The present exemplary embodiment relates to microwave, millimeter and sub millimeter wavelength generation, amplification and processing arts. It finds particular application in conjunction with electron devices, and will be described with particular reference thereto. It is to be appreciated, however, that the present exemplary embodiment is also amenable to other like applications.
Vacuum electron devices, such as a traveling wave tube (TWT), a klystron, and a backward wave oscillator (BWO), are commonly used as amplifiers of electromagnetic signals or as sources of electromagnetic energy for applications that require operation at high frequency or high power. Both the TWT and the BWO operate on the same principle, that the kinetic energy of an electron beam can be converted into electromagnetic energy by passing an electron beam through an interaction region known as a slow wave circuit.
The most common form of a slow wave circuit is simply a helical coil of wire. In the slow wave circuit, the axial propagation of an electromagnetic wave is slowed so that it is moving in approximate synchronism with the electron beam. In the case of a helix, the electromagnetic wave follows the path of the wire so that its axial progress is determined by the pitch of the helix. In the TWT, the electromagnetic wave propagates on the slow wave circuit in the same direction as the electron beam in a mode that amplifies the electromagnetic wave. In the mode of operation of the BWO, an electromagnetic oscillation is produced that actually propagates in the opposite direction to the electron beam, hence its name, backward wave.
The electron beam is formed by an electron gun that typically consists of a source of electrons, such as a thermionic cathode, an electrode nearby the cathode that focuses the beam, and one or more anodes that accelerate the beam. A thermionic cathode emits electrons when it is heated to a high temperature. The resulting electron emission current at the cathode is sometimes too low to successfully operate the VED. Therefore, in some applications, it is necessary to have multiple electron beams to achieve the required total current. At low frequency, the size of the circuit is relatively large, and thus it may be feasible to emit the beams from the cathode at the same central radii that they will occupy within the slow wave circuit. For higher frequency operation, however, this is not satisfactory because the beams must pass through a slow wave circuit that is greatly reduced in size. Accordingly, what are needed are systems and methods to accommodate the small dimensions of the slow wave circuit for proper operation of an electron gun.
In one aspect, an electron gun includes a focus electrode that surrounds two or more cathodes, wherein each cathode emits a beamlet comprised of a plurality of electrons directed to a predetermined location. A first anode receives each beamlet at the predetermined location, accelerates each beamlet and reduces the radius of each beamlet. A second anode receives each beamlet from the first anode, directs each beamlet along a predetermined axis, further accelerates each beamlet, and possibly changes the radius of each beamlet.
In another aspect, an electron gun includes two or more cathodes that each emits a beamlet, the beamlets are divided into a first cluster and a second cluster. A first anode receives the first cluster and the second cluster of beamlets via a first opening and a second opening, accelerates each beamlet and reduces the radius of each beamlet. A second anode receives the beamlets from the first anode, directs each beamlet along a predetermined axis, further accelerates each beamlet, and possibly changes the radius of each beamlet.
In yet another aspect, an electron gun includes at least two cathodes that each emits a beamlet toward a predetermined location. An anode receives the beamlets emitted by the cathode, accelerates each beamlet, reduces the radius of each beamlet and directs each beamlet along a predetermined axis.
The operation of a typical vacuum electron device (VED) requires an electron beam to pass through an interaction region such as a slow wave circuit in order to produce the desired amplification or oscillation. Generally, the current density required is greater than what is practical to achieve with a thermionic cathode. To achieve a suitable current for operation of the VED, an electron gun is used to compress the beam of electrons emitted from the cathode to operate the VED. In some instances, for operation at lower frequency, the current carried by a single electron beam is not sufficient to operate the VED at the desired beam voltage. In these instances, it may be possible to use an array of singly convergent electron beams to achieve the desired current. The electron gun design problem is further exacerbated for operation at higher frequencies where the dimensions of the interaction region are greatly reduced, corresponding to the shorter wavelengths, and the electron beam must be converged a second time to pass through a smaller space.
Although modern microfabrication technology can be applied to achieve the greatly reduced VED dimensions required for operation at millimeter and sub millimeter wavelengths, there is no comparable technology to reduce the diameter of the electron beam. The maximum practical electron beam current density is limited by the strength of the available magnetic focusing field. The required operating current may only be achievable by using multiple electron beams. Because of the reduced dimensions for millimeter and sub millimeter wavelength operation, however, these multiple beams must be compressed twice. Once to achieve higher current density and a second time to pass through the smaller space available in the interaction region.
