A focusing electrode controlled electron gun, traveling wave tube and design method

Abstract

An embodiment of the present invention discloses a focusing electrode controlled electron gun, a traveling wave tube and a design method, wherein the electron gun comprises: a cathode, an anode, a focusing electrode and a conical structure; wherein the cathode is an annular cathode for emitting electrons; the anode is used to apply a positive potential to the cathode; the conical structure has the same potential as the cathode, is embedded in the center of the annular cathode and does not emit electrons, and the conical structure has a geometric shape in which the radial dimension is reduced along the direction of travel of the electron beam so that the inner edge of the annular electron beam has a desired potential distribution along the direction of travel; the focusing electrode surrounds the annular cathode and is used to control the emission and cutoff of the electrons and make the electrons converge into an electron beam. The focusing electrode controlled electron gun, the traveling wave tube and the design method provided by the present invention greatly reduce the cutoff voltage of the focusing electrode controlled electron gun by embedding the conical structure in the center of the annular cathode and making the conical structure and the annular cathode have the same potential.

Description

Technical Field

[0001] The invention relates to the technical field of electron guns, and in particular to a focusing pole controlled electron gun, a traveling wave tube and a design method. Background Art

[0002] The emergence of microwave tubes has greatly promoted the development of electronic technology and information technology. As the most representative device of microwave tubes, traveling wave tubes have the characteristics of wide bandwidth and high gain, and are widely used in satellite communications, radars and electronic countermeasures equipment. Different uses require that traveling wave tubes can work in different working modes of pulse and continuous wave, and require that the modulation voltage amplitude of the electron gun is as low as possible. Pierce proposed a design method for focusing electrode controlled electron guns, and the designed electron gun has a simple structure and long life. The disadvantage is that the cutoff voltage amplitude of the electron gun is relatively high, usually 0.1-0.5 times the working voltage, which is not conducive to rapid modulation of the signal. Wolkstein designed a grid-controlled gun for traveling wave tubes. The cutoff voltage of the grid-controlled gun is very low, and the modulation voltage amplitude is usually 0.01-0.1 times the working voltage, but the grid structure has reliability problems due to the interception of current. Gallagher proposed the structure of a rod-controlled gun on this basis. The control rod at the center of the cathode has the same potential as the focusing electrode, and will not intercept current while reducing the cutoff voltage, which solves the problem of reliability of the grid-controlled gun to a certain extent, but the control rod structure will lead to poor vibration resistance of the gun. In addition, since the control rod and the cathode have different potentials, special attention must be paid to the alignment and insulation of the cathode and the control rod, and high requirements are placed on the processing and assembly accuracy of the electron gun. Summary of the invention

[0003] The object of the present invention is to provide a focusing electrode controlled electron gun, a traveling wave tube and a design method, which significantly reduces the cutoff voltage of the focusing electrode controlled electron gun by embedding a conical structure in the center of an annular cathode and setting the conical structure and the annular cathode to the same potential.

[0004] In order to achieve the above object, the present invention adopts the following technical solutions:

[0005] In one aspect, the present invention provides a focusing electrode controlled electron gun, the electron gun comprising: a cathode, an anode, a focusing electrode and a conical structure;

[0006] in,

[0007] The cathode is a ring-shaped cathode for emitting electrons;

[0008] The anode is used to apply a positive potential to the cathode;

[0009] The conical structure has the same potential as the cathode, is embedded in the center of the annular cathode and does not emit electrons. The conical structure has a geometric shape in which the radial dimension decreases along the traveling direction of the electron beam so that the inner edge of the annular electron beam has a desired potential distribution along the traveling direction.

[0010] The focusing electrode surrounds the annular cathode and is used for controlling the emission and cutoff of the electrons and converging the electrons into electron beams.

[0011] In a specific embodiment, the conical structure has a protrusion located in the center.

[0012] In a specific embodiment, the conical structure has a conical protrusion located in the center.

[0013] In a specific embodiment, the conical structure is used to make the inner electron beam converge and then diverge to the position where the magnetic induction intensity is strongest at the end of the periodic permanent magnet system when the radius is the largest.

