US3381155A

US3381155A - Electron guns having at least one emissive cathode surface and one nonemissive electrode adjacent said cathode surface

Info

Publication number: US3381155A
Application number: US478577A
Authority: US
Inventors: Arnaud Jacques; Wendt George
Original assignee: Individual
Current assignee: Individual
Priority date: 1964-08-26
Filing date: 1965-08-10
Publication date: 1968-04-30
Anticipated expiration: 1985-04-30
Also published as: DE1491318A1; GB1066567A; FR1413184A

Description

April 39, 1968 .1. ARNAUD ETAL ELECTRON GUNS HAVING AT LEAST ONE EMISSIVE CATHODE SURFACE AND ONE NONEMISSIVE ELECTRODE ADJACENT SAID CATHODE SURFACE 5 Sheets-Sheet 1 Filed Aug. 10, 1965 INVENTORS:

J-A/P/VAUZ? AFGWE/VDT ATTORNEY April 30, 1968 J. ARNAUD ETAL 3,381,155

ELECTRON GUNS HAVING AT LEAST ONE EMISSIVE GATHODE SURFACE AND ONE NONEMISSIVE ELECTRODE ADJACENT SAID CATHODE SURFACE Flled Aug 10, 1965 5 Sheets-Sheet 2 IN V E NTORSZ JARA/A U0 8 6. WE/VDT ATTORNEY J. ARNAUD ETAL ELECTRON GUNS HAVING AT LEAST ONE EMISSIVE April 30, 1968 CATHODE SURFACE AND ONE NONEMISSIVE ELECTRODE ADJACENT SAID CATHODE SURFACE 5 Sheets-Sheet 5 Vol Filed Aug. 10, 196

INVENTORS:

JAR/VA U0 A 6. WE/VDT ATTORN EY United States Patent 3,381,155 ELECTRON GUNS HAVING AT LEAST GNE EMISSIVE CATHODE SURFACE AND ONE NONEMlSSWE ELECTRGDE ADJACENT SAID CATHODE SURFACE Jacques Arnaud and Georg Wendt, both of 79 Blvd. Haussmaun, Paris Seme, France Filed Aug. Ill, 1965, Ser. No. 478,577 Claims priority, application France, Aug. 26, 1964, 986,210 9 Claims. (Cl. 313-82) ABSTRACT OF THE DISQLGSURE An electron gun producing, without any focusing magnet acting on the gun space, an electron beam having a substantially linearly variable electron density over its cross-section, this density varying between substantially zero value near the axis of the beam and a maximum value near the periphery of the cathode. The gun comprises at least one emissive cathode surface tilted at substantially 67 with respect to the axis, and at least one nonernissive electrode having an edge adjacent the peripheral edge of the cathode surface, and forming therewith an angle of substantially 157.

'l' he present invention relates to electron guns generating electron beams, in particular to those for use in high power travelling wave tubes. It aims at realizing an electron gun capable of generating a beam having in its crosssection an electron density progressively increasing from one point of this cross-section toward at least one boundary line thereof forming the cross-section of at least one lateral surface of the beam.

It is known in the art that when an electron beam interacts with the delay line of a travelling wave tube, the conditions of interaction are better when the portion of the beam relatively nearest to the delay line has an electron density which is as high as possible. Therefore, it is clear that when, for instance, the beam has a circular cross-section and moves through the interior of a delay line having an annular cross-section, the conditions of interaction would be better if the electron density varied from the center toward the periphery of the cross-section, that is, if the density were substantially zero along the axis of the beam and progressively increased to become maximum near the lateral surface thereof, as compared with a beam having a constant electron density throughout all points of its crosssection. However, in the prior art only guns generating constant-density beams are known, such as a circular beam with constant density at all points of its circular cross-section, or an annular beam with constant density at all points of the annulus representing its crosssection, or a fiat or ribbon-like beam with constant density at all points of the rectangle representing its cross-section.

