A rare gas isotope mass spectrometer ion source

Abstract

The present invention discloses an ion source for a rare gas isotope mass spectrometer, comprising a cathode assembly and an electron receiving stage assembly, an ionization box, a repeller, an extraction focusing lens group, and an ion source fixing seat. The cathode assembly and the electron receiving stage assembly are respectively fixed at the upper and lower ends of the ionization box, the repeller is fixed at the rear end of the ionization box, the extraction focusing lens group is at the front end of the ionization box, the extraction focusing lens group is connected to the ionization box via a connecting porcelain column to achieve fixation and insulation, the extraction focusing lens group is composed of a pull-out electrode, a z focusing electrode, a grounding electrode, a y focusing electrode, and an exit slit arranged in sequence, the extraction focusing lens group realizes extraction and focusing of sample ions in the ionization box, the other end of the connecting porcelain column is connected to the ion source fixing seat, the center of the ion source fixing seat has an exit slit, the structure is simple, the number of pole pieces is small, the internal volume is small, and the sensitivity is greatly improved. The repeller and extraction focusing system has high ion extraction efficiency and good focusing effect.

Description

Technical Field

[0001] The invention belongs to the technical field of ion sources, and in particular relates to an ion source for a rare gas isotope mass spectrometer. Background Art

[0002] An ion source is a device used in a mass spectrometer to ionize a sample and focus the extracted ions. An electron bombardment ion source is an ion source that uses an electron beam of a certain energy to ionize gaseous sample molecules or atoms. It has the characteristics of simple structure, high ionization efficiency, strong versatility, stable performance, and easy operation. It is one of the ionization sources widely used in mass spectrometers and is also the type of ion source commonly used in mainstream noble gas isotope mass spectrometers. Mass spectrometry analysis of noble gases places high demands on the vacuum level of the instrument cavity, measurement accuracy, precision, and sensitivity. Therefore, it has high requirements on the internal volume of the ion source, ion transmission efficiency, and focusing performance. The noble gas isotope mass spectrometers currently used in China are expensive, have high operating and maintenance costs, and slow repair response. A noble gas isotope mass spectrometer is proposed herein. Summary of the Invention

[0003] In order to overcome the above-mentioned shortcomings, the inventors of the present invention have continuously reformed and innovated through long-term exploration and attempts, multiple experiments and efforts, and proposed a rare gas isotope mass spectrometer ion source, which can realize static analysis of rare gas samples. The ion source has a simple structure, few electrodes, a small internal volume and high sensitivity.

[0004] To achieve the above-mentioned objectives, the present invention employs a technical solution: providing an ion source for a noble gas isotope mass spectrometer. The ion source comprises a cathode assembly, an electron receiving stage assembly, an ionization cell, a repeller, an extraction and focusing lens assembly, and an ion source mounting base. The cathode assembly and the electron receiving stage assembly are respectively fixed at the upper and lower ends of the ionization cell. The repeller is fixed at the rear end of the ionization cell. The extraction and focusing lens assembly is located at the front end of the ionization cell and is connected to the ionization cell via a connecting porcelain column for fixation and insulation. The extraction and focusing lens assembly comprises an extraction electrode, a z-focusing electrode, a grounding electrode, a y-focusing electrode, and an exit slit, which are arranged in sequence. The extraction and focusing lens assembly extracts and focuses sample ions within the ionization cell. The other end of the connecting porcelain column is connected to the ion source mounting base, and the ion source mounting base has an exit slit at its center.

[0005] According to the ion source of a rare gas isotope mass spectrometer described in the present invention, a further preferred technical solution is: the cathode assembly is composed of a cathode ceramic part, a filament rack, a cathode cover and a cathode cover short-circuit piece, the left filament rack and the right filament rack of the filament rack are both passed through the cathode ceramic part and fixed by nuts, the filament is installed on the filament rack, the cathode cover is embedded in the notch of the cathode ceramic part through the fixed end with a through hole, the cathode cover is fixed to the cathode ceramic part by the cathode cover short-circuit piece and short-circuited with the right filament rack.

[0006] According to the ion source of a rare gas isotope mass spectrometer described in the present invention, a further preferred technical solution is: the electron receiving stage assembly includes a receiving stage ceramic part, an electron receiving box and a receiving frame, the receiving frame is threaded at the coarse end, and is fixed to the ionization box by a nut after passing through the receiving stage ceramic part.

[0007] According to the ion source for a rare gas isotope mass spectrometer described in the present invention, a further preferred technical solution is: the ionization box is shaped like a square box body, a square hollow space is provided in the center as the area where gas ionization occurs, circular through holes are provided around the square opening for fixing and connecting the ceramic column, rectangular through holes are provided at the upper and lower parts of the rear end surface for fixing the ceramic part, hollow grids are provided on the side of the ionization box as gas exchange holes in the square hollow space, and waist-shaped through grooves are provided on the side for connecting the cathode assembly with the electron receiving stage assembly.

