US2535055A - Space discharge device - Google Patents

Description

Dec. Z6, 1950 J, C, FERGUSQN 2,535,055

SPACE DISCHARGE DEVICE Filed Jan. 4, 1945 INVENTOR JOSEPH C. FERGUSON ATToRNY Patented' Dec. 26, 1950 SPACE DISCHARGE DEVICE .ioseph C. Ferguson, Fort Wayne, Ind., assigner, by mesne assignments, to Farnsworth Research Corporation, a corporation of Indiana Application January 4, 1945, Serial No. 571,265

8 Claims. (Cl. Z50-150) This invention relates generally to space discharge devices and particularly to a novel deflection system for a primary electron beam utilized in connection with an electron multiplier for amplifying signals.

In a conventional electron multiplier primary electrons obtained in any suitable manner are multiplied by means of secondary electron emission. For amplifying signals it has been suggested to control the number of primary electrons entering themultiplier by means of a grid. In another prior electron multiplier utilized as an amplifier an electron beam is deected by the vsignal to be amplified. The deflected beam is then directed through an aperture into the mul- -tiplier where the primary electrons are multiplied. Thus, the number of electrons entering the aperture is made dependent upon the deflec- -tion vof the beam. This method has considerable merit for amplifying modulated carrier signals of the type obtained with a receiving antenna. It is particularly useful when itis desired to obtain cut-off of the electron beam with such a signal. However, considerable diiiiculties have been experienced heretofore with the ampli- `iication of weak signals of the order of magnitude of millivolts. In this case the angle of deflection ofthe 'primary electron beam is very small. In order to increase the angle of deflection of the primary beam it has been proposed to utilize comparatively long electrostatic deection plates so that the electron beam is under the influence of the variable field for an extended length. However, this arrangement is not feasible when the transit time of the electrons is comparable to the rate of change of the electric eld or, in other words, for high and ultra-high frequencies. The actual deflection obtained with a small angle of deflection of the beam may also be increased by using a very long tube. However, there are obvious physical limitations to this scheme.

l; It has also been proposed to use an electron multiplier with a ltarget electrode having different secondary electron emitting properties at different parts of its surface. This target has been used in connection with a primary electron beam to obtain a variable output in dependence upon the deflection of the primary beam. However, this prior method is not sensitive enough for amplifying weak signals.

It is an object of the present invention, therefore, to provide a space discharge device for amplifying weak signals.

A further object of the invention is to provide cumulative deflection of a. primary electron beam in accordance with a signal and to multiply the secondary electrons liberated by the primary beam in an electron multiplier. l

Another object of the invention is to provide a selective multiplication of a cumulatively deflected electron beam to effect amplification of a Weak radio frequency signal.

In accordance with the present invention there is provided a space discharge device including means for developing an electron beam. This electron beam is deflected in accordance with a signal. A secondary electron emissive element having a curved surface is interposed intol the path of the electron beam. The secondary electrons liberated by the beam from the curved surface of the element emanating from predetermined directions are collected. As the number of secondary electrons is largest in a direction normal to the secondary emissive surface of the element, the result is effectively a cumulative deflection of the beam.- Preferably, an electron multiplier is used for multiplying the secondary electrons liberated from the curved surface'of the element. n,

Alternatively, the multiplier used for amplifying the cumulatively deiiected electron beam includes a first stage having a secondary` emissive surface arranged so that the number of.secondary electrons liberated therefrom varies in accordance with the'deflection of the beam.

For a better understanding of the invention. ltogether with other and further objects thereof. reference is made to the following description, taken in connection with the accompanying drawing, and its scope will be pointed out inthe appended claims.

In the accompanying drawing:.

Fig. 1 is a schematic representation of a space discharge tube embodying the present invention; and Figure 1a is a plan view of an electrode utilized in the space discharge tube illustrated in Figure 1;

Fig. 2 is a schematic representation of an'- other discharge tube `where the secondary electrons liberated by a deflected electron beam are selectively multiplied in an electron multiplier; and

Fig. 3 is a plan view of an alternative construction of the first stage of the multiplier illustrated in Fig. 2. l.

Referring now more particularly to Fig. ,1 of the drawing, there is provided a space discharge device including an evacuated envelope l. Electron gun 2 is arranged in envelope l for develop-.- ing and focusing an electron beam indicated att'.

