Medical cyclotron ion source position adjustment method for improving discharge stability

Abstract

This invention relates to the field of devices for accelerating charged particles, specifically to a method for adjusting the position of an ion source in a medical cyclotron accelerator to improve discharge stability. The method includes: first, acquiring arc signal data and beam signal data during the current monitoring period; determining the necessary adjustment indicators for rotating the ion source position under the current state based on the multidimensional fluctuation characteristics of the arc signal; when the necessary adjustment indicators meet preset rotation conditions, determining the adjustment correlation coefficient of the ion source position under the current state based on the emittance characteristics and multidimensional beam spot pattern of the beam signal; finally, determining the knob adjustment step size based on the necessary adjustment indicators and the adjustment correlation coefficient, and performing fine-tuning of the rotation of the medical cyclotron accelerator ion source. This invention combines the initial adjustment necessity, the knob axial distance, and the centering adjustment performance to obtain a more accurate ion source position adjustment result, thus improving the discharge stability of the medical cyclotron accelerator.

Description

Technical Field

[0001] This invention relates to the field of devices for accelerating charged particles, and more specifically to a method for adjusting the position of an ion source in a medical cyclotron accelerator to improve discharge stability. Background Technology

[0002] In adjusting the ion source position, rotational adjustment is a direct and core method to improve discharge stability. It eliminates electric field distortion through circumferential alignment, enabling the arc voltage and arc current to reach the most stable state with minimal noise. Axial adjustment, on the other hand, consolidates this stability by optimizing the inter-electrode distance and lays the foundation for further improving beam quality. Performing both sequentially ensures the stable and efficient extraction of the plasma source.

[0003] In existing medical cyclotron accelerators, the ion source position is typically adjusted by rotating and aligning the ion source based solely on the macroscopic properties of arc voltage and arc current, aiming to improve discharge stability. However, this method neglects the decisive influence of two key degrees of freedom—axial distance and angular alignment—on plasma extraction efficiency and beam transmission quality. When the axial distance is too large, only a small amount of plasma is effectively extracted, resulting in a large accumulation of charged particles near the electrodes. This can disturb the local potential distribution, disrupt plasma equilibrium, and lead to arc current fluctuations. Furthermore, if the beam axis used for angular alignment adjustment is not properly aligned with the subsequent transmission line, beam transmission efficiency and quality will be significantly reduced, potentially even inducing beam loss or vacuum breakdown. Therefore, relying solely on rotational adjustment while neglecting the coordinated optimization of axial and angular alignment makes it difficult to achieve a systematic improvement in discharge stability. Summary of the Invention

[0004] To address the technical problem of poor discharge stability in existing ion source position adjustment methods, the present invention aims to provide a method for adjusting the position of a medical cyclotron ion source that improves discharge stability. The specific technical solution adopted is as follows: One embodiment of the present invention provides a method for adjusting the position of an ion source in a medical cyclotron accelerator to improve discharge stability. The method includes the following steps: Acquire arc signal data and beam signal data of the medical cyclotron during the current monitoring period; the arc signal data includes arc voltage curve and arc flow curve, and the beam signal data includes beam emittance and beam spot morphology. Based on the multidimensional fluctuation characteristics of the arc signal data, the necessary adjustment indicators for rotating the ion source position of the medical cyclotron accelerator under the current state are determined; the necessary adjustment indicators are at least used to characterize the degree of influence of the current rotation position on the abnormal electric field between the electrodes. The preset rotation conditions are determined based on the necessary adjustment indicators. When the necessary adjustment indicators meet the preset rotation conditions, the adjustment correlation coefficient of the medical cyclotron under the current state is determined based on the emission characteristics and multidimensional beam pattern of the electric beam signal data. The adjustment correlation coefficient includes suitability and matching degree. The suitability is used to determine the optimal axial distance of the knob, and the matching degree is used to adjust the knob centering. The current knob adjustment step size is determined based on the necessary adjustment indicators and the adjustment correlation coefficient; the medical cyclotron ion source is then finely rotated using the current knob adjustment step size.

[0005] Furthermore, based on the multidimensional fluctuation characteristics of the arc signal data, the necessary adjustment indicators for the medical cyclotron accelerator in its current state are determined, including: The arc pressure curve is analyzed to determine the curve fitting deviation and the arc pressure distance factor. The arc flow fluctuation factor is determined by analyzing the curve fluctuation based on the arc flow curve. Based on the arc pressure distance factor and the arc flow fluctuation factor, the necessary adjustment indicators for the medical cyclotron under the current state are determined; the arc pressure distance factor, the arc flow fluctuation factor, and the necessary adjustment indicators are positively correlated.

