US2680826A - Stabilized klystron - Google Patents

Description

June 8, 1954 G. D. o'NElLL ET AL 2,680,826

STABILIZED KLYsTRoN Filed May l, 1948 I "E'i Leo CEzZsa/a/i 500 iv" In' 11W/Emmy.;LTS I 'eorge OWelL l I I Patented June 8, A1954 STABILIZED KLYSTRON George D. ONeill, Port Washington, and Leo C. Eisaman, Flushing, N. Y., assignors to Sylvania Electric Products Inc., a corporation of Massachusetts Application May 1, 1948, Serial No. 24,546

(Cl. S15- 5) 3 Claims. 1

The present invention relates to electron discharge devices, and more particularly to electron discharge devices of the velocity modulation type employing a hollow resonator and in which a stream of electrons from a cathode is passed through a gap in said resonator and is reected back through the gap by a reecting electrode. Such devices are commonly known as reflex klystron tubes. In the operation of such devices as generators of high frequency oscillations, a condition has been encountered which made it appear that two sets of operation were possible with any given tube, resulting in two sets of reector mode characteristics which were approximately parallel to each other, and were separated by 50 to 100 volts on the reector voltage characteristic.

These sets of operation were such that the power output of each was approximately the same and the tube appeared to operate equally well in either condition. It was, however, impossible to control or predict which of these conditions the tube would choose to operate under, and frequently the tube would jump from one condition to the other during operation. This alternative operating effect may be called mode jumping. Thus, the tube may operate in a number of distinct and mutually exclusive modes in which the number of the mode is designated N, such that N=fT where f is the resonant frequency and T is the time an electron spends in the drift space; that is, the space between the resonator grid and reflector. Also, N=(n 1,) where n is an integer greater than and the time T depends upon the eld in the drift space. If all other charged bodies are far removed, T depends upon the reector voltage, specifically,

4x eb T V 6be,)

Where :c is the grid-reflector spacing, V is the Velectron velocity at the grid, eb is the grid voltage and er is the reector voltage.

Now, in the tubes in which this condition was observed, the envelope of thetube was made of insulating material, such as glass, at least in the area between the nal resonator electrode and the seal-in point of the reflector electrode. It has been deduced that this mode jumping is indirectly caused by electrons from the cathode of the tube passing through the resonator grids and being scattered by the mesh of the grids. As a result of the scattering some of Vthe electrons strilie'the glass Wall of the tube envelopebetween i the-resonator electrode and the reflector electrode. The electrons striking the glass wall may cause one of two elects; that is, either a negative charge is built up on the glass wall, or the electrons striking the glass wall cause a secondary emission which in turn results in a change in space charge in the reflector field. A study of the potential gradient between the final resonator electrode and the reflector electrode by means of an electrolytic plotting tank indicated that either of the effects stated above would result in a distortion of the reflector field to an extent that mode jumping would occur.

An object, therefore, of the present invention is to provide an arrangement for stabilizing the retarding field between the resonator grid and the reflector electrode of a reex klystron.

Another object of the present invention is the provision of means for stabilizing the mode of operation of a reflex electron beam oscillator.

Still another object of the present invention is the improvement of the stability of operation of a reflex klystron.

Still a further object of the present invention is the provision of an improved means for providing a conductive coating on the interior wall of a glass envelope and the connection between. the conductive coating and a lead-in terminal sealed in the glass wall of the tube.

In accordance with an aspect of the presentI invention, the building up of a charge on the.i glass envelope may be prevented by providing a thin metallic coating on the interior wall of the envelope in conductive connection with the lead through terminal associated with the reflector electrode. The coating is preferably spaced a distance of the order of one thirty-second of an inch from the final resonator electrode.

As a further aspect of the present invention, it is contemplated that an improved contact may be obtained between the conductive coating and the reflector electrode lead by mounting a getter strip on the reflector electrode lead in such a way that, as the getter is flashed, a conductive coating will be established between the reflector electrode lead and the conductive coating within the tube envelope. Alternatively, the conductive coating within the glass envelope may be in the form of a thin aluminum coating evaporated onto the interior surface of the tube envelope prior to assembly of the tube.

