X-ray imaging diagnosis system based on Timepix3 detector

Abstract

The invention discloses an X-ray imaging diagnosis system based on a Timepix3 detector, and belongs to the technical field of plasma diagnosis. The system comprises a Timepix3 detector, a data server, an upper computer, a signal generator and a high-voltage power supply, the signal generator is used for performing remote control on the Timepix3 detector and providing pulses during plasma discharge to ensure that the Timepix3 detector acquires data in a trigger mode; the high-voltage power supply is used for providing bias voltage for a semiconductor sensor of the Timepix3 detector; the upper computer is used for sending an instruction to the Timepix3 detector to carry out data acquisition; and the data server is used for receiving and storing the collected data. The device can be applied to a plasma discharge experiment carried out in a Tokamak device, and has higher spatial resolution, stronger time resolution capability and capability of quickly acquiring an X-ray signal energy spectrum.

Description

Technical Field

[0001] The invention belongs to the technical field of plasma diagnosis, and in particular relates to an X-ray imaging diagnosis system based on a Timepix3 detector. Background Art The radiation during the plasma discharge process reflects the changes in electron density, temperature, and impurity levels, and the radiation signal can be transmitted to the outside of the plasma without attenuation. Therefore, plasma radiation measurement is an effective method for diagnosing many parameters of plasma. At present, the radiation signal measurement systems used in EAST (Experimental Advanced Superconducting Tokamak) are mostly detector arrays. The array system composed of multiple detectors has many advantages. The array detector has a simple structure, strong anti-interference ability, and the overall system is reliable and stable, but it is slightly inferior in spatial resolution performance and rapid acquisition of energy spectrum. The Timepix3 detector has multiple working modes such as counting mode and over-threshold time mode, and has event-driven capabilities. It can obtain information such as the number of X-rays and the energy and arrival time of each X-ray. These provide the possibility of obtaining the spatial distribution of X-rays and quickly acquiring energy spectra. Summary of the invention To solve the above technical problems, the present invention provides an X-ray imaging diagnostic system based on the Timepix3 detector, which can obtain the time evolution law and energy spectrum information of the radiation signal intensity, as well as the spatial distribution information of the radiation signal intensity at different times in the plasma discharge experiment in the Tokamak device. To achieve the above purpose, the technical solution adopted by the present invention is as follows: An X-ray imaging diagnostic system based on a Timepix3 detector, the system comprising a Timepix3 detector, a data server, a host computer, a signal generator, and a high-voltage power supply; wherein: The signal generator is used to remotely control the Timepix3 detector and provide pulses during plasma discharge to ensure that the Timepix3 detector collects data in a trigger mode; The high voltage power supply is used to provide a bias voltage for the semiconductor sensor of the Timepix3 detector; The host computer is used to send instructions to the Timepix3 detector to collect data; The data server is used to receive and save the collected data. Furthermore, the Timepix3 detector includes a semiconductor sensor and a Timepix3 readout chip, each pixel works independently, and each detected photon event is saved in the form of raw data. Furthermore, when the Timepix3 detector works in counting mode, it is used to obtain an image containing information on the count value of each pixel, obtain the evolution law of the X-ray signal intensity over time by calculating all pixel count values ​​within the exposure time of each frame of the image, and obtain the spatial distribution information of the X-ray signal by analyzing the size of the pixel count values ​​at different positions. Furthermore, the Timepix3 detector is used to obtain images and raw data containing energy information of each photon event when operating in the over-threshold time mode, and obtain the energy spectrum of the X-ray signal by analyzing the energy information of all detected photons. Furthermore, a metal protection box is provided outside the Timepix3 detector. The metal protection box uses four lead plates to cover the upper, lower, left and right sides of the rectangular Timepix3 detector respectively, and uses a tungsten plate to cover the front end face where the semiconductor sensor of the Timepix3 detector is located. The four lead plates and one tungsten plate are wrapped and fixed with five 316L stainless steel plates. Furthermore, a conical hole is opened in the center of the tungsten plate, the circular surface of the conical hole faces the Timepix3 detector, and the conical surface faces outward along the central axis of the tungsten plate to cover the sensitive area of ​​the sensor end of the Timepix3 detector. The beneficial effects of the present invention are: The Timepix3 detector is innovatively applied to the imaging diagnosis system, which has two working modes. When the Timepix3 detector works in the counting mode, it can obtain an image containing the number of detected X-ray photons. By calculating the number of X-ray photons detected during the image exposure time, the relative intensity of X-rays at a certain time point can be obtained. The time evolution law of X-ray intensity can be obtained according to the change in the number of X-ray photons in the image, and the spatial distribution information of X-rays can be obtained according to the number of photons detected by pixels at different positions. When the Timepix3 detector works in the over-threshold time mode, it can obtain an image containing X-ray photon energy information. By counting the number of photons of different energies in the image, the energy spectrum of X-rays can be obtained. Compared with the traditional detection array system, the Timepix3 imaging diagnosis system has higher spatial resolution, stronger time resolution and the ability to quickly obtain the energy spectrum of X-ray signals. In addition, a metal protection box is designed for the Timepix3 detector to ensure that the Timepix3 detector can work in a radiation environment. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 This is a structural diagram of an X-ray imaging diagnostic system based on a Timepix3 detector of the present invention; Figure 2 The field of view and top view of an X-ray imaging diagnostic system based on a Timepix3 detector of the present invention; Figure 3This is the structural diagram of the metal protection box; Figure 4 It is a schematic diagram of the location of the tapered hole; Figure 5 This is the working principle diagram of the detector in counting mode; Figure 6 It is a flow chart for obtaining the time evolution information of X-ray signal intensity in the detector counting mode; Figure 7 is the graph of X-ray signal intensity evolution over time; Figure 8 This is the working principle diagram of the detector over-threshold time mode; Fig. 9 Flow chart for obtaining X-ray energy spectrum in detector over-threshold time mode; Fig.10 This is the image collected in the detector over-threshold time mode; Fig.11 for 152 Cluster volume histogram of Eu. Reference numerals: 1. Timepix3 detector, 2. Copper bracket, 3. Lead plate, 4. Tungsten plate, 5. 