US2938138A - Traveling wave electron discharge device - Google Patents

Description

May 24, H. H. SNYDER TRAVELAING WAVE ELECTRON DISCHARGE DEVICE Filed Sept. 5, 1957 United States Patent() TRAVELING WAVE ELEC'IRON DISCHARGE DEVICE Herbert H. Snyder, Montclair, NJ., assgnor to International Telephone and Telegraph Corporation, Nutley, NJ., a corporation of Maryland Filed Sept. 3, 1957, Ser. No. 681,623

4 Claims. (Cl. S15- 3.5)

This invention relates to traveling wave electron discharge devices and more particularly to wave energy slow wave propagating structures employed therein. A

The traveling wave type of tube is particularly useful in wideband microwave systems since it is capable of amplifying radio frequency energy over an unusually wide band of frequencies. The tube includes a form of slow wave propagating structure for transmission of microwave energy for interaction with an electron beam, closely associated with the structure. The most common of all slow wave propagating structures is the helix. The helical characteristic of the helix propagating structure in such that the axial phase velocity of microwave signals conducted along the helical path is approximately the same as or slightly slower than the velocity of the electrons of the beam whereby the electrical field of the microwave signals interact with the electron beam for amplilcation or generation of microwave signals. Thus, the usual helical propagating structure slows down the microwave signal so that its resulting axial phase velocity corresponds to a readily attainable electron beam voltage which estab-I lishes the electron beam synchronous velocity. The axial phase velocity of the wave energy is reduced in the helical propagating structure by a factor sin tb, where 3b equals the helix pitch angle.

An object of this invention is to provide a helical type slow wave propagating structure which will enable a reduction in the required electron beam voltage to produce the desired synchronous phase velocity relationship between the electron beam and wave energy.

Still another object of this invention is to provide a low voltage, low power traveling wave tube whose slow wave propagating structure has dimensions large compared to a wavelength at the operating frequencies.

A feature of this invention is the provision of a slow wave propagating structure for employment in a traveling wave tube which is in the form of a helically wound helix.

Another feature of this invention is the provision of a slow wave propagating structure for employment in a traveling wave tube which is in the form of a helical conductor having a pitch angle ,b1 wound in the form of a relatively large helix having a pitch angle 1pz resulting in an axial phase velocity reduction of the wave energy by the factor sin p1 sin 302. This results in a double axial phase velocity reduction for the wave energy which in turn enables a correspondingly large reduction in electron beam velocity and hence the required electron beam voltage.

The foregoing and other objects and features of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings comprising Figs. l and 2, wherein:

Fig. 1 is a schematic diagram illustrating a traveling wave electron discharge device employing a propagating structure of this invention; and

Fig. 2 is a graph illustrating the advantages achieved by employing the propagating structure of this invention.

Referring to Fig. 1, a traveling wave electron discharge device is illustrated schematically as including an electron gun 1, a slow wave propagating structure 2 and collector electrode 3 disposed in axial alignment within a vacuum housing 4. About the housing 4 and at least coextensive with propagating structure 2 is a magnetic focusing arrangement 5 which may take the form of a solenoid or a permanent magnet to maintain the electron beam focused for passage through propagating structure 2.

In accordance with this invention, slow wave propagating structure 2 is illustrated as including a conductor 6 wound in the form of a helix 7 of relatively small diameter and pitch which is in turn wound into a larger helix 8a. Hence, we have a helically wound helix 8. The slow wave propagating structure also includes a support arrangement of some type to assure that the helically wound helix Sis supported in axial alignment with electron gun 1 and collector electrode 3 and iny interacting relation with the electrons of the electron beam. As illusrtated, the helically wound helix 8 is supported and stitfened by elongated dielectric rods 9 supported and positioned at each end by support members 10 and 11. Members 10 and 11 are transverse of housing 4 and supported and positioned by the inner surface thereof. This type of support arrangement is particularly useful vwhere housing 4 is metallic but not necessarily limited thereto. If housing 4 is made of dielectric material, the helically wound helix 8 could be supported and aligned by the inner surface of the housing itself.

As is known, the electron beam must be in close proximity to the helically wound helix 8 to provide efcient interaction with the wave energy propagated thereon. In certain applications, the inner diameter of helix 8a may be comparable to the outer diameter of pencillike electron beams. Thus, if electron gun 1 projects a pencil-like electron beam, the desired interaction takes place. However, if the inner diameter of helix 8a is greater than the outer diameter of the pencil-like beam, the desired interaction may not take place. Therefore, electron gun 1 would have to be of the type for projecting a hollow electron beam having a sufficient diameter to again obtain the desired interaction. The hollow electron beam could be inside the inner diameter of helix 8 for the outer diameter of the beam being in close proximity thereto or outside the outer diameter of helix 8 with the inner diameter of the beam being in cloes proximity thereto. i

The traveling wave tube employing the helically wound helix 8 of this invention could be employed as an amplier, a backward wave oscillator or a backward wave ampliiier. If the tube is employed as an amplifier, wave energy would be coupled to helically wound helix 8 by means of radio frequency terminal 12. The amplified output would be removed from the helically wound helix 8 by means of radio frequency terminal 13. If the traveling wave tube is employed as a backward wave ampliier, the wave energy is coupled to helically wound helix 8 by means of radio frequency terminal 13. The amplted output would be removed from the helically wound helix by means of radio frequency terminal 12. If, however, the traveling wave tube is employed as a backward wave oscillator, radio frequency terminal 13 would be preferably terminated in an impedance matching the impedance of the helically wound helix 8. The wave energy generated by the backward waves on the helically Wound helix 8 would be removed therefrom by radio frequency terminal 12.

