A method to improve the evaluation of magnetic field stability of small cyclotron

Abstract

The present application relates to the field of magnetic field stability measurement technology, and specifically to a method for improving the evaluation of magnetic field stability of a small cyclotron, the method comprising: obtaining the current data of each coil in the cyclotron, the temperature data of the ferromagnetic field, and the magnetic field strength data of each point in real time; obtaining the current influence coefficient and the temperature influence coefficient of each monitoring period according to the current change characteristics and temperature change characteristics of each coil in each monitoring period, and obtaining the disturbance coefficient of each monitoring period in combination with the degree of mutual dependence between the current influence coefficient and the temperature influence coefficient in each monitoring period, and obtaining the instability coefficient of each monitoring period in combination with the change characteristics of the magnetic field strength data in each monitoring period, and then evaluating the magnetic field stability. The present application improves the accuracy of the evaluation results of the magnetic field stability of the cyclotron by comprehensively analyzing the influence of current data, temperature data, and magnetic field strength data on magnetic field stability.

Description

Technical Field

[0001] The present application relates to the technical field of magnetic field stability measurement, and in particular to a method for improving the magnetic field stability evaluation of a small cyclotron accelerator. Background Art

[0002] Medical cyclotrons, as clinical devices, have seen increased use in recent years, primarily in providing different positron nuclides for positron emission tomography (PET). During normal accelerator operation, the ion source gas is ionized into a plasma. This ion is then extracted through oscillating radio frequency (RF) and accelerated into an acceleration trajectory. Accelerator electrodes and an external magnetic field combine to accelerate the ions, resulting in target bombardment and nuclear reactions. Cyclotrons themselves have high performance requirements, making beam stability crucial during operation.

[0003] High-quality, efficient beam extraction depends on multiple factors, among which magnetic field stability plays a crucial role. During operation, magnetic field stability is susceptible to changes in the shape and ferromagnetic properties of the ferromagnetic material. The entire magnet has a complex configuration, and even small deformations can cause significant changes in the magnetic field. The strong electromagnetic attraction generated by high currents can also cause deformation. Ferromagnetic properties vary with temperature, which reduces magnetic field stability. Furthermore, the interaction between current and temperature changes complicates the evaluation of magnetic field stability. Patent application CN112240993B, "Evaluation System and Method for Compact Cyclotron Magnetic Field Stability Measurement," evaluates the stability of the power supply system, water cooling system, and ambient temperature and humidity individually, but fails to fully consider the complex interactions between these factors, resulting in an inaccurate evaluation of magnetic field stability. Currently, commonly used methods for evaluating magnetic field stability often focus solely on the individual effects of each factor, failing to fully consider the specific variations and interactions between these factors. This results in inaccurate magnetic field stability evaluation. Summary of the Invention

[0004] In order to solve the above technical problems, the present application provides a method for improving the magnetic field stability evaluation of a small cyclotron to solve the existing problems.

[0005] A method for improving the magnetic field stability evaluation of a small cyclotron in the present application adopts the following technical solution:

[0006] One embodiment of the present application provides a method for improving the magnetic field stability evaluation of a small cyclotron, the method comprising the following steps:

[0007] Real-time acquisition of current data of each coil in the cyclotron, temperature data of ferromagnetic field, and magnetic field strength data of each point;

[0008] The data acquisition time is evenly divided into multiple monitoring periods; the current data of each coil in each monitoring period is divided into a step current data segment and a steady-state current data segment according to the curvature and slope corresponding to each current data point of each coil in each monitoring period; the current influence coefficient of each monitoring period is obtained according to the discrete degree of data in all steady-state current data segments of each coil in each monitoring period, the average level of the total time length of all step current data segments of all coils, and the average level of coordination between the current data of all arbitrary two coils;

[0009] The temperature influence coefficient of each monitoring period is obtained based on the significance, average level and dispersion of the temperature data in each monitoring period; the disturbance coefficient of each monitoring period is obtained based on the mutual dependence between the current influence coefficient and the temperature influence coefficient in each monitoring period and the preset number of monitoring periods before it, as well as the current influence coefficient and temperature influence coefficient of each monitoring period;

[0010] According to the degree of discreteness of the magnetic field strength data of all points at each moment in each monitoring period, and the degree of similarity between the magnetic field strength data of all points at adjacent moments, the disorder coefficient of each monitoring period is obtained. Combined with the disturbance coefficient of each monitoring period, the instability coefficient of each monitoring period is obtained, and the magnetic field stability is evaluated.

