US2919380A - Electron discharge devices - Google Patents

Description

Dec. 29, 1959 G, F. BARNETT 2,919,380

ELECTRON DISCHARGE DEVICES Filed July 23, 195'? United States Patent() 2,919,380 Y ELECTRoN DISCHARGE DEVICES Guy F. Barnett, Roslyn, Pa., assignor to Philco Corporation, Philadelphia, Pa., a corporation of Pennsylvania Application July 23, 1957, Serial No. 673,694

' 17 claims. (cl. sis- 30) This invention relates to electron discharge devices and to internal structures therefor which improve the performance and prolong the life thereof. More particularly this invention relates to improved electrode structures for evacuated electron discharge devices for reducing the number of unwanted particles of gases present therein.

One of the factors which limits the length of the useful life of evacuated electron tubes is the number of particles of unwanted gases present within the evacuated envelope thereof. When electrons are emitted within these tubes, they collide with the gas particles (e.g. molecules or atoms) causing the latter to become ionized. Either positive or negative ions, or both, may be formed. The positive ions in the electric field in the vicinity of the cathode emissive surface are attracted by the cathodes negative charge and bombard Iche latter with great destructive force because of the energy they gain in said field and because of their relatively large mass. When the emissive surfaces are not made of a single element but rather are composite in chemical structure they are especially vulnerable to this sort of attrition.

In cathode ray tubes, large numbers of negative ions are also produced by collision of the electrons in the beam with the unwanted gas particles. Since the fluorescent screen is at a relatively positive potential, these negative ions are impelled with great force toward the latter and bombard it, thereby tending to cause its gradual disintegration. This disintegration, in the case of magnetically deflected cathode ray tubes, causes a discoloration known as ion spot. The insertion of an ion-trap diverts many but not all of these negative ions so that they strike the anode rather than the fluorescent screen. To a certain extent the anode also suffers damage from this constant ion bombardment, but this damage does not appreciably impair the tube performance.

In the past, various methods of reducing thefnumber Iof unwanted gas particles freely migrating within the envelope have been employed. Probably the most wellknown method of reducing the number of free gas particles is by the use of so-called getters These getters comprise material such as barium, which is inserted in the tube before evacuation and subsequent sealing-off of the envelope. After sealing-off, the getter is heated to the point where it will evaporate, combine with particles of many of the gases still present -in the vacuum, and then be condensed on the relatively cool walls of the envelope or on some other desired surface. The heating of'the getters is usually done by subjecting the part of the tube structure which contains the getter, to radio frequency energy from outside the tube, a process known as flashing the getter.

While it is true that the getter continues to operate in combining with gases to a certain extent during actual operation of the tube, its effectiveness is usually appre ciably diminished after flashing. Furthermore, getters of known types, being dependent'upon their ability to Patented Dec. 2.9, 1959 combine with gas particles, are not effective to confine particles of noble gases which may be present before flashing of the getter, or ywhich may be released from the getter itself (the getter is sometimes manufactured in an atmosphere of noble gasesv to prevent its entering into chemical combination) during the ashing thereof, or which may diffuse from outside through the envelope walls during actual operation of the tube.

Moreover, once the getter has been flashed it is not effective to any great extent, during actual operation of the tube, in confining gases such as hydrogen or nitrogen which, during manufacture, become adsorbed or occluded within the various internal structures of the tube, and thereafter are gradually released therefrom.

Another method of reducing the free migration of unwanted gas particles involves inserting into certain types of tubes, such as transmitting tubes which operate at high temperatures, elements such as tantalum, zirconium, or titanium. These elements, when heated, may either cornbine with particles of gases like oxygen, or may first adsorb and the absorb particles of gases like hydrogen. Sometimes a particular electrode of the tube, such as the anode, which normally becomes hot during operation, is itself made of zirconium or titanium. Although the absorption action continues during actual operation of the tube, relatively high temperatures are usually required so that it is not adaptable for tubes which operate at relatively low temperatures and, besides, it does not accomplish the confinement of particles of rare gases.

