US2199540A

US2199540A - Electron device

Info

Publication number: US2199540A
Application number: US217682A
Authority: US
Inventors: Diels Kurt
Original assignee: Telefunken AG
Current assignee: Telefunken AG
Priority date: 1937-06-24
Filing date: 1938-07-06
Publication date: 1940-05-07
Anticipated expiration: 1957-05-07

Description

ELECTRON DEVICE Filed July 6, 1938 Allll llllllllll All lllll AAAIAAAAAA All! vvvvv IVIIIIvIvI IIII vvyvv V'IVIVIIIVVVVV INVENTOR KURT D/ELS AT I'ORNEY Patented May 7, 1940 EC R D I Kurt Diels, Berlin-Friedenau,'Germany, asslgnor to Telefunken Gesellschaft fiir Drahtlose Telegraphic m. b. H.,'Berlin, Germany,- a corporation of Germany Application July js, 1938," Serial No.2 217,632

I eme 9 .1, 1; ciai is. (01. 250- 162) This invention relates to" electron devices'and more particularly to those devices using concentrated beams of electrons and provides both method and-means for producing improved fo- 5 cussed beams of electrons by suppressing secondary electronic emission from the electron: optical system used to focus the electrons. I

In cathode-ray tubes, especially where, used for television purposes, secondary electrons'are' apt 0 to be released by the electron ray pencil uponits passage through the aperture of an electrode. provided that the diameter of the pencil of electrons is equal to, or greater than, thediameter of the electrode aperture; These secondarys'electrons prove troublesome in the path of the. rays for the reason that at the point where-:they are emitted they possess a velocity of only a few volts as contrasted to the high velocity .of'the primary electrons, and the. result is that, if another electronlens is mounted at some point in the direction of their travelth'eyrequire :a lens of a different focal length than the primary electrons. If the said electroniclens is so set or dis-'- posed that the electrons are brought to 'focus upon the fluorescent or luminescentscreen or other imagingor focussing surfacethe-spot of impact will appear blurred or out of focus-because of the very fact that the secondary electrons have failed to be concentrated in this spot.

To obviate this disadvantage'it hasbeen'suggested in the prior art to' treat ra'y-lirhitingcOnductor parts-more particularly aperturesgr stops or diaphragms to be imaged and mounted in the discharge path anteriorly of the electron-optic system to be imaged or focussedfinsiich a" way as to prevent theiryielding' secondary "electrons, and/or to mount in the vicinity of such apertures or diaphragins, that is, at points at'clo'se proximity to the ray,v stops designed to "collect sec 40 ondary electrons, While it 'is true that such 'a device insures the desired ,purposejiithas certain undesirable properties. Forinstance, if a. secondary-electrcn collector or shielding electrode of the kind before mentioned is mounted in the neighborhood of the diaphragm to be imaged, the

result is that in the opening of the collector'diaphragm, between the'latter andthe next electrode, which has dissimilar potentialsfa small lens'is produced. This lens'moreoveris'filled as far as the very edge by the cathode'rayso that it is liable to introduced'imagirlgdistortions in the ray path. Inasmuch as it-isimper'ative that the collector diaphragm should be mounted at close proximity to the focussed pencil without touching the same, while, on the other hand, the

diameter the ray may be subject to enlargement'sjand constrictions in the course of modulationjthe'case may moreover arise that the collecting diaphragm, when the aperture of the cathoderay pencil is enlarged, is hit by electrons "5 of the'pencil and is thus caused to yield, in turn, secondary-electrons. Now, these difiiculties are obviated by this invention. r

The invention'shall be explained in more detail as applied to an exemplified embodiment thereof "10 t i by reference to the appended drawing. The electrons emitted from the cathode I, first under the infiuenceofthe field set up by the electrodes I, Z and 3 are directed towards the opening ID of theelectr odei, whereupon, by the action of the 15 condensing field set up between the electrodes 3,

4 and '5 they are concentrated in the aperture ll ofthestop 5. Suppose that this latter aper- 'ture'is'theone'to be focussed and imaged upon the luminescent screen. The electrons passing 20 through this aperture have a speed which is governedby the potential tapped on the potentiometershown undesignated. However, in addition secondary electrons are generated-in the aperture l I" of the disk electrode-5 which possess substan-fizgs :tia-lly lower speed. The next .following electrode 6 which; for reasons to be set forth in more detail further below, is'funnel shap'edpreferably and is kept-at a" potential which-is negative in rela- I tion to; electrode 5. To be more explicit, 6 in rela-v 30 tion to electrode 5 is at least-so much more negative thatthe secondary electrons setup at 5 of low speed willbe unable to'buck the field resulting "betweeni and 6, while the primary electrons of 1 higher speed passing through'the opening-ll in 35 the absence of any impedance and obstruction willbe-capable of doing this. In other words, the