[0008] According to the ion source for a rare gas isotope mass spectrometer described in the present invention, a further preferred technical solution is that the repeller is a concave repeller installed at the rear end of the ionization chamber, and the gap between the circle and the square is used for gas exchange inside and outside the ionization box.

[0009] According to the ion source for a rare gas isotope mass spectrometer described in the present invention, a further preferred technical solution is: the pull-out electrode consists of two electrode halves arranged upper and lower and two corresponding electrode pins. The function of the electrode piece is to pull out the ions ionized in the ionization box. The two electrode halves add a relatively adjustable voltage to control the deflection of the ion beam in the z direction. The four circular through holes around it are used to insert the connecting porcelain columns.

[0010] According to the ion source of a rare gas isotope mass spectrometer described in the present invention, a further preferred technical solution is: the z focusing electrode consists of an electrode sheet and an electrode pin, with an opening in the middle and a straight slot to achieve focusing effects in the z direction and the y direction of the ion beam, and the ratio of the distance between the z focusing electrode and the left pull-out electrode and the distance between the z focusing electrode and the right grounding electrode is 7:3.

[0011] According to the ion source for a rare gas isotope mass spectrometer described in the present invention, a further preferred technical solution is as follows: the grounding electrode comprises an electrode sheet and an electrode pin, with an opening in the middle. The electrode sheet is short-circuited to the ion source fixing base via a lead and then grounded. The electrode sheet functions to form a potential difference with the front z-focusing electrode, enabling the z-focusing electrode to exert a focusing effect, and simultaneously forms a single lens with the rear y-focusing electrode to achieve y-direction focusing of the ion beam.

[0012] According to the ion source of a rare gas isotope mass spectrometer described in the present invention, its further preferred technical solution is: the y-focusing electrode is composed of two electrode halves and two electrode pins. The function of the electrode is to form a single lens equidistant with the grounded electrode on the front side and the grounded ion source fixing seat on the rear side to achieve y-direction focusing of the ion beam. A relatively adjustable voltage is added to the two electrode halves to control the deflection of the ion beam in the y direction.

[0013] According to the ion source for a rare gas isotope mass spectrometer described in the present invention, a further preferred technical solution is: the outlet slit is formed by welding an outlet slit sheet fixed to an ion source fixing seat to achieve the focusing effect of the ion beam in the y direction, the slit width controls the width of the outgoing ion beam in the z direction, and the ion source fixing seat fixes the ion source on the external cavity.

[0014] Compared with the prior art, the technical solution of the present invention has the following advantages / benefits:

[0015] 1. This invention is suitable for use in noble gas isotope mass spectrometers, enabling static analysis of sample gases. The ion source features a simple structure, minimal electrodes, and a compact internal volume, significantly improving sensitivity. Simulations have demonstrated the effectiveness of the repeller and extraction focusing system, resulting in high ion extraction efficiency and excellent focusing.

[0016] 2. The overall structure is compact, which provides a good foundation for miniaturization. By adjusting the number, specifications and spacing of the concave repeller, cathode cover and focusing lens group, a miniaturized ion source can also have a good focusing effect to meet the use environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0018] Figure 1 It is a structural schematic diagram of an ion source for a rare gas isotope mass spectrometer of the present invention.

[0019] Figure 2 The diagram is a schematic diagram of the internal structure of an ion source of a rare gas isotope mass spectrometer according to the present invention.

[0020] Figure 3 This is a schematic diagram of the internal structure of an ion source for a rare gas isotope mass spectrometer from another perspective of the present invention.

[0021] Figure 4 The present invention is a schematic structural diagram of an ionization box of an ion source for a rare gas isotope mass spectrometer.

[0022] Figure 5 The present invention is a schematic structural diagram of an ionization box of an ion source of a rare gas isotope mass spectrometer from a front-end perspective.

[0023] Figure 6 The present invention is a schematic diagram of the structure of a cathode assembly of an ion source of a rare gas isotope mass spectrometer.

[0024] Figure 7 This is a schematic structural diagram from another perspective of a cathode assembly of an ion source of a rare gas isotope mass spectrometer according to the present invention.

[0025] Figure 8 The present invention is a schematic diagram of the structure of an electron receiving stage component of an ion source of a rare gas isotope mass spectrometer.

[0026] Figure 9 The diagram is a schematic diagram of the explosion structure of an extraction and focusing lens group of an ion source of a rare gas isotope mass spectrometer according to the present invention.

[0027] Figure 10 This is a simulation diagram of an ion beam of a convex repeller of an ion source of a rare gas isotope mass spectrometer according to the present invention.

