US2898467A

US2898467A - Electron oscillograph

Info

Publication number: US2898467A
Application number: US574524A
Authority: US
Inventors: Ardenne Manfred Von
Original assignee: Vakutronik VEB
Current assignee: Vakutronik VEB
Priority date: 1955-05-20
Filing date: 1956-03-28
Publication date: 1959-08-04
Anticipated expiration: 1976-08-04
Also published as: NL197896A; GB794603A; CH335756A; DE1018145B

Description

M. VON ARDENNE ELECTRON OSCILLOGRAPH Aug. 4, 1959 Filed March 28. 1956 2 Sheets-Sheet 1 IN VEN TOR.

1959 M. VON ARDENNE 2,898,467

ELECTRON OSCILLOGRAPH 2 Sheets-Sheet 2 Filed March 28, 1956 BY fil /07151 United States Patent 1 2,898,467 ELECTRON OSCILLOGRAPH Manfred Von Ardenne, Dresden-.Weisser Hirsch, Germany, assignor to VEB Vakutronik Dresden, Dresden, Germany v Application March-28, 1956, Serial No. 574,524 Claims priority, application. Germany May 20, 1955, 14 Claims. (Cl. 250-495) The present invention relates to oscillographs, and more particularly to precision oscillographs operating under a vacuum.

It is an object of the present invention tov provide an oscillograph combining an extremely fine writing spot with an amplitude of the oscillographic curve which is of the order of magnitude reached in customary oscillographs.

It is another object of the present invention to increase the ratio of the areas of the writing surface and the writing spot by several orders of magnitude.

It is a further object of the present invention to reduce the aperture angle, associated with the aperture at the side of the Writing surface.

Other objects and advantages of the present invention will become apparent from the following detailed description thereof in connection with the accompanying drawings showing, by way of example, some embodiments of the present invention. In the drawings:

Fig. 1 is a sectional View of an embodiment of an oscillograph according to the present invention,

Fig. 2 is a diagram illustrating the course of the beams in an oscillograph shown in Fig. 1,

Fig. 3 is a sectional elevation on an enlarged scale of a slightly modified part of Fig. 1,

Fig. 4 is a plan view of the device shown in Fig. 3,

Fig. 5 is a diagram showing an oscillographic curve obtained with the oscillograph shown in Fig. 1, and

Fig. 6 is a detail of the diagram shown in Fig. 5 on an enlarged scale.

Referring now to the drawings and first to Fig. l, a tube generally denoted by 10 includes three

sections

12, 14 and 16. The tube 10 is provided with the connecting

lines

18, 20 connected, respectively, to the

sections

12 and 16. The connecting

lines

18 and 20 lead to high vacuum pumps (not shown) by which the interior of the tube 10 may be evacuated.

One end of section 12 is closed by aninsulator 24 provided with a flange 22 and projecting into the interior of the section 12 of the tube 10. A high voltage cable 26 is led through a cover 28 and a bore of the insulator 24. A cathode 30 is connected to the high voltage cable 26 which connects the same with a voltage source (not shown). A control electrode 32 shaped as a Wehnelt cylinder surrounds the cathode 30 and is provided with an opening 34 being axially aligned with the electron emitting part of the cathode 30. At a short distance from the opening 34 of the Wehnelt cylinder 32 an anode 36 provided with an axial opening 38 is arranged and connected by an electroconductive connection 40 with the wall of the section 12. The control electrode 32 is connected with a connection 42 forming part of the high voltage cable 26 and serving for imparting to the control electrode 32 a potential which is negative by some hundreds of volts with respect to the cathode potential. Thus it will be understood that the cathode 30, the Wehnelt cylinder 32 and the anode 36 constitute an electron gun generating a beam of electrons passing through the

openings

34, 38 of the Wehnelt cylinder and the anode 36.

An auxiliary luminous screen 42 provided with a center opening 44 is arranged in the path of the beam of electrons emitted by the

electron gun

30, 32 and 36. The

auxiliary luminous screen 42 is arranged in that part of 1 trons.