The problems presented by the presence of gas particles are particularly troublesome in cathode ray tubes because of the large volume of the enclosed space involved, the many chemicals involved in the various coatings thereof which, on bake-out and thereafter, may release gases, and the large total surface area of the components which may adsorb and absorb these gases. There is, therefore, a great need for electron tubes which contain apparatus therein which continues to confine all types of unwanted gas particles after the getter has been flashed, an objective which has hitherto been impossible to achieve practically in the production of many types of commercial electron discharge devices.

It is, accordingly, an object of the invention to provide improved discharge `devices having a longer useful life.

Another aim of the invention is to provide electron discharge devices Whose cathodes are characterized by greater longevity.

Another object of the invention is to assist in preventing the disintegration ofthe fluorescent screen in cathode ray tubes known as ion spot.

Another aim of the invention is to provide improved electron tubes in which, during operation of the tube, undesired gaseous particles are constantly being confined to regions Where they will not adversely affect the operation of the tube.

Another object of the invention is to provide improved electron tubes in which means are provided for confining particles of unwanted rare gases, during operation of the tube, to regions where they will not adversely affect the operation of the tube.

These objects, as well as others which will appear, are achieved, according to my invention, by providing a cathode assembly having a first emissive area for generating a primary stream of electrons to full the main function for which the tube is used, and having also a second emissive area for generating an auxiliary stream of electrons. Near the second emissive area I provide means for accelerating the electrons of the auxiliary stream so that they collide with, andv capture or ionize particles of the unwanted gases. I also provide, in the path of the auxiliary stream, a collecting body of material toward which the latter particles are attracted or driven, and to which'they become attached. With this apparatus, the number of free gas particles is continuously reduced when the tube is in actual operation, because they are being continuously confined to a predetermined part of the tube by the action ofthe. accelerated electrons ofthe auxiliary stream and the collecting'body of material. Y

Various theories of operation may`be advanced as to how the gas pressure is reduced in this process. `Some believe that the electrons engulf the gas particles, be they atoms, molecules, or ions, and carry them along into contact with the material of the collecting body. Under this theory it is not essential to the operation of this apparatus, thatthe auxiliary stream first cause the production of ions by collision with the free gas particles. Others believe, however, that the theory of operation rests on the fact that the electrons collide with the free gas `particles thereby causing the production of ions which are then impelled into contact with, and adhesion to, a collecting body by an appropriate accelerating eld.

`Regardless of the accuracy of either theory, the fact remains that apparatus constructed according to my invention does reduce the number of free gas particles within the envelope and thereby improves the performance and longevity of the tube.

In one form of the invention I provide, within an evacuated envelope, a cathode assembly having two distinct electron-emissive areas disposed substantially perpendicular to one another, and means for heating them simultaneously. The first area produces the electrons required for generating the primary electron stream which performs the main function of the tube, i.e., display, amplification, data-processing or some other purpose. The second area produces the secondary stream in a direction substantially perpendicular to that of the primary stream, and is used to reduce the number of free particles of unwanted gases.

The two electron-emissive areas are separated from one another so that electrons from the auxiliary stream do not interact with those of the primary stream. l also provide a gas-collecting body, which may be negatively charged, and a grid between said body and said second emissive area. The grid may be helical in form, and be so constructed that either a positive D C. voltage or an A.C. voltage may be applied. Whenever this potential is positive it accelerates electrons emitted from the second emissive area into collision with free particles of the undesired gases. Assuming, for explanation purposes, that the gas particles in the region between the second emissive area and the helical grid are thereby ionized positively, they are attracted toward the gascollecting body because of the negative potential applied thereto. If the tube is a cathode ray tube, the collecting body may comprise the internal surface of the metallic grid cylinder which surrounds the cathode. In other types of tubes the collector may comprise the internal surface of the envelope, if the latter is metallic. Even if the envelope is made of glass, as it is in many cathode ray tubes, there is usually deposited on the internal surface thereof `a very thin coating of metallic particles as an incident of the outgassing process to which most cathode ray tubes Vare subjected. This thin metallic coating may also arise because of the evaporation of the metal of which the cathode is made `during the actual operation of the tube.

