US3322997A

US3322997A - Permanent magnet focused klystron

Info

Publication number: US3322997A
Application number: US287916A
Authority: US
Inventors: Caryotakis George
Original assignee: Varian Associates Inc
Current assignee: Varian Medical Systems Inc
Priority date: 1963-06-14
Filing date: 1963-06-14
Publication date: 1967-05-30
Anticipated expiration: 1984-05-30
Also published as: FR1398559A; DE1491334A1; GB1073297A

Description

y 0, 1967 e. CARYOTAKIS 3,322,997

PERMANENT MAGNET FOCUSED KLYSTRON Filed June 14, 1963 2 Sheets-Sheet l INVENTOR.

GEORGE CARYOTAKIS ATTORNEY May 30, 1967 G. CARYOTAKIS PERMANENT MAGNET FOCUSED KLYSTRON 2 Sheets-Sheet 2 Filed June 14, 1963 N bfx INVENTOR. GEORGE CARYOTAKIS ATTORNEY United States Patent 3,322,997 PERMANENT MAGNET FOCUSED KLYSTRON George Caryotairis, Los Altos, Califi, assignor, by mesne assignments, to Varian Associates, a corporation of California Filed June 14, 1963, Ser. No. 287,916 9 Claims. (Cl. 315-535) This invention relates generally to a permanent magnet focused klystron and more particularly to a permanent magnet periodically focused klystron.

In a klystron, an electron beam is projected through drift tube sections forming one or more interaction gaps. Each of the gaps is coupled to a resonant cavity. The electron stream is bunched or velocity modulated by a signal at the first gap with which it cooperates and amplified energy is subsequently extracted from the beam at the same or a different gap.

For most eflicient operation of the klystron, it is desirable that the beam pass closely adjacent the interaction gaps. However, if electrons strike the drift tube sections, they may damage the tube or give rise to noise. This requires that the beam be maintained in good focus as it travels down the drift tube sections so that it will not strike the drift tube sections.

Heretofore, it has been common practice to provide a magnetic field to maintain the beam in focus. The field can be provided by a permanent magnet or solenoid.

Solenoids require a power source for energizing the same. In many applications, especially in small, low power devices, solenoids are being replaced by permanent magnets. However, in larger devices, the size and weight of the permanent magnet may become impractical.

In the travelling wave tube art, there has been developed electron beam devices in which the beam is focused by a periodic magnetic field generated by ring-like magnets disposed closely adjacent the electron stream. The structure of such devices is relatively light and compact.

It is a general object of the present invention to provide a periodically focused klystron.

It is another object of the present invention to provide a klystron in which the magnetic structure additionally defines a part of the electrical structure of the device.

It is another object of the present invention to provide a periodically focused klystron in which the magnetic structure forms a part of the one or more resonant cavities.

It is another object of the present invention to provide a periodically focused klystron in which the magnetic structure forms a part of the resonant cavities and the drift tube sections whereby the magnetic fields are concentrated at the interaction gaps.

It is still another object of the present invention to proide a periodically focused klystron of the integral cavity type.

It is a further object of the present invention to provide a klystron tube in which the interaction region of the tube is formed of substantially identical stacked magnetic plates and spaced by non-magnetic spacer rings to form the electrical and magnetic structure of the tube.

It is still a further object of the present invention to provide a periodically focused klystron which is simple in construction and easy to assemble.

These and other objects of the invention will become more clearly apparent from the following description when taken in conjunction with the accompanying drawing.

Referring to the drawing:

FIGURE 1 is an elevational view, partly in section, showing a klystron tube incorporating the present invention; and

FIGURE 2 is an end view of the klystron tube shown in FIGURE 1.

FIGURE 3 is an enlarged cross-sectional view of a segment of one cavity of the klystron tube shown in FIG- URE 1.

Generally, the periodically focused klystron illustrated in the drawings includes an elongated metal ceramic envelope having an electron gun 11 disposed at one end to form and project a beam of electrons through a plurality of drift tube sections 12-17 which define interaction gaps 19-24 each cooperating with a respective resonant cavity 29-34. After travelling through the drift tube sections, the electron beam is collected at the collector 36.

The tube envelope includes an end plate 41 which is suitably sealed to a ceramic cylinder 42 as, for example, by the seal assembly 43. The seal assembly includes a first flange 44 suitably sealed to the plate 41 as, for example, by brazing, and a second flange 46 suitably sealed to the ceramic cylinder 42 as, for example, by brazing. A backup ring 47 is attached to the flange 46. The outwardly extending portions of the

flanges

44 and 46 are sealed to one another as, for example, by heliarcing. The other end of the cylinder 42 is sealed to the plate 51 by a similar sealing arrangement 52 including flanges 53 and 54 and backup ring 56.

The end plate 41 supports the electron gun 11, the metal ceramic lead-through assembly 56 which provides means for making electrical connection to the cathode heater and the exhausttubulation 57. The cathode assembly may be of any conventional design well known in the art suitable for forming a high perveance beam.

