US2789247A - Traveling wave tube - Google Patents

Description

A ril- 16, 1957 Filed July 22, 1949 J. H. JONKER 2,789,247

TRAVELING WAVE TUBE 2 Sheets-Sheet 1 I/IVVEATO/P J'O/M/V/VEJ 1005M. Willi/A fan A275 April 6, 1957 J. H. JONKER 2,789,247

TRAVELING WAVE TUBE Filed July 22, 1949 2 Sheets -Sheet 2 &

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2,789,247 Patented Apr. 16, 1957 TRAVELING WAVE TUBE Johannes Lodewijk Hendrik Jonker, Eindhoven, Netherlands, assignor, by mesne assignments, to North American Philips Company, Inc., New York, N. Y., a corporation of Delaware This invention relates to electron discharge tubes for generating, amplifying or modulating waves having a wave-length of a few centimetres or less, in which device an electron-beam interacts with a coiled conductor.

Electron discharge tubes of the above type are also known as travelling wave tubes. In such tubes the electron beam is modulated by applying an A. C. voltage to the beginning of the coil. This A. C. voltage produces density modulation of the beam and the resultant maxima and minima induce voltages in the coiled conductor, these voltages developing into a travelling wave. Owing to the interaction between the coil and the beam, an amplified voltage can be taken from the end of the coil.

If the wavelength of the electrical oscillations is small, it is ditficult to obtain sufficient interaction between the coil and the electron-beam because when the length of one turn becomes comparable to half the wave-length, the interaction decreases markedly. The use of long coils to ensure sufiicient interaction is objectionable for short waves.

According to the present invention, an electron discharge tube, of the travelling wave tube type, for generating, amplifying or modulating waves having a wavelength of a few centimetres or less, is characterized in that the electron-beam travels not only at the inner side but also at the outer side of at least one coil. Thus it is ensured that the interaction between the electron beam and a coil of a given size is materially increased. Moreover, with a coil of any given size, the cross-section of the beam may be greater, so that the beam is adapted to carry more current. Furthermore the lower current density permits simpler focussing. Since, in this event, coils of a very small diameter can be used, shorter Waves can be generated or amplified or modulated.

In a particular form of a tube according to the invention, a plurality of equal and similar coils, that is to say, coils of equal length, diameter and pitch, are stretched between two perforated plates, for example rings, which are housed perpendicularly in a preferably conductive cylinder. The spacing between the coils is preferably approximately 1% to 2 times the diameter of the coils. Furthermore, the coils are arranged in a manner such that the turns are located as much as possible adjacent each other in a section at right angles to the axis of the beam.

Alternatively, only one coil may be provided between two rings in the conductive cylinder. This, also, yields satisfactory results.

At its end, the cylindrical conductive tube containing the coils may be provided with means for radiating the resultant energy or it may be inserted directly into a wave-guide.

In order that the invention may be more clearly understood and readily carried into efiect, two examples will now be described with reference to the accompanying drawings, of which:

Fig. 1 represents an electron discharge tube having a single coil and Figs. 2 and 3 are {a longitudinal view and a cross-section respectively of the electrode system of a tube having a plurality of coils.

