US2860280A - Electric discharge device and methods - Google Patents

Description

Nov. 11, 1958 E. D. MCARTHUR ELECTRIC DISCHARGE DEVICE AND METHODS 2 Sheets-Sheet 1 Filed Jan. 25, 1955 F mA C WM m0 xal/ 4 /7/'s Atzorney.

Nov. 11, 1958 E. D. MCARTHUR ELECTRIC DISCHARGE DEVICE AND METHODS 2 Sheets-Sheet 2 Filed Jan. 25, 1955 /nvenl0r. Elmer 0. Mc Arthur,

United States M Patent 9 ELECTRIC DISQHAR'GE DEVICE AND METHODS Elmer D. McArthur, Scotia, N. Y., assignor to General Electric Company, a corporation of New York Application January 25, 1955, Serial No. 483,943

8 Claims. (Cl. 315--5.46)

This invention relates to electric discharge devices and methods utilizing slow wave structures which may be either periodic or distributed in space. While the practice of this invention may be carried out with a large variety of electric discharge devices and slow wave structures, it can be suitably practiced by utilizing helical slow wave structures and will be particularly described in'that connection.

In conventional beam modulation type electric discharge devices theelectrons in the electron beam are velocity modulated by electromagnetic wave energy. Velocity modulation may be eifected by passing the electron beam through a resonant cavity which is coupled to an electron beam interaction gap so that electromagnetic wave energy within the resonant cavity interacts to vary the velocity of the beam electrons. The electrons are then permitted to drift through a substantially field free region to form electron bunches in accordance with the modulation. This electron bunch energy is extracted by passing the beam containing the bunches through a second electron beam interaction means to excite a resonant cavity and then extracting amplified wave energy from the cavity.

Beam modulating electron discharge devices of this type are commonly described as klystrons. In the multigap klystron or other electron discharge devices which extract amplified energy from electron bunches, one of the most serious limitations on gain and power conversion efficiency is the process known as debunching. This limitation is due to the internal, space charge forces of an electron beam which, by giving the beam elastic properties, prevent ideal axial compression of electrons into the desired dense electron bunches. These internal space charge forces are the result of the mutual repulsion of bodies having like charges, in this case, electrons in the beam.

Prior art methods of effectively minimizing the tendency of closely oriented electrons to debunch have in general been inherently complex and subject to a number of structural or circuit complications. For example methods and apparatus have been proposed which pro vide special electrically long accelerating fields to increase the average electron velocity over selected increments of the drift region and thereby effect enhanced bunching. Another proposed apparatus provides a drift region with a special retarding field to turn back slow moving electrons and thereby eifect relatively instantaneous conversion from velocity modulation to density modulation without the utilization of a standard length field free drift region. Other methods and apparatus incorporate various schemes to vary the effective electron transit time and thereby gain relatively good electron bunching. In accordance with an aspect of this invention relatively simple methods and apparatus are provided for achieving enhanced electron bunching.

Another feature of conventional electron beam modulated electron discharge devices is the utilization of an interaction gap to effect velocity modulation. Generally 2 a circular interaction gap is utilized and the limitations of such a gap are well known. If the ratio of gap diameter to gap length is large, the electric field is often so distorted that it is necessary to use special grids, which have many inherent complications, in order to obtain satisfac= tory electric field distribution across the gap. If the gap length is increased to lower this ratio, the resulting elec-' tron transit angle is increased with a corresponding reduction in the degree of coupling to the electron beam.

Therefore, it is an object of this invention to provide improved electric discharge devices and methods.

Another object of this invention is to provide im-' proved structures and methods for enhancing the gain and efiiciency of electric discharge devices.

A further object of this invention is to provide imtric discharge devices incorporating slow wave interaction structures whereby the bunching due to electron repulsion is effectively minimized and a growing wave of electromagnetic wave energy is obtained as a result of interaction between the slow wave structures. and an electron beam.

According to an important aspect of this invention there is provided an electric discharge device including means providing a beam of electrons. An electron beam interaction modulating means is coupled to the beam to j modulate the velocity of electrons in the beam in accordance with an applied signal whereby electrons in the beam tend to drift and form bunches corresponding to the signal. Electron beam interaction means are oriented in proximity to the beam to interact with the modulated electrons and aid the formation of electron bunches,

whereby the tendency of electrons in the beam to debunch due to mutual electron repulsion is effectively minimized.

