Terahertz gyrotron traveling wave tube low velocity zero spread magnetic control injection electron gun and design method

Abstract

The application discloses a gyrotron traveling wave tube low-speed zero dispersion magnetic control injection electron gun and a design method, and belongs to the field of vacuum electron devices. The electron gun comprises a cathode and an anode; the cathode comprises a cathode bottom table, a rear forming pole, an emission band and a front forming pole, wherein the radius of the cathode bottom table is greater than that of the rear forming pole, the emission band bus is a circular arc curve, and the overall surface of the front forming pole is a circular arc surface; in addition, in the design of the cathode, twice modeling is carried out, and partial parameters are simulated and optimized respectively, so that the parameters of the one-time simulation and optimization process are reduced, the optimization target is more clear, the design difficulty is effectively reduced, and the design time is shortened. The application effectively solves the problem of excessively high electric field in the gun area of the electron gun due to excessively small size of the cathode, simultaneously solves the adverse influence of the sudden change structure of the cathode on the surface electric field of the emission band, and effectively reduces the speed zero dispersion of the electron gun.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of vacuum electron devices, and particularly relates to a low-speed zero velocity magnetic control injection electron gun of a gyrotron traveling wave tube and a design method. BACKGROUND

[0002] The Electron Cyclotron Maser (ECM) mechanism is a mechanism based on relativistic radiation, which utilizes the interaction between a gyro-electron beam and electromagnetic waves to generate high-power microwave radiation. The gyrotron traveling wave tube is a microwave amplifier device based on the ECM mechanism, which has the characteristics of high efficiency, wide frequency band and large power, and is widely used in radar imaging, communication and electronic countermeasures.

[0003] In order to further improve the imaging resolution, guarantee the communication anti-interference ability and bandwidth, it is urgent to develop a wideband and high-power terahertz gyrotron traveling wave tube. Due to the size crossing effect, when the working frequency reaches the G-band, the cathode emission band radius of the traditional magnetic control injection electron gun structure of the TE02 mode gyrotron traveling wave tube is only about 1.7 mm, and the radius of the top of the front forming pole cone is only about 1 mm. In the case that the voltage difference between the cathode and the anode reaches 50 kv, the sharp-pointed electric field is easily formed on the cathode surface, and the electric field can still reach 3x10 7 v / m 3x10 7 v / m under the condition that the edge of the front forming pole cone has been chamfered, which is much larger than the safety electric field 2x10 7 v / m 2x10 7 v / m required under the current vacuum condition. At the same time, the existence of the sharp-pointed electric field leads to uneven distribution of the electric field on the cathode surface, and the electric field difference between the front and rear ends of the emission band is large, so that the electron trajectory is difficult to control, and a large speed dispersion is easily caused, so that the electron beam which can interact with the electromagnetic wave efficiently cannot be obtained.

[0004] At present, researchers have proposed an improved cathode structure for the above-mentioned problems existing in the terahertz gyrotron traveling wave tube electron gun, which mainly replaces the straight line of the cathode emission band and the generatrix of the front forming pole with a curve to reduce the electric field peak value, adjust the electric field distribution on the cathode surface and reduce the speed dispersion of the electron gun. However, the curve is mainly obtained by multi-point fitting, which leads to the fact that many parameters need to be considered in the modeling and optimization process, and the optimization target for the emission band curve is not clear, so that the design time is long and the design difficulty is great. SUMMARY

[0005] In view of the problems of high electric field peak value of the magnetic control injection electron gun of the existing gyrotron, which is prone to strong field breakdown, and uneven electric field distribution on the cathode surface, which is prone to large velocity dispersion, the application provides a gyrotron low-velocity dispersion magnetic control injection electron gun and a design method thereof.

[0006] To achieve the above-mentioned purpose, the application adopts the following technical solutions:

[0007] A gyrotron low-velocity dispersion magnetic control injection electron gun, comprising an electron gun anode and a cathode coaxially arranged inside the electron gun anode.

[0008] The cathode comprises a cathode base platform, a rear forming pole, an emission zone and a front forming pole arranged in sequence along the axial direction and having radii decreasing in sequence.

