CA1065386A - Electron tube provided with a cylindrical ceramic envelope part - Google Patents
Electron tube provided with a cylindrical ceramic envelope partInfo
- Publication number
- CA1065386A CA1065386A CA264,451A CA264451A CA1065386A CA 1065386 A CA1065386 A CA 1065386A CA 264451 A CA264451 A CA 264451A CA 1065386 A CA1065386 A CA 1065386A
- Authority
- CA
- Canada
- Prior art keywords
- electrode
- potential side
- side electrode
- jointed
- ceramic
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J3/00—Details of electron-optical or ion-optical arrangements or of ion traps common to two or more basic types of discharge tubes or lamps
- H01J3/02—Electron guns
- H01J3/027—Construction of the gun or parts thereof
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- Microwave Tubes (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
An electron tube of the type, such as a traveling-wave tube, which includes a cylindrical ceramic envelope part jointed to two spaced metallic electrodes between which a high D.C. voltage is applied is disclosed. The ceramic part has its inner diameter progressively increased so that its inner circumferential surface is flared from the end at which the negative potential electrode is jointed towards the end at which the positive po-tential electrode is jointed. Because electrons emitted from the cathode of the tube are less likely to impinge on this sloping surface, arc gener-ation is reduced or prevented. Additionally, a metallic shield connected concentrical b to the negative electrode is provided, the shield being so spaced with respect to the positive electrode that it concentrates the field between the two electrodes at the shield. This weakens the field at the periphery of the negative electrode and causes reduced emission of electrons at that location.
An electron tube of the type, such as a traveling-wave tube, which includes a cylindrical ceramic envelope part jointed to two spaced metallic electrodes between which a high D.C. voltage is applied is disclosed. The ceramic part has its inner diameter progressively increased so that its inner circumferential surface is flared from the end at which the negative potential electrode is jointed towards the end at which the positive po-tential electrode is jointed. Because electrons emitted from the cathode of the tube are less likely to impinge on this sloping surface, arc gener-ation is reduced or prevented. Additionally, a metallic shield connected concentrical b to the negative electrode is provided, the shield being so spaced with respect to the positive electrode that it concentrates the field between the two electrodes at the shield. This weakens the field at the periphery of the negative electrode and causes reduced emission of electrons at that location.
Description
me present invention relates to an electron tube of the type which has a cylindrical ceramic envelope part separating metallic electrodes across which a high voltage is applied.
A travelling-wave tube is a typical example of such an electron tube. In a traveling-wave tube, a cathode and a focusing electrode disposed coaxially with said cathode are often respectively supported by disc-shaped metal electrode, and an accelerating electrode is also formed as a disc-shaped metal electrode. It is a common practice to braze these metallic electrodes to a hollow cylindrical ceramic part disposed therebetween. In such a construction, for the purpose of generating a high speed electron beam from the cathode, a high voltage of several kilovolts is applied to the metal electrode serving as an accelerating electrode. Under such state, the inner surface of the ceramic part defining the high vacuum space is exposed to strong electric fields directed parallel to the axis of the traveling-wave tube. It has been observed that arc discharge accompanied by intense luminescence often occurs along the inner surface of the ceramic part.
Occurrence of arc discharge is not favorable, because then the vacuum within the tube is degraded resulting in adverse effects upon the performance and life of the traveling-wave tube, and also because faults could occur such that the power supply is over-loaded and damaged.
In general, in order to prevent the internal discharge of the electron tube during ordinary operation, a method is known in which, during in the manufacturing process of an electron tube, a voltage far higher than the operating voltage for ordinary operation is applied to positively gen-erate discharge, and thus various defects which cause the discharge are re-moved by that discharge energy. However, even when this method is employed, the generation of the aforementioned arc discharge during ordinary operation cannot be prevented completely.
As a result of various investigations on the mechanism of generation - 1- ;~
of arc discharge, it has been presumed that due to the fact that the inner surface of the ceramic part which is a rough surface having minute holes and projections and which holds a large amount of adsorbed gas lies parallel to the strong electric fields, electrons emitted from a negative potential side electrode and traveling along the inner surface of the ceramic part towards a positive potential side electrode may possibly ionize the adsorbed gas in the ceramic part.