3 Electron gun 2 includes cathode Il, grid 5, rst anode 6 and focusing cylinder I which are all connected to potentiometer s connected, in turn, to battery I having its positive pole grounded as shown.

Electron beam 3 is directed toward electrode II having a convex surface arranged opposite electron gun 2. The convex surface of electrode II is made ksecondary electron emissive in any suitable manner well known to those skilled in the art. Deflecting plates I2, I2, arranged to deflect electron beam 3, are interposed between focusing cylinder 'I and electrode II having a convex surface.

Deflecting plates I2 are connected to dipole antenna I3 arranged for intercepting modulated carrier Wave signals. As Will beexplained 4hereinner, the connection of deflecting plates I2 to dlpole antenna I3 being shown for purposes of illustration only.

The primary electron beam impinging upon electrode II having a curved surface liberates secondary electrons therefrom. We may assume that only a very small portion of the secondary electrons liberated from the surface of electrode II follows the optical laws of reflection, that is, the angle of incidence equals the angle of deflection. The great majority of the secondary electrons, however, will be distributed following a cosine law with the maximum number of electrons at Vthe normal of the reflecting surface. Hence, we may assume that most of the energy of the ysecondary electrons liberated from the surface of electrode I I hasan angular distribution which depends upon the radius of curvature of the surparticularly suited for amplifying Weak signals of radio and high frequencies, that is, signals having a strength of -the order of magnitude of'milli- Notts.. AAntenna I3 Vis connected to deflecting plates I2 by leads I4, I4. Shunt coil I6 shunts leadsIA. vThemid point of shunt coil :I6 is con- "nected by lead II to focusing cylinder "I and, hence, deflecting plates I2.have an average potential equal to that rof: .focusing cylinder 1.

Blocking condensers I8, I8 are interposed in leads between shunt coil I6 anddipole antenna I3 to block the direct current potential from dipoleantenna I3.

'By'means 'of potentiometer 8 cathode 4.*may,

"for instance, be kept at a potential ofabout1500 volts negative `against ground. Control .grid k5 vshould have a potential that is afew volts more 1 negative than that of cathode vIl. First anode S 'may -have a potential which is about 300 volts positive against cathode 4. Lead I9 vconnecting `electrode II to anode 6 keeps electrode VII at the same potential as anode 6. nlFocusing cylinder I vand' deflecting platesf I2 may be kept at a potential of about 4 00 volts negati-ve against ground.

Anysignals intercepted.l by 5dipole antenna I3 will create electric potentials of opposite polarity ondeflecti-ngplatesHI'Z, I2 and, accordingly,-elec ltror'ifbea-m 3'is deflected inthe thus createdele'ctricfneld SecondaryelectronsV liberated by elec-` tron beam 3 on the onveie-surfaceofelectrode II pass through aperture z'-vin'fshieldZI, shownin plan view in Figurefla. Shield 2I is kept by'lead -uatthesame potentialas first stage 22 of'electron multiplier 23. -Electron multiplier 23com- `prises-further multiplier stages 25,26, 21 'and}28 Vand"a"collector'electrode 30. Multiplier stages :22, 25, 26, '21 and 28 are connected topotentiometer 8 so that each stage is keptzat a vpotential that is about 200 volts more positive thanv that of thepreceding stage. Thus, stage 22 and shield 2 I may be kept at a potential of about 1000 volts negativeagainst ground, while the lastfstage 28 may 'be kept about 200 volts negative against ground.

face. Electron-beam 3`is deflected in accordance rwith vthe signals intercepted by dipole antenna I3'. lIt is to be understood,'however, that the de- `fl'ection of electronbeam 3 in accordance witha 'signal may be effected in any other suitable mantron beam 3.

face of electrode II and the point Where the primary beam impinges upon the surface of electrode -I I. Thus,.by suitably choosing the radius of curvature of the surface of electrode II even'a small angular deflection of primary electron beam 3 will be sufficient to cause a considerable change in the angular distribution of the secondary electrons liberated thereby. It will be appreciated that the surface of electrode -II couldalso be made vconcave instead of convex. `In'this manner a cumulative deflection of the Yelectrons is Yobtained. In other words, the electrons of theprimarybeam are rst deflected by deflection plates I2 in accordance with the signal to kbe amplified. Then secondary electrons liberated by beam V3 from electrode II are Aagain deflected'in accordance with the radius of curvature of the surface of electrode'l I, .and thus a cumulative deflection is obtained.

