US3573537A

US3573537A - Collector electrode for crossed field traveling wave device

Info

Publication number: US3573537A
Application number: US829387A
Authority: US
Inventors: Merle R Boyd
Original assignee: Raytheon Co
Current assignee: Raytheon Co
Priority date: 1969-06-02
Filing date: 1969-06-02
Publication date: 1971-04-06
Anticipated expiration: 1988-04-06

Abstract

A collector electrode for the terminal region of devices having parallel substantially coextensive electrodes defining an interaction path for a beam of electrons is disclosed to provide an optimized collecting surface along a reference plane defined parallel to the direction of the magnetic field. A progressively varying collector surface with respect to the opposing coplanar electrode is provided to substantially match the variations in the magnetic field intensity thereby effectively influencing the electric field and velocity of the electrons in the collection region.

Description

United States Patent R. Bo d 3,271,618 9/1966 Kooyers 3-l5/5.38X l jg f f 3,273,006 9/1966 Osepchuk 315/5.3sx [21 1 Appl. No. 829.387 FOREIGN PATENT 221 Filed l une g, :33? 923,180 4/1963 Great Britain 315/538 [45! Patented pr. I73] Assignee Raython Company Przniary Examznerl-lerman Karl Saalbach Lexington Mass Asszstant Exammer-Saxfield Chatrnon, Jr.

Attorneys-Harold A. Murphy, Joseph D. Pannone and Edgar 0. Rest [54] COLLECTOR ELECTRODE FOR CROSSED FIELD TRAVELING WAVE DEVICE I 10 Claims 5 Drawing gs. ABSTRACT: A collector electrode for the terminal region of [52] U.S.Cl SIS/3.5, devices having parallel Substantially coextensive electrodes 315/ 5 31 5/39-3 defining an interaction path for a beam of electrons is disl5l] Int. Cl H01] 25/34 closed to provide an optimized collecting Surface along a [50] Field of Search 315/35, reference plane defined n to the direction of the 36, netic field. A progressively varying collector surface with respect to the opposing coplanar electrode is provided to sub [56] References Clted stantially match the variations in the magnetic field intensity UNITED STATES PATENTS thereby effectively influencing the electric field and velocity 2,949,558 8/1960 Kompfner et al. 3 l5/5.38X of the electrons in the collection region,

"* 24 l l l f 90 i 10a 11 B I COLLECTOR ELECTRODE EOE CROSSED ElElLll) VELING WAVE DEVTCE BACKGROUND OF THE INVENTION Crossed field traveling wave devices commonly include a periodic slow wave electromagnetic energy propagating structure such as an interdigital delay line coextensive with and spaced from a continuous sole electrode to define therebetween an electron interaction path. An electron gun assembly for the generation of an electron beam is mounted adjacent one end of the structure with a collector region adjacent the other end. A transverse electric field is established between the slow wave structure and sole electrode. A magnetic field extends mutually perpendicular to the electric field with the combined fields influencing the trajectory and interaction of the electron beam with radio frequency waves propagating along the said slow wave structure. Such devices are used as amplifiers or oscillators in microwave energy systems. ln an amplifier the microwave energy input signal is coupled to one end of the slow wave structure and the amplified output signal is extracted from the other end thereof. In an oscillator the electron beam current is adjusted until oscillations can occur and the interaction of the beam with the radio frequency waves will result in generation of microwave energy coupled by means of a suitable conductor disposed at one end of the slow wave structure to a utilization load. In many such devices collection of the electrons remaining in the beam after traversing the interaction path has resulted in high heat concentration in localized areas of the collection structures resulting in melting and erosion. With higher power levels being required in present day microwave systems a severe limitation exists in tube utilization with conventional collector electrode members.

A prior art collector electrode structure to gradually spread the electron impinging area over an extended collector surface is provided by means of longitudinal grooves along a surface inclined to thebeam path. Electrons entering the grooves are shielded from the electric field to result in redistribution downstream until finally collected. In US. Letters Pat. No. 3,032,677, issued to Edward C. Dench, May 1, 1962, and assigned to the present assignee, an example of the grooved col lector electrode configuration is disclosed. Such grooved collectors, however, due to inherent collection problems, are still plagued with localized hot spots to seriously hamper tube performance. A need arises, therefore, for a new approach to the electron beam collection problem in crossed field traveling wave devices, particularly where high average powers are involved.