2,898,467 Patented Aug. 4, 1959 the section 12 which forms the end thereof opposite the

electron gun

30, 32, 36 and may be observed through a window 46 from the outside. The section 12 abuts with its end opposite to the

electron gun

30, 32 and 36 against a magnetic rcducinglens generally denoted by 48. and comprising a coil 50 enclosed in a magnetic structure 52 shaped as shown in Fig. 1 so to converge toward the central opening 54 aligned with the

openings

44, 38 and 34 mentioned hereinabove. The magnetic reduce ing lens 48 abuts against one end of the section 14 of the tube 10 which is provided at the other end portion thereof with a window 56 arranged near an auxiliary luminous, screen 58 and provided with a central opening 60 aligned with the

openings

34, 38;, 44, and 54. The auxiliary luminous screen 58 serves for adjusting the beam of electrons passing through the tube 10.

The, end flange 6-2 of the section 14 rests against a housing 64 consisting of magnetic material of a magnetic principal lens generally denoted by 66 and including a coil 68 enclosed by the magnetic housing 64 shaped so as to allow the beams of electrons to pass through the open center thereof. It abuts with a part 70 thereof against the upper flange 72 of the third section 16. The part 70 is connected with a'structure 74 projecting into the inner hollow space in the center of the coil 68 and ends in a heatable aperture diaphragm or stop 76 having an aperture centeredwith respect to the

openings

60, 54, 44, 38 and 34. A somewhat modified embodiment of a heatable aperture diaphragm or stop is more fully described hereinafter in connection with Figs. 3 and 4.

The wall of the third section 16 is provided with insulators such as 78 through which pass conductors such as 80 for applying an electric voltage acting in the direction y shown in Fig. 5 to two electroconductive deflecting plates 82 arranged in a position inclined to the beam of electrons passing through the instrument at both sides thereof. Furthermore, coils such as 84 are provided symmetrically to the conductors 80 to set up a magnetic deflecting system in the direction x shown in Fig. 5

The beam of electrons passes after the electric and

magnetic deflecting systems

82, 84 into the part 86 of the section 16 which is normally closed by a plate 88 Inside the compartment formed by the part 86 and the plate 88 a photographic plate or film 90 is shiftably arranged in the direction of the arrow 92. The photographic plate or film 90 forms a sensitized surface on which a recording is written or inscribed by the electron beam, and hence this surface is referred to as a writing surface or inscribed surface. Surface 90 is con nected with a screen 94 which may be formed by a grainless fluorescent screen which may be shifted in the direction of the arrow 92 into the path of the beam of elec- The end of the section 16 is closed by a glass plate 96 through which the fluorescing phenomena excited by the beam of electrons on the screen 94 may be observed, for instance, by an adjustable focussing microscope 98 or a magnifying lens having a relatively short focal length.

The operation of the device shown in Fig. 1 will be described in connection with Fig. 2 showing diagrammatically the course of beams through the oscillograph shown in Fig. 1.

In Fig. 2 only the aperture 49 of the magnetic reducing lens 48, the aperture stop 76, the electric deflecting system 82, and the writing surface 90 of the writing spot are shown. The beam of rays emitted by the

electron gun

30, 32, 36 shown in Fig. 1 has a beam crossover 200 an image 206 of which is to be produced by the oscillograph. The beam crossover 200 has a diameter amounting approximately to 0.1 mm., the current density being equal to i The distance between the crossover 200 and the aperture 49 amounts, for example, to 200 mm. The

beam has an initial aperture defined by the angle The vertical arrow 202 shows on an exaggerated scale the focal length of the magnetic reducing lens 48 which produces a reduced intermediate image 204 of the beam crossover 200. At a distance of approximately 200 mm. from the aperture 49 the aperture stop 76 is arranged. The beams pass the deflecting system 82 including the magnetic deflecting system 84 arranged at a distance of approximately 100 mm. from the stop 76. The beams are collected in the area 206 on the surface 90, the aperture a of the beams on the writing spot being determined by the equation where j is the current density in the writing spot which is a reduced image of the beam crossover 200. The writing spot has a diameter between 0.001 mm. and 0.01 mm. and the double headed arrow 208 is equal to 20: equaling twice the beam aperture at the writing spot. The distance between the aperture stop 76 and the writing surface 90 amounts preferably to 300 mm. so that the length of the deflected rays amounts to 200 mm.

