US2275480A - High frequency electrical apparatus - Google Patents

Description

10, 1942. 'v ET 2,275,480

HIGH FREQUENCY ELECTRICAL APPARATUS Filed Jan. 24, 1940- 4 Sheets-Sheet 1 1x1 EN TORS RUSSELL H. VAR/AN WILLIAM \M HANSEN LINDSAY IVLAPPLZGATE BY ATTO NEY.

March 10, 1942. R. H. VARIAN ET AL 2,275,480

HIGH FREQUENCY ELECTRICAL APPARATUS Filed Jan. 24, 1940 4 Sheets-Sheet 2 INVENTORS Russsu. H. VAR/AN WILL/AM W HA NSEN zlrvisxlyA PLEGATE BY TTOR EY.

March 10, 1942. R. H. VARIAN ETAL HIGH FREQUENCY ELECTRICAL APPARATUS Filed Jan. 24, 1940 4 Sheets-Sheet 3 INVENTORS RUSSELL H. l AR/AN WILL/A M WHA NSEN INDSAY A PLE GATE B Y ATTOREY.

Patented Mar. 10, 1942 HIGH FREQUENCY ELECTRICAL APPARATUS Russell H. Varian and William W. Hansen, Stanford University, Calil'., and Lindsay M. Applegate, Portland, Oregn, assignors to The Board of Trustees of the Leland Stanford Junior University, a corporation of California Original application Marclrl, 1932, Serial No.

Divided and this application January 24, 1940, Serial No. 315,324.

4 Claims. (Cl. 250-36) The present invention relates, generally, to the control of electron beams by electromagnetic fields for the excitation of electric circuits,;.and has reference, in particular, to novel electrical high frequency apparatus in which electron beams are subjected to displacement by electromagnetic fields confined in hollow conductors or in conductor arrangements capable of maintaining standing electromagnetic waves.

The present invention is a division of our copending application, Serial No. 193,268, filed March 1, 1938, for High frequency electrical apparatus. The embodiments of the present invention utilize some of the elements of co-pending patent applications Serial No. 92,787, William W. Hansen, filed July 27, 1936, now Patent #2190712, February 20, 1940, and Serial No. 168,355, Russell H. Variarnfiled October 11, 1937, Patent No. 2,242,275, to which applications the present invention is related.

In Patent No. 2,190,712 there is discloseda hollow conducting resonant chamber of novel type having characteristics that render the same particularlyadaptable to use in providing oscillating circuits having frequencies of the order of cycles'or more per second. When operating at frequencies of the order of 10 cycles per second such resonant circuits are of outstanding importance. In the present invention this type of circuit is used as shown in the drawings because of its convenience and usefulness. The present invention can be embodied without the special resonant circuits of the Patent No. 2,190,712 but not in general without some sacrifice of convenience and efiiciency. The enclosed resonant circuit of Patent No. 2,190,712 has come to be known by the name rhumbatron, a word coined from Greek words meaning rhythm and thing. The resonator of Patent No. 2,190,712 is essentially a hollow chamber with conducting walls capable, together with coupled apparatus,

of sustaining electromagnetic oscillations as a very efiicient resonant circuit. It is distinguished from other types of oscillating circuits by its mode of operation even more than by its appearance. It operates so that an electromagnetic field is produced inside the closed conducting chamber by currents confined to the walls of the chamber surrounding the contained field. In the following description, the word "rhumbatron will be used to designate a resonant circuit of the type shown in Patent No. 2,190,712.

In Patent No. 2,242,275 there is disclosed means for controlling a beam of electrons by causing it to pass through an electric field, particularly a field with its electric component parallel to the axis of the electron beam to which is parallel also the axis of a resonator containing the field. Such a beam is made to produce radio frequency oscillations. That invention includes among other things the combination of a resonator and a beam of electrons passing through it for control purposes. The present invention uses this combination in some embodiments thereof. The invention of Patent No. 2,242,275 has come to be known by a coined word klystron derived from two Greek words meaning waves breaking on the beach and thing."

This invention has for its principal object the provision of a novel high frequency electrical apparatus adapted for the excitation of electric circuits by periodically transversely, radially, or rotationally displacing an electron beam, the displacement of which requires less power than that rendered available as high frequency energy as the result of the deflection of the beam, whereby the energy of an electron beam is converted into an alternating current of any desired high frequency.

Another objectv of the present invention is to provide novel apparatus for the control of electron beams by causing transverse types of displacement, resulting in the excitation of circuits by beams periodically transversely displaced, and the amplification of power by the use of transversely displaced electron beams in suitable circuits.

