US2147558A - Electron-optical arrangement - Google Patents

Description

Feb. 14, 1939. K. SCHLESINGER 2,147,558

ELECTRON-OPTICAL ARRANGEMENT Filed June 22, 1936 2 C? 0i 2 3 weekl neg. la zero Patented Feb. 14, 1939 SITE UNETE ELECTRON- OPTICAL ARRANGEIWEN'I Kurt Schlesinger, Berlin, Germany, assignor t Radioaktiengesellschaft D. S. Loewe, Berlin- Steglitz, Germany Application June 22, 1936, Serial No. 86,609 In Germany June 2'7, 1935 18 Claims.

The problem of obtaining an image point which is as small and as bright as possible, such as occurs in the television art and in the construction of oscillographs, is solved, as well known,

by the reproduction of a cathode surface of certain size or of an aperture in an intermediate diaphragm on a luminous screen with the assistance of an electrical or magnetic lens. It is known that the size of the point is determined in the first place by the elementary law of spacing well known from common glass optics and secondly by the ratio of the speeds or in other words by the root of the ratio of the potentials which accelerate the electrons in the object space or the image space respectively. Heretofore only Such arrangements have been proposed in which the electrons traverse the said object space from the diaphragm to the first reproducing lens at a constant speed. In these arrangements there is usually provided a metal tube extending up to the first lens, which metal tube is connected with the diaphragm by a metal connection. If an electrostatic lens is employed, this tubular member possesses in itself a lower potential than the second electrode of the lens, which usually acts as the final anode. In this manner there is utilized in a favourable form in respect of the size ([55 of the image point the known potenas the potential at the diaphragm and in the tubular member is naturally always smaller than the potential behind the anode. In the above formula 4n means the diameter of the image point obtained on the image screen, qbbl. the diameter of the object of electron-optical reproduction, e. g. a diaphragm aperture, is and lb the distances from the lens of the image screen and the said object respectively, 68. and oh the potentials relatively to the cathode prevailing at the image screen and at said object respectively.

The invention will be more fully understood from the following detailed description if taken in connection with the appended drawing,

Fig. 1 of which shows a classic form of a television tube of a kind set forth in the above introduction, whereas Fig. 2 is a diagram including a certain structural detail of an electron-optical system and illustrating the theory underlying this invention.

Fig. 3 shows the essential parts of a cathode ray tube designed according to the invention on a schematic longitudinal section together with certain circuit elements, and

Fig. 4 shows a modified form of a cathode ray tube according to the invention in similar manner as Fig. 3.

Referring now to Fig. 1, the diaphragm l forms the termination of a tubular member 2. This tubular member possesses a lower potential than the anode 3. The anode has the stated spacing is from the screen '4 and the stated spacing lb from the diaphragm, and is connected with the full potential of the battery 5, i. e., with the potential ea, whilst the tubular member on the other hand possesses a part-potential 6b in relation to the cathode 6.

It is the object of the invention to obtain a still smaller image point than results from the above equation, without having to increase the lengths Z in Fig. 1. For this purpose the appli cant has considered as follows:

