US3036237A - Klystron electron tube apparatus - Google Patents

Description

y 1962 1.. T. ZITELLI ETAL 3,036,237

KLYSTRON ELECTRON TUBE APPARATUS Filed March 23, 1953 INVENTOR/S LOUIS T.ZITELLI CURTIS E.WARD

AT ORNEY Patented May 22, 1962 3,036,237 KLYSTRQN ELECTRON TUBE APPARATUS Louis '1. Zitelli and Curtis E. Ward, Palo Alto, Calif., assignors to Varian Associates, San Carlos, Calif., a corporation of California Filed Mar. 23, 1953, Ser. No. 343,855 13 Claims. (Cl. 3155.19)

This invention relates, generally to ultra high frequency electron tube apparatus and the invention has reference, more particularly, to novel velocity modulation tubes of the reflex klystron type which are so Constructed and arranged that the reflected beam is deflected so as not to return to the region of the cathode and which incorporates other novel structural advantages.

Ultra high frequency velocity modulated devices of the reflex klystron class are in wide use at the present time as oscillators for supplying ultra high frequencies. In these known reflex klystrons, electrons are emitted from a cathode, formed into a beam, pass through a positively charged accelerator grid where they are accelerated to a constant velocity, and later pass through the gap formed by the two grids in a high frequency cavity resonator where the electrons are acted upon by the field across the gap to velocity modulate the beam of electrons. The velocity modulated electrons then approach a reflector electrode which is at a negative potential. The reflector repels the electrons, the electrons turning about and passing through the gap between the two resonator grids in bunches, thus imparting ultra high frequency energy to the cavity resonator. Since the electrons have then performed their useful function, their elimination from active operation upon the elements in the tube is desirable. However, in many of the reflex klystrons heretofore employed, the electrons pass back along their original path, through the accelerator grid, and approach the negative cathode region, this negative region repelling the returning electrons to again turn them about and send them over the original path through the accelerator grid, the resonator gap, etc. These multiple transit electrons are again turned about by the reflector and pass through the resonator gap a fourth time and the sequence is repeated. Certain ones of the electrons will be intercepted by the grids and the walls of the tube, but many of the electrons make multiple transits across the resonator gap and produce undesirable effects in the tube such as unstable power output and unstable modulation sensitivity characteristic. Various attempts have been made to eliminate the electrons immediately after the second or return passage across the resonator gap. This present invention discloses a practical and eflicient apparatus for eliminating the multiple transits of the beam electrons.

Heretofore, the flange mounting structures generally used to secure klystrons to output waveguide circuits employ an output coupling window forming a part of the vacuum wall of the tube and located in the mounting flange substantially flush with the outer or mounting surface thereof. In this position it is susceptible to damage from blows inflicted on the mounting surface of the flange and strains exerted on the flange. In the tube of the present invention this disadvantage is eliminated.

It is the principal object of this invention to provide a novel reflex klystron tube which eliminates multiple transits in the tube of the beam electrons.

Another object of this invention is to provide a reflex klystron tube which transmits the electron beam over one path on its initial transit through the tube and over a different path on its reflected or return trip through the tube.

Another object of this invention is to provide a novel reflex klystron wherein the electron beam passes through the resonator gap field parallel to the electric field vector thereof during both its initial and return passage through such gap thereby effecting a maximum interchange of energy between the beam and resonator field, while at the same time the beam of electrons does not return into the cathode region after the return passage through the resonator gap.

Another object of this invention is to provide a reflex klystron tube which employs magnetic means for bending the electron beam in one direction before its first passage through the resonator gap and for then bending the beam in the opposite direction after its return trip through the resonator gap.

Another object of this invention is to provide a reflex klystron tube having a permanent magnet located so as to act upon the beam to change its direction of travel.

Still another object of this invention is to provide a flange mounting structure for mounting klystrons on output waveguide circuits which permits the output coupling window to be mounted a safe distance back from the mounting surface of the flange and which prevents straining the window seal due to forces exerted on the mounting flange.

