US3240983A

US3240983A - High frequency apparatus

Info

Publication number: US3240983A
Application number: US422874A
Authority: US
Inventors: Charles S Biechler; John W Grass; Oscar C Lundstrom
Original assignee: Varian Associates Inc
Current assignee: Varian Medical Systems Inc
Priority date: 1961-01-09
Filing date: 1964-11-20
Publication date: 1966-03-15
Anticipated expiration: 1983-03-15
Also published as: US3240984A

Description

March 15, 1966 c. s. BIECHLER ETAL 3,240,983

HIGH FREQUENCY APPARATUS Original Filed Jan. 9, 1961 47 64 64 ENTORS A s oscA c. u TROM ,5 ::Z9 BY M91 h ORNEY United States

Patent Oflice

3,24%,983 Patented Mar. 15, 1966 3 Claims. (or. 315-539 This application is a divisional application of U.S. Serial No. 81,455, filed January 9, 1961, by Charles S. B-iechler et al., and assigned to the same assignee as the present invention.

The present invention relates in general to high frequency tube apparatus and, more specifically, to a novel high-frequency, high-powered, air-cooled, long-life velocity modulation tube of relatively small size and weight.

Heretofore, multicavity high-power klystron amplifiers which are capable of amplifying, for example, frequencies of about 8000 megacycles were water-cooled and had a beam-guidance magnetic field produced by electromagnets. The water-cooling insured low temperature operation of the tube parts, especially the collector and the tube tuning parts, while the electromagnets constrained the electron beams to their required paths to keep the body currents low. The use of such water-cooling and electromagnets resulted in relative ease of klystron design and substantial over-all weight increase, the electromagnet, for example, adding between 60 to 70 pounds to the klystron tube which, by itself, weighed between 3 to 6 pounds.

The present invention provides a high power multicavity klystron amplifier capable of delivering continuous output power in excess of one kilowatt at frequencies of, for example, about 8000 rnegacycles while being repeatably tunable through a 500 megacycle band. The klystron has a beam-guidance magnetic field produced by a permanent magnet, thereby eliminating the need for an electromagnet and its power supply. The klystron is air-cooled to reduce the weight and thus lend itself more suitable for transportable communications use. For example, the over-all weight of one tube including magnets made in accordance with the present invention is about 40 pounds. In order that the klystron have a high amplification factor, the klystron has a number of successive tunable integral resonant cavities, for example, four. To enable the most eflicient use of the permanent magnet, the cavities are made narrow to ensure the shortest magnet gap spacing and thus the strongest possible magnetic field. Also, since the distance between the input and output cavities is short, a novel waveguide coupling arrangement is provided for the klystron which allows the body of the tube to be efiiciently air-cooled. In addition, the electron gun has a novel construction wherein the cathode emission is increased in order to produce greater high-frequency power.

The principal object of the present invention is to provide a novel high-frequency, high-power, high gain amplifier tube having a long life and exceptionally broad frequency tuning range, which tube is preferably air-cooled and has a permanent magnet for producing a beam-guidance field.

Another feature of the present invention is the provision of a novel waveguide coupling means which couples high frequency energy into a cavity resonator and from a cavity resonator through apertures facing in the same direction.

Other features and advantages of the present invention will become apparent upon a perusal of the following specifications taken in connection with the accompanying drawings wherein:

FIG. 1 is an elevation view in partial section of a novel klystron embodying the present invention,

FIG. 2 is a partial longitudinal section view of the klystron body which houses the high frequency interaction means,