[0006] Furthermore, based on the analysis of the curve fitting deviation of the arc pressure curve, the arc pressure distance factor is determined, including: The least squares fitted straight line of the arc pressure curve is determined based on the arc pressure curve; The arc pressure distance factor is determined based on the proximity of the arc pressure point position at each monitoring moment on the arc pressure curve to the least squares fitted straight line.

[0007] Further, based on the arc pressure distance factor and the arc flow fluctuation factor, the necessary adjustment indicators for the medical cyclotron in its current state are determined, including: The overall dispersion of the arc flow is determined based on the difference between the maximum and minimum values ​​on the arc flow curve. The arc pressure distance factor, the arc flow fluctuation factor, and the overall dispersion of the arc flow are fused together, and the determined fusion value is used as a necessary indicator for adjusting the medical cyclotron in the current state.

[0008] Furthermore, the preset rotation conditions are determined based on the necessary adjustment indicators, including: If the necessary adjustment index is not less than the preset adjustment threshold, it is considered that the necessary adjustment index meets the preset rotation conditions, and the position of the medical cyclotron accelerator ion source after rough adjustment needs to be fine-tuned. If the necessary adjustment index is lower than the preset adjustment threshold, the current adjustment state of the medical cyclotron ion source will be retained.

[0009] Furthermore, based on the emittance characteristics and multidimensional beam pattern of the beam signal data, the adjustment correlation coefficient of the medical cyclotron under the current state is determined, including: A first suitable factor is determined based on the beam emittance under different axial step sizes; the beam emittance is negatively correlated with the first suitable factor. Based on the analysis of the beam spot morphology diagram, the overlap area of ​​the beam spot shape under different axial step size changes is determined to identify the second suitable factor. The suitability is determined for each axial distance based on the first suitability factor and the second suitability factor; Based on the analysis of the beam spot morphology diagram, the first matching factor is determined; The second matching factor is determined based on the elliptic symmetry of the beam emittance analysis. The degree of matching between the beam axis and the transmission line is determined based on the first matching factor and the second matching factor.

[0010] Furthermore, based on the analysis of the beam spot morphology diagram, the overlap area of ​​the beam spot shape under different axial step sizes is determined to identify a second suitable factor, including: The two beam spot morphology images obtained by adjacent axial distances are aligned according to the image registration algorithm, and the difference in beam spot area and the overlap area of ​​beam spot area of ​​the two beam spot morphology images after alignment are determined. Based on the difference in the area of ​​the beam spot region and the overlap area of ​​the beam spot region at each axial distance, a second suitable factor is determined for each axial distance; the second suitable factor is positively correlated with the overlap area of ​​the beam spot region and negatively correlated with the difference in the area of ​​the beam spot region.

[0011] Furthermore, based on the analysis of the beam spot morphology diagram, the beam spot contour is determined to identify the first matching factor, including: The beam spot contour is fitted to the beam spot morphology image obtained after the initial top wire adjustment by a circular fitting algorithm, and the fitted circle of the beam spot contour is determined. In the bundle spot profile fitting circle, the first matching factor is determined based on the overall distance fluctuation from each bundle spot profile edge point to the center of the bundle spot profile fitting circle; the first matching factor is negatively correlated with the overall distance fluctuation.

[0012] Furthermore, based on the beam emittance analysis to determine the emittance elliptic symmetry, a second matching factor is determined, including: The emittance ellipse corresponding to the beam emittance after the initial topwire adjustment is obtained by processing the beam emittance of the medical cyclotron ion source position after the initial topwire adjustment using the emittance ellipse extraction algorithm. The α function value and axis ratio value of the emission ellipse in the X and Y horizontal planes are determined by the emission ellipse processing algorithm. The second matching factor is determined based on the α function value and axial ratio value of the emission ellipse in the transverse plane; the second matching factor is negatively correlated with both the α function value and the axial ratio value.

[0013] Further, determining the current knob adjustment step size based on the necessary adjustment indicators and the adjustment correlation coefficient includes: The axial distance corresponding to the maximum fit is taken as the optimal axial distance, and the axial correction coefficient is determined by the difference between the optimal axial distance and the commonly used preset axial distance. The centering adjustment is performed based on the matching degree between the beam axis and the transmission line during the initial set wire adjustment, and the adjustment angle of each plane when the centering adjustment is completed is obtained. Based on the difference between the adjustment angle of each plane and the preset adjustment angle of the corresponding plane, determine the centering correction coefficient; Using the necessary adjustment indicators, the axial correction coefficient, and the centering correction coefficient, the preset initial knob adjustment step size is corrected to determine the current knob adjustment step size.