[0009] The radius of the cathode base platform is greater than the radius of the rear forming pole, and the connecting part of the cathode base platform and the rear forming pole is chamfered to make the cathode base platform smoothly transition to the rear forming pole.

[0010] The rear forming pole is a circular truncated cone, and the generatrix thereof is a straight line segment.

[0011] The emission zone is a circular truncated cone, and the generatrix thereof is a first circular arc curve.

[0012] The front forming pole has a whole surface of a circular arc surface, and the generatrix thereof is a second circular arc curve.

[0013] Preferably, when the working wave band of the electron gun is the G wave band, the radius of the cathode base platform is 3.63 mm, the rear end radius of the rear forming pole is 3.13 mm, the front end radius is 2.58 mmz, the axial length is 0.83 mm, the front end radius of the emission zone is 1.01 mm, the rear end radius is 2.58 mm, the axial length is 1.41 mm, the convexity of the first circular arc curve is 0.08, the rear end radius of the front forming pole is 1.01 mm, and the convexity of the second circular arc curve is 0.2.

[0014] On the other hand, the application also provides a design method of the gyrotron low-velocity dispersion magnetic control injection electron gun based on the above-mentioned structure, comprising the following steps:

[0015] S1. Calculate the initial values of the center radius R of the emission zone of the magnetic control injection electron gun, the emission zone length L and the anode-cathode distance d1 by formulas (1)-(3): c s

[0016]

[0017] d1=U0 / E0(3)​​

[0018] where fm is the magnetic compression ratio, r g0 is the guiding center radius of electron cyclotron, I0 is the emission current size of the emission band, J c is the current density allowed to emit, U0 is the voltage between the cathode and the anode, and E0 is the space electric field between the cathode and the anode under restriction.

[0019] S2. With the central axis of the electron gun as the z-axis, the generatrix of the emission band is set as a straight line, and the angle between the z-axis and the straight line is θ, the front end radius Rc2 of the emission band is obtained, and the rear end radius Rc3 of the emission band is obtained:

[0020] Rc2 = Rc - Ls x sin θ (4)

[0021] Rc3 = Rc + Ls x sin θ (5)

[0022] The generatrix of the front forming pole is set as a straight line, the length of the straight line is L f , and the angle between the z-axis and the straight line is θ f , and the front end radius Rc1 of the front forming pole is obtained:

[0023] Rc1 = Rc2 - L f x sin θ f (6)

[0024] The generatrix of the rear forming pole is set as a straight line, the length of the straight line is L b , and the angle between the z-axis and the straight line is θ b , and the rear end radius Rc4 (i.e. the radius of the cylindrical part of the cathode base) of the rear forming pole is obtained:

[0025] Rc4 = Rc3 + L b x sin θ b (7)

[0026] The radius of the cathode base is set as Rc5, and Rc5 > Rc4; the fillet radius at the connection between the cathode base and the rear forming pole is r1.

[0027] S3. Given the initial values of θ, θ f , θ b , Rc5 and r1, an initial simulation model is established and simulated and optimized in combination with steps S1 and S2, and a preliminary optimized simulation model is obtained.

[0028] S4. With the central axis of the electron gun as the z-axis, the center of the front end of the emission band as the origin o, and any straight line passing through the origin o and perpendicular to the z-axis as the x-axis, a rectangular coordinate system xoz is established;

[0029] The starting coordinates of the first circular arc curve of the emission band are set as (x1, z1), and the terminal coordinates are set as (x2, z2), and the center position (Xcenter , Z center ) :

[0030]

[0031] Wherein, x1=Rc3, z1=0, x2=Rc2, z2=Ls*cos theta;bulge1 is the convexity of the first circular arc curve, that is, the index describing the concave-convex of the segment of the circular arc.

[0032] Supposing that the starting coordinate of the second circular arc curve of the front forming pole is (x3, z3), and the terminal coordinate is (x4, z4);Since the front end of the front forming pole is a circular arc surface as a whole, the center position of the second circular arc curve is (0, Z center ) :

[0033]

[0034] Wherein, x3=Rc2, x4=-Rc2;bulge2 is the convexity of the second circular arc curve.

[0035] S5. The formula (8)-(10) is brought into the preliminary optimization simulation model obtained in step S3, and the convexity bulge1 and bulge2 are subjected to parameter scanning processing in the simulation software, so as to obtain the value that makes the electron velocity dispersion lowest, and the design of the low-speed dispersion magnetron injection electron gun is completed.

