US2434895A - Electron discharge device - Google Patents

Description

Jan. 27, 1948. v ARD|T| ELECTRON DISCHARGE DEVICE 2 Sheets-Sheet 1 Filed May 1, 1943 INVENTOR M/I01?/6 E 1980/ 7' l GENT.

Jan. 27,1948. M ARD|T| ELECTRON DISCHARGE DEVIE Filed May 1, 1943 2 sheets-sheet 2 INVENTOR mama-flew A ENT.

Patented Jan. 27, 1948 ELECTRON DISCHARGE DEVICE Maurice Arditi, Boulogne, Billancourt, France, assignor to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application May 1, 1943, Serial No. 485,404 In France July 8, 1941 Section 1, Public Law 690, August 8, 1946 Patent expires July 8, 1961 Claims. 1 This invention relates to secondary electronic emission device in general and has reference in particular to light-transformers comprising one or more secondary-emission stages arranged in cascade.

Light-transformers of this type comprise for instance a photo-electric cathode, on which a light-image is formed, a series of secondary electronic emission electrodes and a collecting electrode. The collecting electrode is coated with a fluorescent substance on which appears a visible image reproducing the image formed on the photo-cathode. The photo-cathode may be particularly sensitive to invisible radiations, either with respect to long wave lengths or short wave lengths. As a result, transformation of invisible images into visible images takes place.

However, such light-transformers possess many disadvantages. When such light-transformers are used in well known structures of electron multipliers, disposed in cascade, it is found that the image obtained in the last electrode of the transformer is considerably distorted as compared to the image projected onto the photo-cathode. After careful research, it is discovered that these distortions arise mainly from the fact that the electronic images formed on the successive secondary-emission electrodes show aberrations due to the interference of the primary and secondary beams at each electrode. The optical quality of the electron-optic systems used heretofore in electron multiplier structures is not sufficiently effective to insure a good reproduction of an electronic image from one target to the next which ensues chiefly from the combined actions of the electric and magnetic fields used for the concentration, acceleration and deflection of the electrons. Moreover, the cascade electrode arrangements generally employed in electron multipliers have the drawback that erratic electrons or ions may traverse the entire structure and fall directly on the last electrode. In the case of light-transformers, the result is interfering light effect on the fluorescent screen.

An object of the invention is to overcome the disadvantages mentioned above.

A further object of the invention is to provide special means for reducing, or practically eliminating, in such devices the aberrations of lightimages which result from interference, at each secondary-emission electrode, between the electronic beam falling on a particular electrode and the secondary electronic beam leaving the same.

Briefly, I accomplish these and other results by providing light-transformer structures in which the successive paths of the electrons are well separated, the electronic beams being conditioned so as to produce on the successive electrodes, electron-optic images having a minimum abberration and being free from the effects of erratic ions or electrons. Specifically, these results are obtained by providing a special system of electrostatic lenses. The latter are associated with the electron-emitting electrodes in such manner that a high speed electronic beam is produced from each of these electrodes. This result is accomplished, by creating a zero electric field space into which all these beams pass. The beams passing through this space are subjected to the action of a transverse magnetic field which causes the electrons of each beam to follow circular paths up to the next electrode. This zero electric field space or region is created, according to the present invention, by means of an extra electrode or box which is brought to the same potential as certain electrodes of the electrostatic-lens system. As a result, a zero electric potential gradient is produced between that extra electrode (or the walls of that box) and the particular lenselectrodes. Depending upon the relative strengths of the electric and magnetic fields, any desired enlargement of the image may be obtained on the collecting electrode or the fluorescent screen.

With these and other objects in view, a will become more apparent hereinafter, the present invention is fully explained in the following description, and illustrated, by way of example, in the accompanyingdrawings in which-- Fig. 1 shows schematically the conditions required for formation of an electronic image free from aberrations;

Fig. 2 is a schematic view of an embodiment of a light-transformer, incorporating the novel features of the present invention;

Figs. 3 and 4 are schematic views of two differently charged electrostatic lens systems used in the space comprised between electrostatic lens I 3 and the support on which electronic image I is formed.

In the arrangement according to Fig. 2, electronic beam 5 is formed by electrostatic lens 6; from electrons released by cathode 1, under the influence of light-beam 8 for instance, which is focussed on cathode l by optical lens 9. Electronic beam 5 is subjected, in zero electric field space It], to the action of transverse magnetic field H. Electronic beam 5 is thereupon circularly deflected as indicated at H. As a result, an electronic image of the light image projected on cathode 1 is formed on secondary-emission electrode 12. This electronic image is free from aberrations. When entering electrostatic lens system Hi, the incident electrons are retarded progressively so as to fall upon electrode l2, at a speed corresponding to the maximum secondary emission of electrons. The emitted secondary electrons whose speed is of opposite sign to that of the primary electrons, are in turn accelerated progressively and emerge from lens M at a high speed which corresponds to the electric potential of the last electrode of lens I4. The action of electric field E, beyond electrostatic lens l4, becomes zero and the electrons thus concentrated into a beam are circularly deflected (as indicated at I5) by magnetic field H, whereby an aberration-free image is formed on a high potential target or screen is. The latter is coated with a fluorescent substance such as willemite. Thus a light-image appears on fluorescent target IS. The strength of this light-image is increased by the multiplication of electrons produced on secondary-emission electrode 12. The light-image may be seen by an observer H, either directly or through a suitable optical system (not shown).