[0028] Figure 11 This is a simulation diagram of an ion beam of a concave repeller of an ion source of a rare gas isotope mass spectrometer according to the present invention.

[0029] Figure 12 This is a simulation diagram of an ion beam of an ion source of a rare gas isotope mass spectrometer without a cathode mask according to the present invention.

[0030] Figure 13 This is a simulation diagram of an ion beam of an ion source of a rare gas isotope mass spectrometer according to the present invention when a cathode cover is provided.

[0031] Figure 14 This is a simulation diagram of an ion beam of an ion source of a rare gas isotope mass spectrometer without a pullout stage according to the present invention.

[0032] Figure 15 This is a simulation diagram of an ion beam of an ion source of a rare gas isotope mass spectrometer according to the present invention when it has a pullout stage.

[0033] Figure 16 This is a simulation diagram of an ion beam when the distance between the pull-out electrode and the grounding electrode of an ion source of a rare gas isotope mass spectrometer of the present invention is 3 mm.

[0034] Figure 17 This is a simulation diagram of an ion beam when the distance between the pull-out electrode and the grounding electrode of an ion source of a rare gas isotope mass spectrometer of the present invention is 1 mm.

[0035] Figure 18 This is a simulation diagram of an ion beam when a z-focusing pole is added to an ion source of a rare gas isotope mass spectrometer according to the present invention.

[0036] Figure 19 This is a simulation diagram of an ion beam in the y direction of an ion source of a rare gas isotope mass spectrometer according to the present invention, which has a z focusing electrode and a grounding electrode.

[0037] Figure 20 This is a simulation diagram of an ion beam with a y-focusing lens of an ion source of a rare gas isotope mass spectrometer according to the present invention.

[0038] The markings in the figure are: 1. Ionization box 101. Hollow space 102. Circular through hole 103. Rectangular through hole 104. Hollow grid 105. Waist-shaped through groove 2. Lead-out focusing lens group 201. Pull-out electrode 202. Z focusing electrode 203. Grounding electrode 204. Y focusing electrode 205. Exit slit 3. Ion source fixing seat 4. Exit slit plate 5. Connecting porcelain column 501. Positioning ceramic ring 6. Cathode assembly 601. Cathode ceramic part 602. Left filament holder 603. Right filament holder 604. Cathode cover 605. Cathode cover short-circuit 7. Electron receiving stage assembly 701. Electron receiving box 702. Receiving frame 703. Receiving stage ceramic part 8. Concave repeller 9. Electrode pin. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention are clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. Therefore, the detailed description of the embodiments of the present invention provided below is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention.

[0040] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it may not be further defined or explained in subsequent drawings.

[0041] Example:

[0042] like Figure 1As shown, an ion source for a noble gas isotope mass spectrometer includes a cathode assembly 6, an electron receiving stage assembly 7, an ionization cell 1, a repeller, an extraction and focusing lens assembly 2, and an ion source mounting base 3. The cathode assembly 6 and the electron receiving stage assembly 7 are respectively fixed to the upper and lower ends of the ionization cell 1. The repeller is fixed to the rear end of the ionization cell 1. The extraction and focusing lens assembly 2 is located at the front end of the ionization cell 1. The extraction and focusing lens assembly 2 is connected to the ionization cell 1 via a connecting porcelain column 5 for fixation and insulation. The extraction and focusing lens assembly 2 is composed of an extraction electrode 201, a z focusing electrode 202, a grounding electrode 203, a y focusing electrode 204, and an exit slit 205, which are arranged in sequence. The extraction and focusing lens assembly 2 extracts and focuses sample ions in the ionization cell 1. The other end of the connecting porcelain column 5 is connected to the ion source mounting base 3. The center of the ion source mounting base 3 has an exit slit 205 formed by an exit slit sheet 4.