The other objects and important aspects of this'invention will become apparent from the following specification and claims when considered in connection with the figures of the drawing in which Figure 1 illustrates a partially schematic exemplary embodiment of an electric discharge device incorporating this invention; Figures 2 and 3 illustrate curves useful in explaining a portion of the operation of this invention; Figure 4 is an elevational view in section of a modified form of my invention employing cavity-type input and output circuits in combination with a slow wave structure in the drift space; Figure 5 is a similar view of a still further modification of my invention in which both space charge and velocity modulation of the beam are effected at the input; Figure l 6 is a similar view of a tube which may be considered similar to a three-cavity klystron with active slow wave structures in the drift spaces; Figure 7 illustrates a further modification of my invention in which both a drift tube and an active slow wave structure in the drift space 1 which is heated by winding 13. Heater power is supplied from supply 14 through leads 15 and 16 which pass through glass seal 17. Mounting member 18 supports the cathode 11 and is sealed to glass tube 19 which in turn is hermetically bonded to end Wall 20 of resonant cavity 21. The electron beam 22 passes through cavity 21, cavity 23 and cavity 24 and is collected on collector 25. Resonant cavity 21 is defined by walls 20 and 26 and base wall 27. The cavity 21 incorporates resonant helix 28 and is tuned by plunger 29. Plunger 29 is actuated by rod 30 and is provided with wiper contact fingers 31 to effect electrical connection with the conducting walls of the cavity. Helix 28 is provided with coaxial input lead 32 for coupling electromagnetic wave energy to the helix.

Resonant cavity 23 incorporates substantially resonafit helix 33 and tuning plunger 34. This tuning plunger incorporates rod 35 and contact fingers 36 so that the entire cavity can be tuned to a desired operating frequency. Output cavity 24 incorporates resonant helix section 37 and tuning plunger 38 which is actuated by rod 39 and is provided with contact fingers 40. Electromagnetic wave energy is coupled from the output resonant cavity 24 by means of coaxial lead 41 which is connected to resonant helix 3'1.

The upper wall 42 in combination with end wall 43 completes the evacuated external structure which customarily is maintained at ground potential. The cathode 11 or the electron gun is maintained at a high negative potential by power supply 44, which, through tap 44, provides the necessary beam accelerating voltage for proper operation of this electron discharge device.

The electron discharge device illustrated in Figure l is essentially-a two gap klystron amplifier in which the input interaction gap has been replaced by a resonant helix, section and the output or energy extracting gap has been replaced by a resonant helix and furthermore in which the customary field free drift region has been replaced by a beam interaction slow wave structure, in this case, by helix 33.

The device illustrated in Figure l is operated by applying the necessary heater power to provide an electron beam through the resonant cavities and by applying sufiicient accelerating potential from power supply 44 so that the average velocity of the electrons in the electron beam 22 is approximately equal to the axial velocity of tin-electromagnetic wave traveling along the helical structures. The resonant cavities are tuned approximately to the mid frequency of the band 'over which the deviceis intended to be operated and electromagnetic'wave energy to be amplified is applied through coaxial lead 32 to'resonant helix 28. The electromagnetic wave energy on helix 28 in combination with the electromagnetic fields established in resonant cavity- 21, velocity modulate the electrons in beam 22 so that they tend to form bunches as they pass into the cavity 23. The velocity and density modulated electrons interact with-the helix 33 to establish a traveling electromagnetic wave on the helix which in turn interacts with the electron bunches to enhance the bunching and to form a growing wave of electromagnetic wave energy as each individual bunch travels from left to right through cavity 2 3 and to eifectively minimize the tendency of the electrons to debunch due to mutual repulsion of the electrons in the bunches. When theelectron bunches pass into resonant cavity 24 the cavity is excited and the electromagnetic waveenergy is extracted by means of resonant helix 37 and coaxial output lead 41.

It is therefore apparent that when a slow wave structure such as the helix 33 is used in this way there is provided a discharge device having an active drift space in contrast to the usual field free or passive drift space utilized in previously known velocity modulated beam type electron discharge devices. In addition, it is noted that the utilization of a resonant helix for the conventional interaction gap considerably lessens the aforementioned well known physical and electrical limitations of such gaps.

operated at a beam voltage of 1000 volts, at a center frequency of 1000 megacycles to result in a gain of the order of 20 decibels and efiiciency of the order of 30% over a frequency range of the order of :10%.

