US2889488A

US2889488A - Delay lines for crossed field tubes

Info

Publication number: US2889488A
Application number: US506331A
Authority: US
Inventors: Reverdin Daniel
Original assignee: CSF Compagnie Generale de Telegraphie sans Fil SA
Current assignee: Thales SA
Priority date: 1954-05-13
Filing date: 1955-05-05
Publication date: 1959-06-02
Anticipated expiration: 1976-06-02

Description

June 2, 1959 D. REVERDIN DELAY LINES FOR c ossED FIELD TUBES 3 Sheets-Sheet 1 Filed May 5, 1955 June 2, 1959 D. REVERDIN DELAY LINES FOR CROSSED FIELD TUBES Filed May 5, 1955 5 Sheets-Sheet 2 J n 2, 1 D. REVERDIN' I 2,889,488

DELAY LINES FOR CROSSEID FIELD TUBES Filed May 5, 1955 3 Sheets-Sheet 3 United States Patent DELAY LINES FOR 'CROSSED FIELD TUBES Daniel Reverdin, Paris, France, assignor to Compagnie Generale de Telegraphic Sans Fil, -a corporation of France Application May 5, 1955, Serial No. 506,331 Claims priority, application France May 13, 1954 6 Claims. (21. 315-393 The present invention relates to electron discharge tubes having crossed electric and magnetic fields, this designation including both traveling wave amplifying or oscillating tubes and magnetrons whether of rectilinear or of circular structure, and more particularly to delay lines for use therein. 7

Known tubes of this kind generally comprise an anodic electrode in the form of a delay line along which is propagated a high frequency electromagnetic wave in interaction with a beam. This line, rectilinear or circular is of geometrically periodic structure and comprises elements such as vanes, separating teeth between anode cavities, fingers of an interdigital delay line, rods of a ladder line, etc. e

.It is known that under the action of intense hyperfrequency fields prevailing in the interaction space of these tubes, and under the action of very high densities of space charges normally used, the electron. beam, instead of being propagated in a direction parallel to the delay line, progressively approaches this delay line, so that some electrons impinge upon the latter. As will be shown hereinafter, the impact on the longitudinal faces of the delay line by the electrons may not constitute a major disadvantage provided that the dissipation of heat generated in the delay line is sufficient, but theimpact on the transverse faces is capable of creating a secondary emission which reduces the output of the tube and increases the danger of breakdown. e I The object of the invention, which is to avoid this secondary emission, is attained by providing a tube with crossed electric and magnetic fields which comprises a negative or cathodic electrode and a delay line or anodic in Figs. 3, and

electrode parallel thereto and which includes elements, j

each of which has a first transverse face parallel to the 131m defined by said fields and being the first to be impinged upon by the electrons of the beam, asecond transverse face and at least one longitudinal face intersecting respectively the first, and the second trans- 1 verse faces along a first and asecond. edge, sai d twoedges being parallel to the magnetic field, the distance between the. first edge and the negative electrode being. greater than thedistance between the second edge and the negative electrode. p I The invention will be better understood from the ensuing description with reference to the accompanying drawings, in which: v

Fig. 1 shows in section a known form of delay line in the tubes in question, this figure being intended to indicate the disadvantages of known systems; ".Figs. 2, 3 and 4 show, respectively, in section three {delay lines embodying the invention;

Figsl S and 6 show respectively in cross-section and in axial section an oscillator magnetron tube in which the delay line shown in Fig. ,2 is incorporated;

Fig. 7 shows in longitudinal section a traveling wave Fig. 8 shows in plan View a ladder type delay line suitable for the tube shown in Fig. 7 and having the form shown in Fig. 3.

Fig. 1 is a longitudinal section View of part of a delay line having vanes 2 of known form, the vanes having, in the plane of the drawing, a rectangular shape comprising transverse faces 9 and 10 and a longitudinal face 12. A face 11 separates two successive vanes. This delay line or anodic electrode is brought to a positive potential relative to a cathodic electrode or sole 3 disposed opposite and parallel to the faces 12, so that an electrostatic field E, directed from the sole 3 towards the face 12 and having lines of force 21, is established between the delay line and electrode 3. Further, the interaction space between the two electrodes is immersed in the magnetic field B which is perpendicular to the plane of the drawing and is directed from the observer towards this plane. The electron beam 7 is propagated in the interaction space and, in the absence of ultra-high frequency field, its direction of propagation is parallel to the surface of sole 3 and to the faces 12 that is, perpendicular to the crossed fields E and B.

