A large-area microchannel plate photomultiplier tube with high temporal resolution

Abstract

The present invention discloses a large-area microchannel plate photomultiplier tube with high time resolution, which belongs to the technical field of vacuum photodetectors, and includes: a vacuum glass container, a photocathode, an electron focusing system, an electron multiplication system, an anode and a power supply electrode. The photocathode, the electron focusing system, the electron multiplication system and the anode are placed in the vacuum glass container, the anode is connected to an external circuit through a signal lead through the vacuum glass container, the power supply electrode is connected to an external power supply circuit through a power line through the vacuum glass container, the vacuum glass container is a cylindrical barrel with a curved top, and the photocathode is covered on the inner surface of the curved surface; the electron focusing system includes a cylindrical focusing barrel and a conical or spherical focusing barrel, which is placed at the upper end opening of the conical focusing barrel. The present invention has the advantages of high time resolution and high photoelectron collection efficiency, and can also improve the photocathode coverage.

Description

Technical Field

[0001] The invention belongs to the technical field of vacuum photoelectric detectors, and in particular relates to a large-area microchannel plate photomultiplier tube with high time resolution. Background Art

[0002] Photomultiplier tubes are vacuum photoelectric detection devices that are based on the external photoelectron emission effect, secondary electron emission effect and electron optics theory, and can convert weak light signals into photoelectrons and obtain a multiplication effect. Large-area photomultiplier tubes are a type of photomultiplier tube. Due to their large photocathode coverage area and photon counting capabilities, they are widely used in large-scale high-energy physics detection experiments such as neutrinos and cosmic rays.

[0003] Traditional large-area photomultiplier tubes are of the dynode type, such as Figure 1 As shown, the vacuum glass container 1 adopts an ellipsoidal or nearly spherical glass shell, the photocathode 2 covers a part of the inner surface of the spherical shell that is less than half, and a dynode electron multiplication system 3 is placed at the center bottom. The number of dynodes is generally 8 to 16, and an anode 4 is arranged at the end of the dynode. When light irradiates the vacuum glass container 1, the incident photon 5 will produce photoelectrons 6 by external photoelectric effect at the photocathode 2. The photoelectrons 6 are collected by the dynode under the action of the internal electric field, and are multiplied step by step under the action of the electric field force. Finally, the multiplied electrons are collected by the anode 4 and output as signals. Reference: Hirota S, Nishimura Y, Suda Y, et al. New large aperture, hybrid photo-detector and photo multiplier tube for a gigantic water Cherenkov ring imaging detector [J]. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2014, 766: 152-155. It involves a typical traditional large-area dynode photomultiplier tube with excellent performance: the collection efficiency is 90%, and the transit time dispersion (time resolution) is 2.7ns. Unfortunately, its shape is an ellipsoid, and the photocathode 2 only covers part of the upper hemisphere. If it is placed in the detector to form an array, the coverage rate of the photocathode 2 is less than 80% due to the limitation of the long diameter of the ellipsoid, resulting in a waste of detection space.

[0004] Chinese patent applications with application numbers 200910147915.4 and 201410104388.X disclose a novel large-area microchannel plate type photomultiplier tube, such as Figure 2 As shown, the photomultiplier tube disclosed in the invention has a spherical vacuum glass shell 1; two groups of four microchannel plate assemblies 7 are used to replace the traditional electron multiplication system, which are distributed vertically in the center of the container; the technology of combining the transmission cathode and the reflection cathode is used to achieve full coverage of the photocathode 2, effectively expanding the coverage of the photocathode 2. However, the implementation of this tube type is difficult, and it has not been mass-produced, and there is no report on the development of related sample tubes. At present, the large-area microchannel plate type photomultiplier tubes that have been successfully developed and mass-produced are as follows: Figure 3 As shown, it has an ellipsoidal vacuum glass shell 1, a microchannel plate assembly 7 and an anode 4 placed horizontally at the bottom of the glass handle. Compared with the above-mentioned dynode-type photomultiplier tube of the same size, this large-area microchannel plate-type photomultiplier tube has a large transit time dispersion of 15ns (NNVT, Photomultipliertubes, http: / / www.nvt.com.cn / art / 2020 / 3 / 23 / art_1235_25349.html). In addition, the tube has a long diameter of 508mm and a photocathode 2 diameter of 460mm, and there is also a problem of low coverage of the photocathode 2. Summary of the invention