Therefore, it is one object of the present invention to provide an electron tube having a cylindrical ceramic envelope part which is exposed to a high electric field, in which generation of arc discharge is inhibited by preventing or restricting the adsorbed gas on the inner surface of said ceramic part from being ionized by electrons emitted from the negative potential side metallic electrode.
Another object of the present invention is to provide an electron tube, in which generation of arc discharge is reduced by decreasing emission of such electrons that strike against the adsorbed gas on the inner surface of said ceramic part which is exposed to the high electric fields and that ionize the adsorbed gas.
According to one feature of the present invention, there is pro-vided an electron tube provided with a cylindrical ceramic envelope parthaving metallic electrodes, between which a high D.C. voltage is applied, jointed onto its opposite end surfaces, in which said ceramic part has its inner diameter progressively increased so that its inner circumferential surface is flared from one end surface, onto which a negative potential side electrode of said metallic electrodes is jointed, towards the other end sur-face, onto which a positive potential side electrode is jointed.
In a preferred embodiment, there is disposed radially inwardly of said ceramic part a concentric shielding metallic member maintained at the same potential as said negative potential side electrode and having its one portion positioned at a distance nearer than 2/3 of the axial length of said ceramic part from a circle formed by projecting onto said positive potential side electrode an inner peripheral circle of the joint portion between said negative potential side electrode and said ceramic part in parallel to the axis of said ceramic part.
Since the inner surface of the cylindrical ceramic envelope part is not disposed parallel to the electric field caused by the high voltage applied across said ceramic part, the adsorbed gas on the inner surface of the ceramic part is subjected less to electron bombardment, and thereby generation of arc discharge can be prevented. In addition, since the electron tube is provided with a shielding metallic member for weakening the electric field inside of the joint portion between the negative potential side electrode and said ceramic part, the emission of such electrons that contribute largely to the ionization of the adsorbed gas on the inner sur-face is suppressed, and consequently, the arc discharge caused by these emitted electrons can be almost perfectly prevented.
The above-mentioned and other features and objects of this in-vention will become more apparent by reference to the following description taken in conjunction with the accompanying drawings, in which;
Figure 1 is a longitudinal cross-sectional view of a prior art electron tube provided with a cylindrical ceramic envelope part and showing particularly the vicinity of the electron gun assembly;
Figure 2 is a longitudinal cross-sectional view similar to Figure 1 but showing a first preferred embodiment of the present invention;
~065386 Figure 3 is a longitudinal cross-sectional view similar to Figure 1 but showing a second preferred embodiment of the present invention;
Figure 4 is a longitudinal cross-sectional view of an essential part of a third preferred embodiment of the present invention;
Figure 5 is a longitudinal cross-sectional view similar to Figure 1 but showing a fourth preferred embodiment of the electron tube according to the present invention; and Figure 6 is a longitudinal cross-sectional view of an essential part of a fifth preferred embodiment of the present invention.
Referring now to Figure 1, a conventional traveling-wave tube 1 with an electron gun assembly 2 is illustrated. In the electron gun assembly
A travelling-wave tube is a typical example of such an electron tube. In a traveling-wave tube, a cathode and a focusing electrode disposed coaxially with said cathode are often respectively supported by disc-shaped metal electrode, and an accelerating electrode is also formed as a disc-shaped metal electrode. It is a common practice to braze these metallic electrodes to a hollow cylindrical ceramic part disposed therebetween. In such a construction, for the purpose of generating a high speed electron beam from the cathode, a high voltage of several kilovolts is applied to the metal electrode serving as an accelerating electrode. Under such state, the inner surface of the ceramic part defining the high vacuum space is exposed to strong electric fields directed parallel to the axis of the traveling-wave tube. It has been observed that arc discharge accompanied by intense luminescence often occurs along the inner surface of the ceramic part.
Occurrence of arc discharge is not favorable, because then the vacuum within the tube is degraded resulting in adverse effects upon the performance and life of the traveling-wave tube, and also because faults could occur such that the power supply is over-loaded and damaged.