Under dynamic conditions of operation, as has been indicated above, the beam progressively approaches the anodic electrode and some electrons eventually impinge upon the latter at a small angle of incidence 0 relative to the direction of the faces 11, this angle depending on the conditions particular to the tube in question and which in general does not exceed 20.

The ends of the trajectories of these electrons, which are assumed to be parallel and rectilinear, have been shown in Fig. 1. It can be seen that some electrons strike the faces 12 and others the faces El which face in the direction generally opposite the direction of electron propagation in the interaction space between the cathodic electrode 3 and the delay line.

The fact that the electrons impinge the faces 12 does not constitute a major disadvantage, provided that the anode is capable of dissipating the heat thereby generated. The secondary electrons which might result from the impact of the electrons of the beam cannot leave these faces owing to the constant. electrostatic field directed towards the faces 12. This field is very strong relativeto the amplitude of the ultra-high frequency field of the wave propagated in the anode, so that the resultant electrostatic field is never nil, and is always of suificient intensity for blocking the secondary emission. On the other hand, in the space between the vanes, the electrostatic field is nil or very weak, as evidenced by the distribution of the lines of force; thus the ultra-high frequency field, in a part of its period, is capable of rendering the face 10 positive relative to the face 9, which creates conditions that favor secondary emission on the face 9 when the latter is bombarded by the primary electrons; The above-described phenomena have been ascer 'tained experimentally. They are very harmful as concerns the output of the tube and the output power, since the secondary electrons subtract energy from the ultrahigh frequency field. Furthermore, they tend to cause high frequency arcs to be set up between the elements i of the delay line and in consequence limit the high-l re;

quency voltage at which the'tube may operate without danger of breakdown,

" Further, the secondary electrons emitted from the face 9 follow incurved trajectories 22 owing to the action of a plifier of rectilinear structure usinga ladder-type delay e a the magnetic field B and fall on the

.face

9, 11 or 10, according to their velocity. If their velocity .is high enough, they may result in atertiary emission which reduces still more the output and the gain. J

In the Figs. 2 to 8, like reference characters designate assesses like elements in Fig. 1. In Fig. 2, the longitudinal face 12' is flat and is inclined at an angle relative to the direction of the electrode 3; the angle of incidence of the electrons relative to the faces 11 is as in the delay line shown in Fig. 1. Thus it can be seen that, contrary to that which occurs in the case of the delay line shown in Fig. l, the entire beam strikes the faces 12' whereas the faces 9 receive practically no bombardment and hence emit practically no secondary electrons. The angle determines the difference in the height of the faces 9 and 10. Although the delay line configuration varies slightly in the several embodiments described hereinafter, the reference numerals 9, l0 and 11 are used in each instance to indicate the corresponding faces of the delay line vanes.

The correct choice of the angle o is obtained by trial and error. Generally speaking, it may be stated that if F is the sum of the surface areas of the slots 11 between the anode teeth and S the sum of the surface areas of the faces 12, the ratio /6 increases with F /.S', the first being approximately equal to 1 when the second is equal to 1.

In Fig. 3, the shape of the face 12" is cylindrical, its concave side being directed towards the interaction space. The height of the face 9 is less than that of the face 10, the difference between these two heights being ascertained by trial and error, as in the first example.

In Fig. 4, the face 12" is stepped. The face 12"" is formed by at least two intersecting surfaces which may be for example intersecting planes, one being substantially perpendicular and the other substantially parallel to the face 9, the latter face thus being of less height than the face 1%. he difference between heights of the faces 9 and Ill is also determined experimentally.

