Electron extraction method and system for low-energy electron source

Abstract

The invention relates to an electron extraction method and system for a low-energy electron source. The method comprises the following steps: providing at least one cathode, at least one heating power supply and at least one control electrode; in a first time period, the heating power supply provides heating current for the cathode, so that the temperature of the cathode is increased to be higher than an electron emission threshold value, meanwhile, the potential difference between the control electrode and the cathode is controlled to be a suppression value, and electrons generated by the cathode are prevented from reaching a preset target spot; and in the second time period, the current is stopped from being supplied to the cathode, and meanwhile, the potential difference between the control electrode and the cathode is controlled to reach a guide value, so that electrons emitted by the cathode through waste heat reach the preset target spot and interact with target particles. Cathode heating is controlled in an intermittent energization mode, and accurate extraction of the low-energy scattered electron beam is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of low-energy electron source design, and in particular to an electron extraction method and system for a low-energy electron source. Background Art

[0002] In molecular diagnostic techniques such as mass spectrometry, low-energy electrons often interact with ions to fragment them for analytical purposes. Electron capture dissociation (ECD) and electron induced dissociation (EID) are important ion dissociation techniques. These techniques require the introduction of an electron beam with precisely controlled electron energy into an ion trap to interact with the target ions. Currently, electron beam generation primarily relies on cathode electron emission sources, with a directly heated cathode being a common configuration.

[0003] A directly heated cathode is a simple electron emission source, typically composed of a heated metal wire, such as tungsten or iridium. Patent document CN117594415A, for example, discloses an ion dissociation device in which electrons generated by an electron emission source are accelerated and focused by an electrode assembly before being introduced into an ion confinement chamber. By setting the potential of the electron emission source close to the potential of the central axis of the ion trap, the electrons are decelerated to an energy range suitable for electron capture and dissociation before reaching the central axis of the ion confinement chamber.

[0004] However, direct-heated cathodes have significant drawbacks: the heating current causes a voltage drop across the cathode filament, resulting in inconsistent potential on the emission surface and a wide distribution of emitted electron energies. This broad energy distribution produces significant chromatic aberration in the electron beam, making the focusing electrode (electron lens) inconsistent in its ability to focus electrons of varying energies, making it difficult to optimize the electron lens parameters. More critically, this energy-dispersed electron beam makes it difficult to control the electron energy within a narrow range during collisions with ions, making efficient low-energy electron capture and dissociation impossible.

[0005] To solve the above problems, patent document US20090547358A discloses an electron capture and dissociation device that uses an indirect heated cathode. The specific technical solution is to coat the outside of the filament with a high-temperature insulating layer, then wrap it with a layer of metal, and plate it with an emitting material that emits electrons. The outer metal layer is electrically insulated from the heated filament, and the emitting material can be connected to a fixed potential without being affected by the voltage drop on the heated filament. However, the indirect heated cathode structure and manufacturing process are complex, and the production cost is high. What is even more troublesome is that most indirect heated cathodes cannot be exposed to the atmosphere once activated and used, otherwise they will cause poisoning and failure, which greatly limits their practical application and convenience of maintenance. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the present invention aims to solve the technical problem that the electron energy distribution of the directly heated cathode is wide and it is difficult to accurately control the electron energy.

[0007] To solve the above technical problems, the first aspect of the present invention provides a method for extracting electrons from an ion trap using intermittently heated cathodes, comprising the following steps: S1, providing at least one cathode, at least one heating power supply and at least one control electrode; S2. During a first time period, the heating power supply provides a heating current to the cathode to raise the cathode temperature above an electron emission threshold, and simultaneously controls the potential difference between the control electrode and the cathode to a suppression value to prevent electrons generated by the cathode from reaching a preset target point; S3. In the second time period, stop supplying current to the cathode, and at the same time control the potential difference between the control electrode and the cathode to a guide value, so that the electrons emitted by the cathode using the residual heat reach the preset target point and interact with the target particles.