[0005] In view of the shortcomings of the prior art, the object of the present invention is to provide a large-area microchannel plate photomultiplier tube with high time resolution, high photoelectron collection efficiency and high photocathode coverage.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A large-area microchannel plate photomultiplier tube with high time resolution comprises: a vacuum glass container, a photocathode for receiving light and generating photoelectrons, an electron focusing system for accelerating and focusing the photoelectrons emitted from the photocathode, an electron multiplying system for collecting the photoelectrons accelerated and focused by the electron focusing system and generating multiplied electrons, an anode for collecting the multiplied electrons output by the electron multiplying system, and a power supply electrode for supplying power to the photocathode, the electron focusing system, the electron multiplying system and the anode. The photocathode, the electron focusing system, the electron multiplying system and the anode are placed in the vacuum glass container, the anode is connected to an external signal processing circuit through a signal lead passing through the vacuum glass container, and the power supply electrode is connected to an external power supply circuit through a power line passing through the vacuum glass container. Among them, the vacuum glass container is a cylindrical barrel with a curved top, and the photocathode evenly covers the inner surface of the curved surface; the focusing system is coaxial with the center of the photocathode and is placed directly below it, including 1 to 3 cylindrical focusing barrels and a 1-level conical or spherical focusing barrel placed inside it, and all focusing barrels are open at the top and bottom; the multiplication system is a single-piece or multi-piece microchannel plate assembly, coaxial with the center of the photocathode, and placed near the upper end opening of the conical focusing barrel; the anode is placed in parallel and directly behind the output electrode of the microchannel plate assembly, and its area is greater than or equal to the microchannel plate.

[0008] In order to achieve the purpose of improving the photocathode coverage, the vacuum glass container is a cylindrical barrel with a curved top, and the barrel diameter is equal to the photocathode diameter. After it is placed in the detector to form an array, the photocathode coverage can be improved to a certain extent.

[0009] In order to obtain high collection efficiency, the focusing system is placed directly below the photocathode and coaxial with the photocathode, including 1 to 3 cylindrical focusing barrels and 1 conical or spherical focusing barrel, all of which are open at the top and bottom, and the microchannel plate is placed in the conical or spherical focusing barrel near the top opening, and the applied voltage increases step by step. The mutual cooperation of the cylindrical focusing barrel and the conical or spherical focusing barrel can realize that the photoelectrons are collected by the microchannel plate after effective focusing.

[0010] In order to improve the time resolution, the straight-line distance between the microchannel plate and the photocathode at each latitude is basically the same, and the taper or curvature of the conical or spherical focusing barrel should be determined in accordance with the curvature of the photocathode, so that the path distances of the photoelectrons generated at various positions of the photocathode to reach the microchannel plate are not much different, and the electric field distributions they pass through are basically the same, thereby ensuring that the transit time dispersion is minimized.

[0011] According to a further improvement of the present invention, the top curved surface of the vacuum glass container may be a spherical surface or an ellipsoidal surface.

[0012] According to the need for gain, the microchannel plate assembly is composed of a single or multiple "V"-shaped cascaded microchannel plates, coaxial with the center of the photocathode, with the input electrode (low potential surface) of the microchannel plate facing the interior of the vacuum glass container, and the output electrode (high potential surface) facing the anode.

[0013] According to a further improvement of the present invention, in the electron focusing system, the diameter and height of the cylindrical focusing barrels of levels 1 to 3 are consistent, and the diameter is equal to or slightly smaller than the photocathode.

[0014] A further improvement of the present invention is that the conical or spherical focusing barrel in the electron focusing system is narrow at the top and wide at the bottom, the diameter of the upper opening is equal to or slightly smaller than the microchannel plate assembly, the diameter of the lower opening is larger than the microchannel plate assembly and smaller than the cylindrical focusing barrel, and the height of the conical or spherical focusing barrel is not lower than the thickness of the microchannel plate assembly and the anode.

[0015] A further improvement of the present invention is that the placement height of the conical or spherical focusing barrel requires that its upper edge does not exceed the upper edge of the first-stage cylindrical focusing barrel and does not fall below the lower edge of the final-stage cylindrical focusing barrel.

[0016] According to a further improvement of the present invention, the focusing system, the microchannel plate electron multiplication system and the anode are all coaxial with the center of the photocathode.