Figure 2 illustrates the desirable gain characteristicsavailable with structures in accordance with this invention. The ordinant of this curve where p corresponds to the average charge per unit length which equals I U where v corresponds to the alternating component of velocity which varies as and Where v corresponds to the average velocity of beam electrons.

It can be shown that the velocity modulated electrons in the electron beam and the resulting electron bunches induce electromagnetic fields in a slow Wave structure and if this structure is designed so that the induced fields are of such phase that they add to the original fields, the amplitude of the electromagnetic wave on the helix structure increases exponentially. This electromagnetic wave travels along the helix at a velocity approximately equal to the average electron velocity in the beam and the axial electric fields set up on the helix impart velocity modulation to the electrons in the electron beam which tend to drift and become density modulated by forming electron bunches.

If the induced fields on the helix are in opposite phase to the originally induced fields the Wave amplitude on the helix decreases exponentially. If the induced fields are degrees out of phase with the original field the wave neither increases nor decreases but travels unchanged along the helix except for that attenuation due to lossesin the helix. One wave only, the aforementionedexponentially increasing or growing wave providesthe desired signal amplification and the amplitudes and relative phases of these waves depend upon the initial or input conditions.

The initial or input conditions can be varied by varying the length of the input or resonant helix, the intermediate region between the input helixand the active drift region helix, and by applying, in proper phase, electromagnetic wave energy to the input helix and the drift region helix so as to obtain the desired growing wave of electromagnetic wave energy and to minimize the effect of the natural repulsion between electrons in the resulting bunches.

It can also be shown that when the initial electromagnetic wave energy injected into the drift region is entirely density modulated, i. e. the electrons are completely bunched and have substantially. no velocity components, the least desirable performance is obtained since there is a loss in the transfer of energy to the helix before any amplification takes place. This early loss can be .considerably reduced by applying the proper value of electromagnetic wave energy directly to the drift region helix to accompany the initially introduced density modulation so that space charge repulsion is more effectively nullified. In addition the application of .thiselectromagnetic wave energy to thehelix can becaused to result in substantial elimination of .the waves. on .the'

For example, the device illustrated in Figure 1 can be drift region helix which cause destructive interference with the desired growing wave. The desired rate of wave growth can likewise be achieved by properly combining velocity and density modulation to the electrons injected into the drift region helix.

Line A is representative of the maximum density current obtainable from a given velocity modulation in a field free region. Curve B illustrates the maximum available current density obtainable when the electron beam passing into the helix contains some electrons which are density modulated and some electrons which still have a velocity modulation component and curve C illustrates the maximum current density obtainable when electromagnetic wave energy is also applied directly to the slow wave structure.

It should be understood that all electrons passing an interaction gap are velocity modulated in accordance with the instantaneous electric field across the gap at the instant the electrons pass the gap, i. e. those passing the gap during the presence of a retarding field are slowed down and those passing during the presence of an accelcrating field are speeded up. These velocity modulated electrons when passed into a substantially field free .region, tend to form bunches, the degree of bunching being determined by the initial velocity of the electrons prior to entering the drift region and the natural mutual repulsion between bodies having like charges.

Therefore electrons having relatively higher velocities tend to form tighter electron bunches than those having relatively low velocities. A more satisfactory picture of this phenomenon may be obtained if the electron beam is considered to have certain elastic qualities wherein a relatively high speed electron tends to travel into an elastic medium a distance depending upon its initial velocity until it approaches sufficiently close to a region of charge having sufficient repulsion to slow the electron down to zero velocity. At this point in time the electron or group of electrons are said to be at a period of maximum density. In view of the relatively elastic qualities of the electron beam, the electron then tends to reverse its direction and the bunch expands or debunches.

At this instant in time, when the electron tends to reverse its direction so as to debunch, if an additional accelerating potential is applied, such as through the medium of a slow wave structure, the bunching can be increased and therefore the power available to be extracted from the beam can also be increased.