[0014] In a specific embodiment, the inner diameter and outer diameter of the annular cathode are determined by the electron gun conductivity, the focusing electrode cutoff voltage and the cathode maximum current emission density.

[0015] In a specific embodiment, the conical structure is formed of a conductive metal having a melting point higher than the cathode operating temperature and a thermal expansion coefficient matching that of the cathode material.

[0016] In a specific embodiment, the material of the conical structure is molybdenum with an osmium film on the surface.

[0017] Another aspect of the present invention provides a traveling wave tube, the traveling wave tube comprising:

[0018] The electron gun as described above;

[0019] Input system, output system, slow wave structure and focusing system;

[0020] The input system is used to transmit an excitation signal;

[0021] The slow wave structure is used to obtain energy from the electron beam emitted by the electron gun so that the excitation signal is amplified;

[0022] The focusing system is used to maintain the shape of the electron beam;

[0023] The output system is used to output the amplified excitation signal.

[0024] Another aspect of the present invention provides a method for designing an electron gun, the method comprising:

[0025] The inner diameter and outer diameter of the annular cathode are determined according to the electron gun conductivity, the focusing electrode cut-off voltage and the cathode maximum current emission density;

[0026] Adjust the range of the electron gun so that the converging electron beam meets the initial conditions when entering the focusing system;

[0027] The conical structure is adjusted so that when the converging electron beam diverges to the maximum radius, it is at the position where the magnetic induction intensity of the focusing system is the strongest.

[0028] In a specific embodiment, adjusting the range of the electron gun includes increasing the range of the electron gun by adjusting the size of the focusing electrode, the anode, and the geometric shape of the tapered structure.

[0029] The beneficial effects of the present invention are as follows:

[0030] The present invention provides a focusing electrode controlled electron gun, a traveling wave tube and a design method, which greatly reduces the cutoff voltage of the focusing electrode controlled electron gun and the performance index requirements of the focusing electrode controlled electron gun on the power supply by embedding a conical structure in the center of the annular cathode and setting the conical structure and the annular cathode to the same potential, and is conducive to the miniaturization design of the microwave tube. Compared with the grid-controlled gun and the rod-controlled gun, it has unique advantages and competitiveness and greatly expands the application occasions of the focusing electrode controlled electron gun. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the specific implementation methods of the present application or the existing technical solutions, the drawings required for use in the specific implementation methods or the existing technical descriptions will be briefly introduced below. Obviously, the drawings described below are an implementation method of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0032] Figure 1 A cross-sectional stereoscopic schematic diagram is shown when the focusing electrode controls the electron gun to be incompletely cut off in the prior art.

[0033] Figure 2 A schematic cross-sectional view of the structure of a focusing electrode controlled electron gun in the prior art is shown.

[0034] Figure 3 A schematic cross-sectional view of the structure of a focusing electrode controlled electron gun according to an embodiment of the present invention is shown.

[0035] Figure 4 A schematic structural diagram of a conical structure, an annular cathode and a cathode support tube in a focusing electrode controlled electron gun according to an embodiment of the present invention is shown.

[0036] Figure 5 A cross-sectional stereoscopic schematic diagram of an optimal electron beam simulation result of a focusing electrode controlled electron gun according to an embodiment of the present invention is shown.

[0037] Figure 6 A schematic diagram showing a two-dimensional electron beam trajectory of a focusing pole controlled electron gun RZ plane and the magnetic induction intensity along the Z direction at the corresponding position according to an embodiment of the present invention is shown.

[0038] Figure 7 A schematic diagram of electron beam current density distribution at z=25-45 mm of a focusing electrode controlled electron gun according to an embodiment of the present invention is shown.

[0039] Figure 8 A schematic diagram of electron beam current density distribution at z=50-70 mm of a focusing electrode controlled electron gun according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0040] In order to make the technical solution of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. The present invention is described in detail below through specific embodiments, but these do not constitute a limitation of the present invention. Without departing from the principle of the present invention, those skilled in the art may make variations and improvements, which should also be regarded as the protection scope of the present invention.