In general, in order to prevent the internal discharge of the electron tube during ordinary operation, a method is known in which, during in the manufacturing process of an electron tube, a voltage far higher than the operating voltage for ordinary operation is applied to positively gen-erate discharge, and thus various defects which cause the discharge are re-moved by that discharge energy. However, even when this method is employed, the generation of the aforementioned arc discharge during ordinary operation cannot be prevented completely.
As a result of various investigations on the mechanism of generation - 1- ;~
of arc discharge, it has been presumed that due to the fact that the inner surface of the ceramic part which is a rough surface having minute holes and projections and which holds a large amount of adsorbed gas lies parallel to the strong electric fields, electrons emitted from a negative potential side electrode and traveling along the inner surface of the ceramic part towards a positive potential side electrode may possibly ionize the adsorbed gas in the ceramic part.
Therefore, it is one object of the present invention to provide an electron tube having a cylindrical ceramic envelope part which is exposed to a high electric field, in which generation of arc discharge is inhibited by preventing or restricting the adsorbed gas on the inner surface of said ceramic part from being ionized by electrons emitted from the negative potential side metallic electrode.
Another object of the present invention is to provide an electron tube, in which generation of arc discharge is reduced by decreasing emission of such electrons that strike against the adsorbed gas on the inner surface of said ceramic part which is exposed to the high electric fields and that ionize the adsorbed gas.
According to one feature of the present invention, there is pro-vided an electron tube provided with a cylindrical ceramic envelope parthaving metallic electrodes, between which a high D.C. voltage is applied, jointed onto its opposite end surfaces, in which said ceramic part has its inner diameter progressively increased so that its inner circumferential surface is flared from one end surface, onto which a negative potential side electrode of said metallic electrodes is jointed, towards the other end sur-face, onto which a positive potential side electrode is jointed.
In a preferred embodiment, there is disposed radially inwardly of said ceramic part a concentric shielding metallic member maintained at the same potential as said negative potential side electrode and having its one portion positioned at a distance nearer than 2/3 of the axial length of said ceramic part from a circle formed by projecting onto said positive potential side electrode an inner peripheral circle of the joint portion between said negative potential side electrode and said ceramic part in parallel to the axis of said ceramic part.
Since the inner surface of the cylindrical ceramic envelope part is not disposed parallel to the electric field caused by the high voltage applied across said ceramic part, the adsorbed gas on the inner surface of the ceramic part is subjected less to electron bombardment, and thereby generation of arc discharge can be prevented. In addition, since the electron tube is provided with a shielding metallic member for weakening the electric field inside of the joint portion between the negative potential side electrode and said ceramic part, the emission of such electrons that contribute largely to the ionization of the adsorbed gas on the inner sur-face is suppressed, and consequently, the arc discharge caused by these emitted electrons can be almost perfectly prevented.
The above-mentioned and other features and objects of this in-vention will become more apparent by reference to the following description taken in conjunction with the accompanying drawings, in which;
Figure 1 is a longitudinal cross-sectional view of a prior art electron tube provided with a cylindrical ceramic envelope part and showing particularly the vicinity of the electron gun assembly;
Figure 2 is a longitudinal cross-sectional view similar to Figure 1 but showing a first preferred embodiment of the present invention;
~065386 Figure 3 is a longitudinal cross-sectional view similar to Figure 1 but showing a second preferred embodiment of the present invention;
Figure 4 is a longitudinal cross-sectional view of an essential part of a third preferred embodiment of the present invention;
Figure 5 is a longitudinal cross-sectional view similar to Figure 1 but showing a fourth preferred embodiment of the electron tube according to the present invention; and Figure 6 is a longitudinal cross-sectional view of an essential part of a fifth preferred embodiment of the present invention.
