US2300052A

US2300052A - Electron discharge device system

Info

Publication number: US2300052A
Application number: US333279A
Authority: US
Inventors: Nils E Lindenblad
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1940-05-04
Filing date: 1940-05-04
Publication date: 1942-10-27
Anticipated expiration: 1959-10-27
Also published as: CH224052A; NL62817C; FR950741A

Description

2 Sheets-Sheet 1 N. E. LINDENBLAD ELEGTRON DISCHARGE DEVICE SYSTEM Filed May 4, 1940 ou.y 27, `V1942.

Oct. 27, 1942.

N. E. I KINDENBLAD ELECTRON DISCHARGE DEVICE SYSTEM Filed May v4, 1940 2 Sheecs--Sl'xee'kI 2 INVENTOR. IVILS` E. L/NDE/VBLAD MW ATTORNEY.

wm l-Ill'- Patented Oct. 27, 1942 ELECTRON DISCHARGE DEVICE SYSTEM Nils E. Lindenblad, Port Jefferson, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application May 4, 1940, Serial No. 333,279

20 Claims. (Cl. 179-171) This invention relates to electrical discharge devices and circuits therefore, especially adapted for use at extremely high frequencies.

The primary object of the present invention is to provide an electron discharge device capable of efficiently amplifying a wide band of frequencies such as would be demanded by a multichannel radio relay amplifier.

Another object is to provide a wide band amplifler for use with ultra short wavelengths of the order of one meter and less, which does not depend upon resonance in the output circuit, and which eliminates the need for a sharply resonant circuit In brief, the present invention provides an electrical discharge device wherein energy is derived from a stream of electrons of periodically variable intensity in continuous small energy transfer increments along the length of the stream, such that these increments additively combine as the lumped electrons in th'e stream travel along their path. In accordance with one embodiment of the invention there is provided a vacuum tube having means for producing a narrow or concentrated electron stream, and an energy abstracting or absorbing circuit in the form of a helical conductor placed adjacent the stream of electrons and coaxially arranged relative to the axis of the tube so that there is a gradual pick-up of energy from the electrons as they travel along the axis of the vacuum tube. This helical conductor may surround the electron stream or, where a hollow beam of electrons is employed, may be located within the beam.

The invention is based on the principle that if the speed of the electron aggregates in the stream is made to be substantially equal to the axial velocity of propagation of the electromagneticwave induced in the helical conductor by the electron stream, then the induced currents in the helical conductor which have the same general axial direction as the moving electrons wil ladditively combine. Putting it another Way, the velocity component of the induced electromagnetic wave parallel to the electron stream is made to be substantially the same as the velocity of the charged particles in the stream, thus causing the electrons to cumulatively effect the helical line in the direction of the moving electrons. As for the component traveling in the direction opposite to the moving electrons, th'e net result is of a lesser order.

In order that the present invention may be better understood, a theoretical explanation will now be given. 1t is to be understood, however, that this theoretical explanation is given merely for the purpose of exposition and in order that the invention may be better appreciated. While this theoretical explanation is believed to be correct, it is not of necessity complete; nor does the operation of the invention depend upon its accuracy or otherwise In an electron beam type of vacuum tube with which the present invention is concerned and which employs an electron density modulating element (such as a grid) and a helical conductor in coupling relation to the electron beam, the pulses of electrons which travel down the vacuum tube toward the point where they are collected will produce an electromagnetically induced current, not only in the turns of the helix which are approached by the oncoming electrons, but also in the turns which fall behind the moving electrons. Since both the induced components of current function to decelerate electrons in the electron stream, the continuity of the current wave distribution on the helical line will be undisturbed, whether We consider the turns as a whole being approached by the oncoming electron pulses, or the turns as a whole receding from the traveling electron pulses, or whether we consider some of the turns being approached and some left behind the traveling electrons. The induced current waves in the helical conductor, which have the same general direction along the axis of the helix as the abstract or absorb energy from the moving electrons. The induced current waves in the helical conductor which have the general direction opposite to the moving electrons will not result in such acontinuity, although there will occur resdual energy at the end of the helical conductor which is opposite the utilization end of the helix. This residual energy can be and is preferably absorbed by a resistance.

In order to absorb energy gradually from the electron stream, the velocity component of the induced wave parallel to the electron stream should approximate the velocity of the electrons in the stream. This can be accomplished in either of two ways. The first and preferred method is to decrease (taper) the pitch of the helix to conform with the decrease in the electron velocity as the energy is being picked up from the stream. This method has the advantage of being able to decelerate the electrons to a higher degree and to obtain a higher efliciency than the second method now to be described.