FIG. 3 is a partial view of the klyst-ron taken along line 3-3 of FIG. 2, and

FIG. 4 is a detailed view of the flexible wall enclosed by circle 4-4 of FIG. 3 shown rotated Referring now to the drawings, there is shown a klystron amplifier including an electron gun assembly 11 for projecting an electron beam through the klystron body section 12 which houses the high-frequency tunable cavity resonators and a collector assembly 13 for cooling the electrons after they have passed through the body section 12. The cavity resonator tuning means includes the tuning screws 14 which are accessible on one side of the body section 12. The high-frequency signal to be amplified is coupled through a waveguide 15 into the first cavity resonator 16 in body section 12 through an aperture 17 disposed on the opposite side from the tuning screws 14 while the amplified high-frequency signal is coupled out from the last cavity resonator 18 through an aperture 19 into an output waveguide 21. Two

other cavity resonators

22 and 23 are disposed between

resonators

16 and 17. Cooling fins 24 are disposed on the two remaining opposite sides of the klystron body section 12 to provide sufiicient cooling surface for the klystron body.

This klystron utilizes a magnetic field guidance for the electron beam as the beam passes through the cavity resonators, this field being supplied by a permanent magnet means including two substantially horseshoe sections or halves (not shown) arranged to mate with the

pole pieces

26 and 27. To ensure the strongest possible magnetic field between

pole pieces

26 and 27 the over-all distance from input cavity 16 to output cavity 18 is made as short as practicable. This is accomplished by making the

resonant cavities

16, 22, 23, and 18 as narrow as possible while still insuring their capability of resonating at the proper frehuencies. As a result, the total space into which the

waveguides

15 and 21 must fit is limited. The waveguides are fixed to one wall 28 of the body 12 and since the length of body 12 is short they are disposed adjacent to each other with partition 29 separating the two. When waveguides are disposed adjacent each other, additional sections cannot be satisfactorily added since there is no room on the exterior of the waveguides for placing adequate flanges to which such section may be attached. It the flanges are not adequate, high-frequency energy will radiate from the output waveguide sections into the input waveguide sections, and noise will be produced in the system.

The present klystron has a novel arrangement for the input and output waveguide which is shown in FIG. 3. The

waveguides

15 and 21 extend from the wall 28 of body 12 so that a wedge-shaped transition zone 31 is formed at the end of the waveguide 21 just exterior of its coupling aperture 19, and a similar wedge-shaped transition zone 32 is formed at the end of the waveguide 15' just exterior of its coupling aperture 17. The Waveguides 15 and 21 extend in a different angular direction from wall 28. Therefore, at a short distance from the body 12 there is ample room around the waveguide so that

flanges

33 and 34 can be placed on

waveguides

15 and 21 respectively and a suitable vacuum tight highfrequen-cy window (not shown) is placed in each flange.

As mentioned above, this tube is capable of being tuned over a broad band. Therefore, the cavities are tuned by making one

narrow side wall

36, 37, 38, and 39 in each

cavity

16, 22, 23, and 18, respectively, flexible so that the walls are movable toward and away from the electron beam which passes through

drift tube sections

41, 42, 43, 44, and 45. Since the tube must have broad band tuning, the

walls

36, 37, 38, and 39 must be capable of flexing over a considerable distance. Therefore, in order that the tube can be tuned repeatedly without the walls incurring fatigue failure before the tube life has expired, the flexible walls are made very thin and from a very ductile and good-conductor metal, such as copper. Even though the flexible wall is made of a good conductor, there is considerable high-frequency heating of the flexible walls. Since they are thin this heat flow path is small, and therefore the walls will become very hot. A heat sink in the form of a relatively massive metal bar 47 is placed on the center of each

wall

36, 37, 38, and 39 so that the heat energy now travels a path through the walls which is half as long, thereby helping to cool the walls. The edges of the