Accordingly, it is an object of the present invention to produce electron guns generating electron beams having over their cross-section such an electron density distribution that a relatively better interaction condition with a delay line of a travelling wave tube is attained, as compared to the known constant-density electron beams.

Another object of the present invention is to produce ice a gun generating a ribbon-like electron beam having a progressively variable electron density from one of its flat surfaces to the other.

Still another object of the present invention is to produce a gun generating a ribbon-like electron beam having a progressively increasing electron density distribution from the center thereof toward both fiat lateral surfaces.

A further object of the present invention is to produce a gun generating an electron beam having a symmetry of revolution, in which the electron density distribution progressively increases from the axis thereof, or from a circle of predetermined diameter surrounding the axis, toward the lateral surface thereof.

These and other objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawing, which shows for purposes of illustration only, several embodiments in accordance with the present invention and wherein:

FIGURE 1 is a partial transverse cross-sectional view of a gun generating an electron beam in the form of a double ribbon;

FIGURE 2 is a partial transverse cross-sectional view of a gun generating a single variable-density ribbon-like beam;

FIGURE 3 is a partial transverse cross-sectional view of a gun generating a variable density electron beam having a symmetry of revolution, and

FIGURE 4 is a partial transverse cross-sectional view of an alternative of the gun as shown either in FIGURE 1 or in FIGURE 3, wherein a portion of the emissive surface of the cathode is suppressed, thereby obtaining a hollow fiat or circular beam.

The present invention essentially consists of means whereby the cathode of an electron gun is caused to emit electrons with a substantially linearly increasing density from a region of its surface remote from the periphery, toward the said periphery, together with means for accelerating the electrons to cause them to flow in a pr determined direction, the space between the cathode and the accelerating means being free of any magnetic field. Such structure has the property that the paths of the accelerated electrons converge asymptotically toward the axis of the said direction to form a variable density beam. The effect of such beams, when used to pass parallel to a delay line of a travelling wave tube, is to improve the conditions of interaction with this line, and consequently to increase the etficiency and gain when the tube is operated as an amplifier, or to increase the output power thereof when the tube is operated as an oscillator.

More specifically, the guns according to the present invention include a cathode having at least one emissive surface tilted with respect to the desired direction of the beam, associated with at least one non-emissive electrode, the angle between the non-emissive surface of the lastnamed electrode and the emissive surface of the cathode having a predetermined value dependent on relative potentials of the electrode and cathode, and the angle between the emissive cathode surface and the axis extending in the desired direction having also a well-defined value, which is, however, different for plane and rotational structures, respectively In the case of a plane structure,

' the emissive surface is a plane forming with the axis an angle of substantially 67. Moreover, a pair of such surfaces may be disposed symmetrically to the axis, thereby forming a dihedral with an angle of substantially 134 between the two surfaces. In the case of a structure having a symmetry of revolution, the emissive surface is a cone the surface of which forms with the axis an angle of substantially 45 that is a cone having an opening angle of substantially 90.

Referring now to the drawing, and more particularly to FIGURE 1, reference numerals 1 and 2 designate therein two plane metallic surfaces of a cathode which are electron-emissive when heated by any conventional means (not shown). These surfaces intersect along an edge 3, thereby forming a dihedral having an opening angle of substantially 134. The length of the dihedral in the direction perpendicular to the drawing, i.e., the width of the beam to be produced, is unlimited so that a beam having a very high intensity may be obtained. To avoid spreading of the beam in the direction of its width, conventional terminal electrodes may be provided, these electrodes being not shown herein as they form no part of the present invention. Reference numerals 4 and 5 designate two lateral non-emissive electrodes, having a shape which is easily determined by those skilled in the art to define the position of two extreme paths 6 and 7 between which it is desired that the beam be contained. Assuming that these electrodes are carried, by conventional means (not shown), at the same potential as the cathode surfaces 1 and 2, a value of substantially 157 will be given to the angle between the

surfaces

4 and 1, or 5 and 2, respectively. However, the same paths 6 and 7 could be obtained with electrodes 4 and 5 biased negatively or positively with respect to the surfaces 1 and 2, provided that a corresponding alteration, readily determinable by those skilled in the art, is made either in the shape of the electrodes 4 and 5, or in their angle with respect to the surfaces 1 and 2.