[0043] The cathode assembly 6 is composed of a cathode ceramic member 601, a filament holder, a cathode cover 604, and a cathode cover short-circuit 605. The left filament holder 602 and the right filament holder 603 of the filament holder are both threaded through the cathode ceramic member 601 and secured with nuts. The filaments are mounted on the filament holders, with both ends of the filaments positioned on the left and right filament holders 602 and 603. The filaments are positioned in grooves formed by baffles on either side of the middle portion of the cathode cover 604. The cathode cover 604 is inserted into the notch of the cathode ceramic member 601 via a fixed end with a through hole. The cathode cover is secured to the cathode ceramic member 601 via the cathode cover short-circuit 605 and short-circuited with the right filament holder 603. The cathode assembly 6 is electrically insulated from the ionization box 1 by the cathode ceramic member 601 because the potential applied to it is different. The left and right filament holders 602 and 603 are threaded at their coarse ends and secured with M1.6 nuts after threading through the cathode ceramic member 601. The cathode cover 604 controls the potential near the filament, ensuring that the electrons emitted by the filament acquire a certain energy and enter the ionization cell 1 in a collimated manner. Cathode cover 604 is secured to the cathode ceramic component 601 using an M1.6 nut via a cathode cover shorting connector. This shorting connector is also connected to the right filament holder 603. The filament is spot welded to the filament holder. The filament holder is secured to the ceramic component by tapping the end of the filament holder and then tightening it with an M1.6 hexagonal nut. To ensure the orientation of the filament holder, the ceramic component has straight slots that mate with the steel sheet on the filament holder. To ensure that electrons emitted by the cathode travel downward in a collimated manner into the ionization cell 1, cathode cover 604 is required to control the potential around the filament. Adding cathode cover 604 levels the equipotential lines around the filament, which helps focus the electrons. The cathode cover is at the same potential as one of the filament holders. Therefore, the cathode cover 604 is secured by inserting its fixed end, which has a through hole, into the slot of the cathode ceramic component 601. It is then locked to the ceramic component using a conductive cathode cover shorting connector 605. The cylindrical part of the cathode cover short-circuit 605 passes through the cathode ceramic part 601, and one end connected to the cathode cover is threaded and fixed to the cathode cover 604 on the cathode ceramic part 601 through a nut, and the other end is put on one of the filament racks and fixed by a nut, which not only achieves short circuit but also makes the cathode cover more firmly fixed.

[0044] The electron receiving-level assembly 7 includes a receiving-level ceramic part 703, an electron receiving box 701, and a receiving frame 702. The receiving frame 702 is threaded at the coarse end and is fixed to the ionization box 1 via a nut after passing through the receiving-level ceramic part 703. The electron receiving box 701 and the receiving frame 702 are fixed by welding. The receiving-level ceramic part 703 of the electron receiving electrode assembly is the same as the cathode ceramic part 601 of the cathode assembly 6. The electron receiving box 701 (also called the receiving electrode piece) is fixed to the receiving frame 702 by spot welding. The fixing method of the receiving frame 702 and the receiving-level ceramic part 703 is similar to that of the cathode filament frame. The electron receiving electrode assembly is located below the ionization box 1 and is arranged at a position symmetrical to the cathode assembly 6.

[0045] The ionization chamber 1 is a square box with a central square hollow space 101 serving as the gas ionization area. Circular through-holes 102 surround the square opening, securing the connecting ceramic column 5. Four surrounding circular through-holes 102 are used to insert the connecting ceramic column 5 and subsequently install the lead-out focusing lens assembly 2 (also called the electrode assembly). Rectangular through-holes 103 are located at the upper and lower portions of the rear surface for securing ceramic components (including the cathode ceramic component 601 and the receiving-stage ceramic component 703). A hollow grid 104 is provided on the side of the ionization chamber 1 as a gas exchange aperture in the square hollow space 101. A waist-shaped through-groove 105 connects the cathode assembly 6 and the electron receiving-stage assembly 7. The ionization chamber 1 generates ions by emitting electrons to ionize the gas sample and transmits these ions to subsequent structures for mass spectrometry analysis. The hollow grid 104 uses small holes, 1 mm wide and 8 mm long, as gas exchange channels to prevent ion leakage when the outer grounded cavity is relatively close to the ionization chamber 1. Unlike the traditional single large side opening, this ionization chamber 1 uses six small grid holes with a width of 1 mm and a length of 8 mm as gas exchange channels. This can prevent ion leakage when the outer grounded cavity is relatively close to the ionization chamber 1, and is particularly suitable for ionization chambers 1 with small volumes.

[0046] The repeller is a concave repeller 8, installed at the rear end of the ionization chamber. The gap between the circular and square shapes facilitates gas exchange between the interior and exterior of the ionization chamber 1. Since equipotential lines near the repeller conform to the repeller surface, the shape of these lines is determined by the repeller's shape. A concave repeller has concave equipotential lines on its surface, conforming to the cluster of equipotential lines formed by the extractor 201. This results in more uniform equipotential lines and minimizes ion energy dispersion. Furthermore, concave equipotential lines prevent ions generated near them from initially diverging, resulting in better extraction. Therefore, a concave repeller is selected.

[0047] The pull-out electrode 201 consists of two electrode halves and two electrode pins 9. The function of this electrode is to pull out the ions ionized in the ionization box 1. The two halves can add relatively adjustable voltages to control the deflection of the ion beam in the z direction. The four circular through holes 102 around it are used to insert the connecting porcelain pillars 5. The other electrode pieces are installed in the same way, all of which are installed through the connecting porcelain pillars 5. At the same time, the positioning ceramic ring 501 is added to enhance the positioning capability and the mutual insulation between the electrode pieces. At the same time, the height of the porcelain pillars and the positioning ceramic ring 501 can also be used to adjust the spacing between the electrode pieces, realizing flexible spacing adjustment capability.

