A method of designing a surface ionization mass spectrometer

Abstract

The application provides a design method of a surface thermal ionization mass spectrometer, comprising the following steps: initially designing an ion lens system structure and performing three-dimensional modeling, simulating ion focusing states of ion beams generated from an ion source and passing through the ion lens system, judging whether the transmission effect meets the design requirements, correcting the structure parameters if the transmission effect does not meet the design requirements, and re-simulating, and determining the structure of the ion lens system if the transmission effect meets the design requirements; initially designing an ion optical system structure and performing three-dimensional modeling, simulating flight deflection trajectories of ion beams with different masses from the ion lens system into the ion optical system when a set acceleration voltage is used, judging whether the focusing effect meets the design requirements, correcting the structure parameters if the focusing effect does not meet the design requirements, and re-simulating, and determining the structure of the ion optical system if the focusing effect meets the design requirements; and designing parameters of an ion receiver. The application provides a reliable theoretical basis for the design and development of the thermal ionization mass spectrometer.

Description

TECHNICAL FIELD

[0001] The present application relates to a design method of a surface thermal ionization mass spectrometer. BACKGROUND

[0002] Thermal ionization mass spectrometry (TIMS) is an analytical testing technology for accurate measurement of element isotope abundance and isotope abundance ratio developed in the 1970s, mainly composed of an ion source, a magnetic mass analyzer, a detector system, a measurement and control system, and a software system. The principle is to evaporate and ionize a sample coated on a metal strip by heating, introduce the charged ions into a magnetic field mass analyzer through an ion transmission system, separate them according to their mass-to-charge ratios (m / z), amplify the ion current through a detector, and finally process the measurement and control software to give the isotope abundance or abundance ratio of the measured element. Compared with other analytical techniques, the thermal ionization mass spectrometry has the advantages of high accuracy and high precision. Isotope dilution mass spectrometry is an internationally recognized absolute measurement method and is widely used in the fields of nuclear industry, environment, geology, and archaeology.

[0003] At present, the manufacturing level of China has completely met the needs of the development of large-scale analytical instruments, but the forward design of the surface thermal ionization mass spectrometer has not been carried out. SUMMARY

[0004] The present application solves the technical problems of the prior art, provides a design method of a surface thermal ionization mass spectrometer, and provides a reliable theoretical basis for the design and development of thermal ionization mass spectrometers.

[0005] The technical solution adopted to solve the technical problems of the present application is:

[0006] The present application provides a design method of a surface thermal ionization mass spectrometer, comprising:

[0007] S1: preliminarily designing the structure of the ion lens system according to the design requirements and historical data results of the ion lens system, obtaining the initial structure parameters of the ion lens system, and performing three-dimensional modeling,

[0008] S2: simulating the ion focusing state of the ion beam generated from the ion source through the ion lens system by using ion optical simulation software,

[0009] S3: determining whether the transmission effect meets the design requirements, if not, modifying the structure parameters of the ion lens system, and returning to step S2, if yes, outputting the structure parameters of the ion lens system;

[0010] S4: preliminarily designing the structure of the ion optical system according to the design requirements of the ion optical system, the simulation results of step S3, and historical data results, obtaining the initial structure parameters of the ion optical system, and performing three-dimensional modeling,

[0011] S5: using a three-dimensional electromagnetic field simulation calculation software, simulating the flight deflection trajectory of the ion beams of different masses from the ion lens system into the ion photon system when the acceleration voltage is set,

[0012] S6: judging whether the focusing effect meets the design requirements, if not, modifying the structural parameters of the ion optical system and returning to step S5, if yes, outputting the structural parameters of the ion optical system;

[0013] S7: designing the ion receiver parameters according to the design requirements of the ion receiver and the simulation results of step S6.

[0014] Optionally,

[0015] In step S1, the ion lens system structure is preliminarily designed according to the design requirements of the ion lens system and historical data results, and the structural parameters of the ion lens system are obtained, specifically including:

[0016] According to the design requirements of the analysis mass range and mass resolution, the acceleration voltage and the ion lens exit slit size of the ion lens system are determined, the electrode composition of the ion lens system is determined according to the functional requirements of the ion lens system and historical data results, the slit size of a single electrode of the ion lens system is determined according to the ion transmission efficiency requirement and the height of the flight pipe, the voltage of the single electrode is determined according to the function of the single electrode and the acceleration voltage of the ion lens system, and the spacing of the adjacent two electrodes is calculated according to the ion lens focusing formula.

[0017] Optionally,

[0018] The ion lens focusing formula is:

[0019]

[0020] In the formula, f1 is the focal length of the previous electrode, V1 is the voltage of the previous electrode, V2 is the voltage of the next electrode, and L1 is the spacing between the two electrodes.

[0021] Optionally,

[0022] In step S2, the initial parameters of the ion beam generated from the ion source are simulated, and the initial parameters include the number of ions, the size of the ion beam, the energy dispersion, the ion mass, and the ion beam divergence angle.

[0023] Optionally,

[0024] In step S3, it is judged whether the transmission effect meets the design requirements, including judging whether the ion transmission efficiency and the ion beam exit divergence angle meet the design requirements.

[0025] Optionally,

[0026] In the step S3, the structure parameters of the ion lens system are corrected, specifically including:

[0027] First, the voltage of adjacent electrodes is adjusted, and when the transmission effect design requirement cannot be met by adjusting the voltage of adjacent electrodes, the distance between adjacent electrodes is adjusted from front to back; if the above two methods still cannot meet the transmission effect design requirement, the structure parameters of the ion lens system are recalculated.

[0028] Optionally,

[0029] In the step S4, according to the ion-photon system design requirement, the simulation result of step S3 and the historical data result, the ion-optical system structure is preliminarily designed to obtain the structure parameters of the ion-photon system, specifically including:

[0030] According to the ion lens exit slit size obtained by simulation in step S3 and the historical data result, the slit size and aberration of the Faraday cup receiver are determined,

[0031] According to the magnification design requirement and the mass resolution calculation formula, the dispersion function and mass dispersion of the ion-optical system are determined,

[0032] According to the historical data result, the ion beam incident angle and / or input arm are determined,

[0033] According to the design requirement of the fan-shaped magnetic field deflection angle and the central turning radius, and the fan-shaped magnetic field ion-optical focusing formula, the ion beam incident angle, the input arm, the ion beam exit angle, the output arm and the focusing plane tilt angle are calculated.