316L stainless steel plate. DETAILED DESCRIPTION The present invention will be further described below in conjunction with the accompanying drawings and embodiments. like Figure 1 As shown, the X-ray imaging diagnostic system based on the Timepix3 detector consists of three parts: the Timepix3 detector 1, the data server, and the host computer. The Timepix3 detector 1 needs to be used with a high-voltage power supply and a signal generator. The signal generator can remotely control the Timepix3 detector 1 through the built-in web page, and provide pulses during plasma discharge to ensure that the Timepix3 detector 1 collects data normally in the trigger mode. The high-voltage power supply provides a bias voltage of -200V to -300V for the semiconductor sensor of the Timepix3 detector 1. When X-ray photons hit the semiconductor sensor, charges will be generated. The bias voltage can reduce the drift time of the charges and inhibit the diffusion of charges in adjacent pixels. The user uses the host computer in the control room to send instructions to the Timepix3 detector 1 to collect and save data. The collected data is transmitted to the data server via optical fiber for storage. The Timepix3 detector 1 is composed of a semiconductor sensor and a Timepix3 readout chip. The sensor material used is 1mm cadmium telluride, which has a high efficiency in detecting photons in the soft X-ray energy range. The Timepix3 detector 1 has event-driven capability, that is, each pixel can work independently and save each detected photon event in the form of raw data. like Figure 2As shown, a metal protection box is designed for the Timepix3 detector to shield the radiation generated during the plasma discharge process, ensuring that the Timepix3 detector can work in a radiation environment. The Timepix3 detector 1 and the metal protection box are placed in the F window of the EAST device to observe the middle and lower part of the cross section of the EAST vacuum chamber. Analysis shows that the field of view of the system of the present invention is ±16°, the image distance is 35mm, the object distance is 2500mm, and the spatial resolution is below 10mm: = = in is the spatial resolution, is the distance between pixels of the Timepix3 detector 1, is the object distance, For distance. like Figure 3 As shown, a schematic diagram of the specific structural design of the metal protection box is given. The Timepix3 detector 1 is a rectangular parallelepiped structure, including 6 end faces, including top, bottom, left, right, front and back. The lower end face is supported by a copper bracket 2 to facilitate heat conduction. The sensor end of the Timepix3 detector 1 is the front end face, which is covered with a 15mm thick tungsten plate 4. A conical hole with a diameter of 0.3mm and an angle of 32° is opened in the center of the tungsten plate 4. The conical hole is opposite to the sensor end of the Timepix3 detector 1 to ensure that the imaging surface covers the sensitive area of ​​the Timepix3 detector 1. Ideally, only rays within the field of view of the small hole (such as Figure 2 The radiation outside the field of view is blocked by the metal protection box. When the object distance is fixed, the spatial resolution can be adjusted by changing the diameter of the small hole and the image distance. The four end faces of the Timepix3 detector 1, upper, lower, left and right, are covered with lead plates 3 respectively. The lead plate 3 on the lower end face is set under the copper bracket 2 to fully wrap the Timepix3 detector 1. The outer layer of the tungsten plate 4 and the four lead plates 3 is wrapped by a 316L stainless steel plate 5, and finally fixed to form a double-layer metal protection box. like Figure 4 As shown, a conical hole is opened in the center of the tungsten plate 4, with the circular surface of the conical hole facing the Timepix3 detector and the conical surface facing outward along the central axis of the tungsten plate, ensuring that the light incident from the conical hole completely covers the sensitive area of ​​the sensor end of the Timepix3 detector 1. like Figure 5As shown, the Timepix3 detector 1 has a counting mode, which is the basic working mode of a photon counting detector. X-rays interact with semiconductors to generate electron-hole pairs, which are collected and processed by subsequent circuits. During the shutter time, if the intensity of the charge signal is greater than the set threshold, the pixel counter increases by 1 count, indicating that a photon with energy higher than the threshold is detected, otherwise there is no count. like Figure 6-Figure 7 As shown, Figure 6 This is a flow chart for obtaining the time evolution information of X-ray signal intensity in detector counting mode. Figure 7 This is a graph showing the evolution of X-ray signal intensity over time. The Timepix3 detector 1 collects images in counting mode and calculates the pixel count values ​​of the images at different time points to obtain the time evolution information of the X-ray signal. The count value represents the relative intensity of the X-ray signal. like Figure 8 As shown, the Timepix3 detector 1 has a Time-over-Threshold (ToT) mode, in which a counter starts when the signal exceeds the set threshold and stops when the signal strength drops back below the threshold. If multiple consecutive signals exceed the threshold at the same shutter time, the counts are accumulated. Since the time above the threshold is proportional to the input charge, ToT provides a direct estimate of the integrated energy of the shutter duration. The measurement result is the total amount of charge collected by a single pixel. like Fig. 9 As shown in the figure, the detector collects data in the over-threshold time mode and controls the exposure time to ensure that there is no overlap in the pixel clusters in the collected image. For each frame of the image, all pixel clusters in the image are searched and classified according to the size of the area, and the sum of all pixel count values ​​contained in each pixel cluster (pixel cluster volume) is calculated. The histograms of the volumes of pixel clusters of different areas are drawn according to the area size to obtain the energy spectrum of the X-rays. like Fig.10 As shown, it can be observed that all the energy of some photons is deposited in one detector pixel, which appears as a single independent pixel in the figure, and some photons deposit energy in multiple detector pixels, which appears as multiple adjacent pixels (a pixel cluster) in the figure. like Fig.11 As shown in the figure, in the over-threshold time mode, the measured energy spectrum is often counted according to the pixel cluster area. All pixel count values ​​in each pixel cluster are added together to obtain n values ​​(pixel cluster volume), and the statistical histogram of these n values ​​is the energy spectrum. The energy spectra corresponding to different pixel cluster areas are also different. The larger the pixel cluster volume, the greater the detected photon energy. All area pixel clusters include the 1st, 2nd, 3rd, and 4th area pixel clusters. The radiation during plasma discharge reflects the changes in electron density, temperature, and impurity levels, and the radiation signal can be transmitted to the outside of the plasma without attenuation. The X-ray diagnostic system based on Timepix3 can obtain information such as the time evolution, spatial distribution, and energy spectrum of the radiation signal. By analyzing the acquired signals, various parameters of the plasma can be diagnosed. The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An X-ray imaging diagnostic system based on Timepix3 detector, characterized in that: The system includes a Timepix3 detector, a data server, a host computer, a signal generator, and a high-voltage power supply; wherein, The signal generator is used to remotely control the Timepix3 detector and provide pulses during plasma discharge to ensure that the Timepix3 detector collects data in a trigger mode; The high voltage power supply is used to provide a bias voltage for the semiconductor sensor of the Timepix3 detector; The host computer is used to send instructions to the Timepix3 detector to collect data; The data server is used to receive and save the collected data.