Still another object of the present invention is the provision of a novel high frequency electrical apparatus with associated circuits for performing all the principal functional operations ordinarily associated with the generation, amplification, modulation, transmission, reception and detection of high frequency oscillations.

Other objects and advantages will become apparent from the specification, taken in connec tion with the accompanying drawings wherein the invention is embodied in concrete form.

In the drawings Fig. l is an embodiment in which an electron beam is initially given lateral displacement by a hollow resonator, and electric fields are then used to change the velocities of the electrons of the beam thereby converting transverse movement of the beam to density modulation of the electrons and then absorbing energy from the beam by use of a second hollow resonator.

Fig. 2 is an embodiment of our invention and a showing of one of its applications in which an electron beam is laterally displaced in an electric .space between grids and 6.

field so that the energy of which beam is absorbed in maintaining an electromagnetic field in a hollow resonator, which field is used for accelerating electrons.

Fig. 3 is a simplification of the structure of Fig. 2.

Fig. 4 is an embodiment in which an electron beam is given periodic lateral displacement and caused to enter a resonator at an oblique angle to set up and maintain oscillations therein.

Fi 5 is an embodiment in which an electron beam is given simultaneous transverse and rotational velocities in a steady magnetic field superimposed on a hollow resonator electric field, and

Figs. 6, 7, and 8 are details of construction. Similar characters of reference are used in all of the above figures to indicate corresponding parts. In Fig. 1 an electron source I emits a beam of electrons 2 that is accelerated toward the wall of a resonator 3 and into which it passes through a grid III in the resonator wall. An electric field is produced between faces 4 and 4' of resonator 3. The resonator beam passes between the faces 4 and 4', whereby an oscillating electric field is impressed upon the electron beam acting to deflect the electron beam first toward the face 4 and then toward .the other face 4'. The beam traverses member3 and exits through grid opening 5 where it enters an electrostatic field between grid 5 and an oblique grid 8 maintained by the battery shown. A second electrostatic field is maintained between another oblique grid 1 and a transverse grid 8. After leaving the field through grid 8 the electrons enter an alternating I field between spaced grids II of a second resoent from that of grids 5 and 8, preferably only slightly positive in reference to the electron emitter. An electron entering the field between grids 5 and 6 is either accelerated or decelerated depending upon the relative polarity of grids 5 and 6. For convenience it will be assumed that grids 6 and 1 are negative in respect to grids 5 and 8. Then an electron will be decelerated in the space between grids 5 and 6. Its velocity will be unafiected between grids 6 and 1 and it will be accelerated between grids 1 and 8. The resultant change in velocity between grid '5 and grid 8 will be zero. However, the time taken by an electron in transit from grid 5 to grid 8 will vary depending upon its transverse position in the fields the electron traverses. If it is toward the .left side of the beam as represented in the drawing, and grids 6 and l are negative with respect to grids -5 and 8, the electron is very quickly decelerated and it travels at the reduced velocity the comparatively long distance from grid 6 to grid I. Between grids and 8 it is quickly accelerated to its original'speed. If it is located toward the right side of the beam the electron will be more gradually decelerated in the It will travel a relatively short distance between grids 6 and l at the reduced speed and it will be relatively slowly accelerated to its original speed between grids I and 8. Thus, it will take lesstime for the electron to go from grid 5 to grid 8 in a region where grids 6 and I are close together than where they are farther apart. The reverse is true if the outer grids are made negative and the inner ones positive. When the electron beam is oscillating laterally some electrons will get from the emitter to the region beyond grid 8 in less time than others. The result is that the transit time from grid 5 to grid 8 is a function of beam deflection, and it is possible for electrons leaving grid 5, after some other electrons, to have a shorter travel time between the emitter I and grid 8 and to arrive at grid 8 at the same time as those that left the emitter earlier, thus forming a periodic electron concentration. This has the efiect of making the electron stream where it leaves grid 8 periodically non-uniform, that is, grouped or bunched." The electron beam travels on and enters the field between the spaced grids I lof a resonator 9' which is caused to oscillate by the bunched electron beam as contained in Patent No. 2,190,712. In the terminology used herein in apparatus of this kind, the means included'between the emitter I and grid 8 in Fig. 1 is called a "buncher." Its function is briefly set forth as that of converting a substantially uniform electron beam, or one varying at low frequency, into one that varies in density, that is, grouped, at high frequency. The oscillating resonator 9 delivers energy to the buncher through the interconnected coupling loops I2 and I3.