The number of secondary electrons passing through aperture 20 in shield '2| thus depends upon the cumulative deflection of primary elec- The secondary electrons passing through aperture 2ll1impact first electron multiplier stage 22 Where they liberate, in turn, more secondary electrons. The stream of secondary electrons impacts 'successive multiplier stages, each .time increasingV the `number of electronsA libe erated. The Youtput currentis collected by Vcollector -electrode 30, and an` amplified outputtsi'gnal isideveloped acrosszresistora32.

Ifdesired, electrode I'I havinga curved'surface may be so' arranged vwith respect toprmary-elec- :tron beam 3 and aperture sfthat ,substantially no secondaryV electrons .pass -through 1 aperture 20 when the IbeamV is in its normal` or :undeected position. The 'secondary electrons are 4,then colletced `by shield 2I'or1by deflectingplates I2. In this case thedischargedevice of the invention acts. substantiallyk as a .detector or :morezucorrectly aszahalf-wave rectifier. It'isralso feasible to arrange collector relec-v trode-Si behind aperture 2.3. and toomitthe-elec- .tron multiplier stagesz and 25 to 28. The output signal may then be further amplified -in;a conventional manner.

Referringlnow to Fig.2, in which likefcom ponents are designated vby kthe same :reference numerals as were used inFigyl, electron discharge device V35 -comprises electron gun 2.V Electron gun 2 includescathode 4, control grid 5,.anocle 6 and focusing cylinder I whichzmay beconnested to av source of 'potential'in the same-man- 'ner as illustrated in Fig. 1. Deflectingiplates '-I`2`, I2 are connected through-leads I4, I4 toasource of signals to be amplified. In the manner ex- Y plained in connection ivithFig. -1,felectron`b'eamf3 stage of electron multiplier 3l.

is focused and directed toward electrode l l having a curved secondary electron emitting surface where it liberates secondary electrons. As explained hereinabove, the secondary electrons liberated from the surface of electrode Il have their main energy in a direction normal to the surface of electrode H. Therefore, when the radius of curvature of the surface of electrode Il is sufciently small, a small angle of deflection of beam 3 will produce a considerable change in the direction of the main energy of the secondary electrons liberated from electrode Il.

These electrons now fall upon the secondary emissive surface of electrode 3d forming the first Electron multiplier 3'! includes the further stages 46, il and 42 which may be of the well known box type as illustrated. Each of stages 3?, All, lli and 42 is kept at a suitable potential that is positive with respect to that of the pr eceding stage to attract the secondary electrons liberated therefrom. The electrons liberated from the last electron multiplier stage d2 are collected by collector electrode 43, and an output signal may be obtained from output lead M.

The first multiplier stage 36 is arranged in such a manner that its secondary electron emissive properties vary along its surface. Shaded area 45 diagrammatically indicates that the secondary electron emissive properties of stage 3S increase in the direction towards the second stage 4U. Such a surface can be prepared in a number of different ways. To this end the caesium or caesium oxide layer which is usually used for that purpose may be gradually increased in thickness toward that portion Where the secondary emission factor should be highest.

It is also feasible to prepare the secondary emissive surface of stage 35 as illustrated diagrammatically in Fig. 3. Shaded area 4B indicates a secondary emissive material such as caesium or rubidium or oxides thereof. Area 41 is made of a material which has a secondary electron emission factor of unity or less, such as carbon black. Area 45 is wedge-shaped as shown. Circle d indicates diagrammatieally the approximate area covered by the secondary electro-ns liberated from the surface of electrode ll and attracted by multiplier stage 36. It is of course to be understood that a secondary electron beam does not have a well dened outline. When beam 48 moves from the right to the left in Fig. 3 it will be seen that it covers an increasingly wider portion of secondary emissive area 46 and, hence, the number of secondary electrons liberated thereby is increased correspondingly.

The electron discharge device of Fig. 2 operates in substantially the same manner as the one shown in Fig. l. to be amplified, electron beam 3 is deflected across electrode Il. Depending upon the direction of incidence of beam 3, the angle of the main energy of the secondary electrons changes. These secondary electrons impinge upon rst multiplier f In accordance with the signal gy,

iii

2. In this case multiplier stage 3G provides a selective multiplication of the electrons impinging thereon in dependence upon their direction of incidence.