Perpendicular to the bisecting plane 8 of the dihedral, and at a distance from the edge 3 which is determined solely by the desired convergence to be given to the beam, is located an anode 9 carried by any conventional means (not shown) at a suitable positive potential with respect to the cathode surfaces 1 and 2. This anode is made of soft iron with a View toward magnetically shielding the space between the cathode 1, 2 and the anode 9, so that the electrons emitted from the cathode move in a space free of any magnetic field. The paths of different electrons emitted by the cathode are contained between two extreme paths 6 and 7 and form a beam which passes through a rectangular slot 10 provided in the anode 9, and thereafter enters into the space beyond this anode.

It is assumed, without any intention of limit-ing the present invention to such application that this space is an interaction space of a linear O-type travelling wave tube having a double delay line. For the sake of simplicity, and by reason of the conventional nature thereof, no element of this tube has been shown, except its two parallel delay lines 11 and 16. A longitudinal magnetic field is established in this space as in any conventional O-type tube, but this field does not penetrate into the space of the gun because of the shielding action of the anode 9. It is assumed that both lines 11 and 16 are properly excited in phase, and that their interaction with the beam moving between the two lines 11 and 16 in the direction of the arrow 12 is coherent. No other detail of the travelling wave tube has been shown, as such details are of entirely conventional nature.

A theoretical study made by the applicant on the described structure has ascertained its following properties:

(1) The current emitted from any given point of the cathode surface varies substantially linearly with the distance between this point and the edge 3; its intensity is zero along this edge, therefore there are no electrons moving within the bisecting plane 8, while its maximum lies in the inception points of the paths 6 and 7.

(2) Various intermediate paths such as 13, 14, 15, etc. converge asymptotically toward the bisecting plane 8, without any point of cross-over if the cathode is at the potential of ground, i.e., if the initial velocities of the electrons are zero.

(3) The beam entering into the space beyond the anode 9 has in its cross-section a variable density, the current being zero in the bisecting plane 8, provided that the initial velocities are zero. Therefore, the electrons are focused to form a beam in the form of two parallel ribbons separated by an electron-free region near the plane 8, the densities in each ribbon increasing moreover from their inner surfaces toward their outer surfaces defined by the extreme paths 6 and 7.

This last-named property is extremely advantageous for the purpose of interaction with the delay lines 11 and 16. Taking for sake of comparison a ribbon-like beam having the same width but uniform electron density, and assuming the same amount of power applied to the beam, it is readily seen that in the beam produced by the means according to the present invention, the electromagnetic field is concentrated near the outer surfaces of the ribbons, that is in a region of the beam which is relatively nearest to the delay line; it is known that under these conditions the efiiciency of cumulative energy transfer is improved, so that the tube is able to operate with relatively higher amplification gain or with relatively higher oscillatory power output, under the assumption of equality of all other operational parameters.

Referring now to FIGURE 2 wherein like reference numerals as in FIGURE 1 are used to designate like parts, there is shown a structure wherein a half of the electrode system of FIGURE 1, that is the emissive electrode 2 and the non-emissive electrode 5, have been suppressed. There are maintained in this embodiment the electrode 1, forming with the plane 8 an angle of substantially 67, and the electrode 4 forming with the electrode 1 an angle of substantially 157, provided both electrodes are carried at a common potential. A calculation made by applicants shows that the electrons emitted from the surface of the cathode 1 follow the

same paths

6, 13, 14, 15 as in FIGURE 1, provided that the same distribution of electric field and potential as in FIGURE 1 is restored. According to the present invention, this distribution is restored by replacing the emissive electrode 2 by a non-emissive electrode 17 forming an angle of substantially 45 with the plane '8, so that the dihedral defined by the surfaces 1 and 17 has an opening angle of substantially 112. Moreover, the anode 9 has its lower half suppressed and replaced by an electrode 18 in the form of a hyperbolic cylindrical suface. As a result thereof, the electrons emitted from the cathode 1 are concentrated to form a single ribbon-like beam with non-uniform electron density, passing above the plane 8. This beam could be used for interaction with a single delay line 11.