' focussing the electrons along the axis of preach constancy for a considerable portion of its path', after whichl the phase drag may be so large that an acceleration of the electrons re-Y places the desired deceleration. Such an acceleration is, of course, undesirable sinceit would cause some of the abstracted energy to return to' the electron stream. In employing such a constant pitch coil as just described, it is desirable that the helical line be terminated before such an excessive phase drag occurs which will produce electron acceleration,

A more detailed description of the invention follows, accompanied by drawings, wherein Figs. 1 and 2 show, by way of example only, two different embodiments of the invention; and Fig. 3 shows a detail of the helical wave guide used in Fig. 2.

In these drawings, the same reference numerals indicate the same part throughout the figures.

Referring to Fig. 1, there is shown an evacuated electron discharge device having a closed envelope I containing therein a cathode 2, a heater 3, a grid 4, accelerator electrodes 5, 5, a

collector electrode 6, and a secondary emitter suppressor 1. The accelerator electrodes 5, 5 are narrow ring-like electrodes maintained at a high positive potential relative to the cathode for accelerating the electrons. Although only two of these accelerator electrodes have been shown, it

should he understood that, if desired, additional accelerator electrodes may be employed in the center of the vacuum tube.

Choke coils

8, 8 are .inserted between the accelerator electrodes and thepositive terminal of the source of potential ior preventing the passage of high frequency currents over the accelerator electrode circuit, thus avoiding the occurrence of an extraneous and unnecessary voltage Idrop in the accelerator electrode circuits and an unnecessary -use of power. The collector electrode 6 is maintained at a highpositive potential and the secondary electron suppressor 'I at a lower positive potential relative tothe cathode. The grid I is maintained at a negative potential relative to the cathode, as shown, and is in circuit with \a parallel tuned input circuit 9 which is shownto be inductively coupled to a suitable transmission line feeder or' other suitable circuit I0. Line Ill` may extend to a preceding stage which may be either an oscillator or another amplifier. For the tube in a narrow and concentrated stream, there is provided armagnetic lens system constituted by a plurality of electron lenses in series relation, formed bygapS N, S, these letters being indicative, respectively, of the north and south poles of the magnets produced by coil II, the latter, in turn, being energized by the battery I2 in series with an adjustable resistance I3. Surrounding the glass envelope I of the vacuum tube for the major portion of the path of travel of the electron stream is a helix I4 of continuously decreasing pitchv or taper toward the collector electrode. The turns of the helical conductor I4 are possibly preferably uncoupled relative to each other, by means of a shield of nonmagnetic metal (not shown). though this shield- `other words, the pitch and diameter of the helical conductor are vgiven such suitable values that the velocity of the waves induced in the helical conductor has a projection on the axis of the vacuum tube, or a velocity component parallel to the stream which is substantially the same as the velocity of the charged particles in the stream. The velocity of the wave around the turns of the helix may approach the velocity of light or be reduced substantially below the velocity of light so long as the foregoing rela, tion is maintained. In this way there will be a coupling between the electron stream to each unit length of the helix, which coupling will be very small, although there will be a gradual pick-up of energy, from the electrons as they travel along the axis of the helix. As energy is picked-up from the electron stream, the velocity of the electrons will decelerate and accordingly the pitch the helix will be correspondingly decreased to maintain the required substantially equal velocity relation desired between the electrons and the velocity component of the wave on the. line parallel to the axis. Since the pitch depends only on the relative velocities in the electron stream and the helix, it is not critically dependent upon the wavelength. The end of the helix I4 which is nearest the cathode is terminated by a grounded to a surrounding metallic cylinder I5 of non-magneticl conductive material which acts as a radiation shield. The location of the radiation shield I6 inside the magnetic lens system assures that the helical line will not be exposed to irregular changes in its constants, dueto irregularelectrcstatic eiiects between the turns of the helix and the reference shield. Resistance I5 functions to reduce the residual energy which is induced in a direction opposite to the direction of the. moving electrons. The utilization end of the helix I4 is terminated by a suitable load, such as a transmission line I1, having a characteristic impedance equal to the surge impedance of the helical conductor. sion line I1 may connect to any tion circuit, such as an antenna, uum tube stage. Line Il' may be suitable impedance transforming circuit introduced at the termination of the helix, provided, of course, it is of such character as not to limit the desired band width, and it should be evident that the load may be applied directly to the end o1' the helix without the use of any intermediate connecting line. Cylinder I6 is merely illustrative of any suitable grounding or reference point, which hasa xed alternating current potential. It should be understood that the load connected to line I1 or to the directly associated end of the helix Il is as to absorb the energy induced in helix Il at the rateiat which it arrives, thus preventing reflection at the utilization end of the helix and preventing the occurrence of standing waves on I4'. It is quite important that standing waves be prevented from occurring on lthe helix, since such waves might produce an acceleration elfect on the electronsl and cause some of the abstracted energy tol return to the electron stream, an effect to be avoided in the practice of the invention.