ln another form of the invention as applied to a cathode ray tube, I provide a cathode having a unitary, planar emissive area. Near this area Idprovide a control grid cylinder having a flat portion substantially parallel to the emissive area. `In this at portion there is a primary aperture'through which electrons from a rstportion of `the emissive `area pass tofformaprimary streamwhichzperforms `the main purposeforlwhich the tube `is designed. The Vilatporton of .the-control rgrid `is also provided with ,one or more auxiliary rapertures through which one or more auxiliary electron streams, pass, traveling in the same direction as the electrons of the primary stream. Next to the control grid, I provide a hollow cylindrical screen grid having the end confronting the control grid cylinder closed by a flat portion in which there are primary and auxiliary apertures similar to, and aligned with, their counterparts in the control grid. I also `provide a body of material in the path of the auxiliary electron streams for collecting particles of free gases which are impelledinto contact therewith. In one embodiment the collecting body may take the form of an essentially truncated conical metallic structure inserted in the screen grid cylinder so that its apex is connected to the screen grid, the apex surrounding and 'being concentric-with the primary aperture thereof. The flared end of the conical structure is connected to the inner surface of the screen grid cylinder at allpoints on its periphery. Several openings are preferably provided in the wall of the cylindrical screen grid at points thereof between the flared and narrow ends of the conical structure, so as to permit freely migrating gas particlesto enter into the path of the auxiliary electron streams.

In operation, the control grid is modulated by information signals, -sothat Vamounts `of primary and secondary `stream currents corresponding theretopass through the primary and auxiliary aperturesof the control grid. The primary stream of` currenttraverses the length of the tube until it impinges on the target, which may be the fluorescent screenof an image reproducing tube, for example. The auxiliary streams of current, however, collide with and ionize any free particles of gases which have entered via the openings in the screen `grid cylinder walls. The gases are ionized negatively and are then impelled toward the s external surface` of the conical portion of the positively charged screen grid with force sufficient to lodge them in the surface thereof. The passage ofthe electrons ofthe auxiliary streams Afrom the cathode and through the apertures vof the control and screen electrodes also brings them into collision with other freely migrating gas particles which they ionize `either `positively or negatively. These ions are then `attracted to electrode surfaces of opposite potentials to whichthey become attracted. They thereupon become confined and cannot causeundesired effects on Vthe structures or operation ofthe cathode ray tube. The amounts of current in the primary and auxiliary streams are functions of the amplitude of the signal applied to the control grid. The number of particles of gas removed over a period of time necessarily depends, to a large extent, on the average potential applied to the control grid. To obtain adequate removal of largenumbers of free gas particles, it is preferable to make the `'auxiliary apertures of the control grid and the corresponding apertures inthe screen grid so large that, 4no matter how far negative the potential applied tothe control-grid goes, there will always be 'somesecondary stream current.

Fig. l is a sectional and schematic view of one form of my invention as embodied in acathode ray tube;

Fig. Zais .a sectional view of an electron gun according to another form of the present invention as embodied in a cathode ray'tube.

Fig. 2b is a plan View of the control grid shown in Fig. 2a; and

Fig. 2c is a plan view of the screen grid shown in Fig. 2a.

Since one of the most' important uses for my invention is in a cathode ray tube, the invention will be explained in connection therewith although it is also useful in a number of other applications as well. In Fig. 1, portions of an electron gun 12 relevant ,to this invention are shown within the neck.portion `14 of a cathode ray tube 80. Other elements of the gun 12 andtube 80, such as `the focussing electrode, the beam `accelerating electrode, :and .the associated deilection yoke` are not. shown as they may be conventional and are not believed .necessary for purposes of explaining the invention. 'The elecf tron gun 12 consists of a hollow metallic cylindrical control electrode 13 (which may be made of stainless steel, for example) having an aperture 15 located in its flat, closed end. The open end of the control electrode 13 is partially closed off by an apertured ceramic annular member 16 whose peripheral portion makes contact with the internal surface of the cylinder 13. The member 16 may be held in place by three retaining lugs (only one of which, i.e., lug 42 is shown) and a number vof cooperating indents 40 in the wall of cylinder 13 which extend inwardly making contact with the stepped lportion 41 of the member 16.

The space within the control electrode cylinder 13 is effectively divided into two parts by another annular ceramic member 24 whose edge is also contiguous with the internal surface of the cylinder 13. It is held in place by a flanged retaining ring 23 in the rear and by the anged spacing ring 26 in front. The tubular or sleeve portion 25 of the cathode assembly 20 protrudes through an aperture in the annular member 24 and is maintained in position by the headings 29 and 30 which are formed in the walls of the tubular portion 25.