[0014] The present invention has the following beneficial effects: This invention provides a method for adjusting the position of an ion source in a medical cyclotron accelerator to improve discharge stability. This method integrates the multidimensional fluctuations of arc signals (arc voltage, arc current) with the multidimensional characteristics of beam signals (emissivity, beam spot morphology) to construct a multi-degree-of-freedom collaborative control mechanism. First, the necessity of ion source rotation adjustment is determined based on the fluctuation characteristics of the arc signal. If rotation is required, the suitability (characterizing optimal axial distance) and matching degree (characterizing angular alignment) are extracted from the beam signal as adjustment correlation coefficients, thus expanding the adjustment dimension from the traditional single rotation to two key degrees of freedom: axial distance and angular alignment. Finally, the adjustment step size of the knob is dynamically determined by comprehensively adjusting the necessary indicators and adjustment correlation coefficients, achieving coordinated fine-tuning of rotation, axial direction, and alignment. This method effectively solves the problems of plasma accumulation, potential disturbance, and beam loss caused by neglecting axial extraction efficiency and beam alignment accuracy in existing technologies, significantly improving discharge stability, beam transmission quality, and the overall operational reliability of the medical cyclotron accelerator. Attached Figure Description

[0015] To more clearly illustrate the technical solutions and advantages in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 A flowchart illustrating the steps of a method for adjusting the position of an ion source in a medical cyclotron accelerator to improve discharge stability, as provided in an embodiment of the present invention. Figure 2 A flowchart illustrating the steps for adjusting necessary parameters to determine the ion source position of a medical cyclotron accelerator in the current state during rotational operation, as described in this embodiment of the invention. Figure 3 This is a flowchart illustrating the steps for determining the adjustment correlation coefficient of a medical cyclotron in the current state in an embodiment of the present invention. Detailed Implementation

[0017] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the specific implementation methods, structures, features, and effects of the technical solution proposed according to the present invention are described in detail below with reference to the accompanying drawings and preferred embodiments. In the following description, different "one embodiment" or "another embodiment" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0018] Unless otherwise defined, 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 invention pertains.

[0019] Traditional methods, lacking detailed analysis of arc and beam signals, result in low adaptability of the ion source in medical cyclotron accelerators, leading to poor discharge stability. This invention analyzes arc signal changes to obtain necessary indicators for real-time ion source position adjustment. These indicators are used to refine coarse and fine-tuning assessments. Furthermore, combined with beam signal data, the optimal axial distance and optimal centering adjustment angle of the ion source position are determined. Finally, the relevant parameters under the optimal axial distance and optimal centering adjustment angle are used to refine the fine-tuning process of the ion source knob. This effectively improves the adaptability and discharge stability of the ion source in medical cyclotron accelerators.

[0020] Specifically, this invention provides a method for adjusting the position of an ion source in a medical cyclotron accelerator to improve discharge stability, such as... Figure 1 The above includes the following steps: S1, acquire the arc signal data and beam signal data of the medical cyclotron during the current monitoring period; the arc signal data includes the arc pressure curve and the arc flow curve.

[0021] Among them, the arc signal data refers to the instantaneous strong discharge signal generated by the breakdown of the vacuum cavity by the high voltage electric field in the radio frequency system of the medical cyclotron; the collected arc signal data includes the arc voltage signal and arc current signal under the corresponding monitoring period of the medical cyclotron, and the duration of the arc current and arc voltage signals monitored each time is 60s.

[0022] The acquisition process for arc signal data is as follows: A high-voltage differential probe for safely extracting the cathode high-voltage signal and an isolation current probe fitted onto the arc current feeder are placed inside the ion source high-voltage chamber. The signals are remotely transmitted to a safe location in the control room via shielded BNC cables. The signals are ultimately connected to a high-precision digital oscilloscope in the control room for real-time waveform display and capture. Complete trend curves are generated by the accelerator's central control system monitoring software, which simultaneously acquires and processes data from the underlying instruments, plotting the arc voltage and arc current signals for each monitoring duration.

[0023] It should be noted that the arc signal data is used as a necessary indicator for subsequent analysis of the current ion source status of the medical cyclotron, in order to help determine the coarse position of the ion source and the necessity of fine-tuning.