[0008] The present invention adopts intermittent power-on mode to control cathode heating. During the power-on period, the potential difference between the control electrode and the cathode is used to suppress electron emission, avoiding the electron energy dispersion caused by the cathode voltage drop during the heating stage; during the power-off period, the cathode residual heat is used to emit low-energy scattered electrons, and the potential difference between the control electrode and the cathode is synchronously adjusted to ensure that the kinetic energy of the electrons is consistent when they reach the target.

[0009] As a preferred or optional solution, the method further comprises the following step: S4, alternately performing steps S2 and S3. Periodically alternating heating and power-off emission can continuously inject low-energy scattered electrons into the preset target.

[0010] As a preferred or optional solution, the preset target is an ion confinement space, and the target particles are multivalent positive ions.

[0011] As a preferred or optional solution, the second aspect of the present invention provides an intermittently heated cathode electron extraction system, comprising: an ion control device having an electron introduction channel and an ion confinement space; at least one cathode for emitting electrons; at least one heating power supply electrically connected to the cathode for providing a heating current; At least one current on-off module, used to control the alternating on-off of the heating current; at least one control electrode disposed between the ion confinement space and the cathode, capable of guiding or preventing electrons from entering the ion confinement space; At least one voltage selection module is electrically connected to the control electrode and is used to adjust the voltage of the control electrode.

[0012] The above system integrates an ion trap, a cathode, a heating power supply, a current on-off module, a control electrode and a voltage selection module. It can dynamically adjust the potential of the control electrode and cooperate with the current on-off module to complete a segmented control method of heating suppression and power-off guidance, providing a hardware foundation for the extraction of low-energy scattered electrons.

[0013] As a preferred or optional solution, the system also includes a timing control module, which is signal-connected to the current on-off module and the voltage regulation module, for synchronously controlling the current on-off module and the voltage selection module. The timing control module synchronously controls the heating current on-off and the control electrode voltage selection, ensuring that the control electrode potential switches at the moment of power failure, thereby avoiding timing misalignment between electron emission and transmission.

[0014] As a preferred or optional solution, the voltage selection module is an electronic switch or a high-speed digital-to-analog converter, thereby achieving high-frequency switching of the control electrode voltage.

[0015] As a preferred or optional solution, the current switching module is composed of a MOS switch tube. The MOS switch tube has a low DS on-resistance, can achieve high-frequency on-off switching, and reduce power loss.

[0016] As a preferred or optional solution, the current switching module is connected in series or in parallel with the cathode.

[0017] As a preferred or optional solution, the system further comprises at least one focusing electrode, which is arranged between the ion confinement space and the cathode and is used to focus the electron beam. A good flat electron beam can be formed by the focusing electrode.

[0018] As a preferred or optional solution, the ion control device is an ion trap, which includes a pair of x electrodes and a pair of y electrodes, at least one of the y electrodes is provided with an introduction slot, and the introduction slot constitutes the electron introduction channel.

[0019] As a preferred or optional solution, the y-electrode with the introduction slot constitutes the control electrode. This solution directly uses the y-electrode with the introduction slot of the ion trap as the control electrode. The RF voltage applied to the y-electrode serves as the suppression voltage during the negative half-cycle and forms the pilot voltage during the positive half-cycle, eliminating the need for a separate control electrode.

[0020] As a preferred or optional embodiment, the cathode includes a heating filament having a circular or rectangular cross-section and a straight, spiral, or zigzag shape. The shape and structure of the heating filament can be selected as needed. Changing the structure can increase heat capacity, extend the time it maintains temperature after power failure, and slow down the decay of the emission current density.

[0021] As a preferred or optional solution, the material of the heating filament is selected from tungsten, iridium, rhenium or their alloys.

[0022] As a preferred or optional solution, the cathode includes an emissive layer, which is an yttrium oxide coating applied to the surface of the heating filament, or one or more tantalum sheets disposed on the heating filament. Providing an emissive layer can increase the cathode's heat capacity, reduce electron work function, and improve emission efficiency.

[0023] In summary, compared with the prior art, the present invention has the following beneficial effects: (1) The present invention uses intermittent heating and potential difference to coordinate control. During the power-on stage, the control electrode is used to suppress electron emission to avoid cathode voltage drop interference. During the power-off stage, electrons are emitted with the help of cathode residual heat, thereby obtaining high-quality low-energy scattered electrons. This fundamentally solves the problem of wide electron energy distribution in directly heated cathodes and achieves precise extraction of low-energy scattered electron beams.