Referring now to Figure 1, a conventional traveling-wave tube 1 with an electron gun assembly 2 is illustrated. In the electron gun assembly
2, cylindrical ceramic envelope parts 4, S and 6 having the same diameter are disposed in a coaxially aligned form in the axial direction of the traveling-wave tube 1. Disc-shaped metallic electrodes 7, 8, 9 and 10 are jointed onto the leftmost end surface abutting surfaces and rightmost end surface of the ceramic envelope parts 4, 5 and 6 by brazing so as to main-tain a hermetic seal at each joint. A filament 12 is connected at each of its ends to electrodes 9 and 10. The electrode 8 is jointed by brazing or welding to a focusing electrode 13, and the electrode 9 is jointed by bra~ing or welding to a cathode 11. Reference numeral 3 designates a helix type slow wave circuit portion for performing amplification of signals through interaction with an electron beam emitted from the electron gun asse~bly 2. It will be appreciated that the structural components of the traveling-wave tube 1 comprises a collector for collecting the electron beam which has ceased engagement in the amplification effect, a focusing magnetic field generator for focusing the electron beam, and input and output high frequency coupling devices for high frequency signals, but it is unnecessary to illustrate these components to obtain the background of the invention.
The interior of the traveling-wave tube 1 is, during production, evacuated to a high vacuum of the order of 10 9 Torr through an evacuation pipe 14 pro-vided at the center of the electrode 10.
With regard to operating voltages for this traveling-wave tube 1, a filament heating voltage is applied between the electrodes 9 and 10 from a power supply 16, and an accelerating voltage of several kilovolts is ap-plied between the electrodes 7 and 8 from a power supply 15 so as to main-tain the electrode 7 at a positive potential and the electrode 8 at a neg-ative potential. In addition, the electrode 9 connected to the cathode is wired to the negative potential side electrode 8 for the accelerating voltage, so that the focusing electrode 13 and the cathode 11 are maintained at the same potential.
In such a construction, the outer surfaces of the cylindrical ceramic envelope parts 4, S and 6 are exposed to the atmosphere, while their inner surfaces are exposed to a high vacuum of the order of 10 9 Torr as described above, and by applying the above-described operating voltages the inner ~urface of the ceramic part 4 is exposed to a strong electric field directed in parallel to the axis of the traveling-wave tube 1. In this case, it has been observed that arc discharge accompanied by intense lun-inescence would often occur along the inner surface of the ceramic part 4.
This arc discharge results from the electrons striking pockets of adsorbed gas contained in the rough surface of the ceramic part 4. Occurrence of arc discharge is not favorable, because then the vacuum within the tube is degraded resulting in adverse effects upon performance and life of the trav-eling-wave tube, and also because the power supply tends to be over-loaded and damaged.
Figure 2 illustrates an electron gun assembly according to one preferred embodiment of the present invention, in which except for the dif-ference that the ceramic part 4 in Figure 1 is modified to provide an im-proved ceramic part 4a according to the present invention, the structure is identical to that shown in Figure 1.
Like reference numerals have been used to denote like parts in Figures 1 and 2 and incidentally, in all the other figures. In Figure 2, the cylindrical ceramic envelope part 4a disposed between metallic electrodes 7 and 8 to which a high voltage is applied from the high voltage power supply 15 has its inner diameter progressively increased so that its inner circumferential surface is flared from the portion jointed to the negative potential side electrode 8 towards the portion jointed to the positive po-tential side electrode 7. Consequently, owing to the strong electric fields in the direction of the tube axis 23 of the traveling-wave tube 1, electrons emitted from the inner peripheral portion 21 of the joint between the neg-ative potential side electrode 8 and the ceramic part 4a immediately enter the high vacuum space without traveling along the inner surface of the ceramic part 4a. Thus, the electrons ar~ less likely to strike against the adsorbed gas contained in the rough surface of part 4a and ionize the gas, so that arc discharge is prevented.
Figure 3 illustrates an electron gun assembly in a second pre-ferred embodiment of the present invention, which differs from the prior art apparatus of Figure 1 only in that a shielding metallic member 17 is added.
