Patent Publication Number: US-4059784-A

Title: Electron-beam converter

Description:
The present invention relates to high-vacuum converting devices, and more particularly to an electron-beam converter intended for use at high-power substations of d-c transmission lines or as a controlled switch in high-power switching, protecting and inverter circuits. 
     Known in the art is an electron-beam converter comprising a cathode, an anode, and accelerating and control electrodes. The control electrodes are arranged near the cathode on either side of an electron flow with a cathode-adjacent focusing electrode being arranged behind the control electrode on the cathode side opposite to the accelerating electrode, while an anode-adjacent focusing electrode is inserted between the anode and accelerating electrode; all said electrodes make up an electron-optical system shaping the electron flow into a beam so as to prevent electrons from impinging upon the accelerating electrode. The potentials across the electrodes are distributed so that there is applied to the accelerating electrode a potential which is positive with respect to the cathode and which has a magnitude sufficient for taking off the required amount of current, the anode potential is positive with respect to the cathode but much lower than the accelerating electrode potential, applied to the cathode- and anode-adjacent electrodes are potentials close or equal to the cathode or anode potentials, respectively, and the control electrode potentials are equal to the cathode potential during the positive half-cycle, and are negative with respect to the cathode during the negative half-cycle. 
     To minimize the number of reflected electrons, the anode is made as a hollow member with holes through which electrons are let therein. As a result, the converter is rendered more powerful as well as sharply increased in size. 
     Therefore, the principal object of the present invention is to improve said prior art electron-beam converter. 
     One of the objects of the invention is to provide as small an electron-beam converter as possible, which is still capable of switching heavy currents. 
     Another object of the invention is to suppress secondary electron emission from the anode as well as to enhance the efficiency of the converter. cathode-adjacent 
     Still another object of the invention is to render the converter capable of switching heavier currents without an increase in its size and complication of its structure. 
     Yet another object of the invention is to minimize thermal load on the anode. 
     These and other objects are achieved in that in the proposed electron-beam converter the electron beam is, according to the invention, a curvilinear flow of electrons, broadening as it approaches the anode, for which purpose the angle between normals to the cathode and anode surfaces is greater than zero but less than 180°, the anode having a surface orthoganal relative to the electron flow incident thereupon, and the distance between the accelerating electrode and anode being substantially greater than that between the cathode and the accelerating electrode. 
     The electron beam thus formed permits reduction of the size of the converter without affecting its ability to switch heavy currents. 
     It is advisable to provide a grid in direct proximity to the anode, having a potential equal to or lower than the anode potential, but higher than the cathode potential. 
     This ensures suppression of the secondary electron emission from the anode and a substantially higher efficiency of the converter. 
     It is also advisable that all said electrodes are made elongate to form a curvilinear ribbon electron beam. 
     To minimize the thermal load on the anode, the proposed electron-beam converter should preferably have two anodes, two accelerating and two control electrodes. 
     The cathode, anode, accelerating and control electrodes should advisably be made annular and be arranged concentrically with respect to the axis of symmetry coinciding with the cathode axis. This permits heavier currents to be switched without increasing the size of the converter. 
     The converter may alternatively have two cathodes, two anodes, and accelerating and control electrodes, all being made annular in shape and being arranged concentrically with respect to the axis of symmetry which coincides with the axis of the cathodes, as a result of which the electron flow is emitted in opposite directions, the accelerating and control electrodes being common for both cathodes. Such an arrangement is structurally simpler and permits heavier currents to be switched. 
     In an embodiment with a cathode, two anodes, two accelerating and two control electrodes, the cathode should preferably be made cylindrical in shape, while the accelerating and control electrodes should be made in the form of rings having their axis of symmetry coinciding with that of the cathode and being arranged symmetrically to the cathode on either side thereof. This permits heavier currents to be switched and the efficiency of the converter to be substantially enhanced. 
     The proposed converter may have a plurality of electron-optical systems arranged on a common axis, each including a cylindrical cathode, two annular anodes, two accelerating and two control electrodes. Such an arrangement enables substantially heavier currents to be switched. 
    
    
     The invention will be better understood from the following detailed description with reference to preferred embodiments thereof, taken in conjunction with the accompanying drawings, wherein: 
     FIG. 1 shows schematically the proposed converter; 
     FIG. 2 shows an embodiment of the proposed converter with a grid being provided in proximity to the anode; 
     FIG. 3 shows an embodiment of the proposed converter, in which the electron flow is split into two; 
     FIG. 4 shows an embodiment of the proposed converter, in which the cathode is made annular; 
     FIG. 5 shows an embodiment of the proposed converter, wherein use is made of two electron-optical systems, each having an annular cathode, with accelerating and control electrodes common for both systems; 
     FIG. 6 shows an embodiment of the proposed converter with a cylindrical cathode; 
     FIG. 7 shows an embodiment of the proposed converter, wherein a plurality of electron-optical systems are arranged on a common axis, and each having a cylindrical cathode; 
     FIG. 8 shows an embodiment of the proposed converter, wherein use is made of a plurality of electron-optical systems each having an elongate ribbon-shaped cathode; and 
     FIG. 9 shows an embodiment of the proposed converter, wherein a plurality of electron-optical systems are arranged on a common axis, each system having elongate electrodes and splitting the electron beam into two. 
