Method for improving maximum linear current of micro-channel plate type photomultiplier and micro-channel plate type photomultiplier

Abstract

The invention relates to a micro-channel plate type photomultiplier, in particular to a method for improving the maximum linear current of the micro-channel plate type photomultiplier and the micro-channel plate type photomultiplier, and solves the problem that the maximum linear current of different areas of a micro-channel plate has local difference. And the overall maximum linear current value of the micro-channel plate type photomultiplier is relatively low. According to the method for improving the maximum linear current of the micro-channel plate type photomultiplier, the density of electrons entering each area of the micro-channel plate is modulated, so that all the areas enter a nonlinear output area at the same time, and the large-current output capability of the micro-channel plate is utilized to the maximum extent; therefore, the maximum linear current of the micro-channel plate photomultiplier is improved. The invention further provides a micro-channel plate type photomultiplier tube, the photoelectric cathode adopts a convex surface structure and is matched with the plane structure of the micro-channel plate, modulation of electrons emitted by the photoelectric cathode is achieved, and therefore modulation of the density of the electrons incident to all areas of the micro-channel plate is achieved.

Description

Technical Field

[0001] The invention relates to a microchannel plate type photomultiplier tube, and in particular to a method for increasing the maximum linear current of the microchannel plate type photomultiplier tube and the microchannel plate type photomultiplier tube. Background Art

[0002] Photomultiplier tubes (PMTs) are commonly used photodetection devices that convert weak light signals into instrumentally recordable electrical signals, enabling effective detection of these signals. They are widely used in the nuclear industry, medicine, chemical engineering, astronomical research, and other fields. In the nuclear industry's pulsed radiation field diagnostics, a combination of scintillators and PMTs is often used to detect pulsed radiation signals. Due to the long duration of pulsed radiation, PMTs must possess high sensitivity, a wide dynamic range, and a long measurement time width. The maximum linear current is a key parameter characterizing the dynamic range of a PMT. Within a certain range, the output current of a PMT is linearly related to the input light intensity. However, as the input light intensity increases to a certain level, the output current gradually deviates from this linear relationship, resulting in a nonlinear effect. The maximum linear current is generally defined as the output current at which the PMT deviates from linearity by 5% or 10%.

[0003] Currently, the methods for increasing the maximum linear current of photomultiplier tubes are mainly aimed at electron multipliers. For microchannel plate photomultiplier tubes, the methods for increasing their maximum linear current are mainly as follows:

[0004] (1) Selecting a microchannel plate with high current output capability and performing secondary processing on the secondary electron emission layer of the microchannel plate;

[0005] (2) Finely match the operating voltage of the microchannel plate to suppress the influence of space charge effect;

[0006] (3) Take measures such as voltage stabilization and current supplement through external power supply circuit.

[0007] The above methods can all effectively increase the maximum linear current of an MCP-type photomultiplier tube (PMT). However, an MCP with tens of thousands of microchannels can easily cause local variations in electron multiplication characteristics, which in turn can lead to local variations in the maximum linear current. Under the same electron input density, regions with low maximum linear currents deviate from linearity earlier, causing the PMT's overall output current to deviate (even though regions with high maximum linear currents are still operating in the linear amplification region). This fails to fully utilize the MCP's high-current output characteristics, resulting in the PMT's maximum linear current being far lower than expected. Summary of the Invention

[0008] The purpose of the present invention is to solve the technical problem that the maximum linear current of different areas of a microchannel plate has local differences, resulting in a low overall maximum linear current value of a microchannel plate photomultiplier tube, and to provide a method for increasing the maximum linear current of a microchannel plate photomultiplier tube and a microchannel plate photomultiplier tube.

[0009] To achieve the above object, the technical solution adopted by the present invention is:

[0010] A method for increasing the maximum linear current of a microchannel plate photomultiplier tube, wherein the microchannel plate photomultiplier tube comprises an incident window, a photocathode, a microchannel plate, and an anode arranged in sequence, and the method is special in that it comprises the following steps:

[0011] Step 1: Test and record the maximum linear current values ​​of the microchannel plate regions corresponding to different regions of the photocathode incident surface when the incident areas are the same, to obtain test data;

[0012] Step 2: normalize the test data based on the maximum value in the test data to obtain the proportional relationship between the maximum linear currents in different areas of the microchannel plate;

[0013] Step 3: Based on the proportional relationship between the maximum linear currents in different areas of the microchannel plate, the electron density incident on different areas of the microchannel plate is modulated so that the proportional relationship between the electron density incident on different areas of the microchannel plate is equal to the proportional relationship between the maximum linear currents in different areas of the microchannel plate, thereby increasing the maximum linear current of the microchannel plate photomultiplier tube.