[0048] The z focusing electrode 202 consists of an electrode sheet and an electrode pin 9. The middle opening is a straight slot with a width of 3 mm and a radius of 1.5 mm, which realizes the focusing effect of the ion beam in the z direction and the y direction. The ratio of the distance between the z focusing electrode 202 and the left pull-out electrode 201 and the right grounding electrode 203 is 7:3. Its main function is to realize the focusing of the ion beam in the z direction, but it also has a certain focusing effect in the y direction.

[0049] The grounding electrode 203 consists of an electrode piece and an electrode pin 9, with a central opening 7 mm high and 20 mm wide. The electrode piece is short-circuited with the ion source holder 3 via a lead and then grounded. Its function is to form a potential difference with the front z focusing electrode 202, so that the z focusing electrode 202 can play a focusing role. At the same time, it forms a single lens with the rear y focusing electrode 204 to achieve y-direction focusing of the ion beam.

[0050] The y focusing electrode 204 consists of two electrode halves and two electrode pins 9. The function of the electrode is to form a single lens equidistant with the grounded electrode 203 on the front side and the grounded ion source fixing seat 3 on the rear side to achieve y-direction focusing of the ion beam. The two halves are used to add a relatively adjustable voltage to control the deflection of the ion beam in the y direction.

[0051] The exit slit 205 is formed by welding the exit slit piece 4 to the ion source fixing seat 3, which plays the role of forming a single lens to realize the focusing of the ion beam in the y direction. At the same time, the slit width of the exit slit piece 4 controls the width of the outgoing ion beam in the z direction. The ion source fixing seat 3 fixes the ion source to the external cavity through two M4 countersunk screws.

[0052] The spacing between the above-mentioned pole pieces, the distance of the openings, etc. are only reasonable data and can be adjusted according to needs when necessary to adjust the overall size of the ion source. The data in this embodiment is only data of a certain specification.

[0053] The following is a detailed description of the selection of component structure and the actual use of a specification combined with the simulation of the ion beam. The present invention uses a concave repeller 8, compared with Figure 10 and Figure 11 In both cases, it can be found that since the equipotential lines near the repeller will fit the repeller surface, the shape of the repeller determines the shape of the equipotential lines on its surface. Figure 10 The convex repulsion electrode has protruding surface equipotential lines, which are opposite to the equipotential line cluster formed by the extraction electrode 201. On the one hand, the equipotential lines in the middle part are squeezed, and the equipotential lines are relatively dense, which will cause the energy of the ions to be dispersed more; on the other hand, the convex equipotential lines cause the ions generated near them to diverge first, resulting in a poor extraction effect. Figure 11 The effect of the concave repeller is the opposite. Therefore, the concave repeller is a better choice. The designed repeller structure is as follows Figure 2 Figure 3 As shown in the installation location Figure 1 shown.

[0054] The cathode structure designed by the present invention and the position of the cathode in the ionization box 1 are as follows: Figure 1-Figure 3 As shown, Figure 6 Figure 7 The cathode assembly 6 is shown. The potential applied to cathode assembly 6 is different from that of ionization cell 1, so the filament holder needs to be insulated from the ionization cell 1 by a ceramic component. The protruding portion of cathode ceramic component 601 is positioned so that it fits into the cathode hole in ionization cell 1 and is then secured to the ionization cell 1 using M2 cross-recessed cylindrical head screws.

[0055] The filament holder is fixed to the cathode ceramic piece 601 by tapping the end of the filament holder and then tightening it with an M1.6 hexagonal nut. To ensure the direction of the filament holder, the cathode ceramic piece 601 is provided with a straight notch to match the steel sheet on the filament holder.

[0056] At the same time, in order to allow the electrons emitted by the cathode to move downward in a collimated manner and enter the ionization box 1, a cathode cover is required to control the potential around the filament. Figure 12 and Figure 13 These are the motion trajectories of the ion beam emitted from the cathode with and without a cathode cover. Without a cathode cover, the equipotential lines around the filament are irregularly tilted, and the electrons cannot move straight downward. After adding a cathode cover, the equipotential lines around the filament are horizontal, which has a focusing effect on the electrons.

[0057] The cathode cover 604 is at the same potential as one of the filament racks. In the existing cathode assembly 6, the cathode cover is spot-welded to one of the filament racks to achieve electrical conductivity. In the case of a small filament rack, this method is difficult to process, and the cathode cover is not stable enough and is prone to deviation. The cathode cover of the present invention is fixed in direction by inserting the fixed end with a through hole into the notch of the ceramic part, and is locked to the ceramic part by a conductive cathode cover short-circuit 605. The structure of the cathode cover short-circuit 605 is as follows: Figure 7 As shown, the cylindrical part passes through the ceramic piece, and one end connected to the cathode cover is threaded and fixed to the ceramic piece through an M1.6 hexagonal nut. The other end is sleeved on one of the filament racks and fixed through a nut, which not only achieves short circuit but also makes the cathode cover more firmly fixed.