The plate '51 carries the anode 61 which is suitably sealed thereto and also carries the shield 62. The anode, in turn, supports the disc-like plate 63. A plate 64 made of magnetic material is interposed between the plates 51 and 63 and forms a pole piece for a ring-like ermanent magnet to be presently described.

The interaction portion 66 of the klystron which includes the resonant cavities and interaction gaps comprises a plurality of spaced magnetic discs or plates 71-82 which are made of magnetic material. These plates form part of the tube envelope and define, in part, the resonant cavities.

These plates are maintained in axially spaced relation: ship with one another by a plurality of cylindrical spacer rings. The cylindrical spacer rings 84-89 form a portion of the evacuated envelope and also cooperate with the adjacent magnetic discs to define the resonant cavities.

Cylindrical spacer rings -95 cooperate with the inner edge of adjacent magnetic discs to form the drift tube sections 12-17. These rings also form a wall of the evacuated envelope and a wall for the adjacent cooling chamber which is adaptedto have liquid coolant flow therethrough, as will be presently described.

Cylindrical spacer rings 96-101 serve to support the associated permanent magnet and form another Wall of the cooling chambers 102-107.

Each of the resonant cavities 29-34 is illustrated with tuning means. It will be apparent, however, that the cavities may be fixed tuned. The tuning means for each cavity may include a movable tuning member 109 disposed to cooperate with the adjacent gap. A screw 110 has one end secured to the support 111 and its other end suitably sealed to the respective ring 84-89. Any mechanism can be used to move the support, for example, a compound screw arrangement such as that illustrated at 112.

The first or input cavity includes an input coupler 113. The coupler comprises a coupling loop 114 having one end secured to the associated cavity and its other end secured to the center conductor 115 of the coaxial line 116. A suitable coaxial coupler 117 is associated with the coaxial line 116.

The last or output cavity includes an output coupler 120 which has a coupling loop 118 associated with the center conductor 119 of the coaxial line 121. The line is terminated in a matching section 122 which forms part of the evacuated envelope and provides means for connecting the line to an associated transmission line such as another coaxial transmission line. It will be apparent to one skilled in the art that other types of couplers, for example, an iris coupler may be employed.

Coolant is supplied to the tube through the tube 126 which extends the length of the envelope. The water flows into the cooling chamber 102. A short tube, shown typically in FIGURE 3 as 143, provides communication between the chambers. The coolant, therefore, travels serially along the tube from one chamber to the next. When it leaves the last chamber, it is directed into the manifold 127 and thence through the annular chamber 128 formed about the collector. The coolant then fiows out the outlet 129.

As previously described in accordance with the invention, periodic permanent magnet focusing is employed. For this purpose, there is provided a plurality of ring magnets 131-140 which have their pole pieces in magnetic contact with the magnetic discs whereby these discs form the pole pieces for the magnets. The ring-like magnets are arranged so that adjacent ends of the magnets are of like polarity. The magnetic discs will concentrate the magnetic fields between their adjacent tips.

The magnets may be formed as two semi-circular pieces which can then be applied over the tube with adjacent ends abutting. To maintain a uniform field while still permitting the use of couplers and tuners, the magnets are cut out to accommodate the parts. Any non-uniformity of field due to the cut out may be compensated. The magnetic fields between adjacent pole pieces will be successively of opposite sense as one progresses down the length of the tube. To a first approximation, the fields will vary in a sinusoidal manner along the length of the tube.

There is preferably employed an additional ring magnet which cooperates with a magnetic disc or plate 142 to provide a field at the electron gun which aids in forming the beam. With a dish-shaped cathode, this additional field is preferably shaped so that it is perpendicular to the cathode surface at all points to thereby cause electrons to flow substantially perpendicular to the surface and be focused at the focal point of the dish-shaped cathode surface.

In summary then, it is seen that there is provided a klystron which is simple in construction, being made up of a plurality of magnetic and non-magnetic parts which can be assembled in stacked relationship to form the tube. The magnetic structure of the tube forms additionally part of the evacuated envelope and of the electrical structure to thereby provide a compact design capable of providing relatively high magnetic fields for interaction with the electron beam.

I claim:

1. A klystron including means for projecting an electron beam, at least three drift tube sections surrounding said beam and forming at least two interaction gaps, a resonant cavity surrounding each of said gaps, magnetic means for maintaining said beam in focus including at least two annular axially magnetized permanent magnets, a disc of magnetic material providing a low reluctance path for magnetic flux between said permanent magnets and the intermediate one of said drift tube sections whereby the magnetic field of said permanent magnets is concentrated adjacent the beam, said disc of magnetic material additionally forming a portion of the resonant cavity surrounding the gap associated with said one of said drift tube sections.