[0036] Compared with the traditional structure and design scheme, the innovation of the present application mainly lies in:

[0037] 1. The present application increases the radius of the cathode bottom platform, so that it is greater than the radius of the rear end of the rear forming pole, and chamfers the connecting part, thus creating a discontinuous structure, forming a second extreme electric field, effectively reducing the peak electric field of the electron gun gun area, and improving the overall electric field of the cathode surface, thereby weakening the sensitivity of the emission band and the surface electric field of the front forming pole to the structure.

[0038] 2. The present application sets the emission band bus as a circular arc curve, which on the one hand increases the emission area, so that more electrons can be emitted under the same emission density, creating a larger current;In the case that the emission current size is unchanged, the emission density can be reduced to ensure the service life of the electron gun. On the other hand, according to the formula of the transverse velocity dispersion of the electron gun electron, the surface of the emission band is changed to an arc surface, which can further improve the emission band electric field, make the emission band electric field change uniformly, and be conducive to reducing the velocity dispersion;In addition, the emission band is an overall circular arc surface, which creates a discontinuous structure, which is conducive to improving the overall voltage of the emission band and the transverse velocity of the electron, thereby being conducive to overcoming the problem of backflow of the high-frequency electron gun.

[0039] 3、The present application sets the pre-forming pole integral bus as a circular arc curve, so that the whole is a smooth surface dome structure, avoids the discontinuity caused by the chamfer of the traditional structure, and the high electric field of the front end of the electron gun area, and further affects the over-adjustment of the emitted electrons, affects the electron trajectory, and further affects the problem of the speed dispersion of the electron beam.

[0040] 4、In the design of the electron gun cathode structure, by twice modeling and respectively simulating and optimizing part parameters, the parameters of the first simulation and optimization process are reduced, the optimization target is more clear, the design difficulty is effectively reduced, and the design time is shortened;In addition, in the second simulation process, by bringing the center formula of the first circular arc curve and the second circular arc curve into the preliminary optimization simulation model, the parameters to be optimized are further reduced, and by only scanning the parameters of the two convexities, a better electron gun cathode structure can be obtained.

[0041] In summary, the present application provides a terahertz gyro traveling wave tube low-speed dispersion magnetic control injection electron gun and a design method thereof, effectively solves the problem of high electric field of the electron gun area caused by the too small size of the cathode, and solves the adverse effect of the sudden structure of the cathode on the surface electric field of the emission belt, and effectively reduces the speed dispersion of the electron gun. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 It is a schematic diagram of a traditional magnetic control injection electron gun structure;

[0043] Figure 2 It is a schematic diagram of the structure of the embodiment terahertz gyro traveling wave tube low-speed dispersion magnetic control injection electron gun;

[0044] Figure 3 It is a magnified view of the cathode structure;

[0045] Figure 4 It is a traditional magnetic injection electron gun cathode equipotential line diagram;

[0046] Figure 5 It is a cathode equipotential line diagram of the embodiment terahertz gyro traveling wave tube low-speed dispersion magnetic control injection electron gun;

[0047] Figure 6 It is a comparison diagram of the surface electric field of the traditional magnetic injection electron gun cathode and the surface electric field of the embodiment terahertz gyro traveling wave tube low-speed dispersion magnetic control injection electron gun cathode;

[0048] Figure 7 It is a speed dispersion diagram and a speed ratio diagram of the embodiment terahertz gyro traveling wave tube low-speed dispersion magnetic control injection electron gun;

[0049] Figure 8The electron beam trajectory and muzzle electron distribution diagrams generated by the low-velocity discrete magnetron injection electron gun in the terahertz cyclotron traveling wave tube are shown in the example.

[0050] Explanation of the reference numerals: 1 Cathode, 2 Anode, 2-1 Cylindrical part of cathode base, 2-2 Chamfered part of cathode base, 2-3 Rear forming electrode, 2-4 Emitting strip, 2-5 Front forming electrode. Detailed Implementation

[0051] To better understand the purpose, features, and advantages of this invention, the invention will be further described in detail below with reference to an example of a G-band TE02 mode terahertz cyclotron traveling wave tube electron gun.