Three embodiments of this concept are discussed herein to provide dual compression: 1) a dual anode approach in which a plurality of electron beams are arranged in a circular array; 2) a dual anode, dual beam configuration; and 3) a single anode, dual beam approach. All of these guns are designed to operate with helical slow wave circuits that are so small that it is not possible to pass significant beam current through the helix center as is done conventionally. Instead, multiple electron beams are formed by the doubly convergent electron guns. These pass above and below the helix in the relatively larger space outside of the helix. In each case, the beam convergence is accomplished electrostatically. The beam transmission through the slow wave circuit is controlled by a strong axial magnetic field, which is excluded from the electron gun.
Multibeam Electron Gun
The electron gun 100 contains a focus electrode 120, which holds a plurality of cathodes 132, 134, 136, 138, 140, 142, 144, 146 that each emits a beamlet. A first anode 150 and a second anode 160 are employed to accelerate the electrons within each beamiet emitted from the cathodes 132-146. The first anode 150 and the second anode 160 are each aligned with the focus electrode 120 along a common axis. In one embodiment, the common axis is the axial centerline of the VED. The diameter of the focus electrode 120 is around 2 mm, in one example.
The cathodes 132-146 are disposed in a generally circular pattern and oriented toward a predetermined location for convergence. In one example, the convergence location is the second anode 160, which is located adjacent to the axial centerline (major axis) of the VED. In this exemplary embodiment, the number of cathodes within the focus electrode 120 is even, wherein the cathodes are divided into a first cluster 170 and a second cluster 180. The first cluster 170 includes the cathodes 132, 134, 136, 138 and the second cluster 180 includes the cathodes 140, 142, 144, 146.
The cathodes 132-138 within the first cluster 170 can converge on a first location above the major axis whereas the cathodes 140-146 within the second cluster 180 can converge on a second location below the major axis. In this manner, beamlets can maintain a closer proximity to other beamlets within the same cluster as they progress through the electron gun 100 and are emitted into a VED. The focus electrode 120 can have a concave shape on the front side (side of beamlet emission) to provide suitable orientation for each cathode 132-146. The rear side (side opposite beamlet emission) of the first anode 150 can have a convex shape to match the front side of the focus electrode 120.
The location and orientation of each cathode 132-146 can be dependent on any number of factors such as distance from a convergence point, geometry of arrangement, power requirements, potential values of each structure and/or location within the gun 100, etc. It is to be appreciated that any suitable arrangement and/or number of cathodes with substantially any shape can be employed. In one example, as illustrated in
The beamlets emitted from the cathodes 132-146 are first directed to the first anode 150, wherein each beamlet is accelerated and compressed as it travels between the respective cathode 132-146 to the first anode 150. As depicted in
The rear side of the first anode 150 includes apertures 312′, 314′, 316′, 318′, 320′, 322′, 324′ and 326′ associated with the barrels 312-326 respectively. A conical structure 350 protrudes from the center of the rear of the first anode 150. The conical structure 350 can interact with the second anode 160 to create an electrostatic prism to direct the beamlets along a predetermined axis. Beamlets emitted from the cathodes 132-146 enter the barrels 312-316 and exit the first anode 150 via the apertures 312′-326′. The electrostatic prism can modify the direction of travel for the electrons within each beamlet based on the potential value of each structure within the electron gun 100, the distance between the first anode 150 and the second anode 160, and/or the size and location of structures related to the first anode 150 and the second anode 160.
In this example, a raised structure 510 is circular and disposed in the center of the second anode 160. The structure 510 includes a first opening 520 and a second opening 530 separated by a cross member 540. As shown in
In this example, the size of the first opening 520 and the second opening 530 are the same on the front side and the back side of the second anode 160. Beamlets 132-138 within the cluster 170 can enter the first opening 520 and beamlets 140-146 within the second cluster 180 can enter second opening 530. Beamlets 132-146 enter the structure 510 at a particular angle of incidence from the first anode 150,400 on the front side of the second anode 160. In one example, the angle of incidence of each beamlet 132-146 (e.g., 15-20 degrees) is generally equal relative to the axial centerline. As the beamlets 132-146 travel through the structure 510, they are redirected from the angle of incidence to an alternate axis of travel. In one example, the beamlets are generally parallel to each other and to the major axis of the VED upon exit from the structure 510 on the back side of the second anode 160. As each beamlet exits the second anode 160, it can have a radius of around 40 microns and is located at a radius of about 130 microns from the major axis of the VED.