With reference to Figure 3, inside of the cylindrical ceramic envelope part 4 disposed between metallic electrodes 7 and 8 to which a high voltage is applied from the high voltage power supply 15, there is provided the shielding metallic member 17 projecting from the negative potential side electrode 8 concentrically therewith and having a projecting corner portion 22 positioned at a distance d, that is about 2/3 of the axial length h of the ceramic part 4, from the inner peripheral circle 20 of the joint between the positive potential side electrode 7 and the ceramic part 4. As the distance d is sufficiently shorter than the distance h between the positive and negative electrodes, most of the lines of electric force extending from the positive potential side electrode 7 to the negative potential side electrode 8 con-centrate at the projecting corner portion 22 of the shielding metallic mem-ber 17, so that the electric field in the vicinity of the inner peripheral circle 21 of the joint between the negative potential side electrode 8 and the ceramic part 4 is weakened. In order for this described shielding effect to occur, it is a necessary condition that the distance d is smaller than the distance h, but in order to expect a practically useful effect it is necessary that the distance d is equal to or smaller than 2/3 of the dis-tance h. Of course, a better shielding effect is achieved as the distance d becomes smaller, but the smallest allowable distance d is determined by direct vacuum breakdown discharge between the positive potential side elec-trode 7 and the shielding metallic member 17. If the radial distance be-tween the shielding metallic member 17 and the inner surface of the ceramic member 4 is too small, then direct bombardment of emitted electrons having a radial velocity component against the inner surface of the ceramic part 4 also may possibly occur, and therefore, it is natural that this distance also must be chosen properly. Thus, by providing the shielding metallic member 17, the electric field in the vicinity of the inner peripheral circle 21 of the joint between the negative potential side electrode 8 and the ceramic part 4 can be weakened and electron emission at this portion can be also reduced, so that ionization of the adsorbed gas on the inner surface of the ceramic part 4 in the vicinity of this portion can be suppressed and thereby generation of arc discharge can be prevented.
Figure 4 illustrates an essential part of another preferred em-bodiment of the present invention, in which the focusing electrode 13 and the shielding metallic member 17 in Figure 3 are integrally constructed as the member 18. Since the distance d between the projecting corner portion 22 of the member 18 and the inner peripheral circle 20 of the joint between the positive potential side electrode 7 and the ceramic part 4 is equal to or less than 2/3 of the axial length h of the ceramic part 4, the electric field in the vicinity of the inner peripheral circle 21 of the joint between the negative potential side electrode 8 and the ceramic part 4 is weakened, and so electron emission at this portion is suppressed. In this modified embodiment, the shielding metallic member 18 is shaped integrally and sim-ultaneously with formation of the focusing electrode, and therefore, this embodiment has an additional advantage that it is easier to manufacture in comparison to the embodiment shown in Figure 3.
Figure S illustrates still another preferred embodiment of the present invention, which differs from the first preferred embodiment shown in Figure 2 in that there is provided the shielding metallic member 17 for reducing emitted electrons. More particularly, in Figure 5 the negative potential side electrode 8 is connected with the shielding metallic member 17 of hollow cylindrical shape, which is disposed concentrically with regard to the ceramic part 4a as directed towards the positive potential side el-ectrode 7. The axial length of this metallic member 17 is chosen within such a range that the vacuum breakdown discharge may not arise due to ex-cessively close approach to the positive potential side electrode 7. In addition, for the purpose of attaining the shielding effect for the vicinity of the inner peripheral circle 21 of the joint between the negative potential side electrode 8 and the ceramic part 4a, it is necessary to maintain the distance d, between the projecting corner portion 22 and the circle 20 ob-tained by projecting the inner peripheral circle 21 onto the positive poten-tial side electrode 7 parallel to the axis of the ceramic part 4a, equal to or less than 2/3 of the axial length _ of the ceramic part 4a. Owing to the shielding metallic member 17, the electric field in the vicinity of the inner peripheral circle 21 of the joint is weakened, electron emission at this portion is reduced, so that ionization of the adsorbed gas on the inner surface of the ceramic part 4a is reduced, and therefore, the prevention of ~065386 the arc discharge is even more assured in comparison to the first embodiment shown in Figure 2.
Figure 6 illustrates one example of a modification of the shielding metallic member 17 as used in the embodiment shown in Figure 5. Since the member 18 is shaped so as to form a shielding metallic member and a focusing electrode integrally, this embodiment has an additional advantage that it is easier to manufacture in comparison to the case where the shielding metallic member and the focusing electrode are produced separately and then assembled together.