[0041] The electron gun cathode electron emission formula is

[0042]

[0043] Among them, j is the cathode emission current density; e is the electron charge; m is the electron mass; k is the Boltzmann constant; h is the Planck constant; T is the Kelvin temperature; φ is the work function of the material used; A0 is the emission constant. In actual operation, the cathode works in a space charge limited state. Under the condition of ignoring the influence of the initial electron velocity, the cathode emission current density has the following relationship with the inter-electrode position and inter-electrode potential:

[0044]

[0045] (2) is for the planar diode structure of the electron gun, where ε0 is the vacuum dielectric constant; x represents the position between the cathode and the anode (including the position where the cathode and the anode are located); U' corresponds to the potential at the x position. Substituting x = d a , U'=U' a , d a is the position of the anode, U' a is the potential at the anode, and the cube law of the relationship between anode current and voltage can be obtained.

[0046] For the spherical diode structure of the electron gun, it is necessary to multiply equation (2) by a coefficient related to the electrode shape and size to obtain:

[0047]

[0048] (-α) is the Langmuir function of the spherical diode, which can be expressed in the series form of the following formula (4):

[0049]

[0050] Among them, R K is the cathode curvature radius, a1=1, a2=0.3,

[0051] The first few terms of the Langmuir function (-α) are

[0052]

[0053] It can be seen from equations (3) and (4) that when the cathode is cut off, j = 0, U' must be 0, and x can be any value between the electrodes. For the electron gun structure, the focusing electrode is required to be at a negative potential, and the cathode is cut off from emitting by introducing a zero potential between the anode and cathode. This process can be intuitively understood as the focusing electrode gradually shielding the positive potential of the anode through the negative potential, so that the cathode is cut off from emitting. Whether shielding can be achieved depends on whether the potential of the focusing electrode can make the potential of U' = 0V cover the cathode surface.

[0054] like Figure 1 and Figure 2 As shown, the focusing electrode controlled electron gun in the prior art includes: a focusing electrode, an anode and a cathode. The potential distribution in the electron gun area is determined by the electrode potential distribution and the spatial charge distribution. Combining the above-mentioned electron gun cathode cutoff conditions and the structural distribution of the focusing electrode controlled electron gun, it can be known that: on the one hand, the focusing electrode is far away from the cathode center; on the other hand, the potential distribution in the cathode center area is greatly affected by the spatial charge. Therefore, the efficiency of the focusing electrode in cutting off the cathode center is very low, resulting in a very high cutoff voltage of the electron gun controlled by the focusing electrode. In a specific embodiment, the cathode potential is 0V, the anode potential is +4500V, the focusing electrode potential is -900V, and the electron gun cutoff voltage is -1250V. The focusing electrode has not reached the cutoff voltage, and the electron gun is not completely cut off, such as Figure 1 As shown, there is leakage current emission in the center of the cathode. The cathode part covered by the U'=0V equipotential line cuts off the emission, and the cathode part not covered by the U'=0V equipotential line cannot cut off.

[0055] Based on the cathode cut-off principle of the electron gun, the present embodiment provides a focusing electrode controlled electron gun, such as Figure 3 As shown, the electron gun includes: a cathode, an anode, a focusing electrode and a cone structure.

[0056] Among them, the cathode is an annular cathode for emitting electrons; the anode is used to apply a positive potential to the cathode to lead the electrons in the direction of the anode; the conical structure has the same potential as the cathode, is embedded in the center of the annular cathode and does not emit electrons, and the conical structure has a geometric shape with a radial dimension that decreases along the direction of electron beam travel, so that the inner edge of the annular electron beam has a required potential distribution along the direction of travel, wherein the required potential distribution is the potential distribution that meets the technical indicators of the electron gun in order to meet the design parameters of the microwave tube; the focusing electrode surrounds the annular cathode, and is used to control the emission and cutoff of the electrons and converge the electrons into an electron beam.

