Terahertz gyrotron traveling wave tube low-speed scattered magnetic control injection electron gun and design method

Abstract

The invention discloses a gyrotron traveling wave tube low-speed scattered magnetic control injection electron gun and a design method, and belongs to the field of vacuum electronic 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, the radius of the cathode bottom table is larger than that of the rear forming pole, the generatrix of the emission band is an arc curve, and the overall surface of the front forming pole is an arc surface; besides, in the design of the cathode, through two times of modeling and respective simulation optimization of partial parameters, the parameters in the one-time simulation optimization process are reduced, the optimization target is clearer, the design difficulty is effectively reduced, and the design time is shortened. The problem that the electric field of the gun area of the electron gun is too high due to the fact that the size of the cathode is too small is effectively solved, meanwhile, the adverse effect of the abrupt change structure of the cathode on the surface electric field of an emission band is avoided, and speed scattering of the electron gun is effectively reduced.

Description

Technical Field

[0001] The invention belongs to the field of vacuum electronic devices, and in particular relates to a cyclotron traveling wave tube low-speed scattered magnetron injection electron gun and a design method thereof. Background Art

[0002] The Electron Cyclotron Maser (ECM) mechanism is a relativistic radiation mechanism that uses the interaction between cyclotron electron beams and electromagnetic waves to generate high-power microwave radiation. The cyclotron traveling wave tube is a microwave amplifier device based on the ECM mechanism. The device has the characteristics of high efficiency, wide bandwidth, and high power, and is widely used in radar imaging, communications, and electronic countermeasures.

[0003] In order to further improve the imaging resolution and ensure the anti-interference ability and bandwidth of communication, it is urgent to develop broadband high-power terahertz gyrotron traveling wave tubes. Affected by the size co-transition effect, when the operating frequency reaches the G band, for the traditional magnetron injection electron gun structure of the TE02 mode gyrotron traveling wave tube, the radius of the cathode emission band is only about 1.7mm, and the radius of the top of the front-forming pole cone is only about 1mm. When the voltage difference between the cathode and the cathode reaches 50kV, it is very easy to form a tip electric field on the cathode surface. This electric field can still reach 3×10 7 v / m3×10 7 v / m, which is much larger than the safety electric field 2×10 required under current vacuum conditions. 7 v / m2×10 7 v / m. At the same time, the existence of the tip electric field leads to uneven distribution of the electric field on the cathode surface, a large difference in the electric field between the front and rear ends of the emission band, and difficulty in controlling the electron trajectory, which easily leads to large velocity dispersion and makes it impossible to obtain an electron beam that can interact efficiently with electromagnetic waves.

[0004] At present, some researchers have proposed an improved cathode structure to address the above-mentioned problems of terahertz cyclotron traveling wave tube electron guns. The main purpose is to replace the cathode emission band and the busbar of the front-forming pole from a straight line to a curve to reduce the electric field peak, adjust the electric field distribution on the cathode surface, and reduce the dispersion of the electron gun speed. However, this curve is mainly obtained by multi-point fitting, which leads to more parameters that need to be considered in the modeling and optimization process, and the optimization target for the emission band curve is unclear, the design time is long, and the design difficulty is high. Summary of the invention

[0005] In view of the problems in the prior art that the electric field peak of a gyrotron traveling wave tube magnetron injection electron gun is too high and prone to strong field breakdown, and that the uneven electric field distribution on the cathode surface easily causes large velocity dispersion, the present invention provides a gyrotron traveling wave tube low-speed dispersion magnetron injection electron gun and a design method thereof. By improving the cathode structure of the electron gun, the electron beam velocity dispersion formed is low, which can interact with high-frequency electromagnetic waves more efficiently.

[0006] To achieve the above object, the present invention adopts the following technical solution:

[0007] A cyclotron traveling wave tube low-speed scattered magnetron 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, a post-forming pole, an emission belt and a front-forming pole which are sequentially arranged along the axial direction and have decreasing radiuses;

[0009] The invention is characterized in that the radius of the cathode base is larger than the radius of the post-forming pole, and the connection between the cathode base and the post-forming pole is chamfered to make the cathode base smoothly transition to the post-forming pole;

[0010] The post-forming is extremely truncated cone-shaped, and its generatrix is ​​a straight line segment;

[0011] The emission band is in the shape of a truncated cone, and its generatrix is ​​a first circular arc curve;

[0012] The entire surface of the front forming pole is an arc surface, and its generatrix is ​​a second arc curve.