[0024] (2) The method of the present invention can continuously inject low-energy scattered electrons into the ion confinement space through periodic alternating heating and electron emission, meeting the continuous reaction requirements of electrons and multivalent positive ions; the potential selection of the control electrode at different stages can respectively achieve electron emission suppression and directional extraction, providing a stable electron source for fine dissociation operations.

[0025] (3) The system of the present invention realizes current on-off and potential adjustment simultaneously through a timing control module, a low-loss electronic switch, a focusing electrode and an optimized heating filament structure, thereby reducing heating loss and improving the electron beam focusing accuracy. At the same time, by optimizing heat capacity and reducing work function, the residual heat emission time is extended and the emission efficiency is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the structure of the electron extraction system in an embodiment of the present invention.

[0027] Figure 2 Schematic diagram of various cathode structures in embodiments of the present invention.

[0028] Figure 3 It is a timing control diagram of the electron extraction method in an embodiment of the present invention.

[0029] Figure 4 1 is a temperature change diagram of the cathode power-on and power-off processes in an embodiment of the present invention.

[0030] Figure 5 This is a graph showing the emission current density decay rate test results after the cathode is powered off in an embodiment of the present invention.

[0031] Figure 6 Graph showing the effect of tantalum sheet thickness on emission current density attenuation in an embodiment of the present invention.

[0032] Figure 7It is a structural diagram of an electron extraction system in another embodiment of the present invention.

[0033] Description of reference numerals: 1.1, 1.2 - cathode, 11 - heating filament, 12 - tantalum sheet, 2 - heating power supply, 3.3.1, 3.2 - current on / off module, 4.4.1, 4.2 - control electrode, 5 - voltage selection module, 6.6.1, 6.2 - first focusing electrode, 7.7.1, 7.2 - second focusing electrode, 8 - ion trap, 81, 82 - y electrode, 83 - x electrode, 84, 85 - end cap, 86 - introduction slot, 9 - target particle. DETAILED DESCRIPTION

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0035] It should be noted that similar numbers and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings.

[0036] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "install," "install," "connect," etc. should be understood in a broad sense. For example, "connect" can refer to a fixed connection, a detachable connection, or an integral connection; it can refer to a mechanical connection or an electrical connection. Those skilled in the art will be able to understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0037] The specific embodiment of the present invention provides an electron extraction method for a low-energy electron source and a system for implementing the method. Figure 1 As shown, the electron extraction system includes an ion control device, a cathode 1, a heating power supply 2, a current switching module 3, a control electrode 4, a voltage selection module 5, a focusing electrode and other components.

[0038] In this embodiment, the ion control device is an ion trap 8, which includes a pair of y electrodes 81, 82, a pair of x electrodes 83 (only one is shown in the figure), and a pair of end caps 84, 85. The y electrodes 81, 82 have electron introduction slots 86 for the electron beam to pass through. The potential of the y electrodes 81, 82 is V y , the potential of the x electrode 83 is V xAn ion confinement and trapping space is formed between the y-electrodes 81 and 82 and the x-electrode 83. Target particles 9 enter this space through the small holes in the end caps 84 and 85, where they are trapped, cooled, and gathered near the central axis of the space. Target particles 9 are generally multivalent positive ions. In other embodiments, other ion control devices with electron introduction channels and ion confinement spaces, such as quadrupoles, may be used.

[0039] In the electron extraction system, the cathode 1 is used to emit electrons, and a simple direct-heated cathode is preferred. The main component of the cathode 1 is the heating filament 11, and the material of the heating filament 11 can be tungsten, iridium, rhenium, etc. or their alloys. In a specific embodiment, Figure 2 As shown, the heating filament 11 has a variety of optional structures. Figure 2 As shown in Figure a, in some embodiments, the heating filament 11 is straight and has a rectangular cross section. Figure 2 As shown in FIG. b, in some embodiments, the cross section of the heating filament 11 is circular. Figure 2 As shown in Figure c, in some embodiments, the heating filament 11 is a spiral filament wound into a spiral shape. Figure 2 As shown in FIG. d , in some embodiments, the heating filament 11 is sawtooth-shaped and has a low inductance.

