Electron collection type residual gas ionization chamber without magnetic field constraint

Abstract

The invention discloses an electron collection type residual gas ionization chamber structure without magnetic field constraint, which belongs to the field of nuclear science and technology and comprises an upper polar plate, a lower polar plate, a shimming polar plate and a signal collection device. By setting the potentials of the inlet electrode and the lower electrode plate of the signal collection device, a guide electric field capable of focusing signal electrons is formed to limit profile diffusion caused by the initial momentum of the signal electrons, so that the measurement profile can truly reflect the initial distribution information of incident particles, and the overall size of the residual gas ionization chamber can be reduced. The method has important significance on compact design of the electron collection type residual gas ionization chamber.

Description

Technical Field

[0001] The invention belongs to the field of nuclear science and technology, and relates to an electron collection type residual gas ionization chamber without magnetic field constraint. Background Art

[0002] In recent years, the residual gas ionization chamber based on the principle of electromagnetic induction is an inductive non-intercepting detector. It has been widely used in various accelerator facilities because of its ability to complete online real-time measurement of the beam transverse profile without deteriorating the beam parameters. It is worth noting that the working medium of the residual gas ionization chamber is the residual gas in the vacuum pipe, so the signal electron gain generated by the interaction between the beam and the medium is extremely low, which poses a great challenge to the collection of signal electrons and the restoration of the beam profile. Under the application conditions of proton therapy, the initial velocity of the signal electron perpendicular to the collection direction will cause the measurement profile to diffuse by about 30%. Therefore, setting a reasonable guide field to suppress the lateral deviation caused by the initial velocity of the signal electron has become a research hotspot for the residual gas ionization chamber.

[0003] In the current mainstream guidance field, a composite solution of external magnetic field plus guiding electric field is usually adopted. Both the external magnetic field and the guiding electric field are parallel to the collection direction of signal electrons. In the vertical direction, the guiding electric field accelerates the signal electrons to move toward the lower plate until they are collected; in the horizontal direction, the external magnet makes the signal electrons move in a circular motion, and the radius of the circular motion is the limited lateral offset size. The combined effect of the two makes the signal electrons move downward in a spiral line until they are captured by the signal collection device. The size of the residual gas ionization chamber using this external field is usually about 1.5 meters, which makes it difficult to apply the residual gas ionization chamber to the layout of compact beam lines, which is not conducive to the miniaturization design of beam lines. Summary of the invention

[0004] In view of the defects of the prior art, the purpose of the present invention is to provide an electron-collecting residual gas ionization chamber without magnetic field constraints. In order to solve the problem that the current electron-collecting residual gas ionization chamber needs external magnets to constrain it, resulting in large size and high cost, a scheme is proposed that only utilizes the optimization of the guide electric field potential to make the guide electric field have a focusing effect, thereby achieving the suppression of the signal electron trajectory without the need for an external magnetic field, and then completing the reconstruction of the lateral profile of the incident particle.

[0005] To achieve the above-mentioned purpose, the present invention provides an electron collection type residual gas ionization chamber without magnetic field constraint, comprising an upper plate, a lower plate, a pad plate and a signal collection device, wherein the pad plate is located between the upper plate and the lower plate, the lower plate has a central opening, and the signal collection device is located at a preset height below the hole, and the potential difference between the entrance pole potential of the signal collection device and the lower plate is used to form a guide electric field with focusing ability to control the movement trajectory of electrons in the downward collection process. The signal collection device includes an entrance pole, an exit pole and a fluorescent target from top to bottom. Among them, the area between the upper plate and the lower plate is the central area, and the area between the lower plate and the entrance pole is the potential well area. By optimizing the setting of the guide electric field potential in the potential well area, a potential difference of not less than 6kV is formed between the entrance pole and the lower plate, and a guide electric field with focusing ability is formed, thereby suppressing the diffusion of the measurement profile caused by the initial velocity of the signal electron, so that the reconstructed profile can truly and accurately reflect the initial profile distribution of the incident particle. The electric field formed in the potential well region by the potential difference between the entrance electrode and the lower electrode of the signal collection device has a lateral component away from the center of the beam, which has a focusing effect on the signal electrons. The focusing ability of the electric field in the potential well region can be adjusted by changing the potential of the entrance electrode of the signal collection device to adapt to signal electron profiles with different diffusion sizes in multiple scenarios.

[0006] Furthermore, the potentials of the upper plate and the lower plate are -6 kV and 0 kV respectively.

[0007] Furthermore, the potential of the entrance electrode is greater than or equal to 6 kV, but not more than 20 kV, so as to form a potential difference between the lower electrode plate and the entrance electrode of the signal device.