[0011] Preferably, the specific process of evenly dividing the data collection time into multiple monitoring periods is: starting from the moment when data collection starts, every t minutes is a monitoring period, and the data collection time is evenly divided into multiple monitoring periods, where t is a preset time length.

[0012] Preferably, the process of dividing the current data of each coil in each monitoring period into a step current data segment and a steady-state current data segment is:

[0013] Obtaining the curvature and slope of each current data point of each coil in each monitoring period;

[0014] Calculate the curvature mean of all current data points of each coil in each monitoring period, and take the data point whose curvature in the current data of each coil in each monitoring period is greater than the curvature mean as the step change endpoint;

[0015] If the absolute value of the slope mean of all current data points between two adjacent step change endpoints in the current data of each coil in each monitoring period is greater than the preset slope threshold, the current data between the two adjacent step change endpoints is recorded as a step current data segment; otherwise, the current data between the two adjacent step change endpoints is recorded as a steady-state current data segment.

[0016] Preferably, the process of obtaining the current influence coefficient of each monitoring period is:

[0017] Obtaining the non-steady-state coefficient of each coil in each monitoring period according to the discrete degree of data in all steady-state current data segments of each coil in each monitoring period;

[0018] The calculation formula of the current influence coefficient in each monitoring period is: Where, is the current influence coefficient of the i-th monitoring period, is the cumulative sum of the non-steady-state coefficients of all coils in the i-th monitoring period, is the average of the total time length of all coils in all step current data segments during the i-th monitoring period, is the mean of the maximum mutual information coefficients between the current data of any two coils in the i-th monitoring period.

[0019] Preferably, the non-steady-state coefficient of each coil in each monitoring period refers to the variance of the current data in all steady-state current data segments of each coil in each monitoring period.

[0020] Preferably, the calculation formula for the temperature influence coefficient of each monitoring period is: Where, is the temperature influence coefficient of the i-th monitoring period, is the statistical value z of the temperature data change trend in the i-th monitoring period, exp( ) is the exponential function with the natural constant e as the base, is the product of the mean and variance of the temperature data in the i-th monitoring period; The acquisition process is as follows: the temperature data of the ferromagnetic element in the i-th monitoring period is used as the input of the Mann-Kendall test algorithm, and the statistical value z of the temperature data change trend in the monitoring period is output.

[0021] Preferably, the calculation formula of the disturbance coefficient of each monitoring period is: Where, is the disturbance coefficient of the i-th monitoring period, is the Hoeffding's D coefficient between all current influence coefficients and temperature influence coefficients in the i-th monitoring period and its previous N monitoring periods, where N is a preset number. 、 are the current influence coefficient and temperature influence coefficient of the i-th monitoring period respectively.

[0022] Preferably, the process for obtaining the disorder coefficient of each monitoring period is as follows: calculate the variance of the magnetic field intensity data at all points at each moment; calculate the Jaccard similarity coefficient between all magnetic field intensity data corresponding to all adjacent moments within each monitoring period; take the ratio of the sum of the variances of all moments within each monitoring period to the sum of all Jaccard similarity coefficients as the disorder coefficient of each monitoring period.

[0023] Preferably, the instability coefficient of each monitoring period refers to the product of the perturbation coefficient and the disorder coefficient of each monitoring period.

[0024] Preferably, the specific process for evaluating the magnetic field stability is as follows: set the magnetic field stability evaluation interval: [0, a] indicates good magnetic field stability, (a, b) indicates general magnetic field stability, [b, 1] indicates poor magnetic field stability, where a is a preset first threshold, b is a preset second threshold, and 0 < a < b < 1; obtain the magnetic field stability evaluation results of each monitoring period according to the evaluation interval where the normalized instability coefficient of each monitoring period is located.