2. The X-ray imaging diagnostic system based on the Timepix3 detector according to claim 1, characterized in that: The Timepix3 detector includes a semiconductor sensor and a Timepix3 readout chip. Each pixel works independently and saves each detected photon event in the form of raw data.

3. The X-ray imaging diagnostic system based on the Timepix3 detector according to claim 1, characterized in that: The Timepix3 detector is used to obtain images containing information on the count values ​​of each pixel when working in the counting mode. The evolution law of the X-ray signal intensity over time is obtained by calculating all pixel count values ​​within the exposure time of each frame of the image, and the spatial distribution information of the X-ray signal is obtained by analyzing the size of the pixel count values ​​at different positions.

4. The X-ray imaging diagnostic system based on the Timepix3 detector according to claim 1, characterized in that: The Timepix3 detector is used to obtain images and raw data containing energy information of each photon event when operating in the over-threshold time mode, and obtain the energy spectrum of the X-ray signal by analyzing the energy information of all detected photons.

5. The X-ray imaging diagnostic system based on the Timepix3 detector according to claim 1, characterized in that: A metal protection box is provided outside the Timepix3 detector. The metal protection box uses four lead plates to cover the upper, lower, left and right sides of the rectangular Timepix3 detector respectively, and uses a tungsten plate to cover the front end face where the semiconductor sensor of the Timepix3 detector is located. The four lead plates and one tungsten plate are wrapped and fixed with five 316L stainless steel plates on the outside.

6. The X-ray imaging diagnostic system based on the Timepix3 detector according to claim 5, characterized in that: A conical hole is opened in the center of the tungsten plate, the circular surface of the conical hole faces the Timepix3 detector, and the conical surface faces outward along the central axis of the tungsten plate to cover the sensitive area of ​​the sensor end of the Timepix3 detector.

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