Other objects and advantages will become apparent from perusal of the following specification taken in connection with the accompanying drawings wherein one embodiment of the invention is depicted.

In the drawings,

FIG. 1 is a side elevation partly in section of a reflex klystron embodying the present invention.

FIG. 2 is an end elevation view partly in section of the reflex klystron looking from the left-hand side in FIG. 1.

FIG. 3 is a transverse sectional view of the reflex klystron in a plane indicated by section line 3-3 in FIG. 1, the arrows indicating the direction in which the view is taken.

FIG. 4 is a sectional view of another embodiment of this invention. in FIG. 1 have the same reference numbers.

FIGS. 5(a) and (b) show side and top views, respectively, of another structure for use in a reflex klystron utilizing this invention.

Referring now to FIGS. 1, 2 and 3, the main body of the klystron which embodies this invention for the purpose of disclosure comprises a rectangular block portion 1 as of steel having a multi-diameter bore 2 therethrough and an opening or iris 3 cut in one of the longer sides thereof which, in its lengthwise direction, is perpendicular to the axis of the bore 2. Mounted as by brazing within a smaller diameter portion of bore 2 of this block portion 1 adjacent to the iris 3 is a metallic cup-shaped header 4, which may be of copper-plated steel, having an axially aligned bore 5 therein. A copper honey-combed resonator grid 6 is shown mounted as by brazing on the header 4 aligned with the bore thereof. The reflector assembly comprises a metallic reflector 7 mounted on a reflector post 8 by means of a collar 9, the reflector post 8 being mounted on a metal reflector cup 11 by means of a glass-to-metal seal 12, the reflector cup 11 in turn being mounted as by brazing within the bore of a cylindrical reflector mounting member 13. The mounting member 13 is fixedly secured within one end of the bore 2 of block portion 1 as by silver brazing, the reflector 7 extending into the bore 2 and being closely spaced from the resonator grid 6. The reflector terminal or lead 14 extends into the hollow reflector post 8 and is secured therein.

A metallic header 15 as of copper-plated steel is mounted as by brazing in the other end of the bore 2 in the block portion 1. Secured as by brazing to an annular protruding portion 16 of this header 15 is shown a Elements in this structure similar to those honey-combed resonator grid 17 of, for example, copper which is carefully spaced from the resonator grid 6. Mounted on the header 15 as by brazing is a metallic, such as copper, pole piece mounting cup 18 having a multi-diameter bore therein comprising a smaller diameter bore 19 axially aligned with the bore in the header 15 and the bore 2 in the block portion 1, and a larger diameter bore 22 having its axis at a predetermined angle with respect to the axis of the smaller bore 19 as shown in FIG. 1. In this particular embodiment of the invention, this angle was set at The two axes of the bores 19 and 22 lie in the plane of the sheet of drawings and intersect within the mounting cup 18. Fixedly secured in aligned transverse apertures in the cylindrical wall of the cup 18 as by brazing are two steel pole pieces 23 and 24 extending through the wall and inwardly into the cup and positioned diametrically opposite each other. Mounted in the outer end of this cup is a metallic header 25, as of copper-plated steel, having an axially aligned bore 26 therein which coincides with the axis of the larger diameter bore 22 in the cup 18. A honey-combed accelerating grid 27 of, for example, copper is shown mounted on one surface of this header 25 axially aligned with the bore 26 thereof. A conventional cathode gun assembly 21 comprising a cathode button 28, focusing ring 29 and heater wire 31 is mounted as by brazing in a cylindrical metal cathode mounting member 32 which in turn is mounted in the end of the copper cup 18 as by brazing. The axis of the cathode gun assembly 21 coincides with the axis of the larger diameter bore 22 in the pole piece mounting cup 18.