[0025] This application has at least the following beneficial effects:

[0026] This application proposes a method for improving the evaluation of the magnetic field stability of a small cyclotron. By deeply analyzing the specific influence characteristics of current changes and temperature changes on the magnetic field stability, and then fully considering the disturbance degree of the interaction between the two on the magnetic field stability, the perturbation coefficient under the combined action of multiple factors is calculated. Its advantage is that it more comprehensively analyzes the influence of each factor on the magnetic field stability; and further combines the spatial difference and time-varying abnormal characteristics of the magnetic field intensity itself, calculates the instability coefficient, and evaluates the stability of the magnetic field based on this value, making the stability evaluation result more comprehensive and helping to make up for the deficiency in the accuracy of the magnetic field stability evaluation. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions and advantages in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0028] Figure 1 It is a flowchart of the steps of a method for improving the evaluation of the magnetic field stability of a small cyclotron provided by the present application;

[0029] Figure 2 It is a flowchart for obtaining the non-temperature coefficient of each monitoring period provided by the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] To further illustrate the technical means and effectiveness of this application's implementation of the intended invention, the following, in conjunction with the accompanying drawings and preferred embodiments, details the specific implementation, structure, features, and effectiveness of a method for improving the magnetic field stability evaluation of a small cyclotron accelerator proposed in this application. In the following description, references to different "one embodiment" or "another embodiment" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics of one or more embodiments may be combined in any suitable manner.

[0031] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0032] The following describes in detail a specific solution of a method for improving the magnetic field stability evaluation of a small cyclotron provided by the present application with reference to the accompanying drawings.

[0033] One embodiment of the present application provides a method for improving the magnetic field stability evaluation of a small cyclotron accelerator. Specifically, the following method for improving the magnetic field stability evaluation of a small cyclotron accelerator is provided. Figure 1 , the method comprises the following steps:

[0034] Step 1: Real-time acquisition of current data of each coil in the cyclotron, temperature data of the ferromagnetic field, and magnetic field strength data at each point.

[0035] During the operation of a small cyclotron, magnetic field changes are primarily related to changes in the shape and ferromagnetic properties of the ferromagnetic material. Among these factors, the strong electromagnetic attraction generated by large currents, the magnet's own gravity, and the atmospheric pressure caused by the vacuum inside the magnet can all cause the magnet to deform. Because the current changes frequently and with large amplitudes, the effect on magnet deformation is relatively significant. Furthermore, unstable current fluctuations directly affect the strength and uniformity of the magnetic field, leading to a decrease in the stability of the cyclotron's magnetic field. Furthermore, the thermal effects of beam losses can cause the temperature of the ferromagnetic material to change, thereby altering its magnetization curve. Therefore, temperature is also a significant factor affecting magnetic field stability.

[0036] Given this, the signal acquisition unit of the device in this application acquires the current of each coil in the cyclotron and the temperature of the ferromagnetic material in real time. It randomly samples k points on the plane of the cyclotron's main magnet and acquires magnetic field strength data at each point in real time. In this embodiment, k is 30. All types of data are collected synchronously, with a data collection interval of 1 second. At this point, current data for each coil in the cyclotron, ferromagnetic temperature data, and magnetic field strength data at each point can be obtained.

[0037] Step 2: Evenly divide the data acquisition time into multiple monitoring periods; divide the current data of each coil in each monitoring period into step current data segments and steady-state current data segments according to the curvature and slope corresponding to each current data point of each coil in each monitoring period; obtain the current influence coefficient of each monitoring period based on the discrete degree of data in all steady-state current data segments of each coil in each monitoring period, the average level of the total time length of all step current data segments of all coils, and the average level of coordination between the current data of any two coils.

[0038] The principle of a cyclotron is to use a magnetic field to constrain charged particles to move along a circular orbit, causing them to repeatedly pass through a high-frequency accelerating electric field until they are accelerated to the required energy. A stable magnetic field needs to be maintained to keep the cyclotron frequency of the particles constant, thereby achieving a stable acceleration process. In addition, during the acceleration process, the particle beam needs to be focused in the axial direction. In order to improve the axial focusing force of the particle motion, the small cyclotron in this application uses a spiral fan-shaped magnetic pole structure to improve the beam quality, wherein each fan-shaped structure corresponds to a coil. If the current changes between different coils are not coordinated, the uniformity of the magnetic field will be seriously affected. In addition, the thermal effects caused by beam loss and current changes will cause the temperature of the ferromagnetic material to change, reducing the stability of the magnetic field. The stability of the magnetic field is affected by a combination of factors, and the interaction between the multiple factors further exacerbates the complexity of the stability evaluation. This application conducts a comprehensive assessment of the stability of the magnetic field by analyzing the specific change characteristics of different factors and the interaction between the factors.

