JP3738641B2 - Filament support structure - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is used for an apparatus including a linear filament such as an electron beam irradiation apparatus, an ion source, and an X-ray generation apparatus, for example, and absorbs expansion during energization heating of the filament to deform and break the filament. More specifically, the present invention relates to a means for preventing the filament support plate from melting at the contact portion between the filament and the filament support plate.
[0002]
[Prior art]
FIG. 2 is a schematic cross-sectional view showing an example of an electron beam irradiation apparatus. This electron beam irradiation device is of a non-scanning type that does not scan the electron beam 12, and a cylindrical shield electrode 4 for electric field relaxation is provided in the cylindrical vacuum vessel 2, and a plurality of these are provided in the shield electrode 4. Are arranged side by side in the front and back direction of the paper surface, and such filament rows are arranged in parallel in this example. However, there may be one row or more than three rows. Each filament 8 is supported at a predetermined distance from the insulating table 10 by a filament support structure described later. Each filament 8 is electrically connected to each other in parallel, for example.
[0003]
The shield electrode 4 has an opening in a portion below the filament 8, and a porous lead electrode 6 is provided there, for example. The vacuum vessel 2 has an opening at a portion below the extraction electrode 6, and an irradiation window 16 having a window foil 14 for separating the inside and outside of the vacuum vessel 2 is provided there.
[0004]
With such a configuration, the electrons emitted from the filaments 8 are used as the electron beams 12, passed through the extraction electrode 6 and transmitted through the window foil 14, accelerated to a predetermined energy, extracted outside the vacuum chamber 2, and covered. Irradiated object (not shown) can be irradiated.
[0005]
An example of a filament support structure for supporting the linear filament 8 as described above is described in JP-A-11-133197.
[0006]
3 and 4, this filament support structure is configured such that two filament support plates 32, which are both elastic in this example, are spaced apart from each other on the insulating table 10 as described above. In the state where both filament support plates 32 are bent inward, the filament 8 as described above is placed between the ends of the filament support plates 32, and both ends of the filament 8 are connected to the filaments. It is structured so as to be installed by being hooked on the support plate 32. In this example, both filament support plates 32 are fixed to both end portions of the insulating base 10 by a fixing metal fitting 26 and screws 28 and 30.
[0007]
In this example, a U-shaped bending portion 50 in which the tip 50 b is bent back in the original direction is provided at both ends of the filament 8, and the filament 8 is bent near the tips of both filament support plates 32. A cut groove 52 into which the base portion 50a of the processed portion 50 enters and a hole 54 into which the distal end portion 50b of the bent portion 50 enters are provided. Then, by inserting the root portion 50a and the tip portion 50b of each bending portion 50 of the filament 8 into the cut groove 52 and the hole 54 of each filament support plate 32 and hooking the bending portion 50 on the filament support plate 32, respectively. The filament 8 is attached between the filament support plates 32 in the state where both filament support plates 32 are bent inward by a deflection amount d.
[0008]
According to the above filament support structure, when the filament 8 is expanded by energization heating, the deflection amount d of the filament support plate 32 bent inward is reduced and the expansion can be absorbed. The expansion of time can be absorbed and deformation and breakage of the filament 8 can be prevented. As a result, the stability and reliability of the apparatus employing such a filament support structure can be improved.
[0009]
In addition, since a structure in which both ends of the filament 8 are hooked on the filament support plate 32 is adopted, a metal fitting for fixing the filament 8 to the filament support plate 32 is not required, the structure is simple, and the filament 8 is attached. And replacement work is easy.
[0010]
[Problems to be solved by the invention]
Since the filament 8 is heated to a high temperature, it is generally formed of a refractory metal such as tungsten.
[0011]
On the other hand, each filament support plate 32 is generally formed of stainless steel (for example, SUS304) because it is generally easy to work and inexpensive.
[0012]
The filament 8 is supplied with electricity (energized) through the filament support plate 32 by contacting the filament support plate 32. An example of the contact state between the two is shown in FIG. Since the width of the cut groove 52 is larger than the thickness of the filament 8, the contact portion 56 usually exists on one of the upper and lower sides of the cut groove 52 as shown in the example of the drawing.
[0013]
Since the contact portion inevitably has contact resistance, the contact portion 56 generates heat and is heated to a high temperature as the filament 8 is energized.
[0014]
As a result, in the initial state, for example, the normal state shown in FIG. 6 is used, but when used for a certain period of time, the filament support plate 32 melts at the contact portion 56 and, for example, as shown in FIG. A concave melted portion 58 is formed.
[0015]
Incidentally, since the tungsten filament 8 is not melted and the melted part 58 is formed only on the filament support plate 32 made of stainless steel, the heating temperature of the melted part 58 is estimated to be at least about 1400 to 1500 ° C. Is done.
[0016]
In an electron beam irradiation apparatus or the like, normally, as described above, a plurality of filaments 8 are used. In that case, although it is necessary to replace each filament 8 with a new one by disconnection or the like, it is difficult to think that the replaced filament 8 is always stored in the original melted portion 58 and in the same state as the original. The contact state with the support plate 32 varies. Specifically, the contact resistance, the contact area, and the like vary among the plurality of filaments 8. As a result, the temperature distribution in each filament 8 changes from the initial one, and as a result, the amount of electron emission from each filament 8 varies.