action; of electrode 6 is that-only the primary electrons 'areutilized for the imaging of aperture "ll upon the luminescent screen. The funnel-shaped construction of the electrode 6 is of advantage in several regards in practice Owing to the fact that the narrower funnel aperture is located anteriorly of the aperture of the dia- A phra'gm to be imaged with the result that the ac-' 5 tion therethrough of the following 'electrodes is greatly diminished, it follows that the potential at the electrode 6 need to be but little negative comparedwith that of theelectrode 5 in order to insure the desired retention and arrest offthe '5 secondary electrons. Betwee'nfth'e shielding or "collector electrode 6 and the electrode (being at "a higher'potential, to be sure, lens action may be present. However, since thewide 'funnel'opening is turned towards the electrode 1, there re- 55 sults a lens which has a large diameter compared with the pencil diameter. Insofar as its section is taken up and occupied by the pencil, the said lens will introduce but slight errors or distortions into the electromagnetic system. The lens inside the range of electrode 6 serves as a prefocussing lens. The main lensis formed by ,the field set up between the electrodes 1 and 8. b The inside diameter of the funnel-shaped electrode 5 may be so chosen that also changes in aperture caused upon modulation (which, for instance, may be applied to the electrode 4) will cause no contact between the ray and theelect-rode 6.

In lieu of the funnel electrode "'6 it would .be possible also to use a sequenceor seriesof elec trodes presenting an inside diameter which grows with growth of distance from theldiaphragm the electrode being mounted at greatest proximity to the diaphragm being maintained at negative potential in reference to the diaphragm. The following electrodes along the path of theraymay have impressed upon themselves potentials which become more positive by steps as the distance from the diaphragm increases.

In a practical tube the following potentials were applied in sequence to the rotation symmetric electrodes 1 to 8:

0 volts Cathode 1 and cylinder 2:

Stops

3 and 5 ='+300 Cylindrical electrode 4 50 Funnel electrode 6 =+250 Electrodes '7 and 8 =+600 ancl+5000 v.,

v respectively.

electrode will be so slight that the secondary electrons there released will be arrested by the auxiliary electrode. If this condition is fulfilled,

it will practically be solely those electrons which pass unobstructedly through the diaphragm that are used for electron-optic imaging of the diaphragm so that the imaging of the diaphragm will be invariably adequately sharply focussed.

If in lieu of the funnel electrode a cylinder electrode is employed, then, if the lens set up between it and the next following electrode is to have :the same diameter as in thecase of using a funnel-shaped electrode, it must .have the same inside diameter as the wide aperture of thefunnel electrode. ,However, inorder that, for the same potential atthe cylinder electrode and at the next followingelectrodes, the same through or penetrating action may be secured as with a funnel electrode, the cylinder electrode must be made correspondingly longer and/or its potential must be chosen more negative. These conditions hold good also in the case Where a diaphragm electrode is used which is to have the same diameter as the wide opening of the funnel electrode.

What I claim is:

l. A cathode ray tube comprising a cathode, a concentrating electrode concentric with the cathbeyond :said second anode.

ode, an apertured disk electrode in register with both the concentrating electrode and cathode, followed by in the order named and positioned in register with the disk electrode and spaced longitudinally therefrom and from each other, a cylindrical electrode, a second apertured disk electrode, an apertured imaging annular conical electrode whose minimum internal diameter is larger than the aperture of said second disk electrode, a first anode, and a second anode, meanswithin the tube to maintain the two disk electrodes at the same potential, and a target member positionedin register with all of said electrodes and beyond said second anode.

2. A cathode ray tube comprising a cathode,

a concentrating electrode concentric with the cathode, an apertured disk electrode in register ode, followed by in the order named and positioned in register with the disk electrode and spaced longitudinally therefrom and from each other, a cylindrical electrode, a second apertured disk electrode, an annular conical electrode whose minimum internal diameter is larger than the aperture of said second disk electrode, said conical electrode being positioned with its minimum internal diameter adjacent'to said second disk electrode, a first anode, and a second anode, means within the tube to maintain the two disk electrodes at the same potential, and a target member positionedv in register with all of said electrodes and beyond said second anode.

. 3. A cathode ray tube comprising an envelope having a conical section and an elongated cylindrical neck aiiixed to the conical section at the point of minimum diameter, an end wall closing the larger diameter end of said conical section, a cathode supported within the cylindrical neck, a concentrating electrode concentric with-said cathode, an apertured disk electrode in register with both the concentrating electrode and cathode, a target surface supported on said end wall, .*a combination of electrodes in the order named counting from said apertured electrode positioned intermediate said apertured electrode and said target surface, comprising a cylindrical electrode, asecond apertured disk electrode, an apertured imaging conical electrode adapted to be maintained negative with respect to said second apertured disk electrode to repel secondary electrons from the apertured disk, a first anode and a second anode, and means within the tube to maintain the two disk electrodes at the samepotential.

4. A cathode ray tube comprising a cathode, a concentrating electrode concentric with the cathode, an apertured disk electrode in register withboth the concentrating electrode and cathode, followed by, in the order named and positioned in .register with the disk electrode and spaced longitudinally therefrom and from each other, a cylindrical electrode, a secondlapertured disk electrode, an apertured imaging conical disk, a first anode, a second anode, means within the tube to maintain the two disk'electrodes at the same potential, and -a target surface positioned in register with all of said electrodes and KURT DIELS.