2. A klystron including an electron source for projecting an electron beam, a collector and means defining therebetween a path for the beam of electrons projected by said electron source including an electromagnetic assembly providing a periodic magnetic field which cooperates with said beam to maintain the beam in focus and which additionally carries the electromagnetic energy of said klytron, said electromagnetic assembly comprising a plurality of annular axially magnetized permanent magnets arranged and disposed so that like pole pieces of adjacent magnets confront one another, a plurality of discs of magnetic material each cooperating with one end of at least one of said permanent magnets, each of said discs including means forming a drift tube section, drift tube sections of predetermined discs cooperating to form interaction gaps, and resonant cavities defined in part by said discs surrounding said gaps.

3. A klystron including means for projecting an electron beam, means for collecting said beam, a plurality of transverse plates of magnetic material arranged in spaced relationship with respect to one another along said beam, each of said plates including an opening through which the electron beam passes, means at the opening of pre determined plates serving to form drift tube sections, means at the opening of predetermined adjacent pairs of plates defining an interaction gap, means spaced from and surrounding said interaction gap sealed to said predetermined pairs of plates to define therewith a resonant cavity, and permanent magnet means serving to provide a magnetic field between plates.

4. A klystron including means for projecting an electron beam, a plurality of transverse plates of magnetic material arranged in spaced relationship with respect to one another along said beam, each of said plates including an opening through which the electron beam passes, the openings of predetermined adjacent pairs of plates cooperating alternately with means forrning drift tube sections and means forming interaction gaps, means sealed to said pairs of plates cooperating with the means forming drift tube sections to define in conjunction therewith and with the plates a cooling chamber, means cooperating with the pairs of plates forming interaction gaps to define therewith and with the plates a resonant cavity, and a plurality of annular axially magnetized permanent magnets arranged and disposed so that like pole pieces of adjacent magnets confront one another arranged with one magnet between each adjacent pair of plates to provide periodic field at the openings in said plates.

5. A klystron as in claim 4 together with means providing communication between the cooling chambers, means for supplying coolant to the cooling chamber at one end of said tube, and means for removing coolant from the chamber at the other end of said tube.

6. A klystron as in claim 4 wherein said drift tube sections are formed by cylindrical rings engaging adjacent plates at said opening and wherein one wall of said cooling chamber is defined by a second ring spaced from said first ring and coaxial therewith.

7. A klystron as in claim 4 wherein said means defining the resonant cavity comprises a ring having its ends sealed to the adjacent plates.

8. A klystron as in claim 4 wherein said drift tube sections are formed by cylindrical rings engaging adjacent plates at said opening and wherein one wall of said cooling chamber is defined by a second ring spaced from said first ring and coaxial therewith, and wherein said means defining the resonant cavity comprises a ring having its ends sealed to the adjacent plates.

9. A klystron including an electron source for projecting an electron beam, a collector, and means defining therebetween a path for the beam, said means including an electromagnetic assembly comprising two annular axially magnetized permanent magnets disposed with like poles adjacent, a common pole piece interposed between said magnets, terminal pole pieces located at the other pole of said magnets respectively, said common pole piece being electrically and mechanically connected to one of said terminal pole pieces by a tubular conductive and non-magnetic member, said tubular member being disposed co-axially about said path and providing a drift 5 6 space free of electric fields for said beam, said common 2,940,000 6/1960 Geisler 31384 X pole piece and the other one of said terminal pole pieces 2,971,113 2/1961 Nygard 313-84 X providing an interaction gap of said klystron. 3,227,915 1/ 1966 Levin 3155.46

References Cited 5 HERMAN KARL SAALBACH, Primary Examiner.

UNITED STATES PATENTS RONALD COHN, Assistant Examiner. 2,492,996 1/1950 Haxby BIS-5.46 X

Claims

1. A KLYSTRON INCLUDING MEANS FOR PROJECTING AN ELECTRON BEAM, AT LEAST THREE DRIFT TUBE SECTIONS SURROUNDING SAID BEAM AND FORMING AT LEAST TWO INTERACTION GAPS, A RESONANT CAVITY SURROUNDING EACH OF SAID GAPS, MAGNETIC MEANS FOR MAINTAINING SAID BEAM IN FOCUS INCLUDING AT LEAST TWO ANNULAR AXIALLY MAGNETIZED PERMANENT MAGNETS A DISC OF MAGNETIC MATERIAL PROVIDING A LOW RELUCTANCE PATH FOR MAGNETIC FLUX BETWEEN SAID PERMANENT MAGNETS AND THE INTERMEDIATE ONE OF SAID DRIFT TUBE SECTIONS WHEREBY THE MAGNETIC FIELD OF SAID PERMANENT MAGNETS IS CONCENTRATED ADJACENT THE BEAM, SAID DISC OF MAGNETIC MATERIAL ADDITIONALLY FORMING A PORTION OF THE RESONANT CAVITY SURROUNDING THE GAP ASSOCIATED WITH SAID ONE OF SAID DRIFT TUBE SECTIONS.