[0017]
Accordingly, the main object of the present invention is to prevent melting of the filament support plate at the contact portion between the filament and the filament support plate.
[0018]
[Means for Solving the Problems]
The filament support structure of the present invention is characterized in that the two filament support plates are formed of a refractory metal belonging to Group 4A, 5A or 6A of the periodic table.
[0019]
More specifically, the two filament support plates may be Ti, Zr, Hf (above 4A group), V, Nb, Ta (above 5A group), Cr, Mo or W (above 6A group). Forming.
[0020]
By forming the two filament support plates with such a refractory metal, the heat resistance of the filament support plate is increased, so that even if the contact portion between the filament and the filament support plate is heated by the presence of contact resistance, Melting of the filament support plate at the contact portion can be prevented.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a front view showing an example of a filament support structure according to the present invention. Portions that are the same as or correspond to those in the examples shown in FIGS. 3 to 5 are denoted by the same reference numerals, and the differences from the conventional example will be mainly described below.
[0022]
In this filament support structure, the two filament support plates 32 are formed of a refractory metal belonging to Group 4A, Group 5A or Group 6A of the periodic table.
[0023]
The refractory metals belonging to the above are shown in the following order from the highest melting point. The melting point is shown in parentheses.
[0024]
W (3400 ° C), Ta (2990 ° C), Mo (2620 ° C), Nb (2470 ° C), Hf (2230 ° C), V (1890 ° C), Cr (1860 ° C), Zr (1850 ° C), Ti ( 1660 ° C.).
[0025]
Although all of these have a higher melting point than stainless steel, the filament support plate 32 is preferably formed of a refractory metal having a higher melting point. Specifically, it is preferably formed of W, Ta, Mo or the like. By doing so, since the heat resistance of the filament support plate 32 is further increased, it is possible to more reliably prevent the melted portion from occurring in the filament support plate 32.
[0026]
By forming the two filament support plates 32 with such a high melting point metal, the heat resistance of the filament support plate 32 is increased, so that the contact portion 56 between the filament 8 and the filament support plate 32 (FIGS. 5 and 6). Even if it is heated by the presence of contact resistance, melting of the filament support plate 32 at the contact portion 56 can be prevented.
[0027]
For example, when the filament support plate 32 is formed of tungsten (W) and energized under the same conditions as those of a conventional stainless steel (SUS304), the filament support plate 32 is conventionally melted as shown in FIG. Although the portion 58 was generated, no melted portion was found in the filament support plate 32 when formed of tungsten.
[0028]
Therefore, the above-mentioned disadvantages due to the occurrence of the melted portion in the filament support plate 32, for example, the contact state between the filament 8 and the filament support plate 32 after the filament 8 is changed, and the temperature distribution in the filament 8 and the electrons from the filament 8 are changed. Generation | occurrence | production of dispersion | variation in discharge amount etc. can be prevented.
[0029]
In addition, the shape of each bending process part 50 of the both ends of the filament 8 does not necessarily need to be bent back in U shape like the said example, and L shape etc. may be sufficient. However, in the case of the above example, the bent portion 50 is passed through the filament support plate 32 twice, so that the filament 8 is difficult to come out of the filament support plate 32 even when vibrations are applied, and the position of the filament 8 Deviation and rotation can also be effectively prevented.
[0030]
【The invention's effect】
As described above, according to the present invention, since the filament support plate is formed of the above-described high melting point metal, the heat resistance of the filament support plate is increased, so that the contact portion between the filament and the filament support plate has a contact resistance. Even if heated due to the presence of the filament, the filament support plate can be prevented from melting at the contact portion.
[0031]
As a result, inconvenience due to the occurrence of a melted part in the filament support plate, for example, variation in the contact state between the filament and the filament support plate after replacement of the filament, resulting in variation in the temperature distribution in the filament and the amount of electron emission from the filament. , Etc. can be prevented.
[Brief description of the drawings]
FIG. 1 is a front view showing an example of a filament support structure according to the present invention.
FIG. 2 is a schematic sectional view showing an example of an electron beam irradiation apparatus.
FIG. 3 is a front view showing an example of a conventional filament support structure.
4 is an enlarged perspective view showing the vicinity of the tip of the filament support plate in FIGS. 1 and 3. FIG.
5 is an enlarged cross-sectional view showing an example of a contact state between a filament and a filament support plate in FIGS. 1 and 3. FIG.
6 is an enlarged view of FIG. 5 as viewed from the state P in an initial state in a conventional filament support structure.
7 is an enlarged view of FIG. 5 as viewed from P after a certain period of use in a conventional filament support structure.
[Explanation of symbols]
8 Filament 10 Insulation base 32 Filament support plate 50 Bending part 56 Contact part

Claims (1)

Two filament support plates, at least one of which has elasticity, are attached to an insulating table so that they are opposed to each other with a gap between them, and the tip of both filament support plates is bent inwardly with the elastic filament support plate bent inward. In a filament support structure in which linear filaments are installed by being hooked on each filament support plate between both ends, the two filament support plates are attached to groups 4A and 5A of the periodic table of elements. A filament support structure formed of a refractory metal belonging to Group 6A or Group 6A.

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