SUMMARY OF THE INVENTION The velocity of the beam is synchronized with the phase velocity of the radio frequency waves along the slow wave structure in order for energy to be transferred to the waves. Some of the electrons are collected on the slow wave structure 3 and the remainder pass through to the collector region. In

practical tubes the magnetic field intensity is weakest at the midplane region within the interaction and collector region's. An electron in the crossed field electrostatic system possesses a total energy equal to the sum of its potential and kinetic energy. Electrons traveling in the region of reduced magnetic field intensity will realize a higher drift velocity and correspoiidingly higher kinetic energy which maybe represented by the equation, kinetic energy==ll2 mv Kinetic energy is acquired at the expense of potential energy which promotes collection in the center of the system. Such high velocity electrons in the weakest magnetic field will therefore approach the collector and are the first to be collected. The collection of the center electrons removes the repulsive force arising from their space charge and permits electrons from other portions of the beam to flow toward the center. Concentration of collection in the beam center throughout the collector system results in the intense heating and melting in this area.

The effects of the nonuniformity of collection can be offset by adjusting the local electrostatic field intensity to produce a distribution of local drift velocity so as to spread electron collection. The electric field intensity therefore can be caused to vary in the same manner as the B field to provide the necessary compensation. This electric field is inversely proportional to the spacing of the delay line and sole and is determined by the equation:

the product of Ed may be held as invariant as possible to provide for uniform collection. In the plane parallel to the mag netic field orientation the value of the d dimension is varied.

In accordance with the teachings of the'invention a collector surface is provided varying from the midplane region of the magnetic field system toward the ends with the widest dimension at the center. The electric field intensity between the sole electrode and collector is thereby adjusted to approximately match the variations in the magnetic field intensity.

In the grooved collector electrode embodiments the invention is practiced by cutting back or tapering of the lands in the central region to provide the desired contouring. Other embodiments to be described include a smooth continuous bowed configuration with the spacing between the sole electrodes and collector surface decreasing from the center to the edges of this electrode.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. l is a crosssectional view, partly in elevation, of the illustrative embodiment of the invention;

FIG. 2 is a cross-sectional view, partly in elevation, of the embodiment of P16. 1 taken along the line 2-2;

FIG. 3 is a cross-sectional detailed view taken along the line 3-3 of FIG. 2;

FIG. 4 is a cross-sectional view of an alternative embodiment of the collector electrode of the invention; and

FIG. 5 is a cross-sectional view of another alternative embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, FIGS. l and 2 illustrate a backward wave type crossed field device 10, incorporating a slow wave electromagnetic energy propagating structure 12, of the interdigital delay line type including a plurality of interdigital fingers or

elements

14 and 16 extending from opposing

annular members

18 and 20. The

members

18 and 20 are positioned on the shoulder portion of a cylindrical conductive ring or base member 22 which together with oppositely disposed

cover plates

24 and 26 hermetically sealed thereto form the walls of the evacuated envelope of the overall tube embodithem 110. Sole electrode 2d is disposed concentrically and coextensively with respect to delay line 12 and defines therebetween an interaction space 30. The sole electrode 28 is nonnally biased assembly 34 a negative potential with respect to the delay line. An input electrical lead assembly 32, electron gun assembly 34, including a thermionic cathode 36,

magnetic field producing means 38 comprising pole piece members 40, 41 and output coupling means 42 complete the major subassemblies'of the overall embodiment.

The sole electrode 28 comprises a cylindrical member of an electrically conductive material and includes a web portion 44 bounded by an arcuate portion 46 defining end shields 48 bounding a channel 50 for the purpose of confining the electron beam within the interaction space 30. One end of a hollow supporting member 52 is inserted within a tubular member 54 which is in turn secured to the sole electrode web portion 44. Member 52 in addition to supporting the sole electrode 28 forms a portion of the electrical lead assembly 32 to permit the introduction of external circuit connection leads to the appropriate electrodes within the overall device. A notched section 56 is defined within the sole electrode and the electron gun assembly 34 is disposed therein. A mounting plate 58 secures the gun assembly to the web portion 44. The gun assembly 34 includes a cathode, heater, grid and accelerating electrodes of known configuration and specific details have been omitted for the sake of clarity.

