US2643297A - Gas discharge transmission arrangement - Google Patents

Description

J1me 1953 L. GOLDSTEIN ET AL GAS DISCHARGE TRANSIMISSION ARRANGEMENT Filed Dec. 3, 1948 Patented June 23, 1953 GAS DISCHARGE TRANSMISSION ARRANGEMENT Ladislas Goldstein, Weehawken, and Nathaniel L. Cohen, 'Teaneck, N. J., assignors to Federal Telecommunication Laboratories, Inc., New :YOrk, N. Y., a corporation of Delaware Application December 3, 19,48, Serial No. 63,284

13 Glaims. 1

This invention relates to radio frequency transmission systems and more particularly to systems employing a gas discharge tube as a radio frequency transmission line element.

It has been proposed heretofore to employ a gas plasma set up within a gaseous discharge tube to convey radio frequency wave energy between electrodes immersed in the gas. However when the electrodes of the tube are energized by a low frequency alternating current, or by direct current, the radio frequency conductivity or transmission characteristic of the gas plasma may not be all that is desired. According to the present invention, the radio frequency conductivity and wave transmission characteristics of the gas plasma are increased by using the light quanta generated in the plasma to control the photo-conductance or photo-electron-emissive properties of a coating or coatings applied to the gas tube.

Therefore, one of the principal objects of this invention is to improve the radio frequency conductive properties and wave transmission characteristics between electrodes immersed in an ionizable medium capable of setting up a gas plasma therein.

Another object is to provide a novel radio frequency wave transmission line of the coaxial type, wherein the center conductor is composed in part at least, of a gas plasma.

A feature of the invention relates to a gaseous discharge tube having at least part of its wall surface provided with a photo-emissive material which responds to the light energy developed in the plasma, to enhance the radio frequency conductivity between the tube electrodes;

Another feature of the invention relates to a gaseous discharge tube provided with a coating of a material which increases its electrical conductance in response to incident light energy produced in the gas discharge plasma within the tube.

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be bestunderstood-by reference to the following description of an embodiment of the invention taken in conjunction-with the accompanying drawings, wherein:

Fig. 1 illustrates one embodiment of-the invention.

Fig. 2 illustrates another embodiment of the invention.

It is known that when an ionizable medium such as a gas contained within a bulb or envelope is subjected to suitable ionizingpotentials, there is set up within the medium a plasma or region that contains substantially equal numbers of positive ions and electrons in "addition to gas molecules. It isalso known that in such a gas discharge plasma, there is a large emission of photonsor light energy quanta. It is also known that in such a plasma there is alarge ambipolar diffusion current resulting from a diffusion of the electrons to the walls of the tube. Since this diffusion normally represents a loss of electrons from the gas discharge plasma, the capability of the plasma to act as a radio frequency transmission line element or link is correspondingly reduced. -In order to overcome this drawback, the present invention provides either on the interior wall of the tube or on the exterior wall thereof, or on both walls, a coating of a material which may be either photo-emissive in response to incident photons, or which increases its electrical conductance in response to incident photons. In accordance with the invention, this increase in electron emission or electric conductance of the coating is controlled by the photons which are emitted from the gas discharge plasma itself.

The invention is particularly useful where the gas discharge plasma forms .part of the central conductor of a coaxial wave transmission line, although in its broad aspects the invention is not necessarily limited to that particular field of use.- fulness.

Merely for illustration, therefore, there is shown in Fig. 1 of the drawing a coaxial wave trans mission line embodying the invention. In thisfigure the block i represents any well-known source of radio frequency wave energy, and the block *2 represents any well-known radio frequency load device or terminal equipment to which the radio frequency energy is to be transmittedfrom source I. The source I is connected to the equip-ment 2 by a coaxial wave transmission line havingan outer or hollow pipe conductor 3 and a central or inner conductor 4. Preferably, although not necessarily, the conductor 4 is also in the form of ahollow pipe. The pipe 4 has a gap between its ends-and this gap is bridged by a gaseous discharge tube 5. The tube 5 is of glass and is approximately of the same outside diameter as theinside diameter of pipe conductor 4. Sealed through theleft-hand end of tube 5 is a lead-in conductorfi to which is attacheda cuplike cathode 1. The right-hand end of tube 5 is sealed to a metal cap anode 8. The tube 5, after being suitably evacuated and processed as is well-known in the gaseous conduction tube art, is provided with a filling of a suitable ionizable medium such as gas or vapor. Preferably this filling consists oi? an inert gas such as neon, argon, krypton, helium, and the like, or a mixture thereof, at a suitable predetermined pressure. The left-hand end of tube 5 is provided on the exterior thereof with a metal or other conductive coating 9 surrounding the region of the cathode i. The left-hand end of the tube is adapted to be telefscoped within the open end of the conductor 4, and if desired, the said conductor 4 may be of flexible thin-walled construction, as indicated by the numeral I4, so as to provide a good electrical contact with the coating 9. Likewise the cap 8 is telescoped with the corresponding section of conductor l so as to provide a good electrical contact therewith.