Annular groove 21 is cut into the rear surface of ceramic member 24 for preventing the cathode assembly 20 from being shorted out to the control grid cylinder 13. Were this groove not provided, a metallic lilm would tend to be built up on the entire rear surface of member 24 because of release of metal from the tube elements incident to the operation thereof at elevated temperatures and would provide'a conductive path between the cathode and control grid. The groove acts to shadow portions of the surface of member 24 and thus functions to break the continuity of the metallic film between the electrodes. Annular groove 22 performs a similar function on the front surface of the member 24.

In the forward portion of the space within the control electrode cylinder 12 is a metallic cap 27 situated on the end of the tubular cathode member 25. On the cap 27 is deposited a first emissive area 28 composed of a conventional type of thermionic emissive material such as barium strontium carbonate, or barium strontium calcium carbonate, in a suitable binder, the material becoming an'oxide after the cathode is processed. This first emissive area 28 generates the primary stream 36 of electrons which is used to perform the main function of the tube. In practice this stream may be of the order of 1 milliampere. When the first emissive area 28 is heated by the heating element 34 located within the tubular portion 25, the primary stream 36 is directed, as shown, upon the fluorescent screen 82 of the flared portion 81 of the cathode lray tube 80 to produce a spo of light which may be used for display purposes, as in television receivers, for example.

' In the rear portion of the space within the cylinder 13, i.e., that portionrthereof to the left of the annular member 24, my novel means for improving the vacuum vof the tube 80 are disposed. A second emissive `area 38, which may be composed of the same thermionic emissive material as the lirst emissive area 28, is deposited upon a rearward portion of cathode sleeve 25. This second area-38 is also caused to emit electrons when lthe heating element 34 is energized. Surrounding the second area 38 is a helix 19 of wire comprising, in a typical case, approximately six turns of a nickel-alloy wire having a diameter of .005", which is commonly used for the manufacture of grids in electron tubes. The pitch of the wire may be about .020. The helix 19 is supported by a pair of metallic rods 17 and 18 which extend through apertures in the ceramic annular member 16. A potential of about +50 volts, in the case illustrated, is applied by way of the rod 17 to the helix 19 -from a source of D.C. such as the battery 46.

Whenthe heating element 34 is energized, av secondary 10 to 15 milliamperes is emitted from the second emissive area 38 and is accelerated radially toward the helix 19 because of the positive potential applied thereto. The process by which the gas particles are conned will be explained, for convenience, according to the theory of operation previously mentioned in which it is believed that the gas particles are rst ionized before they are confined. When the electrons in the radial streams indicated by the dashed lines bearing numerals 48 and 50 are accelerated by the positive potential of the helix 19, they cause some of the particles of freely migrating gases with which they collide to become positive ions. These ions are repelled, in the space between the helix 19 and the inner surface 11 of cylinder 13, by the positive charge of the helix and attracted by the negative charge on the cylinder 13 to which a negative bias of about -40 volts is applied together with modulating signals from source 54. Although the value of the potential on the cylinder 13 varies in accordance with the instantaneous voltage level of the signals from modulating signal source 54, the bias applied from battery 52 is preferably such that the cylinder 13 is always negative with respect to the cathode and to the helix 19 so that positive ions are attracted thereto. Thus the positive ions are impelled with considerable velocity into the inner surface 11 of the cylinder 13 during the actual operation of the tube thereby reducing the number of free gas particles present within the entire evacuated envelope. Consequently, the number of freely migrating gas particles within the cathode ray tube is substantially reduced.

If negative ions are produced by the collision of electrons emitted from the second emissive surface 38, the former are attracted to, and become imbedded either in the metal of which the helical grid 19 is composed, or the material of which the supporting rods 17 and 18 are composed, so that even more of the freely migrating gas particles are confined.

It has been observed that freely migrating particles of gases such as helium are not affected by gettering and therefore remain in the tube after the getter has been ashed. They can also diffuse later through the walls of a sealed-off evacuated tube, especially in a case where the walls are made of glass. Since helium is an inert gas, all conventional getters are ineffective to confine particles thereof. My invention, on the other hand, does confine inert as well as active gases, and is operative during actual operation, to confine both inert and active gases.

