US2675431A - Transit time compensated multiplier tube - Google Patents

Description

April 13, 1954 c. F. MILLER TRANSIT TIME COMPENSATED MULTIPLIER TUBE Filed Aug. 18, 1949 CARL F I LLE INVENTOR ATTORNEY Patented Apr. 13, 1954 UNITED STATE TENT FFICE Carl F. Miller, Summit, N. .l., assignor to National Union Radio Corporation, Orange, N. 5., a corporation of Delaware Application August 18, 1949, Serial No. 111,023

2 Claims.

This invention relates to electron tubes of the electron multiplying type, and more especially it relates to such tubes wherein electron transit time is an important factor in the usefulness of the tube.

Heretofore various constructions of tubes have been devised, using dynodes or electrodes which emit secondary electrons when bombarded by primary electrons. Examples of such devices are the well-known electron multiplier tubes. such tubes have found considerable use in varlous fields of application, their utility in systems operating at ultra-high-frequencies has been somewhat limited. In ultra-high-frequency systems, the transit time of the electrons between the cathode and dynode becomes of considerable importance. This is particularly true where the cathode has a somewhat extended surface, portions of which are unequally spaced from the associated dynode.

Accordingly, one of the principal objects of this invention is to provide an electron multiplier tube with a special arrangement of electrodes to compensate for the differences in transit time which would ordinarily occur between the electron trajectories from different portions of the cathode with respect to the dynode.

A feature of the invention relates to an electron tube having an electron-emitting cathode,

a dynode, and an anode or electron collector electrode, the dynode having a special configuration, so that the electrons from various unequally spaced portions of the cathode arrive in substantial like phase at the dynode surface.

Another feature relates to an electron tube having an electron-emitting cathode, a dynode or electron multiplier electrode disposed with respect to the cathode, so that the primary electrons arrive at the dynode at glancing angles and in substantially similar phase even though they originate from different sections of the cathode.

Another feature relates to an electron multiplier tube having a special configuration of dynode and shield electrodes to compensate for the different lengths of electron trajectories between the diflerent portions of the cathode and the dynode surface, whereby more uniform transit time effects are obtained.

A still further feature relates to the novel organization, arrangement and relative location of parts which cooperate to provide an improved electron multiplier tube.

Other features and advantages not specifical- While ly enumerated, will be apparent after a consideration of the following detailed descriptions and the appended claims.

In the drawing,

Fig. 1 is a view, in elevation, of a typical tube according to the invention.

Fig. 2 is a sectional plan view of Fig. 1 taken along the line 22 thereof.

Fig. 3 is a sectional plan view similar to that of Fig. 2 of a tube of known construction.

Fig. 4 is a schematic wiring diagram showing one manner of biasing the various electrodes.

The tube according to the invention may comprise an evacuated bulb or envelope l of any wellknown shape, and carrying the usual base 2 terminating in the usual contact prongs 3. Suitably mounted within the bulb l is an electrode assembly 6, the various electrodes of which are connected to the respective contact prongs 3 in the usual way. In accordance with the invention, the electrode assembly comprises an electron-emitting cathode 5 which may be substantially rectangular in cross-section and having its opposite faces provided with coatings G, l, for emitting primary electrons when the cathode is heated to an emitting temperature. If desired, this cathode may consist of a strip of metal whose opposite ends are arranged to be connected to a suitable source of heating current, and the opposite flat faces of which are coated with the emissive material 6, 1. It will be understood of course that the invention is not limited to any particular manner of heating the cathode. For example, it may consist of a flattened tubular metal sleeve having on the interior thereof, but electrically insulated therefrom, a suitable heating coil or filament such as is well-known in the art of indirectly heated cathodes. Surrounding the cathode is a grid 8 which may be in the form of a fine wire helically wound around the grid support side rods 9, l0. Preferably the grid 8 is shaped so that the grid wires extend parallel to the flat surfaces 6 and 'l of the cathode. Likewise surrounding the grid 8 is another similar grid H attached to respective grid support side rods l2, IS. The grid 8 may form the usual control grid of the tube to which the input signal potentials are applied. The grid ll may constitute a so-called screen grid, and is connected to a suitable positive potential, for example 100 volts direct current. Cooperating with the cathode and two grids is a dynode electrode 14 having a reentrant portion l5 which partially encloses one side of the 55 unit consisting of the grids 8 and II. The dy.

