US2754375A - Device comprising an electric discharge tube of the electron-beam type - Google Patents

Description

July 10, 1956 A. J. w. M. VAN'OVERBEEK ETAL 2,754,375

DEVICE COMPRISING AN ELECTRIC DISCHARGE TUBE OF THE ELECTRON-BEAM TYPE Filed June so, 1951 INVENTORS I A N w MARE von ADRIANUS JOH N ES ILHE OERBEEK JOHANN LODEWIJK HENDRIK JONKER DEVICE COMPRISING AN ELECTRIC DISCHARGE TUBE OF THE ELECTRON-BEAM TYPE Adrianus Johannes Wilhelmus Marie Van Overbeek and Johan Lodewiik Hendrik .lonker, Eindhoven, Netherlands, assignors to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application June 30, 1951, Serial No. 234,484

Claims priority, application Netherlands July 13, 1950 2 Claims. (Cl. 179-171) This invention relates to devices comprising an electric discharge tube of the electron-beam type, with the use of which a very high mutual conductance can be achieved in a simple manner.

It has previously been suggested to increase the deflection-sensitivity of a tube of the deflected-beam type by means of a space charge developed between the beam and the deflection electrode, the deflection due to the deflection electrode being assisted by the space charge. The object here was an improvement in the deflection control itself in a tube having a double control. In addition, according to the present invention it has been found possible to utilise the influence of space charge effects to achieve a very high mutual conductance, even in the case of intensity control, if the electrons are directed to any one of the collecting electrodes only as a result of space charges which are formed by the beam current itself and are in accordance with the intensity control of the beam current. The deflection, or actually dispersion, of the electron paths due to these space charges, which deflection is generally considered undesirable in intensity-control beam tubes, is thus used to direct the electrons normally travelling to a given collecting electrode on to a further collecting electrode. The lastrnentioned collecting-electrode will generally be the output electrode (anode). When the intensity of the beam current is increased by the action of the control electrode an increasing current flows to the collecting electrode (anode) and this increased flow is enhanced because,

simultaneously with the increase of the beam current,

the beam is directed to this electrode to a greater extent. The beam is thus deflected, fully in accordance with the intensity control of the beam current, without any provision for a separate deflection control.

This mode of operation, i. e., deflection added to intensity-control as a result of space-charge effects, is achieved with advantageous results in the device according to the invention comprising an electric discharge tube of the electron-beam type which includes at least a cathode, an intensity-control electrode and two collecting elec trodes and in which the electrons can be directed on to any one of the collecting electrodes by space charges formed by the beam itself in accordance with the intensity control of the beam current, the tube exhibiting during operation a straight beam which, at a given low current strength, travels completely through an aperture in one collecting electrode of disc shape but, as a result of the dispersion brought about by space charges occurring in the axis of the beam, largely reaches the said disc-shaped collecting electrode in the case of sufficiently-high current strength.

The current control-grid voltage characteristic of this electrode consequently has a very high mutual conductance, which may be increased by forming this electrode as a secondary emission auxiliary cathode.

In order that the invention may be more clearly understood and readily carried into eflect, it will now be deatent scribed more fully with reference to the accompanying drawing, in which Fig. 1 shows diagrammatically one embodiment of a tube suitable for use in a device according to the invention, and

Fig. 2 shows the IaVg characteristic curve of such a tube.

Referring to Fig. l, the cathode is designated 1 and the intensity control electrode 2. A screen grid is shown at 3. The control electrode 2 may itself comprise small screens so that the electron flow is concentrated to form a beam but, as an alternative, separate beam-forming electrodes may be provided. In either event a straight beam is formed which passes through an annular electrode 4, the space charge electrode, maintained at zero (ground) or at a low potential and which, in the case of a given low current strength, travels completely through an aperture in a first disc-shaped collecting electrode 6 and reaches a second collecting electrode 5. The first collecting electrode 6 is preferably coated with secondaryemissive material and consequently acts as a secondaryemission auxiliary cathode. Owing to the presence of the electrode 4, which may be separated, if desired, to form two spaced but electrically interconnected electrodes, the development of a space charge within the electrode 4 and adjacent thereto in the axis of the beam in the case of an increasing beam current is assisted, with the result that the electron paths are deflected, i. e., the beam crosssection is enlarged, and more and more electrons reach the auxiliary cathode or first collecting electrode 6 as the beam current rises. The secondary electrons from this electrode 6 are collected by a grid-like output anode 7 which is connected to an output circuit 8. Since an increase in beam current arriving at the auxiliary cathode or first collecting electrode 6 is assisted by the dispersion of the beam due to this current increase, a greatly increased mutual conductance is obtained.

Fig. 2 shows the Ia-Vg characteristic curve of a normal tube which has intensity control but without the use of space charge dispersion (curve 1). Curve II is the IaVg characteristic curve to the same scale of a similar tube in which space charge dispersion is used. In order to provide a true comparison between the two tubes, the current Ia is taken from an electrode 6 (Fig. l) which is not coated with a secondary emitting substance. These curves clearly show the intense increase in mutual conductance, the advantage being that the latter is obtainable without the necessity of very accurate electrode machining or very small electrode spacings.

What we claim is:

l. A circuit arrangement comprising a tube having a high mutual conductance characteristic; said tube comprising a cathode, a control electrode, a screen grid, at first collecting electrode having an aperture therein for the passage of an electron beam therethrough and having a secondary-electron-emissive surface facing the cathode, a second collecting electrode on the side of the first collecting electrode remote from the cathode, a grid-like anode disposed adjacent the secondary-electron-emissive surface of said first collecting electrode in a position to receive electrons emitted therefrom, and a space charge electrode disposed between the screen grid and said gridlike anode and spaced therefrom and surrounding the beam of electrons; means to apply constant positive potentials with respect to said cathode to said grid-like anode and said second collecting electrode, means to apply to said space charge electrode a constant potential between zero and a positive amount which is small with respect to the potentials applied to the collecting electrodes whereby a portion of the electron beam alternately impinges upon the first and second collecting electrodes with high and low beam intensities, respectively, in accordance with the intensity of the beam, means for applying a positive in which the space charge electrode comprises a conpotential to said screen rid, mean' 'fd ap lying gm'input sinuous annular electrode through which the beam passes. signal to said control electrode to vary the intensity of References Cited in th file of this patent we beam Q e ec n a d QutPu g m n lc i 2: ai

grid-like anode for deriving therefrom anamplified 'elc- 5 UNITED STATES PATENTS tricahsignal correspondingto the input signal applied to 23394-3393 95 -t----v --t--- a 9 saidcontrolielectrede. 2 h v v 253835160 f ay 1 1951 2. An electron discharge device as claimed in 'claim -1 2,559,524 Thompson July 1951 2,563,482 Nelson Aug. 7,1951

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