[0017] Beneficial effects of the present invention:

[0018] The present invention improves the photocathode coverage by utilizing a cylindrical shape design with a curved top; ensures high electron collection efficiency by designing 1 to 3 levels of cylindrical focusing barrels and 1 level of conical or spherical focusing barrel; and achieves basically the same path for photoelectrons generated at various positions of the photocathode to reach the microchannel plate assembly and the distribution of the electric field along the path by reasonably setting the distance between the microchannel plate assembly and the photocathode, and the taper or curvature of the conical or spherical focusing barrel, thereby achieving high time resolution. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0020] Figure 1 This is a schematic diagram of the structure of a large-area dynode photomultiplier tube in traditional technology;

[0021] Figure 2 It is a schematic diagram of the structure of a large-area microchannel plate photomultiplier tube (the microchannel plate is placed vertically);

[0022] Figure 3It is a schematic diagram of the structure of a large-area microchannel plate photomultiplier tube (the microchannel plate is placed horizontally);

[0023] Figure 4 is a schematic structural diagram of an embodiment of a photomultiplier tube of the present invention;

[0024] Figure 5 It is a schematic diagram of the electric field simulation result of the photomultiplier tube of the present invention.

[0025] Description of the numbers in the figure:

[0026] 1. Vacuum glass container; 2. Photocathode; 3. Dynode electron multiplication system; 4. Anode; 5. Incident photons; 6. Photoelectrons; 7. Microchannel plate assembly; 8. Electron focusing system; 81. Primary cylindrical focusing barrel; 82. Secondary cylindrical focusing barrel; 83. Conical focusing barrel; 9. Supply electrode and signal lead wire; 10. Insulating rod. DETAILED DESCRIPTION

[0027] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in 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. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] In the description of the present invention, it is necessary to understand that the terms "opening", "upper", "lower", "thickness", "top", "middle", "length", "inside", "all around" and the like indicate orientation or positional relationship, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the components or elements referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention.

[0029] A large-area microchannel plate photomultiplier tube with high temporal resolution, such as Figure 4As shown, it mainly includes a photocathode 2 uniformly covered on the top curved surface of the vacuum glass container 1, and an electron multiplication system, an electron focusing system 8, a microchannel plate assembly 7, an anode 4, a supply electrode and a signal lead 9, and an insulating rod 10 placed in the vacuum glass container 1. The vacuum glass container 1 is a cylinder with a curved surface on the top, and the curved surface can be a spherical surface or an ellipsoidal surface. The specific shape depends on the requirements for the diffusion of the photoelectron transit time in the project. Here, the present invention is described in detail by taking a cylindrical vacuum light-transmitting container with an ellipsoidal surface on the top, but the protection scope of the present invention is not limited. The diameter of the cylindrical vacuum glass container 1 is equal to the diameter of the top photocathode 2. The photomultiplier tube of this shape is placed in the detector to form an array. The distance between the photocathodes 2 of adjacent tubes is closer, and the coverage rate of the photocathode 2 can be improved to a certain extent; the electron focusing system 8 is placed directly below the photocathode 2 and coaxial therewith, including 1 to 3 cylindrical focusing barrels, conical or spherical focusing barrels. In this embodiment, a first-stage cylindrical focusing barrel 81, a secondary cylindrical focusing barrel 82 and a conical focusing barrel 83 are used. All focusing barrels are opened up and down, and the microchannel plate assembly 7 is placed at the top opening of the conical focusing barrel 83. The design of the electron focusing system 8 can form a focusing electric field inside the photomultiplier tube, effectively focusing the photoelectrons on the microchannel plate assembly 7, and achieving high photoelectron collection efficiency; the straight-line distance from the microchannel plate assembly 7 to the photocathode 2 at each latitude is basically the same, The taper of the conical focusing barrel 83 matches the curvature of the photocathode 2, so that the path distances of the photoelectrons generated at various positions of the photocathode 2 to reach the microchannel plate assembly 7 are not much different, and the electric field distribution they pass through is basically the same, thereby ensuring that the transit time dispersion is minimized. The microchannel plate assembly 7 is used as an electron multiplier to collect and multiply the focused photoelectrons. The multiplied photoelectrons are collected by the anode 4 and output through the supply electrode and the signal lead 9. Figure 4 The middle supply electrode and the signal lead line 9 are represented by a straight line. On the one hand, as a signal lead line, it can output the electron flow signal collected by the anode 4; on the other hand, as a supply electrode, it is connected to the external power supply circuit through a power line to supply power to the photocathode 2, the electron focusing system 8, the microchannel plate assembly 7 and the anode 4, so that an electric potential difference is formed between them in turn to ensure the normal operation of the photomultiplier tube.