As fully described above, in the electron tube according to the present invention, since the inner surface of the cylindrical ceramic envel-ope part across which a high voltage is applied, is flared from the negative potential side towards the positive potential side, electrons emitted from the inner peripheral portion of the joint between the negative potential side electrode and the ceramic part would travel towards the positive pot-ential side electrode without interception, and electrons striking against the inner surface of the ceramic part are few. Therefore, ionization of the adsorbed gas on the inner surface is also reduced, and as a result, occur-rence of arc discharge is prevented. Furthermore, by additionally providing a shielding metallic member, the electric field in the vicinity of the inner peripheral circle of the joint between the negative potential side electrode and the ceramic part is weakened, and thereby electron emission from this portion is suppressed. Consequently, ionization of the adsorbed gas on the inner surface of the ceramic part caused by bombardment of these electrons is reduced, and thus arc discharge can be further prevented, so that the electron tubes according to the present invention have a stable performance and a long lifeO
While the present invention has been described above in connection to an electron gun assembly in a traveling-wave tube, it is a matter of course that the invention is equally applicable to other types of electron tubes such as klystrons.
The interior of the traveling-wave tube 1 is, during production, evacuated to a high vacuum of the order of 10 9 Torr through an evacuation pipe 14 pro-vided at the center of the electrode 10.
With regard to operating voltages for this traveling-wave tube 1, a filament heating voltage is applied between the electrodes 9 and 10 from a power supply 16, and an accelerating voltage of several kilovolts is ap-plied between the electrodes 7 and 8 from a power supply 15 so as to main-tain the electrode 7 at a positive potential and the electrode 8 at a neg-ative potential. In addition, the electrode 9 connected to the cathode is wired to the negative potential side electrode 8 for the accelerating voltage, so that the focusing electrode 13 and the cathode 11 are maintained at the same potential.
In such a construction, the outer surfaces of the cylindrical ceramic envelope parts 4, S and 6 are exposed to the atmosphere, while their inner surfaces are exposed to a high vacuum of the order of 10 9 Torr as described above, and by applying the above-described operating voltages the inner ~urface of the ceramic part 4 is exposed to a strong electric field directed in parallel to the axis of the traveling-wave tube 1. In this case, it has been observed that arc discharge accompanied by intense lun-inescence would often occur along the inner surface of the ceramic part 4.
This arc discharge results from the electrons striking pockets of adsorbed gas contained in the rough surface of the ceramic part 4. Occurrence of arc discharge is not favorable, because then the vacuum within the tube is degraded resulting in adverse effects upon performance and life of the trav-eling-wave tube, and also because the power supply tends to be over-loaded and damaged.
Figure 2 illustrates an electron gun assembly according to one preferred embodiment of the present invention, in which except for the dif-ference that the ceramic part 4 in Figure 1 is modified to provide an im-proved ceramic part 4a according to the present invention, the structure is identical to that shown in Figure 1.
Like reference numerals have been used to denote like parts in Figures 1 and 2 and incidentally, in all the other figures. In Figure 2, the cylindrical ceramic envelope part 4a disposed between metallic electrodes 7 and 8 to which a high voltage is applied from the high voltage power supply 15 has its inner diameter progressively increased so that its inner circumferential surface is flared from the portion jointed to the negative potential side electrode 8 towards the portion jointed to the positive po-tential side electrode 7. Consequently, owing to the strong electric fields in the direction of the tube axis 23 of the traveling-wave tube 1, electrons emitted from the inner peripheral portion 21 of the joint between the neg-ative potential side electrode 8 and the ceramic part 4a immediately enter the high vacuum space without traveling along the inner surface of the ceramic part 4a. Thus, the electrons ar~ less likely to strike against the adsorbed gas contained in the rough surface of part 4a and ionize the gas, so that arc discharge is prevented.
Figure 3 illustrates an electron gun assembly in a second pre-ferred embodiment of the present invention, which differs from the prior art apparatus of Figure 1 only in that a shielding metallic member 17 is added.