[0057] The cathode is set as an annular cathode so that there is no electron emission in the center area of ​​the cathode, which is the most difficult to cut off. At the same time, a conical structure is designed in the center of the cathode to improve the control ability of the focusing electrode over the cathode. Different from the rod-controlled electron gun, the focusing electrode controlled electron gun provided in this embodiment has a conical structure that has the same potential as the cathode regardless of whether the electron gun is in normal working state or cut-off state. When the electron gun is working normally, the conical structure is used to maintain the potential distribution of the center area of ​​the electron beam, that is, the edge of the inner electron beam, to maintain the laminar flow of the electron beam; when the electron gun is cut off, the conical structure protrudes in front of the cathode, which can reduce the potential of the center of the electron gun, reduce the influence of space charge on space potential, and cooperate with the focusing electrode to enable the focusing electrode to cut off the cathode at a lower voltage.

[0058] The conical structure is located inside the annular cathode and is formed by a high melting point conductive metal. The working temperature of the annular cathode is about 1350K. The melting point of the conical structure material is higher than the working temperature of the annular cathode and has a high thermal conductivity. At the same time, at the working temperature, the conical structure cannot have thermal electron emission. The conical structure is embedded in the center of the annular cathode and has an important influence on the electron injection potential distribution in the electron gun area. It is required that the thermal expansion coefficient of the conical structure must match the thermal expansion coefficient of the cathode material. In a specific embodiment, metal molybdenum is selected and an osmium film is plated on its working surface as the material of the conical structure. Molybdenum is in the fifth period VIB group of the periodic table, with an atomic number of 42 and an atomic weight of 95.95. The melting point of molybdenum is 2895K±10K, the work function is 4.20eV, and the work function after coating with osmium film is about 4.00~4.10eV to ensure that there is no electron emission at the working temperature. Molybdenum has a small thermal expansion coefficient and the working temperature is about 5.5×10 -6 At the same time, the thermal conductivity of metal molybdenum is relatively high.

[0059] Adding a conical structure to the center of the cathode can significantly reduce the cutoff voltage of the electron gun, but for electron guns with the same parameter requirements, the emission area of ​​the annular cathode is smaller and the cathode load (i.e., cathode emission current density) is larger. In the design process of the electron gun, the cathode load needs to be given priority. The inner and outer diameters of the annular cathode need to be determined by the electron gun conductivity, the focusing electrode cutoff voltage, and the maximum cathode current emission density. Under the conditions of a given electron gun conductivity and cutoff voltage, the cathode portion that the focusing electrode can cut off is also determined, that is, the width r of the annular cathode ring is determined. 外 -r 内 . Then according to the ring cathode emission current density

[0060]

[0061] The outer diameter r of the annular cathode can be calculated 外 and inner diameter r 内 The shape of the annular cathode surface should be determined according to the spatial potential distribution when the electron gun is working normally. This is because the average load of the annular cathode of the electron gun is large and may be very close to the maximum load allowed by the annular cathode. Therefore, it is necessary to optimize the focusing electrode structure, change the shape of the cathode surface, etc. to ensure the emission consistency of the cathode surface.

[0062] The conical structure is mainly used to maintain the required potential distribution of the inner edge of the annular electron beam emitted by the annular cathode along the traveling direction, but the existence of the conical structure will also affect the transition zone matching of the electron beam entering the magnetic field. Because the radius of the electron beam will become very small before entering the high-frequency structure of the traveling wave tube, the inner electrons will eventually converge under the action of the outer electron space charge force, which means that the trajectory of the inner electrons does not meet the ideal initial incidence condition of the periodic permanent magnet focusing system. The electron gun structure with a larger compression ratio and a shorter range is less conducive to the transition zone matching of the magnetic field. The minimum size of the annular cathode has been given according to the cathode load, and the electron beam radius is also limited by the inner diameter of the traveling wave tube helix. Therefore, this embodiment provides a method for solving the problem of introducing a conical structure to affect the transition zone matching of the electron beam entering the magnetic field: on the one hand, the range of the electron gun is increased, so that the slope of the inner electrons when converging is reduced, as close as possible to the ideal incidence condition of the periodic permanent magnet focusing system; on the other hand, the end effect of the magnetic induction intensity of the periodic permanent magnet system is reasonably utilized to reduce the pulsation of the electron beam. The 1st, 2nd, 3rd, and 4th peak magnetic induction intensities at the end of the periodic permanent magnet system will be the weakest, strongest, second weakest, and second strongest in turn. By adjusting the conical structure, that is, adjusting the radial dimension of the conical structure along the direction of electron beam travel, the inner electron beam converges and then diverges to the maximum radius at the second peak of the periodic permanent magnet system, that is, the position with the strongest magnetic induction intensity at the end of the periodic permanent magnet system, the pulsation of the electron beam can be effectively reduced, such as Figure 4As shown, in a specific embodiment, a schematic diagram of the structure of a conical structure, an annular cathode and a cathode support tube, wherein the cathode support tube can be any existing suitable cathode support tube, and the conical structure has a protrusion located in the center. Those skilled in the art can understand that the shape of the conical structure can be adjusted as needed, and the present application does not specifically limit the shape of the conical structure. When assembling the electron gun, the conical structure, the annular cathode and the cathode support tube can be brazed together. The brazed structure is led out in the form of an electrode to achieve the same potential of the conical structure and the annular cathode, thereby simplifying the structure of the electron gun.