A U-shaped magnet mounting member 33 of nonmagnetic material such as brass is placed over the copper cup 18 in straddling fashion with its two legs 34 and 35 extending down adjacent to the pole pieces 23 and 24, respectively, and is secured to the block portion 1 by screws 39. A bore through the cross piece of this U- shaped brass member 33 is used to hold a small cylindrical magnet 360. A threaded bore extends through each leg 34 and 35 of this U-shaped member perpendicular to the magnet bore and each is fitted with an adjusting screw 37 and 38, respectively, of a magnetic material such as iron. These adjusting screws extend from the ends of the magnet 36 down the legs 34 and 35 of the member 33 where they protrude through the inside surface of the member adjacent to the pole pieces 23 and 24 which are mounted in the side of the copper cup 18. The screws 37 and 38 may be threaded into or out of their bores to vary the magnetic gap between the ends of the screws and the magnet 36 or pole pieces 23 and 24. A magnetic field may be traced from one pole of the small cylindrical magnet 36 across to the adjacent one of the screws 37, through the screw 37 across to the adjacent one of the pole pieces 23, across the gap between the two pole pieces to the other pole piece 24, across to the other screw 33, through the screw and across to the other end of the small magnet.

A relatively thin walled rectangular waveguide section 41 having a flanged end 40 is mounted at the flanged end to the body portion 1 over the iris or opening 3. A waveguide flange 42 adapted for mounting the klystron tube on an output waveguide circuit is included in a subassembly comprising a waveguide window adapter cup 43 and a glass sheet 44 sealed across the inner open end of this adapter. The waveguide flange 42 has a rectangular opening centrally located therein with the edges of the opening bent so as to form a flanged edge 49 to thereby strengthen the flange 42 and also form a mounting surface for the adapter cup 43. The rectangular window adapter cup 43 with the glass window sealed therein is fixedly mounted within the opening of the flange 42 as by brazing to the flanged edge 49 with the window 44 extending away from the flange 42. This subassembly is then fixedly mounted on the klystron within the outer end of the waveguide section 41 as by brazing, the window 44 extending into the waveguide section. The glass window 44 is thus setback from the outer surface of the flange 42 for protection from damage. The thin walled waveguide section 41 enables relative expansion and contraction of block 1 and flange 42 without any leaks developing. An cxhaust tube 45 extends through the wall of the block portion 1 for use in evacuating the tube, the end of the exhaust tube being crimped and sealed off after pumping out.

In operation, a current passing through the heater wire 31 produces a beam of electrons from the cathode button 28 which is focused by the focusing ring 29 and accelerated by the accelerating grid 27 which is at a positive potential with respect to the cathode. The accelerated beam of electrons passes through the portion of the re-entrant tube formed by the bore 26 of the header 25 and passes through the magnetic field across the gap between the two pole pieces 23 and 24. The magnetic field will act upon the electrons in the beam and will bend the beam from the path coinciding with the axis of the bores 26 and 22 in the header 25 and cup 18, respectively, to the path coinciding with the axis of the bores in the headers 15 and 4 and block portion 1. To bend the beam in the proper direction, the north pole of the magnet 36 is on the left hand side looking at FIG. 3. The angle through which the beam is bent is determined by the strength of the magnetic field. The screws 37 and 38 provide a convenient means for varying the strength of the field by varying the magnetic gaps as above stated. The beam will pass through the gap between the two resonator grids 17 and 6 where it will be velocity modulated. The negative reflector 7 will repel the electrons and they will turn about and again pass through the gap between the two resonator grids 6 and 17 in bunches to give up energy to the field in the cavity resonator. The stream of electrons will then continue through the bore of the header 15 into the region of the magnetic field between the pole pieces 23 and 24 where the electrons will again be acted on and the beam will be bent downwardly looking at FIG. 1. The electrons will collect on the walls of the header 25 and the tube and on the accelerating grid 27 and will not pass axially through the accelerator grid 27 into the cathode region. Thus the electron beam will not be turned about and transmitted along its original path through the tube to make a third passage through the resonator gap. The path of electrons through the tube is approximately as traced by the arrowed line in FIG. 1 for clarity.

