the filaments 3a and 3b are heated to a high temperature, thermoelectrons are emitted from each filament.

The emitted thermoelectrons are transferred to the anode 1 and the filament 3a,
Accelerated by the electric field formed between 3b and 30KeV
The electron beam passes through the electron beam extraction holes 21a, 21b and la and is emitted into the space above the anode 1 as an electron beam having an energy of . The electrons forming the electron beam repel each other due to their own negative charges, and the electron beam tends to diverge along its range. Therefore, a predetermined negative potential is applied to the grids 2a and 2b located in the middle of the accelerating electric field to converge the electron beam.

Next, the shape characteristics of the grids 2a and 2b will be explained. 1st
As shown in the figure, regarding the dimensional form of the electron beam extraction hole 21a in the long axis direction, the filaments 2a and 2b are formed asymmetrically with respect to the center position line A, with the outside being GI1 and the inside being G and 2. ing. In this case, Gfl<GI2, and describing the relationship between each length G, , G, 2 and the length in the long axis direction of the filament, in the area of length Gtl outside the center position line A, the grid is is formed to generate a flat area, while the center position line A
In a region of length G, 2 inside, the grid is formed to generate a divergent region. As a result, the electron beam emitted from the filament 3a diverges inward in FIG. 1, but hardly diverges outward. Similarly, the electron beam emitted from the filament 3b is also
Divergence occurs inwardly, but hardly any divergence occurs outwardly. As a result, as shown in FIG. 2(b), the electron beam intensity in the gap between the two filaments 3a and 3b increases due to mutual divergence, and the second
Compared to the electron beam intensity characteristics of the linear filament type electron gun with the conventional configuration shown in FIG. 3(a), the distribution is flatter.

In addition, in FIG. 2(b), the broken line indicates the filament 3a.
, 3b shows the intensity characteristics of the electron beams emitted from each of them.

Next, a second embodiment of the present invention will be described with reference to FIGS. 3 and 4. In this embodiment, three basic linear filament type electron guns are arranged in series to form a longer linear filament type electron gun. In FIG. 3, elements that are substantially the same as those explained in FIG. 1 are designated by the same reference numerals.

1 is an anode, 1a is an electron beam extraction hole, 4 is an anode support, and 5 is a flange. In each case, the overall length in the major axis direction is increased due to the increase in the number of linear filament type electron guns. Of the three grids 2a, 2b, 2c and the three filaments 3a, 3b, 3c, the grids 2a, 2b and filaments 3a, 3 located on the left and right sides
b is the same as that explained in the first embodiment. Therefore, regarding the configuration of their surroundings, for example, the configuration of the grid current introduction terminal 8a, the filament current introduction terminal 9a, etc., and the asymmetry regarding the shape of the electron beam extraction holes 21a and 21b in the long axis direction of the grid, the above-mentioned first This is the same as in the embodiment. On the other hand, grid 2 located in the center
C is formed such that the dimension in the long axis direction of the electron beam extraction hole 21c is formed symmetrically with respect to the above-mentioned center position line, and the length thereof forms a divergence region with respect to the filament. Therefore, the electron beam emitted from the filament 3c has a characteristic that it diverges to both sides. In addition, filament 3C and grid current introduction terminal 8a
The configurations of the filament current introducing terminal 9a, etc. are the same as the others, and the electrical conditions are also the same as in the first embodiment.

According to the elongated linear filament type electron gun having the above configuration, the electron beam diverges inside the linear filament type electron guns on both sides, and the electron beam diverges at both ends of the linear filament type electron gun located in the center. Since the electron beam diverges at a certain point, an electron beam current intensity distribution as shown by the solid line in FIG. 4 can be obtained. According to this embodiment, a relatively high electron beam current intensity can be obtained even in the gaps between the linear filament type electron guns 3a, 3b, and 3c. Furthermore, there is almost no dispersion in the distribution of the electron beam current intensity at the outer ends of the linear filament type electron guns on both sides, which is the same as in the first embodiment. In FIG. 4, the broken line indicates the electron beam current intensity distribution from each linear filament type electron gun.

In the second embodiment described above, three linear filament type electron guns are installed in a row, but the linear filament type electron guns on both sides remain as they are, and if the number of linear filament type electron guns in the center position is further increased, more linear filament type electron guns will be generated. It is possible to increase the number of guns that can be connected in series, and thereby it is possible to further increase the length of the linear filament type electron gun.

In the above embodiment, a filament was used as the electron generating means, but even if a cathode that emits electrons and a heater that heats the cathode are used, it is possible to maintain the same dimensional relationship in the long axis direction and create a long filament. A linear filament type electron gun can be manufactured. Furthermore, although the voltage application to each of the grids is performed independently, in principle, it is also possible to configure the grid so that the current is supplied all at once from a single power source.

However, even in such a case, it is desirable to be able to adjust the applied voltage for each grid.

Further, in a plurality of linear filament type electron guns arranged in series, the object of the present invention can be achieved if at least one of the electron guns at both ends is configured as described above.

FIG. 5 is a configuration diagram showing an example of the use of the linear filament type electron gun according to each of the embodiments described above. In this example,
The metal 31 housed in the crucible 32 is irradiated with an electron beam 34 emitted from the elongated linear filament type electron gun 33 according to each of the embodiments described above, and the metal 31 is evaporated. . 35 is metal vapor, and the metal vapor 35 rises in a space surrounded by a vapor enclosing plate 36 and is supplied to a sample 37. The crucible 32 is disposed within a main vacuum vessel 38, and the main vacuum vessel 38 is brought to a predetermined vacuum state by a main vacuum pump 39. On the other hand, the linear filament type electron gun 33 is disposed within a sub-vacuum container 40, and this sub-vacuum container 40 is brought into a predetermined vacuum state by a sub-vacuum pump 41. electron beam 34
is radiated into the main vacuum vessel 38 through a window formed in the wall 42 at the boundary between the main vacuum vessel 38 and the sub-vacuum vessel 40.

This window is provided with a shutter device 43 that can be opened and closed.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, a plurality of existing linear filament type electron guns are used and connected in series to produce a long linear filament type electron gun that operates effectively. Furthermore, by using a grid having an asymmetrical shape, various electron beam current distributions can be generated depending on the purpose.

[Explanation of symbols]

11 ・ ・ ・ １　a　・・・・・ 2b. 3b. 3a. 2a. 5th ・ ３３　・・ ·anode ・Electron beam extraction hole C ·grid C ·filament ・Flange ・Linear filament type electron gun

Claims (2)

[Claims] (1) In a linear filament type electron gun that is elongated by arranging a plurality of three-electrode type electron guns including an anode, a grid, and a filament in the longitudinal direction, at least one of the electron guns located at both ends A linear filament type electron gun characterized in that one of the grids has an asymmetrical shape with respect to the long axis direction. (2) In the linear filament type electron gun according to claim 1, the asymmetrical shape of the grid of the electron gun is such that the inner side of the grid forms a divergent region with respect to the generation state of the current intensity distribution of the electron beam emitted from the filament. A linear filament type electron gun characterized in that the outside of the grid forms a flat area.