[0034] Optionally,

[0035] The mass resolution calculation formula is shown in formula (2):

[0036]

[0037] In the formula,

[0038] R: mass resolution; m: ion mass; s': incident slit width;

[0039] ∑A: aberration; D0: dispersion function; Δm: ion mass difference;

[0040] s": exit slit width; M: magnification; D m : mass dispersion.

[0041] Optionally,

[0042] The fan-shaped magnetic field ion-optical focusing formula is shown in formulas (3)-(5):

[0043]

[0044] M = l2 / l1 (4)

[0045]

[0046] where ψ is the magnetic field deflection angle; ε1 is the ion beam incident angle, ε2 is the ion beam exit angle, r0 is the central turning radius; l1 is the input arm, and l2 is the output arm.

[0047] Optionally,

[0048] In the step S6, it is judged whether the focusing effect meets the design requirement, and the step S6 specifically includes:

[0049] It is judged whether the mass dispersion function and the mass resolution meet the design requirement, and each ion beam has a corresponding focus point and all ion beam focus points are arranged on an approximately straight focusing plane.

[0050] Optionally,

[0051] In the step S6, the structure parameters of the ion optical system are corrected, and the step S6 specifically includes:

[0052] Firstly, the input arm length is adjusted, and when the arm length adjustment cannot meet the design requirement of the focusing effect, the ion beam incident angle is adjusted at the best value of the input arm length; if the above two methods still cannot meet the design requirement, the structure parameters of the ion optical system are recalculated.

[0053] Optionally,

[0054] The step S6 further includes:

[0055] According to the output structure parameters of the ion optical system and the electromagnetic related calculation formula, the structure of the sector magnet in the ion optical system is preliminarily designed, and the sector magnetic field simulation optimization is performed to obtain the final structure parameters of the sector magnet.

[0056] Optionally,

[0057] The step S7 specifically includes:

[0058] The slit width of the Faraday cup receiver should be greater than the width of a single ion beam,

[0059] The width of a single Faraday cup should be less than the distance between the center lines of the two ion beams with the largest mass number,

[0060] After the height of a single Faraday cup is set to be consistent with the height of the flight tube, the height is adjusted according to the ion transmission efficiency,

[0061] The depth of a single Faraday cup is greater than 10mm,

[0062] According to the simulation of the ion optical structure, a plurality of Faraday cups are arranged at different ion beam focus positions and different ion beam focus position angles.

[0063] The present application realizes the design operation of the surface thermal ionization mass spectrometer through theoretical modeling, solves the problem that the self-developed surface thermal ionization mass spectrometer cannot meet the actual needs of the spent fuel reprocessing plant, and provides a more reliable theoretical basis for the design and development of the thermal ionization mass spectrometer. BRIEF DESCRIPTION OF DRAWINGS

[0064] Figure 1 The surface thermal ionization mass spectrometer provided for embodiment 1 is shown in the schematic diagram of the principle structure of the surface thermal ionization mass spectrometer;

[0065] Figure 2 The structure schematic diagram of the ion lens system is shown in the structure schematic diagram of the ion lens system;

[0066] Figure 3 The electrode focusing schematic diagram of the ion lens system is shown in the electrode focusing schematic diagram of the ion lens system;

[0067] Figure 4 The focusing effect schematic diagram of the ion lens system is shown in the focusing effect schematic diagram of the ion lens system;

[0068] Figure 5 The electromagnetic structure schematic diagram is shown in the electromagnetic structure schematic diagram;

[0069] Figure 6 The ion deflection principle diagram in the magnetic field is shown in the ion deflection principle diagram in the magnetic field;

[0070] Figure 7 The ion mass dispersion schematic diagram is shown in the ion mass dispersion schematic diagram;

[0071] Figure 8 The model diagram of each electrode in the SIMION software is shown in the model diagram of each electrode in the SIMION software;

[0072] Figure 9 The example of the potential definition is shown in the example of the potential definition;

[0073] Figure 10 The example of the voltage setting on the ion lens group is shown in the example of the voltage setting on the ion lens group;

[0074] Figure 11 The example of describing the initial parameters of the particles is shown in the example of describing the initial parameters of the particles;

[0075] Figure 12 The simulation simulation diagram of the ion beam in the ion optical lens is shown in the simulation simulation diagram of the ion beam in the ion optical lens;

[0076] Figure 13 The ion deflection trajectory simulation simulation diagram is shown in the ion deflection trajectory simulation simulation diagram;

[0077] Figure 14 The simulation ion mass separation dispersion diagram is shown in the simulation ion mass separation dispersion diagram;

[0078] Figure 15 The design model diagram of the electromagnet is shown in the design model diagram of the electromagnet;

[0079] Figure 16 For analyzing the beam direction magnetic field distribution of the electromagnet;

[0080] Figure 17 For simulating the beam trajectory and whether the design is consistent with the example;

[0081] Figure 18 For the size of the electromagnet pole shoe;

[0082] Figure 19 For the schematic diagram of the magnet power supply device design principle;

[0083] Figure 20 For the component machining flowchart. DETAILED DESCRIPTION

[0084] The technical solutions in the application will be described in detail below with reference to the drawings in the application. Obviously, the described embodiments are part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of the application.

[0085] In the description of the application, it should be noted that the "upper" indicating position or location relationship is based on the position or location relationship shown in the drawings, and is only for the convenience and simplification of description, and does not indicate or imply that the device or element must be set with a specific position, constructed and operated with a specific position, and therefore cannot be understood as a limitation of the application.

[0086] In the description of the application, the terms "first", "second" are only for the purpose of description, and cannot be understood as indicating or implying relative importance.

[0087] In the description of the application, it should be noted that unless otherwise explicitly specified and limited, the terms "connection", "setting", "installation", "fixing" and the like should be understood broadly, for example, it can be fixedly connected or detachably connected, or integrally connected; it can be directly connected or indirectly connected through an intermediate medium; it can be the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the application can be understood according to the specific circumstances.