As mentioned previously, helically wound helix 8 is formed by theusual yhelix 7 being wound to form a helix 3H. The advantage 'l'l'iell this type Of SlOW Wye propagating structure is a double axial phase velocity reduction of the wave energy coupled thereto. This double reduction of axial phase veloeity of wave energy enables a corresponding reduction in the axial phase velocity of the electron beam and hence a relatively large reduction in the required beam voltage which controls the electron beam velocity.

If it is assumed that the usual helix has a pitch angle of tpl, the axial phase velocity of the wave energy will be reduced by a factor Vsin 1p1. The do'tted curve 14, Fig. 2, relates phase velocity and frequency and as illustrated is asymptotic to the line v1S which is identified as c sin tpl, Where c equals the free 'space electromagnetic velocity. Hence, -the beam voltage can be taken no lower than that value which will produce the 'proper beam velocity for approximate synchronization with the axial phase velocity of the energy wave on curve 14 for a particular operating frequency desired.

lNow if the conventional helix, such a`s helix 7, having a pitch angle 1]/1 is wound to form a larger helix 8a with a pitch angle 302, there is obtained a reduction of wave energy axial phase velocity by the factor sin gbl sin tbz. Curve 16, Fig. 2, relates axial phase velocity of the energy wave to frequency and is asymptotic to line 17 which is identified as c sin 1p1 sin 1,02. Hence, for the same operating frequency as mentioned above with respect to curve 14, the axial phase velocity is greatly reduced as shown by curve 16. Therefore, the beam velocity may be greatly reduced to produce the desired velocity synchronization. This results in a correspondingly large rcduction in the required beam voltage to produce 'the electron beam velocity.

While I have described above the principles of 'my invention in connection with specific apparatus, itis to be clearly understood that this description is made only by way of example and not as a limitation to the scope of my invention a's set forth in the objects thereof and in' the accompanying claims.

I claim:

l. A traveling wave electron discharge device comprising means to project a rectilinear electron beam along the axis of said device including a relatively low electron beam voltage, a wave venergy slow wave propagating structure including a single wire of relatively low attenuation formed into a helica'lly Wound helix, the Wave energy propagated along said structure traversing the entire length of each 'turn of said Wire, .and means to support said helix in energy increasing interacting relation with the electrons of said electron beam.

2. A traveling wave electron discharge device comprising 'a collector electrode, means to project a hollow rectilinear electron beam along the longitudinal axis of said device to said collector electrode including a relatively low electron lbeam Voltage, a wave energy slow wave propagating structure including a single helical conductor of relatively low attenuation wound in the form of a helix,

the wave energy 'propagated along said structure traversing the entire length of each turn of said conductor, and means to support said helix coaxial of said axis in energy increasing 'interacting relation with the electrons of said electron beam.

3. A traveling wave electron discharge device comprising a collector electrode, 'means to project a hollow rectilinear electron beam along the longitudinal axis of said device to said collector including a relatively low electron beam voltage electrode, a wave energy slow wave propagating structure including a single conductor of relatively low attenuation wound to have a rst helical conguration, said iirst helical configuration being wound to have a second helical conguration, the Wave energy propagated Valong said structure traversing the entire length of each turn of said conductor, and means to support said second helical configuration coaxial of said axis in energy increasing interacting relation with the electrons of said electron beam and wave energy connections disposed adjacent each end of said helical configuration.

4. A traveling wave electron discharge device comprising means to' project a rectilinear electron beam along the axis of said device including a relatively 'low electron beam voltage, a wave energy slow Wave propagating structure including a single helical conductor of relatively low attenuation having a pitch angle 1,!/1 wound in the form of a helix having a pitch angle 1,02 whereby the axial velocity of the wave energy is reduced by the factor sin ,b1 'sin 1,1/2, the wave energy propagated along said structure traversing the entire length of each turn of said condire-- tor, and means to support 'said helix -in energy increasing interacting relation with the electrons of `said electron beam.

References Cited in the tile of this patent UNITED STATES PATENTS 2,752,523 Goodall lune 26, 1956 2,760,111 Kurnpfer Aug. 2'1, 1956 2,809,321 Johnson et al. Oct. 8, i957 2,829,300 Wilson Apr. l, 1.958 2,851,630 YBirdsall Sept. 9, 1958

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