From whathas been said before, it should be suitable utilizaor another vac- This transmisreplaced by any of such impedance value'- apparent that the motion of the electrons through the vacuum tube produces a current in the helical conductor I4 which causes a voltage drop therein with a consequent deceleration of the electrons in conformance with Lenzs law. In eiect then, the helical conductor absorbs or abstracts energy from the electrons. Since the moving electron clouds or pulses in the electron tube produced by the action of the grid on the electron stream, in known manner, (i. e., the grid modulates the density of the electron stream in accordance with the signal modulation in the input circuit) represents a high voltage and a low current per unit length of electron stream, the electron discharge device of the invention will 'be most efcient when the helical conductor has a high characteristic impedance. If the length of the electron ath and the helical conductor are made suflicitly long to enable several successive electron clouds (pulses) to exist along this length, these clouds will always produce correspondingly positioned induced charges in the line regardless of the wavelength. As the electron velocity attenuates, these clouds (pulses) will come closer together, and the correpondingly produced charges which are induced in the helix will thus axially also come closer together and maintain the same relative position between them (induced charges) as exist between the clouds throughout the length of the helix. The space occupied by each pulse or cloud of electrons is large compared to the distance between two successive turns of the helical conductor, and preferably such space occupied by each pulse or cloud of electrons is at least as large as the projections of two or more of the turns of the helix as measured along the axis of the tube.

It is preferred that the vacuum tube be as long,

as possible, in order to obtain most eiective operation.

In one particular embodiment of the present invention tried out in practice and mentioned herein by way of example only and not by way of limitation, it was possible to amplify a frequency band of 30 megacycles at a carrier of 390 megacycles with only a three decibel variation over the entire band.

Fig. 2 illustrates another modification of the invention and differs from Fig, 1 essentially in the substitution of the wire or conductor type of transmission line by means of a hollow semicylindrical spiral wave guide i4. The magnetic lens focussing system of Fig. 1 has been replaced by a magnetic field coil i8, which, it will be appreciated, is an alternative for the preferred magnetic lens system, the one being replaceable by the other. Semi-cylindrical wave guide I4' changes in pitch (decreases) along the length of the vacuum tube in the direction of electron travel in accordance with the teachings set forth above in connection with Fig. 1, the utilization end of this wave guide terminating in a gradual diverging tapered horn or wave guide 2l. 'I'his wave guide I4 has an open end adjacent the envelope of the tube so that the electrons in their passage through the tube will induce currents across the open end or gap of the guide continuously along the length of the vacuum tube. In effect, the waveguide comprises a U-shaped hollow conductor whose open end is adjacent the electron stream and which spirals along the length of the tube. In order to insure that the currents induced in the spiral wave guide traverse a path which is longer than the smallest diameter of the wave guide there are provided slots system of Fig. 1, either one of which can be used Y maintaining the helix ata direct current potenn to produce the desired electron focussing action.

It should be distinctly understood that the structure set forth in the drawing and described in the specification is entirely illustrative and not definitive, it being clearly understood that various changes may be made in the form, shape and arrangement of the various elements. For example, the helical conductors of Fig. l as well as the spiral wave guide of Fig. 2 can, if desired, be placed within the envelope of the tube and surrounding the electron stream. Further. by

tial, which is positive with respect to the cathode, the coil can be a continuous accelerator at the input end thereof for the electrons, but will provide a substantially field-free space between the ends of the helix so far as direct current is concerned. If desired, the electron stream can be in the form of a hollow beam by suitably shaping and shielding the cathode and the helix placed within the beam. In order to achieve a hollow beam, the cathode may be made substantially circular and positioned concentrically with respect to the axis of the tube.

What is claimed is:

1. The metho'd of abstracting energy from a stream of charged particles which comprises modulating said stream in accordance with signal energy obtained independently of said stream to thereby produce successive clouds of said particles, causing said clouds of charged particles to induce a traveling electromagnetic wave in a path adjacent to said stream and in the same general direction as the stream and at such velocity relativeto the velocity of the charged particles in the stream that the velocity component of said electromagnetic wave parallel to said stream approximates the velocity of the charged particles in the stream.