[0088] The application provides a design method of a surface thermal ionization mass spectrometer, comprising:

[0089] S1: according to the ion lens system design requirements and historical data results, the preliminary design of the ion lens system structure is carried out, the initial structure parameters of the ion lens system are obtained, and three-dimensional modeling is carried out,

[0090] S2: simulate the ion focusing state of the ion beam generated from the ion source passing through the ion lens system by using ion optics simulation software,

[0091] S3: determine whether the transmission effect meets the design requirement, if not, correct the structure parameters of the ion lens system, and return to step S2, if yes, output the structure parameters of the ion lens system;

[0092] S4: according to the ion optics system design requirement, the simulation result of step S3 and the historical data result, preliminarily design the ion optics system structure, obtain the initial structure parameters of the ion optics system, and perform three-dimensional modeling,

[0093] S5: simulate the flight deflection trajectory of the ion beam of different masses entering the ion optics system from the ion lens system under the set acceleration voltage by using three-dimensional electromagnetic field simulation calculation software,

[0094] S6: determine whether the focusing effect meets the design requirement, if not, correct the structure parameters of the ion optics system, and return to step S5, if yes, output the structure parameters of the ion optics system;

[0095] S7: design the ion receiver parameters according to the ion receiver design requirement and the simulation result of step S6.

[0096] Embodiment 1:

[0097] Figure 1 For the principle diagram of the surface thermal ionization mass spectrometer, the ions generated in the ion source chamber are introduced, accelerated and focused into a rectangular ion beam by the ion lens system, and finally enter the mass analyzer. The mass analyzer separates different ions according to their mass-to-charge ratio (m / z), amplifies the ion current through the ion receiver, and finally gives the measurement element isotope abundance or abundance ratio by the measurement and control software processing.

[0098] The embodiment provides a design method of a surface thermal ionization mass spectrometer, comprising:

[0099] S1: according to the ion lens system design requirement and the historical data result, preliminarily design the ion lens system structure, obtain the initial structure parameters of the ion lens system, and perform three-dimensional modeling,

[0100] S2: simulate the ion focusing state of the ion beam generated from the ion source passing through the ion lens system by using ion optics simulation software,

[0101] S3: determine whether the transmission effect meets the design requirement, if not, correct the structure parameters of the ion lens system, and return to step S2, if yes, output the structure parameters of the ion lens system;

[0102] S4: According to the ion-photon system design requirements, the simulation results of step S3 and the historical data results, a preliminary design of the ion-optical system structure is performed, initial structure parameters of the ion-photon system are obtained, and a three-dimensional model is established,

[0103] S5: Using three-dimensional electromagnetic field simulation calculation software, the flight deflection trajectories of ion beams of different masses entering the ion-photon system from the ion lens system under a set acceleration voltage are simulated,

[0104] S6: It is judged whether the focusing effect meets the design requirements. If not, the structure parameters of the ion-optical system are corrected, and step S5 is returned. If yes, the structure parameters of the ion-optical system are output.

[0105] S7: According to the ion receiver design requirements and the simulation results of step S6, the ion receiver parameters are designed.

[0106] Therefore, the design of the surface thermal ionization mass spectrometer is realized through theoretical modeling, the problem that the existing self-developed surface thermal ionization mass spectrometer cannot meet the actual needs of the spent fuel reprocessing plant is solved, and a more reliable theoretical basis is provided for the design and development of the thermal ionization mass spectrometer.

[0107] The historical data results refer to the research results of the surface thermal ionization mass spectrometer produced by foreign manufacturers.

[0108] In this embodiment,

[0109] In step S1, according to the ion lens system design requirements and the historical data results, a preliminary design of the ion lens system structure is performed, the structure parameters of the ion lens system are obtained, and the specific steps include:

[0110] According to the design requirements of the analysis mass range and the mass resolution, the acceleration voltage and the ion lens exit slit size of the ion lens system are determined, according to the functional requirements of the ion lens system and the historical data results, the electrode composition of the ion lens system is determined, according to the ion transmission efficiency requirements and the height of the flight tube, the slit size of the single electrode of the ion lens system is determined, according to the function of the single electrode and the acceleration voltage of the ion lens system, the voltage of the electrode is determined, and the spacing of the adjacent two electrodes is calculated according to the ion lens focusing formula.

[0111] In this embodiment,

[0112] The ion lens focusing formula is:

[0113]

[0114] In the formula, f1 is the focal length of the previous electrode, V1 is the voltage of the previous electrode, V2 is the voltage of the next electrode, and L1 is the distance between the two electrodes.

[0115] In this embodiment,

[0116] In step S2, initial parameters of the ion beam generated from the ion source are set before simulation, including ion number, ion beam size, energy spread, ion mass, and ion beam divergence angle.

[0117] In this embodiment,

[0118] In step S3, it is determined whether the transmission effect meets the design requirements, including determining whether the ion transmission efficiency and the ion beam exit divergence angle meet the design requirements.

[0119] In this embodiment,

[0120] In step S3, the structure parameters of the ion lens system are corrected, specifically including:

[0121] First, the voltage of adjacent electrodes is adjusted. When the voltage adjustment of adjacent electrodes cannot meet the design requirements of the transmission effect, the distance between adjacent electrodes is adjusted from front to back. If the above two methods still cannot meet the design requirements of the transmission effect, the structure parameters of the ion lens system are recalculated.

[0122] In this embodiment,

[0123] In step S4, according to the ion-photon system design requirements, the simulation results of step S3, and historical data results, the ion-optical system structure is preliminarily designed to obtain the structure parameters of the ion-photon system, specifically including:

[0124] According to the ion lens exit slit size obtained by step S3 simulation and historical data results, the slit size and aberration of the Faraday cup receiver are determined,

[0125] According to the magnification design requirements and the mass resolution calculation formula, the dispersion function and mass dispersion of the ion-optical system are determined,

[0126] According to the historical data results, the ion beam incident angle and / or input arm are determined,

[0127] According to the design requirements of the sector magnetic field deflection angle and the central turning radius, and the sector magnetic field ion-optical focusing formula, the ion beam incident angle, the input arm, the ion beam exit angle, and the output arm are calculated.

