A Faraday tube with high electron collection efficiency

Abstract

This invention relates to a Faraday cup with high electron collection efficiency, comprising a collection cavity, a permanent magnet, and a particle injection channel. An inclined surface is provided inside the collection cavity near the side wall, creating a conical space with a gradually increasing volume from the inlet to the bottom of the cavity, which alters the collision direction of particles within the cavity. The permanent magnet is located outside the collection cavity and generates a magnetic field to change the trajectory of incident and secondary electrons within the cavity. The particle injection channel is located at the inlet of the collection cavity. The first end of the particle injection channel connects to the inlet of the collection cavity, and the second end has a suppression electrode located at the front end of the second end of the particle injection channel. The advantages of this invention are that it allows electrons to collide with the inclined side wall, reducing reflected electrons emitted towards the cup opening, and the permanent magnet alters the electron path, reducing escape and improving electron collection efficiency.

Description

Technical Field

[0001] This invention relates to the technical field of electron measurement based on particle accelerators, and in particular to a Faraday tube with high electron collection efficiency. Background Technology

[0002] A Faraday cup is a fundamental device for measuring the current intensity of a charged particle beam. Its principle is to intercept the charged particle beam and collect its charge, then measure the current intensity to determine the current intensity. The main factor affecting the collection efficiency of a Faraday cup is the error in particle collection caused by the escape of secondary electrons generated after the particle beam enters the cup. These secondary electrons are generally divided into low-energy true secondary electrons and high-energy reflected electrons.

[0003] The main problem with existing Faraday cups is that incident particles collide with the bottom of the Faraday cup, causing most of the reflected particles in the sputtered secondary electrons to move in a direction parallel to the incident direction. This prevents the reflected particles from being completely collected by the Faraday cup, resulting in measurement errors.

[0004] Existing methods for suppressing secondary electrons in Faraday cups mainly include: increasing the length of the Faraday cup to reduce the probability of secondary electrons escaping from the cup opening; adding a suppression voltage to decelerate secondary electrons under the influence of an electric field, reducing their escape from the Faraday cup entrance; adding a suppression magnetic field to change the direction of motion of secondary electrons generated after collisions with the bottom; and adding an outward-facing inclined plane or baffle at the bottom of the Faraday cup to change the direction of secondary electrons generated after collisions with the bottom. However, these methods can only suppress low-energy true secondary electrons and do not fundamentally solve the problem of reflected electrons reflecting towards the Faraday cup entrance. For applications requiring high-precision measurement of strong electron beams, the escaped electrons from these methods still cannot meet the accuracy requirements. Therefore, a technology that can effectively reduce the escape of reflected electrons is needed. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a Faraday cup with high collection efficiency, comprising:

[0006] The collecting chamber has an inclined surface near the side wall, which forms a cone-shaped space with a gradually increasing volume from the inlet to the bottom of the collecting chamber, in order to change the direction of the impact motion of particles in the collecting chamber.

[0007] A permanent magnet is located outside the collecting cavity and can generate a magnetic field to change the trajectory of incident electrons and secondary electrons inside the collecting cavity.

[0008] A particle incident channel is provided at the entrance of the collection cavity; the first end of the particle incident channel is connected to the entrance of the collection cavity, and the second end is provided with a suppression electrode, which is located at the front end of the second end of the particle incident channel.

[0009] Furthermore, the shape, size, and placement of the permanent magnet need to be calculated based on the energy of the particles. The magnitude of the magnetic field it generates is sufficient to allow the incident electrons to collide with the side wall of the Faraday cylinder without colliding with the bottom of the cylinder. The magnetic field generated by the permanent magnet in the electron movement region can be calculated using finite element simulation. The magnitude of the magnetic field needs to be calculated together with the shape of the cavity mentioned above.

[0010] Furthermore, the permanent magnets are located on both sides of the center of the collecting cavity.

[0011] Furthermore, the shape and size of the collecting cavity are determined based on the parameters of the electron beam and the magnetic field strength; the size of the cavity is determined by calculating the magnetic stiffness Br based on the energy of the electron beam, using the following formula: The electron beam energy is expressed in W, and its unit is MeV; λ is the rest energy of the electron, with a value of 511 keV; z is the charge number of the electron, with a value of 1; Br is in T·m.

[0012] Assuming a uniform magnetic field, if the electron deflection angle is less than 90 degrees, the cavity length L and cavity radius R must satisfy the following: Where r is the electron deflection radius. Let L be the angle between the direction perpendicular to the inclined sidewall and the direction when the electron collides with the cavity sidewall; if the deflection angle is greater than 90 degrees, the cavity length L and cavity radius R need to satisfy: If the electron deflection angle is less than 90 degrees, the relationship between the magnetic field B and the cavity radius R is expressed as: .