If desired, the surface of electrode Il may be arranged in such a manner with respect to electron beam 3 and first multiplier stage 36 that substantially no secondary electrons are liberated from multiplier stage 36 when beam 3 is undeected. Thus, the discharge device of the invention may be used as a detector or rather a half-wave rectier.

Although a box type electron multiplier has been shown in Fig. 2, it is to be understood that any type of multiplier having any desired number of stages may be used in connection with the discharge device of the invention.

While there has been described what are at` present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modiiications as fall within the true spirit and scope of the invention.

What is claimed is:

l. A space discharge device including means for developing an electron beam, means for deflecting said electron beam in accordance with a signal to be amplied, an element having a secondary electron emissive convex surface interposed into the path of said electron beam to obtain a cumulative deflection of the said beam, means for collecting secondary electrons liberated by said beam from said surface, and means in terposed between said surface and said collecting means for selecting a number of secondary electrons varying in accordance with the deflection of said beam and with the angular distribution of said secondary electrons.

2. A space discharge device including means for developing an electron beam of substantially constant intensity, means for deflecting said electron beam in accordance with a signal to be amplified, an element having a secondary electron emissive curved surface interposed into the path of said electron beam to obtain a cumulative deflection of said beam, an electron mulitplier mounted adjacent said secondary emissive curved surface to receive secondary electrons liberated by said beam from said surface, and means interposed between said surface and said multiplier for selecting a number of secondary electrons varying in accordance with the deection of said beam and with the angular distribution of said secondary electrons.

3. A space discharge device including means for developing an electron beam, means for deecting said electron beam in accordance with a signal, an element having a secondary electron emissive curved surface interposed into the path of said electron beam to obtain a comparatively large deflection of said beam with a comparatively weak signal, means for collecting secondary electrons liberated by said beam from said surface, and a shield having an aperture interposed between said surface and said collecting means.

4. A space discharge device including means for developing an electron beam, means for initially deflecting said electron beam in accordance with a received signal, an element having a secondary electron emissive curved surface disposed in the path of said electron beam for in effect magnifying the deflection of said initial electron beam, electron multiplier means, and an apertured electrode positioned between saidcurved surface and said multiplier means for passing electrons emitted by said curvedrsurface in accordance with the degree of deflection.

- 5. .A space discharge device including means for developing and focusing an :electron beam, means for deflecting said electron beam in accordance with a signal, an element having a sec ondary electron emissive outwardly curved surface interposed into the path of said electron beam, an electron multiplier mounted adjacent said secondary emissive curved surface to receive secondary electrons liberated by said beam from said surface, and a shield having an aperture interposed between said surface and said multiplier, said aperture being arranged to pass a selected portion of the secondary electrons liberated from said surface, thereby to make the number'of secondary electrons passing through said aperture dependent upon the deiiection of said beam.

6. A space discharge device including means for developing and focusing an electron beam,

means for deecting said electron beam in accordance with a signal, an element having a secondary electron emissive convex surface interposed into the path of said electron beam, an electron multiplier mounted adjacent said secondary emissive curved rsuriace to receive secandary electrons liberated by said beam from vsaid surface, and a shield having an aperture 8 from v.predetermined directions, said secondary electronsbeing Aliberated by said beam from said surface, said multiplier including a rst stage having :a secondary electron emissive surface aCingsaid curved surface-so that the-,number of secondary electrons -liberated therefrom lvaries in accordance WithLthe deflection of said beam..

v8. A space discharge device including means for developing and focusing an electron beam, means for deecting said electron beam in accordance With a signal, an element having a secondary electron emissive convex surface interposed nto thepath of said electron beam,.and,an electron multiplier mounted adjacent said .secondary -emissive curved surface to receive secondary electrons from predetermined directions, saidsecondaryelectrons being liberatedby said beam from said surface, said multiplier including a first `stage .having 'a secondary electronernissive surface facing said curved surface so that the secondary emission factor varies therealong, thereby to provide an output current from said multiplier varying in accordance with the deflection of said beam.

JOSEPH C. FERGUSON REFERENCES CITED The following*references'are of recordin 'the le of this patent:

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