US3593057A

US3593057A - Injected beam crossed-field amplifier employing rf control of the injected beam current

Info

Publication number: US3593057A
Application number: US664686A
Authority: US
Inventors: George Berstein; Hunter L Mcdowell
Original assignee: Individual
Current assignee: Individual
Priority date: 1967-08-31
Filing date: 1967-08-31
Publication date: 1971-07-13
Anticipated expiration: 1988-07-13

Abstract

An injected beam crossed-field amplifier is disclosed. The crossed-field tube includes a cylindrical nonemitting cathode sole electrode structure surrounded by a concentrically disposed slow wave anode circuit to define a magnetron-type interaction region in the annular space therebetween. An electron gun assembly is disposed at one end of the magnetron interaction region for injecting a beam of electrons into the magnetron interaction region axially thereof. A beam collector structure is disposed for collecting the electron beam after passage thereof through the magnetron interaction region. Radio frequency wave energy to be amplified is applied to the annular slow wave circuit, such circuit including a circuit sever to prevent reentrance of the wave energy on the circuit and to provide a drift space for debunching of the reentrant electron beam. By passing the electron beam through the magnetron interaction region to a collector structure, the dynamic range of the amplifier is extended down well into the low input signal regime, thereby providing an extremely wide dynamic range for the amplifier.

Description

[72] lnventors George Berstei n Mlllburn; Hunter L. McDowell, Chatham, both of, NJ.

[21] Appl. No. 664,686

[22] Filed Aug. 31, 1967 [45] Patented July 13,197]

[54] INJECTED BEAM CROSSED-FIELD AMPLIFIER EMPLOYING RF CONTROL OF THE INJECTED BEAM CURRENT 4 Claims, 5 Drawing Figs.

[52] US. Cl 315/3951,

[51] Int. Cl ..H0lj 25/50,

HOlj 25/58 [50] Field ofSearch 315/393, 3.6, 3.5, 39.51

[56] References Cited UNITED STATES PATENTS 3,376,463 4/1968 Feinstein 315/3951 3,433,992 3/1969 Tancredi et a1 3 l 5/3.6

CATHODE SUPPLY Primary Examiner-Richard A. Farley Assistanl Examiner-William T. Riflcin Attorneys-William J. Nolan and Leon F. Herbert ABSTRACT: An injected beam crossed-field amplifier is disclosed. The crossed-field tube includes a cylindrical nonemitting cathode sole electrode structure surrounded by a concentrically disposed slow wave anode circuit to define a magnetron-type interaction region. in the annular space therebetween. An electron gun assembly is disposed at one end of the magnetron interaction region for injecting a beam of electrons into the magnetron interaction region axially thereof. A beam collector structure is disposed for collecting the electron beam after passage thereof through the magnetron interaction region. Radio frequency wave energy to be amplified is applied to the annular slow wave circuit, such circuit including a circuit sever to prevent reentrance of the wave energy on the circuit and to provide a drift space for debunching of the reentrant electron beam. By passing the electron beam through the magnetron interaction region to a collector structure, the dynamic range of the amplifier is extended down well into the low input signal regime, thereby providing an extremely wide dynamic: range for the amplifier.

ACCELERATOR J SUPPLY Billiiiil SUPPLY i SOLE . SUPPLY INJECTED BEAM CROSSED-FIELD AMPLIFIER EMPLOYING RF CONTROL OF THE INJECTED BEAM CURRENT In one embodiment of the present invention, a magnetron injection type electron gun is employed. The magnetron gun is dimensioned to be closely spaced to the anode circuit and to be relatively open such that the RF fields from the slow wave circuit may penetrate into the region of the electron gun. In

such a case, the injected beam current increases and decreases with increases and decreases in the amplitude of the RF wave energy on the circuit. Thus, when high power operation is required for amplifying high power input signals the. RF fields control the injected beam intensity to supply more beam current. Conversely, when the tube is operating in the relatively low signal regime the RF fields on the slow wave circuit are relatively weak and cause less beam current to be injected into the magnetron interaction region. As a result, the noise figure, which is proportional to the beam current, is improved in the low signal regime and, in addition, the efficiency of the amplifier is improved in the low signal regime.

