US2621304A - Vacuum tube with ultrahigh frequency - Google Patents

Description

Dec. 9, 1952 v. A. ALTOVSKY ETAL 2,621,304

VACUUM TUBE WITH ULTRAHIGH FREQUENCY Filed May 21, 1947 3 Sheets-Sheet 1 I N V EN TOR .5' VLAD/Ml/P A. AUOKSA? GEO/P655 GQl/DET BY ATTORNEY Dec. 9, 1952 v. A. ALTOVSKY El'AL 2,621,304

' VACUUM TUBE WITH ULTRAHIGH FREQUENCY Y m/M k ATTORNEY 5 v. A. ALTOVSKY ETAL 2,621,304

VACUUM TUBE WITH ULTRAHIGH FREQUENCY Filed May 21, 1947 3 Sheets-Sheet 5 INVENTORS VLAD/M/f? ,4. nzrarsxy GEORGES 600057 A T TORNZ'Y Patented Dec. 9, 1952 VACUUM TUBE WITH ULTRAHIGH FREQUENCY Vladimir Arcadie Altovsky and Georges-Goudet,. Paris, France, assignors to International Standard Electric Corporation, New York, N. Y., a

corporation of Delaware Application May 21, 1947, Serial No. 749,514

In France September 19, 1944 Section 1, Public Law 690, August 8,1946 Patent expires September .19., 1.964

4 Claims. (Cl. 315 -6 The present inventionrelates to" electron dis.- charge devices, particularly to ultra-high fre-'. quency devices of the kind in which the electrons of a beam are modulated in velocity.

A typical velocity-modulation tube comprises an electron beam source and two reentrant type cavity resonators. The beam is directed through the central opening of one resonator and hence through a metal cylinder, called a drift or slip tube, and finally through the central opening of the second resonator. When the resonators are excited, the electrons are alternately accelerated and retarded in the first cavity opening, causing them to be grouped into traveling bunches in the drift tube. In the second cavity opening the electron bunches give up energy to the oscillating field in the second cavity. For correct operation of the device, particularly as a self-excited generator of oscillations, a coupling is provided between the two resonators, which coupling may be loose or tight.

In the case of a loose coupling, it is necessary to exactly tune the natural frequencies of the two cavity resonators. This makes the manufacture of the devices particularly difficult, because the cavity resonators must be made deformable or be provided with auxiliary adjusting devices. On the other hand, in the case of a tight coupling between resonators it becomes unnecessary to tune the resonant volumes to the same frequency, and this makes their construction much easier.

From the viewpoint of intrinsic output of energy and the maximum power that canbe obtained from the device, it has been found that the high frequency voltage applied to the modulation space of the first cavity opening must be less than the high frequency voltage applied to the pick-up space of the second cavity opening and that the ratio of these voltages must possess a quite definite value less than unity, depending upon the order or mode of oscillation. The condition for maximum power output is explained, for example, in an article by Clavier and Le Boiteux published in the Revue Generale de lElectricite, vol. 56, year 1941, pages 109 ff.

In the case of tubes with tight coupling, it has so far not been possible to obtain the optimum voltage ratio at the two cavity openings except with changes to the electron optical system that cletrimentally affect the speed modulation of the electrons. It has not beenpossible, heretofore, to obtain: thenecessary-diiference between the modulation and. pickup voltagesexcept by changing; the: geometric characteristics of the modulation and pick-up spaces. The structure 2 then no longer-operates under optimum conditions from the viewpoint of its action on the electron beam, and this brings about a loss of energy which lessens the improvement that might other-I wise be expected;

The. object of the present invention consequently is an electron dis-charge device-ofthe velocity-modulation type which has the proper geometric relation of parts for best electron optics and. which provides the optimum ratio of high frequency voltages at the two'cavity openings for maximum high frequency output power.

The two cavity resonators of the velocity-mod ulationdevice are effectively combined according to one feature of this'inventi'on, in a single cavity resonator so that the -modulating voltage and pick-up voltage at the ends of the drift tube are tightly coupled and so that the modulating and pick-up frequencies are always synchronized. Yet, the single .cavity resonator, according to this invention, is asymmetrical with respect to the opposite ends of the drift tube so as to apply the desired voltages to the modulating and pickup openings.

