US3368104A

US3368104A - Electron beam tube included depressed collector therefor

Info

Publication number: US3368104A
Application number: US352457A
Authority: US
Inventors: Jack A Mccullough
Original assignee: Varian Associates Inc
Current assignee: Varian Medical Systems Inc
Priority date: 1964-03-17
Filing date: 1964-03-17
Publication date: 1968-02-06
Anticipated expiration: 1985-02-06

Description

Feb. 6, 1968 .1. A. M CULLOUGH 3,368,104

ELECTRON BEAM TUBE INCLUDING DEPRESSED CCLLECTOR THEREFOR Filed March 17, 1964 BODY VOLTAGE 62 -5O% OR MORE MOBODY VOLTAGE A BODY VOLTAGE e I; 44 62 +25% OR LESS 5 M 50 6 K Iv 42 'i 56 VIIII4 IIIII A" '1 45 40 'I III,

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CATHObE I JACK A. MccuLL uOH POTENTIAL BY W MW ATTORNEYS United States Patent Ofifice 3,368,104 ELECTRON BEAM TUBE INCLUDED DEPRESSED COLLECTOR THEREFGR Jack A. McCullough, Los Altos, Caiifl, assignor, by mesne assignments, to Varian Associates, a corporation of California Filed Mar. 17, 1964, Ser. No. 352,457 2 Claims. (Cl. 315-538) ABSTRACT OF THE DISCLOSURE A collector for the spent beam of a beam tube the operation of which produces a wide distribution of axial velocities among the electrons in the spent beam, such collector comprising a plurality of segments the first segment to be encountered by the spent beam having a potential with respect to the cathode which is greater than the potential of the interaction portion of the device the remaining segments being at lower potentials with respect to the cathode. Such first segment of the collector having a hollow frusto-conical shaped portion with its apex adjacent the interaction means and preferably having a tubular extension connected to such apex. In a preferred embodiment the collector comprises three sections, the first hav ing a potential with respect to the cathode which exceeds that of the interaction section by an amount up to 25%, the intermediate section having a potential with respect to the cathode equal to that of the interaction section and the final section of the collector having a potential with respect to the cathode that is 50% or less of that of the interaction section.

This invention relates generally to an electron beam tube and more particularly relates to an electron beam tube having an improved depressed collector arrangement.

Beam-type tubes in the present state of the art are considered to include klystrons and continuous interaction devices, such as traveling wave tubes. Although the invention will be described with particular reference to klystrons, it is also applicable to any type of beam tube in Which the spent beam contains electrons having a distribution of axial velocities other than a single velocity.

According to conventional practice, beamtube cllectors are one-piece devices'operated at a high enough potential to collect the slowest electrons in the beam. This, of course, means that all of the electrons are collected at a very high potential which is an ineflicient way of collecting electrons.

It has been shown that it is possible to increase the efliciency of klystrons and traveling wave tubes by operating the collector at a potential that is negative with respect to the body of the tube. When so operated with appropriate circuitry, it is possible to feed the energy that would normally be dissipated as heat, back into the power supp However, it has also been found that if the collector potential is reduced below the potential necessary to collect the slowest electrons in the spent beam, such slow electrons will in effect be repelled by the collector and will travel back down the beam and disrupt proper operation of the tube. In addition to slow primary electrons which are repelled back down the beam, secondary electrons can escape from a collector and head down the beam with the same disruptive eifect.

3,368,104 Patented Feb. 6, 1968 Collectors using a plurality of sections with each of the sections being biased at a diiferent potential have been tried in the past, but none of these collector arrangements have been able to provide a complete, simple and practical solution to the problem.

In fact, some complex collector arrangements, using crossed electric and magnetic fields, have also been used. One such arrangement, entitled Electron Tube Apparatus and Method of Operation, Serial No. 56,824, filed September 19, 1960, by Donald A. Dunn and Peter A. Sturrock, now US. Patent 3,202,863, is assigned to the assignee of this invention.

Accordingly, an important object of this invention is to provide an improved collector and method of collecting an electron beam which permits more efiicient collection of electrons than was heretofore possible.

Another object of the invention is to provide a beamcollecting structure, which in addition to collecting primary electrons at reduced potential, will also minimize the escape of a secondaries from the collector.