It should be noted that if desired, a plurality of magnetic reducing lenses such as 48 may be provided although in Figs. 1 and 2 only one reducing lens 48 is shown.

In Fig. 1 the photographic plate or film 90 is shown in a position in which it is hit by a beam passing through the oscillograph. If it is desired to bring the screen 94 into this position the photographic plate or film 90 is moved in the direction of the arrow 92 to the left and the screen 94 connected with the photographic plate or film 90 is shifted into the position originally assumed by the photographic plate or film 90. The means for shifting the photographic plate or film 90 and the screen 94 and suitable film holders, light sluices, etc. are well known in the art and have not been indicated in the drawing.

Referring now to the modification shown in Figs. 3 and 4 an electron beam 100 is propagated in axial direction and passes the aperture 102 of a diaphragm or stop 104 arranged substantially at right angles to the beam 100. The stop 104 is designed as a platinum strip which is, for instance, three millimeters wide and 0.05 millimeter thick. The band 104 is electrically heatable as will be explained hereinafter.

A stationary insulated member 106 is arranged in a sleeve 108 so as to project above the upper rim of the same. The member 106 is shaped at its upper part 110 as an element holding the platinum strip 104 at one of its ends which is secured by a screw 112 to the upper part 110. The member 106 serves as a current lead to the platinum strip 104. A second member 114 has an upper part 116 serving as a support for the other end of the platinum strip 104 which is secured to the part 116 by a screw 118. The second member 114 is pivotally supported at 120 and is acted upon by tension spring 122 one end of which is connected to a member 124 arranged in a slot 126 provided in the wall of the sleeve 108. The second member 114 serves as a second current lead to the platinum strip 104 and is preferably maintained at the potential of the sleeve 108. Preferably the members 106 and 114 are guided through openings of the sleeve 108, the member 106 being held in position by insulating disks 128 and a screw connection such as 130, and connected with the pivot 120 of the second member 114.

In operation the platinum strip 104 is heated by an electric current supplied by the first and second members 106 and 114. The second member 114 is under the influence of the tension spring 122 so that the platinum strip 104 is maintained in a taut condition irrespective of the temperature imparted to the same by the electric current flowing through the current leads 106 and 114.

Referring now. to Figs. and 6, a photographic plate or film 90 is shown which is intended for being placed on a carrier not shown in Figs. 1 and 2, and forming the ,4 inscribed or writing surface thereon which has, for instance, a size of 9 x 12 square centimeters. The beam of electrons traces on the photographic plate an oscillographic curve 302 as a result of the deflections of the writing spot traced by the beam of electrons and having a width of, for instance, 2;! The abscissae traced in the direction x correspond to the deflections due to the magnetic deflecting system 84 shown in Fig. l. The ordinates are traced in the y direction and correspond to the deflections due to the electric deflecting system 82 shown in Figs. 1 and 2. The oscillographic curve 302 is hardly discernible with the naked eye on the photographic plate 90, the density of the same amounting, for instance, to S=l.

Fig. 6 shows a much enlarged segment 304 of the photographic plate 90 with a much enlarged reproduction 306 of the peak 308 of the curve 302. In order to show the relation between the

curves

302 and 306, an arrow 210 connects the peak of the curve 302 which has to be enlarged with the segment 304. The segment 304 may be 10 x 10 square centimeters corresponding to an enlargement of, for instance, V=l00. The width 312 of the oscillographic curve 306 corresponds to the hundred fold magnified diameter of the writing spot, and amounts, for instance, to the V-fold, that is 0.2 millimeter. The impression of the image of the enlarged section 306 corresponds approximately to the oscillographic curve obtained with a usual electron beam oscillograph. At 314 the magnified curve 306 shows a detail which is not discernible in curves obtained by a usual electron beam oscillograph, the detail 314 corresponding to a voltage reduction due to a flashover.