[0052] This embodiment provides a novel low-speed discrete magnetron injection electron gun for terahertz cyclotron traveling wave tubes, such as... Figure 2 As shown, it includes an electron gun anode and a cathode coaxially disposed inside the electron gun anode; the cathode is as follows Figure 3 As shown, it includes a cathode base, a rear forming electrode, an emission strip, and a front forming electrode arranged sequentially along the axial direction.

[0053] The cathode base is cylindrical with a radius of 3.63 mm. The connection between the cathode base and the post-formed electrode is chamfered with a radius of 1.5 mm to ensure a smooth transition from the cathode base to the post-formed electrode.

[0054] The post-formed part is extremely frustum-shaped, with its generatrix being a straight line segment, a rear end radius of 3.13 mm, a front end radius of 2.58 mm, and an axial length of 0.83 mm.

[0055] The launching strip is shaped like a frustum, with its generatrix being the first circular arc curve. Its front end radius is 1.01 mm, its rear end radius is 2.58 mm, its axial length is 1.41 mm, and the convexity of the first circular arc curve is 0.08.

[0056] The overall surface of the front-formed electrode is an arc surface, its generatrix is ​​a second arc curve, its rear end radius is 1.01mm, and the convexity of the second arc curve is 0.2.

[0057] To achieve better emission performance, a material that suppresses electron emission is applied to the front and rear ends of the emission strip to reduce the impact of electric field abrupt changes caused by discontinuities at the junction of the rear and front forming electrodes and the emission strip on electron beam.

[0058] In this embodiment, the process of obtaining the cathode size parameters is as follows:

[0059] S1. The emission zone center radius R of the magnetron-injected electron gun is calculated using formulas (1)-(3). c Launch belt length L s Initial value of the anode-cathode spacing d1:

[0060]

[0061] d1=U0 / E0(3)

[0062] Where fm is the magnetic compressibility ratio, r g0 I0 is the radius of the electron cyclotron's guiding center, I0 is the magnitude of the emission current in the emission band, and J0 is the emission current in the emission band. c R is the permissible emission current density, U0 is the voltage between the anode and cathode, and E0 is the restricted electric field between the anode and cathode; in this embodiment, R c The initial value is 1.8mm, and the length of the launching band is L. s The initial value is 2.1 mm, and the initial value of the anode-cathode spacing d1 is 16 mm.

[0063] S2. Taking the central axis of the electron gun as the z-axis, and setting the generatrix of the emission belt as a straight line with an angle θ with the z-axis, we obtain the front radius Rc2 and the rear radius Rc3 of the emission belt:

[0064] Rc2=Rc-Ls×sinθ(4)

[0065] Rc3=Rc+Ls×sinθ (5)

[0066] The generatrix of the preformed electrode is set to a straight line with a length of L. f The angle of inclination with the z-axis is θ f The front end radius Rc1 of the preformed electrode is obtained as follows:

[0067] Rc1=Rc2-L f ×sinθ f (6)

[0068] The generatrix of the formed electrode is set to be a straight line with a length of L. b The angle of inclination with the z-axis is θ b The radius of the rear end of the formed electrode, Rc4 (i.e., the radius of the cylindrical part of the cathode base), is obtained from the degree of gradation.

[0069] Rc4=Rc3+L b ×sinθ b (7)

[0070] The radius of the cathode base is set to Rc5, and the chamfer radius at the connection between the cathode base and the post-formed electrode is set to r1.

[0071] S3. Given θ, θ f θ b The initial values ​​of Rc5 and r1 are determined, and combined with steps S1 and S2, an initial simulation model is established and optimized to obtain a preliminary optimized simulation model; where θ is 48 degrees, θ f 40 degrees, θb 34 degrees, Rc5 is 3.64mm, r1 is 1.5mm.

[0072] S4. With the central axis of the electron gun as the z-axis, an arbitrary straight line through the origin o of the front end center of the emission band and perpendicular to the z-axis is defined as the x-axis to establish a rectangular coordinate system xoz.

[0073] Supposing that the starting coordinate of the first circular arc curve of the emission band is (x1, z1) and the terminal coordinate is (x2, z2), the center position (X center , Z center ) of the circular arc curve of the emission band is calculated.