[0024] Among them, the electric beam signal data refers to the electrical signal generated by the interaction between the charged particle beam and the beam position detector during the transmission process in the medical cyclotron; the collected electric beam signal data includes the beam emittance and beam spot morphology generated during the operation of the medical cyclotron.

[0025] The acquisition process for the beam signal data is as follows: The beam spot morphology of the medical cyclotron is acquired using a fluorescent observation target mounted on the side of the vacuum tube of the beam transmission line. The fluorescent observation target is made of fluorescent materials such as yttrium oxide and emits visible light when bombarded by the beam. The acquired light signal is transmitted through a high-transmittance optical glass observation window directly in front of the target, and its image is captured by a high-resolution CCD camera located outside the vacuum chamber. The image data is transmitted to a computer in the control room and processed by dedicated beam diagnostic and image analysis software to generate beam emissivity and beam spot morphology maps.

[0026] It should be noted that the beam signal data is used to analyze the adjustment correlation coefficient of the fine-tuning process when adjusting the necessary indicators to meet the preset rotation conditions, so as to assist in the fine-tuning process after the ion source is roughly determined.

[0027] S2, based on the multidimensional fluctuation characteristics of the arc signal data, determine the necessary adjustment indicators for the rotation operation of the ion source position of the medical cyclotron accelerator in the current state.

[0028] Here, adjusting the necessary indicators is at least used to characterize the degree of influence of the current rotation position on the abnormal electric field between the electrodes.

[0029] In this embodiment, the multidimensional fluctuation characteristics may include an arc pressure distance factor and an arc current fluctuation factor. The arc pressure signal corresponding to the current monitoring period of the medical cyclotron is processed using the least squares method to obtain a fitted straight line. Based on the deviation between the arc pressure signal and the fitted straight line, the arc pressure distance factor is determined. The fluctuation performance of the arc current signal is analyzed to determine the arc current fluctuation factor. Based on the positive correlation between the arc pressure distance factor, the arc current fluctuation factor, and the necessity of knob adjustment, necessary adjustment indicators are determined. These adjustment indicators are then used for coarse determination and fine-tuning of the ion source position of the medical cyclotron.

[0030] As an exemplary implementation, the necessary adjustment parameters for rotating the ion source position of the medical cyclotron accelerator in the current state are determined, such as... Figure 2 As shown, it includes: S21. Analyze the curve fitting deviation based on the arc pressure curve and determine the arc pressure distance factor.

[0031] Here, the arc pressure distance factor is determined by the difference between the actual arc pressure signal of the medical cyclotron accelerator and the arc pressure fitted line during the current monitoring period.

[0032] In medical cyclotrons, when the rotation position is not properly adjusted, the electric field between the electrodes will be distorted or uneven, making the plasma discharge unstable. This is reflected in the increased fluctuation amplitude of the arc voltage, which may result in high-frequency spikes or low-frequency oscillations. Therefore, the overall arc voltage trend can be determined based on the arc voltage fitting line, and the abnormal performance of the arc voltage can be evaluated based on the actual local changes of the actual arc voltage signal and the distance difference between the fitting line, thereby reflecting the appropriateness of the current adjustment position.

[0033] In this embodiment, the arc pressure curve obtained from the medical cyclotron under commonly used preset parameter settings is fitted with a straight line using the least squares method to obtain a fitted straight line; the distance between the arc pressure point position corresponding to the current monitoring time and the fitted straight line is calculated within the monitoring period. The number of all monitoring moments within the monitoring period The distance between the superimposed value of the arc pressure point and the fitted straight line Summation yields The superimposed value is recorded as the arc pressure distance factor of the arc pressure signal from the medical cyclotron accelerator during the current analysis and monitoring period. The smaller the arc pressure distance factor, the better the stability of the arc pressure signal. The implementation process of the least squares method is existing technology and is not within the scope of this invention; therefore, it will not be described further here.

[0034] S22, Analyze the curve fluctuation based on the arc flow curve and determine the arc flow fluctuation factor.

[0035] Here, the arc flow fluctuation factor is determined by the fluctuation performance of the arc flow signal during the current monitoring period.

[0036] In this embodiment, the plasma discharge instability caused by improper rotation adjustment of the medical cyclotron accelerator leads to drastic changes in plasma density and extraction efficiency, which in turn significantly increases the noise of the arc current signal, resulting in violent fluctuations in the arc current reading. Therefore, the absolute value of the difference between adjacent monitoring times i and i-1 in the calculated arc current curve is crucial. ;statistics Number of adjacent monitoring units The number of adjacent monitoring Let be denoted as the arc flow fluctuation factor, where This represents the total value range for the current monitoring period.

