US3119044A - Electrostatic type focussing device for hollow tubular electron beams - Google Patents

Description

Jan. 21, 1964 w. HENNE ETAL & 3 ELECTROSTATIC TYPE FOCUSSING DEVICE'FOR HOLLOW TUBULAR ELECTRON BEAMS Filed March 8, 1960 l/l/I//l/l/I/l/I//l///////////////? ll///l//l//l/l//l/l//l//l/l I/I/fl//I INVENTORS t'l/l/l/ will i ba d Henne a I Rudolf John`e & fla

ATTORNEY United States Patett O 3,119,044 ELECTROSTATIC TYPE FOCUSSING DEVICE FOR HOLLOW TUBULAR ELECTRON BEAMS Wiliibaid Henne and Rudolf Johne, Ulm (Danube), Germany, assignors to Teiefunken Aktiengesellschaft, Berlin, Germany Filed Mar. 8, 1960, Ser. No. 13,581 Claims priority, application Germany Mar. 12, 1959 3 Claims. (Ci. SIS-3.6)

The present invention relates to a focussing device of a tubular electron beam in an electron ray tube, particularly tubes of the travelling wave-tube type.

In general, it is often necessary to keep an electron beam constant with respect to its cross-sectional dimensions and its thickness over a distance which is large as compared with the diameter of the beam if the latter is of tubular shape. Such linear and straight propagating electron beans are used, for example, in travelling wave tubes in which an electromagnetic wave propagates along a delay line and interacts with the electron beam migrating adjacent thereto. Basically, two types of focussing devices for electron beams are known, one type Operating with the aid of magnetic fields and the other type operating with the aid of electrostatic fields. The present invention pertans to focussing systems Operating on the electrostatic principle.

It is known in the art to focus a tubular electron beam by means of two electrodes which are positioned inside and outside, respectively, of the tubular beam. The focussing electrodes are coaxial with the beam, and they are connected to respective voltage potential sources. It is desirable to use one of these electrodes as a delay line and wave conductor along which the electromagnetic wave travels, so as to interact with the electron beam. For reasons of input and output coupling, only the outer focussing electrode can reasonably be used as delay line or wave conductor.

It is, therefore, an object of the present invention to provide a new and improved focussing device for tubular electron beams which overcome the deficiencies outlined above.

It is another object of the present invention to provide a new and improved focussng system and device for a tubular electron beam with inner and outer focussing means in which the outer focussing means are of a uniform structure and serve as a single part for D.C. potential distribution as well as for high frequency conduction.

With the above objects in View, one aspect of the in- Vention, in a preferred embodiment thereof, comprises a first integral electrode, preferably in the form of a helical coil, which is positioned around the tubular electron beam and is connected to a D.C. voltage source so asoto be maintained at a constant and substantially uniform potential to produce a radially directed electrostatic field. Inside of the electron beam there is positioned an electrode assembly adapted to produce a radially directed electrostatic field which is constant as to time but varies in axial direction according to a periodic function.

Additional objects and advantages of the present invention will become apparent upon consideration of the following description when taken in conjunction with the accompanying drawings in which:

FIGURE 1 is a cross-sectional View through a portion of an electron beam tube incorporating one embodiment of the present invention; electrical connections as far as necessary are shown in schematical form.

FIGURE 2 is a cross-sectional View through a tube modified as compared with the one shown in FIGURE 1.

In FIGURE 1, a tubular enclosure 1 made, for example, of ceramic or glass, houses the various parts of an electron ray tube whose cathode or electron gun, grid anode and target electrode, if any, are not shown, inasmuch as they are of conventional type and mounted inside of tube 1 in a conventional manner.

The electron gun produces a tubular electron' beam 2. Inside of the space enclosed by this tubular electron beam 2. are two helical coils 3 and 4 which extends symmetrically with respect to the axis of the electron beam 2, i.e., coaxially with the beam. Coils 3 and 4 are similar to a bifilar coil, but they are separated from each other electrically.

Outside of beam 2, in coaxial relationship thereto, is a single helical coil 5 positioned in close proximty to the beam. Coils 3 and 4 are mounted on ceramc or glass rods such as 6, while coil 5 is supported by similar rods such as '7. These supporting rods are conventional.