It can be seen that with a sufliciently long helix, enhanced bunching can be obtained over that obtainable in a field free drift region by the utilization of a slow wave interaction means such as a periodic structure or a continuous structure such as the herein illustrated helices. In addition, by applying electromagnetic wave energy directly to the helix a further enhanced growing wave of energy on the helix and a corresponding increase in maximum density current obtainable is observed as is apparent from curve C in Figure 2 of the drawing.

Increased enhancement of the modulation and of the electromagnetic fields interacting on the electron beam accompany the utilization of a helix and/or helix and resonant cavity structure which have a resonant mode at a frequency substantially the same as the center operating frequency.

In order to obtain an appreciation of the parameters associated with an interaction gap consider the basic relation,

i =fli where i is the current induced in the circuit, i is the alternating current available in the beam and 8 is the well known gap coefficient. From Equation 1 it is apparent that the available power, P is defined by the expression,

'where R is the gap load. A consideration of Equation 2 indicates that 13 R can be considered a figure of merit for the efiiciency of the entire system including the interaction gap and associated circuit.

Figure 3 illustrates how ,8, the gap coeificient, varies with 0 the electron transit angle across the gap in a conventional interaction gap and resonator. Since the transit angle must always be greater than 0 the gap coefficient must always be less than 1 so that the power conversion of the gap, even with the most ideal designs may be in the order of 0.5 to 0.6 of the available beam power.

In addition it is noted that in order to utilize easily obtainable beam current densities and still operate at high power levels it is desirable to use a relatively large diameter tube through which the electron beam passes and this necessarily results in considerable distortionof the electric fields across the tube particularly when the tube diameter is equal to or greater than the gap width.

Previously known methods and structures for obtaining a relatively uniform electric field distribution across the tube and a high gap coefficient have resulted in relatively elaborate and complicated structures which are expensive to produce and relatively difficult to manufacture in large quantities of uniform quality. Thus, the

' utilization of a helix provides a relatively uniform elecrim-0. aft-0. B l sln )+cos 6,, sm

ZV L 0,-0. 0.,+0.)

where the upper sign is taken for open helix gaps and the lower sign is taken for shorted helix gaps and where 0,=the electron transit angle E the amplitude of axial electric field in the resonant helix gap V =the gap voltage L=the gap length It is therefore apparent that the utilization of resonant helices and/or non-resonant helices can be utilized to obtain 7 highly efficient conversion of electromagnetic wave energy to velocity modulated electrons in an electron beam, to obtain a desired greatly enhanced growing electromagnetic wave along the drift region through which the velocity modulated electrons pass and due to the obvious reciprocity of the foregoing, to utilize helices both resonant and non-resonant to obtain optimum efficiency and gain in extracting amplified electromagnetic wave energy from an electric discharge device.

It will be readily apparent from the preceding -discus-..

sionthat the utilization of slow wave structures may be applied in whole or in part to velocity modulated electric For example, Figure 4 illustrates in' discharge devices. schematic form an electric discharge device consisting of resonant cavity 45 with electron beam interaction gap 46, active drift region 47 incorporating helix A8 and electron beam energy extracting resonant cavity 4i incorporating interaction gap 50. Electron gun 51 provides electron beam 52 which passes through the cavities 45, 47 and 49 and is collected by collector 53. Cavities 45,

47 and 49are grounded and maintained at a high posi enormou tive potential bypower supply SS a'ndma'y be tuned in any conventionalmanner'and/or as illustrated in Figure I l. Electromagnetic wave' energy toexciterreson'a-nt cavin accordance with the-signal applied 'by coaxial input 56. The velocity modulated electrons -dr-ift into active drift region 47 and interact with helix 48 to provide a growing 'wave along the helix which growing wave successively enhances the bunching ofelectrons along the beam path as these electrons travel from the cathode 'toward the collector and these bunches further enhance the growing wave on helix 48. In addition, the dimensions are so chosen as toeffect maximum bunching and to effectively minimize the tendency of the electrons to debunc'h due tothe natural electron repulsion between electrons. These bunches pass into theregion of res onant cavity 49 and in'passing through gap 50 to "collector 53 the bunches excite a standing wave field of electromagnetic energy in resonant cavity 49 so that electromagnetic wave energy in amplified form is extracted through coaxial output lead 57.