An electron in the aperture of the diaphragm I may have a direction of speed '0 which deviates from the axial direction. This speed 22 is composed of an axial one 17:; and a transverse one 713;. The basic idea of the invention consists in leaving 0y, i. e;, the transverse speed, unaffected, but making '0'}; as small as possible up to the time of reaching the lens, so that the electrons require a long time to pass from the diaphragm to the lens, and then to increase 'Ux considerably within the lens. The ideal solution of the problem, which is not quite accomplished by the following form of embodiment, but should be sought to be attained, is illustrated in Fig. 2. In Fig. 2 there is shown a short lens, which in itself acts on the electrons only in the y-direction, i. e., in the transverse direction, and represents the necessary refractive power. This lens, a structural form of which has already been described in an earlier application No. 730,111, filed on July 11, 1934, Patent No. 2,126,286, August 9, 1938, Figs. 3, 4 and 5, comprises two closure discs I and 8 maintained at the same potential. Between the two closure discs there is located a cylinder 9, which is linked up with a low positive potential. An electronic ray entering this lens is neither accelerated nor retarded, but merely refracted. In conjunction with this lens there should be imagined, for the purpose of comprehension of the invention, an electrical double-layer Ill, H having the property of exerting an accelerating action on the electrons solely in the x-direction, i. e., in the longitudinal direction, but having no refractive power. The layer ll of the double layer is, therefore, connected with the plate I, and the layer I II has a lower potential. The whole is to be regarded as small in relation to the dimensions of the tubular memher and the distance of the double layer from the screen. If an electron arrives at the point I2 with the small speed 22X and has proceeded from the aperture of the diaphragm I, the double layer II], II causes'in the first place merely an acceleration of the a: component, of the speed to the value VX. The y component 22;; is not affected by this double layer. The parallelogram of the speeds I2, I3, I4 is accordingly converted with the passage through the double layer I0, II into the parallelogram I2, I5, I6. If the diagonals I2/I6 are extended towardsthe rear, there is obtained a new seeming point of origin I of the electrons, which appears to be disposed more towards the rear away from the lens than I to the extent of the ratio VxI'Ux. The law of spac-- sioned by the distance law of common'glass optics. I

In View of the explanation furnished the applicant regards the subject matter of the in the following measures:

1. An electron-optical system, in which the electrons traverse the diaphragm with the lowest possible speed and require the longest possible time to reach the lens and retain this low speed as far as possible up to reaching the main lens.

2. A system having the stated property and having a main lens, which imparts to the electrons an after-acceleration as strong as possible, so that they traversethe space up to the screen at a considerably increased speed. a

In the following there will be described some methodsof carrying out these physical conditions.

Insulated mounting of the diaphragm: In Fig. 3 there is again shown the tubular member according to Fig. 1, but with the difference that the diaphragm I is insulated from the tubular member 2. It is possible, therefore, to apply to the diaphragm I a still lower potential than to the tubular member 2. For this purpose the anode battery 5 is sub-divided twice. The tapping of higher potential on the potentiometer I1 is connected with the tubular member 2, and to the diaphragm I there is applied a still lower potential than to 2. In order not to accelerate the electrons too early, but to maintain the same at the lowest speed as long as possible, the spacing #3 between the edge of the tubular member 2 and the diaphragm I is furthermore made as large as possible in accordance with the invention. To

avoid electrostatic disturbances the glass wall IQ of the tube, in respect of which it is moreover assumed that the same in practice is spaced infinitely far away from the ray, may be linked up with a definite potential, for example the potential of the diaphragm I. It is essential that the diameter of the tubular member and the neck of the valve, 1. e., all transverse dimensionsare large as compared with the thickness of the bundle of rays, so that the potential lines for the ray are plane discs. In these circumstances the electrons traverse the first part of their path in straight line with the speed directions which they had in the aperture of the diaphragm.

To obtain planes, 1. e., not curved or bulging between the two potentials I and 2.

' ascent.

invention methochThe tubular member is not made of metal, but of a high resistance layer. It is connected with its two terminating cross-sections The wall potentials then form a function of rectilinear The same also applies to the interior of the tubular member. Since no transverse potential gradients of any kind are present, there is also in this case not exerted any refractive force on electrons which enter a resistance tube of this kind with inclined initial direction. Thisis exactly the ideal condition called for by the general idea according to the invention. Within the tubular member, therefore, the cathode rays traverse a curved path which exactly corresponds with the parabola of fall of an inclined throw. In this way there is obtained a seeming increase in the distance of the object and accordingly the desired reduction of the size of the image point, via, to all the greater extent the lower the input potential of I.

It, has been found in the meantime that a tubular member of this nature composed of a homogeneous resistance material may also be replaced in practice by a resistance screw with a narrow pitch. This method is identical in its eifect with the method of production described in the earlier application, and is also to be placed under protectionin conjunction with the electronic lens system according to the invention.