[0040] In some embodiments, a material with a lower work function is provided on the heating filament 11 to form an emission layer, so as to reduce the work function and the required heating power. Figure 2 As shown in Figure e, in some embodiments, the material of the heating filament 11 is tungsten, and a long tantalum sheet 12 is spot-welded on the tungsten filament. Tantalum has a lower work function than tungsten and becomes the main emitter, while the adjacent tungsten filament serves as a heat source. Figure 2 As shown in FIG. 5 , in some embodiments, a plurality of rectangular tantalum sheets 12 are spaced apart on the heating filament 11 to increase the area of ​​the emitter and the coverage of the electrons in the axial direction. Figure 2 As shown in FIG. 5( g ), in some embodiments, the side surface of the tantalum sheet 12 is a curved surface. In other embodiments, the emission layer is an yttrium oxide coating (not shown) coated on the surface of the heating filament 11 .

[0041] Combine Figure 1 As shown, the cathode 1 is electrically connected to the heating power supply 2, which is used to provide a heating current to the cathode 1. The external power supply V0 provides the potential of the heating power supply 2 and the cathode 1. The current on-off module 3 is used to control the on-off of the heating current. In this embodiment, the current on-off module 3 is composed of a MOS switch tube, which is controlled by the control voltage V on the gate. c Control to achieve fast turn-on and turn-off.

[0042] In this embodiment, the current on-off module 3 is connected in series with the cathode 1. When the current on-off module 3 is in the on state, a heating current is generated on the cathode 1; when the current on-off module 3 is disconnected, the current on the cathode 1 stops. In other embodiments, the current on-off module 3 is connected in parallel with the cathode 1. When the current on-off module 3 is in the off state, a heating current is generated on the cathode 1; when the current on-off module 3 is in the on state, the current on the cathode 1 tends to stop.

[0043] In this embodiment, a group of control electrodes 4 are separately provided, combined with Figure 1 As shown, the control electrode 4 is arranged near the cathode 1 and is used to guide electrons. The voltage selection module 5 is electrically connected to the control electrode 4 and is used to adjust the voltage of the control electrode 4. In this embodiment, the control electrode 4 can switch between two high and low potentials, V2 and V1. Among them, V1-V0 is equal to the suppression value, and the suppression value is generally less than or equal to -10V. Under this potential difference condition, the electrons are suppressed and cannot be emitted from the cathode 1, and the emitted electron flow is cut off; V2-V0 is equal to the guidance value, and the guidance value is generally greater than 0V. Under this potential difference condition, electrons can be emitted from the cathode 1 and pass through the control electrode 4 into the downstream focusing electrode. In other embodiments, the focusing electrode can also be selected as the control electrode 4, or the electrode in the ion trap 8 can be selected as the control electrode.

[0044] In this embodiment, the voltage selection module 5 is an electronic switch that can achieve high-frequency switching of potential. In other embodiments, the voltage selection module 5 is a high-speed digital-to-analog converter that can achieve continuous adjustment of the voltage of the control electrode 4.

[0045] Combine Figure 1 As shown, the system has two focusing electrodes: a first focusing electrode 6 and a second focusing electrode 7, disposed between the ion trap 8 and the control electrode 4. The potential of the first focusing electrode 6 is V3, and the potential of the second focusing electrode 7 is V4. The control electrode 4, the first focusing electrode 6, the second focusing electrode 7, and one of the y-electrodes 81 form an electron optical system that focuses electrons into a flat electron beam. Once the electron beam enters the ion confinement space through the introduction slot 86, it interacts with the target particles 9 stored there, achieving electron capture and dissociation.