In another embodiment, an electron gun is provided of the magnetically confined flow -type having a relatively open accelerating beam passageway and being closely spaced to the anode circuit such that the RF fields from the anode circuit may penetrate into the region of the electron gun for controlling the injected beam current in the manneras previously described.

DESCRIPTION OF THE PRIOR ART Heretofore, injected beam crossed-field amplifiers have been built having a beam of electronsflowing through the interaction region orthogonally to the direction-of microwave power flow on the RF slow wave circuit. Such a tube. is described and claimed in copending U.S. Application Ser. No. 561,220, filed June 28, 1966, and assigned to the same assignee as the present invention. Such a tube has substantially improved operation in the low input power regime since the electrons do not remain in the magnetron interaction region, but instead drift through theinteraction region andare collected on separate collector electrodes. When the-electrons do not remain in the magnetron interaction region the noise power in the beam is not coupled to the circuit and, therefore, the tube may be operated in the low power regime. The noise power which is coupled to the RF slow wave circuit is a function of the beam current, and therefore, in the low power regime it is desirable to have a relatively low beam current whereas in the high power regime it is desired to have a relatively high beam current such that relatively high power output may be obtained.

The prior art tube did not include means for controlling the injected beam current in accordance with the amplitude of the signal to be amplified. While it would be possible to detect the amplitude of the signal to be amplified and to provide a control electrode for controlling the injected beam current in accordance with the intensity of the detected signal to be amplified, such an arrangement would be relatively complicated and expensive. Therefore, it is desired to obtain a simple means for controlling the injected beam current in accordance with the amplitude of the RF signal to be amplified.

SUMMARY OF THE PRESENT INVENTION The principal object of the present invention is the provision of an improved injected beam crossed-field amplifier of the type wherein the injected beam is caused to driftthrough the magnetron interaction region to a beam collector structure.

One feature of the present invention is the provision, in an injected beam crossed-field amplifier of the type wherein the injected beam drifts through a magnetroninteraction region to a beam collector structure, of arranging the electron gun assembly such that the RF fields on theslow wave circuit may penetrate into the region of the electron gun for controlling the level of beam current produced by the electron gun, whereby the radio frequency energy on the slow wave circuit controls the injected beam current level.

Another feature of the present invention is the same as the preceding feature wherein the electron gun assembly is of the magnetron injection type having an annular thermionic emitter surrounded by an accelerating electrode with the axial spacing from the electron gun to the anode circuit and the spacing from the thermionic emitter to the accelerating electrode being dimensioned such that the radio frequency fields on the slow wave circuit may penetrate into the region of the electron gun for controlling the current level drawn therefrom into the magnetron interaction region.

Another feature of the present invention is the same as the first feature wherein the electron gun is of the (Hype having a relatively large annular beam passage in the accelerating elec trode structure which is closely spaced to the slow wave circuit such that the RF fields. on the slow wave circuit may penetrate through the annular beam passage in the accelerat ing electrode into the electron gun for controlling the electron beam current drawn from the thermionic emitter.

Other features and advantages of the present invention will become apparent upon a perusal of the following specification taken in connection with the accompanying drawings wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic longitudinal sectional view, partly in block diagram form, of an injected beam crossed-field amplifier employing features of the present invention,

FIG. 2 is a schematic sectional view of a portion of the structure of FIG. 1 taken along line 2--2 in the direction of the arrows,

FIG. 3 is an enlarged detailed view of a portion of the structure of FIG. 1 delineated by line 3-3 and depicting the magnetron injection gunof the present invention,

FIG.4 isan enlarged detail view of a portion of the structure of FIG. 1 delineated by line 44 and depicting the type-0 electron gun of the present invention, and I FIG. 5 is a plot of injected beam current versus RF input drive power depicting the increase of beam current with the increase in input RF drive power.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIGS. 1 and 2, there is shown the injected beam crossed-field amplifier tube 1 incorporating features of the present invention. The tube 1 includes a cylindrical nonemissive sole electrode 2 surrounded by a cylindrical anode structure including an annular slow wave circuit 3 such as atoroidal helix having an input terminal 4 at one end and an output terminal 5 at the other end. An annular magnetron interaction region 7 is defined by the annular space between the sole 2 and the anode structure. An axially directed magnetic field B is provided in the magnetron interaction region 7 by means of a magnet structure, not shown. A circuit sever 6 is provided between the ends 4 and 5 of the slow wave circuit 3 to prevent RF feedback from the output terminal 5 to the input terminal of the helix and to debunch the reentrant stream of electrons.