[0013] Furthermore, the permanent magnet has a remanence of 1.17T, a length of 30mm, and a thickness of 5mm.

[0014] Specifically, the permanent magnets are located on both sides of the center of the particle collecting cavity, close to the particle collecting cavity. They can generate a magnetic field in the central region of the particle collecting cavity, changing the direction of motion of the incident electrons in the collecting cavity from moving towards the bottom of the collecting cavity to moving towards the side wall. At the same time, they can change the trajectory of the secondary electrons generated after the particles hit the side wall to move towards the bottom of the collecting cavity, thus preventing the secondary electrons from escaping from the cup opening.

[0015] Furthermore, a magnetic field shield is provided outside the collection cavity, which includes an outer shielding cylinder and a front shielding layer; the outer shielding cylinder is a cylindrical tube surrounding the permanent magnet to prevent magnetic lines of force from spreading outward, and the front shielding layer is a shielding layer for the permanent magnet in the incident direction to concentrate the magnetic field of the permanent magnet in the cavity area.

[0016] Specifically, by placing a magnetic field shield outside the permanent magnet, the magnetic field lines can pass directly through the iron shielding layer and return, no longer spreading outward, thus suppressing the magnetic field. The entire shield can make the magnetic field strength in the motion area before the electron enters the cavity close to zero, so that the incident electron is not affected by the magnetic field in the incident channel.

[0017] Furthermore, the magnetic field shield is constructed using a high-permeability material. Specifically, the high-permeability material allows magnetic field lines to propagate as far as possible along the interior of the material, reducing the distribution of the external magnetic field.

[0018] Furthermore, the magnetic field shield is made of iron.

[0019] Specifically, the front shielding layer is 1mm thick and covers a length of 50mm along the electron incident direction. The outer shielding cylinder is 1mm thick, with an outer diameter of 50mm and an inner diameter of 30mm, further reducing magnetic field leakage. This shielding structure can reduce the magnetic field strength in the electron incident area to near 0, allowing the magnetic field to be concentrated in the cavity.

[0020] Furthermore, a serrated baffle is provided on the side wall inside the collection cavity, and the serrated baffle is set close to the side wall.

[0021] Furthermore, the collision region of incident electrons inside the collection cavity is provided with a low-reflectivity material film.

[0022] Furthermore, the diameter and length of the particle incident channel are determined based on the values ​​of the electron beam diameter and divergence angle.

[0023] Specifically, increasing the length of the particle incident channel, which is the circular tube-shaped channel through which electrons pass before entering the Faraday cylinder particle collection chamber, allows secondary electrons entering the channel to be reflected multiple times within the channel, reducing particle energy and decreasing the number of secondary electrons escaping from the cup opening.

[0024] Furthermore, the particle incident channel is cylindrical in shape with a diameter of 20 mm and a length of 50 mm along the particle incident direction. Specifically, the longer channel length can effectively prevent secondary electrons generated in the cavity from escaping from the cup opening.

[0025] Furthermore, the suppression electrode is a ring-shaped conductor with a radius larger than the particle incident channel; it generates an electric field by applying voltage through an external wire to suppress secondary electrons.

[0026] Furthermore, both the particle incident channel and the collection cavity are made of copper.

[0027] Furthermore, the particle incident channel is coaxially arranged with the collection cavity.

[0028] In summary, the beneficial technical effects of the present invention are as follows: The collecting cavity of the Faraday tube in the present invention adopts a conical flask-shaped cavity structure and adds permanent magnets around the cavity to deflect the electric field, so that the incident electrons no longer collide with the bottom of the collecting cavity of the Faraday tube as usual, but collide with the side wall, reducing the reflected electrons emitted towards the mouth of the cup and improving the electron collecting efficiency of the Faraday tube; a magnetic field shielding device is added around the collecting cavity of the Faraday tube to limit the magnetic field distribution, so that the magnetic field is concentrated in the conical cavity region of the Faraday tube, which can prevent the magnetic field from affecting the electron beam and other equipment on the incident path. Attached Figure Description

[0029] The above and other objects, features, and advantages of the present invention will become clearer from the following description of embodiments of the invention with reference to the accompanying drawings. The drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings.

[0030] Figure 1 This is a schematic diagram of the overall structure of the present invention;

[0031] Figure 2 This is a schematic diagram of the structure of the collecting cavity in this invention;

[0032] Figure 3 This is a diagram illustrating the electron deflection angle and the angle at which the incident electron collides with the inclined plane.