Figs. and 6 show respectively in cross-section and axial section a magnetron whose anode comprises a delay line 31 of the type shown in Fig. 2 disposed in circular manner. The delay line 31 comprises vanes 32 defined by recesses machined in the cylindrical delay line 31 constituting the envelope of the magnetron. The negative electrode 33 carries an emitting layer and operates as a cathode having indirect heating by a filament 34 supplied by a source 5 through leads 8. A source 6 brings the envelope 31 to a positive potential relative to the filament 34, which is connected to the cathode 33. The magnetic field B is created by the polar elements of a magnet 19. The oscillating energy is extracted by means of the loop 20. The vanes 32 present flat inclined faces 42 to the impact of the electron beam as in the embodiment shown in Fig. 2. The inclined faces 42 each indicate an angle with respect to a tangent to a circle concentric with the cathode 33 at a point where the radial axis of the vane intersects the circle. By suitably selecting the direction of the field B, the beam is made to describe a trajectory in the clockwise direction, in the interaction space between vanes 32 and electrode 33.

Fig. 7 is a sectional view of a traveling wave amplifying tube 1 with crossed electric and magnetic fields. The tube comprises a cathode heated by a filament 4 supplied by a source 5 and the envelope is positively ener- 'gized relative the filament and cathode by a source 6. The electron beam from the cathode 15 passes between a delay line 44 and the negative electrode 45 and is received by a collector 16. The delay line 44, shown in plan in Fig. 8, is for example a ladder delay line, the rods of which have a shape similar to that shown in Fig. 3. An ultra-high frequency wave is fed into the tube through an input 17, is propagated along the delay line 44 and is received at the output 29 after having been amplified, in the known manner, by interaction with the electron beam which travels near the delay line 44. The magnetic field B, perpendicular to the plane of the draw ing, is produced by polar elements not shown in this fixt The invention is not limited to the embodiments de- 4. scribed hereinbefore, since it is applicable to any crossed electric and magnetic field tube, for example a backward traveling wave oscillator.

What I claim is:

1. An electron tube having a delay line and an electrode parallel thereto and defining therewith an electron and wave interaction space, means for positively biasing said line with respect to said electrode, thereby establishing in said space an electrostatic field having lines of force transverse thereto, means for establishing in said space a transverse magnetic field having lines of force crossed with said lines of force of said electrostatic field, and means comprising an electron source for injecting an electron beam into said space, said beam propagating normally in a direction substantially perpendicular to said electrostatic and magnetic fields: said delay line comprising a series of periodically spaced elements, each element comprising first and second faces substantially parallel to each other and to the lines of force of said electrostatic and magnetic fields, said first face facing said electron source, and a third face intersecting respectively said first and second faces along a first and a second edge, the distance between said first edge and said electrode being greater than the distance between said second edge and said electrode, so that said third face is turned toward said electron source, whereby electrons deviating from said normal direction are absorbed by the third face of said elements.

2. A tube in accordance with claim 1, wherein said third face is a plane.

3. A tube in accordance with claim 1, wherein said third face is a concave surface.

4. A tube in accordance with claim 1, wherein said third face is composed of at least two intersecting surfaces.

5. A tube in accordance with claim 4 wherein said intersecting surfaces are two planes, the one being substantially perpendicular and the other substantially parallel to said first face.

6. In an electron tube having a delay line and an elec trode opposed thereto and defining therewith an electron and wave interaction space, means for positively biasing said line with respect to said electrode, thereby establishing in said space an electrostatic field having lines of force transverse thereto, means for establishing in said space a transverse magnetic field having lines of force crossed with said lines of force of said electrostatic field, and means comprising an electron source for propagating electrons into said space, said electrons being propagated normally in one direction in said space: said delay line comprising a series of periodically spaced ele ments, each element comprising first and second faces substantially parallel to the lines of force of said electrostatic and magnetic fields, said first face facing in the direction opposite said direction of propagation of electrons, and a third face intersecting respectively said first and second faces along first and second edges of said element, the distance between said first edge and said electrode being greater than the distance between said second edge and said electrode so that electrons impinging on said elements are absorbed by said third faces hereof.

References Cited in the file of this patent UNITED STATES PATENTS 2,414,121 Pierce Jan. 14, 1947 2,687,777 Warnecke et a1 Aug. 31, 1954 2,702,370 Lerbs Feb. 15, 1955 2,730,678 Dohler et al. Jan. 10, 1956 2,774,913 Charles Dec. 18, 1956 FOREIGN PATENTS 677,587 Great Britain Aug- 20, 1952