[0063] Therefore, an embodiment of the present invention further provides an electron gun design method, which includes: determining the inner diameter and outer diameter of the annular cathode according to the electron gun conductivity, the focusing electrode cutoff voltage and the cathode maximum current emission density; adjusting the range of the electron gun so that the converged electron beam meets the initial conditions when entering the focusing system; adjusting the conical structure so that the converged electron beam is at the position where the magnetic induction intensity of the focusing system is the strongest when it diverges to the maximum radius. Wherein, adjusting the range of the electron gun includes increasing the range of the electron gun by adjusting the size of the focusing electrode and the anode and the geometric shape of the conical structure.

[0064] Taking an existing conventional structure focusing electrode controlled electron gun as an example, its conductivity is 0.53μP, working voltage is 4500V, cut-off voltage is -1250V, and cathode allowable load is 4A / cm 2 . A conical structure design is now adopted to reduce its cut-off voltage to -600V. By simulating the potential distribution of the electron gun focusing electrode at -600V, it is found that the focusing electrode can cut off the annular cathode with a width of about 0.7mm. Considering the insulation between the annular cathode and the focusing electrode, the width of the annular cathode should be 0.4mm. According to the allowable current density of the annular cathode, it can be determined that the outer diameter of the annular cathode should be 1.8mm and the inner diameter should be 1.4mm. The conical structure is embedded in the annular cathode, and the radius should also be 1.4mm, but the shape design of the conical structure is not unique. Since the function of the conical structure is to maintain the required potential distribution of the inner edge of the annular electron beam along the direction of travel, it can be a combination of one or more geometric shapes as long as it can satisfy the required potential distribution of the inner edge of the annular electron beam along the direction of travel. A more representative conical structure is selected here, such as Figure 4 As shown, the conical structure has a conical protrusion located in the center and with a radial dimension that decreases along the direction of electron beam travel. The conical protrusion can reduce the influence of part processing errors on the electron beam edge potential. Since the current emission density of the annular cathode design is very close to the maximum current emission density allowed by the annular cathode, the emission consistency of the annular cathode surface is very important. The shape of the annular cathode needs to be modified according to the current emission density distribution on the annular cathode surface at the end of the electron gun design.

[0065] In order to make the effect achieved by the focusing electrode controlled electron gun provided by this embodiment more intuitive, this embodiment performs a simulation calculation on a focusing electrode controlled electron gun provided by this embodiment and gives corresponding simulation results.

[0066] Ignoring the self-magnetic field of the electron beam, the optical equations of the high-current electrons of the focusing electrode controlling the electron gun can be simplified to

[0067]

[0068]

[0069]

[0070] In formulas (7), (8), and (9), ρ is the space charge density; ε0 is the vacuum dielectric constant; U represents the potential distribution in the electron gun region under the influence of space charge; is the Hamiltonian operator; e is the electron charge; m is the electron mass; is the electric field direction vector; is the electron velocity direction vector; is the field intensity direction vector of the periodic permanent magnet focusing system; is the cathode emission current direction vector.

[0071] (7)(8)(9) The equations are mutually constrained. U is related to the space charge density ρ, which in turn depends on the motion state of the electrons, which in turn depends on the electric field. Or U. The equation is solved by iterative method until convergence, and the trajectory of the electron can be obtained.