[0033] In the diagram, 1 is the suppression electrode, 2 is the particle injection channel, 3 is the collection cavity, 4 is the permanent magnet, 5 is the inclined plane, 6 is the magnetic field shield, and 7 is the height of the inclined plane.

[0034] 31. Bottom of the collection chamber; 32. Side wall of the collection chamber; 33. Serrated baffle; 61. Front shielding layer; 62. External shielding cylinder. Detailed Implementation

[0035] The present invention will be further described in detail below with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the disclosure to those skilled in the art. It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0036] Reference Figure 1-2 As shown, this invention discloses a Faraday cup with high electron collection efficiency, comprising a collection cavity 3, a permanent magnet 4, and a particle injection channel 2. The collection cavity 3 has an inclined surface 5 near its side wall 32, forming a conical space with a gradually increasing volume from the entrance to the bottom 32, which alters the collision direction of particles within the cavity. The permanent magnet 4 is located outside the collection cavity 3 and generates a magnetic field to change the trajectory of secondary electrons within the cavity. The particle injection channel 2 is located at the entrance of the collection cavity 3. The first end of the particle injection channel 2 connects to the entrance of the collection cavity 3, and the second end has a suppression electrode 1 located at the front end of the second end of the particle injection channel 2.

[0037] Reference Figure 1 As shown, it should be understood that adding a sloping shape to the sidewall of the collecting cavity, with the sloping surface located in the sidewall region and the direction perpendicular to the sloping surface pointing towards the bottom of the collecting cavity, transforms the interior of the collecting cavity into a conical flask shape with a small inlet area and a large end area. Most of the reflected electrons generated after an electron collides with the plane will move in a direction perpendicular to the plane. This shape allows more reflected electrons generated after a particle collides with the sloping surface on the cavity sidewall to be emitted towards the bottom of the flask, reducing the number of secondary electrons moving towards the rim. Simultaneously, the less perpendicular the electron is to the plane during incident, the fewer secondary electrons are generated. The sloping structure reduces the angle between the incident electron and the sloping surface during collision, which also reduces the generation of secondary electrons and further reduces their escape.

[0038] The shape and size of the collecting cavity 3 are determined based on the parameters of the electron beam and the magnetic field strength; the size of the collecting cavity 3 is determined by calculating the magnetic stiffness Br based on the energy of the electron beam, and the calculation formula is as follows: The electron beam energy is expressed in W, and its unit is MeV; λ is the rest energy of the electron, with a value of 511 keV; z is the charge number of the electron, with a value of 1; Br is in T·m.

[0039] Assuming a uniform magnetic field, if the electron deflection angle is less than 90 degrees, the cavity length L and cavity radius R must satisfy the following: Where r is the electron deflection radius. Let L be the angle between the direction perpendicular to the inclined sidewall and the sidewall when electrons collide with it; if the deflection angle is greater than 90 degrees, the cavity length L and cavity radius R must satisfy: If the electron deflection angle is less than 90 degrees, the relationship between the magnetic field B and the cavity radius R can be expressed as: .

[0040] Reference Figure 3 The diagram shows the electron deflection angle and the impact angle between the incident electron and the inclined plane.

[0041] It should be understood that, with reference Figure 1 As shown, the particle collection chamber 3 is used to collect particles and is shaped like a conical flask with a large volume and a small inlet. The particle injection channel 2 is connected to the inlet of the collection chamber 3. The suppression electrode 1 is located at the front end of the particle injection channel 2. The suppression electrode 1 is a ring-shaped conductor with a radius slightly larger than that of the particle injection channel 2. A voltage is applied through an external wire to generate an electric field that suppresses secondary electrons.

[0042] In this embodiment, copper is used as the material for the particle incident channel 2 and the particle collection cavity 3 in the Faraday cup, thereby improving the thermal and electrical conductivity of the Faraday cup. The specific dimensions of the particle collection cavity 3 are designed based on the electron energy, conforming to the improved Faraday cup method described in this invention, and are all within the protection scope of this invention.

[0043] like Figure 1 As shown, a slope 5 is added to the side wall 32 of the collection chamber. When viewed from the cup opening, the slope 5 is a reverse slope, which makes the inside of the particle collection chamber 3 into the shape of a conical bottle. The slope height 7 is 10mm, which increases the angle between the particle incident direction and the impact plane.