[0037] S23, based on the arc pressure distance factor and the arc flow fluctuation factor, determine the necessary adjustment indicators of the medical cyclotron in the current state.

[0038] Here, necessary indicators are adjusted to achieve a rough determination of the position of the ion source in the medical cyclotron accelerator and subsequent fine-tuning.

[0039] As an exemplary implementation, the necessary adjustment parameters for the medical cyclotron accelerator in its current state are further determined, including: The first step is to determine the overall dispersion of the arc flow based on the difference between the maximum and minimum values ​​on the arc flow curve.

[0040] In this embodiment, the difference between the maximum and minimum values ​​on the arc flow curve is calculated as the overall dispersion of the arc flow.

[0041] The greater the overall dispersion of the arc flow curve, the wider the scope of the overall quantization of the arc flow signal during the monitoring and analysis period, which indicates a higher probability of strong amplitude changes in the overall arc flow curve.

[0042] The second step involves performing data fusion processing on the arc pressure distance factor, the arc flow fluctuation factor, and the overall dispersion of the arc flow, and using the determined fusion value as a necessary indicator for adjusting the medical cyclotron in the current state.

[0043] The plasma discharge instability phenomenon caused by improper ion source position in medical cyclotron accelerators is reflected in abnormal changes in arc voltage and arc current signals. Therefore, the necessity of adjusting the current ion source position can be more accurately assessed by combining the arc voltage distance factor and the arc current fluctuation factor.

[0044] As an example, the necessary indicators for adjusting the position of the ion source of the medical cyclotron accelerator during the current analysis and monitoring period. The calculation formula can be: In the formula This indicates the total number of monitoring moments within the current monitoring period; This indicates the arc pressure distance factor of the medical cyclotron during the current monitoring period; This indicates the overall dispersion of the arc flow in the medical cyclotron during the current monitoring period; This indicates the arc flow fluctuation factor of the medical cyclotron during the current monitoring period; This represents the maximum and minimum value normalization function; The range of values ​​for the necessary adjustment indicators will be determined to be... .

[0045] Adjust necessary indicators In the calculation formula, through The range of values ​​for the necessary adjustment indicators will be determined to be... This leads to the determination of necessary adjustments to the indicators. The rough direction of regulation, when When the value is greater than 0, the control is clockwise rotation; when... When the value is less than 0, it is a counter-clockwise rotation adjustment. Therefore, this embodiment adopts a trial adjustment strategy for coarse direction adjustment: when When the value is greater than 0, first control the ion source to rotate clockwise by a small trial step of 0.1 degrees in the preset direction. If necessary, recalculate and adjust the required parameters. If the direction decreases, then the direction is confirmed as correct; if If the value increases, then clockwise is confirmed as the correct direction.

[0046] Thus, this embodiment has determined the necessary adjustment indicators for the current position of the ion source in the medical cyclotron accelerator through the analysis of anomalous behavior of the arc current signal and arc voltage signal, reflecting the excellence of the current ion source position. The necessary adjustment indicators serve two purposes in this embodiment: firstly, to perform the initial coarse-setting process for the medical cyclotron accelerator; and secondly, to assist in determining the rotational conditions for fine-tuning. During the initial coarse-setting process, the value of the necessary adjustment indicator is increased by 1 and multiplied by the preset initial rotation adjustment step of 10°. This 10° is used to assist in the coarse-setting process using the knob, while the remaining angle adjustment is determined by the knob's fine-tuning. The final coarse-setting angle is determined by rotating clockwise when the necessary adjustment indicator is positive and counterclockwise when it is negative.

[0047] S3. Determine the preset rotation conditions based on the necessary adjustment indicators. When the necessary adjustment indicators meet the preset rotation conditions, determine the adjustment correlation coefficient of the medical cyclotron in the current state based on the emission characteristics and multidimensional beam pattern of the electric beam signal data.

[0048] Here, the adjustment of the correlation coefficients includes suitability and matching degree. Suitability is used to determine the optimal axial distance of the knob, and matching degree is used to perform knob centering adjustment.

[0049] In this embodiment, the position adjustment process of the medical cyclotron ion source is divided into an initial coarse adjustment and subsequent fine-tuning processes. The specific steps of the initial coarse adjustment are given in step S23. Then, it is necessary to combine the necessary adjustment indicators and rotation conditions to determine whether rotation adjustment is required. When the necessary adjustment indicators meet the rotation conditions, the current adjustment state of the medical cyclotron ion source is retained. When the necessary adjustment indicators meet the rotation conditions, it is necessary to combine the axial distance of the ion source knob and the centering adjustment for comprehensive analysis to obtain a highly adaptable fine-tuning evaluation method.