[0072] The peak value of the magnetic field intensity of the minimum pulsating electron beam obtained by the periodic permanent magnet focusing system has the following relationship with the magnetic field value of the complete shielding flow

[0073]

[0074] Where B0 is the peak value of the periodic magnetic field of the periodic permanent magnet focusing system, I0 is the electron injection current, U represents the potential distribution in the electron gun area under the influence of space charge, and r b is the electron beam radius, B b is the Brillouin flow magnetic induction intensity. Due to the influence of factors such as the non-ideal initial conditions of electron injection, the inhomogeneity of the periodic field and the initial thermal velocity of electrons, the actual selection of the peak value of the periodic magnetic field is usually 1.5-2 times B0.

[0075] According to the above simulation calculation formula, Opera software is used to simulate a focusing electrode control electron gun provided in this embodiment, and the electrode structure of the electron gun is optimized according to the method according to the present invention to obtain the optimal electron beam, such as Figure 5As shown in , it can be seen that the hollow electron beam can still pass through the periodic permanent magnetic focusing system without satisfying the initial conditions of the periodic permanent magnetic focusing magnetic field. Figure 6 As shown, Figure 6 The figure shows the two-dimensional electron beam trajectory in the RZ plane (i.e., radial-axial section) of the electron gun and the magnetic induction intensity along the Z direction (axial direction) at the corresponding position, where the cathode center is taken as the origin, the direction of the anode is the positive direction of the Z axis, and the direction upward from the cathode center is the positive direction of the R axis. Figure 6 Only the electron beam trajectory in the positive direction of the R axis is shown. Those skilled in the art will understand that the electron beam trajectory in the negative direction of the R axis of the annular cathode is symmetrical and the same as the positive direction. It can be seen that there is a relatively obvious pulsation in the electron beam trajectory envelope. It is worth noting that the generation of this pulsation is not caused by the unreasonable setting of the magnetic field peak value. In essence, it is caused by the destruction of the laminar flow of the electron beam in the transition zone. At z = 10-20mm, the inner electrons converge and then diverge, causing the outer electrons to lose the space charge force of the inner electrons and converge, which means that the space charge force is not stably distributed along the z direction. Under the action of the periodic permanent magnet system, pulsation will inevitably occur. However, according to the above solution to the problem that the introduction of a conical structure will affect the matching of the transition zone where the electron beam enters the magnetic field, on the basis of increasing the range of the electron gun, the end effect of the magnetic field is reasonably used to reduce the pulsation of the electron beam and control the electron beam radius within 0.5mm.

[0076] After the peak value of the periodic magnetic field stabilizes (i.e., the 4th peak), sections are set at different positions of the electron beam trajectory to plot the current density distribution of the electron beam at different positions, such as Figure 7 and Figure 8 As shown, Figure 7 is the electron beam current density distribution at z = 25-45 mm, Figure 8 is the electron beam current density distribution at z = 50-70mm, where lines 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10 represent the electron beam current density distribution at z = 25mm, 30mm, 35mm, 40mm, 45mm, 50mm, 55mm, 60mm, 65mm, and 70mm, respectively. It can be seen that after the electron beam converges from the hollow beam, the current density is not uniformly distributed along the cross section, but is mainly concentrated between r = 0.15 and 0.30mm, and the peak position fluctuates slightly with the change of z. On the other hand, when r = 0, the current density of the cross section tends to zero. This is because when the electron enters the magnetic field, r = 0, and the velocity v in the r direction is r ≠ 0. This means that electrons cannot exist stably at r = 0, and the hollow electron beam passes through the periodic permanent magnetic focusing system after convergence, presenting a "quasi-hollow beam" state.

[0077] The electron gun cut-off state is simulated. Table 1 shows the performance parameters of the electron gun with a cone structure and the conventional focusing electrode control electron gun under the same conductivity coefficient. By appropriately increasing the load under the conditions allowed by the cathode and reducing the pulsation of the electron beam by increasing the electron gun range, the cut-off voltage of the electron gun can be reduced by more than half.