In accordance with one feature of the invention, the greater part of the length of the tube 5 has on its interior surface a coating I of any well-known material which emits photo-electrons in response to impinging light energy, such as those conventionally employed inphoto-electric cells such for example as sodium, potassium, and the like. In accordance with the invention, this light energy is produced by the gaseous filling within the tube 5, and for this purpose-the cathode i can be connected to the negative terminal of a suitable D. C. voltage supply, and the cap 8 which forms the anode, can be connected to the positive terminal of this or any other D. C. voltage supply. In accordance with the well-known operation of gaseous discharge tubes, by applying an appropriate voltage across the electrodes 7 and 8, there is set up within the tube a gaseous discharge plasma which contains a high intensity of photons or light energy quanta. It is also known that in such a plasma there is a large ambipolar diffusion current. Ordinarily such difiusion would represent a loss of electrons to the gas discharge plasma. However, by providing the light-responsive electron-emissive coating it, the light energy from the plasma which strikes this coating is absorbed and photo-electrons are released from the coating and directed toward the axis of the tube to counteract the loss of conductivity. This action provides a more efilcient radio frequency energy conduction path between the sections of the line conductor 4 which is bridged by the tube 5. Probably one explanation for this is that the electrons which are normally bound to the atoms of the coating material, be-

come energized by the light energy from the gas discharge plasma, and they are then free to move with very high mobility through the plasma towards the anode 8, thus increasing the conductivity of the tube. While the gaseous conduction medium has normally a certain amount of conductivity, its conductivity is greatly increased or supplemented by the photo-emission from the coated surface 5 when excited by the light energy from the plasma.

Preferably a radio frequency choke coil H is connected between the cathode l and the ionizing potential source, so that the radio frequency energy from the source I passes from the line conductor 5 and cOating 9, and thence by capacitive coupling, to the cathode 7. As a result of the enhanced conductivity of the tube 5 as above mentioned, this radio frequency energy passes through the gas plasma within the tube 5 to the anode 3, line conductor 4' and thence to the radio frequency load 2.

It will be understood, of course, that the invention is not necessarily limited to the use of a 4 D. C. ionizing potential on the electrodes 1 and 8, and if desired a suitable low frequency alternating current source may be used for that purpose.

From the foregoing description it will be seen that the tube 5 with its gas plasma, forms in effect a continuity of the central conductor 4 of the coaxial wave transmission line. It will be understood, of course, that the tube 5 can be used in any other system wherein it is desired to increase the conductivity of the tube between the electrodes thereof.

Fig. 2 shows a modification of Fig. l, and the elements of Figs. 1 and 2 which are structurally and functionally the same, are designated alike. The essential difference between the embodiment of Fig. 2 and. that of Fig. l, is that in Fig. 2 the light responsive coating 12 on the interior of tube 5, instead of being of a character which emits photo-electrons in response to incident light energy, is of a type Which increases its electric conductance in response to incident light energy. An example of such material is selenium. In Fig. 2, as in Fig. l, the coating extends along the greater part of the length of the internal surface of the tube 5, but terminates short of the cathode 1 and the anode 8. If desired, the outer surface of the tube 5 can be provided with a similar coating 53 of a material like the coating 52. When the gaseous medium within the tube 5 is ionized as above described, it sets up a gaseous discharge plasma, and the light energy from this plasma acts on the coatings i2 and i3 to increase their conductivity, thus providing a more efficient radio frequency conduction path between the sections of the center line conductor l.

It will be understood, of course, that if desired, the coating which is used to increase the radio frequency wave energy conductivity, may consist of a combination of a light-responsive electronemissive material, and a light-responsive material which increases its conductivity.

While we have described above the principles of our invention in connection with specific ap= paratus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of our invention.

What is claimed is:

l. A gaseous discharge device comprisin an enclosing envelope having :a filling of an ionizable medium, a pair of spaced electrodes for initiating and sustaining a gaseous discharge plasma within said medium, and a coating of light-responsive electron-emissive material on the wall of said envelope in the space between said electrodes, but conductively isolated from said electrodes, for increasing the conductivity of the plasma.

2. A gaseous dischargedevice comprisin an enclosing envelope having a filling of an ionizable medium, a pair of spaced electrodes for initiating and sustaining a gaseous discharge plasma within said medium, and a coating, on the wall of said envelope in the space between said electrodes, but conductively isolated from said electrodes, of a material which changes its electrical conductance in response to incident light energy derived from the discharge plasma for increasing the electrical conductivity between asid electrodes.