[0008] Furthermore, the padding plate includes a plurality of plates whose potential increases at equal intervals from top to bottom, so that the lower plate is at zero potential, and at the same time, the potential of the entrance electrode of the signal collection device is 6 kV higher than that of the lower plate, but the entrance electrode does not exceed 20 kV, thereby forming a potential difference between the lower plate and the entrance electrode, guiding the equipotential lines of the electric field to bulge upward, and having a focusing effect in the horizontal direction. The potential difference between the entrance electrode, the exit electrode and the fluorescent target belongs to the working voltage of the signal collection device, has no effect on the guided electric field, and can be set separately according to the working parameters of the signal collection device.

[0009] Furthermore, the hole is a square hole, and the signal electrons pass through the square hole and are acquired by the signal collecting device.

[0010] Furthermore, the distance between the inlet electrode and the lower electrode plate is 20 to 30 mm.

[0011] Furthermore, in the potential setting method as described above, by changing the potential size of the entrance electrode of the signal collection device, the focusing strength control of the guide electric field can be achieved. The electric field formed in the potential well region has a lateral component away from the center of the beam. By adjusting the strength of the focusing effect, the lateral deviation of the signal electrons is reduced, and the collection trajectory of the signal electrons is controlled, so that the profile information obtained by signal particle restoration is more similar to the real profile of the beam, thereby inferring more accurate initial beam lateral distribution information.

[0012] Compared with the prior art, the above technical solutions conceived by the present invention can achieve the following

[0013] Beneficial effects:

[0014] 1. The present invention can form a guiding electric field with focusing ability only through the potential difference between the entrance pole potential and the lower pole plate of the signal collection device, and the focusing ability of the electric field can be controlled by adjusting the potential difference; there is no need to introduce an external magnetic field by installing a dipole magnet to constrain the lateral deviation of the signal electrons, and the collection trajectory of the signal electrons is controlled only by the guiding electric field, which effectively reduces the size and cost of the residual gas ionization chamber.

[0015] 2. The padding plate and the upper and lower plates in the ionization chamber provided by the present invention are powered by series voltage division. Without occupying additional power supply channels, the edge shape of the electric field can be shaped, which helps to form a guiding electric field with focusing capability, thereby collecting electrons. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A schematic structural diagram of an electron collection type residual gas ionization chamber without magnetic field constraint provided by the present invention.

[0017] Figure 2 The three-dimensional electric field equipotential line diagram is disclosed in an embodiment of the present invention in an electron collection type residual gas ionization chamber without magnetic field constraint.

[0018] Figure 3 It is the lateral offset size of the signal electrons under a current power supply scheme disclosed in an embodiment of the present invention.

[0019] Figure 4 This is a reconstruction diagram of the signal electron cross-section under a current power supply scheme disclosed in an embodiment of the present invention.

[0020] Figure 5 This is an electric field line diagram of the potential well region disclosed in an embodiment of the present invention.

[0021] Figure 6 A three-dimensional model diagram of the detector disclosed in an embodiment of the present invention. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0023] The present invention provides an electron collection type residual gas ionization chamber without magnetic field constraint, comprising an upper electrode plate, a lower electrode plate, a pad electrode plate and a signal collection device, wherein the pad electrode plate is located between the upper electrode plate and the lower electrode plate, the center of the lower electrode plate is opened, and the signal collection device is located at a preset height below the hole. The potential difference between the entrance electrode potential of the signal collection device and the lower electrode plate is used to form a guiding electric field with focusing capability to control the collection trajectory of electrons.

[0024] like Figure 1 As shown, the inlet electrode potential of the signal collection device is set to 20kV, the potential of the upper and lower plates and the padding plate is -6kV increasing to 0kV, the inlet electrode potential is higher than the potential of each plate, and the guide electric field is directed from the hole of the lower plate to the upper and lower plates and the padding plate. The vertical component of the guide electric field makes the signal electrons move downward and be collected, and the lateral component of the guide electric field makes the signal electrons move toward the center of the ionization chamber and be focused, so that the horizontal and vertical speeds of the signal electrons are v x and v y , the components of the guided electric field in the horizontal and vertical directions are E x and E y , the collection time of the signal electron is Δt, and the displacements Δx and Δy of the signal electron collection trajectory in the horizontal and vertical directions are as follows:

[0025]

[0026] Comparing the two equations, we can get:

[0027]

[0028] Where P x and P y is the momentum of the signal electron in the horizontal and vertical directions, and q is the charge of the signal electron.

[0029] pass Figure 1 It can be seen that the signal electron starts from the center of the detector and moves downward until it is captured by the signal collection device. Therefore, the vertical displacement Δy during the signal electron collection process can be regarded as half of the vertical dimension of the electric field frame. When the size of the detector is fixed, the vertical displacement Δy is a fixed value; and the horizontal momentum P of the signal electron xand vertical momentum P y Determined by the collision process between the incident particles and the gas medium.