Another embodiment of our invention using an electron beam given periodic transverse displacement for control is shown in Figs. 2 and 3. In Fig. 2 a beam of electrons is accelerated from an emitter 2| by a grid 22 and is projected between a. pair of deflecting p1ates'24 and 25 into a resonator 26 where the electrons impinge alternately on two plates 21. and 28 after entering through grid 38". The electron beam is shifted from one plate to the other by an alternating field caused to exist between plates 24 and 25 which receive excitation from a loop 29 inside resonator 26 and a symmetrically arranged pair of leads 3| and 32 outside the resonator. These leads would ordinarily be close together or in the form of a concentric line but are shown-far apart for convenience in the drawings. The energy of the electron beam is coupled into the resonator 26 by a pair of coupling loops 33 and 34 connected to the plates2'l and 28.

The process of oscillation of Fig. 2 and Fig. 3 is similar to that of Fig. 1 except that in Figs, 2 and 3 the electron beam energy is absorbed alternately in the fields between grid 38" and the plates 21 and 28, conveying pulses of energy alternately to the coupling loops 33 and 34. The arrangement provides a pulsation of current in the loops 33 and 34 every half cycle, the alternate pulsations being of opposite polarity.

Resonator 26 is illustrated as a right circular cylinder whose axis is horizontal and transverse of the figure. The faces 30 and 30' in such case are circular and they are at a uniform distance apart as the heads of a drum. The openings where the electron beam 23 enters are in the curved side of the drum-shaped container. In it, the electric field exists most strongly in the center extending from side to side in the figure, across the space between the two sides 30 and 30. The magnetic field in the resonator at a section corresponding to that of .the plane of the drawing exists perpendicularly to the plane of the drawing and is strongest at the curved sides of the resonator,-where it is interlinked with the coupling loops. The elements 2| to 34, inclusive, cause, as a result of powerful oscillations in the resonator 25, high differences of potential to exist between the side'36 and side 36 of the resonator 26. This difference of potential is used to accelerate electrons to high velocity for various applications one of which is illustrated.

An electron emitter 4| and an accelerating grid 42 project a stream of electrons 43 between two deflecting plates 44 and 45 into the resonator 26 through an opening in the side 30. If the resonator is oscillating, the plates 44 and excited thereby will swing the beam of electrons 43 back and forth so that during alternate half cycles the electrons. will alternately miss and enter the hole 35 in the side 30 of the resonator. The polarity of the plates 44 and 45 is arranged so that the electrons enter and pass through the resonator during the half cycles when the integrated value of the accelerating force on an electron is a maximum. This occurs generally when the electrons are admitted to the hole 35 of resonator 26 just as the other side 30 thereof begins to accumulate a positive charge. The potential difierence between the grid 42 and the emitter 4| is made great enough so that the electrons enter the resonator with a fairly high velocity and preferably of the order of ninetenths of the velocity of light.

The dimensionof the resonator 26 from the side 36 to the side3fl is made a little less than the distance a particle with the speed of light will travel in a half period of the resonator oscillation. Thus, any electron whose velocity approaches that of light can make several circuits from side to side of the resonator 26 and back without getting out of phase with the oscillations of the system inasmuch as the maximum velocity any electron can attain will be less than that of light. An electron admitted to the resonator through the hole 35 crosses the resonator and reaches the side 36' in about a half period. It passes through the hole 36 and enters the field of a magnet 46 where its motion is reversed. The electron, after the direction of its motion has been reversed by the field of magnet 45, re-enters the resonator 26 through a hole 36. The electron then travels back to the side 30 and through a hole 35 in the next half period and is reflected again by a second magnet 41. This is repeated "as many times as required to get the electron velocity desired. In Fig. 2 there are three reflections at the side 36' and two at the side 30 of the member 26. After the last reflection at the side 30' the electron passes through an aperture 35" in side 36 and passing below magnet 41 impinges upon a target 48 where the impact is shown as producing X-rays.

Fig. 3 shows an arrangement for producing X-rays using only a single. trip of the beam through the .resonator 25 for the acceleration of electrons. The structure of Fig. 3 is similar to that of Fig. 2 except for the different mechanical arrangement resulting from the omission of the magnets 46 and 41.

In Fig. 4 the interaction of a periodically transversely displaced uniform electron beam and an electric field obliquely disposed relative to the axis of the beamexcites a circuit connected with the electric field. In this figure a beam of electrons is produced by an emitter 5|, accelerated by a grid 52, and projected between a. pair of deflecting plates 53 into an electric field between a grid 54 and a plate which are parts of a resonator 56. The plates53 are excited by connection to a coupling loop 51 in the resonator.