Referring to FIG. 4, there is shown in section view a klystron similar to that shown in FIGS. 1 through 3, inclusive, which can be used to realize this invention. Fixedly embedded in the legs 34 and 35 of the U-shaped magnet mounting member 33, which is made of nonmagnetic material such as aluminum, are two ribbons of iron 46 and 47 bent inwardly at their lower ends adjacent the pole pieces 23 and 24. The bore in the cross-piece of this member 33 extends through the two iron ribbons. A section of this bore fixedly holds a small magnet 36 while the remaining portion of the bore is threaded and contains a gap-adjusting screw 48 for varying the size of the gap between the screw 48 and the magnet 36.

Referring to FIGS. 5(a) and (b), there is shown a portion of a reflex klystron tube which may also be used in carrying out the present invention. A header 51 on which an accelerating grid 27 is mounted has an extended cylindrical portion 52 thereon with an axially aligned bore 53 therein. The end of this cylindrical portion is cut olf at an angle to give a sloping end surface 54. Header 55 also has an extended cylindrical portion 56 with an axially aligned bore 57 therein, the end surface 58 of this portion being slanted to correspond to the slanting end surface of the cylindrical portion 52 of the header 51. The two headers 51 and 55 are mounted ina reflex klystron (not shown) in positions corresponding to the positions of headers 25 and 15 in FIG. 1, the two end surfaces 54 and 58 having a small uniform gap therebetween. A permanent magnet 59 is mounted on the reflex klystron so that a magnetic circuit is established through the magnet and the two headers and across the gap. One component of the magnetic field across the gap is in a transverse direction with respect to the beam looking at FIG. (a). This component of magnetic field will bend the electron beam in a manner similar to that described for the reflex klystron in FIG. 1.

In the above embodiments, the magnetic field Was established by use of a small permanent magnet. It is obvious that other magnetic field producing apparatus could be used in lieu of permanent magnets such as, for example, current carrying coils properly associated with the reflex klystrons.

In heretofore existing reflex klystrons wherein attempts were made to prevent the beam from returning into the cathode region after passing through the resonator gap, one example of which employs a spike in the center of the reflector to produce an umbrella-shaped reflected beam, the electron beam does not travel parallel to the electric field vectors across the resonator gap during both passages thereacross and, therefore, the optimum interchange of energy between the beam and resonator field does not occur. In this present invention, the electron beam travels parallel to the electric field vectors across the r-.sonator gap on both passages therethrough to give the maximum energy exchange even though the electron beam does not re-enter the negative cathode region on its return trip through the klystron.

Since many changes could be made in the above construction of the novel reflex klystrons and many apparcntly widely different embodiments of this invention could be made without departing from the scope thereof as, for example, the use of other structure for changing the direction of the beam in its transit through the tube, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. An electron beam discharge device comprising cathode means for producing a beam of electrons, a body portion having a longitudinal path therethrough over which the electron beam travels in passing through the discharge device, the cathode means being positioned with respect to the body portion so that the axis of the beam emitted from the cathode means is at an angle with respect to and intersects the axis of the path through the body portion of the tube, means for producing a magnetic field transverse to the beam axis and the path and located between the cathode means and the body portion to thereby change the direction of the ham flow from the cathode to coincide with the axis of the path through the body portion, and means positioned in the path in the body portion for repelling the electrons in the beam to reverse the direction of flow of the beam along the body axis, said magnetic field producing means serving to eliminate multiple transit electrons in the discharge device.