    
    
     In the electron-beam converters described below, use is made of an electron-optical system with centrifugal-electrostatic formation of an electron flow. In such a system, electrons follow curvilinear paths. As it moves along curvilinear paths, an electron is acted upon by a normal component of the electric intensity, a space charge and the centrifugal force. The action of space charge forces in combination with high-intensity external fields and the centrifugal force transverse to the electron path results in an additional rigidity of the electron beam since variations in the space charge level in the beam practically do not affect the beam trajectory. The presence of high-intensity electrostatic fields transverse to the electron paths provides for removal of positive ions from the electron flow, which is especially important in modes of operation preceding the start of oscillations in the case of a sharp deceleration of the electron beam. 
     Obviously, the additional rigidity of the electron beam and removal of ions from the electron flow are determined by the curvilinearity of the paths. 
     Thus, the more curvilinear the beam, the more effective the system. 
     In the proposed electron-optical system, the anode is shaped so that its surface is orthogonal with respect to the electron flow incident thereupon. This results in a minimum electron speed difference, and, as a consequence, a sufficiently low anode potential can be obtained, i.e. the electron flow can be sharply decelerated. 
     The possibility of forming a divergent electron flow in the electron-optical system rules out formation of a virtual cathode in the vicinity of the anode. 
     Evidently, if the accelerating electrode is arranged so that the distance between said electrode and the anode is substantially greater than that between the cathoe and accelerating electrode, it becomes possible to reduce the accelerating electrode potential required for taking off a predetermined amount of current for a given value of the voltage being switched. As a result, the efficiency of the converter is improved. 
     The proposed electron-optical system makes it possible to use elongate electrodes thereby enablng heavier currents to be switched. 
     The totality of the above-mentioned advantages can be realized while solving the expanding curvilinear electron flow problem. 
     Referring now to the drawings, the electron-beam converter comprises a cathode 1 (FIG. 1), an anode 2, an accelerating electrode 3 and elongate control electrodes 4 and 4&#39;. The anode 2 has a surface orthogonal with respect to the cathode 1 so that the angle between normals to the surfaces of these electrodes is greater than zero but less than 180°. The accelerating electrode 3 is disposed in the opening of this angle, and the distance between the accelerating electrode 3 and anode 2 is substantially greater than that between the cathode 1 and accelerating electrode 3. The control electrodes 4 and 4&#39; are arranged near the cathode 1 on either side of an electron flow. Arranged behind the control electrode 4&#39;, on the side of the cathode 1 opposite to the accelerating electrode 3, is a cathode-adjacent focusing electrode 5, while inserted between the anode 2 and accelerating electrode 3 is an anode-adjacent electrode 6. All of said electrodes make up an electron-optical system with centrifugal-electrostatic formation of an electron flow in the form of a curvilinear beam broadening towards the anode. 
     The potentials across the electrodes are distributed so that there is applied to the accelerating electrode 3 a potential positive with respect to the cathode 1, the magnitude of said potential being sufficient for taking off the required amount of current, and the potential across the anode 2 is positive with respect to the cathode 1 but much lower than that across the accelerating electrode 3. Applied to the cathoe-adjacent focusing electrode 5 is a potential close or equal to the cathode potential, while the control electrodes 4 and 4&#39; have a potential equal to the cathode potential during the positive halfcycle, and a potential negative with respect to the cathoe 1 during the negative half-cycle. 
     The electron-beam converter shown in FIG. 2 also comprises a cathode 1, an anode 2, an accelerating electrode 3 and control electrodes 4, and 4&#39;, all of these electrodes being made elongate. The anode 2 has a surface orthoganal with respect to the diverging electron flow and is so arranged relative to the cathode 1 that the angle between normals to the surfaces of these electrodes is greater than zero but less than 180°, the accelerating electrode 3 being disposed in the opening of this angle. 
     Arranged adjacent to the cathode 1 on either side thereof are the control electrodes 4 and 4&#39;. For the electron beam to be focused, two focusing electrodes are provided: a cathode-adjacent focusing electrode 5 arranged near the control electrode 4&#39; on the side opposite to the accelerating electrode 3, and an anode-adjacent focusing electrode 6 arranged between the accelerating electrode 3 and anode 2. As distinct from the embodiment of FIG. 1, the one under consideration has a grid 7 provided in proximity to the anode 2. By applying to the grid 7 a potential lower than that across the anode 2 but higher than the cathode potential it is possible to create a minimum potential area near the anode 2, which enables retention of the secondary electrons knocked out of the anode 2 by the electron flow incident thereupon. Suppressing the secondary electrons minimizes losses at the electrodes and enhances the efficiency of the converter. 