walls

36, 37, 38, and 39 being fixed to

end Walls

48 and 49 of cavity 16,

end walls

49 and 51 of cavity 22, end walls 51 and 52 of cavity 23, and end walls 52 and 53 of cavity 18, respectively, are adequately cooled, but the bars 47 being dispersed within a vacuum need an efiicient heat path to keep them cool. Although each bar 47 is connected to a tuning screw 14 which is outside the vacuum envelope, the heat path is very long and does not provide efiicient cooling. This heat path from the bar 47 may be traced through guide 54 which is supported within the vacuum envelope of the klystron on sapphire bearing rods 56 and adjustment rod 57 which is threaded at one end into internal screw threads on the tuner screw 14. Screw 14 also has external screw threads which coact with the body 12. The internal screw threads have a different pitch than the external screw threads, so that rod 57 will move into and out of the body section 12 as the screw 14 rotates, causing the guide 54 to follow. A tubular bellows 59 is disposed around the rod 57 to provide the necessary flexibility in the vacuum wall of the klystron. Since the total length of the body 12 is short the tuning screws 14 are staggered. Thus, in order to cool the bar 47 effectively, additional

flexible members

62 and 63 which guide the heat to the end walls are disposed behind

flexible walls

36, 37, 38, and 39.

For ease of construction,

walls

36, 37, 38, and 39 are composed of one corrugated metal sheet with the areas 64 (FIG. 4) which are shown disposed between

end walls

48, 49, 51, 52, and 53 and associated bars 47 preferably are made thinner than the areas 66 which are brazed to the end walls and bars 47 since most of the flexing of the wall is performed in these areas 64. The corrugated metal sheet with two different thicknesses allows the metal to be more readily brazed than a corrugated sheet metal having one very thin thickness which must correspond to the thickness of areas 64.

Flexible members

62 and 63 are made similar to the corrugated sheet metal which forms

flexible walls

36, 37, 38, and 39.

Capacitive tuning horns 67 (FIG. 3) are attached to each end of bars 47 making two horns for each

cavity

16, 18, 22, and 23 which further increases the tuning rate of the cavity as the flexible walls are moved, thereby increasing the tuning band of the klystron tube.

The tube has a novel electron gun structure which aids in increasing its high-frequency power. The cathode 68 is preferably made of porous tungsten and impregnated with suitable oxide mixes, as is well known in the art, with a pancake type heater 69 suitably supported behind the cathode. A focusing electrode 71 is disposed in front of the cathode 68 so that the part of the cathode disposed around its periphery is shielded from the positive potential of the anode 41. This outside part of the cathode is difficult to maintain at the uniform temperature at which the central portion 68' is maintained, and therefore the emissive current density of this part is lower than the emissive current density of the central portion 68. This arrangement of the focusing electrode permits only the electrons emitted from portion 68' to be focused into the beam, thereby increasing the current density of the beam.

A high density beam when it is collected by the collector liberates large amounts of energy as heat on a smaller area thereby causing localized melting of the collector. In order not to melt the collector, the energy must be spread over a large area. This is accomplished by shaping the magnetic field so that it helps defocus the beam in the collector region as well as guide the beam through the body 12. The magnetic pole pieces 26 and 27 (FIG. 4) which are disposed at each end of the drift space are made with apertures 73 and 74, respectively, through which the beam passes. Aperture 73 being larger than aperture 74 has disposed therein drift tube section and anode 41 made of non-magnetic material. This allows the magnetic lines of force to penetrate into the gun assembly 11, thereby increasing the focusing characteristic of the electron gun and also, because the electrons are traveling substantially parallel to the magnetic field disposed between the region from the cathode 68 to the anode 41 less noise is produced in the system. The beam rapidly spreads after it passes through aperture 74. Since aperture 74 is small, the magnetic field therein is substantially transverse and there is no or very little magnetic field in the collector. Though the beam spreads, the collector must still be cooled by a series of radial fins 76 which are oriented circumferentially around the anode. The fins 76 may be either a series of thin washers, brazed to the collector, or a thin member helically wound around and brazed to the collector. The fins are enclosed by a cylindrical member 77 which has four openings 78 extending its full length and disposed at 90 intervals around the member 77. Cooling air is introduced into two diametrically opposed openings 78 and exhausted through the remaining two openings. This arrangement provides a multitude of short paths for the cooling air and consequently the amount of energy necessary to drive the cooling air is low. Member 77 may be made of magnetic material to further bypass the magnetic field from the collector.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, 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. In a linear beam high-frequency amplifier, an electron gun for producing and directing an electron beam along a central beam axis, a collector for collecting said electron beam, and a high frequency interaction means positioned between said gun and said collector comprising a plurality of cavity resonators, said electron gun, collector and plurality of tunable cavity resonators lying along and defining an elongated central axis along which said electron beam travels between the electron gun and collector, the respective end cavity resonators of said plurality of cavity resonators disposed at the ends of said interaction means each having a coupling aperture facing in the same direction the respective axes of said coupling apertures being substantially perpendicular to said central axis along which said electron beam travels, and a waveguide coupled to said each end cavity resonator through said coupling aperture therein, each of said waveguides being disposed at an acute angle to the axis of its respective coupling aperture forming a transition zone in said waveguides exteriorly of said cavity resonators said Waveguides each defining a central axis, said central 5 axes of said waveguides lying in a pair of spaced parallel planes disposed normal to the central beam axis of said amplifier.