[0128] In this embodiment,

[0129] The mass resolution calculation formula is shown in formula (2):

[0130]

[0131] In the formula,

[0132] R: mass resolution; m: ion mass; s': entrance slit width;

[0133] ∑A: aberration; D0: dispersion function; Δm: ion mass difference;

[0134] s": exit slit width; M: magnification; D m : mass dispersion.

[0135] In this embodiment,

[0136] The focusing formula of the sector magnetic field ion optics is shown in equations (3)-(5):

[0137]

[0138] M = l2 / l1 (4)

[0139]

[0140] In the equation, ψ is the magnetic field deflection angle; ε1 is the ion beam incidence angle, ε2 is the ion beam exit angle, r0 is the central turning radius; l1 is the input arm, and l2 is the output arm.

[0141] In this embodiment,

[0142] In step S6, it is determined whether the focusing effect meets the design requirements, specifically including:

[0143] It is determined whether the mass dispersion function and the mass resolution meet the design requirements, and each ion beam has a corresponding focus point and all ion beam focus points are arranged on an approximately straight focusing plane.

[0144] In this embodiment,

[0145] In step S6, the structure parameters of the ion optical system are corrected, specifically including:

[0146] First, the input arm length is adjusted. When the arm length adjustment cannot meet the design requirements of the focusing effect, the ion beam incidence angle can be adjusted at the best value of the input arm length. If the above two methods still cannot meet the design requirements, the structure parameters of the ion optical system are recalculated.

[0147] In this embodiment,

[0148] Step S6 further includes:

[0149] According to the output structure parameters of the ion optical system and the electromagnetic related calculation formula, the structure of the sector magnet in the ion optical system is preliminarily designed, and sector magnetic field simulation optimization is performed to obtain the final structure parameters of the sector magnet.

[0150] In this embodiment,

[0151] Step S7 specifically includes:

[0152] The slit width of the Faraday cup receiver should be greater than the width of a single ion beam.

[0153] The width of a single Faraday cup should be less than the distance between the center lines of the two ion beams with the highest mass numbers.

[0154] Once the height of a single Faraday cup is set to match the height of the flight channel, it is then adjusted based on the ion transport efficiency.

[0155] The depth of a single Faraday cup is greater than 10 mm.

[0156] Multiple Faraday cups are arranged based on the focusing plane tilt angle and different ion beam focal point positions obtained from ion optical structure simulation.

[0157] Example 2:

[0158] This embodiment provides a specific design example of a surface thermal ionization mass spectrometer, including:

[0159] 1. Basic Determination of the Physical Structure of the Surface Thermal Ionization Mass Spectrometer

[0160] Based on the technical requirements of the surface thermal ionization mass spectrometer and the structural characteristics of the designed instrument, the basic structure of the instrument was determined according to the equations of motion of ions in electric and magnetic fields.

[0161] Analytical quality range: 1–280 amu;

[0162] Quality resolution (at 10% peak of uranium): ≥550;

[0163] Sensitivity: ≥500C / kg;

[0164] Internal accuracy of uranium isotope measurements: ≤0.008%;

[0165] Static multi-acceptance measurements of uranium in natural isotope composition ( 235 U / 238 When considering U) isotope ratios, the allowable range of relative standard deviation is ±0.05%.

[0166] 1.1) Determination of the structure of the ion lens system

[0167] Ion lens system is an important part of ion source structure, which is composed of several groups of metal electrode pieces with different voltages. The ions generated in the ion source chamber are accelerated, focused into a rectangular ion beam by the ion lens system, and finally enter the mass analyzer. A good ion lens system can make the ion beam enter the mass analyzer with small beam width and scattering angle, thereby improving the resolution and abundance sensitivity of the mass spectrometer. Through the research and study of surface ionization mass spectrometers produced by foreign manufacturers, the structure of the ion lens system is basically the same, mainly composed of acceleration electrode, extraction electrode, focusing electrode, R deflection electrode, ground electrode, Z deflection, and outlet slit. The ion lens structure composed of five electrodes and outlet slit is designed as shown in Figure 2 The effects of electrode voltage, ion lens structure, and lens electrode structure on ion transmission are explored by simulation using ion optical simulation software, and the ion lens system is optimized to obtain the relevant parameter law, providing a design basis for the development of surface ionization mass spectrometer ion source.

[0168] For surface ionization mass spectrometer, the main function of ion lens system is to extract, accelerate, focus and form the ions generated in the ion source into a rectangular ion beam with a length not greater than 6 mm and a width not greater than 0.2 mm; the acceleration voltage of the ion lens system is 10 kV, and the ion transmission efficiency is not less than 90%.

[0169] Before simulation, the design target and basic initial conditions of the ion lens system need to be determined. The acceleration and focusing effect of the ion lens system is shown in Figure 3 and Figure 4 The initial condition calculation of the ion lens system is based on the Dehmson-Kelvin lens focusing formula, from which the ion lens focal length f formed between V1-V2 electrodes can be derived as:

[0170]

[0171] In the formula, f1 is the focal length of the previous electrode, V1 is the voltage of the previous electrode, V2 is the voltage of the next electrode, and L1 is the distance between the two electrodes.

[0172] The ion beam scattering angle θ caused by the lens effect is:

[0173]

[0174] Where δ is the distance from the ion beam to the center axis of the electrode, and f is the focal length of the lens. Therefore, by adjusting the ion lens focal length f and the ion beam divergence angle θ, the ions generated by thermal ionization can be focused into a rectangular ion beam with a length of less than 6 mm and a width of less than 0.2 mm. When the ion lens focal length f and the ion beam divergence angle θ are determined, the electrode slit width can be calculated according to formulas (2)-(5): 4 mm; exit slit width: 0.2 mm; inter-electrode distance: d1 = 1 mm, d2 = d3 = d4 = d5 = 4 mm; inter-electrode voltage: V1 = -10 kV, V2 = -9 kV, V3 = -9.5 kV, V4 = -500 V.