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

[0014] On the other hand, the present invention also provides a design method for a gyrotron traveling wave tube low-speed scattered magnetron injection electron gun based on the above structure, comprising the following steps:

[0015] S1. Calculate the emission band center radius R of the magnetron injection electron gun using formulas (1)-(3): c , emission band length L s And the initial value of the anode-cathode distance d1:

[0016]

[0017] d1=U0 / E0(3)

[0018] Where, fm is the magnetic compression ratio, r g0 is the radius of the guiding center of the electron cyclotron, I0 is the emission current of the emission band, J c is the current density allowed for emission, U0 is the voltage between the cathode and cathode, and E0 is the restricted electric field in the space between the cathode and cathode.

[0019] S2. Taking the central axis of the electron gun as the z-axis, setting the generatrix of the emission belt as a straight line and the inclination angle with the z-axis as θ, the front radius Rc2 and the rear radius Rc3 of the emission belt are obtained:

[0020] Rc2=Rc-Ls×sinθ(4)

[0021] Rc3=Rc+Ls×sinθ(5)

[0022] Set the busbar of the front forming pole to a straight line with a length of L f , the inclination angle with the z-axis is θ f , and obtain the front end radius Rc1 of the front forming pole:

[0023] Rc1=Rc2-L f ×sinθ f (6)

[0024] Set the busbar of the post-forming pole to be a straight line with a length of L b , the inclination angle with the z-axis is θ b The rear end radius Rc4 of the post-forming electrode (i.e. the radius of the cylindrical part of the cathode bottom platform) is obtained:

[0025] Rc4=Rc3+L b ×sinθ b (7)

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

[0027] S3. Given θ, θ f ,θ b , Rc5 and the initial values ​​of r1, combined with step S1 and step S2, an initial simulation model is established and simulation optimization is performed to obtain a preliminary optimized simulation model.

[0028] S4. Take 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 to establish a rectangular coordinate system xoz;

[0029] Assume that the starting coordinates of the first arc curve of the emission belt are (x1, z1) and the ending coordinates are (x2, z2). Calculate the center position (Xcenter , Z center ):

[0030]

[0031] Among them, x1=Rc3, z1=0, x2=Rc2, z2=Ls×cosθ; bulge1 is the convexity of the first arc curve, that is, the index describing the convexity of this arc segment.

[0032] Assume that the starting coordinates of the second arc curve of the front forming pole are (x3, z3) and the ending coordinates are (x4, z4). Since the front end and the side of the front forming pole are circular arc surfaces, the center position of the second arc curve is (0, Z center ):

[0033]

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

[0035] S5. Substitute formulas (8)-(10) into the preliminary optimization simulation model obtained in step S3, perform parameter scanning on bulges bulge1 and bulge2 in the simulation software, obtain the value that minimizes the electron velocity dispersion, and complete the design of the low-speed dispersion magnetron injection electron gun.

[0036] Compared with the traditional structure and design, the innovation of the present invention is mainly reflected in:

[0037] 1. The present invention increases the radius of the cathode base to make it larger than the rear end radius of the post-forming pole, and chamfers the connection to create a discontinuous structure and form a second extreme electric field, thereby effectively reducing the peak electric field in the gun area of ​​the electron gun, improving the overall electric field on the cathode surface, and further weakening the sensitivity of the emission band and the front forming pole surface electric field to the structure.

[0038] 2. The present invention increases the emission area by setting the emission band busbar as an arc curve, so that more electrons can be emitted at the same emission density, creating a larger current; when the emission current remains unchanged, the emission density can be reduced to ensure the life of the electron gun. On the other hand, according to the transverse velocity dispersion formula of electrons in the electron gun, changing the emission band surface to an arc surface can further improve the emission band electric field, making the emission band electric field change uniformly, which is conducive to reducing velocity dispersion; in addition, the emission band is an arc surface as a whole, creating a discontinuous structure, which is conducive to increasing the overall voltage of the emission band and increasing the transverse velocity of electrons, thereby helping to overcome the problem of easy backflow in high-frequency band electron guns.

[0039] 3. The present invention sets the overall busbar of the front-molded pole as an arc curve, so that the overall dome structure has a smooth surface, thereby avoiding the excessive electric field at the front end of the electron gun area caused by the discontinuity of the truncated cone chamfer in the traditional structure, which in turn affects the excessive adjustment of the electrons just emitted from the emission band, affects the electron trajectory, and further affects the problem of scattered electron injection velocity.