[0030] The photocathode 2 is made of appropriate photocathode material and is coated with a uniform thickness on the top curved surface of the vacuum glass container 1. The photocathode 2 material can be a double alkali or multi-alkali metal material. Its thickness and structure are determined according to specific use requirements during the coating process. In this embodiment, the diameters of the photocathode 2 and the vacuum glass container 1 are both 460 mm. The potential of the photocathode 2 is the lowest in the entire photomultiplier tube, generally 0V.

[0031] The above-mentioned photomultiplier tube adopts a three-electrode electron focusing system 8, which includes a primary cylindrical focusing barrel 81, a secondary cylindrical focusing barrel 82 and a conical focusing barrel 83. The first cylindrical focusing barrel 81 and the secondary cylindrical focusing barrel 82 are coaxial with the center of the photocathode 2, and their diameters and heights are equal. The diameter cannot be too small, and should be equal to or slightly smaller than the diameter of the photocathode 2. The barrel height, placement height and spacing should be determined in combination with the actual project requirements for focusing effect and time response. The electric potential of the first cylindrical focusing barrel 81 should be higher than the electric potential of the photocathode 2, which is adjustable from 10V to 300V, and the electric potential of the secondary cylindrical focusing barrel 81 should be higher than the electric potential of the first cylindrical focusing barrel 82, which is adjustable from 200V to 1000V; the design of the conical focusing barrel 83 has two functions: on the one hand, it cooperates with the above-mentioned first cylindrical focusing barrel 81 and secondary cylindrical focusing barrel 82 to achieve electron focusing and obtain high time resolution; on the other hand, it plays a shielding role, shielding the electric field generated by the microchannel plate assembly 7 and the anode 4 assembly in the barrel to prevent the performance of the photomultiplier tube from deteriorating due to the overflow of the electric field. The conical focusing barrel 83 is coaxial with the center of the photocathode 2, narrow at the top and wide at the bottom, with two upper and lower openings. To ensure high collection efficiency, the upper opening is not larger than the diameter of the microchannel plate assembly 7, and the lower opening is not larger than the diameter of the primary cylindrical focusing barrel 81 and the secondary cylindrical focusing barrel 82. The height of the conical focusing barrel 83 needs to cover the microchannel plate assembly 7 and the anode 4. The specific height value, taper and placement position need to be determined in combination with the collection efficiency and time characteristics. The potential of the conical focusing barrel 83 should be higher than the potential of the secondary cylindrical focusing barrel 82, and is adjustable from 1000V to 2000V.

[0032] The number of microchannel plate assemblies 7 depends on the gain requirements in engineering practice. It can be a single microchannel plate or multiple "V"-shaped cascades. In this embodiment, two microchannel plates are cascaded, and the input electrode of each microchannel plate faces the upper opening of the conical focusing barrel 83, and the output electrode faces the anode 4. The potential of the input electrode of the first microchannel plate should be higher than the potential of the conical focusing barrel 83, and the potential difference between the two is adjustable from 100 to 1000V. In order to obtain an ideal multiplication effect, so that the photomultiplier tube can obtain sufficient electron magnification when detecting weak light or performing single photon measurement counting, the bias voltage of the microchannel plate assembly 7 is adjustable from 600 to 1000V, and the gap voltage of the two microchannel plates is adjustable from 100 to 800V.

[0033] The anode 4 is a collector for multiplying electrons and receives the electron flow from the microchannel plate assembly 7. The anode 4 can be made of copper or other metal materials, and its area should be greater than or equal to the area of ​​the microchannel plate assembly 7, so as to better collect the electron flow from the microchannel plate assembly 7. The potential of the anode 4 should be the highest, and the potential difference with the output electrode of the last microchannel plate is generally adjustable at 50 to 500V.

[0034] The microchannel plate electron multiplication system and anode 4 are supported by an insulating rod 10, which is usually a ceramic frame. The photocathode 2, the electron focusing system 8, the supply electrode and the signal lead wire 9 required by the electron multiplication system and the anode 4 are placed in the insulating rod 10, and a fusion welding process can be used between the metal lead wire and the ceramic frame to maintain a vacuum seal.

[0035] In this way, when the working voltage is applied to the photocathode 2, the electron focusing system 8, the electron multiplying system and the anode 4, an accelerating and focusing electric field is formed between the photocathode 2, the electron focusing system 8 and the electron multiplying system, and the electron multiplying system and the anode 4 form a collecting electric field. The light vacuum glass container 1 enters the photocathode 2 to irradiate the photocathode 2 to generate photoelectrons, which are collected by the electron multiplying system under the accelerating and focusing of the focusing electric field. The electron flow after the electron multiplication and amplification enters the anode 4 under the acceleration of the collecting electric field, and the current signal after collection is output as the final signal.

