US2459806A - Velocity-modulated electron discharge device - Google Patents

Description

Jan. 25, 1949. J, H. FREMLIN ET AL VELOCITY MODULATED ELECTRON DISCHARGE DEVICE Filed 001:. 28, 1942 em M Maw 1T3 A WMM W n Patented Jan. 25, 1949 John Heaver Fremlin and Christopher Henry Foulkes, London, England,.assignors,- by mesne assignments, to International Standard Electric Corporation, New York, Ni Y., a corporation of Delaware Application October 28,1942, Serial No; 463,700

In Great Britain January 9, .1942

3 Claims.

The present invention relates to electron discharge devices of the kind employing velocity modulation of anelectron beam, and in particular concerns means for simplifying the construction of such. devices used at wave lengths of the order oflO cm. a

It is Well. known to generate oscillations .in hollow conducting bodies by directing a. beam of electrons through a series of such bodies. For example, oscillations may be generated in a coaxial conductor system by firing the electrons diametrally through slots in the inner and outer conductors of such a system; or a Lecher Wire system may be similarly excited. by connecting it to a pair of hollow bodies through which an electron beam is passed. This is theprinciple of the well known Hell tube, from which the present invention is derived.

When the frequencies to be generated are very high, it is essential to use properly shielded oscillatory circuits, and previous arrangements have usually employed hollow metal resonators constructed from continuous copper sheet. Such resonators are expensive to make and troublesome to evacuate, and moreover lead to difilculties in preserving the continuity of the circuits inside and outside the containing envelope of the device. The present invention reduces the cost of suchdevicesby providing a new and simplified construction in which the oscillating bodies are designed in the form of wire-wound grids like those commonly used for. thecontrol grid and other grids in the ordinary thermionic valve,

The oscillating grids are connected directly to a Lecher wire system or trifilar line for extracting the wave energy, instead of to a-co-axial conductor system as usual with a Hell tube, because such a Lecher system or trifilar line is more easily sealed through the envelope of the device.

With the arrangement of the invention, the construction of the device becomes substantially the same as that of any ordinary thermionic valve and requires no special manufacturing equipment. v

The invention accordingly provides an electron discharge deviceof the electron velocity modulationtype having .a resonating. system. which. is solely constituted by the grids through which the electron beam is proj ected, there being no .hollow 2 bodies, co-axial lines or other resonating devices or circuits connected to the said grids for the purpose of determining the frequency of operation of the device.

The invention will be more clearly understood by reference to the following detailed description of preferred embodiments-ancltothe accompanying-drawingsin which:

Fig. 1 shows a side view of a velocitymodulation type of electron. discharge device. according to theinvention; V V

Fig. 2 shows .-av section at 2-2. of Fig. 1;-

Flg. 3-showsva perspective: view of the device of I Fig. 1 with the. envelopeand other parts broken away to show the .arrangementwmore clearly; and

Fig. 4 shows asectionview to illustrate a modified arrangement. of ltheinvention.

The embodiment shown in Figs 1, 22nd 3 will now be described; Thedevice-is-mounted on a stem l3 insidean evacuated: envelope; ll of insulating. material such as glass. The base [4 carries external pin term-inals I5 for the leads to the electrodes, which leads are sealedthrough-the stem l3-inthe usual-way.

The electrodes of the. device-are mounted between tWo-insulating plates l6 (shown cut away in .Fig. 3);,. and 1 1, which are themselves supportedonthestem. l3.. Fig. 2:shows clearly how the electrodes are" arranged- An electron gun system is located at one side and comprises a cathode 5 surrounded-in turn by the first and second grids l and 2. The gridq2 is used for accelerating. the electrons. and grid i for controlling and. modulatingthe beam. A shield- 6 is provided behind thegun systemfor absorbing electrons projected backwards. This shield: is shown-cut awayin Figs. land 3.

The. electrons projected from the gun encounter two more grids 3 and-4=arrangedone inside thecther, and are eventually refiectedback by a -platel arrangedwbehind the gr'idsi and 4. Some of the electrodes. justdescribed: are also visible in Figsrl: and 3 where they are designated by the same-reference numerals. The --cathode heater H- can be seen in Fig. 1 just below the cathode-5.-

'Eaehcof the grids- I to t is constructed inthe wellknownway by taking two parallel still wires and windingthereon anumberof evenlyv spaced. turns of .fine wire so: astto form a flattenedcoil,

each of the turns usually being afterwards firmly fixed to the supporting wires. This construction is shown clearly in Figs. 1 and 3. The wires 8 and H! on which the grid 3 is wound are continued upwards and are sealed through the envelope at I8 and 20 and constitute the two outer conductors of a three wire Lecher system. Similarly the wires 9A and 93 on which the grid 4 is wound are clamped and welded at 2i to the central wire 9 of the Lecher system, which is sealed through the envelope at l 9. The wires on which the grids l and 2 are wound are made only long enough to enable the grids to be properly located between the plates l6 and l! and to allow connections to be made to the lead out wires which pass through the stem l3.