[0058] Electron receiving electrode components such as Figure 8 As shown, the ceramic component has the same specifications as the cathode ceramic component 601. The electron receiving box 701 is spot-welded to the receiving frame 702. The receiving frame 702 is fixed to the receiving ceramic component 703 in a manner similar to the filament frame of the cathode assembly 6. The electron receiving electrode assembly is located below the ionization box 1 and is installed symmetrically with the cathode assembly 6.

[0059] From the perspective of the ion extraction path, it is first necessary to install an extraction lens at a position close to the ionization chamber. Its effect is similar to that of the repeller, which plays the role of extracting ions from the ionization chamber. Here it is called the "extraction electrode 201". When there is only a repeller without the extraction electrode 201, the equipotential lines and ion trajectories in the ionization chamber are as follows Figure 4 As shown, it can be seen that if only the high potential of the repeller "pushes" the ions out, although the ions can move outward, there is no focusing effect. A large part of the ions will hit the inner wall of the ionization chamber, reducing the sensitivity.

[0060] As shown in FIG15 , a pull-out electrode 201 having a lower potential than that of the ionization box 1 is provided near the outlet of the ionization box 1 , which will form a relatively strong electric field between the ionization box 1 and the pull-out electrode 201 , so that the equipotential lines are recessed into the ionization chamber, forming a focusing electric field, which allows the ions to be focused near the outlet slit 205 and capture the ions generated in the ionization chamber.

[0061] Figure 15 It can also be seen in the figure that although the ions are focused and pulled out, the direction of their velocity after being pulled out is at a certain angle to the axial direction, and the ions will diverge. Therefore, corresponding focusing poles are required in both the horizontal and vertical directions to limit the divergence of the ion beam.

[0062] In the z direction, according to the focusing principle of the electrostatic lens, an electric field with a weak left side and a strong right side needs to be formed on both sides of an electrode sheet to achieve a converging effect. Figure 15 Since the field strength between the pull-out electrode 201 and the ionization box 1 is large, and the right side is farther from the ground, the field strength is weak, so the equipotential lines are "concave" and the ions diverge. If you want to achieve a focusing effect at the pull-out electrode 201, you need to set a low potential at a position closer to its right side, such as Figure 16 As shown, the distance between the ionization box 1 and the extraction electrode 201 is 1 mm, the voltage difference is 300 V, the distance between the extraction electrode 201 and the ground electrode 203 is 3 mm, and the voltage difference is 2700 V. The focusing effect is not good, and the distance between the ground electrode and the extraction electrode 201 needs to be further reduced. Figure 17 The distance between the middle ionization cell 1 and the extraction electrode 201 is 1 mm, and the voltage difference is 300 V. The distance between the extraction electrode 201 and the ground electrode 203 is 1 mm, and the voltage difference is 2700 V. As can be seen, because the ionization cell 1 and the extraction electrode 201 are relatively close (necessary for the extraction effect), achieving a focusing effect at the extraction electrode 201 requires the ground electrode 203 to be very close. This results in an excessively high field strength (1 kV / mm) between the two plates, potentially leading to air breakdown discharge.

[0063] Since the theory of gas discharge is still imperfect, the breakdown voltage of the air gap cannot be accurately calculated. In practice, it is mostly determined through experiments or estimated approximately using empirical formulas. There is a risk of discharge at about 1kV / mm, and the field strength in the above case has reached this threshold. Therefore, it is difficult to achieve focusing at the pull-out electrode 201, and a "focusing electrode" is added behind it to play a focusing role. The potential of the focusing electrode is set between the pull-out electrode 201 and the grounding electrode 203, which is required to focus the ion beam in the z direction near the exit slit 205. According to the Davisson-Calbick membrane aperture lens focal length formula, the slit lens form is:

[0064]

[0065] in, is the focal length of the focusing lens, is the focusing electrode voltage, and are the electric field strengths on the left and right sides of the focusing electrode, and their relationship with the distance between the focusing electrode and the pole pieces on both sides is:

[0066]

[0067]

[0068] According to the lens imaging formula

[0069]

[0070] in is the object distance, which is approximately the distance between the focusing pole and the pulling pole ; is the image distance, is the distance between the focusing pole and the exit slit 205. and The relative size of , here we first calculate the case where the image distance is infinite, that is ,at this time

[0071]

[0072]

[0073] Simplified

[0074]

[0075] Right now

[0076]