Briefly described, this invention relates to an electron beam tube which contains means for forming an electron beam, means for interacting with the beam, and means for collecting the beam of electrons. The interacting means are maintained at a given positive potential with respect to the beam forming means. The collecting means, which are insulated from the interacting means, contain a number of electrically conductive segments that are insulated from each other. The electrically conductive segment that is closest to the interacting means is maintained at a higher potential than the given positive potential of the interacting means. Each of the remainder of the electrically conductive segments is maintained at a lower potential than the potential of the electrically conductive segment closest to the interacting means.

The objects, features and advantages of the invention will become apparent from the following specification and claims when read in connection with the drawing in which:

The sole figure is a cross-sectional view showing a klystron embodying a collector according to the invention.

Referring to the sole figure, a klystron 10 has a beam forming gun 12, beam interacting means 14 and a collector 1b. The electron gun 12 is a conventional structure employing a cathode 18, focus electrode 20 and anode 22. The anode 22 is electrically insulated, by preferably a ceramic cylinder 24, from a metal base plate 26 on which is mounted a cathode support cylinder 28. The cathode 18 is preferably heated by a heater assembly (not shown) located within the cathode support cylinder 28. A pair of

conventional sandwich seals

30 and 32 are provided between the ceramic cylinder 24 and the base plate 26 and between the ceramic cylinder 24 and the anode 22, respectively.

The beam interaction structure 14 comprises

drift tube sections

34, 36 and 38 spaced apart to form three interaction gaps 40. The drift tube sections are connected together by cavity resonators 42.

During operation of the klystron, the cathode 18 of the electron gun 13 forms a beam of electrons which travel through the interaction means 14 and on into the collector 16. The cavities 42 interact with the beam in a well known manner so that the first two gaps d0 operate to decelerate some electrons and accelerate others in a manner that causes the electrons in the beam to pass the last or output gap in bunches which drives the output cavity.

Loops

43 and 45 serve to introduce and remove electromagnetic energy in the input and output cavities, respectively. As a result of this type of modulation, the electron beam, as it enters the collector 16, is made up of electrons having a variety of axial velocities.

The collector 16 comprises three electrically

conductive segments

44, 46 and 48. The

conductive segments

44, 46 and 48 are made of non-magnetic material, preferably copper. The electrically conductive segment 44, which is closest to the interacting means 14, has a hollow frustoconical portion 50 located between a first cylindrical portion 52 and a second cylindrical or tubular portion 54. The second cylindrical portion 54 has a smaller crosssectional area than the first cylindrical portion 52. The second cylindrical portion 54 is connected to the hollow frusto-conical portion 50 substantially at the apex thereof and longitudinally extends in the direction of the interaction means 14. A pole piece 56 of magnetic material is provided between the last or output cavity 42 and the collector 16. A pair of

sandwich type seals

58 and 60 are provided between the pole piece 56 and a first flange portion 62 associated with the electrically conductive segment 44 and between each of the other flange portions 62 associated with the electrically

conductive segments

46 and 48 of the collector 16. Dielectric cylinders 64 are provided between the

sandwich seals

58 and 60 so as to further electrically insulate electrically

conductive segments

44, 46 and 48 from each other.

In operation, the interaction section 14 of the klystron is normally surrounded by an external magnetic circuit (not shown) which develops axial magnetic field lines through the

drift tube sections

34, 36 and 38 to focus the electron beam in the interaction section 14 and prevent it from spreading. The pole piece 56 is part of the external magnetic circuit used in forming magnetic field lines that run axially through the drift tubes.

When the klystron 10 is operated, one or more power supplies are used to apply different potentials to the various parts of the klystron 10. A number of separate power supplies can be used since certain of the circuits carry very little current and therefore can employ inexpensive supplies. The cathode 18 is at the lowest potential, and the anode 22 (or tube body) is maintained at a positive potential with respect to the cathode 18. The electrically conductive segment 44 of the collector 16, which is the closest conductive segment to the interaction section 14, is maintained at a more positive potential than the anode 22 (or tube body), but preferably at a potential no greater than approximately 25% more than the potential of the anode 22. The electrically conductive segment 46 of the collector 16 is maintained at the potential of the anode 22 (or tube body). The electrically conductive segment 48 of the collector 16 is maintained at less than the potential of the anode 22. Typically, the electrically conductive segment 48 is provided with a potential up to approximately 50% of the potential of the anode 22. Suitable leads are shown in the figure for electrically connecting the various parts of the klystron 16 to the desired potential sources.