The same principles are applied according to the present invention to gun systems having a symmetry of revolution. The emissive cathode electrode is then a cone as indicated by reference numeral 19 in FIGURE 3. Applicants calculation has shown that the same properties as described above are maintained if the opening angle of the cone is of substantially i.e., if the cathodic surface forms an angle of substantially 45 with the axis of the cone. In front of the base of the cone is located a non-emissive electrode 29, having a symmetry of revolution and a suitable profile, with an opening of substantially the same diameter as the base of the cone 19. The surface of the electrode 20 forms with the internal surface of the cone 19 an angle of substantially 157 provided both electrodes are carried at a common potential. The function of the electrode 20 is the same as that of the electrodes 4 and 5 in FIGURE 1. The electrons emitted from the cathode 19 are then concentrated to form a variable density cylindrical beam 21 having zero density along its axis. This beam passes through the aperture 10 in the anode 9 and may thereafter be used to pass through the interior of a helix 22 operating as delay line of a travelling wave tube.

It is not necessary that the cathodic emissive surface of the examples described above extend up to the edge 3 or to the apex of the cone 19, since the electron emission in the vicinity of this edge or apex is very small so that the corresponding emissive area of the cathode could be suppressed without substantially reducing the total current intensity emitted from the cathode. Thus, FIG- URE 4 shows a cross-section of a cathode electrode which might correspond, for instance, either to the plane structure of FIGURE 1 or to the rotational structure of FIG- URE 3, wherein a portion of the emissive surface neighboring the edge of the dihedral or the apex of the cone has been suppressed, thus leaving an aperture 23. However, in order to maintain the described properties, the same distribution of electric field and potential as in the preceding figures should be restored. This is done by providing a non-emissive electrode 24 having its edge facing the periphery of the aperture 23. The shape, potential and angle with respect to the cathode surface are determined for this electrode by calculation or experimentation by any means known to those skilled in the art, so that the same field distribution is restored as for the same configuration without aperture 23 and without electrode 24. The behavior of the gun is then the same as in the preceding figures, and the beam generated by this gun has the same property of non-uniform electron density.

While we have shown and described several examples of embodiments in accordance with the present invention, it is understood that the same is not limited thereto but is susceptible of numerous changes and modifications as known to a person skilled in the art, and we therefore do not wish to be limited to the details shown and described herein but intend to cover all such changes and modifications as are encompassed by the scope of the appended claims.

We claim:

1. An electron gun for generating an electron beam, comprising emissive cathode means having a periphery and a region remote from said periphery, and means for emitting by said cathode means an electron current with substantially linearly increasing density from said remote region toward said periphery, thereby generating an electron beam With variable electron density over its crosssection, and anode means for accelerating the electrons to cause the same to flow in a predetermined direction, said anode and cathode means defining a space substantially devoid of a magnetic field, an aperture being provided in said anode means to enable the flow therethrough of said electrons to form a beam, and a utilization space beyond said anode means for utilizing said beam, wherein said cathode means includes at least one substantially plane emissive surface tilted with respect to said direction at angle of substantially 67, and at least one nonemissive electrode located near said periphery and forming an angle of substantially 157 with the surface of said cathode means, said beam being ribbon-like and means for carrying said cathode means and said non-emissive electrode means at a common potential.

