Optimization method of high-voltage electron gun equipment

Abstract

The invention discloses a method for optimizing high-voltage electron gun equipment. The method comprises the following steps: establishing a general model for designing a geometric structure of an electron gun; the Vaughan comprehensive iteration method is modified and perfected; programming of geometric parameters of the electrostatic lens and the magnetic lens of the electronic gun is realized based on a C + + assembly language; geometric parameters of the electron gun electrostatic lens are calculated and optimized; constructing an electronic gun electrostatic lens and magnetic lens model by using UG software; importing the model into comsol electromagnetic simulation software, and simulating an electronic space-time evolution track; a variable control method is adopted, geometric parameters of the electrostatic lens and the magnetic lens are optimized and adjusted, and the judgment standard is beam spot energy density and distribution uniformity; and establishing a relation that the image distance changes along with focusing current. The method solves the problems that the trial-and-error iteration cost is high during design and manufacturing of the high-voltage electron gun, and the subsequent electron beam quality is difficult to accurately and quantitatively regulate and control, can improve the beam spot quality, and provides theoretical basis and guidance for structural design and optimization of the high-voltage electron gun.

Description

Technical Field

[0001] The present invention relates to an optimization method for a high-voltage electron gun device. Background Art

[0002] Electron beam welding is to accelerate electrons to 1 / 2 to 2 / 3 of the speed of light by using a high-voltage device, and then form a high-energy density electron beam through double focusing of an electrostatic lens and a magnetic lens. The electron beam bombards the surface of the workpiece to be welded, so that the temperature of the workpiece can reach above 104 °C, and the surface material of the workpiece quickly melts to form a molten pool, which becomes a welded joint after flowing and solidifying, thereby realizing welding.

[0003] During the electron beam welding process with poor electron beam spot quality, defects such as poor fusion, pores, and welding cracks often occur. In order to obtain a welded joint with good morphology (penetration depth, weld width, shape, etc.) and excellent properties (no pores, no cracks, etc.), it is necessary to accurately control the size and spatial position of the electron beam spot.

[0004] During the electron beam welding process, the electron beam spot size and spot position are affected by the geometric structure of the electron gun, the relative position relationship between components, and the focusing magnetic field and deflection magnetic field. Optimizing the geometric structure of the electron gun to obtain an electron beam spot with good quality is an important prerequisite for ensuring a welded joint with excellent shape and properties.

[0005] In recent years, with the continuous upgrading of the requirements of production processes, the types of electron guns for welding have increased, and the available working power range has been continuously expanded. However, since the working principles of different types of electron guns are the same, their geometric structures are very similar, and they are all composed of two main parts: an electrostatic lens and a magnetic lens. The electrostatic lens mainly includes a cathode, an anode, and a buncher electrode, and the magnetic lens mainly includes a focusing coil and a deflection coil, as Figure 1 shown.

[0006] At present, foreign countries have conducted in-depth research on high-power high-voltage electron guns, and their excellent performance has been widely recognized by users. The electron guns used in China are still mainly medium and low-power models of 6 kW and 15 kW, and their acceleration voltages are generally in the range of 60 - 80 kV. The research on high-power electron guns above 30 kW is more limited, which greatly restricts the diversity of welding materials and the achievable welding depth. This is mainly because the geometric structure of the high-voltage electron gun is relatively complex, there are many geometric and technological parameters, and the influence law of each parameter and their interaction on the beam quality is unclear, resulting in a lack of scientific basis for optimization design. At present, the experimental trial-and-error method is mainly used for the optimization design of the geometric structure of the electron gun, which has practical problems such as high cost, large design difficulty, and difficulty in precise quantitative control. Summary of the Invention

[0007] To address the deficiencies of the existing technology, the present invention provides an optimization method for a high-voltage electron gun device (structural optimization and control method optimization), including the following steps: establishing a general model for the geometric structure design of the electron gun; modifying and improving the Vaughan comprehensive iteration method; implementing the programming of the core geometric parameters of the electrostatic lens and magnetic lens of the electron gun based on C++ assembly language; calculating and optimizing the geometric parameters of the electrostatic lens of the electron gun; using UG software to construct models of the electrostatic lens and magnetic lens of the electron gun; importing the models into electromagnetic simulation software such as Comsol to simulate the temporal and spatial evolution trajectories of electrons; adopting the method of controlling variables to optimize and adjust the geometric parameters of the electrostatic lens and magnetic lens in sequence, with the judgment criteria being the beam spot energy density and distribution uniformity, etc.; establishing the relationship between the image distance and the focusing current.