Figure 5 illustrates the application of an active drift region to further increase the efficiency of anelectron discharge device which may be termed a superbuncher type beam modulated electron discharge device. Superbuncher electron discharge devices utilizing substantially passive electron drift regions are more completely described in my copending application Serial No. 265,014, filed January 4, 1952, now U. S. Patent No. 2,793,316, entitled Methods and Translation of Electromagnetic Waves, and assigned to the same assignee as this invent1on.

Figure 5 illustrates electron emitting cathode 58 which produces a beam of electrons "5'9 which pass through control grid 60 and resonant cavity electron beam interaction gap grid 61, helix 62, electron beam energy extracting gap 63 in resonant chamber 64, and are collected by collector 65. Resonant chamber 66 can be provided with one or more tuning stubs and is excited by coaxial input lead 67. Output energy is extracted from output resonant cavity 64 by coaxial output lead 68. The control grid 60 is maintained at a negative potential with respect to the cathode and the remainder of the electron discharge device structure, which is maintained at a positive potential by power supply 69. Isolating capacitors 70 insulate the control grid from the cathode and from they drift region 71 for direct currents and provide a high frequency bypass.

This'e'le'ctric discharge device is operated by exciting I interaction with the helix 62 takes place in orderto obtain a growing'wave of electromagnetic Wave energy on the helix and a corresponding increased and enhanced electron bunching in the beam. The bunched electron beam excites the output resonator '64 to establish a standing wave of electromagnetic wave energy in the output resonator and this energy is extracted through coaxial coupler 68.

"Figure 6 illustrates a three gap electron beam modulated discharge device of the klystron type utilizing a helix slow wave structure in the drift regions. There -is provided cathode 73, electron beam :power supply .74 which provides an electron beam 75 which passes-through the discharge device andis collected on' collector 76. Elm- 8v. tromagnetic wave energy excites r-esonantcavity 77 :to

establish an electric :fieldacross gap 7-8 to velocity modulate electrons, in the electron beam-75. the electrons drift into active. driftregion 79 they tend to bunchrand also to interact with helix 80 in the previously described manner to form enhanced bunches of electrons.

As these electron bunches .pass across gap 81 in tertiary or fly wheel resonator 82 an electromagnetic oscillation is established in this resonator which, in a wellsk-nown manner interacts-with electrons in the electron 'beamrto further enhance'the electron bunching Thesefibunches then continue'todrift into second driftlregion 83tofurther bunch and to interact with helix 84. The. electron bunches then excite output resonator 85 by establishing- .an electric field across gap 86 so that electromagnetic wave eneregy in amplified form can be extracted thriough output coaxial coupler -87.

It is readily apparent that anyone or all ofthe regions and gaps illustrated in Figure 6 can be provided'with auxiliary tuning means such as shorted .stub's and/ or. plungers and that the helices can be provided .in the form of resonant helices or that there may be substituted therefor other well known forms of slow wave structures either of a continuous type such as the herein illustrated helix or of a periodic type such as any of theimany well known interdigital or labyrinth slow wave-structures. Alternatively, a resonant helix or a plurality of resonant helices may be substituted for the resonant chambersand interaction gaps to obtain the aforedescribed benefits of resonant helices. l

Figure 7 illustrates an embodiment which 't-ak-es'advantage of the fact that the greatestainitial rise inwradio frequency beam current can be shown to occur when density modulation of the electrons in the electron beam is accompanied by both velocity modulation and ,direct radio frequency excitation of the helix .in proper combination and phase to excite only a growing Wave. :In this structure there is provided beam power supplyv88 and cathode 89 which provides an electron beam 90 which travels through the interaction device and is collected on collector 91. Electromagnetic wave energy is introduced into cavity 92 by means of input coaxial coupler 93. Cavity 92 is made resonant and helix 94 can be designed to be resonant in a mode which interacts with the dominant mode of resonantchamber 92 orto have a resonant mode which is substantially independent of this dominant mode.

Electromagnetic wave energy introduced through coaxial coupler 93 excites a standing wave in chamber and causes an'ele'ctric field to be established across gap 95 which velocity modulates the electrons in electron beam 90. These electrons then drift into drift tube 96,' which may be supported from the side wall by dielectric support members 97, and start to form into bunches. The

3 length of drift tube 96 is so designed that there is the proper amount of velocity and density modulation-of the electrons in the electron beam at the instant they leave the end of drift tube 96 and enter into helix"-94.'