[0050] As an exemplary implementation, determining preset rotation conditions based on adjusting necessary indicators includes: Adjusting the real-time level of the necessary indicators can reflect the current state of the medical cyclotron ion source. Therefore, if the necessary indicators are not less than the preset adjustment threshold, it is considered that the necessary indicators meet the preset rotation conditions, and the position of the medical cyclotron ion source needs to be fine-tuned. If the necessary indicators are less than the preset adjustment threshold, it is considered that the current position of the medical cyclotron ion source is relatively ideal, and the current adjustment state of the medical cyclotron ion source is retained.

[0051] In this embodiment, the preset adjustment threshold can be 0.6. When the necessary adjustment index is greater than or equal to 0.6, the necessity of adjusting the position of the reaction ion source is high, and the rotation judgment condition is considered to be met. Otherwise, it is not met.

[0052] For the optimal axial distance, when the necessary indicators are adjusted to meet the preset rotation conditions, the suitability of the axial adjustment is determined based on the degree of change in beam spot shape under the change of beam emittance and axial distance, and then the optimal axial distance is determined. The optimal centering adjustment of the ion source is achieved by the state of the beam spot shape and the elliptic symmetry of emittance obtained by emittance measurement. Then, subsequent fine-tuning evaluation can be carried out by the correlation coefficient between the optimal axial distance and the optimal centering adjustment.

[0053] As an exemplary implementation, when the necessary indicators are adjusted to meet preset rotation conditions, the adjustment correlation coefficient of the medical cyclotron accelerator in the current state is determined, such as... Figure 3 As shown, it includes: S31, determine the first suitable factor based on the beam emittance under different axial step size changes.

[0054] When the necessary adjustment index is less than the preset adjustment threshold, the necessary adjustment index meets the preset rotation conditions, and further fine-tuning analysis is required. Since the rotation adjustment of the ion source position is a process of "alignment," with axial adjustment being the core step, if the axial distance is too large, only a small amount of plasma can be effectively extracted to form a beam, and a large number of charged particles accumulate near the electrodes, potentially altering the local potential and interfering with plasma balance. This may ultimately manifest as arc instability. Therefore, beam emittance at different axial step sizes can be analyzed to assist in determining the optimal axial distance of the ion source knob. The beam emittance is negatively correlated with the first suitability factor; a negative correlation means that the larger the beam emittance, the smaller the first suitability factor.

[0055] In this embodiment, starting from a preset axial reference position of 0.1 mm, the position is gradually changed in preset steps of 0.1 mm, so that it varies within a small neighborhood, for example... Local detection was conducted inside. The emission can be adjusted according to the actual scenario, and the refractive power corresponding to the m-th axial distance can be obtained using the three-gradient method, denoted as . Where m is the axial distance number; the three-gradient method is a conventional beam emittance measurement method in this field. It measures the corresponding beam spot size by changing the three different magnetic field gradient settings of the quadrupole on the transmission line, and then solves the beam emittance parameters by inversely solving the beam transmission matrix equations. The implementation process of the three-gradient method is existing technology and is not within the scope of protection of this invention, so it will not be described in detail here.

[0056] As an example, the first suitable factor for the m-th axial distance. The calculation formula can be: In the formula, This represents the magnitude of the reactivity corresponding to the m-th axial distance. To avoid the denominator of a fraction being zero, it can also be 0.001 or 0.0001.

[0057] S32. Based on the analysis of the beam spot morphology diagram, the overlap area of ​​the beam spot shape under different axial step size changes is determined to identify the second suitable factor.

[0058] When switching the axial distance between different adjacent ion sources, the discharge stability will decrease. This phenomenon can be further quantified by the change in beam spot shape during the axial distance switching. If the overlap area between two adjacent beam spots is larger during a certain ion source axial distance switching process, that is, the difference in beam spot morphology is smaller, it reflects the higher suitability of the current axial distance.

[0059] As an exemplary implementation, determining the second suitability factor includes: The first step is to align two beam spot morphology images obtained from adjacent axial distances using an image registration algorithm, and then determine the difference in beam spot area and the overlap area of ​​the beam spot regions in the two aligned beam spot morphology images.