Coil 5 is connected to a voltage potential source 8 producing a voltage which preferably is positive relative to the potential of the electron beam, i.e., positive relative to the electron gun producng the beam. The voltage potential source should have a Very low ohmic resistance so that a current produced by stray electrons which strike the electrode S and flow to ground via the voltage potential source will not change the uniform potential all along coil 5. Thus, a uniform radially-directed field is produced which compensates for the outwardly directed space charge of the tubular beam.

Coils 3 and 4 are connected to D.C. voltage sources 10 and 11, respectively. The voltages applied to coils 3 and 4 preferably are positive with respect to the potential of the electron gun producing the electron beam 2 and they are selected or adjusted dilferently. As a result, there is produced inside of the tubular beam, a spatially stationary but axially periodically Variable electric field which compensates for the inwardly directed space charge of the tubular beam.

The entire device as described thus far serves as a focussing means for the tubular electron beam. In addi ton, the outwardly positioned focussing electrode, i.e., the coil 5 can serve also as a delay and transmission line for electromagnetic waves, so that no difliculties are encountered as far as coupling and damping are concerned. This is particularly important because in this case the wave propagation Will be carried out along a unifilar coil.

FIGURE 2 illustrates a modification of the structure shown in FIGURE 1. The outer focussing electrode is also the coil 5 but the inner electrodes are formed by a plurality of rings 14, 14', 14", etc., which alternate with rings 15, 15', 15", etc. All rings are similar in size and dimension, but rings 14, 14', 14", etc., are connected via a common, low ohmic conductor 1461 to a voltage source 10'. Rings 15, 15', 15" are electrically interconnected by a low ohmic conductor lsa to a voltage source 11'. Rings 14, 14', 14" are maintained at a potential which is different from the potential of the rings 15, 15', 15". Thus, the rings cooperate with each other to produce an axially periodic and symmetric electric field which does not vary in time.

lt will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.

We claim:

1. A combined transmission line and focussing device for a tubular electron beam, comprising: a two-threaded electrode coil positioned inside of the electron beam and arranged coaxially therewith; means for applying two different constant voltage potentials to the two threads of said electrode coil; a unifilar coil positioned outside of said beam and arranged coaxially therewith, said coil constituting a transmisson line for electromagnetic waves;

3 and means for applyng a constant voltage to said unifilar coil.

2. A combined transmisson line and focussing device for an electron beam, comprising: a unifilar coil surrounding the beam and constituting a transmission line therefor, means for maintaining said col at a constant potential for producing a substantially radially directed constant electrc field, a piurality of first eiectrode rings coaxially postioned inside of said beam, a plurality of second electrode rings coax'ally positoned inside of said beam in alternating 'elatonship to said plurality of first rngs; first conductive means for electrically interconnecting said first plurality of electrode rings; second conductive means separate from said first conductive means for electrically interconnecting said plurality of second electrode rings; and means for applying dissmilar constant voltage potentials to said first rings and said second rings, respectively.

3. A combined transmission line and focussing device as defined in claim 2 wherein said rings are of the same size dimension.

References Cited in the file of this patent UNITED STATES PATENTS 2,823,333 Quate Feb. 11, 1958 2,843,776 Tien July 15, 1958 2,843,792 Pierce July 15, 1958 2,887,609 Dodds May 19, 1959

Claims (1)

1. A COMBINED TRANSMISSION LINE AND FOCUSSING DEVICE FOR A TUBULAR ELECTRON BEAM, COMPRISING: A TWO-THREADED ELECTRODE COIL POSITIONED INSIDE OF THE ELECTRON BEAM AND ARRANGED COAXIALLY THEREWITH; MEANS FOR APPLYING TWO DIFFERENT CONSTANT VOLTAGE POTENTIALS TO THE TWO THREADS OF SAID ELECTRODE COIL; A UNIFILAR COIL POSITIONED OUTSIDE OF SAID BEAM AND ARRANGED COAXIALLY THEREWITH, SAID COIL CONSTITUTING A TRANSMISSION LINE FOR ELECTROMAGNETIC WAVES; AND MEANS FOR APPLYING A CONSTANT VOLTAGE TO SAID UNIFILAR COIL.

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