[0040] 4. In the design of the electron gun cathode structure, the present invention performs two modeling and simulates and optimizes some parameters respectively, so that the parameters of one simulation optimization process are reduced, the optimization target is clearer, and the design difficulty and design time are effectively reduced; in addition, in the second simulation process, the center formula of the first arc curve and the second arc curve is brought into the preliminary optimization simulation model, so the parameters to be optimized are further reduced, and a better electron gun cathode structure can be obtained only by performing parameter scanning on the two convexities.

[0041] In summary, the present invention provides a terahertz cyclotron traveling wave tube low-speed scattered magnetron injection electron gun and a design method thereof, which effectively solves the problem of excessively high electric field in the gun region of the electron gun caused by the small size of the cathode, and solves the adverse effect of the cathode's sudden structure on the emission band surface electric field, effectively reducing the electron gun speed dispersion. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a schematic diagram of the structure of a conventional magnetron injection electron gun;

[0043] Figure 2 This is a schematic diagram of the structure of a low-speed scattered magnetron injection electron gun for a terahertz cyclotron traveling wave tube in an embodiment;

[0044] Figure 3 This is an enlarged view of the cathode structure;

[0045] Figure 4 This is the cathode equipotential line diagram of the traditional magnetic injection electron gun;

[0046] Figure 5 This is a cathode equipotential line diagram of a low-speed scattered magnetron injection electron gun of a terahertz cyclotron traveling wave tube in an embodiment;

[0047] Figure 6 A comparison diagram of the cathode surface electric field of a conventional magnetic injection electron gun and the cathode surface electric field of a terahertz cyclotron traveling wave tube low-speed scattered magnetically controlled injection electron gun in an embodiment;

[0048] Figure 7 It is a velocity dispersion diagram and velocity ratio diagram of a low-speed dispersion magnetron injection electron gun of a terahertz cyclotron traveling wave tube in an embodiment;

[0049] Figure 8It is an electron beam trajectory diagram and a muzzle electron distribution diagram generated by a low-speed scattered magnetron injection electron gun of a terahertz cyclotron traveling wave tube in an embodiment;

[0050] Explanation of the accompanying numbers: 1 cathode, 2 anode, 2-1, cylindrical part of cathode base, 2-2 chamfered part of cathode base, 2-3 rear formed pole, 2-4 emission band, 2-5 front formed pole. DETAILED DESCRIPTION

[0051] In order to more clearly understand the purpose, features and advantages of the present invention, the present invention is further described in detail below in conjunction with an example of a G-band TE02 mode terahertz gyrotron traveling wave tube electron gun.

[0052] This embodiment provides a new type of low-speed scattered magnetron injection electron gun for a terahertz gyrotron traveling wave tube. Figure 2 As shown, it includes an electron gun anode and a cathode coaxially arranged inside the electron gun anode; the cathode is as shown in Figure 3 As shown, it includes a cathode base, a rear forming pole, an emission belt and a front forming pole which are arranged in sequence along the axial direction.

[0053] Among them, the cathode base is cylindrical with a radius of 3.63mm. The connection between the cathode base and the post-forming pole is chamfered with a chamfer radius of 1.5mm, so that the cathode base can smoothly transition to the post-forming pole.

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

[0055] The emission band is in the shape of a truncated cone, and its generatrix is ​​a first circular arc curve, with a front end radius of 1.01 mm, a rear end radius of 2.58 mm, an axial length of 1.41 mm, and a convexity of the first circular arc curve of 0.08.

[0056] The overall surface of the front forming pole is an arc surface, whose generatrix is ​​a second arc curve, whose rear end radius is 1.01 mm, and the convexity of the second arc curve is 0.2.

[0057] In order to obtain a better emission effect, materials that suppress electron emission are coated at the front and rear ends of the emission band to reduce the impact on electron injection caused by the electric field mutation caused by the discontinuity at the junction of the rear-formed pole and the front-formed pole with the emission band.

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

[0059] S1. Calculate the emission band center radius R of the magnetron injection electron gun using formulas (1)-(3): c , emission band length L s And the initial value of the anode-cathode distance d1:

[0060]

[0061] d1=U0 / E0(3)

[0062] Where, fm is the magnetic compression ratio, r g0 is the radius of the guiding center of the electron cyclotron, I0 is the emission current of the emission band, J c is the current density allowed for emission, U0 is the voltage between the cathode and cathode, and E0 is the restricted space electric field between the cathode and cathode. In this embodiment, R c The initial value is 1.8 mm, and the emission band length L s The initial value of is 2.1mm, and the initial value of the cathode-cathode distance d1 is 16mm.