After operation of the gas-removing apparatus in the rear portion of the space within cylinder 13 for some time, a great number of particles of gases will become imbedded in the internal surface 11. However, there is vlittle chance that the internal surface 16 will become saturated with gas particles and thereby lose its efficacy since, during actual operation of cathode ray tubes, the heat of the cathode causes a continuous evaporation of some of the materials of which the emissive surface is composed as well as of the metal of which cathode tubular sleeve 25 is composed. Therefore, as gas particles become imbedded in the metal of which the grid cylinder 13 is composed, they will subsequently be covered up by evaporation of the emissive materials and metal there upon. Thus a new collecting or imbedding surface is presented to the gas particles which are attracted into contact therewith.

Figures 2a, 2b and 2c depict another embodiment of the present invention as used in a cathode ray tube. Only the electron gun portion thereof is shown therein and it will be noted that parts identical to those shown in Fig. 1 bear the same number, and their description will not be repeated Whereas similar parts bear corresponding numbers which are primed. In this form of the invention only a single emissive surface 28' is deposited on the cap127'` at lthe end of the cathode cylinder 125. :The con:-

trol `grid cylinder 60` difers from the control igrid 13 in l Fig. yl in that itcontains three apertures, a cen'tral'aperture l', and a pairof semi-circular or crescent-like apertures '63 and 64. The primary electronstream 36passcs tends- `to beneutralized and theeicacy ofthetube is diminished. f i A'nther example Offits `possible usel is in so-called i field-emission types. of tubes, in which ythe sharpnessk of ,the `point cathode ydirectly ,determinesy the. emission thereof. hesetubes have` sometimes been used asy cold is essentially cylindrical in shape vexcept that its. closed,

the grid` cylinder 60 and be z planar rend 72v is adjacent theclosed endy of ythe grid `cylinder 6l);` The lclosedend 72 has apertures 73, `'I4' and `75 which may be of exactlyr thesame shape` asaper- r tures 63, 64 andlS" of aiigned therewith.'

l,Withinzthcscreenfcylinder 701 is .disposed a truncated,

When thez ainriliaryl streams 66 and; 67.'pass through their vrespective apertures :in the control. and :screen cylinders.,l they collide with gas particles in their lpaths.l -Anyi negative ions formed bythe collision are attracted. through the apertures 63,' l64,71*y 'and'74 by the ield dueA ..to the positive potential ofthe screen cylinder 70 and kbecome attached thereto. Any -positivedons formed by the',y collision will. be attracted `to and :imbedded jin kthe n material of either the control electrode 60 ofrrthe cathode', both. of .which are l negative. with respect Kthereto. lt is I possible to obtainja total maximumlcurrent in the tvvof.y

`streams 66 and 67 of about l2`n1illiamperes. However, n the modulating signal source 54' is rarely at a maximumy potential so that the average current in the two auxiliary streams 66 and 67 may be of the order of about 5 milliamps. A greater average current in the secondary stream may be obtained by increasing" the potential applied to the screen grid which, in turn, would necessitate driving the grid harder by applying signals of larger arnplitude thereto thus necessitating increased current output from the cathode driving stage. The apertures-84 permit gases to enter intothe `paths 66 and 67 of the electrons in the electrode 70. The apertures 63, 64, '73, `and 74 should berfairly large so that, even when the potential on the control grid is quite negative, there will nevertheless be a certain amount of current flowing so as to make the vacuum-improving process operative at all times during tube operation.

It is possible to embody the invention in a two-element device rather than in a three-element device Aas explained in connection with Figs. l and 2a. Instead of employing a separate electrode to `accelerate the electrons, the charge on the collecting body itself may be made so positive as-to cause the emittedelectrons to'be accelerated suiiiciently to cause particles of gas between the electrodesto be ionized. Negative ions will then be attracted to, and become lodged in the material of which the collecting body is made.