[0046] The prior art uses continuous cathode heating to emit electrons. Combined with the aforementioned system structure, the current switching module 3 is continuously on, and the heating power supply 2 ensures a continuous heating current flows through the cathode 1. Because the heating filament 11 of cathode 1 is of a certain length and exhibits significant resistance, the heating current creates a voltage drop across the heating filament 11. The potentials at different points on the heating filament 11 vary: the lower end has a potential of V0, while the upper end has a potential of V0 plus the voltage of the heating power supply 2. The potential difference between the two ends can reach 5 to 10 volts. Upon reaching the central axis saddle point of the ion trap 8, the emitted electrons' kinetic energy also varies by 5 to 10 eV. Furthermore, the electron optical system, comprised of the control electrode 4, first focusing electrode 6, second focusing electrode 7, and y-electrode 81, exhibits varying focusing characteristics for electrons of varying energies. Consequently, some electrons fail to achieve adequate focus and, therefore, fail to reach the intended target (i.e., the multiply charged ions concentrated near the central axis saddle point).

[0047] In order to solve the above problems, this embodiment adopts an intermittent heating cathode electron extraction method, the specific process is as follows: Figure 3 As shown, during the first time period t1, the current on-off module 3 is turned on, and the heating power supply 2 provides current to the cathode 1, causing its temperature to rise above the electron emission threshold. Simultaneously, during this time period, the voltage selection module 5 switches the potential of the control electrode 4 to V1, causing the potential difference between the control electrode 4 and the cathode 1 to reach a suppression value, suppressing electron emission. During the second time period t2, the current on-off module 3 is turned off, ceasing current flow to the cathode 1. The temperature is maintained by utilizing the heat capacity of the heating filament 11, and electron emission continues. Simultaneously, during this time period, the voltage selection module 5 switches the potential of the control electrode 4 to V2, causing the potential difference between the control electrode 4 and the cathode 1 to reach a guide value, allowing electrons to pass through the control electrode 4 and the focusing electrode and enter the ion confinement space of the ion trap 8. Because the voltage drop across the heating filament 11 is significantly reduced during time period t2, electrons emitted from different positions of the heating filament 11 have the same or similar kinetic energy, forming a well-defined flat electron beam. The electrons can effectively reach the predetermined target and interact with the target particle 9, with minimal kinetic energy dispersion. Periodically alternating heating and power-off emission allows for continuous injection of low-energy scattered electrons into the predetermined target.

[0048] In some preferred embodiments, the system further includes a timing control module, which is signal-connected to the current on-off module 3 and the voltage selection module 5 for synchronously controlling the current on-off module 3 and the voltage selection module 5. The timing control module is typically a high-precision timing circuit, which ensures synchronous switching of the potential of the control electrode 4 at the moment of power on / off.

[0049] COMSOL Multiphysics 6.2 multi-physics simulation software was used to simulate and confirm the emission current density decay law of the cathode within a certain period of time after the heating current was cut off. Figure 2Taking the structure shown in Figure e as an example, the heating filament is a tungsten wire with a diameter of 0.25 mm and a length of 16 mm, and the specifications of the long tantalum sheet are 0.1 mm × 0.8 mm × 4 mm (thickness × width × length). A 1V voltage is applied to the cathode to heat for 1 second and then the power is turned off for 1 second. The simulation software obtains the following Figure 4 The temperature variation curve is shown in the figure. The simulation results show that the maximum temperature of the heating filament is 2723K after heating for 1s, and the temperature drops to 2330K after 50ms of power off, a temperature drop of 393K. This temperature still meets the conditions for electron emission, indicating that the cathode can still emit electrons during the 50ms power off period, enabling dissociation reactions such as ECD and electron-ion interactions.

[0050] The cathode emission current density is determined by the Richardson-Dushman emission equation, which shows that thermal electron emission is closely related to the temperature of the emitter and the electron work function. From this, the effect of temperature change on the cathode emission capacity can be obtained. The emission current density at the beginning of power failure is set to , the emission current density at the nth second after power off is , then the emission current density at the beginning of power failure decreases at the emission current density decay rate in the nth second %. Still taking the cathode of the above structure as the test object, the emission current density decay rate within 100ms after power failure was tested. The results are as follows: Figure 5 As shown in the figure, it can be seen that when the power is off for 20ms, the emission current density decreases by 50%, and when the power is off for 30ms, the emission current density decreases by 70%.