[0077] Since the focusing electrode voltage exist between, ,therefore , that is, to make the focusing electrode achieve the focusing effect, the distance between the focusing electrode and the left pull-out electrode 201 is It should be the distance between the focusing electrode and the right grounding electrode 203 It should be noted that since the classical formula for electrostatic lens imaging needs to meet the paraxial condition, and the actual electrode sheet is affected by factors such as the large opening slit, the asymmetric shape due to the limitation of processing precision, the different electrode thicknesses, and the complex internal structure of the ion source, its focusing situation is somewhat different from the theoretical derivation of the classical formula. Therefore, the theoretical derivation is used as a means of qualitative analysis, and its numerical value is used as a reference. The actual focusing effect is analyzed and adjusted using the electron ion simulation software SIMION.

[0078] Based on the above analysis and simulation adjustment, we set a "z focusing electrode 202" behind the pull-out electrode 201 to achieve the focus of the ion beam in the z direction. At the same time, a grounding electrode 203 is set behind the z focusing electrode 202. The distance ratio between the z focusing electrode 202 and the left and right pole pieces is 7:3. Since the conditions for z-direction deflection adjustment are already available, it adopts the form of a whole piece. Among them, the ionization box is 3000V, the pull-out electrode is 2700V, and the z focusing electrode is 2400V. Figure 18 As shown, compared with only the pull-out electrode 201, after adding the z focusing electrode 202, although the ion beam diverges near the pull-out electrode 201, it is focused at the z focusing electrode 202, and the focusing ability is strong enough. Overall, the focusing effect in the z direction is significantly improved, and focusing is achieved near the exit slit 205, which greatly improves the extraction efficiency.

[0079] Next, let's observe the focusing in the y direction. At present, the ion beam in the y direction after the ionization box 1 is equipped with the pull-out electrode 201, the z-focusing electrode 202 and the grounding electrode 203 is as follows: Figure 19 As shown in the figure, after the ion beam is extracted from the ion chamber, the area near the pullout electrode 201 has no effect on the y-direction ion beam. While the area near the z-focusing electrode 202 also has a certain focusing effect in the y-direction, it diverges after passing through the grounding electrode 203. This is because the pullout electrode 201 has no slit in the y-direction. The y-direction width of the z-focusing electrode 202 is adjusted to an appropriate width (6 mm) to achieve a certain degree of y-direction focusing of the ion beam, but the focusing effect is relatively weak. The field strength to the left of the grounding electrode 203 is much greater than that to the right, causing the ion beam to diverge after passing through the concave equipotential line region of the pullout electrode 201.

[0080] As can be seen, while the z-direction focusing effect can be achieved by adjusting the y-direction slit length of the z-focusing electrode 202, it is still insufficient to achieve a good focusing effect. Therefore, a new electrode is needed for further focusing in the y-direction. Observing the existing electrode, we can see that we need to add an electrode between the two 0V potentials of the ground electrode 203 and the exit slit 205. This is perfectly suited for using an "Einzel lens" (also known as a single lens) to achieve focusing.

[0081] A single lens consists of three electrodes: two outer electrodes at equal potential and a middle electrode at a different potential. The resulting saddle-shaped equipotential lines can be divided into three regions. For positive ions, if the middle potential is high, the center is a converging region, while the two sides are diverging regions. Since the middle potential is high, the ions have a low axial velocity, so they spend more time in the converging region and less time in the diverging region, resulting in an overall converging effect.

[0082] Based on the principle of a single lens, we need to adjust the y-direction slit width of the previous ground electrode 203 to be close to the y-direction length of the ion beam to achieve a focusing effect; the high-potential middle lens is called the y-focusing lens; in order to reduce the number of pole pieces, the exit slit 205 of the right ground electrode 203 is directly used as the right ground electrode 203 of the single lens. The plot and simulation results after implementation are shown as follows: Figure 20 As shown:

[0083] The ionization box is powered at 3000V, the extraction electrode at 2700V, the z-focusing electrode at 2400V, and the y-focusing electrode at 3000V. The grounding electrode is grounded to the exit slit 205. As can be seen, the addition of a pair of y-focusing electrode halves 204 forms a single lens that further focuses the ion beam in the y direction, meeting the desired design objectives. The y-focusing electrode 204 is configured as an upper and lower halves to achieve y-direction deflection adjustment. The z-direction slit has no width, thus preventing it from affecting z-direction focusing.