[0008] Preferably, the geometric parameters of the electrostatic lens of the electron gun include the cathode curvature radius, anode curvature radius, distance between the cathode and anode, beam waist position, and anode aperture, etc.

[0009] Preferably, the optimization method for the high-voltage electron gun device provided by the present invention (structural optimization and control method optimization) includes the following specific steps:

[0010] Step 1: Adopting the Pierce electron gun design method to establish the basic structure of the electrode, where the cathode is a "V"-shaped tungsten strip, the model emission surface is set as a plane consistent with the actual situation, and the side length of the cathode emission surface is calculated using the relationship between the cathode emission current density and the cathode temperature; the Pierce electron gun uses a spherical electron gun with a conical electron beam.

[0011] Step 2: Modifying and improving the iterative synthesis method, revising the formula for calculating the cathode emission surface radius to half of the diagonal of a square to calculate the geometric parameters of the electrostatic lens, and using the Sharma anode aperture revision formula.

[0012] The formulas in Step 2 include:

[0013]

[0014] θ' = θ{1 - (1 / 3)(R c - R a )(1 / (-α))(d(-α) / d(R c - R a ))};

[0015] Among them,

[0016] -α = ln R c / R a + 0.3(ln R c / R a ) 2 + 0.075(ln R c / R a ) 3 +0.014378(ln R c / R a ) 4 +0.002160877(ln R c / R a ) 5 +0.00026796(ln R c / R a ) 6 ,

[0017] d(-α) / d(R c -R a )=1 / R c / R a left{1 + 0.6(ln R c / R a ) + 0.225(ln R c / R a ) 2 + 0.057272(lnR c / R a ) 3 + 0.010804385(ln R c / R a ) 4 + 0.0016077(ln R c / R a ) 5 right};

[0018] Step 3: Compile the program using the C++ language on the vs compiler; with this program, the user only needs to input the acceleration voltage, beam current, work function of the cathode material, cathode heating temperature, and waist radius to calculate the geometric parameters of the electrostatic lens of the electron gun. The geometric parameters of the electrostatic lens of the electron gun include the cathode curvature radius, anode curvature radius, distance between the cathode and anode, waist position, and anode aperture, etc.;

[0019] Step 4: Design the magnetic lens structure, using a short magnetic lens with a hollow cylindrical energized short coil winding and a magnetic yoke is set outside; revise the coil inner radius calculation formula to:

[0020] R = (1.5e -5 Uatanθ) / 0.6 + t,

[0021] The ratio μ of the magnetic yoke gap height (S) to the coil inner diameter (D) is between 0.4 and 1.2, and the initial value is set to 0.6;

[0022] Calculate the focal length, ampere-turns, etc. according to the optical equation:

[0023]

[0024] Step 5: The empirical formula for magnetic lens geometry calculation is also written in the program for electrostatic lens geometry parameter calculation using C++; through the improved program, when the acceleration voltage, beam current, work function of the cathode material, cathode heating temperature, image distance, beam waist, and beam spot radius are input, the important geometry parameters in the electrostatic lens and magnetic lens of the electron gun can be calculated;

[0025] Step 6: Based on the above parameters, establish a geometric simulation model of the electron gun, and simulate the electron trajectory and the morphology of the electron beam spot at a specific cross-section (working plane);

[0026] Step 7: Adopt the method of controlling variables, taking the uniformity of energy density distribution, beam spot size, image distance, etc. as the judgment criteria, and comprehensively consider optimizing the anode aperture, anode-cathode spacing, spherical radius of the grid, inner diameter of the coil, magnetic yoke gap width, etc., to obtain the optimal parameter group of the core components of the electron gun.