2. In an electrical discharge device, means for producing a stream of charged particles, a helical conductor adjacent said stream and in coupling relation thereto, said helical conductor having a decreasing pitch in the direction in which said particles move, whereby said charged particles produce cumulative effects on said conductor and the velocity component of the wave produced on said conductor parallel to said stream is substantially the same as the velocity of the particles in said stream.

3. The method of operating an electron discharge device ampliiier which comprises the steps of producing a beam of electrons, modulating the density of said beam in accordance with signalling energy obtained independently of said amplier in order to produce clouds of electrons, producing from said clouds induction currents by the modulated beam which cumulate in the direction of movement of the electrons, and utilizing the cumulated induction currents.

4. The method of operating an electron dis-- charge device amplifier which comprises the steps of producing a beam off electrons, modulating the density of said beam in accordance with signalling energy obtained independently of said ampliiier, producing induction currents by the modulated .beam which cumulate in the direction of movement of the electrons and are substantially ineffective in the direction opposite to the moving electrons, and utilizing the cumulated induction currents.

means for producing a moving stream of charged particles, a coaxially arranged non-resonant coil system adjacent said stream and in coupling relation thereto along the length of said coil system, i

means for focussing said stream of electrons to travel linearly along the axis of said device, and

means for interrupting said stream to produce successively appearing clouds of particles, said device being so constructed and arranged that said clouds of charged particles cumulatively induce currents in said coaxial conductor and product on said conductor an electromagnetic wave having a velocity component parallel to said stream which is substantially the same as the velocity oi the charged'fparticles in said stream.

6. In an electrical discharge device, means for producing a stream of charged particles, a heli'cal conductor adjacent said stream and in coupling relation thereto, means for focussing said stream of electrons to travel linearly, and means for modulating the density of said stream in accordance with a signal modulation, said helical conductor having a decreasing pitch in the direction in which said particles move, whereby said charged particles produce cumulative eiects on said helical conductor.

7. In an electron discharge device circuit, a cathode at one end of said device to prcduce a stream .of electrons, a collector electrode at the other end of said device, an accelerator electrode intermediate said cathode and collector, means for focussing said electrons, and a helical conductor coaxially arranged relative to said stream and in coupling relation thereto, a load coupled to that end of said helical conductor which is nearest said collector electrode, -said load having an impedance substantially equal to the characteristic impedance off said conductor, said electrons cumulatively affecting said helical conductor to produce an electromagnetic wave thereon with a velocity component parallel to said stream which is substantially the same as the velocity of the elecl trons in said stream.

8. A system in accordance with claim 7, char-` acterized in this that said helical conductor surrounds said stream and has a decreasing pitch in the direction of travel of the moving electrons.

9. A system in accordance with claim 7, characterized in this that said stream of electrons is inthe form of a hollow beam, said helical conductor being arranged in the interior of said hollow beam and having a decreasing pitch in the direction oi travel of the moving electrons.

10. An amplier circuit for amplifying a wide band of frequencies comprising an electron discharge device having within anv evacuated envelope a cathode, a gr-id, an accelerator electrode and a collector electrode in the order named, a

ileld coil externally of said envelope for focussing in a stream the electrons emitted by said cathode, and a helical conductor surrounding said stream and coaxial therewith and in couplingv relation thereto, said helical conductor having a decreasing pitch in the direction of the,

moving electrons, whereby clouds of said moving electrons induce an electromagnetic wave on said helical conductor which has a velocity component parallel to the axis of the conductor and substantially equal to the speed of propagation of the electrons ln said stream.

11. An amplier circuit for amplifying a Wide band of vfrequencies comprising an electron discharge device having within an evacuated envelope a cathode for producing an electron stream,

a grid for modulating the density of said stream, an accelerator electrode, and, a collector electrode in the order named. a magnetic lens system surrounding the envelope for focussing into a concentrated beam the electrons in said stream. and a helical conductor also surrounding said stream and in coupling relation thereto, said helical conductor having the same axis as said stream, said helical conductor having -a decreasing pitch in the direction of the moving electrons, whereby clouds of said Imoving electrons induce an electromagnetic wave on said helical conductor which has a velocity component parallel to the axis of the conductor and substantially equal to the speed of propagation of the electrons in said stream.