[0014] Furthermore, in step 3, the specific method of modulating the electron density incident on different areas of the microchannel plate is:

[0015] Modulating the shape of the electron emission surface of the photocathode region corresponding to different regions of the microchannel plate, the distance between the photocathode and the microchannel plate, and the voltage difference between the photocathode and the microchannel plate;

[0016] Alternatively, the transmittance of different regions of the microchannel plate corresponding to the incident window glass substrate region is modulated;

[0017] Alternatively, a modulation electrode is provided between the photocathode and the microchannel plate.

[0018] Furthermore, in step 3, the specific method of modulating the shape of the electron emission surface of the photocathode area corresponding to different areas of the microchannel plate, the distance between the photocathode and the microchannel plate, and the voltage difference between the photocathode and the microchannel plate is:

[0019] First, an electron optics simulation software was used to establish a photocathode-emission electron beam model including the photocathode and the microchannel plate, and the electron density incident on different regions of the microchannel plate in the photocathode-emission electron beam model was calculated;

[0020] Second, with the proportional relationship between the maximum linear currents in different areas of the microchannel plate as the goal, the shape of the electron emission surface in different areas of the photocathode, the distance between the photocathode and the microchannel plate, and the voltage difference between the photocathode and the microchannel plate are adjusted, and the electron density incident on different areas of the microchannel plate under different conditions is calculated until the proportional relationship between the electron density incident on different areas of the microchannel plate is equal to the proportional relationship between the maximum linear currents in different areas of the microchannel plate.

[0021] Furthermore, step 1 is specifically as follows:

[0022] Step 1.1, dividing the incident surface of the photocathode into N regions, and then placing an aperture in one of the regions of the incident surface of the photocathode so that only the aperture passes light on the incident surface of the photocathode; wherein N is an integer and 4≤N≤10;

[0023] Step 1.2, applying an operating voltage to the photomultiplier tube, testing the maximum linear current value of the photomultiplier tube, and obtaining the maximum linear current value of the microchannel plate region corresponding to the region of the photocathode incident surface;

[0024] Step 1.3: Move the aperture to another area of ​​the photocathode incident surface.

[0025] Step 1.4: Repeat steps 1.2 to 1.3 until N regions of the incident surface of the photocathode are traversed to obtain the maximum linear current value of each region of the microchannel plate, i.e., the test data.

[0026] Furthermore, in step 1.1, the light-transmitting area of ​​the aperture is smaller than 1 / 10 of the effective area of ​​the photocathode.

[0027] The present invention also provides a microchannel plate type photomultiplier tube for implementing the above-mentioned method of increasing the maximum linear current of a microchannel plate type photomultiplier tube, comprising an incident window, a photocathode, a microchannel plate, and an anode arranged in sequence, wherein the microchannel plate type photomultiplier tube has the following characteristics:

[0028] The photocathode comprises a cylindrical substrate and a convex structure; the convex structure is conical and located at the center of the exit surface of the cylindrical substrate; the convex structure is used to adjust the electron density emitted by different regions of the photocathode so that the proportional relationship between the electron densities emitted by different regions of the photocathode is equal to the proportional relationship between the maximum linear currents of the corresponding microchannel plate regions;

[0029] Alternatively, the glass substrate of the incident window is composed of filters with different transmittances, and the proportional relationship between the transmittances of the filters is equal to the proportional relationship between the maximum linear currents of the corresponding microchannel plate regions;

[0030] Alternatively, a modulation electrode is provided between the photocathode and the microchannel plate, and the modulation electrode is used to adjust the electron density incident to different areas of the microchannel plate so that the proportional relationship between the electron densities incident to different areas of the microchannel plate is equal to the proportional relationship between the maximum linear currents of the corresponding microchannel plate areas.

[0031] Furthermore, the diameter of the cylindrical base is 18 mm;

[0032] The diameter of the convex structure is 14 mm, the height is 4 mm, and the distance between the convex structure and the microchannel plate is 4 mm.

[0033] Furthermore, the voltage of the microchannel plate is higher than that of the photocathode, and the voltage difference between the two is 200V.