While the invention has been described with particular reference to employment in cathode ray tubes, it may alsobe used profitably in other types of tubes. VFor eX- ample, certain types of storage tubes maintain a charge for a period of time as an inverse function of the number of ions within the evacuated area. When these ions bombard the `target of such a storage tube, the charge conical, 'metallic member 76' Lwhosef 'flared edge v79: is n i .connected `to thelinternal 'surfaceiof the cylinder; 70 `as shown and whosenarrowend iis'connectedto thatpor-l l vtioncfthe flatl end-portion '72;arou'ndthe 'central aperkture 75 therein.r Bya 'connection tobattery i78 .the l screen cylinderl 7i) is maintained at a positive. potentiall with respect'to therpotential applied' to the gridL cylinder n .'60, i It is ,to bei noted: that in this form of the Yinven-'f- 1 i -tion there isa'unitaryemissive surface 28'., and also: that `there',is'no'extra lgrid such asy thehelix 19 .discussedabovey l Lin connection rwith Fig'. l. i

m WhaLLclaim is:`

cath-ode rectiers. -If positive ions, for-med within the; evacuated `arealby the collision of gas particles .and electrons, areattractedtoward the point cathode and bombardthelatter causingit to become dulled, theemission' therefrom is substantiallyrcduced.` By employing .ap-

paratus similar tothe embodiments described herein, the

.number of free gas particlesmay be reduced considerl ably resultingin the preservation of thesharpness of the point cathode forarnuch longer time.

vIt will. beunderstood ythat lstill other embodiments and applications Lot' apparatus constructedy according .to the invention willoccur to those 'skilled' in the art. Consequeutly,= 1: desire the scope of ,thisinventionto be limited n only bythe appended claims. l

electrons .emittedffrom' a second Vet 1 said plurality` of l i means along apredetermined 'path rdistinct `from the path f disposed inthe path 'offsaid accelerated electrons only l l Y l' whichv is constructed to contne-pa'rtielcsofgasy impelled 1 ofsaidelectronsiemitted'by said first means, and means into contact therewith.'

- '2. The `device laccrding .to claimf 1; wherein;y sph-stan- Vtially more electronsareemitted frornsaid second emitc tingnieans; than from vsaid rst emitting means.y j

' 3.1 :T he device according yto claim 1 whereinl `said acl l' Acelerating,means includes an .electrode to which a posif 2 tive potentialv is applied and wherein said means. disposed in` thelpath of said accelerated electrons isl a material to f `which .anegativelpotential is applied. `f

4. "I'hefdeviceaccording to claim 1 wherein said predcterminedpath of the electrons emitted from said secondemitting means-isisubstantially perpendicular to the path of `electrons emitted from said first emitting means.

5. The device according to claim l wherein said first and second emitting means are disposed perpendicular to one another.

6. The device according to claim l wherein said means inthe path of said accelerated electrons comprises metallic particles.

.7. Antelectron discharge device comprising: an evacuated t envelope, first means therein for emittingelectrons for performing a data processing function having utility outside said device, second means therein for ,emitting V substantially more electrons than are emitted by said `impelled into contact therewith may adhere.

`8. `An electron discharge device comprising: an envelope from which substantially all `particles of gases `have `beenrernoved, a unitary cathode assembly comprisingfrst and second means therein for emitting electrons,

ymeans for utilizing some ofsaid emitted electrons for a lpredetermineddata-processing function,imeans to which a positive potential'is `supplied for accelerating others of `said emitted electrons so that they collide with particles of gases remaining in said envelope thereby producing fpositive ions thereof, and means to Which a negative potential issupplied disposed in the path of said accele- Iatdtclectrons ,andconstructed of a material which conlingedevicel comprising: `an evac-j l f l f cated envelope,- a. single; integral cathodetherein which. includes afplurality of means for. emitting electrons,

means-.for ntlizingelectrous emittedv from .atirst of .said @plurality oflrnean's` for a predetermined functionhaying ,utility ,outside lsaid tube, Etneans 'solely for accelerating i fines positive ions of said gases which are impelled into contact therewith,

9. A high vacuum electron discharge device comprising: an envelope, means therein for emitting electrons, means utilizing a first portion of said emitted electrons to perform a function which has utility outside said device, and lgas-confinement means therein comprising means for causing a second portion of said emitted electrons to be accelerated along a path distinct from lthe path of said first portion at velocities suicient to ionize residual gases in said former path, means for preventing positive ions caused thereby from bombarding said emitting means, and means to which positive ions are attracted into substantially permanent contact.