[0175] 1.2) Basic structure of the fan-shaped magnetic field

[0176] The fan-shaped magnetic field of the surface thermal ionization mass spectrometer is provided by a C-shaped electromagnet, mainly including two U-shaped yokes, two pole shoes, four coil skeletons, power supply coils, and induction coils, as shown in Figure 5 . The magnetic yoke and the pole shoe are made of engineering pure to ensure the demagnetization speed and avoid material magnetic memory. The size of the magnetic yoke and the area of the pole shoe are the main parameters affecting the stability of the magnetic field area.

[0177] (1) Calculation of mass resolution

[0178] Mass resolution is an important technical indicator reflecting the ability of the instrument to analyze adjacent peaks, mainly depending on the structure of the fan-shaped magnetic field and the width of the entrance and exit slits, as shown in Figure 6 , Figure 7 . The classical calculation formula is as follows:

[0179]

[0180] R: mass resolution m: ion mass s′: entrance slit width ∑A: aberration

[0181] D0: dispersion function Δm: ion mass difference s″: exit slit width

[0182] M: magnification D m : mass dispersion b: ion beam exit width.

[0183] For the fan-shaped magnetic field of the surface thermal ionization mass spectrometer, the entrance slit width s′ = 0.2 mm, the exit slit width s″ = 0.8 mm, the magnification M ≈ 1.5, and the aberration ∑A is about 0.15 mm, then the mass dispersion D m ≈ 1.25 mm. If the instrument resolution R ≥ 550, the dispersion function D0 must be greater than 687.5 mm.

[0184] (2) Calculation of magnetic field parameters

[0185] 1) Calculation of magnetic induction

[0186] The magnetic induction of the sector magnetic field is provided by the electromagnet. According to the basic equation of mass spectrum, taking r0=200mm, the maximum mass number M=280, and the acceleration voltage U=10kV, the maximum adjustable magnetic induction B of the sector magnetic field is required to be 1.24T. Considering the overall performance of the instrument, the maximum magnetic induction B is designed to be 1.3T. max

[0187]

[0188] 2) Calculation of pole shoe area

[0189] The electromagnet is composed of two pole shoes, and the area between the two pole shoes is the sector magnetic field, which is the place where ions are separated. The area of the pole shoe depends on the central turning radius r0, the magnetic field deflection angle ψ and the pole shoe width E. The numerical calculation formula of E is as follows:

[0190] E=2l g +D m +2αl2+Δ (8)

[0191] l g is the pole gap of the electromagnet, D m is the mass dispersion, the ion beam divergence angle 2α=3°, and Δ is the design allowance. l g is an important parameter affecting the performance of the electromagnet. If the pole gap is too large, the dispersion field will increase, the magnet will be too heavy, and the sensitivity will be reduced. For the sector magnetic field with a deflection radius of not more than 200mm, l g is usually between 5mm and 15mm, and 12mm is selected here. The design allowance Δ is selected to be 20mm, and thus the pole shoe width E=50.7mm is obtained.

[0192] Then the pole shoe area A=160cm 2 is obtained according to the following formula:

[0193]

[0194] 3) Calculation of the number of turns of the electromagnet coil

[0195] First, the ampere-turns IBN of the electromagnet coil need to be calculated, and the calculation formula is as follows:

[0196]

[0197] Substitute B max =1.3T and l g =12mm into formula (10) to obtain the ampere-turns I B ​N ~ 9554 ampere turns. The exciting current I of the electromagnet B Generally between 2.4A and 4A, the exciting current is too small, the number of turns N is too large, the electromagnet is bulky; the exciting current is too large, the coil heat increases, affecting the performance of the electromagnet. Therefore, the exciting current IB = 3A is selected, and the number of turns N ~ 3185 is calculated. Considering the factors such as iron loss, non-working air gap loss and leakage magnetic field, the number of turns of the coil is increased by 20% than the theoretical value, which is designed as 3821 turns, which is wound in upper and lower coils.

[0198] (3) Determination of basic physical parameters

[0199] The magnetic field parameter calculation includes the calculation of the center turning radius r0, the magnetic field deflection angle ψ, the ion beam incidence angle ε1, the ion beam exit angle (ε2, the distance l1 between the source point S1 (ion source outlet slit position) and the magnetic pole boundary (referred to as the input arm), and the distance l2 between the image point S2 (ion receiver inlet slit position) and the magnetic pole boundary (referred to as the output arm). The calculation of the magnetic field parameters is based on the confocal theory of uniform magnetic field and dispersion field of William G. Cross. If the ions are to be focused in the magnetic field (both horizontally and vertically), the conditions described in the following equations (3) and (4) must be met.

[0200]

[0201] M = l2 / l1 (4)

[0202]

[0203] In the formula, ψ is the magnetic field deflection angle; ε1 is the ion beam incidence angle, ε2 is the ion beam exit angle, r0 is the center turning radius; l1 is the input arm, and l2 is the output arm. There are many magnetic field parameters that satisfy the above equations. The mass spectrometer used in this design is asymmetric, which can minimize the size of the mass analysis electromagnet while ensuring the mass dispersion required by the Faraday cup detector. The overall design parameters of the ion optical system are: magnification M = 1.5, magnetic field deflection angle ψ = 90°, center turning radius r0 = 200mm. By selecting different ion beam incidence angles (ε1), ion beam exit angles (ε2), input arms (l1), output arms (l2) and other parameters, and according to the above focusing formula and the correlation formula, the following parameters of the ion optical system of the mass spectrometer are obtained:

[0204] - The magnetic field deflection angle ψ of the magnetic field center path is 90°;

[0205] - The center turning radius r0 is 200mm;

[0206] - The ion beam incidence angle ε1 is 28°;

[0207] - Ion beam exit angle ε2 = 30°;

[0208] - Input arm 11 = 430 mm;

[0209] - Output arm 12 = 580 mm;

[0210] 2. Simulation of surface ionization mass spectrometer

[0211] With the development of software technology, there are many kinds of software for three-dimensional electromagnetic field simulation calculation at present, such as ANSYSHFSS, SIMION, OPERA, Zeland IE, etc. The software commonly used for electromagnetic field simulation calculation of magnetic mass spectrometer is mainly SIMION (for electric field calculation) and OPERA (for magnetic field calculation). The ion optical simulation software SIMION is a software specially used for calculating and simulating the electric field intensity and ion motion trajectory of ion optical system. The working principle of the software is to solve the electric field and ion motion trajectory according to Maxwell equation group. When solving the spatial electric field with different characteristics, different evolution formulas will be used, such as Laplace equation, Poisson equation, etc. Combined with finite element analysis method (through grid division of the calculation space, the partial differential and integral problems that cannot be solved analytically are processed), the calculation results with controllable precision are obtained.