The input electrical lead assembly 32 comprises a sleeve member 60 secured to cover plate 24 together with a dielectric sealing member 62 joined in its outer end to a second conductive sleeve member 64. A terminal glass bead seal 66 supports the electrical leads in spaced relationship and hermetically seals the tube envelope. Electrical energy from appropriate sources is supplied to the cathode, heater, grid electrode and accelerating electrode by way of respective lead-in

wires

68, 70, 72 and 74 which extend through the glass bead 66.

The electric field between the delay line 12 and the sole electrode 28 may be supplied by means of a unidirectional voltage supplied, for example, by a battery 76 connected between sleeve 60 and cathode lead 68. The delay line 12 is preferably maintained at a positive potential relative to the cathode by means of the voltage supply. The sole electrode 28 is biased negatively with respect to the cathode by means of a source 78 connected between the cathode lead 68 and the sleeve member 64 with sole electrode supporting member 52 connected thereto. The accelerating electrode of the electron gun assembly 34 is maintained at a positive potential relative to the cathode 36 by means of an appropriate voltage source 80 connected between leads 68 and 74. The control grid lead 72 may be connected by means of terminal 82 to an appropriate source for controlling the optics of the electron beam current in the traveling wave device 10. The heater voltage for the cathode 36 is connected to a voltage source 84 by means of heater lead 70 and cathode lead 68.

The output coupling means 42 comprises a coaxial transmission line having an inner conductor 86 and an outer conductor 88 with the inner end of the inner conductor secured illustratively to delay line element 14 adjacent to the electron gun assembly 34. In this manner the crossed field traveling wave device will operate in the backward wave mode of oscillation or amplification.

The magnetic field is disposed with the flux lines varying along a reference plane extending parallel to the axis of the traveling wave device 10. The field intensity as hereinbefore stated tends to be at its weakest point in the midplane region approximately in the center of the channel member 50. The magnetic assembly 38 includes cylindrical pole pieces 40 and 41 which are positioned on or adjacent to the

envelope cover plates

24 and 26. Permanent magnet members or any suitable electromagnetic means will contact the pole piece members to supply the required magnetic fields. Adjustment of the magnitude and polarity of the transverse magnetic and electric fields will exert a combined influence on the electron beam traveling along the substantially circular interaction space 30.

The improved electron collection system of the invention will now be described with reference also being directed to FIG. 3 along with FIGS. 1 and 2. A precollector electrode 90 which may be formed as an extension of the delay line 12 is secured to the inside wall of the conductive ring member 22. In the illustrative embodiment now to be described the precollector electrode 90 is provided with a plurality of grooves 92 arranged in the direction of the electron beam defining therebetween lands 94 substantially throughout the length of the precollector electrode. In the grooved precollector electrode embodiment employed in traveling wave devices substantial melting as well as even, cracking due to thermal stress is quite prevalent in the midplane region of the precollector surface. In accordance with the teachings of the invention the precollector surface at the midplane region is varied by means of cutting back the lands 94a and 94b. The distance d shown between the electron precollecting surface and the surface of the opposing director 102 to be hereinafter described is varied. By adjustment of the dimension d the product of this value and the magnetic field intensity will become substantially invariant and thereby spread the effective electron collection surface over the entire precollector electrode. It may be noted that the adjustment of the dimension d tends to match the electric field intensity to the magnetic field intensity locally. It has been noted that in those embodiments where the dimension d was increased too much the localized heating was transferred to the lands at the ends of the grooved precollector configuration to result in surface deterioration. In an exemplary embodiment distance between the lands 94a and 94b and the surface 100 was approximately 10 percent greater than the distance of the end lands which distributed collection substantially uniformly over all four lands of the precollector electrode surface.

A director structure 102 in accordance with US. Letters Pat. No. 3,054.0]6, issued to H. F. Chapell, Sept. 11, 1962 and assigned to the present assignee, is provided to enhance structure beam collection. Such structure is disposed substantially parallel to the precollector electrode and provides an extension of the sole electrode 28. As detailed in FIG. 3, as well as FIG. 1, this member is secured by means of a plate 104 to a notched out portion of the sole electrode 28 by means of screws 106. The director member provides a first surface 100 substantially parallel to the collector electrode 90 together with end shields 108. Another surface inclined to the first surface 100 further enhances electron beam collection. Since the director is affixed to the sole electrode structure. the potential on this member will be substantially the same as that applied to the sole electrode. To further enhance total collection and prevent reentry of the electron beam a post-collector 112 is provided affixed to the inside wall of the conductive ring member 22.