As regards the carrying out of the method making use of the low-biassed diaphragm I, a

limit is very quickly found in practice. Certainly a. very large diaphragm aperture may be very well reduced, and accordingly. a small sharp image point produced on the screen 4, in other words there may be entered in the reproduction equation a lower potential in respect of the object accordance with the invention to include a special screening grid system between the cathode 6 and the diaphragm I. According, therefore, to the invention, there is provided between the cathode IS, in front of which there may also be provided a control grid 20 in the form of a perforated diaphragm, and the diaphragm I a screening grid 2I. This screening grid 2| may be raised without objection to a higher potential than the diaphragm I, A very powerful electronic current may accordingly be obtained from the cathode 6. This electronic current is preliminarily concentrated by a concentration cylinder 22. For this purpose 22 must have a lower potential than 2I. This potential may either be finely adjusted at a potentiometer tapping 33, or a tapping of this kind may also be dispensed with and the cylinder 22 may be directly connected with the diaphragm I if the adjustment of the focal distance is performed by geometric adjustment of the length or the ratio between diameter and length of 22. The arrangement 22 and I then acts as a retarding lens, which thus concentrates and simultaneously retards the electrons. In this manner it is possible to pass an electron current through the aperture of the diaphragm I with a good economy and at a low speed, and to obtain large amounts of current from the cathode 6.

The applicant has been able to work with a tube of this kind, in which the potential of the anode 3 relatively to the cathode amounted to 2,000 volts, the potential of the tubular member 2 to 800 volts, and the potential of the diaphragm l to volts only. The screening grid 2! had 250 volts and was disposed in front of a cathode spot of K mm. diameter at a distance of only 2 mm. thereof, which cathode spot with the stated screen grid bias and with a control grid 20 connected with the cathode was able to supply a current of about milliampere. The concentration cylinder 22 was 3 mm. in length and 5 mm. in diameter, and with these dimensions could be directly mounted on the diaphragm l, in order, with the .stated biasses and a spacing Zl/l amounting to approximately 1 cm., to force the 250 volt electrons practically without loss through the 100 volts diaphragm. The diaphragm had a square shaped aperture of 1 mm. diameter, which appeared on the luminous screen with a diameter of 2 mm. when the ratio 15: 1b was equal to 6:1. It has accordingly become possible to obtain an only two-fold eifective enlargement with a six-fold increase in distance, which agrees with the assumption that the electrons traversed the space between i and 3 with a speed of somewhat more than 100 volts, as the potential reducing factor amounts in this case to 100 t 1 1 -approx1 a e y 45 There was measured /3. This corresponds with a mean speed of approximately 200 volts. If the diaphragm l were connected with the tubular member 15, as in the case of Fig. 1, the reducing factor would be only m i 2cc0 1,6 and there should be observed an image point of approximately 3 mm. on the screen, which was also what actually happened. The distance it between the diaphragm i and the edge of the tubular member amounted in the case of the testing tube to A; of the length of 60 mm. of the tubular member 2, and the providing of this spacing proved to be helpful.

Other methods also appear to be possible for carrying out the basic idea of the invention, which is explained in Fig. 2, viz., that of leaving the electronic ray unaffected in the transverse directicn and accelerating it in the longitudinal direction. In this connection the acceleration should preferably take place shortly before the electrons enter the lens, so that the lens is reached at the largest possible distance from the axis.

The aforesaid tubular member composed of resistance material may naturally also be combined with the above described screening grid system provided in the space between the cathode and the diaphragm. There principle to a resistance tubular member of this nature a tube, the cross-sectional dimensions of which are large in relation to the size of the ray, so that it is unnecessary to take into consideration the potentials of the wall, and it may be assumed that the field, which effects the acceloration between the diaphragm and the lens, has not transverse components but is homogeneous in the direction of the ray.