The device operates in the following manner. Electrons leaving the cathode are accelerated by the grid 2 and pass through the grid 3, entering the electric field between grids 3 and 4. Assuming this electric field to be oscillating, the electrons will be acted upon in accordance with its direction and magnitude and their velocity on reaching grid 4 will be modulated in the well known manner. Bunchingtakes place in the field free space inside grid No. 4, and when the bunched electrons emerge therefrom on the opposite side, they interact with the oscillating field and give up their energy in such a manner as to maintain the oscillations. The reflecting electrode 1 is provided to increase the efficiency of the device. The potential of this electrode is adjusted so that the electrons are reflected back into the oscillating field in the proper phase to contribute their energy to the field. They continue to oscillate backwards and forwards until they are ultimately collected by the grids.

It will be observed that a tri-filer Lecher system isv used. It is electrically connected to the grids 3 and 4, and will be excited by the oscillations of the grids; the outer wires 8 and [6, which are both connected to 3, will be in the same phase, and the central wire 9 will be in the opposite phase. The system may be tuned by means of a sliding bridge in the well known-way.

A device as just described has been constructed to operate satisfactorily at a wave-length of about 10% cm.

A modified arrangement, which operates in a similar way, is shown in Fig. 4, which is a section view similar to Fig. 2. The construction of the device will be generally similar to that described in connection with Figs. 1 and 2, suitably adapted to the modifications. Corresponding elements have been given the same designation numbers as in Figs. 1, 2 and 3.

At the left-hand side of Fig. 4 is shown the electron gun system consisting of the cathode with its heater II and the two grids I and 2 which are exactly the same as before. The oscillating system, however, consists of three parallel grids 3A, 4, and-3B. Velocity modulation occurs between grids 3A and 4, bunching inside 4, andcommunication of energy to the field takes place between 4 and 3B. The reflector 1 in this case is generally cylindrical in shape, and almost completely surrounds the oscillating grids, a narrow opening being left opposite the gun asshown to-admit and define the electron beam. Noshield corresponding to 6 in Fig. 2 is requiredin this case, because the cathode is wide enough to absorb any returning electrons, the beam being limited by the aperture in hf The grid 4 is substantially the same as before, except that instead of continuing the stiff supporting wires upwards through the envelope in the manner shown in Figs. 1 and 3, one of them, for example 24, is continued downwards instead to make connection through the stem l3 to one of the terminals [5. The other wire is left only long enough for locating the grid between the plates [6 and i1, shown in Figs. 1 and 2.

The grids 3A and 3B, which correspond to the grid 3'in Fig. 2 differ from it in that in each of them, all the fine wires on one side are cut away after Winding to produce a single-sided grid, as indicated in Fig. 4. It is not essential that this should be done, but the extra wires serve no purpose and in fact tend to reduce the efliciency by collecting some of the electrons which would otherwise do useful work. The supporting wires 22A, 22B and 23A, 23B of the grids 3A and 33, respectively, are continued upwards through the envelope through suitable seals, and constitute a balanced two-wire Lecher system, the two conductors of which respectively comprise the pairs of wires 22A, 22B and 23A, 23B, and which may be tuned as usual by a sliding bridge. The two wires corresponding to each Lecher conductor are both brought out for convenience for connecting to a pair of parallel copper strips whose width is chosen so that the capacity between them is the same as that between the grids 3A and 3B, in order to eliminate undesirable reflections. One wire of each pair, for example 22A and 23A, could be cut short inside the envelope, if desired, and not brought out at all, but the efficiency of the device would be reduced. The grid 4 will be maintained at constant potential in order that the Lecher conductors may oscillate strictly in opposite phase.

Although the invention has been described for clearness in terms of particular embodiments, it

is not intended to be limited thereto, and various 0 modifications within its scope will occur to those grids including a first set of turns of wire forming a tubular shaped inner structure about said drift space, said turns of wire of said first set being electrically connected together, said wire grids further including a second set of turns of wire forming an outer concentric tubular shaped structure, the turns of wire of said second set being electrically connected together, said two sets of wire turns forming the cavity resonator there-between, an electron beam generator mounted to direct an electron beam along a path through said two sets of wire grids and through said drift space, and an envelope enclosing said resonator and said beam generator.

2. A velocity modulation device according to claim 1 in which said resonator comprises a plurality of parallel means supporting said wire grids and extending transversely to the direction of the beam path, said wire grids forming said inner grid structure comprise turns of wire about some of said supports, and said wire grids forming said outer grid structure comprise turns of wire about other of said supports.

3. A velocity modulation device according to claim 2 in which said turns of wire are connected electrically to said supports and said device further comprises a Lecher wire system extending 5 outsidesaid envelupe, one wire of said system ingmp extension of oiie of the supports for ith-e irgner igi id structure gtlier wire of said system mggain extension 0 e-pf the supports in miter gi'id structurel CHRISTORHER HENRY FOULKES.

REFERENCES CITED z '-'The 'tollowing refei'efices are of record in the m Bfilebf this patent::

JOHN HE ER FREMLIN.

UNITED STATES PATENTS Number Name Date Dallenbach Aug. 30, 1938 Hollmann 1- Mar. 28, 1939 Cage Feb. 3, 1940 Wolff July 16, 1940 Varian et a1 June 30, 1942 Black Dec. 29, 1942 Fremlin June 1, 1943 Fremlin Feb. 22 1944 Ryan Aug. 21, 1945

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