[0034] Compared with the prior art, the present invention has the following beneficial technical effects:

[0035] 1. The present invention provides a method for increasing the maximum linear current of a microchannel plate-type photomultiplier tube. This method modulates the incident electron density of each region of the microchannel plate to address differences in the maximum linear current values ​​of different regions of the microchannel plate, allowing all regions of the microchannel plate to simultaneously enter the nonlinear output region. This maximizes the high current output capability of the microchannel plate, thereby increasing the maximum linear current of the microchannel plate photomultiplier tube.

[0036] 2. The present invention provides a microchannel plate type photomultiplier tube, in which the photocathode adopts a convex structure that matches the planar structure of the microchannel plate, thereby modulating the electron emission of the photocathode so that the ratio of the electron density incident on different areas of the microchannel plate is equal to the ratio of the maximum linear current values ​​of the corresponding microchannel plate areas, thereby increasing the maximum linear current of the microchannel plate photomultiplier tube. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a flow chart of a method for increasing the maximum linear current of a microchannel plate photomultiplier tube according to an embodiment of the present invention;

[0038] Figure 2 Schematic diagram of the test position of the aperture in step 1.1 of the method for increasing the maximum linear current of a microchannel plate photomultiplier tube according to an embodiment of the present invention;

[0039] Figure 3 This is a statistical graph of test data obtained in step 1 of the method for increasing the maximum linear current of a microchannel plate photomultiplier tube in an embodiment of the present invention;

[0040] Figure 4 Schematic diagram of the structure of the photocathode and microchannel plate in a microchannel plate photomultiplier tube in an embodiment of the present invention. DETAILED DESCRIPTION

[0041] The following is a further detailed description of a method for increasing the maximum linear current of a microchannel plate photomultiplier tube and a microchannel plate photomultiplier tube proposed in the present invention, in conjunction with the accompanying drawings and specific embodiments. It should be understood by those skilled in the art that these embodiments are merely intended to explain the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0042] A method for increasing the maximum linear current of a microchannel plate type photomultiplier tube, wherein the microchannel plate type photomultiplier tube comprises an incident window, a photocathode, a microchannel plate and an anode arranged in sequence, such as Figure 1 As shown, the following steps are included:

[0043] Step 1: Test and record the maximum linear current values ​​of the microchannel plate areas corresponding to different areas of the photocathode incident surface when the incident area is the same, and obtain test data. Specifically:

[0044] Step 1.1: Divide the photocathode incident surface into five zones: east, south, west, north, and center. Then, place an aperture in one of these zones so that only the aperture passes through the photocathode incident surface. The light-transmitting area of ​​the aperture should be less than 1 / 10 of the photocathode's effective area.

[0045] Step 1.2: Apply an operating voltage to the photomultiplier tube, test the maximum linear current value of the photomultiplier tube, and obtain the maximum linear current value of the microchannel plate area corresponding to the area on the photocathode incident surface.

[0046] Step 1.3: Move the aperture to another area of ​​the incident surface of the photocathode.

[0047] Step 1.4, repeat steps 1.2-1.3 until the five areas of the incident surface of the photocathode are traversed, and the maximum linear current value of each area of ​​the microchannel plate is obtained, which is the test data. The position of the aperture after five tests is as follows Figure 2 shown.

[0048] like Figure 3 As shown, there are individual differences in the maximum linear current values ​​in different areas of the microchannel plate. The maximum linear current values ​​in the edge area and the center area are quite different, and the maximum linear current value in the edge area is higher than that in the center area.

[0049] Step 2: normalize the test data based on the maximum value in the test data to obtain the proportional relationship between the maximum linear currents in different areas of the microchannel plate.

[0050] Step 3: Based on the proportional relationship between the maximum linear currents in different areas of the microchannel plate, the electron density incident on different areas of the microchannel plate is modulated so that the proportional relationship between the electron density incident on different areas of the microchannel plate is equal to the proportional relationship between the maximum linear currents in different areas of the microchannel plate, thereby increasing the maximum linear current of the microchannel plate photomultiplier tube.

[0051] The specific method for modulating the electron density incident on different regions of the microchannel plate is as follows:

[0052] Modulating the shape of the electron emission surface corresponding to the photocathode area of ​​different areas of the microchannel plate, the distance between the photocathode and the microchannel plate, and the voltage difference between the photocathode and the microchannel plate, the specific method is as follows:

[0053] First, an electron optics simulation software was used to establish a photocathode-emission electron beam model including the photocathode and the microchannel plate, and the electron density incident on different regions of the microchannel plate in the photocathode-emission electron beam model was calculated;

[0054] Second, with the proportional relationship between the maximum linear currents in different areas of the microchannel plate as the goal, the shape of the electron emission surface in different areas of the photocathode, the distance between the photocathode and the microchannel plate, and the voltage difference between the photocathode and the microchannel plate are adjusted, and the electron density incident on different areas of the microchannel plate under different conditions is calculated until the proportional relationship between the electron density incident on different areas of the microchannel plate is equal to the proportional relationship between the maximum linear currents in different areas of the microchannel plate.