[0212] The simulation of ion lens system is realized by SIMION software, and the specific steps are as follows:

[0213] First, the ion lens model file is established in the SIMION software according to the basic structure determined by the theoretical formula, as shown in Figure 8

[0214] Through the Refine function, the voltage of all points in the volume to be calculated is defined, and the grid size is 0.2 mm, as shown in Figure 9

[0215] The software "Workbench" function is used and the space volume to be simulated is set; then the software "Pas" function is used, the voltage of each pole of the ion lens group is set according to the theoretical calculation, and the "Fast Adjust Voltages" button is used to set the voltage on the ion lens group, as shown in Figure 10

[0216] The software "Particles" option is used, the "Define…" button is clicked, and the initial parameters of the ion beam formed by the ion generator of the ion source are set, as shown in Figure 11

[0217] ​​​​Start the simulation to evaluate the focusing effect of the ion ion lens system using the "Fly'm" function at the bottom of the software main window or the same named button on the "Particles" tab, as shown in Figure 12 .

[0218] By continuously iterating and optimizing the parameters of the ion lens system, such as lens size, electrode spacing, inter-electrode voltage, and slit width, until the ion focusing effect and ion beam divergence angle meet the design requirements, the theoretical calculation and simulation of the ion lens system are completed.

[0219] 2) Simulation of the ion optical system

[0220] According to the initial conditions determined in the previous section, use the OPERA simulation software to establish the model and set the parameters, and perform simulation calculation and parameter optimization on the ion optical system. The magnetic induction lines at the center of the pole shoe are uniformly distributed, but there is a certain width of the diffusion field at the edge of the pole shoe. Due to the existence of the diffusion field, the ions have been deflected before entering the uniform magnetic field, so the fan-shaped magnetic field needs to be optimized to ensure that the ion motion is not affected by the diffusion field. Mainly includes:

[0221] (1) The influence of pole shoe gap on the width of diffusion field

[0222] The pole shoe gap of the electromagnet is an important factor affecting the width of the diffusion field. By simulating the influence of the width of the diffusion field under different pole shoe gaps, the optimal design parameters are obtained.

[0223] (2) The influence of ion beam incidence angle (ε1) and magnetic field deflection angle (ψ) on focusing effect

[0224] From the aforementioned William G. Cross's theory of co-focusing of uniform magnetic field and diffusion field, it can be known that the incidence angle of ions entering the magnetic field has an important influence on the focusing effect. By setting different incidence angles, the focusing effect and mass dispersion of ions are verified.

[0225] The theoretical calculation and simulation of the magnetic field are also completed by SIMION software. The operation steps and simulation methods of the software are similar to those of the ion lens system and will not be repeated here. By simulating the flight deflection trajectories of ions of different masses (m1 = 238, m2 = 236, m3 = 235, m3 = 234) at an acceleration voltage of 10 kV using SIMION software, the detailed design parameters of the magnetic field are obtained, as shown in Figure 13 .

[0226] Theoretical calculation and simulation of the magnetic field require continuous iteration and optimization of parameters such as magnetic field strength, incident angle, exit angle, flight tube size, ion source outlet slit, and receiver slit, and finally the design parameters that meet the design requirements are obtained according to the dispersion distance and focusing effect of ions of different masses (m1 = 238, m2 = 236, m3 = 235, m3 = 234). The dispersion effect of different ion beams is shown in Figure 14 Performance evaluation of the magnetic field: after completing the theoretical calculation and simulation of the ion optical system, the Opera software is used to simulate and analyze the designed mass analyzing electromagnet according to the detailed design parameters of the magnetic field to determine whether the magnetic field distribution and beam trajectory are consistent with the design. The specific steps are as follows:

[0227] Model import: first, import the detailed design model file of the analysis electromagnet into the Opera software, as shown in Figure 15

[0228] Parameter design: set the parameters of the analysis electromagnet such as material, main coil wire gauge, induction coil wire gauge, main coil current, induction coil current, etc. using the software, and use a grid size of 0.2 mm grid to model the electromagnet (the maximum grid size can be adjusted according to the required calculation accuracy), and use the software magnetic field evaluation function to evaluate the beam direction magnetic field distribution of the analysis electromagnet, as shown in Figure 16

[0229] Beam simulation: after the magnetic field distribution evaluation meets the design requirements, use the software beam simulation function to put in 1000 238 U ions, beam energy E = 10 keV, magnetic field B = 1.11 T, and simulate whether the beam trajectory is consistent with the design, as shown in Figure 17

[0230] This process can continue to iterate and optimize parameters such as magnetic field strength, incident angle, exit angle, and flight tube size until the theoretical calculation and simulation parameters of the magnetic field fully meet the performance design requirements of the instrument. And according to the structure after iteration and optimization, the final design of the electromagnet pole shoe is completed, as shown in Figure 18

[0231] (3) Faraday cup parameter verification

[0232] The calculation of the size of the Faraday cup includes the calculation of the cup width (w), cup depth (d), and cup length (l). The size of the cup width (w) mainly depends on the mass dispersion function D0 and the maximum mass number of the ion beam spacing, the size of the cup depth (d) mainly depends on the magnification M of the Faraday cup and the ion secondary escape ability, and the cup length l mainly depends on the overall insulation, signal transmission, and other structural design of the Faraday cup. According to the theoretical calculation and simulation formula and simulation results of the magnetic field and Figure 14 ​​​​The dispersion distance of different ion beams was determined, and the parameters of the Faraday cup, such as cup width (w), cup depth (d), cup length (l), and focusing plane tilt angle θ, were designed. The instrument resolution was then verified to ensure it met the design requirements.