[0060] In this embodiment, firstly, based on the beam spot morphology map at each axial distance, the beam spot shape at different axial distances is obtained using fluorescence target imaging. Secondly, through an image registration algorithm, displacement and rotation caused by mechanical vibration or micro-motion of the imaging system are corrected, so that the beam spot morphology maps at adjacent m-th and (m-1)-th axial distances are strictly aligned in the pixel coordinate system. Then, the overlap area of ​​the beam spot morphology maps at two adjacent axial distances is obtained, denoted as […]. Simultaneously, the area of ​​the beam spot region in the beam spot morphology diagram at the adjacent m-th and (m-1)-th axial distances is obtained and denoted as . and The implementation processes of the fluorescence target imaging method and the image registration algorithm are existing technologies and are not within the scope of protection of this invention; therefore, they will not be described in detail here.

[0061] The second step is to determine the second suitable factor for each axial distance based on the difference in the area of ​​the beam spot region and the overlap area of ​​the beam spot region at each axial distance.

[0062] Here, the second suitability factor is positively correlated with the overlap area of ​​the beam spot region and negatively correlated with the difference in area of ​​the beam spot region.

[0063] It should be noted that the smaller the area difference between the current axial distance and the adjacent axial distance corresponding to the beam spot region, and the more significant the overlap area, the better the stability of the beam at that axial distance when the axial distance changes. Therefore, the second suitable factor can be determined by the beam spot region area difference value and the beam spot region overlap area.

[0064] As an example, the formula for calculating the second suitability factor at the m-th axial distance can be: In the formula, This represents the overlap area of ​​the beam spot regions at the m-th and (m-1)-th axial distances. This represents the size of the beam spot region in the beam spot morphology diagram at the m-th axial distance. This represents the size of the beam spot region in the beam spot morphology diagram at the (m-1)th axial distance. This represents the difference in the area of ​​the beam spot region in the beam spot morphology diagram at the m-th and (m-1)-th axial distances; To prevent zero coefficients, which are used to avoid the denominator of fractions being zero, it can also be 0.1 or 0.001.

[0065] S33, determine the suitability for each axial distance based on the first suitability factor and the second suitability factor.

[0066] In this embodiment, the first suitability factor and the second suitability factor at the same axial distance are both positively correlated with the suitability. The larger the first suitability factor and the second suitability factor are, the greater the suitability at the corresponding axial distance.

[0067] As an example, the suitability of the ion source at the m-th axial distance. The calculation formula can be: ; In the formula, The first suitability factor representing the current axial distance m of the ion source location; The second suitability factor represents the current axial distance m of the ion source location; and This represents the preset weighting coefficient, which can be set to 0.5 and adjusted according to the actual scenario.

[0068] In the formula for calculating suitability, the larger the first and second suitability factors are, the better the emission performance of the ion source at the m-th axial distance, and the better the stability of the beam spot shape at that position under the change of adjacent axial distances, which further reflects the higher suitability of the ion source at the m-th axial distance.

[0069] Referring to the calculation process of the suitability at the m-th axial distance described above, the suitability at each axial distance can be obtained.

[0070] The fine-tuning process of the ion source in a medical cyclotron accelerator is mainly determined by axial distance and centering adjustment. The previous step determined the suitability of the axial distance. Therefore, without angular centering adjustment, even if the arc voltage is stable and the axial distance seems appropriate, it will cause serious problems affecting beam transmission efficiency and quality. For example, an inclined beam will generate a larger transverse oscillation amplitude in the tube, which will quickly impact the vacuum tube wall, causing a large amount of beam loss, secondary radiation, and additional heat load. Therefore, to avoid such problems, the matching degree used to achieve ion source centering adjustment should be analyzed based on the obtained beam spot shape and the symmetry of the emittance ellipse, as shown in steps S34 to S36 below.

[0071] It should be noted that the ion source position alignment adjustment is mainly achieved by adjusting the set wire, so the analysis can be performed based on the matching degree between the beam axis and the transmission line after each set wire adjustment.

[0072] S34. Analyze the beam pattern profile based on the beam pattern morphology diagram to determine the first matching factor.

[0073] It should be noted that an inclined beam will generate a larger lateral oscillation amplitude in the tube, quickly impacting the vacuum tube wall and causing significant beam loss. The vertical beam loss, however, is relatively smaller. Therefore, this step uses the near-circularity of the beam spot profile to evaluate the vertical beam performance. A higher beam spot circularity reflects a better beam pattern, which indirectly reflects a better match between the beam axis and the transmission line.

[0074] As an exemplary implementation, the formula for determining the first matching factor can be: The first step is to fit the beam pattern outline in the beam pattern image obtained after the initial topwire adjustment using a circular fitting algorithm, and then determine the fitting circle for the beam pattern outline.