[0055] In other embodiments, the electron density incident on different areas of the microchannel plate may be modulated by modulating the transmittance of different areas of the microchannel plate corresponding to the incident window glass substrate area, or by setting a modulation electrode between the photocathode and the microchannel plate.

[0056] Based on the proportional relationship between the maximum linear currents of different regions of the microchannel plate obtained after normalizing the test results, step 3 of this embodiment reduces the number of incident electrons in regions with smaller maximum linear current values ​​of the microchannel plate, and increases the number of incident electrons in regions with larger maximum linear current values. This allows different regions of the microchannel plate to operate in the linear region and simultaneously reach the nonlinear output region, effectively utilizing the high current output performance of the microchannel plate and improving the overall maximum linear current value of the microchannel plate-type photomultiplier tube.

[0057] Because the output waveform of an MCP PMT is a linear superposition of the output waveforms from each region of the MCP, without electron density modulation, under the same incident light conditions, the MCP region with the largest maximum linear current is far from reaching saturation, while the MCP region with the smallest maximum linear current has already experienced waveform distortion, leading to a nonlinear output current characteristic for the MCP PMT as a whole and a low maximum linear current value for the MCP PMT as a whole. After electron density modulation in this embodiment, the maximum linear current values ​​in different regions of the MCP are proportional to the input charge, causing each region of the MCP to exhibit saturation characteristics simultaneously. This allows the maximum linear current value of each region of the MCP to reach its limit, greatly improving the maximum linear current value of the MCP PMT.

[0058] This embodiment also provides a microchannel plate type photomultiplier tube, based on the above method of increasing the maximum linear current of the microchannel plate type photomultiplier tube, comprising an incident window, a photocathode, a microchannel plate and an anode arranged in sequence. Figure 4 As shown, the photocathode comprises a cylindrical substrate and a convex structure. The convex structure is conical and located at the center of the cylindrical substrate's exit surface. The convex structure is used to adjust the electron density emitted from different regions of the photocathode, so that the ratio of the electron density emitted from different regions of the photocathode is equal to the ratio of the maximum linear current of the corresponding microchannel plate region.

[0059] according to Figure 3 The proportional relationship between the maximum linear currents in different regions of the microchannel plate is shown. Electron optics simulation software was used to design the photocathode's structural and electrical parameters: the cylindrical base has an 18mm diameter, the convex structure has a 14mm diameter and a height of 4mm, and the distance between the convex structure and the microchannel plate is 4mm. The voltage applied to the microchannel plate is higher than that applied to the photocathode, with a voltage difference of 200V.

[0060] In other embodiments, the glass substrate of the incident window can be formed from filters of different transmittances, with the ratio of the transmittances of the filters equal to the ratio of the maximum linear currents of their corresponding microchannel plate regions. A modulation electrode can also be disposed between the photocathode and the microchannel plate to adjust the electron density incident on different regions of the microchannel plate, such that the ratio of the electron density incident on different regions of the microchannel plate is equal to the ratio of the maximum linear currents of their corresponding microchannel plate regions. The method for disposing the modulation electrode can be referred to the applicant's authorized Chinese patent CN108257844A.

Claims

1. A method for increasing the maximum linear current of a microchannel plate photomultiplier tube, wherein the microchannel plate photomultiplier tube comprises an incident window, a photocathode, a microchannel plate, and an anode arranged in sequence, characterized in that: The following steps are involved: Step 1: Test and record the maximum linear current values ​​of the microchannel plate regions corresponding to different regions of the photocathode incident surface when the incident areas are the same, to obtain test data; Step 2: normalize the test data based on the maximum value in the test data to obtain the proportional relationship between the maximum linear currents in different areas of the microchannel plate; Step 3: Based on the proportional relationship between the maximum linear currents in different areas of the microchannel plate, the electron density incident on different areas of the microchannel plate is modulated so that the proportional relationship between the electron density incident on different areas of the microchannel plate is equal to the proportional relationship between the maximum linear currents in different areas of the microchannel plate, thereby increasing the maximum linear current of the microchannel plate photomultiplier tube.