The use of the apertured diaphragm of low potential or low-potential diaphragm, is not limited to the fact that an electrostatic lens is employed for the reproduction. According to the diagram in Fig. 2, there always occurs the reducing effect of the low-potential diaphragm when the electrical double layer provides for after-acceleration prior is also equivalent in to entry of the electrons into the lens system. According, therefore, to the invention, the refractive force may be produced by a magnet coil, whilst the after-acceleration takes place by means of an electrical double layer ifi/H at the point disposed at substantially the same place where the electrons are influenced by the magnet coil. It is dificult in the case of two large diaphragms situated close together to obtain a purely axial acceleration without the occurrence at the same time of disturbing transverse effects, 1. e., lens cflfects. For carrying out the pure longitudinal acceleration it will be necessary to make the spacing between ill and l l large in relation to the diameter of the apertures of these diaphragms, i. e., to employ for the acceleration a tubular member, preferably a resistance tubular member of high resistance material, the limiting edges of which are connected with the limiting potentials.

In Fig. 4 there is shown a tube of this kind for electrical after-acceleration and magnetic concentration. The emission of the cathode 6 is controlled by a preferably plate shaped grid 20.

By means of a likewise preferably plate shaped screening grid 2i electrons are liberated with constant speed and in the largest possible numoer. By means of a cylinder 22 acting as an electron optical condenser lens this electronic current, owing to the negative bias of the cylinder in relation to the ray, are concentrated on to a diaphragm l. The diaphragm l, in accordance with the invention, possesses a very low potential near the cathode potential, which low potential represents a decelerating potential against which the electrons in the antespace are required to run. With the diaphragm there is connected the inlet edge of a tubular member 2 consisting of a high resistance material. The end of the tubular member in this case may be directly connected with the anode 3. The potential levels form in the example shown flat piano-parallel discs. The acceleration aflfects solely the x-direction. The movements in the y-direction are unaffected, so that an inclined projection parabola results. Substantially in the plane of the end 3 of the tubular member there is arranged a short and possibly screened magnet coil 23, which provides for the transverse refractive power, so that there occurs a reproduction of the electrons on the screen 4. This reproduction again follows the law:

the indices herein employed corresponding to the elements shown in Fig. 4 in an obvious manner.

The possible biases of a valve of this kind are indicated in Fig. 4 against the electrodes. Cathode zero, control grid weakly negative to zero,

screening grid 2! approximately 300 V., condensing cylinder 22 weakly positive, approximately zero to 100 volts dependent on its length and diameter, diaphragm 1:100 volts. In the case of still lower diaphragm potentials there occur at times strong reflection effects, which prohibit a reduction performed to excessive extent with the systems according to the invention. Anode 3:2,000 to 5,000 volts or more. The conductivity of the tubular member 2 should be chosen so great that the current flowing through the tube exceeds the maximum ray current .by approximately one order of magnitude. The wall of the bulb may be formed by a coating 24 connected with the anode and having the same potential as the anode.

I claim:

1. Electric apparatus: comprising a cathode ray tube including an image screen, a cathode, a main anode mounted between said cathode and said image screen, and an electrode mounted near said cathode between said cathode and said main anode, means for applying to said' electrode a positive potential relatively to said' cathode for causing said electrode to free a large number of electrons from said cathode, means for applying a high positive potential relatively to said cathode to said main anode to cause said main anode to accelerate in the direction towards said image screen the electrons freed from said cathode, a diaphragm having an aperture interposed between said electrode and said main anode in the path of the electrons freed from said cathode, means for electron-optical reproducing the aperture of said diaphragm on said image screen and means for applying to said diaphragm a potential which is considerably lower than that applied to said electrode.

2. Electric apparatus comprising a cathode ray tube including an image screen, a cathode, an electrode mounted near said cathode between said cathode and said image screen, means for applying to said electrode a positive potential relatively to said cathode for causing said electrode to free a large number of electrons from said cathode, accelerating means mounted between said electrode and said image screen for strongly accelerating the electrons freed from said cathode in the direction towards the screen to cause the electrons to produce a bright fluorescence on said screen, a diaphragm having an aperture interposed between said electrode and 7 said accelerating means in the path of the electrons freed from said cathode, means for electron-optically reproducing the aperture of said diaphragm on said image screen, and means for applying to said diaphragm a potential which is considerably lower than that applied to said electrode.