A light-transformer provided with the arrangement of electrodes according to the present invention produces a visible image without appreciable distortion, owing to the separate action of the electric and magnetic fields, which entails a more homogeneous distribution of the electric potential gradients and a more definite impedance of the primary and secondary electronic beams of each electrode. light efiects are eliminated because erratic electrons or ions cannot pass directly from photocathode 1' to fluorescent screen Hi.

It will be clear that any desired number of secondary-electronic-emission stages may be used to increase the luminosity and/or the dimensions of the final image. p g

- Figs. 3 and 4 illustrate schematically two difierently charged electrostatic-lens structures which may be used advantageously in the light-transforming device according to Fig. '2. It should be clear, however, that the potential charges recited in'the following are not given by way of limitation. On the contrary, these potential values may be varied at will according to the Moreover, interfering 4 dimensions and the arrangement of electrodes constituting the lens systems.

The electrostatic lens system according to Fig. 3 is intended for primary electron emission and comprises photo-cathode l which is brought to a zero potential. Photo-cathode l is surrounded by electrode 18 forming a Wehnelt cylinder having a negativepotential .of .-100 volts, for instance, with respect to cathodel. Concentration ring i9 is brought to a high positive potential for instance, +2,000 volts, with respect to cathode '1. Ring 16 serves as electron-accelerating. electrode. The electrostatic lens system is completed by fiat ring 20 and cylindrical ring 2|, which are both brought to a still higher positive potential, for instance +6,000 volts, with respect to cathode l.

The device according to Fig. 4 is intended for secondary electron emission and comprises a secondary emission electrode l2. Electrodes 22 to 25 0f the structure according to Fig. 4 are ar- {ranged in the same manner as electrodes 18 to 21 of Fig. 3. However, since secondary-emission electrode l2 must be brought to a certain positive potential with respect to photo-cathode I, which is suflicient to insure the extraction of secondary electrons under the impact of the primary electrons emitted by photo-cathode l, or by a preceding secondary-emission electrode (such potential being for example of +500v volts), Wehnelt cylinder 22 must be brought to a positive potential with respect to the cathode which is lower than that of electrode l2; for instance of +350 volts. The distribution of potentials on electrodes 23 to 25 is, preferably, the same as on electrodes 19 to 2| of Fig. 3, although other potential values may of course be used.

In order to provide a zero electric field space below all the electro-static lenses 6, Hi, etc., of the structure according to Fig. 2, the arrangement shown in Fig. 5 may be used. In Fig. 5, the photocathode, secondary-emission electrodes, fluorescent screen and electrostatic lenses are shown in the same manner as in Figs. 2 to 4, like reference numerals being used to designate like parts. According to Fig. 5, the potentials of the various electrodes are taken from a common potentiometer 25. The potentials of the secondaryemission electrodes or associated electrostaticlens elements may be the same for a particular structure and hence have a common connection to potentiometer 26. It should be noted, however, that it may be advantageous, in certain cases, to provide independent connections for these electrodes and electrostatic-lens elements in order to be able to make finer adjustments of potentials and obtain better images.

Rings 20, 24 and screen electrode 16 are brought to the same electric potentialand connected electrically to plate 21. The latter is disposed below the entire structure and provided with openings such as 28 and 29 in order to permit passage of light- beams 8 and 30, respectively. Moreover, rings 20, 24 as well as the support of screen It may consist of a single plate provided with openings for the passage of electronic beams. In the alternative, these two plates may constitute the two opposite sides of a box which is wholly closed and brought to a high positive potential with respect to the photo-cathode. Interfering phenomena, due to the accumulation of electric charges on the Walls of theassembled tube, are avoided in this manner. 'In order to prevent aberrations due to the magnetic fields, it

is desirable to use a non-magnetic metal for all these electrodes. The potential gradient between plate 2?! and ring electrodes 20, 24 is practically zero. If a transverse magnetic field H is applied in this zero electric field region, the electrons emitted by photo-cathode l and thereafter accelerated by electrode 20, will describe circular paths, indicated by the arrows 3i, 32. The electrons produce an image on the first secondaryemission electrode l2. The secondary electrons issuing from the latter electrode have speeds of the opposite sign and, in the same way, form a second electronic image on the second electrode 12. This process is repeated as many times as there are secondary-emission electrodes. Finally, a visible electronic picture is formed on fluorescent screen I6 which is raised to a high potential.