2. The method for increasing the maximum linear current of a microchannel plate photomultiplier tube according to claim 1, characterized in that: In step 3, the specific method of modulating the electron density incident on different areas of the microchannel plate is: Modulating the shape of the electron emission surface of the photocathode region corresponding to different regions of the microchannel plate, the distance between the photocathode and the microchannel plate, and the voltage difference between the photocathode and the microchannel plate; Alternatively, the transmittance of different regions of the microchannel plate corresponding to the incident window glass substrate region is modulated; Alternatively, a modulation electrode is provided between the photocathode and the microchannel plate.

3. The method for increasing the maximum linear current of a microchannel plate photomultiplier tube according to claim 2, characterized in that: In step 3, the specific method of modulating the electron emission surface shape of the photocathode area corresponding to different areas of the microchannel plate, the distance between the photocathode and the microchannel plate, and the voltage difference between the photocathode and the microchannel plate is as follows: First, an electron optics simulation software was used to establish a photocathode-emission electron beam model including the photocathode and the microchannel plate, and the electron density incident on different regions of the microchannel plate in the photocathode-emission electron beam model was calculated; Second, with the proportional relationship between the maximum linear currents in different areas of the microchannel plate as the goal, the shape of the electron emission surface in different areas of the photocathode, the distance between the photocathode and the microchannel plate, and the voltage difference between the photocathode and the microchannel plate are adjusted, and the electron density incident on different areas of the microchannel plate under different conditions is calculated until the proportional relationship between the electron density incident on different areas of the microchannel plate is equal to the proportional relationship between the maximum linear currents in different areas of the microchannel plate.

4. A method for increasing the maximum linear current of a microchannel plate photomultiplier tube according to any one of claims 1 to 3, characterized in that: Step 1 is as follows: Step 1.1, dividing the incident surface of the photocathode into N regions, and then placing an aperture in one of the regions of the incident surface of the photocathode so that only the aperture passes light on the incident surface of the photocathode; wherein N is an integer and 4≤N≤10; Step 1.2, applying an operating voltage to the photomultiplier tube, testing the maximum linear current value of the photomultiplier tube, and obtaining the maximum linear current value of the microchannel plate region corresponding to the region of the photocathode incident surface; Step 1.3: Move the aperture to another area of ​​the photocathode incident surface. Step 1.4: Repeat steps 1.2 to 1.3 until N regions of the incident surface of the photocathode are traversed to obtain the maximum linear current value of each region of the microchannel plate, i.e., the test data.

5. The method for increasing the maximum linear current of a microchannel plate photomultiplier tube according to claim 4, characterized in that: In step 1.1, the light-transmitting area of ​​the aperture is smaller than 1 / 10 of the effective area of ​​the photocathode.

6. A microchannel plate photomultiplier tube, used to implement the method of increasing the maximum linear current of a microchannel plate photomultiplier tube according to any one of claims 1 to 5, comprising an incident window, a photocathode, a microchannel plate, and an anode arranged in sequence, characterized in that: The photocathode comprises a cylindrical substrate and a convex structure; the convex structure is conical and located at the center of the exit surface of the cylindrical substrate; the convex structure is used to adjust the electron density emitted by different regions of the photocathode so that the proportional relationship between the electron densities emitted by different regions of the photocathode is equal to the proportional relationship between the maximum linear currents of the corresponding microchannel plate regions; Alternatively, the glass substrate of the incident window is composed of filters with different transmittances, and the proportional relationship between the transmittances of the filters is equal to the proportional relationship between the maximum linear currents of the corresponding microchannel plate regions; Alternatively, a modulation electrode is provided between the photocathode and the microchannel plate, and the modulation electrode is used to adjust the electron density incident to different areas of the microchannel plate so that the proportional relationship between the electron densities incident to different areas of the microchannel plate is equal to the proportional relationship between the maximum linear currents of the corresponding microchannel plate areas.

7. The microchannel plate photomultiplier tube according to claim 6, characterized in that: The diameter of the cylindrical base is 18 mm; The diameter of the convex structure is 14 mm, the height is 4 mm, and the distance between the convex structure and the microchannel plate is 4 mm.

8. The microchannel plate photomultiplier tube according to claim 7, characterized in that: The voltage of the microchannel plate is higher than that of the photocathode, and the voltage difference between the two is 200V.

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