[0051] A cathode was designed as a test object. Its filament was a tungsten wire with a diameter of 0.25 mm and a length of 16 mm. The tantalum sheet had dimensions of 0.2 × 0.8 × 4 mm (thickness × width × length). By adjusting the voltage, it reached 2723 K even after heating for 1 second. The emission current density decay rate after 100 ms after power failure was shown in the following figure. Figure 6 As shown in FIG, the emission current density decreases by 35% when the power is off for 20 ms, and decreases by 52% when the power is off for 30 ms.

[0052] Comparing the two sets of simulation data shows that appropriately thickening the cathode's tantalum sheet can effectively slow the temperature drop, maintaining a higher emission current density for a longer period of time. It's understandable that changes in the heating filament material, size, structure, and shape will affect the heat capacity and emission current density decay, so the appropriate heating filament and emission layer structure can be selected based on the application scenario.

[0053] The intermittently heated cathode electron extraction system of the above embodiment can be used in the ion trap electron capture and dissociation device disclosed in US Patent No. 7,755,034 B2. It injects electrons into the ion trap only during half a cycle of the radio frequency voltage. In this embodiment, the y electrode of the ion trap serves as a control electrode with adjustable potential. When the y electrode is in a positive phase and the x electrode is in a negative phase, electrons can pass through the introduction slot on the y electrode into the ion trap and slowly decelerate, interacting with the multivalent ions in the center of the ion trap. When the y electrode is in a negative phase and the x electrode is in a positive phase, the ions are repelled upon entering the y electrode introduction slot and cannot enter the ion trap. The potential is continuously switched between the positive half-cycle t2 of the y radio frequency and the negative half-cycle t1, resulting in electrons emitted by the cathode being blocked during t1 and utilized during t2. Because the ion trap radio frequency half-cycles t1 and t2 are generally in the microsecond or sub-microsecond range, even with a filament with a very small heat capacity, the temperature will not drop significantly during t1. The heating current is quickly restored during t2, thus ensuring that low-energy scattered electrons are continuously injected into the ion trap and interact with the target particles. .

[0054] Combine Figure 7 As shown, this embodiment provides another electron extraction system that can introduce electrons from two directions to interact with ions. The system includes an ion trap 8, a heating power supply 2, two cathode units, and two electron optical systems. One electron optical system consists of a set of control electrodes 4.1, a first focusing electrode 6.1, a second focusing electrode 7.1, and a y-electrode 81. The other electron optical system consists of another set of control electrodes 4.2, a first focusing electrode 6.2, a second focusing electrode 7.2, and an x-electrode 83.

[0055] A cathode 1.1 is connected in parallel with the current switching module 3.1 to form a first group of cathode units, which are controlled by the voltage V c1 Control; the other cathode 1.2 is connected in parallel with the current on-off module 3.2 to form a second group of cathode units, which are controlled by the voltage V c2 The two cathode units are connected in series and then connected to the heating power supply 2, and the midpoint of the two cathode units is connected to the potential V0 terminal.

[0056] During operation, during the t1 half-cycle, the y phase of the quadrupole field of ion trap 8 is positive and the x phase is negative. One current-disconnect module 3.1 is turned on, while the other current-disconnect module 3.2 is turned off, causing the voltage of heating power supply 2 to be substantially entirely applied to cathode 1.2. Because current-disconnect module 3.1 is short-circuited, there is essentially no voltage at both ends of cathode 1.1, resulting in a potential equal to or approximately equal to V0. Although cathode 1.2 is heated, the electrons emitted by it cannot pass through the narrow slit of x-electrode 83, which is at negative high voltage, and cannot enter ion trap 8 to react with target particles. Conversely, during the t2 half-cycle, the x phase of the quadrupole field is positive and the y phase is negative. Current-disconnect module 3.2 is turned on, while current-disconnect module 3.1 is turned off, causing the voltage of heating power supply 2 to be substantially entirely applied to cathode 1.1. Although cathode 1.2 is not heated at this time, the residual heat from the early stage causes it to continue emitting electrons, and the potential of its heating filament is approximately equal to V0 at all locations, ensuring low electron energy dissipation. The electrons are focused by the electron optical system, pass through the slits of x-electrode 83, and enter the vicinity of the center axis of ion trap 8, where they effectively dissociate with target particles 9. Because cathode 1.1 is heated during half-cycle t2, it uses the residual heat to emit low-energy scattered electrons during the next half-cycle t1. These electrons enter ion trap 8 and effectively dissociate with the target particles.