The present invention will be more fully understood by reference to the following detailed description which is accompanied by a drawing in which y l Fig.V 1 illustrates in partiallongitudinal crosssection a tube embodying the principles f the present invention, while Fig. 2 is a graph illustrating the potential gradient along a line between the resonator grid and the reflector electrode of the tube in Fig. 1, while Fig. 3 is an enlarged fragmentary longitudinal cross-section of the tube of Fig. l with the equipotential contour lines in the space between the resonator grid and reiiector electrode plotted 'for two conditions of operation.

In Fig. 1 of the drawing, reference numeral Il! indicates the evacuated glass envelope of an electron discharge device having at one end. a cathode structure l2. The cathode structure l2 incorporates a heated electron emissive surface and focusing means for projecting a beam of electrons through grid i3 in apertured electrode it, and further, through grid I in apertured electrode I6. Electrodes Hi and It' are in the form of conductive metal discs passing through the wall of the glass envelope It of the tube.

Preferably, electrodes i4 and i5 terminate in cylindrical rims it and 2G adapted to make good contact with the walls of an exterior resonating chamber. The resonating chamber is not shown since it may be of various forms and of varying dimensions, depending upon the desired fre- Quency or" operation of this system.

The stream of electrons from cathode l2, after passing through grids i3 and i5, is reflected back through the resonator gap between grids I3 and I5 by a suitable negative potentiai applied to reector electrode 22. The energizing potentials on the electrodes of the tube are so related to the dimensions of the tube and the associated resonating chamber as to cause the reflected electrons to pass back through the gap between electrodes i3 and I5 in bunches, thus exciting the associated resonant cavity into oscillation.

In the tube, as so far described, and without the provision of some special means of preventing such action, electrons may so far fail to be inuenced by the reflector eiectrode 22 as to pass between the edges of theV reiiector electrode 22 and the electrode l5 and strike the glass wall of the envelope H3. Alternatively, they may be scattered by a diiracting action of the wires constituting grid l5. The electrons striking theY inner glass wall of envelope I0 cause a charge to be built up on said wall, which can only slowly be dissipatedv due to the high resistance of the glass surface. When a suiiicient charge has been accumulated on the interior surface of the glass envelope it, the shape of the neld between the resonator grid l5 and the reflector electrode 22 may be so i influenced or redistributed; that the tube will iail to continue to oscillate inits original mode, or if the tube does continue to oscillate in its original mode when the tube is turned o and then again turned on, it may begin to oscillate in a diierent mode, dependent upon the new voltage distribution. However, we have found that if the interior wall of glass envelope lil is coated with athin conductive coating of metal, such as aluminum evaporated onto the interior surface, andY if. this coating is connected to the lead forv reflector electrode 22 `by some suitable means, the potential gradient between reector electrode 22 and resonator gridv it is maintained at a constant value, so that, no matter how many times the tube is turned on and oit, it always oscilla-tes in the same mode of operation.

We have found that a convenient way for-assuring good electrical contact ,betweenY theslead for reflector electrode 22 and the conductive coating 30, is to so mount the getter strip 32 on the reilector electrode lead that, as the getter is flashed, the material from the getter is deposited on the seal between the reflector electrode lead and the conductive coating 30, thus assuring a continuous conductive path between the coating 3i) and the reflector lead. Contact between these two conductive elements may also be established. by a conductive cats Whisker attached to the reflector electrode and contacting the conductive coating.