     The electron-beam converter of FIG. 3 comprises a cathode 1, two anodes 2 and 2&#39;, two accelerating electrodes 3 and 3&#39; and two control electrodes 4 and 4&#39;, all of there electrodes being made elongate. Both anodes 2 and 2&#39; have surfaces orthogonal with respect to the divergent electron flow and are so arranged relative to the cathode 1 on either side thereof that the angle between normals to the surfaces of the cathode and each anode is greater than zero but less than 180°. The accelerating electrodes 3 and 3&#39;are disposed in the openings of these angles, and the distances between the accelerating electrodes 3, 3&#39; and anodes 2, 2&#39; are substantially greater than those between the cathode 1 and accelerating electrodes 3, 3&#39;. The control electrodes 4 and 4&#39; are arranged between the cathode 1 and each accelerating electrode 3, 3&#39; with anode-adjacent focusing electrodes 6 and 6&#39; being arranged between the acclerating electrodes 3, 3&#39; and the anodes 2, 2&#39;. Arranged above the emitting surface of the cathode 1, symmetrically with the common axis of the converter and between the anodes 2, 2&#39;, is a cathode-adjacent focusing electrode 5. Such an arrangement permits the thermal loads on the anodes to be minimized due to the larger surface of the latter, thereby minimizing total losses in the converter and enhancing its efficiency. 
     The electron-beam converter illustrated in FIG. 4 comprises a cathode 1, an anode 2, an accelerating electrode 3 and a control electrode 4, all of these electrodes being made annular and being arranged concentrically with respect to the axis of symmetry of the converter, coinciding with that of the cathode 1. The latter is made as a ring with a flat emitting surface, while the anode 2 has a surface orthogonal relative to the divergent electron beam and is arranged with respect to the cathoe 1 so that the angle between normals to these surfaces is greater than zero but less than 180°. The annular acclerating electrode 3 is disposed in the opening of this angle. The distance between the accelerating electrode 3 and anode 2 is substantially greater than that between the cathode 1 and accelerating electrode 3. 
     The annular control electrode 4 is disposed between the outer edge of the cathode 1 and the accelerating electrode 3. The following focusing electrodes are provided to focus the electron flow: two cathode-adjacent electrodes 5, 5&#39; and an anode-adjacent electrode 6. The electrode 5 is conical in shape and arranged in the center of the anode 2, while the electrode 5&#39; has a cylindrical shape with a beveled edge and is arranged in the center of the cathode 1. Such an arrangement allows heavier currents to be switched owing to the expanded cathode surface. 
     The electron-beam converter of FIG. 5 has two cathodes 1 and 1&#39;, two anodes 2 and 2&#39;, an acceleratng electrode 3 and a control electrode 4. The cathodes 1 and 1&#39; are annular and have flat emitting surfaces, the arrangement of these cathodes being such that electrons are emitted in opposite directions, and each cathode has a respective anode 2,2&#39; with a surface orthogonal relative to the divergent electron flow and disposed with respect to its cathode 1 or 1&#39; so that the angle between normals to these surfaces is greater than zero but less than 180°. Arranged in the openings of these angles is the accelerating electrode 3 which is common for both cathodes 1, 1&#39;, and the distances between the accelerating electrode 3 and anodes 2,2&#39; are substantially greater than those between the cathodes 1, 1&#39; and the accelerating electrode 3. The control electrode 4 is inserted between the outer edges of the cathodes 1, 1&#39; and the accelerating electrode 3, the electrode 4 being common for both electron-optical systems, too. Such an arrangement enables heavier currents to be switched due to the expanded cathode surface and is structurally simpler. 