10. A cathode ray tube comprising: an envelope from which substantially all particles of gases have been re- 'moved, a cathode assembly therein which includes first and second emissive areas disposed substantially perpendicular to one another, means for utilizing electrons emitted from said first emissive area for producing a scanning beam, an electron-sensitive beam-interceptin'g structure disposed in the path of said beam, and means for improving the vacuum of said tube during the operation thereof comprising means for accelerating electrons emitted from said second area in a path substantially perpendicular to the path of said utilized electrons, and a material disposed in the path of said accelerated electrons so constructed and arranged that particles of gas impelled into contact therewith may become attached thereto.

11. An electron discharge device comprising: an evacuated envelope, an integral cathode assembly which includes first and second electron emissive areas, means disposed adjacent said second area to which a positive y potential is supplied for causing electrons emitted from electrode having a control portion near said first emissive l area for controlling the emission therefrom and a gas collecting portion in the path of electrons emitted from said second area, said control electrode being at a potential and constructed of a material so that positively ionized gaseous particles impelled into contact therewith by said electrons from said second area may adhere.

12. An electron gun structure for a cathode ray device comprising: a unitary cathode assembly which includes first and second electron emissive areas, a control electrode to which a control voltage is to be supplied which is negative with respect to the potential of said second emission area for regulating the intensity of electrons emitted from said first area, said control electrode being arranged to surround said second area, and means intermediate said control electrode and said second area for accelerating electrons fromsaid second area toward said control electrode.

13. An electron discharge device comprisingzan envelope from which substantially all particles of gases have been removed, an essentially tubular cathode assembly therein which includes first and second electron emissive area disposed substantially perpendicular to one another, means for utilizing electrons emitted from said first emissive area for a predetermined function, a helical grid surrounding said second area and an essentially cylindrical metallic electrode surrounding said cathode assembly and said helical electrode, said electrode having a portion near said first emissive area for controlling the intenity of the electron stream produced thereby in response to signals applied thereto which are negative with respect to the potential of said cathode.

14. An electron discharge device comprising: an envelope from which substantially all particles of gases have been removed, a cathode assembly therein including a unitary emissive area, mean for utilizing electrons emitted from a first portion of said unitary area for a predetermined function, means for accelerating electrons emitted from a second portion of said unitary area in at least one given path parallel to, but distinct from, the path of said electrons emitted from said rst portion whereby said accelerated electrons ionize residual particles of said gases, and a metallic body disposed in the paths of electrons emitted from said second portion constructed and arranged to attract said ionized particles of gas into permanent contact therewith.

l5. An electron discharge device comprising: an envelope from which substantially all particles of gases have been removed, va cathode assembly therein having a unitary emisive area, a irt electrode disposed in proximity to said unitary area having primary and secondary apertures for passing respective primary and secondary streams of electrons, and a second, essentially cylindrical, electrode disposed in proximity to said first electrode, said second electrode having a flat end portion in which l apertures corresponding to those of said first electrode are arranged, said second electrode also containing therein a conical member whose flared end is contiguous with the internal surface of said second electrode and whose tapered end is contiguous with the inner surface of said flat end portion at points thereon surrounding the aperture thereof which corresponds to the primary aperture of said first electrode.

16. In a high vacuum cathode ray tube comprising an envelope, a liuorescent screen, and means within said envelope for generating an electron beam adapted to impinge on said screen, thel improvement which consists in apparatus for continuously reducing the number of free gas particles within said envelope during the operation of said tube, said apparatus comprising means for emitting auxiliary electrons, means for accelerating said auxiliary electrons into an electron stream independent of said electron beam, said electron stream having a current substantially greater than said electron beam, and collecting means in the path of said electron stream for entrapping gas molecules, said accelerating means and collecting means jointly comprising a conductive member Whose potential is positive with respect to the potential of said auxiliary electron emitting means.

17. An electron gun structure for a cathode ray tube comprising: a unitary cathode assembly which includes first and second electron emissive areas, a control electrode for regulating the intensity of electrons emitted from said rst area in response to signals applied to said electrode, said control electrode being arranged to surround said second area, barrier means disposed between said rst and second emissive areas within the confines of said control electrode and constructed to separate said first and second emissive areas from one another, and means intermediate said control electrode and said second area for accelerating electrons from said second area toward and into contact with said control electrode.

References Cited in the file of this patent UNITED STATES PATENTS

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