[0233] The beam spacing between ion beams of different mass numbers can be calculated using the following formula:

[0234]

[0235] The above formula shows that the beam spacing d for ion numbers of 279 (m1) and 280 (m2) is... m1m2 The diameter of the Faraday cup is approximately 2.09 mm, therefore the width (w) of the Faraday cup must be less than 2.09 mm. Considering the lateral movement space of the Faraday cup, the width w = 2 mm is selected. After the sample ions are separated by the fan-shaped magnetic field, a rectangular ion beam with a length of approximately 6 mm and a width of approximately 0.3 mm is formed. Considering the magnification M of the Faraday cup, the secondary escape capability of ions, and the overall structure of the instrument, the cup depth d = 15 mm is selected. Considering the insulation requirements of the Faraday cup, signal transmission requirements, and relevant design experience, the cup length l is generally designed to be around 30 mm.

[0236] The auxiliary system and mechanical structure were designed based on the basic physical structure of the surface thermal ionization mass spectrometer. The auxiliary system includes calculations of the vacuum system and selection of vacuum pump parameters, calculations and selection of equipment parameters such as the amplification factor, dark noise, dead time, and dynamic range of the secondary electron multiplier, selection of parameters and related physical designs of the power supply and electrical control system, glove box design, and software development.

[0237] The secondary electron multiplier power supply module provides power to the secondary electron multiplier. The output voltage can be set via computer software and adjusted using a 16-bit DAC digital-to-analog converter output port.

[0238] The main parameters of the secondary electron multiplier power module are as follows:

[0239] 1) Output voltage range: 0.5kV~2.6kV, output voltage adjustable;

[0240] 2) Operating load current: 1mA;

[0241] 3) Voltage adjustment step: 5.0±0.5V;

[0242] 4) Voltage instability: Output voltage instability ≤ 0.01% within 30 minutes;

[0243] 5) Output voltage ripple: ≤40mV.

[0244] The mass analysis electromagnet power supply device mainly includes an electromagnet power supply, a shaper, a scanning stabilizer, an electromagnet coil, a measuring coil, and the like. A design schematic diagram is shown in Figure 19 The electromagnet power supply converts a 220V AC power supply into an electromagnet coil power supply. The power supply supplies power to the electromagnet coil through the shaper for accurate current control. The scanning stabilizer receives signals from the measuring coil and the control computer, processes the signals, and controls the output current of the shaper to ensure that the magnetic field strength generated by the electromagnet remains stable at the set value of the control computer.

[0245] The sealed glove box is connected to the mass spectrometer sample inlet system through a sealing flange. The glove box has a design size of 900 mm in length, 500 mm in width, and 700 mm in height. The glove box is internally provided with sample preparation equipment, a sample turntable, a support, and other necessary sample preparation instruments. The pressure in the glove box is micro-negative. A sample access transition chamber is connected to the sealed glove box through an isolation gate valve, which is used as a sample isolation and access area during sample addition or replacement. The glove box equipment mainly includes a glove box, a transition chamber, a viewing window, a filter, a negative pressure gauge, and the like.

[0246] According to the detailed design, machining production and installation debugging are performed. The machining production is mainly mechanical machining manufacturing, and the process flow steps are: raw material storage, raw material inspection, raw material classification storage, raw material preparation, rough machining, finish machining, size detection, surface treatment, part assembly, part detection, and part finished product storage. A mechanical machining process flow chart is shown in Figure 20 .

[0247] After the surface ionization mass spectrometer is processed, installation and debugging are performed. The mass spectrometer is installed in a dry ventilation room equipped with exhaust and gas supply devices. The walls of the room should be painted, and the floor should be smooth and crack-free. The air in the room must be kept clean, with the least amount of dust and harmful impurities, otherwise it will cause a significant increase in mass spectrometry residues (when atmospheric air is poured into the system), and cause corrosion of metal parts and destruction of insulation

[0248] Sudden temperature fluctuations are not allowed during the operation of the mass spectrometer. The mass spectrometer must be protected from perceptible air currents. The recommended working conditions are a relative humidity of up to 80% and an air temperature of 20±2℃.

[0249] There must be a grounding circuit in the room. The mass spectrometer must be properly grounded. The cross section of the grounding wire must be greater than 2.5mm 2 .

[0250] The amplitude of floor vibration should not exceed 0.1mm at a frequency of up to 25Hz.

[0251] The room should be prepared with 220 V voltage, 50 Hz frequency, and single-phase alternating current power higher than 2.5 kVA. The power quality should meet the requirements of the relevant national power standards. During uranium analysis on the mass spectrometer and preparation of the sample (coating of the uranyl nitrate solution on the sample belt of the ion source carousel), the corresponding precautions must be observed. Uranyl nitrate is a highly toxic radioactive substance, which is quite dangerous in terms of radioactivity and chemistry. Possible causes of accidents are poisoning, and dispersion of solid deposits of uranium compounds during sampling, changing the carousel to the ion source, or preventive work under the vacuum mass spectrometer system.

[0252] In the working room using uranyl nitrate, during installation and removal of the ion source sample disc and maintenance of the mass spectrometer, the environment and the surface of the mass spectrometer should be regularly monitored for dosimetry according to the safety instructions for operating the mass spectrometer of the mass spectrometer company.

[0253] Radiac, dosimeter or other similar devices should be used to monitor the surface contamination with active nuclides and gamma-ray radiation power.

[0254] It can be understood that the above embodiments are only exemplary embodiments for illustrating the principles of the present application, and the present application is not limited thereto. Various modifications and improvements can be made by those of ordinary skill in the art without departing from the spirit and essence of the present application, and these modifications and improvements are also considered to be within the protection scope of the present application.