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

[0064] Rc2=Rc-Ls×sinθ(4)

[0065] Rc3=Rc+Ls×sinθ (5)

[0066] Set the busbar of the front forming pole to a straight line with a length of L f , the inclination angle with the z-axis is θ f , and obtain the front end radius Rc1 of the front forming pole:

[0067] Rc1=Rc2-L f ×sinθ f (6)

[0068] Set the busbar of the post-forming pole to be a straight line with a length of L b , the inclination angle with the z-axis is θ b The rear end radius Rc4 of the post-forming electrode (i.e. the radius of the cylindrical part of the cathode bottom platform) is obtained:

[0069] Rc4=Rc3+L b ×sinθ b (7)

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

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

[0072] S4. Take 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 to establish a rectangular coordinate system xoz;

[0073] Assume that the starting coordinates of the first arc curve of the emission belt are (x1, z1) and the ending coordinates are (x2, z2). Calculate the center position (X center , Z center ):

[0074]

[0075] Among them, x1=Rc3, z1=0, x2=Rc2, z2=Ls×cosθ; bulge1 is the convexity of the first arc curve, that is, the index describing the convexity of this arc segment.

[0076] The starting coordinates of the second arc curve of the front forming pole are (x3, z3), and the ending coordinates are (x4, z4). Since the front end and the side of the front forming pole are arc surfaces as a whole, the center position of the second arc curve is (0, Z center ):

[0077]

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

[0079] S5. Substitute formulas (8)-(10) into the preliminary optimization simulation model obtained in step S3, perform parameter scanning on the bulges bulge1 and bulge2 in the simulation software, and obtain the value that minimizes the electron velocity dispersion, correspondingly bulge1=0.08, bulge2=0.2, completing the design of the low-speed dispersion magnetron injection electron gun.

[0080] When the electron gun of the present invention is working, the anode is grounded to a zero potential, the cathode is subjected to negative high voltage, and the electron gun as a whole is in a superconducting magnetic field that converges toward the axial direction and slowly increases to a specified size. The cathode emission band emits electrons, and under the joint action of the electric and magnetic fields of the cathode and cathode, the electrons are first accelerated in the gun area, and then adiabatically compressed in the transition area, converting the longitudinal energy into transverse energy, and finally forming a stable cyclotron electron beam with a certain transverse and longitudinal velocity ratio and velocity dispersion in the drift area.

[0081] Figure 5 The cathode equipotential line diagram of the low-speed scattered magnetron injection electron gun of the terahertz cyclotron traveling wave tube in this embodiment is shown in FIG. Figure 4Comparison with the cathode equipotential line diagram of the conventional magnetic injection electron gun shows that the electric field of the electron gun of this embodiment is reduced as a whole, and the peak electric field is reduced from 3.06e7 to 1.85e7, which effectively avoids strong field breakdown due to excessively high electric field.

[0082] Figure 6 : is a comparison diagram of the cathode surface electric field of the electron gun of this embodiment and the surface electric field of the traditional electron gun. Figure 5 It can be found that the electric field of the electron gun of the present invention is improved on the surface of the emission band, which effectively increases the electron energy; and the electric field distribution on the surface of the emission band is uniform. According to the formula for determining the lateral velocity dispersion, it can be determined that the present invention effectively reduces the velocity dispersion of the electron gun. The difference between the electric field of the front and rear forming poles and the emission band is not large, which can ensure that its influence on the velocity dispersion is reduced.

[0083] Figure 7 The speed dispersion diagram and speed ratio diagram of the low-speed scattered magnetron injection electron gun of the terahertz cyclotron traveling wave tube in this embodiment are shown in FIG. It can be seen that the final electron gun speed ratio is stabilized at about 1.1, and the speed ratio can reach below 2.4%, which can ensure that the electron injection can achieve effective interaction in the high-frequency structure.

[0084] Figure 8 The electron beam trajectory diagram and the muzzle electron distribution diagram generated by the low-speed scattered magnetron injection electron gun of the terahertz cyclotron traveling wave tube in this embodiment are shown in Figure 1. It can be seen that the electrons can flow efficiently, and the center of the electron ring formed at the muzzle is about 0.42 mm, which meets the requirements of the 220GHz cyclotron traveling wave tube beam interaction.

[0085] In summary, the novel low-speed scattered magnetron injection electron gun and design method of the terahertz cyclotron traveling wave tube of the present invention can effectively solve the problem of too high peak electric field when the electron gun size is too small. And the surface electric field can be changed by adjusting the cathode surface shape by design, thereby improving the electron quality, reducing the electron injection speed scattered, and realizing the efficient electron injection-wave interaction of the cyclotron traveling wave tube.