[0036] According to the above embodiments, the structure and performance of the large-area microchannel plate photomultiplier tube are simulated using the finite integration method. Figure 5 As shown in the figure, the electric field distribution results show that: 1. The electric field exhibits obvious focusing properties, and the electrons emitted from the cathode surface will move toward the microchannel plate along the direction of the electric field lines. 2. The electric field distribution consistency from the cathode to the microchannel plate is high, which means that the electric field distribution along the path taken by the photoelectrons from the cathode to the microchannel plate is similar, resulting in a small dispersion of the electron transit time. 3. Except for the opening at the upper end of the conical focusing electrode, the electric fields generated by the microchannel plate and the anode are effectively shielded. The simulation results show that the photoelectron collection efficiency of the photomultiplier tube with this structure reaches 100% on the entire cathode surface; the electron transit time dispersion on the entire cathode surface can reach 1.2ns, which is more than 10 times higher than the above-mentioned mass-produced large-area microchannel plate photomultiplier tube, and more than 1 times higher than the large-area dynode photomultiplier tube with excellent performance.

[0037] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0038] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected.

Claims

1. A large-area microchannel plate photomultiplier tube with high temporal resolution, comprising: A vacuum glass container (1), a photocathode (2) for receiving light and generating photoelectrons, an electron focusing system (8) for accelerating and focusing the photoelectrons emitted from the photocathode (2), an electron multiplying system for collecting the photoelectrons accelerated and focused by the electron focusing system (8) and generating multiplied electrons, an anode (4) for collecting the multiplied electrons output by the electron multiplying system, and a power supply electrode for supplying power to the photocathode (2), the electron focusing system (8), the electron multiplying system and the anode (4); the photocathode (2), the electron focusing system (8), the electron multiplying system and the anode (4) are placed in the vacuum glass container (1); the anode (4) is connected to an external signal processing circuit via a signal lead passing through the vacuum glass container (1). The power supply electrode is connected to an external power supply circuit through a power line passing through the vacuum glass container (1), and is characterized in that the vacuum glass container (1) is a cylindrical barrel with a curved top, and the photocathode (2) evenly covers the inner surface of the curved surface; the electron focusing system (8) is coaxial with the center of the photocathode (2) and is placed directly below it, including 1 to 3 cylindrical focusing barrels and a first-level conical or spherical focusing barrel placed inside it, and all focusing barrels are open at the top and bottom; the electron multiplication system is a single-chip or multi-chip microchannel plate assembly (7), coaxial with the center of the photocathode (2), and placed near the upper end opening of the first-level conical or spherical focusing barrel; the anode (4) is placed in parallel to the back of the output electrode of the microchannel plate assembly (7), and its area is greater than or equal to that of the microchannel plate.

2. A large-area microchannel plate photomultiplier tube with high time resolution according to claim 1, characterized in that: The top curved surface of the vacuum glass container (1) may be a spherical surface or an ellipsoidal surface.

3. The large-area microchannel plate photomultiplier tube with high time resolution according to claim 1, characterized in that: In the electron focusing system (8), the first to third levels of cylindrical focusing barrels have the same diameter and height, and the diameter is equal to or slightly smaller than the photocathode (2).

4. The large-area microchannel plate photomultiplier tube with high time resolution according to claim 1, characterized in that: The conical or spherical focusing barrel in the electron focusing system (8) is narrow at the top and wide at the bottom, the diameter of the upper opening is equal to or slightly smaller than the microchannel plate assembly (7), the diameter of the lower opening is larger than the microchannel plate assembly (7) and smaller than 1 to 3 levels of cylindrical focusing barrels, and the height of the conical or spherical focusing barrel is not less than the thickness of the microchannel plate assembly (7) and the anode (4).

5. The large-area microchannel plate photomultiplier tube with high time resolution according to claim 1, characterized in that: The placement height of the conical or spherical focusing barrel requires that its upper edge should not exceed the upper edge of the first-stage cylindrical focusing barrel and should not be lower than the lower edge of the final-stage cylindrical focusing barrel.

6. The large-area microchannel plate photomultiplier tube with high time resolution according to claim 1, characterized in that: The electron focusing system (8), the microchannel plate electron multiplication system and the anode (4) are all coaxial with the center of the photocathode (2).

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