These features, as well as others, are explained in detail in the following description given with reference to the appended drawings, in which:

Fig. 1 illustrates schematically in longitudinal section a conventionalrelectrode structure for velocity modulators; with two tightly coupled cavity resonators. I

Fig. 2 illustratesschematically in longitudinal section an electrode structureproviding the optimum geometric dimensions of parts for best modulation of .the electron beam and, associated, according to features of the invention, with a complex cavity having theresonance properties of a single cavity, and also, through its asymmetry, providing an optimum ratio of modulation and pick-up voltages.

Figs. 3, 4, 5 and 6 illustrate schematically in section other examples of arrangements of speed modulation tubes each with an asymmetrical complex cavity resonator, according to the basic features of the invention, and

Figs. 7 and 8 illustrate a variant structure of an asymmetrical cavity, according to one feature of the invention, having a shape that is not one of revolution around the axis of the electron beam.

In conventional speed modulation tube ,strucv tures such as shown in Fig. 1, the electrode. assembly is foundto be satisfactory for. modulation, of the electrons andfor pickingnptthe energy of the modulated beam. The structure consists of three tubes or cylinder segments I, 2 and 3 aligned along the path of an electron beam derived at the cathode C and focused by electrode F. An accelerating electrode A may be sealed in at the opposite end of the device. The conditions of optimum action on the beam are made possible by the dimensioning of the cylinder segments I, 2 and 3, and especially by the selection of their diameter cl, the lengths Z1 and Z2 of spaces 4 and 5 between segments I--2 and 2-3, respectively, and by the length 13 of cylinder 2. Space 4 is called the modulation space, and space 5 is called the pick-up space, and electrode 2 is usually called the slip electrode or drift tube. Two cavity resonators 6 and T, which are symmetrical in known embodiments, are respectively coupled to the spaces 4 and 5 and serve as resonant or oscillatory circuits for the complete tube. The coupling between these cavities is efiected by slots 8 in the middle wall 9, which is common to the two resonators. If these slots are made of large size, the coupling between the volumes 6 and I will be tight, and this will make it possible to dispense with devices for the precise adjustment of the resonance frequencies of the two resonators with respect to each other.

In tight coupled structures of this kind, it is apparent that the high frequency voltage applied to the modulation space 4 will be, owing to the structural symmetry of the parts equal to the high frequency pick-up voltage applied to the pick-up space 5. The conditions of maximum power output will consequently not be complied with. It is recognized in the invention, however, that the use of a very tight coupling effected by large size slots 8, or even by the elimination of wall 9, makes it possible to dispense with all necessity of symmetry. Contrary to expectations, modification of the dimensions of the tube openings to obtain the mentioned optimum voltage ratio, does not result in a higher output. Unequal alteration of the values Z1, Z2 would change the action of the electrode assembly I-23 on the electrons. The action on the beam would then no longer be uniform in all the straight sections of the beam from the viewpoint of the high frequency fields, and the transit times of the electrons would become incorrect for optimum operation of the tube.

In the tube of this invention, the electrode structure I-2-3 is dimensioned to provide optimum conditions of action on the beam, including proper electron transit times. A complex cavity resonator having the resonance properties of a single cavity at the operating frequency is associated with the electrode structure I23 and is made asymmetrical with respect to the modulation and pick-up spaces so as to obtain the optimum ratio of high frequency voltages that is necessary for obtaining maximum power output.

This complex cavity resonator, with asymmetrical distribution of the potentials of the high frequency oscillations at the two cavity openings, may be designed in various ways, particularly with a structural configuration that provides the desired effect. Figs. 2 and 3 show two examples of complex cavity resonators of this kind associated with an electrode assembly I, 2 and 3 having electron optics for optimum action on the beam. Corresponding parts are indicated by the same reference numbers as in Fig. 1.

In the example shown in Fig. 2, to the electrode assembly I, 2 and 3, there is associated a complex cavity resonator consisting of a conductive envelope I0 and a portion of conductive wall II shunting the modulation space. This wall portion II may even be reduced to a simple conductive loop. Element II is given such shape and dimensions that the obtained complex cavity resonator, while having a single resonance frequency in the selected range, provides an asymmetry of the modulation and pick-up high frequency voltages that is in the desired ratio.

The slip electrode 2 may, as shown in Fig. 2, be supported mechanically by the bridge element I I which may also serve as lead-in conductor for this electrode. It is however evident that the slip electrode 2 may be supported and placed under voltage independently of element II of the complex volume.