The electron bunches and velocity modulated electrons then interact with helix 94 and the electromagnetic wave energy traveling along 94 .as a result of direct helix energization from the. cavity. This results 'in a greatly enhanced growing wave traveling along helix 94 and resulting maximum enhancement. of the. electron bunching and a nearly-complete effective elimination of the tendency of the electrons to debunch due to mutual repulsion jet-- fects. That is, the relative phasing of the wave energy on the helix and the bunching and velocity modulation of the electrons in the electron beam is such that there only remains a growing wave of energy such that the: maximum possible bunching of the electrons in the elec-' tron beam is accomplished before they enter into output resonant cavity 98.

The bunches in passing-across; gap 99 excite resonant When a standing wave of electromagnetic wave energy is established in resonant cavity 105 an electric field appears across gap 106 to velocity modulate electrons in electron beam 107. These velocity modulated electrons drift into the active drift region 108 which consists of folded wave guide section defined by partitions 109, 110, 111, 112, 113 and 114. This folded wave guide structure is tuned by means of tuning plunger 115 which is actuated by rod 116 and makes electrical contact with the side walls by means of spring contact fingers 117. The electron bunches excite gap 118 of resonant cavity 119 so that electromagnetic wave energy can be extracted through output coaxial lead 120.

It is readily apparent that the slow wave structure illustrated in Figure 8 provides the same general type of interaction as do the helices utilized in the previously described examples. This structure can be tunable or may be utilized in a relatively broad band form wherein no specific tuning means is provided.

Furthermore, the slow wave structure can be provided with external means of applying electromagnetic wave energy directly to the slow wave structure so as to obtain a more greatly enhanced growing wave throughout the drift region 108 and resulting increased bunching of the electrons. In addition it should be noted that other input means for modulating the electrons in the electron beam and extracting the energy from the electron beam may be utilized such as, for example, the aforedescribed helices.

From the foregoing it will be readily apparent that there have been described only a few of the very large number of forms which this invention may take. For example, the embodiments herein illustrated will readily suggest any number of combinations of means of modulating the electrons in an electron beam and enhancing this modulation to obtain high gain and high efficiency electric discharge devices.

In addition, the examples of coupling to the beam as by means of coaxial input and output conductors are given merely by way of example, since it will be readily apparent that other means such as wave guides can equally well be used. In addition only a few of the many varieties of slow wave structures which can be used to couple to the beam and to enhance the modulation of the beam have been described since the teachings of this invention can be carried out with any one type or a combination of types of slow wave structures wherein there is interaction with the electrons in an electron beam to result in an electric discharge device having enhanced gain and efliciency.

Therefore, it is intended in the appended claims to cover all modifications and variations which come within the true spirit and scope of this invention.

What I intend to claim and protect by Letters Patent of the United States is:

1. A high frequency electric discharge device comprising means for establishing an electron beam along a predetermined path, an input structure resonant at a predetermined frequency including spaced conducting members positioned transverse to said predetermined path and apertured for the passage of the beam and a helix extending between said transverse members so that said input structure is in energy exchanging relation with the beam, input means exciting said input structure at a frequency near said predetermined frequency for modulating the beam in accordance with an input signal im- I10 pressed on said input means and a conductive structure spaced along the beam path from said input structure and supported for interaction with the modulated beam'for extracting energy therefrom in accordance with the modulation produced by said input circuit.

2. A high frequency electric discharge device amplifier comprising means for establishing an electron beam along a predetermined path, a conductive structure sup ported in energy exchanging relation with the beam and providing an input circuit for modulating the beam in accordance with an input signal impressed thereon and an output circuit including a pair of spaced transverse walls apertured for the passage of the beam and a helix extending between said transverse walls and therewith constituting a resonant circuit resonant at a predetermined frequency and supported for interaction with the modulated beam for extracting energy therefrom in accordance with the modulation produced by said input circuit.