The precollector electrode structure may be provided with a double tapered surface as well as fluid cooling to assist in the dissipation of the generated thennal energy by means similar to those disclosed in the previously referred-to U.S. Letters Pat. Nos. 3,032,667 and 3,054,016.

In FIG/4 another embodiment of the invention is illustrated. Collector electrode 114 is provided with a substantially curvilinear surface 116 contoured to provide for the widest dimension d at the midplane region indicated by the dotted line 118 and progressively decreasing laterally towards the ends of the collector. In this configuration the smooth continuously varying contoured surface will provide an idealized condition whereby the influence of the crossed electric and magnetic fields will provide for uniform electron beam collection throughout the surface of the collector.

In FIG. 5 a collector structure 120 is provided wherein the lands 122 of the multigrooved configuration are curved so that the locus of the tips follow or approximate a smooth contour designated by the dotted line 124. In this configuration the distances are decreasing and the tips of the lands 122 are suitably machined in order that the contour line will be followed.

It will be obvious to those skilled in the art that many other modifications, alterations or variations may be made in the collector electrode structures under consideration. The details of the individual configurations will be more or less dictated by the factors involving the weakness of the magnetic field intensity in the midplane region as well as any other parameters which give rise to localized electron beam collection with its attendant disadvantages. It is the paramount feature of the invention that a means is provided for adjustment locally of the electric field intensity in crossed field traveling wave devices. It will also be obvious that while a crossed field device having a circular configuration has been described, the invention will be equally applicable to tubes of the linear-type. The new and improved structure disclosed will facilitate operation of all such crossed field devices at higher average powers due to the improved electron beam collection provided by the contoured surface.

It is apparent, therefore, that this invention may be practiced in numerous configurations without departing from the spirit and scope of the invention as defined in the appended claims. Accordingly, it is understood that all matter shown and described herein is to be interpreted broadly as illustrative of the scope of the invention and not in a limiting sense.

I claim:

1. A crossed field traveling wave device comprising:

a slow wave energy propagating structure;

a coextensive electrode spaced from said slow wave structure to define therebetween an interaction space;

means for producing and directing an electron beam along said interaction space;

means for establishing an electric field in said interaction space transverse to the path of said beam;

means for producing a magnetic field having flux lines extending within said interaction space transverse to the electric field;

means including a collector electrode for collecting electrons which traverse said interaction space; and

said collector electrode including means for matching the electric field intensity substantially to the contour of the magnetic field flux lines by contouring the face of said collector electrode to vary its spacing with respect to the opposing coextensive electrode in a direction along a reference plane extending parallel to the direction of the magnetic field.

2. A crossed field traveling wave device comprising:

a slow wave energy propagating structure;

means for producing an electron beam disposed at one end of said interaction space;

means for producing a magnetic field having flux lines extending transverse to the electric field along a reference plane extending parallel to the longitudinal axis of the device;

means including a collector electrode for collecting electrons disposed at the other end of said interaction space; and

said collector electrode including means for matching the electric field intensity to variations in the magnetic field flux lines by varying the shape of the face of said collector electrode opposite to said coextensive electrode in a direction along said reference plane.

3. A crossed field traveling wave device comprising:

a slow wave structure;

a sole electrode spaced from and substantially coextensive with said slow wave structure to define therebetween an interaction space;

means for providing mutually perpendicular electric and magnetic fields in said interaction space with said magnetic field having flux lines extending parallel to the longitudinal axis of the device to compel electrons to move through said interaction space;

said magnetic field varying in intensity with the lower values oriented along the midplane region of the interaction space;

a collector electrode at the other end of said interaction space; and

said collector electrode having the surface opposite the sole electrode contoured to match the electric field intensity to the magnetic field intensity variations by adjustment of the spacing across the interaction space in a direction extending parallel to the magnetic field orientation.

d. A crossed field traveling wave device comprising:

a slow wave structure;

an electron beam source at one end of said interaction space;

means for providing mutually perpendicular electric and magnetic fields in said interaction space;

said magnetic field varying in intensity in a direction parallel to the longitudinal axis of the device;

a collector electrode at the other end of said interaction space; and

said collector electrode having a surface opposite said sole electrode shaped to provide variations in spacing across said interaction region along a reference plane extending parallel to the direction of the magnetic field.