With reference to Figure 3, inside of the cylindrical ceramic envelope part 4 disposed between metallic electrodes 7 and 8 to which a high voltage is applied from the high voltage power supply 15, there is provided the shielding metallic member 17 projecting from the negative potential side electrode 8 concentrically therewith and having a projecting corner portion 22 positioned at a distance d, that is about 2/3 of the axial length h of the ceramic part 4, from the inner peripheral circle 20 of the joint between the positive potential side electrode 7 and the ceramic part 4. As the distance d is sufficiently shorter than the distance h between the positive and negative electrodes, most of the lines of electric force extending from the positive potential side electrode 7 to the negative potential side electrode 8 con-centrate at the projecting corner portion 22 of the shielding metallic mem-ber 17, so that the electric field in the vicinity of the inner peripheral circle 21 of the joint between the negative potential side electrode 8 and the ceramic part 4 is weakened. In order for this described shielding effect to occur, it is a necessary condition that the distance d is smaller than the distance h, but in order to expect a practically useful effect it is necessary that the distance d is equal to or smaller than 2/3 of the dis-tance h. Of course, a better shielding effect is achieved as the distance d becomes smaller, but the smallest allowable distance d is determined by direct vacuum breakdown discharge between the positive potential side elec-trode 7 and the shielding metallic member 17. If the radial distance be-tween the shielding metallic member 17 and the inner surface of the ceramic member 4 is too small, then direct bombardment of emitted electrons having a radial velocity component against the inner surface of the ceramic part 4 also may possibly occur, and therefore, it is natural that this distance also must be chosen properly. Thus, by providing the shielding metallic member 17, the electric field in the vicinity of the inner peripheral circle 21 of the joint between the negative potential side electrode 8 and the ceramic part 4 can be weakened and electron emission at this portion can be also reduced, so that ionization of the adsorbed gas on the inner surface of the ceramic part 4 in the vicinity of this portion can be suppressed and thereby generation of arc discharge can be prevented.
Figure 4 illustrates an essential part of another preferred em-bodiment of the present invention, in which the focusing electrode 13 and the shielding metallic member 17 in Figure 3 are integrally constructed as the member 18. Since the distance d between the projecting corner portion 22 of the member 18 and the inner peripheral circle 20 of the joint between the positive potential side electrode 7 and the ceramic part 4 is equal to or less than 2/3 of the axial length h of the ceramic part 4, the electric field in the vicinity of the inner peripheral circle 21 of the joint between the negative potential side electrode 8 and the ceramic part 4 is weakened, and so electron emission at this portion is suppressed. In this modified embodiment, the shielding metallic member 18 is shaped integrally and sim-ultaneously with formation of the focusing electrode, and therefore, this embodiment has an additional advantage that it is easier to manufacture in comparison to the embodiment shown in Figure 3.
Figure S illustrates still another preferred embodiment of the present invention, which differs from the first preferred embodiment shown in Figure 2 in that there is provided the shielding metallic member 17 for reducing emitted electrons. More particularly, in Figure 5 the negative potential side electrode 8 is connected with the shielding metallic member 17 of hollow cylindrical shape, which is disposed concentrically with regard to the ceramic part 4a as directed towards the positive potential side el-ectrode 7. The axial length of this metallic member 17 is chosen within such a range that the vacuum breakdown discharge may not arise due to ex-cessively close approach to the positive potential side electrode 7. In addition, for the purpose of attaining the shielding effect for the vicinity of the inner peripheral circle 21 of the joint between the negative potential side electrode 8 and the ceramic part 4a, it is necessary to maintain the distance d, between the projecting corner portion 22 and the circle 20 ob-tained by projecting the inner peripheral circle 21 onto the positive poten-tial side electrode 7 parallel to the axis of the ceramic part 4a, equal to or less than 2/3 of the axial length _ of the ceramic part 4a. Owing to the shielding metallic member 17, the electric field in the vicinity of the inner peripheral circle 21 of the joint is weakened, electron emission at this portion is reduced, so that ionization of the adsorbed gas on the inner surface of the ceramic part 4a is reduced, and therefore, the prevention of ~065386 the arc discharge is even more assured in comparison to the first embodiment shown in Figure 2.
Figure 6 illustrates one example of a modification of the shielding metallic member 17 as used in the embodiment shown in Figure 5. Since the member 18 is shaped so as to form a shielding metallic member and a focusing electrode integrally, this embodiment has an additional advantage that it is easier to manufacture in comparison to the case where the shielding metallic member and the focusing electrode are produced separately and then assembled together.