Claims

1. A method of designing a surface ionization mass spectrometer, characterized in that, Comprise: S1: according to ion lens system design requirements and historical data results, the preliminary design of ion lens system structure, obtain the initial structure parameters of ion lens system, and carry out three-dimensional modeling, S2: using ion optical simulation software, simulate the ion focusing state of the ion beam generated from the ion source through the ion lens system, S3: determine whether the transmission effect meets the design requirements, if not, modify the structure parameters of the ion lens system, and return to step S2, if yes, output the structure parameters of the ion lens system; S4: according to the ion optical system design requirements, the simulation results of step S3 and the historical data results, the preliminary design of ion optical system structure, obtain the initial structure parameters of ion optical system, and carry out three-dimensional modeling, S5: using three-dimensional electromagnetic field simulation calculation software, simulate the flight deflection trajectory of different mass ion beams from the ion lens system into the ion optical system under the set acceleration voltage, S6: determine whether the focusing effect meets the design requirements, if not, modify the structure parameters of the ion optical system, and return to step S5, if yes, output the structure parameters of the ion optical system; S7: according to the design requirements of the ion receiver and the simulation results of step S6, design the parameters of the ion receiver.

2. The design method of the surface thermal ionization mass spectrometer according to claim 1, wherein, in step S1, according to the ion lens system design requirements and historical data results, the preliminary design of ion lens system structure is carried out, and the initial structure parameters of ion lens system are obtained, specifically comprising: According to the design requirements of the analysis mass range and the mass resolution, the acceleration voltage and the ion lens exit slit size of the ion lens system are determined, according to the functional requirements and historical data results of the ion lens system, the electrode composition of the ion lens system is determined, according to the ion transmission efficiency requirements and the height of the flight tube, the slit size of the single electrode of the ion lens system is determined, according to the function of the single electrode and the acceleration voltage of the ion lens system, the voltage of the electrode is determined, and the distance between the adjacent two electrodes is calculated according to the ion lens focusing formula.

3. The design method of the surface thermal ionization mass spectrometer according to claim 2, wherein, the ion lens focusing formula is: In the formula, f1 is the focal length of the previous electrode, V1 is the voltage of the previous electrode, V2 is the voltage of the next electrode, and L1 is the distance between the two electrodes.

4. The design method of the surface thermal ionization mass spectrometer according to claim 1, wherein, in step S2, the initial parameters of the ion beam generated from the ion source are simulated, the initial parameters including the number of ions, the size of the ion beam, the energy dispersion, the ion mass and the ion beam divergence angle. In step S3, it is judged whether the transmission effect meets the design requirements, including: judging whether the ion transmission efficiency and the ion beam exit divergence angle meet the design requirements. In step S3, the structure parameters of the ion lens system are modified, specifically including: ​ 5. The method of designing a surface ionization mass spectrometer according to claim 1, wherein, ​ 6. The method of designing a surface ionization mass spectrometer according to claim 1, wherein, ​ Firstly, the voltage of the adjacent electrode is adjusted, and then the distance between the adjacent electrodes is adjusted from front to back if the transmission effect design requirement cannot be met by adjusting the voltage of the adjacent electrode. If the above two methods still cannot meet the transmission effect design requirement, the structure parameters of the ion lens system are recalculated.

7. The method of claim 1, wherein the ion optical system is designed according to the ion optical system design requirement, the simulation result of step S3 and the historical data result. In step S4, the ion optical system structure is preliminarily designed according to the ion optical system design requirement, the simulation result of step S3 and the historical data result, and the structure parameters of the ion optical system are obtained, which specifically includes: The slit size and aberration of the Faraday cup receiver are determined according to the ion lens outlet slit size obtained by the simulation of step S3 and the historical data result, The dispersion function and mass dispersion of the ion optical system are determined according to the magnification design requirement and the mass resolution calculation formula, The ion beam incident angle and / or input arm are determined according to the historical data result, The ion beam incident angle, input arm, ion beam exit angle and output arm are calculated according to the design requirement of the sector magnetic field deflection angle and central turning radius, and the ion optical focusing formula of the sector magnetic field.

8. The method of claim 7, wherein the mass resolution calculation formula is shown as formula (2): In formula (2), R represents the mass resolution, ∑A represents the aberration, D0 represents the dispersion function, and Δm represents the ion mass difference. s" represents the exit slit width.

9. The method of claim 7, wherein the ion optical focusing formula of the sector magnetic field is shown as formula (3)-(5): m: ion mass; s ' : incident slit width; In formula (3)-(5), ψ represents the magnetic field deflection angle, ε1 represents the ion beam incident angle, ε2 represents the ion beam exit angle, r0 represents the central turning radius, l1 represents the input arm, l2 represents the output arm, M represents the magnification, and D0 represents the dispersion function. In step S6, it is determined whether the focusing effect meets the design requirement, which specifically includes: M: magnification; D m : mass dispersion. It is determined whether the mass dispersion function and mass resolution meet the design requirement, and each ion beam has a corresponding focus point and all ion beam focus points are arranged on an approximately straight focusing plane. In step S6, the structure parameters of the ion optical system are modified, which specifically includes: M＝l2 / l1 (4) Firstly, the input arm length is adjusted, and then the ion beam incident angle is adjusted at the best value of the input arm length if the arm length adjustment cannot meet the focusing effect design requirement. If the above two methods still cannot meet the design requirement, the structure parameters of the ion optical system are recalculated.

10. The method of designing a surface ionization mass spectrometer according to claim 1, wherein, In step S6, it further includes: According to the structure parameters of the output ion optical system and the electromagnet related calculation formula, the structure of the sector magnet in the ion optical system is preliminarily designed, and the sector magnetic field simulation optimization is performed to obtain the final structure parameters of the sector magnet.

11. The method of designing a surface ionization mass spectrometer according to claim 1, wherein, 13. The method of claim 1-12, wherein step S7 specifically includes: The slit width of the Faraday cup receiver should be greater than the width of a single ion beam, 12. The method of designing a surface ionization mass spectrometer according to claim 1, wherein, The width of a single Faraday cup should be less than the distance between the center lines of the two ion beams with the largest mass number, ​ ​ ​ ​ ​ The height of the single Faraday cup is set to be consistent with the height of the flight tube, and then adjusted according to the ion transmission efficiency, The depth of the single Faraday cup is greater than 10 mm, A plurality of Faraday cups are arranged according to the tilt angle of the focusing plane obtained by simulation of the ion optical structure and different ion beam focus positions.

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