In such an arrangement, the efficiency of the secondary-emission electrodes is very good because the impact speed of the incident electrons corresponds to the maximum secondary emission. The image formed on screen I6 is very bright because the electrons strike this high potential electrode at great speed. Owing. to the high potentials of electrodes 20 and 24, the electrons issuing from the various emitting electrodes come out at the level of these electrodes at very high speeds. It has been found that, in practice, the magnetic field has no influence in the regions comprised between cathodes l and I2 and electrodes 2|] and 24. On the other hand, starting from electrodes 20 and 24, the electric potential gradient becomes zero and the magnetic field acts only on the electrons of high initial speed. Furthermore, such an arrangement prevents the contamination of the secondary-emission surfaces by particles of the photo-electric substance of cathode I because there is no direct passage or accelerating electric potential gradient from this photo-cathode to the secondaryemission surfaces.

The structure shown in Fig. 6 as a whole, corresponds to that of Fig. 5. For claritys sake, like reference numerals have been applied to like parts. Element 21 represents a high potential screen. The same consists of a non-magnetic conductive coating applied to the wall of glass vessel 33, within which the entire structure is mounted. Elements 34, 35 and 36 designate pressed legs of vessel 33 for accommodatin the supports and outlet connections of the electrodes. If desired, potentiometer 26 (of Fig. 4) may be arranged within vessel 33 and the connecting wires, of which there are but few, and which serve as supports, may be sealed directly through the wall of vessel 33.

It should be noted that the present invention is not limited to the embodiments shown and described, but that on the contrary, numerous modifications and adaptations may be made without departing from the spirit and scope of the same. I therefore do not wish to be understood as limiting myself to the details of construction and arrangement described herein.

I claim:

1. In an electronic discharge device, at least one electrode for emitting secondary electrons upon receiving primary electrons, an electronic lens in front of said electrode to project both primary and secondary electrons onto and from said electrodes respectively, means for separating primary and secondary electrons prior to their entrance and after their exit from the electronic lens respectively to form two paths diverging to opposite sides of the axis of the common electronic lens comprising means for producing an electromagnetic field transverse to said paths, and means for establishing a substantially equipotential electrostatic field along said paths.

2. In an electronic discharge device, an electron-emitting electrode, an electron-receiving electrode, at least one intermediate electrode arranged between said emitting and receiving electrodes to receive primary electrons from a preceding emitting electrode to emit secondary electrons to a succeeding receiving electrode, at least one of said intermediate electrodes having in front thereof an electronic lens to project primary and secondary electrons onto and from said intermediate electrode respectively, means for separating primary and secondary electrons prior to their entrance and after their exit from the electronic lens respectively to form two paths diverging to opposite sides of the axis of the common electronic lens comprising means for producing an electromagnetic field transverse to said paths, means for establishing a substantially equipotential electrostatic field along said paths.

3. A device according to claim 2, wherein said means include means for producing a magnetic field perpendicular to said axis.

4. A device according to claim 2, wherein said receiving electrode comprises a fluorescent anode.

5. A device according to claim 2, wherein said electronic lens consists of a first electrode acting as a Wehnelt cylinder, a concentrating electrode serving as accelerator, and a third and fourth control electrode.

6. A device according to claim 1, wherein said electronic lens consists of a cylindrical electrode surrounding said cathode and acting as a Wehnelt cylinder, a concentrating ring surrounding said cylindrical electrode, an annular electrode spaced from said concentrating ring, and a flat ring electrode interposed between said annular electrode and said concentrating ring.

7. A device according to claim 2, comprising as emitting electrode a light-sensitive cathode, optical means for projecting an image thereon, a receiving electrode comprising a fluorescent anode, optical means for indicating the image produced by said electrons on said anode.

8. In an electron discharge device, a source of primary electrons, means for controlling the primary electrons leaving said source comprising a first electron-optic system, means for emitting secondary electrons upon receiving primary electrons comprising a secondary emitter electrode, means for controlling the primary electrons entering onto and the secondary electrons leaving from said sec-ondary emitter electrode comprising a second electron-optic system, means for collecting said secondary electron comprising a collector electrode, means for deflecting the primary controlled electrons along a path onto said secondary emitter electrode and said secondary controlled electrons along a path onto said collector electrode comprising means for producing a magnetic field transverse to the paths of said electrons, and means for establishing a substantially equipotential electrostatic field in the paths of said electrons.

9. A device as set forth in claim 3, wherein said source of primary electrons comprises a light sensitive cathode, comprising optical means for projecting an image thereon, said electron-optic systems comprising electrostatic lens systems, said collector electrode comprising a fluorescent screen for, reproducing the images formed on the light sensitive cathode, said equipotential electrostatic field comprising a zone having non-magnetic, conductive walls wherein said electron paths are established, said magnetic field comprising a uni- 5 form field established within said zonev 10. A device as set forth in claim 8, wherein said means for emitting secondary electrons upon receiving primary electrons comprises a plurality of secondary emitter electrodes, said secondary l0 emitter electrodes being serially electron coupled.

MAURICE ARDII'I.

REFERENCES CITED The following references are of record in the 15 file of this patent:

Number 7 UNITED STATES PATENTS Name Date Ploke May 23,1939 Coeterier June 20, 1939 Iams et a1 Aug. 27, 1940 Iams Sept. 16, 1941 Brett Dec. 31, 1940 Nicoll Dec. 2, 1941 Klemperer June 4, 1940 Gray Oct. 28, 1941 Diels May 7, 1940 Hillier Mar. 27, 1945

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