An electron gun assembly 8 is provided at one end of the magnetron interaction region 7 for injecting a beam of electrons axially into the magnetron interaction region 7 and through the interaction region 7 to a beam collector structure 9 disposed at the other end of the sole 2. The electron gun 8 may be either of the magnetron injection type or of the 0- type, more fully described below with regard to FIGS. 3 and 4. A vacuum envelope ll encloses the aforedescribed'elements and is evacuated to a low pressure such as 10" Torr.

A cathode supply 12 supplies a negative potential as of l,l40 volts to the thermionic emitter of the electron gun 8. An accelerator supply 13 supplies a. positive accelerating potential, as of +610 volts relative to the cathode-potential, to

the accelerating electrode of the electron gun 8. A depressed collector supply 14 supplies a positive potential to the collector electrode 9 relative to the cathode potential. A suitable depressed collector potential is +450 volts. A sole supply supplies a negative potential, as of l40 volts, to the sole electrode 2 relative to the cathode potential. The slow wave structure 3 forms an anode structure and is operated at ground potential.

In operation, the electron gun 8 injects a beam of electrons axially through the magnetron interaction region 7 to the beam collector 9. Radio frequency wave energy to be amplified is applied via terminal .4 to the slow wave structure 3 for cumulative magnetron-type interaction with the electron beam to produce an amplified output signal which is extracted from the slow wave circuit 3 at output terminal 5 and fed to a suitable utilization device, not shown. The power flow of wave energy on the slow wave circuit 3 is orthogonally directed to the drift direction of the electrons as they pass through the magnetron interaction region 7. As a result, noise energy in the electron beam is not coupled to the slow wave circuit.

However, the intense electric fields of the slow wave circuit interact with the beam in the magnetron interaction region to form the beam into spokes of charge which are caused to spiral around the sole electrode 2 for cumulative interaction with the RF wave on the slow wave circuit 3. The electron gun 8 is designed such that the radio frequency fields on the anode slow wave circuit 3 may penetrate into the gun structure 8 to cause the current emitted from the emitter to vary in variable accordance with the intensity of the RF drive signal applied to the slow wave circuit 3 for amplification amplified. The gun designs are more fully described below with regard to FIGS. 3 and 4. However, as a result of the RF drive control of the intensity of the injected electron beam the low noise characteristics of the device are further enhanced in the low signal regime while permitting relatively high output powers to be obtained in the high power regime. In addition, the efficiency of the tube is improved because the DC power drawn by the tube is reduced in the low signal regime, thereby substantially increasing the efficiency of the tube in the low power regime.

Referring now to FIG. 3, there is shown the magnetron injection gun 8 incorporating features of the present invention. The gun 8 includes a cylindrical thermionic cathode emitter 21, for example, of the dispenser type heated to thermionic emission temperature by means of a heater 22. An annular accelerating electrode 23 concentrically surrounds the cylindrical cathode emitter 21. An electron beam focusing ring 24 is disposed adjacent to the emitting surface of the cathode emitter 21 at the upstream end of the beam for causing the electrons to drift into the magnetron interaction region 7. In such an electron gun, a virtual cathode is formed at the plane identified by 25 at the downstream end of the thermionic emitter 21.

Electron gun 8 is designed to have a relatively open structure and to be relatively closely spaced to the anode 3 such that the radio frequency fields from the anode slow wave circuit 3 may penetrate into the region of the virtual cathode 25 and also into the region of the gun 8 for controlling the intensity of the injected beam current.