12. In an electrical discharge device having means for producing a moving streamrcf charged particles, al coaxially arranged conductor adjacent saild stream and in coupling lrelation thereto, terminations lfor both ends of said coaxially arranged conductor, said terminations having impedances which match the surge impedance of said conductor, means for focussing said stream of electrons to travel linearly along the aXis of said device, and means for interrupting said stream to produce successively appearing clouds of particles, said device being so constructed anld arranged that said clouds of charged particles cumulatively induce currents in said coaxial conductor and produce on said conductor an electromagnetic wave having a velocity component parallel to said stream which is substantially the same as the velocity of the charged particles in said stream.

13. In an electrical discharge device having means for producing amoving stream of charged particles, a coaxially arranged helical conductor adjacent said stream and in coupling relation thereto, said helical conductor being in the form of a` hcllcw wave guide having a gap adjacent said stream, means for focussing said stream of electrons to travel linearly along the axis of said device, means for interrupting said stream to produce successively appearing clouds of particles, and a load circuit having an impedance substantially equal to the surge impedance of said guide coupled to that end of said wave guide nearest the point of termination of said moving stream, said device being so constructed and arranged that said clouds of charged particles cumulatively induce currents in said coaxial conductor and produce on said conductor an electro- -magnetic wave having a velocity component parallel to said stream which is substantially the same as the velocity of the charged particles in said stream.

14.'In an electron discharge device circuit, a

vcathode at one end of said device to produce a .fecting said helical conductor to produce an electrcmagnetic wave thereon with a velocity Vcomponent parallel to said stream which is substantially the same as the velocity of the electrons in said stream.

15. A wide band amplifier comprising an electron discharge device having a cathode for producing a stream of electrons, a grid and an electron collector electrode, means for focussing said electrons to travel in av stream from said cathode to said collector electrode, means for impressing upon said grid the signal energy to be amplied, a helical conductor arranged coaxially 'relative to said stream and in coupling relation thereto, a load coupled to that end of said helical conductor which is nearest said collector electrode, said helical conductor being so constructed and arranged that the electrons produce an electromagnetic wave thereon with a velocity component parallel to said stream` which is substantially the same as the velocity of the electrons in said stream. d y

16. A wide band amplifier comprising an electron discharge device-'having a cathode for producing a streamr of electrons,` a grid and an electron collector electrode, means for focussing said electrons to travel in a stream from said cathode to said collector electrode, means for impressing upon'saidgrid the signal energy to be amplified, a helical conductor arranged coaxially relative to said stream and in coupling relation thereto, a load coupled to thatv end of said helical conductor which is nearest said collector electrode, and a resistance connected to the other end of said helical conductor, said helical conductor being so constructed and arranged that the electrons produce an electromagnetic wave thereon with a velocity component parallel to said stream which is substantially the same as the velocityof the4 electrons in said stream. I

v17,. In an electrical discharge device having 5w means for producing a moving stream of .charged particles, a coaxially arranged non-resonant coil system adjacent said stream and in coupling relation thereto, said coil system comprising a helix which has a decreasing pitch in `the direction of travel of the moving stream, means for focussing said stream of 'electrons to travel linearly along the axis of said device, and means for interrupting said stream to produce successively appearing clouds of particles, said device being so constructed and arranged that said clouds of charged particles cumulatively induce currents in' said coaxial conductor and produce on said conductor an electromagnetic wave having a velocity component parallel to said stream which is substantially the same as the velocity of the charged particles in said stream.

d 18. In an electrical discharge device, means for producing a stream of charged particles, means for modulating said stream to produce along its path lof travel a plurality of clouds of electrons, a helical conductor having a changing pitch located adjacent said stream and in coupling relation thereto, said `helical conductor being so constructed and arranged that the distance between anytwo successiveturns thereof is smaller than the space occupied by each cloud of electrons.

19. In an electrical discharge device, means for producing a stream of charged particles, means for` modulating said stream to produce along its pathof travel a plurality of clouds of electrons, a helical conductor adjacent said stream and in coupling relation thereto and carrying a traveling electric wave, said helical conductor being so arranged that the velocity component of said wave parallel to said stream is substantially the same as the velocity of the charged particles in the stream, the distance between any two successive turns of saidjhelical conductor being small compared to the `space occupied by each cloud o electrons.

20. In an electrical discharge device, means ior producing a stream of charged particles, means for modulating vsaid stream to produce along its path of travel a plurality of clouds of electrons, a helical conductor located adjacent said stream and in coupling relation thereto, said helical-conductor being so constructed and arranged that the distance between any two successive turns thereof is smaller than the space occupied by each cloud of electrons.

NILs E. LmDENBLAD-`