[0044] Continue to refer to Figure 1 As shown, the particle incident channel 2 is cylindrical in shape with a diameter of 20 mm and a length of 50 mm along the particle incident direction. The longer channel length effectively prevents secondary electrons generated in the collection cavity 3 from escaping from the inlet. Figure 1 The opening of the collection cavity 3 of the Faraday tube shown is connected to the particle incident channel 2. The collection cavity 3 is cylindrical in shape and coaxial with the particle incident channel 2. The cavity diameter is 50 mm and the length along the particle incident direction is 50 mm. The larger cavity area is left for the particles to deflect to the side wall after being subjected to the magnetic field.

[0045] In this embodiment, the permanent magnet 4 is located on both sides of the center of the collecting cavity 3, close to the particle collecting cavity. The permanent magnet has a remanence of 1.17T, a length of 30mm, and a thickness of 5mm. It can generate a magnetic field in the central region of the particle collecting cavity, changing the direction of motion of the incident electrons in the cavity from moving towards the bottom 31 of the collecting cavity to moving towards the side wall 32. At the same time, it can change the trajectory of the secondary electrons generated after the particles collide with the side wall 32 to move towards the bottom 32 of the collecting cavity of the Faraday cylinder, thus preventing the secondary electrons from escaping from the inlet.

[0046] Continue to refer to Figure 1 As shown, the magnetic field shield 6 is located outside the permanent magnet and surrounds the permanent magnet 4. It is made of iron, with a front shield layer 61 that is 1 mm thick and covers a length of 50 mm along the electron incident direction. The outer shielding cylinder 62 is 1 mm thick, with an outer diameter of 50 mm and an inner diameter of 30 mm, further reducing magnetic field leakage. Through simulation analysis, this shielding structure can reduce the magnetic field strength in the electron incident area to near 0, making the magnetic field concentrated in the cavity.

[0047] like Figure 1 As shown, an annular suppression electrode 1 is set in front of the particle incident channel. A voltage is applied to the ring to suppress the secondary electrons escaping from the inlet, thereby controlling the secondary electrons as much as possible in the collection cavity and improving the efficiency of the Faraday cylinder collection cavity.

[0048] like Figure 2 As shown, a sawtooth-shaped baffle 33 or a comb-shaped baffle is added to the side wall 32 of the collecting cavity, so that the secondary electrons generated after the particle collision are reflected multiple times in the baffle, and the energy is gradually reduced or absorbed by the baffle, further reducing the escape of secondary electrons.

[0049] Furthermore, in this embodiment, a film of low-reflectivity materials such as carbon and aluminum is added to the collision area between the incident electron channel 2 and the collecting cavity 3 to reduce the secondary electron emission coefficient and further reduce the generation of secondary electrons.

[0050] In this embodiment, a permanent magnet 4 is added around the collecting cavity 3 to generate a magnetic field, causing the incident particles to change their direction of motion under the influence of the magnetic field. The shape, size, and placement of the permanent magnet 4 need to be calculated based on the energy of the particles. The magnitude of the magnetic field it generates is sufficient to ensure that the incident electrons collide with the side wall 32 of the collecting cavity of the Faraday cylinder without colliding with the bottom 31 of the collecting cavity. The magnetic field generated by the permanent magnet 4 in the electron motion region can be calculated using finite element simulation. The determination of the magnetic field magnitude needs to be calculated together with the shape of the collecting cavity.

[0051] In this embodiment, a magnetic field shield 6 is constructed around the permanent magnet using a high-permeability material to prevent the magnetic field from leaking outwards. Since the permanent magnet 4 generates a magnetic field not only inside the electron collection cavity 3 but also in the electron incident region (electron incident channel), affecting electron incidence and potentially preventing electrons from completely entering the collection cavity 3, it is necessary to shield the magnetic field leaking outwards. A high-permeability material allows magnetic field lines to propagate along the interior of the material as much as possible, reducing the external magnetic field distribution. By placing a cylindrical magnetic field shield outside the permanent magnet, the magnetic field lines can directly pass through the iron shielding layer and return, preventing further outward diffusion. This achieves the effect of suppressing the magnetic field. The magnetic field shield 6 includes an outer shielding cylinder 62 and a front shielding layer 61. The outer shielding cylinder 62 is a cylindrical tube surrounding the permanent magnet to prevent magnetic field lines from diffusing outwards. The front shielding layer 61 is a shielding layer for the permanent magnet in the incident direction, used to concentrate the magnetic field in the cavity region. The entire magnetic field shield 6 can make the magnetic field strength in the motion area before the electron enters the collection cavity 3 close to zero, so that the incident electron is not affected by the magnetic field in the electron incident channel.