3. A gaseous discharge device comprising an enclosing envelope of insulating material, said envelope having a filling of an ionizable medium, a pair of spaced electrode within said envelope, a coating of light-responsive electron-emissive material on the inner wall of said envelope in the space between said electrodes but conductively isolated from said electrodes, said electrodes adapted to initiate and sustain a gaseous discharge plasma therebetween upon application thereacross of a potential from an ionizing source and to excite said coating by photons derived from such discharge plasma to increase the high frequency electrical conductivity of the space between said electrodes.

4. A gaseous discharge device comprising an enclosing envelope of insulating material, said envelope having a filling of an ionizable medium, a pair of spaced electrodes Within said envelope, a coating, on the inner wall of said envelope in the space between said electrodes but conductively isolated from said electrodes, consisting of a material which increases its electric conductivity in response to incident light energy, said electrodes adapted to initiate and sustain a gaseous discharge plasma therebetween upon application thereacross of a potential from an ionizing source, thereby to excite said coating by photons to increase the high frequency electric conductivity of the space between said electrodes.

5. A radio frequency transmission line conductor having two ends defining a gap therebetween, a gaseous discharge tube coupled between the two ends of said conductor defining said gap, said tube having a pair of spaced electrodes therein, means to energize said electrodes to initiate a gaseous discharge plasma, said tube having on the wall thereof in the space between said electrodes a coating of light-responsive material for altering the radio frequency conductivity between said electrodes.

6. A coaxial wave transmission line adapted to couple a source of high frequency energy to a utilization circuit comprising an outer hollow conductor, an inner central conductor having two ends defining a gap therebetween, a gaseous discharge tube connected between the two ends of said conductor defining said gap, said tube having a pair of spaced electrodes adapted to be coupled to a source of ionizing potential, said electrodes adapted to initiate and to sustain a gaseous discharge plasma therebetween, a coating of light-responsive material on the wall of said tube in the space between said electrodes for increasin the high frequency conductivity of the plasma in response to the light energy derived therefrom, and means to isolate said sources from each other.

7. A coaxial wave transmission line as claimed in claim 6, wherein said electrodes are disposed at opposite ends of said tube and said isolation means comprises a capacitive coupling between one of said electrodes and the central conductor of said coaxial line.

8. A coaxial wave transmission line as claimed in claim 6, wherein said isolation means further comprises an inductive impedance serially connected in the ionization discharge path of said tube.

9. A radio frequency transmission line comprising a metal line conductor having two ends defining a gap therebetween, a gaseous discharge tube having an envelope of transparent, insulating material, said tube disposed across the two ends of said conductor definin said gap, said tube having a pair of electrodes within said envelope at opposite ends thereof, said electrodes adapted to be coupled to a source of ionizing potential and to initiate and to sustain a gaseous discharge plasma therebetween, a first coating of a photo conductive material on the exterior of said envelope, said material electrically insulated from each of the ends of said conductor defining said gap, a second coating of a light-responsive material on the inner wall of said envelope electrically insulated from each of said electrodes, whereby the light energy derived from the discharge plasma acts on both of said material coatings to increase the radio frequency conductivity thereof.

10. A radio frequency transmission line according to claim 9 in which both coatings on said envelope are of a light-responsive electron emissive material.

11. In combination, a radio frequency transmission line conductor having two ends thereof defining a gap therebetween, a gaseous discharge tube having an enclosing envelope with a filling of an ionizable medium, a pair of spaced electrodes Within said envelope at opposite ends thereof, said electrodes adapted to be coupled to a source of ionizing potential and to initiate and to sustain a gas discharge plasma therebetween, said envelope having a coating of light-responsive material in the space between said electrodes, which material responds to light energy derived from said plasma, said tube disposed across the two ends of said conductor defining said gap, means to couple radio frequency energy from said line conductor into said plasma, said lightresponsive material adapted to enhance the radio frequency conductivity between the two ends of said conductor defining said gap.

12. A combination according to claim 11, in which said ionizing potential is a D. 0. potential.

13. A combination according to claim 11, in which said ionizing potential is a low frequency potential.

LADISLAS GOLDSTEIN. NATHANIEL L. COHEN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,955,335 Knowles Apr. 1'7, 1934 2,229,135 Schade Jan. 21, 1941 2,258,472 Ruttenauer et a1. Oct. 7, 1941 2,259,040 Inman Oct. 14, 1941 2,351,895 Allerding June 20, 1944 2,412,659 Thomas Dec. 17, 1946 2,438,873 McCarthy Mar. 30, 1948

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