[0027] The advantages and beneficial effects of the present invention are as follows: The present invention provides a method for optimizing the structure and regulating the beam spot position of a Pierce electron gun based on theoretical calculation and simulation, belonging to the field of electron gun design. The present invention systematically solves the problems of high trial-and-error iteration cost in the design and manufacture of new high-voltage electron guns and the difficulty in accurately quantitatively regulating the subsequent electron beam quality, can improve the beam spot quality, and provides a theoretical basis and guidance for the structural design and optimization of high-voltage electron guns. Brief Description of the Drawings

[0028] Figure 1 is the structural schematic diagram of the electron gun;

[0029] Figure 2 is the structural schematic diagram of the spherical electron gun;

[0030] Figure 3 is the flow chart of the revised Vaughan comprehensive iteration method; Figure 3 where: Γ is the anode lens correction factor; k is the correction factor of the cathode half-cone angle θ and the cathode curvature radius R c of; r b (Z a )θ is the radius at the anode head position; r a is the anode aperture; P is the perveance; α, γ, R, Z are intermediate variables; θ T , R cT are the corrected results;

[0031] Figure 4 is the calculation process of Step 5;

[0032] Figure 5 is the schematic diagram of the calculation result of Step 5;

[0033] Figure 6 It is a schematic diagram of the beam spot morphology in step 6;

[0034] Figure 7 It is a schematic diagram of the cross-sectional energy density distribution of the electron beam spot at different coil inner radii in step 6;

[0035] Figure 8 It is a diagram showing the relationship between the beam spot radius and the beam spot position changing with the coil inner radius in step 6; Figure 8 In (a), it is the beam spot radius, and in (b), it is the image distance. Specific implementation manners

[0036] The following combines the accompanying drawings and embodiments to further describe the specific implementation manners of the present invention. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and cannot be used to limit the protection scope of the present invention.

[0037] The technical solutions for the specific implementation of the present invention are as follows:

[0038] The present invention provides an optimization method for a high-voltage electron gun device (structural optimization and control method optimization), including the following steps:

[0039] Establish a general model for the geometric structure design of the electron gun; modify and improve the Vaughan comprehensive iterative method; implement the programming of the core geometric parameters of the electrostatic lens and magnetic lens of the electron gun based on C++ assembly language; calculate and optimize the geometric parameters of the electrostatic lens of the electron gun, and the geometric parameters of the electrostatic lens of the electron gun include the cathode curvature radius, anode curvature radius, distance between the cathode and anode, beam waist position, and anode aperture, etc.; use UG software to construct models of the electrostatic lens and magnetic lens of the electron gun; import the models into electromagnetic simulation software such as Comsol to simulate the electron spatio-temporal evolution trajectory; adopt the method of controlling variables to optimize and adjust the geometric parameters of the electrostatic lens and magnetic lens in turn, and the judgment criteria are the beam spot energy density and distribution uniformity, etc.; establish the relationship between the image distance and the focusing current.

[0040] The optimization method for the high-voltage electron gun device provided by the present invention (structural optimization and control method optimization) includes the following specific steps:

[0041] Step 1: Adopt the Pierce electron gun design method to establish the basic structure of the electrode. The cathode is a "V"-shaped tungsten strip, and the model emission surface is set as a plane consistent with the actual situation. Calculate the side length of the cathode emission surface using the relationship between the cathode emission current density and the cathode temperature; the Pierce electron gun adopts a spherical electron gun with a conical electron beam; the structure of the electron gun is as Figure 1 shown;

[0042] Step 2: Modify and improve the iterative synthesis method, revise the formula for calculating the radius of the cathode emission surface to half of the diagonal of a square to calculate the geometric parameters of the electrostatic lens, and use the Sharma anode aperture revision formula;

[0043] The formulas in Step 2 include:

[0044]

[0045] θ' = θ{1 - (1 / 3)(R c -R a )(1 / (-α))(d(-α) / d(R c -R a ))};

[0046] Where,

[0047] -α = ln R c / R a + 0.3(ln R c / R a ) 2 + 0.075(ln R c / R a ) 3 + 0.014378(ln R c / R a ) 4 + 0.002160877(ln R c / R a ) 5 + 0.00026796(ln R c / R a ) 6 ,

[0048] d(-α) / d(R c -R a ) = 1 / R c / R a left{1 + 0.6(ln R c / R a ) + 0.225(ln R c / R a ) 2 + 0.057272(lnR c / R a ) 3 + 0.010804385(ln R c / R a ) 4 + 0.0016077(ln R c / R a ) 5right};