[0039] First, the magnetic field strength is directly proportional to the coil current. This relationship is widely used in cyclotron magnetic field regulation, and the steady state of the coil current directly affects the stability of the magnetic field. Furthermore, in an isochronous cyclotron, to maintain a constant cyclotron period for the particles, regardless of energy changes, the radial distribution of the magnetic field must be altered by adjusting the coil current to compensate for the relativistic increase in particle mass. Therefore, the coil current is precisely controlled based on the particle's energy and orbital radius. However, current changes can cause eddy current effects. These eddy current effects significantly prolong the time it takes for the magnetic field to reach one steady state, hindering magnetic field stability. The rate of change of the coil current is the most significant factor influencing the eddy current effect. The longer the current rise time during the adjustment process, the less conducive it is to rapid magnetic field stabilization. Furthermore, the less coordinated the current changes between different coils, the more unbalanced the magnetic field state in the cyclotron. Based on these characteristics, the following processing is performed.

[0040] The operation of a small cyclotron accelerator is a negative feedback control process, with the current undergoing dynamic changes. The dynamic changes in each coil are characterized by a step response. After the step response, the coil current remains highly stable to ensure stable beam output. However, due to interference from the power supply system and equipment hardware, the stable state also exhibits small, irregular fluctuations. Current data includes both relatively stable processes and step-change processes. When a step response occurs, the current amplitude varies significantly. To capture the rate of change characteristics of the step response and the degree of irregular fluctuations in the stable state, the coil current data is divided into multiple monitoring periods, evenly spaced every t minutes from the start of data acquisition. T represents a preset time duration; in this embodiment, t is 10. The following analysis uses the i-th monitoring period as an example. First, the least squares method is used to fit the current data of each coil in the i-th monitoring period to obtain a current fitting curve for each coil. The curvature of all data within each current fitting curve is then calculated. The curvature corresponding to the endpoint position of the current step change is relatively large, while the curvature corresponding to the other non-step response endpoint positions is relatively small. There is a large difference between the curvature of the step change endpoint and other data points. Therefore, the curvature mean of all data points is calculated, and the data point with a curvature greater than the curvature mean is taken as the step change endpoint. The slope corresponding to the curve of the relatively stable process of the current is close to 0, while the absolute value of the slope of the curve corresponding to the step change process is relatively large. Based on the absolute value of the slope, the relatively stable current data and the step change current data are divided. In this embodiment, the preset slope threshold is set to 0.5. If the absolute value of the slope mean of all current data points between two adjacent step change endpoints is greater than the preset slope threshold, then the current data segment is recorded as a step current data segment. Otherwise, the current data segment is recorded as a steady-state current data segment.

[0041] Then the variance of the current data of all steady-state current data segments of each coil in the i-th monitoring period is taken as the unsteady-state coefficient of each coil in the i-th monitoring period, and the sum of the unsteady-state coefficients corresponding to all coils in the i-th monitoring period is recorded as . Income It reflects the irregular fluctuation degree of all coil currents in steady state during the i-th monitoring period. Then the total time length of all step current data segments of each coil during the i-th monitoring period is obtained, and the mean of the total time length of all coils is recorded as . Income The larger the value, the greater the influence of the coil current change adjustment on the magnetic field steady state. In addition, the current changes of different coils are not coordinated, which may cause local magnetic field distortion and affect the motion trajectory of particles in the magnetic field. In order to obtain the synergistic characteristics of the current changes between different coils, this application obtains the maximum mutual information coefficient between the corresponding current data of all two coils in the i-th monitoring period, and records the average of all maximum mutual information coefficients as . Income It reflects the degree of coordination between the changes in the currents of different coils. The smaller it is, the more uncoordinated the current changes between different coils are.

[0042] As a preferred embodiment, the current influence coefficient of each monitoring period is obtained based on the discrete degree of data in all steady-state current data segments of each coil in each monitoring period, the average level of the total time length of all step current data segments of all coils, and the average level of coordination between the current data of all any two coils, which is used to characterize the degree to which the magnetic field stability of the cyclotron is affected by current changes in each monitoring period.

[0043] In this embodiment, the current influence coefficient of the i-th monitoring period is recorded as , its specific expression is: Where, is the current influence coefficient of the i-th monitoring period, is the cumulative sum of the non-steady-state coefficients of all coils in the i-th monitoring period, is the average of the total time length of all coils in all step current data segments during the i-th monitoring period, is the mean of the maximum mutual information coefficient between the current data of any two coils in the i-th monitoring period. The larger the value is, the more the magnetic field stability of the cyclotron is affected by the current change during the i-th monitoring period.