3. Electric apparatus comprising a cathode ray tube including an image screen, a cathode, a main anode mounted between said cathode and said image screen,'and an electrode mounted near said cathode between said cathode and said main anode, means for applying to said electrode a positive potential of about 300 volts relatively to said cathode for causing said electrode to free a large number of electrons from said cathode, means for applying a positive potential of about 3000 volts relatively to said cathode to said main anode to cause said main anode to accelerate in the direction towards said image screen the electrons freed from said cathode, a diaphragm having an aperture interposed between said electrode and said main anode in the path of the electrons freed from said cathode, means for electron-optically reproducing theaperture of said diaphragm on said image screen and means for applying to said diaphragm a positive potential of about volts relatively to said cathode.

4. Electric apparatus comprising a cathode ray tube including an image screen, a cathode, a main, anode mounted between said cathode and said image screen, and an electrode mounted near said cathode between said cathode and said main anode, means for applying to said electrode a positive potential relatively to said cath-' ode for causingsaid electrode to free a large.

number of electrons from said cathode, means for applying a high positive potential relatively to said cathode to said main anode to cause said main anode to accelerate in the direction towards said image screen the electrons freed from said cathode, a diaphragm having an aperture interposed between said electrode and said main anode in the path of the electrons freed from said cathode, means for electron-optically reproducing the aperture of said diaphragm on said image screen, means for applying to said diaphragm a potential which is considerably lower than that applied to said electrode and means to produce a fieldless space of a considerable length between said diaphragm and said main anode, in which fieldless space the electrons have the low speed determined by the potential of said diaphragm;

5. Electric apparatus comprising a cathode ray tube including an image screen, a cathode, a main anode mounted between said cathode and said image screen, and an electrode mounted near said cathode between said cathode and said main anode, means for applying to said electrode a positive potential relatively to said cathode for causing said electrode to free a large number of electrons from said cathode, means for applying a high positive potential relatively to said cathode to said main anode to cause said main anode to accelerate in the direction towards said image screen the electrons freed from said cathode, a diaphragm having an aperture interposed between said electrode and said main anode in the path of the electrons freed from said cathode, means for electron-optically reproducing the aperture of said diaphragm on said image screen, means for applying to said diaphragm a potential which is considerably lower than that applied to said electrode, and means to keep the speed of the electrons at the low value determined by the potential of said diaphragm substantially up to the place where they are influenced by said electron-optically reproducing means.

6. Electric apparatus comprising a cathode ray tube including an image screen, a cathode, an electrode mounted near said cathode between said cathode and said image screen, means for applying to said electrode a positive potential relatively to said cathode for causing said electrode to free a large number of electrons from said cathode, accelerating means mounted between said electrode and said image screen for strongly accelerating the electrons freed from said cathode in the direction towards the screen to cause the electrons to produce a bright fluorescence on said screen, a diaphragm having an aperture interposed between said electrode and said accelerating means in the path of the electrons freed from said cathode, means for electron-optically reproducing the aperture of said diaphragm on said image screen, said accelerating means and said electron-optically reproducing means comprising electrodes common to both of them, and means for applying to said diaphragm a potential which is considerably lower than that applied to said electrode.

'7. Electric apparatus comprising a cathode ray tube including an image screen, a cathode, an electrode mounted near said cathode between said cathode and said image screen, means for applying to said electrode a positive potential relatively to said cathode for causing said electrode to free a'large number of electrons from said cathode, accelerating means mounted between said electrode and said image screen for strong- (ill 1y accelerating the electrons freed from said cathode in the direction towards the screen to cause the electrons to produce a bright fluorescence on said screen, a diaphragm having an aperture interposed between said electrode and said accelerating means in the path of the electrons freed from said cathode, means for electron-optically reproducing the aperture of said diaphragm on said image screen, and means for applying to said diaphragm; a potential which is considerably lower than that applied to said electrode, said accelerating means being adapted to produce an electric accelerating field which has no component transverse to the axis of the oathode ray tube and is uniform at least across that portion of any cross-section of the tube which is filled out by electrons which have passed through the aperture of said diaphragm.