[0057] The above system is characterized by connecting a current on-off module in parallel with the cathode and then to the heating power supply circuit. When the current on-off module is disconnected, a heating current is generated on the corresponding cathode. When the current on-off module is turned on, the voltage on the cathode is zero and the heating current tends to stop, but the residual heat provides the temperature required for electron emission. When the two sets of cathode units are alternately turned on and off, electrons can continuously enter the ion trap and react with ions during the two high-frequency half-cycles. The electrons entering the ion trap are all emitted by the cathode, which has basically no current, so the electron energy dissipation is extremely small. In addition, due to the use of high-frequency, rapidly switching heating current, the thin heating filament structure will not reduce the emission efficiency due to the small heat capacity.

[0058] Although the present invention is disclosed as above, the protection scope of the present invention is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, and these changes and modifications will fall within the protection scope of the present invention.

Claims

1. A method for extracting electrons from a low-energy electron source, characterized in that: The following steps are involved: S1, providing at least one cathode, at least one heating power supply and at least one control electrode; S2. During a first time period, the heating power supply provides a heating current to the cathode to raise the cathode temperature above an electron emission threshold, and simultaneously controls the potential difference between the control electrode and the cathode to a suppression value to prevent electrons generated by the cathode from reaching a preset target point; S3. In the second time period, stop supplying current to the cathode, and at the same time control the potential difference between the control electrode and the cathode to a guide value, so that the electrons emitted by the cathode using the residual heat reach the preset target point and interact with the target particles.

2. The electron extraction method according to claim 1, characterized in that: The following steps are also included: S4. Execute steps S2 and S3 alternately.

3. The electron extraction method according to claim 1, characterized in that: The preset target point is an ion confinement space, and the target particles are multivalent positive ions.

4. A system for implementing the electron extraction method according to any one of claims 1 to 3, characterized in that: include: an ion control device having an electron introduction channel and an ion confinement space; at least one cathode for emitting electrons; at least one heating power supply electrically connected to the cathode for providing a heating current; At least one current on-off module, used for controlling the alternating on-off of the heating current; at least one control electrode disposed between the ion confinement space and the cathode, capable of guiding or preventing electrons from entering the ion confinement space; At least one voltage selection module is electrically connected to the control electrode and is used to adjust the voltage of the control electrode.

5. The system according to claim 4, characterized in that It also includes a timing control module, which is signal-connected to the current on-off module and the voltage selection module, and is used to synchronously control the current on-off module and the voltage selection module.

6. The system according to claim 5, characterized in that The voltage selection module is an electronic switch or a high-speed digital-to-analog converter.

7. The system according to claim 4, wherein: The current on-off module is composed of a MOS switch tube.

8. The system according to claim 4, wherein: The current on-off module is connected in series or in parallel with the cathode.

9. The system according to claim 4, wherein: The device further comprises at least one focusing electrode, which is arranged between the ion confinement space and the cathode and is used to focus the electron beam.

10. The system according to claim 4, wherein: The ion control device is an ion trap, which includes a pair of x electrodes and a pair of y electrodes. At least one of the y electrodes is provided with an introduction groove, and the introduction groove constitutes the electron introduction channel.

11. The system according to claim 10, wherein: The y electrode having the introduction groove constitutes the control electrode.

12. The system according to any one of claims 4 to 11, characterized in that: The cathode includes a heating filament, the cross section of the heating filament is circular or rectangular, and the shape of the heating filament is straight, spiral or zigzag.

13. The system according to claim 12, wherein: The material of the heating filament is selected from tungsten, iridium, rhenium or alloys thereof.

14. The system according to claim 12, wherein: The cathode includes an emission layer, which is an yttrium oxide coating coated on the surface of the heating filament, or the emission layer is one or more tantalum sheets arranged on the heating filament.

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