[0044] Step 3: Obtain the temperature influence coefficient of each monitoring period based on the significance, average level and dispersion of the temperature data change trend in each monitoring period; obtain the disturbance coefficient of each monitoring period based on the mutual dependence between the current influence coefficient and the temperature influence coefficient in each monitoring period and the preset number of monitoring periods before it, as well as the current influence coefficient and temperature influence coefficient of each monitoring period.

[0045] Furthermore, during the operation of a small cyclotron, changes in magnet temperature will cause changes in the material's magnetization curve, thereby affecting the isochronous magnetic field and reducing the quality of the beam. Its magnetization intensity decreases as the temperature rises, and the higher the temperature, the faster the rate of decrease in magnetization intensity. Therefore, the higher the current temperature state of the ferromagnetic material or the greater the degree of temperature increase, the more significant the impact on the magnetic field stability. Based on this, the temperature data of the ferromagnetic material in the i-th monitoring period is used as the input of the Mann-Kendall test algorithm, and the statistical value z of the temperature data change trend in the monitoring period is output, which is recorded as The Mann-Kendall test algorithm is a well-known technique, and the specific process will not be described in detail. The larger the value is, the more significant the rising feature of the temperature data of the ferromagnetic material in the i-th monitoring period is. Then the product of the mean value and the variance of all temperature data in the i-th monitoring period is recorded as , income It reflects the temperature status and degree of instability during the operation period.

[0046] As a preferred embodiment, the temperature influence coefficient of each monitoring period is obtained based on the significance of the change trend, average level and dispersion of the temperature data in each monitoring period, which is used to characterize the degree to which the cyclotron magnetic field stability is affected by temperature changes.

[0047] In this embodiment, the temperature influence coefficient of the i-th monitoring period is recorded as , and its calculation formula is: Where, is the temperature influence coefficient of the i-th monitoring period, is the statistical value z of the temperature data change trend in the i-th monitoring period, exp( ) is the exponential function with the natural constant e as the base, is the product of the mean and variance of the temperature data in the i-th monitoring period. The larger it is, the more the stability of the magnetic field is affected by temperature.

[0048] Furthermore, there is an interaction between current changes and temperature changes. For example, current changes may also cause temperature changes, and temperature changes will cause fluctuations in magnetic field strength. The increase or decrease in magnetic field strength will affect the acceleration efficiency and trajectory of particles. This instability may further affect the stable supply of current, exacerbating the instability of the magnetic field. Similarly, temperature changes may also cause current fluctuations and interfere with the stability of the magnetic field. From this, it can be seen that there is a certain interaction relationship between current changes and temperature changes. The stronger this interaction relationship is, the greater the impact on the stability of the magnetic field. The more significant the positive correlation between the current influence coefficient and the temperature influence coefficient, the greater the degree of disturbance of the stability of the cyclotron magnetic field by the interaction between the two. In view of this, the Hoeffding's D coefficient between all current influence coefficients and temperature influence coefficients in the i-th monitoring period and its previous N monitoring periods is calculated, and recorded as N is a preset number, and its value range is an integer in [10,12]. In this embodiment, N is 10. It reflects the mutual dependence between current change and temperature change. The larger the value of , the stronger the interaction between the current change and the temperature change in the i-th monitoring period and the N previous monitoring periods, and the stronger the impact on the magnetic field stability. The calculation process of Hoeffding's D coefficient is a well-known technology and the specific process will not be repeated here.

[0049] As a preferred embodiment, the disturbance coefficient of each monitoring period is obtained based on the degree of mutual dependence between the current influence coefficient and the temperature influence coefficient in each monitoring period and a preset number of monitoring periods before it, as well as the current influence coefficient and the temperature influence coefficient of each monitoring period, to characterize the degree of disturbance influence on the stability of the cyclotron magnetic field in each monitoring period under the combined action of multiple factors.

[0050] In this embodiment, the disturbance coefficient of the i-th monitoring period is recorded as , its specific expression is: Where, is the disturbance coefficient of the i-th monitoring period, is the Hoeffding's D coefficient between all current influence coefficients and temperature influence coefficients in the i-th monitoring period and its previous N monitoring periods, where N is a preset number. 、 are the current influence coefficient and temperature influence coefficient of the i-th monitoring period respectively. The larger the value is, the more the cyclotron magnetic field stability is affected by the disturbances of current, temperature and the interaction between the current and temperature during the i-th monitoring period.