[0030] Therefore, the electric field is guided by E x / E y The size of the ratio affects the lateral offset of the signal electrons. Figure 2 The equipotential lines of the electric field bulge upward, guiding the lateral component of the electric field from the center of the detector to the pad plate, focusing the signal electrons in the horizontal direction.

[0031] like Figure 3 As shown in the figure, the signal collection device is set with the entrance electrode potential of 6kV, 10kV, 15kV and 20kV respectively, the signal electron is introduced to perform particle tracking simulation, and the profile of the incident particle is reconstructed based on the collection position information of the signal electron. In the simulation, the initial transverse profile of the incident particle is a typical Gaussian distribution. It can be seen that with the increase of the entrance electrode potential, the focusing ability of the guided electric field becomes stronger, and the measurement profile size and measurement deviation will be further reduced; the initial profile size σ = 3.75mm, among which the measured profile size is σ = 3.821mm when the entrance electrode potential is 20kV, and the measurement deviation is the smallest: 0.071mm.

[0032] like Figure 4 As shown in the figure, the upper and lower curves are the variation of the residual gas ionization chamber profile measurement size and measurement error with the entrance electrode potential. As the entrance electrode potential increases, the size and error of the residual gas ionization chamber measurement profile decrease, but the curvature of the curve also decreases, which means that as the entrance electrode potential of the microchannel plate increases, the focusing ability of the guided electric field tends to a limit value, which is consistent with the Figure 2 The electric field focusing effect shown in the figure is consistent with the theoretical analysis. The increase in potential difference will lead to an increase in the vertical and horizontal components of the guide electric field, and the focusing suppression of the electric field on the lateral deviation of the signal electrons depends on the ratio of the guide electric field in the two directions. Therefore, under the current electric field structure, when the entrance electrode potential increases to 40kV, the signal electron collection trajectory along the The ratio tends to be stable, about 0.386, the cross-section size measurement error has been reduced to 0.026mm, and the maximum field strength in the potential well region has reached about 2.857×10 6 V / m; Continuing to increase the entrance electrode potential is difficult to significantly improve the measurement performance of the detector, and high-voltage breakdown or sparking is likely to occur.

[0033] Figure 5 The electric field line diagram of the potential well region when the entrance electrode of the signal collection device is 20kV is given. In the figure, the Y axis is located at the center of the detector. It can be seen that the lateral component of the guided electric field is directed from the Y axis to the pad. The signal electrons receive the electric field force directed to the Y axis, so they are focused during the collection process and their diffusion is suppressed.

[0034] Figure 6 The three-dimensional model of the detector is given. The insulating back plate is made of G10 resin material, and the left and right insulating back plates are clamped at one time to ensure the position accuracy requirements of the upper and lower plates and the padding plates.

[0035] It can be concluded that the method of suppressing the lateral deviation of signal electrons by guiding electric field focusing can suppress the lateral deviation of signal electrons without the need for external magnetic field constraints, reduce the size of the detector, and reduce costs. It can then reconstruct the size of the incident particle profile with sub-millimeter accuracy, and can control the strength of the guided electric field focusing by adjusting the potential of the signal collection device. This allows the detector to reduce errors caused by fluctuations in incident particle parameters, stray particles, etc., and obtain more accurate beam profile information in actual applications.

[0036] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, any modification, equivalent substitution and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. An electron collection type residual gas ionization chamber without magnetic field constraint, the ionization chamber is a vacuum chamber, characterized in that: It includes an upper electrode plate, a lower electrode plate, a padding electrode plate and a signal collecting device, wherein the padding electrode plate is located between the upper electrode plate and the lower electrode plate, the lower electrode plate has a central opening, and the signal collecting device is located at a preset height below the hole. The potential difference between the entrance electrode potential of the signal collecting device and the lower electrode plate is used to form a guiding electric field with focusing capability to control the movement trajectory of electrons during the downward collection process.

2. The electron collection type residual gas ionization chamber without magnetic field constraint according to claim 1, characterized in that: The potentials of the upper plate and the lower plate are -6 kV and 0 kV respectively.

3. The electron collection type residual gas ionization chamber without magnetic field constraint according to claim 1, characterized in that: The signal collection device comprises an inlet pole, an outlet pole and a fluorescent target from top to bottom.

4. The electron collection type residual gas ionization chamber without magnetic field constraint according to claim 3, characterized in that: The potential of the entrance electrode is greater than or equal to 6 kV, but not more than 20 kV, so as to form a potential difference between the lower electrode plate and the entrance electrode of the signal device.

5. The electron collection type residual gas ionization chamber without magnetic field constraint according to claim 1, characterized in that: The padding plate includes a plurality of plates whose potential increases at equal intervals from top to bottom.

6. The electron collection type residual gas ionization chamber without magnetic field confinement according to claim 1, characterized in that: The hole of the lower electrode plate is a square hole.

7. The electron collection type residual gas ionization chamber without magnetic field confinement according to claim 3, characterized in that: The preset height is 20-30 mm.

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