Claims

1. A cyclotron traveling wave tube low-speed scattered magnetron injection electron gun, comprising an electron gun anode and a cathode coaxially arranged inside the electron gun anode; The cathode comprises a cathode base, a post-forming pole, an emission belt and a front-forming pole which are sequentially arranged along the axial direction and have decreasing radiuses; It is characterized in that The radius of the cathode base is greater than the radius of the post-forming pole, and the connection between the cathode base and the post-forming pole is chamfered to make the cathode base smoothly transition to the post-forming pole; The post-forming is extremely truncated cone-shaped, and its generatrix is ​​a straight line segment; The emission band is in the shape of a truncated cone, and its generatrix is ​​a first circular arc curve; The entire surface of the front forming pole is an arc surface, and its generatrix is ​​a second arc curve.

2. A gyrotron traveling wave tube low speed scattered magnetron injection electron gun as claimed in claim 1, characterized in that: When the electron gun works in the G band, the radius of the cathode base is 3.63 mm; the rear end radius of the post-forming pole is 3.13 mm, the front end radius is 2.58 mmz, and the axial length is 0.83 mm.

3. A gyrotron traveling wave tube low speed scattered magnetron injection electron gun as claimed in claim 2, characterized in that: The front end radius of the emission band is 1.01mm, the rear end radius is 2.58mm, the axial length is 1.41mm, and the convexity of the first arc curve is 0.08; the rear end radius of the front forming pole is 1.01mm, and the convexity of the second arc curve is 0.

2.

4. A cyclotron traveling wave tube low speed scattered magnetron injection electron gun as claimed in claim 1, characterized in that: The design method of the magnetron injection electron gun comprises the following steps: S1. Calculate the emission band center radius R of the magnetron injection electron gun using formulas (1)-(3): c , emission band length L s And the initial value of the anode-cathode distance d1: d1=U0 / E0 (3) Where, fm is the magnetic compression ratio, r g0 is the radius of the guiding center of the electron cyclotron, I0 is the emission current of the emission band, J c is the current density allowed for emission, U0 is the voltage between the cathode and cathode, and E0 is the electric field in the restricted space between the cathode and cathode; S2. Taking the central axis of the electron gun as the z-axis, setting the generatrix of the emission belt as a straight line and the inclination angle with the z-axis as θ, the front radius Rc2 and the rear radius Rc3 of the emission belt are obtained: Rc2=Rc-Ls×sinθ (4) Rc3=Rc+Ls×sinθ (5) Set the busbar of the front forming pole to a straight line with a length of L f , the inclination angle with the z-axis is θ f , and obtain the front end radius Rc1 of the front forming pole: Rc1=Rc2-L f ×sinθ f (6) Set the busbar of the post-forming pole to be a straight line with a length of L b , the inclination angle with the z-axis is θ b The rear end radius Rc4 of the post-forming electrode (i.e. the radius of the cylindrical part of the cathode bottom platform) is obtained: Rc4=Rc3+L b ×sinθ b (7) The radius of the cathode base is set to Rc5, Rc5>Rc4; the fillet radius of the connection between the cathode base and the post-forming electrode is r1; S3. Given θ, θ f ,θ b , Rc5 and the initial values ​​of r1, combined with step S1 and step S2, establish an initial simulation model and perform simulation optimization to obtain a preliminary optimized simulation model; S4. Take 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 to establish a rectangular coordinate system xoz; Assume that the starting coordinates of the first arc curve of the emission belt are (x1, z1) and the ending coordinates are (x2, z2). Calculate the center position (X center , Z center ): Wherein, x1=Rc3, z1=0, x2=Rc2, z2=Ls×cosθ; bulge1 is the convexity of the first arc curve; Assume that the starting coordinates of the second arc curve of the front forming pole are (x3, z3) and the ending coordinates are (x4, z4). Since the front end and the side of the front forming pole are circular arc surfaces, the center position of the second arc curve is (0, Z center ): Wherein, x3=Rc2, x4=-Rc2; bulge2 is the convexity of the second arc curve; S5. Substitute formulas (8)-(10) into the preliminary optimization simulation model obtained in step S3, perform parameter scanning on convexity bulke1 and bulke2 in the simulation software, obtain the value that minimizes the electron velocity dispersion, and complete the design of the low-speed dispersion magnetron injection electron gun.

Images