[0049] Among them, r c is the radius of the cathode cross-section, I is the beam current, and j c is the cathode emission current density; θ is the initial value of the cathode semi-cone angle; θ ’ is the corrected cathode semi-cone angle; R a is the anode curvature radius; R c is the cathode curvature radius; α is an intermediate variable;

[0050] Step 3: The program was compiled using the C++ language on the vs compiler;

[0051] The flow chart of the revised Vaughan comprehensive iterative method is as Figure 3 shown;

[0052] Using this program, the user only needs to input the acceleration voltage, beam current, work function of the cathode material, cathode heating temperature, and beam waist radius to calculate the geometric parameters of the electrostatic lens of the electron gun. The geometric parameters of the electrostatic lens of the electron gun include the cathode curvature radius, anode curvature radius, distance between the anode and cathode, beam waist position, and anode aperture, etc.;

[0053] Step 4: Design the magnetic lens structure. Use a short magnetic lens with a hollow cylindrical energized short coil winding and set a yoke outside; Revise the calculation formula for the inner radius of the coil to:

[0054] R = (1.5e -5 Uatanθ) / 0.6 + t,

[0055] where, R is the inner radius of the focusing coil; U is the acceleration voltage; a is the object distance, and t is the yoke thickness;

[0056] The ratio μ of the yoke gap height (S) to the inner diameter (D) of the coil is between 0.4 and 1.2, and the initial value is set to 0.6;

[0057] Calculate the focal length, number of ampere-turns, etc. according to the optical equation:

[0058]

[0059]

[0060] where, f is the focal length; a and b are the object distance and image distance respectively; NI is the number of ampere-turns; F is the influence coefficient of the yoke, and the value range is 0.5 to 0.9;

[0061] Step 5: The empirical formula for magnetic lens geometric calculation is also written into the program for calculating the geometric parameters of the electrostatic lens using C++. The overall calculation process and idea are as Figure 4 shown;

[0062] Through the improved program, when the accelerating voltage, beam current, work function of the cathode material, cathode heating temperature, image distance, beam waist and beam spot radius are input, the important geometric parameters in the electrostatic lens and magnetic lens of the electron gun can be calculated; specifically, the calculation results are as Figure 5 shown;

[0063] Step 6: According to the above parameters, establish a geometric simulation model of the electron gun, and simulate the electron trajectory and the morphology of the electron beam spot at a specific cross-section (working plane); specifically, the beam spot morphology is as Figure 6 shown; The energy density distribution of the electron beam spot cross-section under different inner radii of the coil is as Figure 7 shown; The relationship between the beam spot radius and the beam spot position changing with the inner radius of the coil is as Figure 8 shown, Figure 8 where (a) is the beam spot radius and (b) is the image distance;

[0064] Step 7: Adopt the method of controlling variables, taking the uniformity of the energy density distribution, the beam spot size, the image distance, etc. as the judgment criteria, and comprehensively consider optimizing the anode aperture, the anode-cathode spacing, the spherical radius of the grid, the inner diameter of the coil, the yoke gap width, etc., to obtain the optimal parameter set of the core components of the electron gun.

[0065] The above is only the preferred implementation mode of the present invention. It should be pointed out that for those of ordinary skill in the art of this technology, without departing from the technical principle of the present invention, several improvements and retouches can still be made, and these improvements and retouches should also be regarded as the protection scope of the present invention.

Claims

1. An optimization method for a high-voltage electron gun device, characterized in that, It includes the following steps: establishing a general model for the geometric structure design of an electron gun; modifying and improving the Vaughan comprehensive iteration method; programming the core geometric parameters of the electrostatic lens and magnetic lens of the electron gun based on C++ assembly language; calculating and optimizing the geometric parameters of the electrostatic lens of the electron gun; using UG software to construct models of the electrostatic lens and magnetic lens of the electron gun; importing the models into the Comsol electromagnetic simulation software to simulate the temporal and spatial evolution trajectories of electrons; adopting the method of controlling variables to optimize and adjust the geometric parameters of the electrostatic lens and magnetic lens in sequence, with the judgment criteria being the beam spot energy density and the degree of distribution uniformity; establishing the relationship between the image distance and the focusing current.