In Fig. 1, the reference numeral 1 designates the base of a tube, made of sintered powdered glass and in which a number of pins 2 are provided. An incandescent cathode 3 having a heater coil .4 is secured to thecentral pins 2. Over the incandescent cathode 3, a nickel cup 5 is provided at a distance of approximately 1 mm. from the cathode, which cup is provided with a central aperture having a diameter of approximately 1.5 mm. In front of the nickel cup 5 is provided a cylindrical tube 6 of an iron-nickel alloy having an internal diameter of 3 ms. and a length of approximately 10 mms. A copper tube 8 has its lower peripheral edge tapered and is sealed toa glass bulb 7,'which is in turn sealed to the base 1. Two insulating, ceramic plates 9, each having an aperture of diameter 3 mms., are arranged normally to the axis of tube 8. Between these plates, a tungsten coil 12, i. e., a helical wire conductor, is stretched. This coil has a pitch of 0.3 mm. and is wound on a mandrel 1 mm. thick, the thickness of the wire being 0.1 mm. The tube 8 is closed at its end in a vacuum tight manner by means of a glass plug 10, which also serves as an energy outlet for the tube. A focussing coil 11 is arranged coaxially with the tube 8. During operation of the tube, the electrode 5 has a voltage of approximately 0 v. and the tubes 6 and 8 attain a potential of 1000 v. and 2000 v. to 4000 v., respectively. The focussing magnetic field has a value of 200 gauss. As will be evident from the foregoing description, the elements 3, 5, 6 and 8 cooperate to produce and project an electron beam through the cylinder 8 such that part of the beam passes along the inside and another part along the outside of the coil 12.

In Figs. 2 and 3, the parts corresponding to those shown in Fig. 1 have the same reference numerals. Be tween the plates 9, six coils 12 are stretched, all having the same pitch and the same diameter as each other and wound alternately leftand right-handed. The spacing between the coils is 1 /2 to 2 times the diameter of the coils in order that no dead spaces exist at which velocity modulation of the beam fails to occur. The alternate directions of winding of the coils enables the production of an intense modulating field without deflecting the beam.

What I claim is:

1. A travelling wave tube comprising an evacuated envelope, a helical wire conductor for guiding high-frequency electromagnetic waves disposed within said envelope and having a central axis and defining a discharge space of given cross-sectional area at right angles to said axis through said helical conductor, and means for producing and projecting a beam of electrons of solid crosssectional area greater than said given cross-sectional area in the direction of the axis of said conductor, whereby a portion of the beam passes along the inside of the helical conductor and a portion passes around the outside of the entire conductor.

2. A travelling wave tube comprising an evacuated envelope including a conductive cylinder having a longitudinal axis, a helical wire conductor for guiding highfrequency electromagnetic waves disposed coaxially within said cylinder and spaced therefrom, said helical conductor having a central axis and defining a discharge space of given cross-sectional area at right angles to its axis through said helical conductor, and means for producing and projecting a beam of electrons of solid crosssectional area greater than said given cross-sectional area in the direction of the axis of said conductor, whereby a portion of the beam passes along the inside of and a portion around the outside of the entire conductor.

3. A travelling wave tube comprising an evacuated envelope, a plurality of spaced, parallel, helical wire conductors for guiding high-frequency electromagnetic waves a '2 t V a disposed within said envelope and defining a discharge 7 space of given cross-sectional area at right angles to said conductors, and means for producing and projecting a beam of electrons of solid cross-sectional area greater than s'a'id'given cross-sectional area in the direction of saidconductors, whereby a portion ofthe beam passes through and a'portion around the outside of all of the conductors.

4. A travelling wave tube comprising an evacuated envelope including a conductive cylinder having a longitudinal axis, a plurality, of spaced, parallel, helical wire conductors for guiding high-frequency electromagnetic waves disposed lengthwise within said cylinder and defining a discharge space of given cross-sectional area at right angles to said conductors, said conductors being of substantially equal length, diameter and pitch, and means for producing and projecting a beam of electrons of solid cross-sectional area greater than said given cross-sectional area in the direction of said conductors, whereby a por tion of the beam passes through and a portion around the outside of all of the conductors.

5. A travelling wave tube as claimed in claim 4 in which the conductors are spaced apart a distance of approximately twice the said conductor diameter, a portion of said helical conductors being right-hand wound and the remainder of said conductors being left-hand Wound.

References Cited in the file oftthis patent UNITED STATES PATENTS 2,064,469 Haeff Dec. 15, 1936 2,211,859 Percival Aug. 20, 1940 2,300,052 Lindenblad Oct. 27, 1942 2,578,434 Lindenblad Dec. 11, 1951 2,641,730 Touraton et al. June 9, 1953 2,643,353 Dewey a June 23, 1953

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