     The electron-beam converter shown in FIG. 6 comprises a cathode 1, two anodes 2 and 2&#39;, two accelerating electrodes and 3 3&#39;, and two control electrodes 4 and 4&#39;. The cathode 1 is cylindrical in shape with the side surface of the cylinder serving as the emitting surface. The anodes 2, 2&#39; are made annular and arranged on either side of the cathode 1, their axis of symmetry coinciding with that of the cathode 1. The surfaces of the anodes 2 and 2&#39; are orthogonal relative to the divergent electron flow, and the angle between normals to the surfaces of the cathode 1 and each anode 2,2&#39; is greater than zero but less than 180°. The annular accelerating electrodes 3, 3&#39; are disposed in the openings of these angles, and the distances between the accelerating electrodes 3, 3&#39; and the anodes 2, 2&#39; are substantially greater than those between the cathode 1 and the accelerating electrodes 3, 3&#39;, just as in the embodiments described above. Both control electrodes 4 and 4&#39; are arranged near the cathode 1, between the latter and each accelerating electrode 3, 3&#39;. The control electrodes 4, 4&#39; and accelerating electrodes 3, 3&#39;are arranged symmetrically with the cathode 1 on either side thereof. Disposed opposite the cathode 1 is an annular cathode-adjacent focusing electrode 5 with a conical inner surface, while inserted between the accelerating electrodes 3, 3&#39; and anodes 2, 2&#39; are anode-adjacent focusing electrodes 6, 6&#39;. Such an arrangement permits heavier currents to be switched due to the larger emitting surface of the cathode without any increase in the size of the converter, while expanding the anode surface minimizes thermal losses and, hence, enhances the efficiency of the converter. 
     The electron-beam converter of FIG. 7 comprises a plurality of electron-optical systems each being similar to that shown in FIG. 6 and comprising a cathode 1, two anodes 2 and 2&#39;, two accelerating electrodes 3 and 3&#39; arranged on a common axis, and two control electrodes 4 and 4&#39;. 
     The systems are arranged on a common axis which is the axis of symmetry for each system. In this embodiment, anode-adjacent focusing electrodes 6 and 6&#39; may be common for two adjacent systems (e.g. electrode 6). The use of a plurality of similar electron-optical systems enables substantially heavier currents to be switched due to the expanded emitting surface of the cathode. 
     The electron-beam converter illustrated in FIG. 8 includes several electron-optical systems each having a cathode 1, an anode 2, an accelerating electrode 3, a control electrode 4, a cathode-adjacent focusing electrode 5, and an anode-adjacent focusing electrode 6. All of the systems are arranged relative the common axis of the converter so that anodes 2 are, in cross section, arcs of a common circumference. In each electron-optical system, the electrodes are made elongate, the anode 2 has a surface orthogonal with respect to the divergent electron flow, and the angle between normals to the cathode and anode surfaces is greater than zero but less than 180°, with the accelerating electrode 3 being disposed in the opening of this angle. The distance between the accelerating electrode 3 and the anode 2 is substantially greater than that between the cathode 1 and the accelerating electrode 3, the cathode-adjacent focusing electrode 5 being arranged on the side of the cathode 1 opposite to the accelerating electrode 3. To simplify the structure of the converter, the cathode-adjacent focusing electrode 5 is made in the form of an elongate cross and arranged along the axis around which individual electron-optical systems are grouped while the anode-adjacent focusing electrode 6 is inserted between the anode 2 and accelerating electrode 3. This particular embodiment of a simplified arrangement of individual electron-optical systems permits heavier currents to be switched owing to the expanded emitting surface of the cathode. 
     And finally turning to FIG. 9, the electron-beam converter therein comprises a plurality of electron-optical systems each being similar to that of FIG. 3, i.e. includes a cathode 1, two anodes 2 and 2&#39;, two accelerating electrodes 3 and 3&#39; and two control electrodes 4 and 4&#39;. 
     All the systems are so arranged with respect to the common axis of the converter, that the anodes 2, 2&#39; are, in cross section, arcs of a common circumference, with all the electrodes in each electron-optical system being made elongate. The anodes 2, 2&#39; are disposed on either side of the cathode 1, and their surfaces are orthogonal with respect to the divergent electron beam, while the angle between normals to the surfaces of the cathode 1 and each anode 2, 2&#39; is greater than zero but less than 180°, the acclerating electrodes 3, 3&#39; being disposed in the openings of these angles on either side of the cathode 1. The distances between the accelerating electrodes 3, 3&#39; the anodes 2, 2&#39; are substantially greater than those between the cathode 1 and the accelerating electrodes 3, 3&#39;. The control electrodes 4 and 4&#39; are located between the cathode 1 and each accelerating electrode 3, 3&#39;. Arranged opposite the cathode 1 is a cathode-adjacent focusing electrode 5 having a conical inner surface, and disposed between the accelerating electrodes 3, 3&#39; and anodes 2, 2&#39; are anode-adjacent focusing electrodes 6 and 6&#39;. The arrangement of individual electron-optical systems is such that the accelerating electrodes 3, 3&#39;, control electrodes 4, 4&#39; and anode-adjacent focusing electrodes 6, 6&#39; are common for two adjacent electron-optical systems. Such an arrangement permits switching heavier currents due to the larger emitting surface of the cathode with individual electron-optical systems being arranged in a convenient simple manner. 
     In the embodiments of the proposed electron-beam converter, described above and illustrated in FIGS. 2 to 9, the distribution of the electrode potentials is similar to that in the embodiment of FIG. 1.