node [4 has portions [5, i1, curved back upon themselves, but located out of the direct path of the electron trajectories normal to the cathode surfaces B and l. The dynode also has bentback wing portions l8, 19, which terminate in reversely bent end sections 2!), 2|. The portions IS, 20, and the portions l9, 2|, form respective chambers wherein are located the respective channel- shaped anodes 22, 23.

The dynode it may be connected to a suitable high positive direct current potential, for example 200 volts, and the anodes 22 and 23 can also be connected to a suitable high positive di-- rect current potential, for example 300 volts. As shown in Fig. 2, the anodes are located so that their channelled portions face the sections 20, 2 respectively of the dynode. Mounted in spaced relation to the remaining electrodes and on opposite sides of the cathode are two curved electro- static deflector plates 26, 25, which may be connected to ground or to a suitable negative or positive potential. The curvature of these shields is such that they act as electron deflectors to cause the primary electrons to curve towards the dynode wings l8, :s, and prevent anysubstantial number of primary electrons from the cathode, reaching the anodes 22, 23. The design of the flat type cathode is preferably such that in the absence of the deflecting and accelerating fields, the primary electrons are emitted from the respective cathode faces S and l in the form of respective beams with the electrons of each beam tending to follow substantial linear and parallel paths normal to the surfaces 6, l.

lvierely for explanatory purposes, there are represented by the dotted lines 2B, 27, 28, three typical primary electron trajectories. The electrons of trajectory 23 originate at a portion of the cathode surface which is farthest removed from the dynode, while the electrons of trajectory 28 originate from a portion of the cathode surface which is closest to the dynode. On the other hand, the electrons of trajectory 2.6 are closest to the deflector shield so that they are .subjected to a greater deflecting action and reach the dynode over a shorter curved path than the electrons of the remaining trajectories which are deflected to the same extent. In other Words, the electrons from the difierent portions of the cathode surface follow decreasing lengths of trajectory paths, which lengths are in inverse relation to the distance of .the respective cathode portions from the dynode. However, the electrons from the portions of the cathodeclosest to the dynode, for example those of trajectory 28, are subjected to a greater positive accelerating field which causes them to move with greater velocity towards the dynode than those of the remaining trajectories. In other words, the primary electrons which reach the dynode over the shorter paths, also have the lower electron velocity, While the primary electronswhich reach the dynode over the longer paths have correspondingly greater electron velocities. By suit.- able choice of potentials and arrangement of the electrodes therefor, it is possible to insure that most or a great part of the primary electrons reach the dynode at the same time or in phase. By the well-known action of the dynode M, the impingement of the electrons, thereon, causes the release of secondary electrons which are attracted by the respective anodes 22 and 23, and since the quantity of the primary electrons can be controlled by the signal potentials applied to grid 8, a corresponding control is effected over the secondary electrons which reach the respective anodes 22, 23, that are connected to the out put circuit. It will be understood of course, that the surface of the dynode [4 upon which the primary electrons impinge, can be treated or coated with any well-known material such as magnesium oxide to increase the percentage of secondary electrons emitted per primary electron striking the dynode.