[0084] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0085] In the present invention, unless otherwise expressly specified or limited, the terms "mounted," "connected," "connect," "fixed," etc. should be understood broadly. For example, they may refer to fixed connection, detachable connection, or integration; mechanical connection or electrical connection; direct connection or indirect connection through an intermediate medium; internal communication between two components or interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0086] The above are merely preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be construed as limiting the present invention, and the scope of protection of the present invention should be determined by the scope defined in the claims. Persons skilled in the art will appreciate that improvements and modifications may be made without departing from the spirit and scope of the present invention, and such improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A noble gas isotope mass spectrometer ion source, characterized in that: The invention comprises a cathode assembly and an electron receiving stage assembly, an ionization box, a repeller, an extraction focusing lens group, and an ion source fixing seat. The cathode assembly and the electron receiving stage assembly are respectively fixed at the upper and lower ends of the ionization box, the repeller is fixed at the rear end of the ionization box, the extraction focusing lens group is at the front end of the ionization box, the extraction focusing lens group is connected to the ionization box through a connecting porcelain column to achieve fixation and insulation, the extraction focusing lens group is composed of a pulling-out electrode, a z focusing electrode, a grounding electrode, a y focusing electrode and an exit slit arranged in sequence, the extraction focusing lens group realizes the extraction and focusing of sample ions in the ionization box, the other end of the connecting porcelain column is connected to the ion source fixing seat, and the center of the ion source fixing seat has an exit slit.

2. The noble gas isotope mass spectrometer ion source according to claim 1, characterized in that: The cathode assembly consists of a cathode ceramic part, a filament rack, a cathode cover and a cathode cover short-circuit piece. The left filament rack and the right filament rack of the filament rack are both fixed by nuts after passing through the cathode ceramic part. The filament is installed on the filament rack. The cathode cover is embedded in the notch of the cathode ceramic part through the fixed end with a through hole. The cathode cover is fixed to the cathode ceramic part through the cathode cover short-circuit piece and short-circuited with the right filament rack.

3. The noble gas isotope mass spectrometer ion source according to claim 1, characterized in that: The electron receiving stage assembly includes a receiving stage ceramic piece, an electron receiving box and a receiving frame. The receiving frame is threaded at the coarse end and is fixed on the ionization box through a nut after passing through the receiving stage ceramic piece.

4. The noble gas isotope mass spectrometer ion source according to claim 1, characterized in that: The ionization box is shaped like a square box body, with a square hollow space in the middle as the area where gas ionization occurs, circular through holes for fixing and connecting porcelain columns are arranged around the square opening, and rectangular through holes for fixing ceramic parts are respectively arranged on the upper and lower parts of the rear end surface. A hollow grid is arranged on the side of the ionization box as a gas exchange hole in the square hollow space, and a waist-shaped through groove is provided on the side for a channel connecting the cathode assembly and the electron receiving stage assembly.

5. The noble gas isotope mass spectrometer ion source according to claim 1, characterized in that: The repeller is a concave repeller, which is installed at the rear end of the ionization box. The gap between the circle and the square is used for gas exchange between the inside and outside of the ionization box.

6. The noble gas isotope mass spectrometer ion source according to claim 1, characterized in that: The pull-out electrode consists of two electrode halves arranged one above the other and two corresponding electrode pins. The function of the pull-out electrode is to pull out the ions generated by ionization in the ionization box. The two electrode halves add relatively adjustable voltages to control the deflection of the ion beam in the z direction. The four circular through holes around it are used to insert the connecting porcelain columns.

7. The noble gas isotope mass spectrometer ion source according to claim 1, characterized in that: The z focusing electrode consists of an electrode sheet and an electrode pin, with an opening in the middle and a straight slot to achieve the focusing effect of the ion beam in the z direction and the y direction. The ratio of the distance between the z focusing electrode and the left pull-out electrode and the distance between the z focusing electrode and the right grounding electrode is 7:

3.

8. The noble gas isotope mass spectrometer ion source according to claim 1, characterized in that: The grounding electrode consists of an electrode sheet and an electrode pin with an opening in the middle. The grounding electrode is short-circuited with the ion source fixing seat through a lead and then grounded. Its function is to form a potential difference with the front z focusing electrode so that the z focusing electrode can play a focusing role. At the same time, it forms a single lens with the rear y focusing electrode to realize the y-direction focusing of the ion beam.

9. The noble gas isotope mass spectrometer ion source according to claim 1, characterized in that: The y-focusing electrode consists of two electrode halves and two electrode pins. The function of the y-focusing electrode is to form a single lens equidistant from the grounded electrode on the front side and the grounded ion source holder on the rear side to achieve y-direction focusing of the ion beam. The two electrode halves add relatively adjustable voltages to control the deflection of the ion beam in the y direction.

10. The noble gas isotope mass spectrometer ion source according to claim 1, characterized in that: The outlet slit is formed by welding an outlet slit sheet to the ion source fixing seat, realizing the ion beam focusing in the y direction. The slit width controls the width of the outgoing ion beam in the z direction. The ion source fixing seat fixes the ion source on the external cavity.

Images