As fully described above, in the electron tube according to the present invention, since the inner surface of the cylindrical ceramic envel-ope part across which a high voltage is applied, is flared from the negative potential side towards the positive potential side, electrons emitted from the inner peripheral portion of the joint between the negative potential side electrode and the ceramic part would travel towards the positive pot-ential side electrode without interception, and electrons striking against the inner surface of the ceramic part are few. Therefore, ionization of the adsorbed gas on the inner surface is also reduced, and as a result, occur-rence of arc discharge is prevented. Furthermore, by additionally providing a shielding metallic member, the electric field in the vicinity of the inner peripheral circle of the joint between the negative potential side electrode and the ceramic part is weakened, and thereby electron emission from this portion is suppressed. Consequently, ionization of the adsorbed gas on the inner surface of the ceramic part caused by bombardment of these electrons is reduced, and thus arc discharge can be further prevented, so that the electron tubes according to the present invention have a stable performance and a long lifeO
While the present invention has been described above in connection to an electron gun assembly in a traveling-wave tube, it is a matter of course that the invention is equally applicable to other types of electron tubes such as klystrons.
Claims (5)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An electron tube including a cylindrical ceramic envelope part having metallic electrodes, between which a high D.C. voltage is applied, jointed onto its opposite end surfaces, in which said ceramic part has its inner diameter progressively increased so that its inner circumferential surface is flared from one end surface, onto which a negative potential side electrode of said metallic electrode is jointed, towards the other end surface, onto which a positive potential side electrode is jointed.
2. An electron tube including a cylindrical ceramic envelope part as claimed in Claim 1, in which said negative potential side electrode is associated with a focusing electrode disposed concentrically with first said electrode for focusing an electron beam.
3. An electron tube including a cylindrical ceramic envelope part having metallic electrodes, between which a high D.C. voltage is applied, jointed onto its opposite end surfaces, in which said ceramic part has its inner diameter progressively increased so that its inner circumferential surface is flared from one end surface, onto which a negative potential side electrode of said metallic electrodes is jointed, towards the other end surface, onto which a positive potential side electrode is jointed; and in which inside there is disposed radially inwardly of said ceramic part a concentric shielding metallic member maintained at the same potential as said negative potential side electrode and having its one portion positioned at a distance nearer than 2/3 of an axial length of said ceramic part from a circle formed by projecting onto said positive potential side electrode an inner peripheral circle of the joint portion between said negative potential side electrode and said ceramic part in parallel to the axis of said ceramic part.
4. An electron tube including a cylindrical ceramic envelope part as claimed in Claim 3, in which said negative potential side electrode is con-nected with a focusing electrode disposed concentrically with first said electrode for focusing an electron beam.
5. An electron tube including a cylindrical ceramic envelope part as claimed in Claim 4, in which said shielding metallic member and said focusing electrode jointly form an integral structure.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP13190375A JPS5255468A (en) | 1975-10-31 | 1975-10-31 | Electron tube containing ceramic surrounding parts |
| JP15890375A JPS5280771A (en) | 1975-12-26 | 1975-12-26 | Electronic tube containing ceramic surrounding parts |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1065386A true CA1065386A (en) | 1979-10-30 |
Family
ID=26466613
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA264,451A Expired CA1065386A (en) | 1975-10-31 | 1976-10-29 | Electron tube provided with a cylindrical ceramic envelope part |
Country Status (2)
| Country | Link |
|---|---|
| CA (1) | CA1065386A (en) |
| DE (1) | DE2649617A1 (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2046511B (en) * | 1979-04-09 | 1983-04-20 | Tektronix Inc | Electron gun having a low capacitance cathode and grid assembly |
| DE29823118U1 (en) | 1998-12-28 | 1999-02-25 | Siemens AG, 80333 München | Tube neck for a cathode ray tube |
-
1976
- 1976-10-29 CA CA264,451A patent/CA1065386A/en not_active Expired
- 1976-10-29 DE DE19762649617 patent/DE2649617A1/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| DE2649617A1 (en) | 1977-05-12 |
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