In operation, the electron beam swings back and forth between the plates 53, from left to right and reverse ln-the drawing. The dimensional relationships of the principal parts of the arrangement shown in Fig. 4 are such that the difference between the time of travel of an electron from the plates 53 to the edge of grid 54 at the left side of the beam and the time from plates 53 to the edge of grid 54 at the right side is about equal to the time required for the electron beam to sweep, over the grid from the left end to the right end. The effect is that during the half cycle when the beam swings from left to I right the electrons projected toward the grid 54 as the beam moves toward the right will all arrive at the grid at about the time the beam has reached the right hand edge of the grid 54.

Thus, a large number of electrons enter the fleld between the grid 54 and the plate 55 in an interval only a fraction of a half period long. As the beam moves back toward the left, the distances the electrons have to travel to get to the grid 54 increase with the time so by the time the beam has reached the left edge of the grid 54 all the electrons to the right of the beam will have entered the field between grid 54 and plate 55. The effect is that during the half cycle of beam shift from left to right the entrance of the electrons into grid 54 is delayed to the end of the half cycle but that during the half cycle while the beam travels from right to left there is no delay. Accordingly the entrance of electrons into the field between grid 54 and plate 55 is accomplished at the beginning of and during alternate half cycles. This is the same in efiect as if the electrons were delivered in a bunch each cycle, and is-of course a condition sufiicient for the excitation of a resonant circuit.

It will be noticed in Fig. 4 that the grid 54 and the plate 55 are shown curved, although they may be made straight. The straight lines are the most convenient to make and are sufiicient for operation; but when it is desired to regulate the relationship of the time of entry of electrons along the grid 54 in regard to the time the beam arrives in its transverse motion at specified places along 'the grid, the grids are curved to accomplish the desired tim relationship and to increase the efficiency of utilization of the beam. In the illustration, the sinusoidal curve is intended to make the bunching more sharply defined by having the rate of change of distance from plates 53 to grid 54 inversely proportional to the velocity of sweep of the beam in its transverse movement. This is somewhat sinusoidal, as in simple harmonic motion, and accordingly the curve of the grid 54 and plate 55 surfaces is of sinusoidal form. The principles of excitation involved in resonator 56 are similar to those in resonators of Ser. No.'193,268 and 9 in Fig. 1 and are explained with reference to the above referred to patents and co-pending applications.

In Figs. 1 to 4 we have shown our invention in embodiments in which electron beams were accelerated transversely and radially. A third type of acceleration is shown in Figs. 5 to 8 in which rotational transverse velocities are imparted to the beam. A stream of electrons is accelerated from an emitter 6| through an electrode 62 and through an evacuated tube 63. The tube 53 extends through a magnetic field parallel to the tube axis and of uniform strength across the tube. the magnetic field being produced between the poles G4 and 65 of a magnet 65. Superimposed on the magnetic field at right angles to it there is an alternating electric field produced by an oscillating resonator 61, excited by a cou-- pling coil 68. Where the tube 63 passes through the magnet poles 64 and there are coils 69 and 1| concentric with tube 63 that are to maintain uniformity of field in the direction of'the length of tube 63 over the entire cross-section of the holes where the tube 63 goes'through. These coils make it possible to have a uniform magnetic field with the magnetic flux in the direction of the axis of the tube 63 over its entire cross-section. Facing the end of the tube 63 where it leaves the magnet pole 65 there is a plate 12 with a hole 13 in it. Beyond plate 12 is a solid plate 14. These two plates are enclosed in an enlarged extension of tube 63. Plates 12 and 14 are connected to an amplifier 15 that can be of any suitable form or it can be a receiver 16,

shown in Fig. 6. The plate 12 is made either with a round hole 13 as shown at Fig. '7 or with a hole of approximately semicircular shape as shown at Fig. 8.