[0052] In this embodiment, the length of the particle incident channel 2 is increased. The particle incident channel 2 is a cylindrical channel through which electrons pass before entering the collection cavity 3 of the Faraday cylinder particles. Increasing the length of the particle incident channel 2 allows secondary electrons entering the channel to be reflected multiple times within the channel, reducing particle energy and minimizing the escape of secondary electrons from the cup opening. The diameter and length of the particle incident channel 2 need to be calculated based on the electron beam diameter and divergence angle to ensure that the incident electron beam does not collide with the sidewalls of the channel while reducing the escape of secondary electrons.

[0053] In summary, the beneficial technical effects of the present invention are as follows: The collecting cavity of the Faraday tube in the present invention adopts a conical flask-shaped cavity structure and adds permanent magnets around the cavity to deflect the electric field, so that the incident electrons no longer collide with the bottom of the collecting cavity of the Faraday tube as usual, but collide with the side wall, reducing the reflected electrons emitted towards the mouth of the cup and improving the electron collecting efficiency of the Faraday tube; a magnetic field shielding device is added around the collecting cavity of the Faraday tube to limit the magnetic field distribution, so that the magnetic field is concentrated in the conical cavity region of the Faraday tube, which can prevent the magnetic field from affecting the electron beam and other equipment on the incident path.

[0054] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0055] Finally, it should be noted that the above embodiments are merely examples for clearly illustrating the present invention and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A Faraday cup with high electron collection efficiency, characterized in that, include: The collecting chamber has an inclined surface near the side wall, which forms a cone-shaped space with a gradually increasing volume from the inlet to the bottom of the collecting chamber, in order to change the direction of the impact motion of particles in the collecting chamber. A permanent magnet is located outside the collecting cavity and can generate a magnetic field to change the trajectory of incident electrons and secondary electrons inside the collecting cavity. A particle incident channel is provided at the entrance of the collection cavity; the first end of the particle incident channel is connected to the entrance of the collection cavity, and the second end is provided with a suppression electrode, which is located at the front end of the second end of the particle incident channel; The shape and size of the collecting cavity are determined based on the parameters of the electron beam and the magnetic field strength; the size of the cavity is determined by calculating the magnetic stiffness Br based on the energy of the electron beam, using the following formula: The electron beam energy is expressed in W, and its unit is MeV; λ is the rest energy of the electron, with a value of 511 keV; z is the charge number of the electron, with a value of 1; Br is in T·m. Assuming a uniform magnetic field, if the electron deflection angle is less than 90 degrees, the cavity length L and cavity radius R must satisfy the following: Where r is the electron deflection radius. Let L be the angle between the electrons and the cavity sidewalls when they collide. If the deflection angle is greater than 90 degrees, the cavity length L and cavity radius R must satisfy the following: ; If the electron deflection angle is less than 90 degrees, the relationship between the magnetic field B and the cavity radius R is expressed as follows: .

2. The Faraday cup with high electron collection efficiency according to claim 1, characterized in that: The collection cavity is also provided with a magnetic field shield, which includes an outer shielding cylinder and a front shielding layer; the outer shielding cylinder is a cylindrical tube surrounding the permanent magnet to prevent the magnetic field lines from spreading outward, and the front shielding layer is a shielding layer for the permanent magnet in the incident direction to concentrate the magnetic field of the permanent magnet in the cavity area.

3. The Faraday cup with high electron collection efficiency according to claim 1, characterized in that: A serrated baffle is also provided on the side wall inside the collection cavity, and the serrated baffle is set close to the side wall.

4. The Faraday cup with high electron collection efficiency according to claim 1, characterized in that: The collision region of incident electrons inside the collection cavity is provided with a low-reflectivity material film.

5. The Faraday cup with high electron collection efficiency according to claim 1, characterized in that: The diameter and length of the particle incident channel are determined based on the values ​​of the electron beam diameter and divergence angle.

6. The Faraday cup with high electron collection efficiency according to claim 1, characterized in that: The suppression electrode is a ring-shaped conductor with a radius larger than that of the particle incident channel; It generates an electric field by applying voltage through an external wire to suppress secondary electrons.

7. The Faraday cup with high electron collection efficiency according to claim 1, characterized in that: Both the particle injection channel and the collection cavity are made of copper.

8. The Faraday cup with high electron collection efficiency according to claim 1, characterized in that: The particle incident channel is coaxially arranged with the collection cavity.

9. The Faraday cup with high electron collection efficiency according to claim 2, characterized in that: The magnetic field shield is made of iron.

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