[0051] Step 4: According to the degree of dispersion of the magnetic field intensity data of all points at each moment within each monitoring period, and the similarity degree between the magnetic field intensity data of all points at adjacent moments, obtain the disorder coefficient of each monitoring period, and combine the disturbance coefficient of each monitoring period to obtain the non-stability coefficient of each monitoring period, and then evaluate the magnetic field stability.

[0052] Furthermore, the magnetic fields at different positions in the small cyclotron are not exactly the same. For example, during the adjustment process, the magnetic field near the coil changes rapidly and reaches a steady state first, while the magnetic field around the coil reaches a steady state relatively slowly. During the stability evaluation process, it is necessary to consider the difference relationship and time-varying characteristics of the magnetic field intensities at different positions, calculate the variance of the magnetic field intensity data of all points at each moment, and then calculate the Jaccard similarity coefficient between all the magnetic field intensity data corresponding to all adjacent moments within the i-th monitoring period. The ratio of the sum of the variances of all moments within the i-th monitoring period to the sum of all Jaccard similarity coefficients is used as the disorder coefficient of the i-th monitoring period. The calculation of the Jaccard similarity coefficient is a well-known technology, and the specific process will not be elaborated. The larger the obtained disorder coefficient, the more obvious the spatial difference and time-varying abnormal characteristics of the magnetic field intensity within the corresponding monitoring period. Under the interference of the above various factors, there is a certain hysteresis characteristic in the change of the magnetic field, and thus it is necessary to combine the disturbance effects of various factors to evaluate the magnetic field stability. In view of this, the product of the disturbance coefficient and the disorder coefficient of the i-th monitoring period is used as the non-stability coefficient of the i-th monitoring period, and this value reflects the non-stability characteristics of the magnetic field during the operation of the cyclotron within the i-th monitoring period. Among them, the flowchart for obtaining the non-temperature coefficient of each monitoring period is as Figure 2 shown. The larger the non-stability coefficient, the worse the stability of the magnetic field during the operation of the cyclotron within the corresponding monitoring period.

[0053] The obtained non-stability coefficient reflects the non-stable characteristics of the magnetic field state, and this application evaluates the magnetic field stability based on this value. First, use the tanh function to normalize the non-stability coefficients of each obtained monitoring period, and set the magnetic field stability evaluation interval: [0, a] indicates good magnetic field stability, (a, b) indicates general magnetic field stability, [b, 1] indicates poor magnetic field stability, where a is a preset first threshold, b is a preset second threshold, 0 < a < b < 1. In this embodiment, a takes 0.7 and b takes 0.9. According to the evaluation interval where the normalized non-stability coefficients of each obtained monitoring period are located, obtain the magnetic field stability evaluation results of each monitoring period. Evaluating the magnetic field stability through the above method helps to compensate for the defect of insufficient accuracy in magnetic field stability evaluation.

[0054] It should be noted that the order in which the embodiments of the present application are presented is for illustrative purposes only and does not necessarily represent the superiority or inferiority of the embodiments. Furthermore, the foregoing descriptions of specific embodiments of this specification are provided. Furthermore, the processes depicted in the accompanying drawings do not necessarily require the specific order or sequential sequence shown to achieve the desired results. In certain embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0055] The various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments.

[0056] The above-described embodiments are only used to illustrate the technical solutions of the present application, and not to limit them. Modifications to the technical solutions described in the aforementioned embodiments, or equivalent replacements of some of the technical features therein, do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application, and should all be included in the scope of protection of the present application.