2. The amplifier defined in claim 1 wherein said plurality of cavity resonators are tunable and wherein said cavity resonators include tuning means disposed at 180 space rotated portions of said cavity resonators with respect to said coupling apertures.

3. The amplifier defined in claim 1 wherein the respec- 90 angles relative to each other.

References Cited by the Examiner UNITED STATES PATENTS Crapuchettes et a1. 315-539 HERMAN KARL SAALBACH, Primary Examiner.

tive axis of said waveguides are disposed at substantially 10 ELI LIEBERMAN Examiner S. CHATMON, IR., Assistant Examiner.

Claims

1. IN A LINEAR BEAM HIGH-FREQUENCY AMPLIFIER, AN ELECTRON GUN FOR PRODUCING AND DIRECTING AN ELECTRON BEAM ALONG A CENTRAL BEAM AXIS, A COLLECTOR FOR COLLECTING SAID ELECTRON BEAM, AND A HIGH FREQUENCY INTERACTION MEANS POSITIONED BETWEEN SAID GUN AND SAID COLLECTOR COMPRISING A PLURALITY OF CAVITY RESONATORS, SAID ELECTRON GUN, COLLECTOR AND PLURALITY OF TUNABLE CAVITY RESONATORS LYING ALONG AND DEFINING AN ELONGATED CENTRAL AXIS ALONG WHICH SAID ELECTRON BEAM TRAVELS BETWEEN THE ELECTRON GUN AND COLLECTOR, THE RESPECTIVE END CAVITY RESONATORS OF SAID PLURALITY OF CAVITY RESONATORS DISPOSED AT THE ENDS OF SAID INTERACTION MEANS EACH HAVING A COUPLING APERTURE FACING IN THE SAME DIRECTION THE RESPECTIVE AXES OF SAID COUPLING APERTURES BEING SUBSTANTIALLY PERPENDICULAR TO SAID CENTRAL AXIS ALONG WHICH SAID ELECTRON BEAM TRAVELS, AND A WAVEGUIDE COUPLED TO SAID EACH END CAVITY RESONATOR THROUGH SAID COUPLING APERTURE THEREIN, EACH OF SAID WAVEGUIDES BEING DISPOSED AT AN ACUTE ANGLE TO THE AXIS OF ITS RESPECTIVE COUPLING APERTURE FORMING A TRANSITION ZONE IN SAID WAVEGUIDES EXTERIORLY OF SAID CAVITY RESONATORS SAID WAVEGUIDES EACH DEFINING A CENTRAL AXIS, SAID CENTRAL AXES OF SAID WAVEGUIDES LYING IN A PAIR OF SPACED PARALLEL PLANES DISPOSED NORMAL TO THE CENTRAL BEAM AXIS OF SAID AMPLIFIER.