[0078] Table 1

[0079]

[0080] Another aspect of the present invention provides a traveling wave tube, which comprises: the above-mentioned focusing pole controlled electron gun, an input system, an output system, a slow wave structure, a periodic permanent magnet system, a concentrated attenuator and a collecting pole.

[0081] Among them, the input system is used to transmit the excitation signal; the slow-wave structure is used to obtain energy from the electron beam emitted by the electron gun to amplify the excitation signal; the periodic permanent magnet system is used to maintain the shape of the electron beam; the output system is used to output the amplified excitation signal; the concentrated attenuator is used to prevent self-excited oscillation; the collector is used to collect electrons after handing over the fundamental wave energy.

[0082] The present invention provides a focusing pole controlled electron gun, a traveling wave tube and a design method, which greatly reduce the cut-off voltage of the focusing pole controlled electron gun by adding a conical structure at the center of the annular cathode. In view of the problem that the introduction of the conical structure affects the matching of the transition zone where the electron beam enters the magnetic field, a method of increasing the range of the electron gun and utilizing the end effect of the periodic permanent magnet system is proposed. The periodic magnetic field is successfully utilized to maintain the electron beam radius within 0.5 mm when the electron beam does not meet the initial incidence condition, thereby reducing the performance index requirements of the focusing pole controlled electron gun on the power supply, facilitating the miniaturized design of the microwave tube, having unique advantages and competitiveness compared with the grid controlled gun and the rod controlled gun, and greatly expanding the application occasions of the focusing pole controlled electron gun.

[0083] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the protection scope of the present invention.

Claims

1. A traveling wave tube, characterized in that: The traveling wave tube comprises: The focusing electrode controls the electron gun; Input system, output system, slow wave structure and focusing system; The focusing system is used to maintain the shape of the electron beam; The electron gun comprises: a cathode, an anode, a focusing electrode and a cone structure; The cathode is a ring-shaped cathode for emitting electrons; The anode is used to apply a positive potential to the cathode; The conical structure has the same potential as the cathode, is embedded in the center of the annular cathode and does not emit electrons. The conical structure has a geometric shape in which the radial dimension decreases along the traveling direction of the electron beam so that the inner edge of the annular electron beam has a desired potential distribution along the traveling direction. The focusing electrode surrounds the annular cathode and is used to control the emission and cutoff of the electrons and to converge the electrons into electron beams. The radial dimension of the conical structure along the traveling direction of the electron beam enables the inner electron beam to converge and then diverge to the position where the magnetic induction intensity at the end of the periodic permanent magnet system is the strongest when the radius is the largest.

2. The traveling wave tube according to claim 1, characterized in that: The conical structure has a protrusion located in the center.

3. The traveling wave tube according to claim 2, characterized in that: The conical structure has a conical protrusion located in the center.

4. The traveling wave tube according to claim 1, characterized in that: The inner diameter and outer diameter of the annular cathode are determined by the electron gun conductivity, the focusing electrode cut-off voltage and the cathode maximum current emission density.

5. The traveling wave tube according to claim 1, characterized in that: The conical structure is formed of a conductive metal having a melting point higher than the cathode operating temperature and a thermal expansion coefficient matching that of the cathode material.

6. The traveling wave tube according to claim 5, characterized in that: The material of the cone structure is molybdenum with an osmium film on the surface.

7. The traveling wave tube according to claim 1, characterized in that: The input system is used to transmit an excitation signal; The slow wave structure is used to obtain energy from the electron beam emitted by the electron gun so that the excitation signal is amplified; The output system is used to output the amplified excitation signal.

8. A traveling wave tube design method according to claim 1, characterized in that: The method includes: The inner diameter and outer diameter of the annular cathode are determined according to the electron gun conductivity, the focusing electrode cut-off voltage and the cathode maximum current emission density; Adjust the range of the electron gun so that the converging electron beam meets the initial conditions when entering the focusing system; The conical structure is adjusted so that when the converging electron beam diverges to the maximum radius, it is at the position where the magnetic induction intensity of the focusing system is the strongest.

9. The traveling wave tube design method according to claim 8, characterized in that: The adjusting the range of the electron gun includes increasing the range of the electron gun by adjusting the size of the focusing electrode, the anode and the geometric shape of the conical structure.

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