Thus it is seen that in the oscillograph according to the invention an extremely fine writing spot is maintained,

'the diameter of the writing spot being even smaller than in the micro-oscillographs known in the art and amounting to 2-5;r. The photographic system 90 may be arranged within the tube 10 and an anode voltage may be applied which is as large as in oscillographs known in the art. In consequence thereof the oscillogram 302 is traced with amplitudes corresponding to those of the usual oscillograms.

In ordinary electron beam oscillographs the ratio between the diameter of the writing spot and the length of the sides of the writing surface amounts to 1:300 which is equivalent with a quadratic writing surface to a ratio of the areas of the surface of the writing spot to the writing surface amounting to 1:10 In the precision oscillograph according to the invention the ratio of the diameter of the Writing spot to the length of the edge of the writing surface amounts, for instance, to 3 lO cm. to 10 cm. or to 130,000. This corresponds with a quadratic Writing surface to a ratio of writing spot surface to writing surface of 1:10 (10 picture points). This ratio differs from the ratio obtainable with customary electron beam oscillographs by 4 orders of magnitude.

In order that with a writing surface of about l0 l0 cm. the electron focal spot shall retain the small diameter thereof amounting of a few a even in the rounded portions, the present invention suggests in contradistinction to the above mentioned micro-oscillograph using a very small beam aperture on the side of the Writing spot, this beam aperture amounting to a =5 l0- to 2 l0 With this aperture even at the corresponding large deflecting angles, the error 5 of the deflection may be kept in the order of magnitude of a few a. A numerical summary of the magnitude of the error of deflection in dependence on the beam aperture a on the side of the focal spot may be obtained from the accompanying Table I in which the values of the electrostatic and magnetic deflections and of the geometry of the system are taken from a practical example.

In order to obtain the very small beam aperture m the principal lens 66 of the oscillograph is provided with 5 an effective aperturestop 76 which stops down'the'beam so much that the aperture error of the principal lens 66- becomes negligible. of the beam alone does not secure, as a rule, the small spot diameter amounting to a few ,1 because the sensitivity ofthe beam having a minimal aperture to deviations by weak deflecting fields is high. Such disturbing beam deflections are formed at the aperture stop 76 of the principal lens 66 by the polarizing charges setup at the edges of the stop 76.

Experiments-have shown that these polarizing charges which are poorly defined and liable to change in time,

cause distortions of the focal spot which magnify the size of the focal spot considerably, and convert the shape of the focal spot from a circular shape into ashape whichis asymmetrical with respect to rotation. Thus writing spots of a diameter amounting to a few are as a rule only obtained when the stopping down of the principal lens 66 and/or thepreceding lenses such as 48 is effected by stops free from polarizing charges. Such diaphragms orstops may be formed by heatable or heated platinum strips such as 104 shown in Figs. 3 and 4 in which the formation of insulating layers and thus the formation of polarizing charges is avoided by converting the insulating condensate of organic residual vapors in sufficiently conductive carbon layers at temperatures of about 500 C and evaporation of insulating layers of platinum oxide at these temperatures;

In order to be able to scan the large writing surface with a normal deflecting angle, a deflecting distance L has to be appliedwhich has approximately the size of the diagonal of the writing surface. shown in Fig. 2 the deflecting distance L is indicated by the distance of the surface 90- from the conductors 80. This distance L is very large-in relation to the diameter of the writing spot and imparts to the precision oscillograph according to theinvention a large deflecting sensitivity related to the diameter of the writing spot. The orders of magnitude of the obtained deflecting sensitivities may be seen from the accompanying Table II for the system of an example taken from practice.

Since the value of the image distance of the principal lens of an oscillograph is always larger than the deflecting pointer length, with the fixing of the same also the minimum length of the image distance of the principal lens is established. In order to impart the highest possible electron current to the electron writing beam with the small beam aperture mentioned hereinabove and the relatively large image distance" the following electronoptical arrangement has been found very satisfactory.

However, the great stopping down.