[0074]

[0075] Wherein, x1 = Rc3, z1 = 0, x2 = Rc2, z2 = Ls x cos theta; bulge1 is the convexity of the first circular arc curve, that is, the concave-convex index of the circular arc.

[0076] The starting coordinate of the second circular arc curve of the front forming pole is (x3, z3) and the terminal coordinate is (x4, z4); since the front end of the front forming pole is a circular arc surface as a whole, the center position of the second circular arc curve is (0, Z center ):

[0077]

[0078] Wherein, x3 = Rc2, x4 = -Rc2; bulge2 is the convexity of the second circular arc curve.

[0079] S5. The formula (8)-(10) is brought into the preliminary optimization simulation model obtained in step S3, and the parameters of the convexities bulge1 and bulge2 are scanned in the simulation software to obtain the value that makes the electron velocity dispersion lowest, and correspondingly bulge1 = 0.08 and bulge2 = 0.2, so that the design of the low-speed dispersion magnetron injection electron gun is completed.

[0080] When the electron gun works, the anode is grounded as a whole and the cathode is applied with a negative high voltage, and the whole electron gun is in a superconducting magnetic field that converges to the axial direction and slowly increases to a specified size. The cathode emission band emits electrons, which are accelerated in the gun zone under the joint action of the cathode and anode electric field and the magnetic field, and then complete adiabatic compression in the transition zone to convert the longitudinal energy into transverse energy, and finally form a stable revolving electron beam with a certain transverse-longitudinal velocity ratio and velocity dispersion in the drift zone.

[0081] Figure 5 It is the cathode equipotential line diagram of the terahertz revolving wave tube low-speed dispersion magnetron injection electron gun of the embodiment, and Figure 4A comparison of the equipotential lines of the cathode of a conventional magnetically injected electron gun shows that the overall electric field of the electron gun in this embodiment is reduced, with the peak electric field decreasing from 3.06e7 to 1.85e7, effectively avoiding strong-field breakdown due to excessively high electric fields.

[0082] Figure 6 This is a comparison diagram of the surface electric field of the electron gun cathode in this embodiment and the surface electric field of a conventional electron gun. (Combined with...) Figure 5 It can be observed that the electric field on the surface of the electron gun in this invention is enhanced, effectively increasing electron energy; moreover, the electric field distribution on the surface of the electron gun is uniform. According to the formula for determining transverse velocity dispersion, it can be determined that this invention effectively reduces electron gun velocity dispersion. The difference between the electric field of the front and rear forming electrodes and the electron gun is not significant, which ensures that its influence on velocity dispersion is reduced.

[0083] Figure 7 This diagram shows the velocity dispersion and velocity ratio of the electron gun in the low-velocity discrete magnetron injection of the terahertz cyclotron traveling wave tube in this embodiment. It can be seen that the final electron gun velocity ratio stabilizes at around 1.1, and can reach below 2.4%, ensuring effective interaction of the electron beam in the high-frequency structure.

[0084] Figure 8 The diagrams show the electron beam trajectory and muzzle electron distribution generated by the low-velocity discrete magnetron injection electron gun in this embodiment of the terahertz gyrotron traveling wave tube. It can be seen that electrons can flow efficiently, with the electron ring formed at the muzzle having a center size of approximately 0.42 mm, meeting the injection-wave interaction requirements of a 220 GHz gyrotron traveling wave tube.

[0085] In summary, the novel low-velocity discrete magnetron injection electron gun and its design method for terahertz gyroscopic traveling wave tubes of this invention can effectively solve the problem of excessively high peak electric field caused by excessively small electron gun size. Furthermore, by designing and adjusting the cathode surface shape to change the surface electric field, the electron quality can be improved, the discreteness of the electron beam velocity can be reduced, and efficient electron beam-wave interaction can be achieved in the gyroscopic traveling wave tube.