2. The optimization method of the high-voltage electron gun device according to claim 1, characterized in that, The geometric parameters of the electrostatic lens of the electron gun include the cathode curvature radius, anode curvature radius, distance between the cathode and anode, beam waist position, and anode aperture.

3. The optimization method of the high-voltage electron gun device according to claim 2, characterized in that, It includes the following specific steps: Step 1: Adopting the Pierce electron gun design method to establish the basic structure of the electrode. The cathode is a "V"-shaped tungsten strip, and the model emission surface is set to a plane consistent with the actual situation. Calculate the side length of the cathode emission surface using the relational formula between the cathode emission current density and the cathode temperature; The Pierce electron gun uses a spherical electron gun with a conical electron beam.

4. The optimization method of the high-voltage electron gun device according to claim 3, characterized in that It also includes the following specific steps: Step 2: Modify and improve the iterative synthesis method. Revise the formula for calculating the cathode emission surface radius to half of the diagonal of a square to calculate the geometric parameters of the electrostatic lens, and use the Sharma anode aperture revision formula; The formulas in Step 2 include: θ' = θ{1 - (1 / 3)(R c -R a )(1 / (-α))(d(-α) / d(R c -R a ))}; Among them, -α = ln R c / R a + 0.3(ln R c / R a ) 2 + 0.075(ln R c / R a ) 3 + 0.014378(ln R c / R a ) 4 + 0.002160877(ln R c / R a ) 5 + 0.00026796(ln R c / R a ) 6 , d(-α) / d(R c -R a )=1 / R c / R a {1 + 0.6(ln R c / R a ) + 0.225(ln R c / R a ) 2 + 0.057272(ln R c / R a ) 3 + 0.010804385(ln R c / R a ) 4 + 0.0016077(ln R c / R a ) 5}。 5. The optimization method of the high-voltage electron gun device according to claim 4, characterized in that It also includes the following specific steps: Step 3: Compile the program using C++ language on the vs compiler; With this program, the user only needs to input the accelerating voltage, beam current, work function of the cathode material, cathode heating temperature, and beam waist radius to calculate the geometric parameters of the electrostatic lens of the electron gun. The geometric parameters of the electrostatic lens of the electron gun include the cathode curvature radius, anode curvature radius, distance between the cathode and anode, beam waist position, and anode aperture.

6. The optimization method of the high-voltage electron gun device according to claim 5, characterized in that It also includes the following specific steps: Step 4: Design the magnetic lens structure. Adopt a short magnetic lens with a hollow cylindrical energized short coil winding, and set a magnetic yoke outside; Revise the formula for calculating the inner radius of the coil to: R = (1.5e -5 Uatanθ) / 0.6 + t, The ratio μ between the magnetic yoke gap height (S) and the inner diameter (D) of the coil is between 0.4 and 1.2, and the initial value is set to 0.6; Calculate the focal length and ampere-turns according to the optical equation:

7. The optimization method of the high-voltage electron gun device according to claim 6, characterized in that, It also includes the following specific steps: Step 5: Also write the empirical formula for magnetic lens geometric calculation into the program for calculating the geometric parameters of the electrostatic lens using C++; Through the improved program, when the accelerating voltage, beam current, work function of the cathode material, cathode heating temperature, image distance, beam waist, and beam spot radius are input, the important geometric parameters in the electrostatic lens and magnetic lens of the electron gun can be calculated.

8. The optimization method of the high-voltage electron gun device according to claim 7, characterized in that, It also includes the following specific steps: Step 6: According to the above parameters, establish a geometric simulation model of the electron gun, and simulate to obtain the electron movement trajectory and the morphology of the electron beam spot at a specific cross-section (working plane).

9. The optimization method of the high-voltage electron gun device according to claim 8, characterized in that It also includes the following specific steps: Step 7: Using the method of controlling variables, with the uniformity of energy density distribution, spot size, and image distance as the judgment criteria, comprehensively consider optimizing the anode aperture, anode-cathode spacing, grid spherical radius, coil inner diameter, and yoke gap width to obtain the optimal parameter set for the core components of the electron gun.

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