The potential of the first anode 150 is greater than the potential of the focus electrode 120 to facilitate beamlet acceleration and compression. In one embodiment, the potential of the focus electrode 120 is around 0 V and the potential of the first anode 150 is 2-5 kV. To further increase acceleration, the second anode 160 can have a potential greater than the first anode 150,400, such as 6-8 kV for example. In this manner, the potential of the beamlets increase as they are drawn from the cathode 120, to the first anode 150,400 and on to the second anode 160, commensurate with the respective potential of these structures. Moreover, the radius of each beamlet can be altered as they pass from the focus electrode 120 to the first anode 150 and again from the first anode 150 to the second anode 160.
Dual Beam Doubly Convergent—Dual Anode Gun
The beamlets emitted from the cathodes 1330, 1332 are compressed between the cathode 1330, 1332 and the first anode 1350. An electric field created between the first anode 1350 and the second anode 1360 creates an electrostatic prism that directs the beamlets into a path parallel to the major axis. Thus, similar to the operation of the electron gun 100, the electron gun 1300 utilizes a dual stage convergence to first compress beamlets emitted from the cathodes and subsequently directs the compressed beamlets along predetermined axes.
The element 1510 includes a central component 1520 and a wall 1530 to guide beamlets received. In one example, both the first anode 1350 and the central component 1520 are circular, wherein the central component 1520 is concentric to the first anode. The central component 1520 includes a post centrally disposed to facilitate guidance of beamlets received, in this exemplary embodiment. A first opening 1550 and a second opening 1560 are defined by the central component 1520 and the wall 1530. The size and location of each opening 1550 and 1560 can be relative to the number, angle and size of beamlets, however, emitted from the focus electrode 1320. The central component 1520 receives beamlets from the cathode 1330, 1332 to direct it to the second anode 1360. The angle, location and diameter of each barrel can be commensurate with the angle, location and diameter of the beamlet associated therewith.
The size and location of the first opening 1620 and the second opening 1630 can vary proportionate to size of the beamlets, number of beamlets, potentials within the electron gun 100, etc. The function and structural features of the second anode 1360 are generally the same as the second anode 160 described in detail above. As discussed with regard to the electron gun 100, an electrostatic prism is created between the first anode 1350 and the second anode 1360 to direct the beamlets along predetermined axes. To create the electrostatic prism, predetermined distances can be utilized to separate the first anode 1350 and the second anode 1360.
An exemplary detail of the second anode 1360 is set forth in
Dual Beam Doubly Convergent—Single Anode Gun
The electron gun 1900 varies from the electron guns 100 and 1300 discussed herein in that the gun utilizes only a single anode as opposed to two anodes to accomplish the suitable modification of the beamlets prior to their emission into a vacuum electron device. In one example, this single anode electron gun 1900 is suitable for operation of a vacuum electron device at relatively low current. In this manner, current can be obtained from a smaller cathode surface such that the cathode can be placed near to the predetermined axes. Accordingly, it is not necessary to translate the beamlets over a large radial distance, thereby allowing double convergence to be accomplished via the single anode 1950. The shell 1910 is employed to interface with the focus electrode 1920 and the anode 1950 to steer the beamlets emitted from the cathodes 1930, 1932. The size and strength of the field created can be dependent on the size, relative location and potential of the shell 1910, the focus electrode 1920 and the anode 1950 among other factors. If made out of an appropriate material, the shell 1910 could also minimize interference with outside magnetic activity.
It is to be appreciated that each of the embodiments 100, 1300 and 1900 of the electron gun can achieve a high current beam based on the convergence of a plurality of beamlets that can be directed down a predetermined axes within a vacuum electron device. The exemplary embodiment has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the exemplary embodiment be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
This application claims the priority of provisional application 61/090,285, filed Aug. 20, 2008.
This project was funded in part by U.S. Government contracts FA9550-07-C-0076 and W911NF-06-C-0086. Therefore, the United States government may own certain rights to this invention.
Number | Date | Country | |
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61090285 | Aug 2008 | US |