In a preferred embodiment of the magnetron injection gun 8, the radial spacing d, from the thermionic emitter 21 to the accelerating electrode 23 is preferably greater than one-half the radial spacing 11;, from the thermionic emitter 21 to the inside diameter of the slow wave circuit 3. In addition, the axial spacing d from the end of the thermionic emitter 21 to the adjacent end of the slow wave-circuit 3 is preferably less than the radial spacing from the thermionic emitter 21 to the inside diameter of the slow wave circuit 3. In a typical example, the electron gun 8 had dimensions as shown on FIG. 3 and produced an RF control over the beam current as shown in FIG. 5. More specifically as shown in FIG. 5, with an input RF drive power of one-tenth of a watt the beam current was approximately 60 ma., whereas at an input drive power of 40 watts the beam current was 150 ma., thus, representing a substantial RF control over the beam current.

Referring now to FIG. 4, there is shown the type-O electron gun 8 incorporating features of the present invention. In this embodiment, the gun 8 includes an annular thermionic emitter 31 as of thedispenser type heated to thermionic emitting temperature by means of a heating element 32. The annular emitter 31 is axially aligned with the annular magnetron interaction region 7. An annular beam focusing electrode structure 33 axially projects toward the magnetron interaction region 7 for focusing the beam emitted from the emitter 31 through an annular beam passageway 34 in an accelerating electrode 35. In this embodiment, the radial dimension d of the annular beam passageway 34 in accelerating electrode 35 is preferably greater than one-half the radial thickness of the magnetron interaction region d,,. In addition, the axial spacing d from the slow wave structure 3 to the accelerating electrode 34 is preferably less than the radial thickness d of the magnetron interaction gap 7. As a result, a relatively open electron gun structure 8 is provided such that the radio frequency fields on the slow wave structure 3 may penetrate through the beam passageway 34 into the region of the gun 8 for controlling the electron current drawn from the emitter 31 in use.

Since many changes could be made in the above construction and many apparently widely different 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 we claim is:

1. The method for controlling the beam current level in an injected beam crossed-field amplifier tube comprising the steps of, subjecting electron emitted from a thermionic cathode to an accelerating field to produce a beam of electrons which is passed axially through an annular magnetrontype interaction region defined between a curved and nonreentrant slow wave circuit operating at anode potential and a concentrically disposed nonemitting cathode sole electrode, collecting the beam after passage thereof through at least a portion-of the magnetron-type interaction region, applying a radio frequency signal to the slow wave circuit for cumulative interaction between the radio frequency energy on the slow wave circuit and the beam of electrons to produce an amplified output radio frequency signal, TI-IE IMPROVEMENT COMPRISING, causing the radio frequency fields on the anode slow wave circuit to penetrate into the region of the electron beam producing accelerating fields to cause the electron current drawn from the thermionic emitter to increase with an increase in the intensity of the radio frequency signal energy on the slow wave circuit, whereby the beam current level is controlled by the intensity of the input signal to be amplifier.

2. In an injected beam crossed-field amplifier tube, means forming a nonemitting sole electrode structure, means forming a curved anode structure concentrically surrounding said sole electrode to define an annular reentrant stream magnetron-type interaction region therebetween, said anode structure including a curved slow wave circuit portion and a circuit sever portion, means forming a thermionic electron gun structure disposed at one axial end of the annular magnetron interaction region for injecting a beam of electrons axially through the annular magnetron interaction region for cumulative interaction with radio frequency wave energy on the slow wave circuit to produce an output signal, means forming an electron collector for collecting the beam after passage thereof through the interaction region, TI-IE IMPROVE- MENT WHEREIN, the spacing from said thermionic electron gun to said slow wave circuit is dimensioned sufficiently close such that the radio frequency fields on the slow wave circuit penetrate into the region of said thermionic electron gun to cause the electron current level injected into said magnetron type interaction region to increase and decrease in variable accordance with increases and decreases in the radio frequency power level on said slow wave circuit, whereby the radio frequency energy on said slow wave circuit controls the injected beam current.