Claims

1. A method for improving the magnetic field stability evaluation of a small cyclotron, characterized in that: The method comprises the following steps: Real-time acquisition of current data of each coil in the cyclotron, temperature data of ferromagnetic field, and magnetic field strength data of each point; The data acquisition time is evenly divided into multiple monitoring periods; the current data of each coil in each monitoring period is divided into a step current data segment and a steady-state current data segment according to the curvature and slope corresponding to each current data point of each coil in each monitoring period; the current influence coefficient of each monitoring period is obtained according to the discrete degree of data in all steady-state current data segments of each coil in each monitoring period, the average level of the total time length of all step current data segments of all coils, and the average level of coordination between the current data of all arbitrary two coils; The temperature influence coefficient of each monitoring period is obtained based on the significance, average level and dispersion of the temperature data in each monitoring period; the disturbance coefficient of each monitoring period is obtained based on the mutual dependence between the current influence coefficient and the temperature influence coefficient in each monitoring period and the preset number of monitoring periods before it, as well as the current influence coefficient and temperature influence coefficient of each monitoring period; According to the degree of dispersion of the magnetic field strength data of all points at each moment in each monitoring period, and the degree of similarity between the magnetic field strength data of all points at adjacent moments, the disorder coefficient of each monitoring period is obtained, and combined with the disturbance coefficient of each monitoring period, the instability coefficient of each monitoring period is obtained, and then the magnetic field stability is evaluated; The process of obtaining the current influence coefficient of each monitoring period is as follows: Obtaining the non-steady-state coefficient of each coil in each monitoring period according to the discrete degree of data in all steady-state current data segments of each coil in each monitoring period; The calculation formula of the current influence coefficient in each monitoring period is: Where, is the current influence coefficient of the i-th monitoring period, is the cumulative sum of the non-steady-state coefficients of all coils in the i-th monitoring period, is the average of the total time length of all coils in all step current data segments during the i-th monitoring period, is the mean of the maximum mutual information coefficient between the current data of any two coils in the i-th monitoring period; The non-steady-state coefficient of each coil in each monitoring period refers to the variance of the current data in all steady-state current data segments of each coil in each monitoring period; The calculation formula of the temperature influence coefficient of each monitoring period is: Where, is the temperature influence coefficient of the i-th monitoring period, is the statistical value z of the temperature data change trend in the i-th monitoring period, exp( ) is the exponential function with the natural constant e as the base, is the product of the mean and variance of the temperature data in the i-th monitoring period; The acquisition process is as follows: the temperature data of the ferromagnetic element in the i-th monitoring period is used as the input of the Mann-Kendall test algorithm, and the statistical value z of the temperature data change trend in the monitoring period is output; The calculation formula of the disturbance coefficient of each monitoring period is: Where, is the disturbance coefficient of the i-th monitoring period, is the Hoeffding's D coefficient between all current influence coefficients and temperature influence coefficients in the i-th monitoring period and its previous N monitoring periods, where N is a preset number. 、 are the current influence coefficient and temperature influence coefficient of the i-th monitoring period respectively; The process of obtaining the disorder coefficient of each monitoring period is as follows: calculating the variance of the magnetic field strength data of all points at each moment; calculating the Jaccard similarity coefficient between all magnetic field strength data corresponding to all adjacent moments in each monitoring period; and taking the ratio of the cumulative sum of the variances of all moments in each monitoring period to the cumulative sum of all Jaccard similarity coefficients as the disorder coefficient of each monitoring period; The instability coefficient of each monitoring period refers to the product of the disturbance coefficient and the turbulence coefficient of each monitoring period.

2. The method for improving the magnetic field stability evaluation of a small cyclotron according to claim 1, wherein: The specific process of evenly dividing the data collection time into multiple monitoring periods is as follows: starting from the moment when data collection begins, every t minutes is a monitoring period, and the data collection time is evenly divided into multiple monitoring periods, where t is a preset time length.

3. The method for improving the magnetic field stability evaluation of a small cyclotron according to claim 1, wherein: The process of dividing the current data of each coil in each monitoring period into a step current data segment and a steady-state current data segment is as follows: Obtaining the curvature and slope of each current data point of each coil in each monitoring period; Calculate the curvature mean of all current data points of each coil in each monitoring period, and take the data point whose curvature in the current data of each coil in each monitoring period is greater than the curvature mean as the step change endpoint; If the absolute value of the mean slope of all current data points between two adjacent step change endpoints in the current data of each coil during each monitoring period is greater than the preset slope threshold, the current data between these two adjacent step change endpoints is recorded as a step current data segment; otherwise, the current data between these two adjacent step change endpoints is recorded as a steady-state current data segment.

4. The method for improving the magnetic field stability evaluation of a small cyclotron according to claim 1, wherein: The specific process for evaluating the magnetic field stability is as follows: Set the magnetic field stability evaluation intervals: [0, a] indicates good magnetic field stability, (a, b) indicates general magnetic field stability, and [b, 1] indicates poor magnetic field stability, where a is the preset first threshold, b is the preset second threshold, and 0 < a < b < 1; According to the evaluation interval where the normalized non-stability coefficient of each monitoring period is located, the magnetic field stability evaluation result of each monitoring period is obtained.

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