The operation of the improved collector of this invention is as follows: Electrons from the cathode 18 traveling through the interaction means 14 are accelerated or slowed down to create bunches of electrons where the individual electrons of each bunch have different axial velocities.

The very slow traveling electrons are accelerated toward the collector 16 because of the high potential on the electrically conductive segment 44 of the collector 16,

and they are collected by the electrically conductive segment 44. The tubular or cylindrical portion 54, which is attached to the hollow frusto-conical portion 50 of the electrically conductive segment 44, aids in collecting the slow electrons of the electron beam and prevents them from traveling in a reverse direction toward the cathode 18.

The electrically conductive segment 46, which is at body potential, collects some of the electrons from the beam which are traveling at a velocity greater than the velocity of the slow electrons. The electrically conductive segment 43 functions as the depressed collector portion of the collector 16 and serves to slow up the fastest traveling electrons and collect them.

Secondary electrons that are emitted anywhere within the collector 16 are collected by either the electrically conductive segment 46 which is at a higher potential than the electrically conductive segment 48 or by the electrically conductive segment 44, which is at a higher potential than the electrically conductive segment 48. In this manner, the electrically conductive segment 44 with its tubular or cylindrical portion 54 functions both to accelerate slow electrons out of the interaction section to prevent their traveling back towards the cathode and also serves to prevent the escape of secondary electrons that are generated in the collector 16. Suitable feedback means (not shown) are connected to each of the electrically

conductive segments

44, 46 and 48 of the collector for feeding the energy back into the power supply.

No effort has been made to exhaust the possible embodiments of the invention. It will be understood that the embodiments described are merely illustrative of the preferred form of the invention and various modifications may be made therein without departing from the scope and spirit of the invention.

What I claim is:

1. A klystron type beam tube comprising means for forming an electron beam, means for interacting with said beam, and means for collecting the electrons in the beam arranged along the beam in the order named, said interacting means being maintained at a given positive potential with respect to said beam forming means, said collecting means being insulated from said interacting means and comprising electrically conductive segments insulated from each other, the electrically conductive segment of said collecting means closest to said interacting means being maintained at a more positive potential with respect to said beam forming means than said given potential of said interacting means, said collecting means comprising at least two other electrically conductive segments, one of said two electrically conductive segments being maintained at the given positive potential of said interacting means, the other of said two electrically conductive segments being maintained at a potential up to approximately one-half of the given positive potential of the interacting means, said electrically conductive segment closest to said interacting means being maintained at a potential greater than and up to approximately 25% more than the given positive potential of said interacting means.

2. A klystron type beam tube comprising means for forming an electron beam, means for interacting with said beam, and means for collecting the electrons in the beam arranged along the beam in the order named, said interacting means being maintained at a given positive potential with respect to said beam forming means, said collecting means being insulated from said interacting means and comprising electrically conductive segments insulated from each other, the electrically conductive segment of said collecting means closest to said interacting means being maintained at a more positive potential with respect to said beam forming means than said given potential of said interacting means, said collecting means comprising at least two other electrically conductive segments, one of said two electrically conductive segments being maintained at the given positive potential of said interacting means, the other of said two electrically conductive segments being maintained at a potential up to approximately one-half the given positive potential of said interacting means, said electrically conductive segment closest to said interacting means being maintained at a potential greater than and up to approximately 25% more than the given positive potential of said interacting means, said electrically conductive segment which is maintained at the given positive potential of said interacting means being located between said electrically conductive segment that is maintained at a potential greater than and up to approximately 25% more than the given positive potential of said interacting means and said electrically conductive segment which is maintained at a potential up to approximately one-half of the given positive potential of the interacting means.

6 References Cited UNITED STATES PATENTS 2,853,641 9/1958 Webber 315-3.5 2,949,558 8/1960 Kornpfner et al. 315-538 X 3,172,004 3/1965 Von Gutfeld et a1. 315-5.38 X

HERMAN KARL SAALBACH, Primary Examiner. S. CHA'DMON, 111., Assistant Examiner.