Claims

1. A low-velocity discrete magnetron injection electron gun for a gyroscopic traveling wave tube, comprising an electron gun anode and a cathode coaxially disposed inside the electron gun anode; The cathode includes a cathode base, a rear-formed electrode, an emission strip, and a front-formed electrode arranged sequentially along the axial direction with decreasing radii. Its features are, The radius of the cathode base is larger than the radius of the post-formed electrode, and the connection between the cathode base and the post-formed electrode is chamfered to make the cathode base smoothly transition to the post-formed electrode. The post-formed part is extremely frustum-shaped, and its generatrix is ​​a straight line segment; The emission strip is shaped like a frustum, and its generatrix is ​​a first circular arc curve; The overall surface of the preformed electrode is an arc surface, and its generatrix is ​​a second arc curve; The design method of the magnetron-injected electron gun includes the following steps: S1. The emission zone center radius R of the magnetron-injected electron gun is calculated using formulas (1)-(3). c Launch belt length L s Initial values ​​for the anode-cathode spacing d1: d1=U0 / E0 (3) Where fm is the magnetic compressibility ratio, r g0 I0 is the radius of the electron cyclotron's guiding center, I0 is the magnitude of the emission current in the emission band, and J0 is the emission current in the emission band. c U0 is the allowed emission current density, U0 is the voltage between the anode and cathode, and E0 is the restricted electric field between the anode and cathode. S2. Taking the central axis of the electron gun as the z-axis, and setting the generatrix of the emission belt as a straight line with an angle θ with the z-axis, we obtain the front radius Rc2 and the rear radius Rc3 of the emission belt: Rc2=Rc-Ls×sinθ (4) Rc3=Rc+Ls×sinθ (5) The generatrix of the preformed electrode is set to a straight line with a length of L. f The angle of inclination with the z-axis is θ f The front end radius Rc1 of the preformed electrode is obtained as follows: Rc1=Rc2-L f ×sinθ f (6) The generatrix of the formed electrode is set to be a straight line with a length of L. b The angle of inclination with the z-axis is θ b The radius of the rear end of the formed electrode, Rc4 (i.e., the radius of the cylindrical part of the cathode base), is obtained from the degree of gradation. Rc4=Rc3+L b ×sinθ b (7) The radius of the cathode base is set to Rc5, where Rc5 > Rc4; the radius of the fillet at the connection between the cathode base and the post-formed electrode is r1. S3. Given θ, θ f θ b The initial values ​​of Rc5 and r1 are used to establish an initial simulation model and perform simulation optimization in combination with steps S1 and S2, resulting in a preliminary optimized simulation model. S4. Establish a rectangular coordinate system xoz with the central axis of the electron gun as the z-axis, the center of the front end of the emission belt as the origin o, and any straight line passing through the origin o and perpendicular to the z-axis as the x-axis; Let the starting coordinates of the first arc of the launch zone be (x1, z1) and the ending coordinates be (x2, z2). Calculate the center position (X1, z1) of the arc of the launch zone. center Z center ): Where x1 = Rc3, z1 = 0, x2 = Rc2, z2 = Ls × cosθ; bulge1 is the convexity of the first circular arc curve; Let the starting coordinates of the second circular arc curve of the preformed electrode be (x3, z3) and the ending coordinates be (x4, z4); since the front end and side of the preformed electrode are circular arc surfaces, the center position of the second circular arc curve is (0, Z). center ): Where x3 = Rc2, x4 = -Rc2; bulge2 is the convexity of the second circular arc; S5. Substitute formulas (8)-(10) into the preliminary optimized simulation model obtained in step S3, perform parameter scanning processing on the convexity bulge1 and bulge2 in the simulation software, obtain the value that minimizes electron velocity dispersion, and complete the design of the low-velocity dispersion magnetron injection electron gun.

2. The low-velocity discrete magnetron injection electron gun for a gyroscopic traveling wave tube as described in claim 1, characterized in that, When the electron gun operates in the G-band, the radius of the cathode base is 3.63 mm; the rear radius of the post-formed electrode is 3.13 mm, the front radius is 2.58 mm, and the axial length is 0.83 mm.

3. The low-velocity discrete magnetron injection electron gun for a gyroscopic traveling wave tube as described in claim 2, characterized in that, The front end radius of the transmitting strip is 1.01 mm, the rear end radius is 2.58 mm, the axial length is 1.41 mm, and the convexity of the first arc curve is 0.08; the rear end radius of the front forming electrode is 1.01 mm, and the convexity of the second arc curve is 0.2.

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