As contrasted with the arrangement of Fig. 2, there is shown in Fig. 3 a typical known construction of electron multiplier which does not have the in-phase arrival of the primary electrons at the dynode. In Fig. 3, the cathode 29 has flat emitting surfaces 38, 3|, and is surrounded by a control grid 32, a screen grid 33. The dynode i l is mounted in symmetrical spaced relation to the cathode, and the anode 35 is likewise mounted in symmetrical spaced relation to the cathode. Deflector plates 36, 31, are also provided on opposite sides of the cathode, and abarrier or shield 32 is located between the cathode and the anode. Typical primary electron trajectories are represented by the dotted lines. However, it will be observed that the portions of the cathode farthest removed from the dynode give rise to electron trajectories, for example trajectory 39, which are much longer than the length of the trajectories from the portions of the cathode closer to the dynode, for example as represented by trajectory 46. Since the electrons of trajectory 39 are closest to the deflector 36, they are, in their region of emission from the cathode, subjected to a greater deflecting action tending to curve the electrons over a longer path which at its terminating portion is more tangential to the dynode 3. 3, whereas the electrons of trajectory it are not subjected to the sameextent of deflection, and therefore strike the dynode 3 3 at a smaller tangential action. The net result is that the electrons of the shorter trajectory lengths, for example those of trajectory til move at a higher electron velocity than the electrons of the longer trajectory paths, for example path 39, Which arrive at the dynode 34. at a lower electron velocity. That is. to say, the electrons arrive in diiferent phases. or times even though they originate at the same instant from different sections of the cathode.

t should also be observed, that. in the device according to the invention as illustrated in Fig. 2, it is not necessary to employ a separate baffle corresponding to the baffle 38 of Fig. 3. The deflectors 2d, 25, serve to control the deflection of the electron trajectories in such a way that the primary electrons do not reach the anodes.

It has been found by actual tests on. rubber membrane analogue devices, that the greatest time difference in phase between, electrons striking the dynode over the long and short paths was not over 2.9%. For example, in one rubber membrane analogue test set-up, wherein the membrane was deflected to represent the cathode 5 and the deflectors 24 and 25 at zero volts, and to represent a screen grid at volts, 2. dynode at 200 volts, and the plates or anodes at 300 volts, the following time intervals were observed:

Seconds Trajectory 26 1.71 Trajectory 27 1.73 Trajectory 28 1.72

It will thus be seen that actually.v the compensation of phase arrival of. the electrons. at. the.

dynode, is carried; out so well that. the slow electron on trajectory 26 consumes the least time to reach the dynode. A similar rubber membrane test set-up of an array of electrodes corresponding to that of Fig. 3, showed a time difference of as much as 25% between the arrival of the slow and fast electrons at the dynode 34.

Fig. 4 shows in schematic form a typical circuit arrangement using the tube of Figs. 1 and 2, and wherein like parts are designated by the same numerals in Figs. 2 and 4.

While one particular embodiment has been described herein, it will be understood that various changes and modifications may be made therein without departing from the spirit and scope of the invention. For example, in Fig. 2 the primary electrons from the cathode are formed into respective oppositely directed beams by reason of the flat type of cathode and by reason of the shielding or focussing action of the grid side rods 9, II], in the manner well-known in the action of so-called beam power tubes (see U. S. Patent #2,107,520). It will be understood however, that any other well-known arrangement for forming the primary electrons into the welldefined beams having substantially restricted beam widths can be employed.

What is claimed is:

1. An electron tube having a' cathode for emitting from opposite sides thereof respective electron beams of a predetermined restricted Width, a signal-control grid surrounding the cathode, a dynode having a central reentrant portion and a pair of inclined lateral wing portions diposed on opposite sides of the cathode, said cathode being mounted with certain areas thereof closer to the dynode wings than are other cathode areas, a pair of electron deflector elements located on opposite sides of said cathode each element being closer to said other cathode areas than to the first-mentioned cathode areas said deflector elements being biased negatively with respect to the dynode Wings for causing the electrons of the beams to follow curved trajectories to the respective dynode wings with the slower accelerated electrons confined to shorter length paths as compared with the faster accelerated electrons.

2. An electron tube according to claim 1, in which said wings of the dynode are bent back upon themselves to form respective electron chambers, and an output anode is mounted in each of said chambers.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,164,892 Banks July 4, 1939 2,272,232 Wagner Feb. 10, 1942 2,273,546 Van Weel Feb. 17, 1942 2,293,418 Wagner Aug. 18, 1942 2,340,631 Van Overbeek Feb. 1, 1944 2,537,923 Van Overbeek Jan. 9, 1951

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