In the embodiment A standard electron gun asshown in Fig. 1 comprising a thermo cathode 30, a Wehnelt cylinder 32. and an anode 36, is operated with an anode voltage of 20-55 kilovolts. The anode current is adjusted by a corresponding adjustment of the negative voltage of the Wehnelt cylinder 32 toabout 30400 microamps. By thisarrangement a beam crossover 200 shownin Fig. 2 is ob tained near the anode opening 38 having a diameter of approximately 100p which is reduced by one or more. reducing lenses 48' with magnetic objectives (pole shoe lenses 52, 50) or electrostatic objectives, to 1-3 corresponding to a reducing. ratio of 1:100 to' 1:33. In order to reduce the overall length of the oscillograph an arrangement is; applied in the principal lens stage 66 which. results in amagnification of about 1.5. Thus the total resultant reduction. of the crossover amounts to 1:66 to 1:221 An oscillograph reduced to practice, andoperating only with one single reducing stage 48 had a magnetic pole shoe lens. 48- of short focal'length so that the object. distancefrom the crossover to the pole shoe lens 48-mounted toabout 2110 mm, the focal lengthof the pole shoe lens 48 amounting. approximately to 46. mm.- As a principal lens an iron shielded magnetic lens 66 was used having a focal length of 120 mm. and a magnifying-ratio of 1.511 corresponding to a radius of the inner pole shoe diameter of 20 millimeters. The length l of the deflecting field behind the principal lens 66 was chosen relatively large in order to maintain. the deflection error small and amounted to 50 or 70 mm. as shown in Table I and thus" amounted to more than 15% of the deflection distance L of the electron beam.

In order to facilitate the centering and the focussing of the oscillograph aluminous screen obtained by vaporizing zinc sulfide was used' so as to obtain a grainless fluorescent substance. This fluorescent screen has a very high resolving power of about 3 1. and may be visually observed by a focussing microscope 98 shown in Fig. 1. The writingvelocity related to the diameter of the writing spot amounted in the described oscillograph for aphotographic density of thewriting lines S=0.1 to about 2 l0' per second. This is the same value which holds for'normal oscillograph types, for instance, for the Du Mont oscillograph-SL1 7 and outdoor shots.

I; have describedhereinbefore preferred embodiments of an oscillograph, and particularly a precision oscillograph operatingunder a vacuum. However, I wish it to be understood that many changes, alternatives, and substitutions of equivalents may be made in the embodiments described hereinabove without departing from my invention which is defined in the appended claims.

TABLE I Illustrating the errors of deflection Electrostatic defi'ectionin y- Magnetic'deflection in zdirection direction Size of the photographic plate of the electron precision oscillograph: 11 9 cm. z=12 cm.

Exploited writing surface 8 cm. 10 cm.=

square cm.

Principal error (ii-deflection:

Line error due to cylinderlens effect. of the deflecting condenser 2 ri g -aw mm.

Principal error of deflection: Defiecting astigmatism (transverse axis of the error ellipse) L=deflecting distance=200 mm.

l=length of deflecting field= aL=beam aperture 0=deflecting angle in radians A,=6.L=spot deflection Diameter of diphragm of Beam principal lens aperture 5m 6M 01, A.=:i=20 mm. A.==l:40 mm. Am==i=2O mm. Am==t=40 mm. 5X10 11.4 45 1.2 28.8. 1.6X1O' 3.6 14.4 2.3 9.2. 6X10 1.14 4.5 0.72 2.88.

Image width=dead distance-l-the deflecting distance-=300 mm.

TABLE II To the magnitude ft he deflection sensitivities Electrostatic deflection in Magnetic deflection in x-direction fig 2:2. U3 volts y-direction Deflection sensitivity Deflection sensitivity A 1.L mm. A 0.24 w.h.Z.L mm.

J 2 2 amps.

A=spot deflection Up=defleetion voltage l=length of deflecting plates=70 mrn.

L=deflecting distance=200 ti =mean distance of deflecting plates=0 mm.