In Fig. 2 we have plotted the potential gradient between the resonator grid I5 and the reector electrode 22. In this family of curves, voltages are plotted as ordinates against distances along a line between grid and reiiector electrodes as abscissae. In this diagram, curve illustrates the variation of potential from the reflector electrode to the resonator grid under the condition when no current is flowing through the tube; It is apparent that the voltage distribution follows a straight line in this case. Now, if current is drawn through the tube, the potential distribution between the reflector electrode and resonator grid changes to that shown by curve. 5! As a voltage is built up on the interior of the glass wall of the envelope, the potential distribution may change to that shown by curve 52. A mode of operation may then be possible with the field represented by this curve. The distance indicated by the double headed arrow A indicates the amount oi readjustment of electrode potentials that is necessary in order to assure operation in the same mode as along linev 5l. Now it has been found that i1 a conductive coating is applied to the interior of the glass envelope, operation is stabilized along the curve 53 of Fig. 2. It will be noted that this line follows very closely the line 5l so that no substantial change in operating mode is encountered as the tube continues to operate. Further, each time the tube is turned on again it operates in the same mode as before.

In Fig. 3 we have shown in greatly enlarged g detail the upper portion or" the tube of Fig. 1' with the equi-potential contour lines plotted in the space between the reflector electrode 22 and the resonator grid' l5. The location of the conductive coating and the connection between that coating and thelead-in wire for electrode 22 is also more apparent in this gure.

The solid line curves in Fig. 3 illustrate potential contour lines determined by the use of an electrolytic plotting tank for the condition where a conductive coating is present on the interior of the envelope while dotted contourlines El indicate potential contour lines for the condition where the conductive coating is not present. It should be noted tha-t the dotted contour lines terminate at different points along the glass envelope of the tube, If the potential of the glassvaries, the termination points of the contour lines may shift over the surfaceof the envelope, thus permitting a general reformation of theeld within the space between grid l5 and electrode 22. In the case where the tube envelope is provided with a conductive coating, all contour lines terminate within a very narrow band, the limits of which are fixed by the lower edge of the conductive coating. Thus, there can be substantially no shifting of the potential distribution and no mode jumping is. encountered.

While we have describedr a particular embodiment of the present invention for purposes of illustrationg it will be understood. thatl various modications and adaptations thereof may be made within the spirit of the invention.

What is claimed is:

1. A reflex klystron having an evacuated envelope of insulating material containing an electrode for providing a stream of electrons, first and second apertured disc electrodes interposed in the path of said stream, a reilector electrode towards which said stream is to be directed, said reilector electrode being substantially symmetrical with and disposed substantially transverse to the path of said electrons, a rst conductive coating on the inside of said envelope extending to a point adjacent said second apertured disc electrode, and a second coatingof conductive getter material overlying said first coating and in electrical contact With said first coating and said reflector electrode.

2. A reflex klystron having an envelope containing an electron source electrode and an eleotron reflector electrode, a pair of cavity resonator electrodes passing through said envelope and positioned between said source electrode and said reflector electrode, and a continuous conductive coating on the interior Wall of said envelope and in electrical contact with said reflector electrode, said coating extending from a region adjacent said resonator electrodes to a region on the side of said reflector electrode away from said resonator electrodes.

3. A reflex klystron including an electron source electrode and a reflector electrode, said electrodes being mounted in an evacuated insulating envelope, a pair of apertured cavity resonator electrodes passing through said envelope and positioned between said source electrode and said reflector electrode, said reilector electrode being separated by a space from the next adjacent cavity resonator electrode, and a shield connected to said recctor electrode and covering said envelope, said shield extending from a point adjacent said next adjacent cavity resonator electrode in said space between said cavity resonator electrode and said reflector electrode to a point on the side of said reflector electrode away from said next adjacent cavity resonator electrode.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,571,257 Freeman Feb. 2, 1926 1,860,210 Spanner May 24, 1932 1,906,037 Zecher et al Apr. 25, 1933 2,128,070 W`Bahls Aug. 23, 1938 2,160,593 Kling May 30, 1939 27,197,625 Teves et al Apr. 16, 1940 2,407,607 Cairns Sept. 10, 1946 2,417,551 Hill Mar. 18, 1947 2,420,314 Hansen May 13, 1947 2,431,103 Bradley Nov. 18, 1947 2,445,404 Mayo July 20, 1948 2,445,771 Fremlin et al July 27, 1948 2,452,062 Le Van Oct. 26, 1948

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