In the embodiment shown in Fig. 3, the desired asymmetry of the modulating and pickup voltages is obtained by increasing the radial. dimensions of the opposing surfaces I2 and I3 that define the modulation space 4 between electrodes I and 2. The walls of said electrodes. may be thickened as shown, or provided with out-turned flanges, to increase the distance be-- tween the cavity and the beam in the drift tube, as compared with the corresponding opposing surfaces of electrodes 2 and 3 that define the pick-up space. The increased thickness of the wall I2I3 reduces the voltage applied by the cavity to the beam.

Mechanical stability of the slip electrode 2 within the complex cavity resonator I4 may be effected by one or more stays of conductive or insulating material. In case of insulating supports for electrode 2, separate voltages may be applied to the electrode by a connection wire I50. insulated in the wall of the cavity resonator I4, as shown in Fig. 3. This arrangement makes it possible to employ slip electrode 2 as a modulation electrode of the wave produced by the oscillator.

In the embodiment shown in Fig. 4, the desired asymmetry is obtained by the use of a sleeve H which is supported by or is integral with the cylinder segment I and which more or less completely caps or overlies the modulation space while in Fig. 5, the sleeve I9 is supported by or is integral with the slip electrode 2. In either Fig. 4 or 5, the drift tube is supported by spokes 16 or I8. In Figs. 4 and 5, as in Fig. 3, the modulating space 4 is removed from the full intensity of the high frequency electric field existmg in the cavity. The reduction in the field in the modulating space 4, and the corresponding reduction of the percentage of modulation of the electron velocities may be accurately adjusted to the optimum value by adjusting the length of the sleeve II or I9. Such adjustments, according to this invention, require no compromise with the best dimensions, Z1, Z2, 13 or d, Fig. l, of the optical portion of the device.

The desired asymmetry of voltages at openings 4 and 5 may also be obtained by deforming the outer wall of the cavity resonator. In Fig. F, for example, the outer wall 2| has been constricted at 22 opposite the modulating space 4. 20 indicates support of the slip electrode 2, which is shown here at the point of passage from one section to the other.

Use may be made of embodiments in which the complex cavity is also asymmetrical in shape around the mean axis of the beam. In Figs. 7 and 8, for example, the peripheral wall 26 and the support 21 of the central conduit 2 have been deformed asymmetrically with respect to the modulation and pick-up spaces. Further, the wall is flattened somewhat in the plane of the supports 21. In this example, the support is such that it delimits the slip channel. In Figs. '7 and 8, the axial length of tube 3 is quite short, being equal, approximately to the thickness of the wall.

Although the invention has been described with particular embodiments, it is evident that the invention is by no means limited thereto but, on the contrary, is capable of numerous variants and adaptations in the construction of the asymmetrical complex cavity resonator in question. It is evident that numerous arrangements and shapes of the complex cavity resonators will provide the desired asymmetrical distribution of the high frequency potentials at the modulation and pick-up spaces without departing from the scope of the invention.

We claim:

1. An electron discharge device comprising three spaced and aligned metal tubes, an electron gun disposed axially of said tubes for projecting a beam of electrons therethrough, a single cavity resonator communicating with the spaces between adjacent ends of said tubes, the electrical dimensions of said metal tubes at one of said spaces being different from those at the other space for causing the high frequency voltages across said spaces to be unequal.

2. An electron velocity modulating device comprising metal walls defining a single cavity res onator with re-entrant portions and two spaced openings in said re-entrant portions, means mounted adjacent said resonator for projecting a beam of electrons through said re-entrant portions successively past said openings, the walis of said resonator at one of said openings being 6 of different thicknesses from those at the other opening for producing unequal high frequency voltages at the openings.

3. An electron velocity modulator comprising two cavity resonators, each having re-entrant wall portions spaced apart and axially aligned for the projection therethrough of an electron beam, the thicknesses of said re-entrant wall portions at the spaces therebetween being different from each other to couple said cavity resonators unequally to the electron beam, and said resonators being coupled together with suflicient tightness to insure synchronous operation thereof.

4. An electron velocity modulator comprising spaced and axially aligned metal tubes, a metal envelope enclosing said tubes and forming resonators therewith communicating with the interior of said tubes through the spaces between adjacent ends thereof, and means mounted adjacent one of said spaces increasing the length in said one communicating passage between said resonator and the interior of said metal tubes.

VLADIMIR ARCADIE ALTOVSKY. GEORGES GOUDET.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,272,211 Kohler Feb. 10, 1942 2,289,952 Zworykin July 14, 1942 2,364,732 Ludi Dec. 12, 1944 2,405,611 Samuel Aug. 13, 1946 2,466,064 Wathen et a1 Apr. 5, 1949 2,466,704 Harrison Apr. 12, 1949

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