U =beam voltage=3 10 volts dr=diametcr of writing spot A=spot deflection J current in deflecting coils w=total number of turns-=25 X h=height of deflecting coil-=50 l=axial length deflecting coils= L=defloeting distance=200 mm.

b=11.3h=iorm factor of coils=63 mm. Un=beam voltage=3 10 volts d =diameter of writing spot 1. a P UP.dF UP J.dr J

,1 volts mmJvolts millimrn./milamps liamps Electron prec.

oscillograph 2 20 4X10 2, 200 4. 4 U =30 kilovolts- 10 4 4X10- 440 4. 4 Electron beam osc. Du Mont type 248, UB=4 kilovolts 500 0. 58 29 10- *Total resistance 10,000 ohms (Cu-wire 0.1 mm).

With postacceleration.

I claim:

1. In an electron precision oscillograph, in combination, a member having a surface, means for causing a writing spot to be inscribed over a given area of said surface by a beam of electrons, means for controlling the electron beam so as to make the ratio between said area and said writing spot larger than 5.l0 :l, a diaphragm having an aperture in the path of said beam of electrons before said writing spot, said electron beam controlling means including means for keeping said diaphragm free from polarizing charges near the aperture thereof.

2. In an electron precision oscillograph, in combination, a member having a surface, means for causing a writing spot to be inscribed on said surface by a beam of electrons, the ratio between said surface and said writing spot being larger than 5.10 1, a diaphragm having a bore forming an aperture stop and being arranged in the path of said electron beam before said writing spot, means for heating said diaphragm, a reducing stage having at least one electron lens having a relatively short focal length, said electron lens being arranged in the path of said electron beam before said aperture stop, and a main electron lens having a relatively long focal length, said main electron lens being arranged in the path of said electron beam near said aperture stop.

3. In an oscillograph according to claim 2, wherein said diaphragm is a platinum strip.

4. In an oscillograph as claimed in claim 3, said electron lens having a relatively short focal length, reducing the crossover of said electron beam to an image having a diameter of a few n.

5. In an oscillograph as claimed in claim 3, said main electron lens having a magnetic system being structurally combined with said aperture stop.

6. In an oscillograph as claimed in claim 3, said main electron lens having an image distance amounting to more than 10 centimeters.

7. In an oscillograph as claimed in claim 3, and means deflecting said electron beam, said deflecting means being arranged between said main electron lens and said writing spot and deflecting said electron beam magnetically and electrically.

8. In an oscillograph as claimed in claim 7, said deflecting means setting up a deflecting field having an extension in the direction of said electron beam amounting at least to 20 millimeters.

9. In an oscillograph as claimed in claim 8, said deflecting field including an electrostatic field having an axial extension of substantially millimeters and a magnetic field having an axial extension of substantially 50 millimeters.

10. In an oscillograph as claimed in claim 9, said defleeting field having a length in the direction of the axis of the oscillograph exceeding .15% of the distance between the deflecting field and said surface.

11. In an electron precision oscillograph, in combination, a member having a surface, means for causing a writing spot to be inscribed on said surface by a beam of electrons, the ratio between said surface and said writing spot being larger than 5.10 1, a platinum strip having a bore forming an aperture stop and being arranged in the path of said electron beam before said writing spot, means for heating said platinum strip, a reducing stage having at least one electron lens having a relatively short focal length, said electron lens being arranged in the path of said electron beam near said aperture stop, a main electron lens having a relatively long focal length, said main electron lens being arranged in the path of said electron beam near said aperture stop, a screen arranged movably across the axis of the oscillograph, said screen being connected with said member having the surface to be inscribed by said beam of electrons, said screen being adapted to be moved into the path of said beam of electrons and serving in this position for centering the oscillograph, and means for observing the effects of said beam of electrons on said screen.

12. In an oscillograph as claimed in claim 11, said main electron lens being arranged immediately before said aperture stop.

13. In an oscillograph as claimed in claim 11, said screen being a grainless fluorescent screen.

14. In an oscillograph as claimed in claim 11, said observing means including a magnifying lens having a relatively short focal length.

References Cited in the file of this patent UNITED STATES PATENTS