8. In a cathode ray tube including an image screen, a cathode, a suction anode mounted near said cathode between said cathode and said image screen, an apertured diaphragm shaped decelerating electrode mounted between said suction anode and said image screen, and means for electron-optically reproducing the aperture in said decelerating electrode on said image screen: accelerating means comprising a metallic cylinder mounted between said decelerating electrode and said screen with its axis directed from the aperture in said decelerating electrode to said screen, said cylinder having a diameter which is large as compared with the diameter of the stream of electrons having passed through said aperture, the edge facing said decelerating electrode of said cylinder being spaced from said diaphragm to a distance of the same order as the diameter of said cylinder.

9. In a cathode ray tube including an image screen, a cathode, a suction anode mounted near said cathode between said cathode and said image screen, an apertured diaphragm shaped decelerating electrode mounted between said suction anode and said image screen, and means for electron-optically reproducing the aperture in said decelerating electrode on said image screen: accelerating means comprising a tubular member mounted between said decelerating electrode and said screen with its axis directed from the aperture in said decelerating electrode to said screen, said tubular member being adapted to distribute any potential difference applied between its ends substantially uniformly along its length.

10. In a cathode ray tube including an image screen, a cathode, a suction anode mounted near said cathode between said cathode and said image screen, an apertured diaphragm shaped decelerating electrode mounted between said suction anode and said image screen, and means for electron-optlcal1y reproducing the aperture in said decelerating electrode on said image screen: accelerating means comprising a tubular member mounted between said decelerating electrode and said screen with its axis directed from the aperture in said dec crating electrode to said screen, said tubular member consisting of a uniform layer of a high resistance material and being adapted to have two difierent potentials applied to its edges.

11. In electric apparatus comprising a cathode ray tube including an image screen, a cathode, a suction anode mounted near said cathode between cathode and said image screen, an aper ured diaphragm shaped decelerating electrode mounted between said suction anode and said image screen, and means for electron-optically reproducing the aperture in said decelerating electrode on said image screen: accelerating means comprising a tubular member mounted between said decelerating electrode and said screen with its axis directed from the aperture in said decelerating electrode to said screen, said tubular member consisting of a uniform layer of a high resistance material, means for applying a high positive potential to the edge of said tubular member facing said screen, and means for maintaining the edge of said tubular member facing said decelerating electrode at equal potential with said decelerating electrode.

12. In a cathode ray tube including an image screen, a cathode, a suction anode mounted near said cathode between said cathode and said image screen, an apertured diaphragm shaped decelerating electrode mounted between said suction anode and said image screen, and means for electron-optically reproducing the aperture in said decelerating electrode on said image screen: accelerating means comprising a tubular member mounted between said decelerating electrode and said screen with its axis directed from the aperture in said decelerating electrode to said screen, said tubular member consisting of a layer of a high resistance material subdivided in the direction of the axis of said tubular member into subdivisions every two adjacent ones of which are conductively connected to each other, those two of said subdivisions which are disposed remotest from each other being adapted to have two different potentials applied thereto.

13. In electric apparatus comprising a cathode ray tube including an image screen, a cathode, a suction anode mounted near said cathode between said cathode and said image screen, an apertured diaphragm shaped decelerating electrode mounted between said suction anode and said image screen, and means for electron-optically reproducing the aperture in said decelerating electrode on said image screen: accelerating means consisting of a tubular member mounted between said decelerating electrode and said screen with its axis directed from said decelerating electrode to said screen, said tubular member consisting of a layer of a high resistance material subdivided in the direction of the axis of said tubular member into subdivisions every two adjacent ones of which are conductively connected to each other, means for applying a high positive potential to that one of said subdivisions nearest said screen, and means for maintaining that one of said subdivisions nearest said decelerating electrode at equal potential with said decelerating electrode.