3. A high frequency electric discharge device amplifier comprising means for establishing an electron beam along a predetermined path, a conductive structure supported in energy exchanging relation with the beam and providing an input circuit for modulating the beam in accordance with an input signal impressed thereon and an output circuit including a pair of transverse conducting members apertured for the passage of the beam and a slow wave structure positioned between said transverse members and constituting therewith a structure resonant at a predetermined frequency, said structure being supported for interaction with the modulated beam over an extended length thereof for extracting energy therefrom in accordance with the modulation produced by said input circuit.

4. A high frequency electric discharge device comprising means for establishing an electron beam along a predetermined path, a first conductive structure supported in energy exchanging relation with the beam for modulating the beam in accordance with an input signal impressed on said structure, a second conductive structure supported in energy exchanging relation with said beam at a region thereof spaced from said input conductive structure for deriving energy from the beam and energizing an external load circuit and a circuit intermediate said first and second conductive structures and including a pair of transverse conducting members spaced along the beam path and a helix extending between said members and constituting therewith an extended structure resonant at the operating frequency of the deviceand supported in energy exchanging relation with said beam over an extended region intermediate said first and second conductive structures for enhancing the bunching of electrons initiated by the modulation produced by said first conductive structure.

5. A high frequency electric discharge device comprising means for establishing an electron beam along a predetermined path, a first conductive structure supported in energy exchanging relation with the beam for modulating the beam in accordance with an input signal impressed on said structure, asecond conductive structure supported in energy exchanging relation with said beam at a region thereof spaced from said input conductive structure for deriving energy from the beam and energizing an external load circuit and a circuit intermediate said first and second conductive structures and including a pair of transverse conducting members spaced along the beam path and a slow wave structure extend-- ing between said members and constituting therewith an.

extended structure resonant at the operating frequency of the device and supported in energy exchanging relation with said beam over an extended region intermediate said first and second conductive structures for enhancing the bunching of electrons initiated by the modulation produced by said first conductive structure.

6. A high frequency electric discharge device com-- aaenpao prising means for establishing an electron beam along a predetermined path, a ifirst conductive structure supported in energy exchanging relation with the beam for modulating the beam in accordance with an input signal impressed on .said structure, :asecond conductive structure supported in energy exchanging relation With said beam at a region thereof spaced from said input conductive structure .for deriving energy-from the beam and energizing an external load circuit and a slow Wave structure including transverse conducting walls separating said slow waveistructure from said first and second conducting structures and resonant at the operating frequency of the device, said slow wave structure being supuported in energy exchanging relation with said beam "over an extended region intermediate said first and second conductive structures for enhancing :the launching of electrons initiated by :the modulation produced by said first conductive structure.

7. A high frequency electric discharge device comprising means for establishing an elongated electron beam along apredetermined beam path, .an input :circuit including a pair of transverse conducting walls and a helix extending therebetween, said input circuit being resonant at -a predetermined frequencysupported :in energy exchanging relation with the beam for modulating the beam in accordance with an input signal impressed on said helix, an output circuit including a pair of transverseconducting walls and a helix extending therebetween, said output circuit being resonant at said frequency'and supported in energy exchanging relation with the beam at a region thereof spaced from said input helix and a third circuit including a pair of transverse conducting walls spaced along the beam pathand a helix 12 extending therebetween, :said third circuit being resonant at said frequency positioned in energy exchanging relation with the beam over an extended region thereof intermediate said first and second helices.

8. .-A .high frequency electric discharge device comprising means for establishing an elongated electron beam along a predetermined beam path, an input circuit including a pair of transverse conductive members and a slow wave structure extending therebetween, said input circuit :being resonant at a predeterminedvrfrequency supported in energy exchanging relation with :the beam for modulating the beam in accordance with an input' signal impressed on said slow wave structure, an output circuit including a pair of transverse conductive unembers .and a slow wave structure extending therebetween,

said output circuit being resonant at said frequency supported in energy exchanging relation with the beam at a region thereof spaced from said input structure :and a third .circuit including a pair of transverse conducting walls spacedalong the beam path and .a slow wave structure extending therebetween, said third circuit being resonant at said frequency positioned in energy exchanging relation with .the beam over an extended region thereof intermediate said first and second structures.

References Citedzin the file of this patent UNITED STATES PATENTS 2,595,698 Peter May 6, 1952 2,681,951 Warnecke et .al. June 22, 1954 2,708,236 Pierce May 10, 1955 2,740,917 Haefi Apr. 3, 1956

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