2. A reflex klystron comprising a first resonator grid, a second resonator grid and a reflector electrode axially align d within the reflex klystron, a cathode gun assembly for producing a beam of electrons mounted in said klystron and positioned with its axis at an angle with respect to the axis of said aligned grids and reflector so as to produce a beam of electrons which intersects the axis of these elements, and means for providing a magnetic field within the klystron perpendicular to the axis of the produced beam of electrons and the axis of the grid and reflector elements and located at a point between the elements and the cathode gun assembly for changing the direction of the beam of electrons to coincide with the axis of said elements,

3. A reflex klystron as claimed in claim 2 wherein said means comprises a pair of magnet poles mounted in the wall of the klystron body and a magnet associated with the poles for producing a magnetic field across the pole gap.

4. A reflex klystron as claimed in claim 3 including means associated with the magnet for varying the strength of the magnetic field across the pole gap.

5. In a reflex klystron, cathode means for producing a beam of electrons, a cavity resonator comprising two spaced resonator grids through which the beam passes on its first transit through the klystron, a reflector aligned with the resonator grids for r pelling the electrons passing through the resonator grids from the cathode and returning them back through the resonator grids, and means for providing a unidirectional magnetic field in the klystron perpendicular to the electron beam to change the direction of the travel of the beam before its first transit through the grids and to again change the direction of the beam after its return transit through the grids.

6. A reflex klystron as claimed in claim 5 wherein said means comprises a pair of magnet poles mounted in the wall of the klystron body and a permanent magnet associated with the poles for producing a magnetic field across the pole gap.

7. A reflex klystron as claimed in claim 6 including means associated with the magnet for varying the strength of the magnetic field across the pole gap.

8. A thermionic tube comprising an emitter for directing a beam of electrons therewithin, a resonator gap having an electric field thereacross through which the beam of electrons is directed, a reflector for repelling the beam of electrons to thus turn them about and return them through the resonator gap, the electrons traveling parallel to the electric field during both passages therethrough, and means adjacent the path of the beam and acting thereon for preventing the electrons from reentering the emitter region.

9. A thermionic tube of the character described comprising spaced electrodes adapted to have an alternating electric field applied therebetween, an emitter for producing a stream of electrons for passing through the space between said electrodes in a direction substantially parallel to the electric field, a reflector electrode for returning said stream back through said space in the reverse direction while remaining substantially parallel to said field, and means removed from said emitter for collecting said returning electrons, thereby eliminating multiple transit electrons Within said thermionic tube.

10. A thermionic tube having a relatively thick walled body provided with an energy conveying iris opening through the wall thereof, a relatively thick walled coupling member provided with a sealing window positioned inwardly of the exposed surface thereof, and a relatively thin walled conduit means rigidly interconnecting said body and said coupling means.

11. A flange mounting structure for mounting a high frequency electron device on a waveguide output circuit comprising a section of waveguide mounted on the device, a rectangular cup-shaped waveguide adapter having a window opening in the bottom surface thereof mounted within the other end of the waveguide section with the window opening and extending into the waveguide section, and a waveguide mounting flange having a rectangular opening therein, the edges of the opening being flang:d, the mounting flange being mounted on the rectangular waveguide adapter with the flanged edge of its opening in contact with the waveguide adapter.

12. A reflex klystron including a reflector electrode, cathode means for emitting a beam of electrons within said klystron traveling at an angle with respect to the longitudinal axis of said reflector electrode and means for providing a magnetic field within the klystron between the cathode means and the reflector electrode perpendicular to the axis of the beam of electrons for changing 7 8 the direction of the emitted beam of electrons to coincide References Cited in the file of this patent with the longitudinal axis of the reflector electrode.

13. A reflex klystron as claimed in claim 12 including UNITED STATES PATENTS a resonator cavity having a gap therein, said resonator 2,211,614 Bowie Aug. 13, 1940 being positioned within said klystron such that said gap 5 2,518,954 Steele Aug. 15, 1950 is in the path of the electron beam between the reflector 2,567,674 Linder Sept. 11, 1951 electrode and the field producing means.

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