14. Electric apparatus comprising a cathode ray tube including an image screen, a cathode, an electrode mounted near said cathode between said cathode and said image screen, means for applying to said electrode a positive potential relatively to said cathode for causing said electrode to free a large number of electrons from said cathode, accelerating means mounted between said electrode and said image screen for strongly accelerating the electrons freed from said cathode in the direction towards the screen to cause the electrons to produce a bright fiuo rescence on said screen, a diaphragm having an aperture interposed between said electrode and said accelerating means in the path of the electrons freed from said cathode, means for electron-optically reproducing the aperture of said diaphragm on said image screen, means for applying to said diaphragm a potential which is considerably lower than that'applied to said elec I trode, and means mounted between said cathode and said diaphragm for accelerating the electrons freed from said'cathode.

15. Electric apparatus comprising a cathode ray tube including an. image screen, a cathode, an electrode mounted near said cathode between said cathode and said image screen, means for applying to said electrode a positive potential relatively to said cathode for causing said electrode. to free a largenumber ofelectrons from said cathode, accelerating means mounted between said electrode and said image screen for strongly accelerating the electrons free from said cathode in the direction towards the screen to'cause the electrons to produce a'bright fluorescence on said screen, a diaphragm. havingan aperture interposed between said electrodeand said accelerating meansin the path of the electrons freed fromsaid cathode, means for electron-optically reproducing the aperture'of said diaphragm on said image screen, means for applying to; said dia phragm a potential which is considerably lower than that appliedto said electrode, and means mounted between said cathode and said diaphragm: for concentrating. the electrons freed from said; cathode.

16'. Electric apparatus comprising a cathode ray tube including an image screen, a cathode, an

electrode mounted nearsaid cathode between said cathode and said image screen,:means for apply- I ing to said electrode a positive potential relatively to said cathode f or causing said electrode to free a large number of electrons'from saidcathode,-ac- I celerating means-mounted between said electrode and said image screen for strongly accelerating the electrons freed from said cathode in the direction towards the screen to cause the electrons to produce a bright fluorescence on said screen, a diaphragm having an aperture interposed be- I I tween said electrode and said accelerating means in the path of the electrons freed from said cathode, means for electron-optically reproducing the aperture of said diaphragm on said image screen, means for applying to said diaphragm a potential which is considerably lower than that applied to said electrode, means for accelerating and means for concentrating the electrons freed from said cathode, the two last said means being mounted between said cathode and said diaphragm.

I 17. Electric apparatus comprising a cathode ray tube including an image screen,acathode a main 1 anode mounted between said cathode and said image screen, an electrode mounted near said cathode between said cathode and saidm'ain anode, means for applying to said electrodea positive 7 potential relatively to said cathode 'for causing said electrode to free a large'number of electrons from said cathode, means for applying a high positive potential relatively. to said cathode to said main anode to cause said main anode'toacceler ate in thedirection towards said image screen the electrons freedfrom said cathcgde','a diaphragm having an aperture interposed between said electrade and said main anode. in the-path of the.

electrons freed from said. cathode, means for electron-optically reproducing the aperture of said diaphragm on said image screen, and means for applying to said diaphragm a potential which is considerably lower than that applied to'said eleccomprising. a magnet coil slid over said cathode ray tube to surround same substantiallyin the 25' cross-section containingsaid main anode.

.18. Electric apparatus comprising a cathode ray tube including an image screen, a cathode, an

electrode mounted near said cathode between said cathode and said imagescreen, means'for apply ing to said electrode a positive potentialrelatively to said cathode for causing said-electrode to .free I a large number of electrons from said cathode,

accelerating means mounted between said eleci 5 trode and said image screen for, strongly accelerating the electrons freed from said cathode in the direction towards the screen to cause the electrons to produce a bright fluorescence on said KURT SCHLESIN GER.

20 trode, said electron optically reproducing, means I, I

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