In the operation of the system shown in these figures, a beam of electrons is projected from the emitter 6| toward the plate 12 with a velocity depending on the size of the apparatus but corresponding to a few hundred volts or more. The beam is made so it is projected nicely through the tube 63 without undue spreading. If it is formed of substantially parallel rays, it will not be affected appreciably by the magnetic field which, as specified, has its fiux lines'parallel to the axis of the tube 63'. When a signal of suitable frequency is introduced into the resonator 61 an alternating electric field is produced at right angles to the magnetic field and to the axis of the tube 63. In the drawing the direction of the magnetic flux is indicated bythe arrow field subjects them to a rotating effect of the magnetic field so the electrons move up and sidewise and down and toward the other side. The result is that as they move through the tube 63 they are subjected repeatedly to simultaneous vertical and horizontal acceleration transverse to their direction of movement and as a con-- sequence are accelerated in a helix of continuously increasing radius.- By the time the electrons leave the tube, 63 they will have a considerable velocity of rotation'and the beam of electrons will produce a rotating spot following a circular path on plate 12 about the axis of the tube 63 and the hole 13. The radius of the rotation will be a function of the strength of the signal introduced into the resonator 61 by loop 68. Tube 63 is subjected inside to the effects of space charge resulting from the presence of the electron beam and unless measures are taken to avoid it the tube may become objectionably charged on its inner surface. To avoid this we coat the tube inside with a conductingmaterial having high resistance but with sufiicient conductivity to carry away the electrons that stop on the tube surface. This prevents inner surface charge but does not impair the insulation character of the tube generally.

The apparatus is proportioned preferably so that with no signal in resonator 61 the beam of electrons goes straight through the hole 13. If a round hole is used as at Fig. 7 it is made pref erably of the same diameter as the beam so the beam will just fill it. Then when a signal is introduced, the beam begins to rotate and extend partially or wholly beyond the circumference of the hole with the result that less of the electrons go through the hole than when the signal is zero. Consequently the portion of the electrons that go through the hole 13 will be a function of the signal strength. With a strong enough signal the beam may rotate around the outside of the hole missing it entirely. The electrons that enter the hole 13 will produce a field between the plates 12 and 14 proportional to the number that get through. The variation of this field can be amplified as desired by the amplifier 15. The collection of electrons by the plate 12 produces a unidirectional pulsating current that is a function of the strength of the signal in resonator 61. The increase in current from plate 12 is accompanied by a corresponding decrease in current from plate 14. This is the condition necessary and sumcient for signal detection. An alternative form for hole 13 is as shown at Fig. 8 as a semicircle. The beam may be adjusted relative to the hole so that it is obstructed by the part of the plate 12 bounding the diameter of the hole 13. Then when a signal is impressed on the resonator G1 the electron spot rotates partly or entirely crossing the boundary of the hole and letting electrons enter the hole periodically thus producing a pulsating direct current which may be used for exciting a resonator in the manner shown in Ser. No. 193,268 such resonator energizing loop 68. The number of electrons thatgo through the hole will be a function of the signal strength. The shapes of hole described are only two examples of a great variety possible. If a plurality of holes are used in a circle swept by the rotating beam, the frequency of undulations impressed between plates 12 and 14 will be a multiple of the signal frequency of resonator 61 and frequencies can be multiplied accordingly.

As many changes could be made in the above construction and many apparently widely difierent embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. The method of exciting an electric circuit which consists of projecting a beam of electrons through a substantially unvarying magnetic field and an alternating electric field superimposed on it and perpendicular to it with the magnetic force vector of the magnetic field parallel to and concentric with the axis of the electron beam,

thereby producing in the electron beam rotat onal velocities, causing the rotation of the cam to regulate the entry of its electrons into a second electric field producing in the second field fluctuations which are a function of the strength of the first electric field.

2. The combination of means for producing a beam of electrons, means for producing a substantially unvarying magnetic field having its magnetic axis parallel to the axis of the beam, and resonant circuit means for producing an alternating electric field superimposed on and in quadrature with the magnetic field, the two fields coacting to impart spiral rotation to electrons in the electron beam.

3. The method of producing rotation of the point of intersection of an electron beam with a plane comprising projecting a beam of electrons along the axis of a magnetic field, such field having substantially uniform intensity over at least a part of the path of said electron beam, subjecting the electrons of said electron beam to the action of a sinusoidal electric field transverse to the motion of the electrons of said electron beam and relating the strength of the said magnetic field to the frequency of said transverse electric field so that the electrons of the beam follow a spiral path, the frequency of rotation of electrons while traversing their spiral path being equal to that of said transverse electric field.

4. The combination of means for producing an electron beam, means for producing a nonvarying magnetic field with its axis substantially parallel to the axis of said electron beam, means for producing an alternating electric field having a component substantially perpendicular to the axis of said electron beam, means for regulating the strength of said magnetic field and the frequency of said alternating electric field so that the electrons of said electron beam take a spiral path, whereby the electron beam is caused to have a circular motion with respect to its initial axis, the frequency of said circular motion being substantially the same as that of said alternating electric field, and means for segregating the electron of the beam in accordance with the amplitude of such circular motion.

RUSSELL H. VARIAN.

WILLIAM W. HANSEN.

LINDSAY M. APPLEGATE.

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