3. The apparatus of claim 2 wherein said electrongun structure is a magnetron injection gun including, an annular thermionic cathode emitter coaxially aligned with said nonemitting sole electrode, means forming an'electron accelerating electrode concentrically disposed surrounding said thermionic emitter with a radial spacing from the emitting surface of said emitter greater than one-half the radial spacing from the emitting surface of said emitter to the inside diameter of said slow wave circuit, and the axial spacing from said gun to said slow wave circuit being less than the radial spacing from said emitter to said slow wave circuit.

4. The apparatus of claim 2 wherein said electron gun includes, an annular thermionic cathode emitter coaxially aligned with the annular magnetron-type interaction region,

means forming an accelerating electrode structure axially spaced from said emitter and disposed between said cathode emitter and the magnetron interaction region, said accelerating electrode having an annular beam passageway therein for passage of the beam therethrough into the magnetron-type interaction region, the radial dimension of said annular beam passageway in said accelerating electrode being greater than one-half the radial thickness of the magnetron interaction region to provide a relatively open electron gun structure, and the axial spacing from said slow wave structure to said electron gun being less than the radial thickness of said magnetron-type interaction gap.

Claims

1. The method for controlling the beam current level in an injected beam crossed-field amplifier tube comprising the steps of, subjecting electron emitted from a thermionic cathode to an accelerating field to proDuce a beam of electrons which is passed axially through an annular magnetron-type interaction region defined between a curved and nonreentrant slow wave circuit operating at anode potential and a concentrically disposed nonemitting cathode sole electrode, collecting the beam after passage thereof through at least a portion of the magnetron-type interaction region, applying a radio frequency signal to the slow wave circuit for cumulative interaction between the radio frequency energy on the slow wave circuit and the beam of electrons to produce an amplified output radio frequency signal, THE IMPROVEMENT COMPRISING, causing the radio frequency fields on the anode slow wave circuit to penetrate into the region of the electron beam producing accelerating fields to cause the electron current drawn from the thermionic emitter to increase with an increase in the intensity of the radio frequency signal energy on the slow wave circuit, whereby the beam current level is controlled by the intensity of the input signal to be amplifier.

2. In an injected beam crossed-field amplifier tube, means forming a nonemitting sole electrode structure, means forming a curved anode structure concentrically surrounding said sole electrode to define an annular reentrant stream magnetron-type interaction region therebetween, said anode structure including a curved slow wave circuit portion and a circuit sever portion, means forming a thermionic electron gun structure disposed at one axial end of the annular magnetron interaction region for injecting a beam of electrons axially through the annular magnetron interaction region for cumulative interaction with radio frequency wave energy on the slow wave circuit to produce an output signal, means forming an electron collector for collecting the beam after passage thereof through the interaction region, THE IMPROVEMENT WHEREIN, the spacing from said thermionic electron gun to said slow wave circuit is dimensioned sufficiently close such that the radio frequency fields on the slow wave circuit penetrate into the region of said thermionic electron gun to cause the electron current level injected into said magnetron type interaction region to increase and decrease in variable accordance with increases and decreases in the radio frequency power level on said slow wave circuit, whereby the radio frequency energy on said slow wave circuit controls the injected beam current.

3. The apparatus of claim 2 wherein said electron gun structure is a magnetron injection gun including, an annular thermionic cathode emitter coaxially aligned with said nonemitting sole electrode, means forming an electron accelerating electrode concentrically disposed surrounding said thermionic emitter with a radial spacing from the emitting surface of said emitter greater than one-half the radial spacing from the emitting surface of said emitter to the inside diameter of said slow wave circuit, and the axial spacing from said gun to said slow wave circuit being less than the radial spacing from said emitter to said slow wave circuit.

4. The apparatus of claim 2 wherein said electron gun includes, an annular thermionic cathode emitter coaxially aligned with the annular magnetron-type interaction region, means forming an accelerating electrode structure axially spaced from said emitter and disposed between said cathode emitter and the magnetron interaction region, said accelerating electrode having an annular beam passageway therein for passage of the beam therethrough into the magnetron-type interaction region, the radial dimension of said annular beam passageway in said accelerating electrode being greater than one-half the radial thickness of the magnetron interaction region to provide a relatively open electron gun structure, and the axial spacing from said slow wave structure to said electron gun being less than the radial thickness of said magnetron-type interaction gap.