2. An electron gun for generating an electron beam, comprising emissive cathode means having a periphery and a region remote from said periphery, and means for emitting by said cathode means an electron current With substantially linearly increasing density from said remote region toward said periphery, thereby generating an electron beam with variable electron density over its crosssection, and anode means for accelerating the electrons to cause the same to how in a predetermined direction, said anode and cathode means defining a space substantially devoid of a magnetic field, an aperture being provided in said anode means to enable the flow therethrough of said electron to form a beam, and a utilization space beyond said anode means for utilizing said beam, wherein said cathode means includes a pair of plane emissive surfaces located in planes intersecting along a straight line forming edge of a dihedral having an opening angle of substantially 134, said predetermined direction being substantially located in the bisecting plane of said dihedral substantially perpendicular to said edge, said beam being in the form of double ribbon, and a pair of non-emissive electrode means located respectively near each periphery of both of said emissive surfaces opposite said edge, and each forming with the respective emissive surface an angle of substantially 157, means being provided for carrying both said emissive surfaces and both said non-emissive electrode means at a common potential.

3. A gun as claimed in claim 2, wherein .both said emissive surfaces are extended to physically intersect along said edge.

4. A gun as claimed in claim 2, wherein both said emissive surfaces are limited on the side of said edge by a periphery, both of said last mentioned peripheries defining a slot in the apex of said dihedral, and auxiliary electrode means having an edge facing each of said peripheries to obtain a predetermined distribution of electric field.

5. An electron gun for generating an electron beam, comprising emissive cathode means having a periphery and a region remote from said periphery, and means for emitting by said cathode means an electron current with substantially linearly increasing density from said remote region toward said periphery, thereby generating an electron beam with variable electron density over its cross-section, and anode means for accelerating the electrons to cause the same to flow in a predetermined direction, said anode and cathode means defining a space substantially devoid of a magnetic field, an aperture being provided in said anode means to enable the flow therethrough of said electrons to form a beam, and a utilization space beyond said anode means for utilizing said beam, wherein said cathode means includes at least one substantially plane emissive surface tilted with respect to said direction at angle of substantially 67, and at least one non-emissive electrode means located near said periphery and forming an angle of substantially 157 with the surface of said cathode means, and said nonemissive electrode means at a common potential, and a plane non-emissive electrode tilted with respect to said direction by an angle of substantially 45 and forming with said plane emissive surface an angle of substantially 112.

6. A gun as claimed in claim 5, wherein said anode means includes a portion in the shape of hyperbolic cylindrical surface, said anode portion extending, with respect to the plane passing through the intersection line of said emissive and non-emissive surfaces and containing said predetermined direction, on the same side of said plane as said non-emissive electrode.

7. An electron gun for generating an electron beam, comprising emissive cathode means having a periphery and a region remote from said periphery, and means for emitting by said cathode means an electron current with substantially linearly increasing density from said remote region toward said periphery, thereby generating an electron beam with variable electron density over its crosssection, and anode means for accelerating the electrons to cause the same to flow in a predetermined direction, said anode and cathode means defining a space substantially devoid of a magnetic field, an aperture being provided in said anode means to enable the flow therethrough of said electrons to form a beam, and a utilization space beyond said anode means for utilizing said beam, wherein said cathode means include at least one emissive surface tilted with respect to said direction, and at least one nonemissive electrode means located near said periphery and forming an angle of substantially 157 with the surface of said cathode means, said emissive surface being the internal surface of a cone having an opening angle of substantially said beam being of cylindrical shape with a substantially electron-free region along its axis.

8. A gun as claimed in claim 7, wherein means are pro- 7 8 vided for carrying said cone and said non-emissive elec- References Cited trode means at a common potential, and wherein said UNITED STATES PATENTS angle between the surfaces of said cone and of said non- 2 268 196 12/1941 Pierce 313*82 emissive electrode means is of substantially 157. 2843776 7/1958 Tien T X A gun as claimed in claim wherein said is 5 2 936 396 5/1960 Currie 313-s2 x cut near its apex substantially perpendicular to its axis 2:996:64O 8/1961 Eichenbaum to form a substantially circular hollow base, and auxiliary electrode means having an edge facing the circumference HERMAN KARL SAALBACH, P imary Examiner. of said base, said auxiliary electrode means being located ELI LIEBERMAN Examiner within said cone to obtain a predetermined electric field 10 distribution. P. L. GENSLER, Assistant Examiner.