5. A crossed field traveling wave device according to claim 4 wherein said collector electrode surface is spaced from the sole electrode at its widest point in the region along the center of the interaction space.

6. A crossed field traveling wave device according to claim 4 wherein said collector electrode surface is provided with lands defining grooves therebetween extending along the direction of travel of the electron beam.

7. A crossed field traveling wave device according to claim 6 wherein said lands adjacent the center region of said interaction space are spaced furthest from the opposing electrode structure.

8. A crossed field traveling wave device according to claim 4 wherein said collector electrode is provided with a continuously varying contoured surface with the spacing with respect to the opposing sole electrode decreasing from the center of said surface in directions extending towards the opposing ends of the collector electrode.

9. A crossed field traveling wave device according to claim 6 wherein the locus of the tips of the lands at the midplane region along said interaction space are further away from the opposing sole electrode surface than said lands at the edges of said collector electrode.

110. A crossed field traveling wave device according to claim 6 wherein the locus of the tips of said lands follows a continuously varying contour with the narrowest spacing with respect to the opposing electrode structure at ends of the collector surface and the widest spacing adjacent to the center of said surface.

Claims

1. A crossed field traveling wave device comprising: a slow wave energy propagating structure; a coextensive electrode spaced from said slow wave structure to define therebetween an interaction space; means for producing and directing an electron beam along said interaction space; means for establishing an electric field in said interaction space transverse to the path of said beam; means for producing a magnetic field having flux lines extending within said interaction space transverse to the electric field; means including a collector electrode for collecting electrons which traverse said interaction space; and said collector electrode including means for matching the electric field intensity substantially to the contour of the magnetic field flux lines by contouring the face of said collector electrode to vary its spacing with respect to the opposing coextensive electrode in a direction along a reference plane extending parallel to the direction of the magnetic field.

2. A crossed field traveling wave device comprising: a slow wave energy propagating structure; a coextensive electrode spAced from said slow wave structure to define therebetween an interaction space; means for producing an electron beam disposed at one end of said interaction space; means for establishing an electric field in said interaction space transverse to the path of said beam; means for producing a magnetic field having flux lines extending transverse to the electric field along a reference plane extending parallel to the longitudinal axis of the device; means including a collector electrode for collecting electrons disposed at the other end of said interaction space; and said collector electrode including means for matching the electric field intensity to variations in the magnetic field flux lines by varying the shape of the face of said collector electrode opposite to said coextensive electrode in a direction along said reference plane.

3. A crossed field traveling wave device comprising: a slow wave structure; a sole electrode spaced from and substantially coextensive with said slow wave structure to define therebetween an interaction space; means for producing an electron beam disposed at one end of said interaction space; means for providing mutually perpendicular electric and magnetic fields in said interaction space with said magnetic field having flux lines extending parallel to the longitudinal axis of the device to compel electrons to move through said interaction space; said magnetic field varying in intensity with the lower values oriented along the midplane region of the interaction space; a collector electrode at the other end of said interaction space; and said collector electrode having the surface opposite the sole electrode contoured to match the electric field intensity to the magnetic field intensity variations by adjustment of the spacing across the interaction space in a direction extending parallel to the magnetic field orientation.

4. A crossed field traveling wave device comprising: a slow wave structure; a sole electrode spaced from and substantially coextensive with said slow wave structure to define therebetween an interaction space; an electron beam source at one end of said interaction space; means for providing mutually perpendicular electric and magnetic fields in said interaction space; said magnetic field varying in intensity in a direction parallel to the longitudinal axis of the device; a collector electrode at the other end of said interaction space; and said collector electrode having a surface opposite said sole electrode shaped to provide variations in spacing across said interaction region along a reference plane extending parallel to the direction of the magnetic field.

10. A crossed field traveling wave devicE according to claim 6 wherein the locus of the tips of said lands follows a continuously varying contour with the narrowest spacing with respect to the opposing electrode structure at ends of the collector surface and the widest spacing adjacent to the center of said surface.