[0075] In this embodiment, the least squares method is used to perform circular fitting on the beam spot morphology map obtained after the initial topwire adjustment, thereby obtaining a fitted circle for the beam spot contour. The implementation process of the least squares method is existing technology and will not be described in detail here.

[0076] The second step is to determine the first matching factor for the initial topwire adjustment based on the overall distance fluctuation from the edge points of each bundle spot profile to the center of the bundle spot profile fitting circle in the bundle spot profile fitting circle.

[0077] Here, the first matching factor is negatively correlated with the overall distance fluctuation.

[0078] In this embodiment, the distances from each edge point of the fitted circle of the bundle spot profile corresponding to the initial setter adjustment to the center of the circle are calculated, and the standard deviation of each distance is calculated. Take the reciprocal of this standard deviation and record it as the first matching factor for the ion source position after the initial setwire adjustment. The larger this value, the more regular the beam spot shape is after topwire adjustment at the current ion source position. In analyzing overall distance fluctuations, in addition to calculating the standard deviation, the variance of the distance can also be calculated.

[0079] S35, determine the second matching factor based on the elliptic symmetry of the beam emittance analysis.

[0080] It should be noted that the worse the ellipticity of the beam emittance, the greater the energy loss of the beam after impacting the vacuum tube wall. Therefore, this step further analyzes the matching situation based on the ellipticity of the beam emittance.

[0081] As an exemplary implementation, determining the second matching factor includes: The first step is to process the beam emittance of the medical cyclotron ion source after the initial topwire adjustment using an emittance ellipse extraction algorithm, and obtain the emittance ellipse corresponding to the beam emittance after the initial topwire adjustment.

[0082] In this embodiment, if the topwire adjustment of the ion source position is not well adapted, it will simultaneously affect the symmetry of the emittance ellipse. Therefore, based on the beam emittance after the initial topwire adjustment, the three-gradient method is used to obtain the emittance ellipse after the initial topwire adjustment.

[0083] The second step is to determine the α function value and axis ratio of the emission ellipse in the X and Y horizontal planes using the emission ellipse processing algorithm.

[0084] In this embodiment, the magnitudes of the α function of the emittance ellipse in the X and Y horizontal planes are obtained by fitting the beam envelope equation and using the toolkit of beam optics software such as TRACE-3D. and axis ratio .

[0085] The third step is to determine the second matching factor for the initial setter adjustment based on the α function value and axial ratio value of the emission ellipse in the transverse plane.

[0086] Here, the second matching factor is negatively correlated with both the α function value and the axial ratio value. The α function value includes values ​​in both the X and Y horizontal planes. and .

[0087] In this embodiment, when The closer it is to 0, the larger the axial ratio. The closer the value is to 1, the better the beam axis matches the transmission line. Therefore, the expression for the second matching factor after the initial setwire adjustment of the current ion source position can be: In the formula, This represents the absolute value of the function in the X-axis horizontal plane. This represents the absolute value of the function in the Y-plane. Indicates the axial ratio value; This represents the coefficient for dividing the denominator by zero, set to 0.001.

[0088] S36, determine the degree of matching between the beam axis and the transmission line based on the first matching factor and the second matching factor.

[0089] Here, determining the matching degree between the beam axis and the transmission line is used to determine the optimal alignment adjustment angle for judging the position of the ion source of the medical cyclotron accelerator.

[0090] It should be noted that, since the inclined beam loses a lot of energy after impacting the vacuum tube wall, and the higher the circularity of the beam profile and the better the elliptic symmetry of the emittance, the better the beam impact performance. In this case, the first matching factor and the second matching factor can be used to characterize the matching degree between the beam axis and the transmission line.

[0091] As an example, the matching degree between the ion source position and the beam axis and transmission line after the initial setwire adjustment. The calculation formula can be: In the formula, The first matching factor represents the position of the ion source after the initial setwire adjustment. The second matching factor represents the position of the ion source after the initial setwire adjustment; This represents the maximum and minimum value normalization function; This represents the coefficient for dividing the denominator by zero, and can be set to 0.001.

[0092] In the formula for calculating the matching degree, the matching degree between the beam axis and the transmission line corresponding to the ion source position after the initial setwire adjustment is defined. The larger the value, the better the centering effect of the initial top wire adjustment of the reaction ion source position.

[0093] Thus, the suitability and matching parameters are obtained through the above steps. Suitability is used to determine the optimal axial distance, and matching is used to determine the optimal centering angle. Then, the relevant parameters of the optimal axial distance and the optimal centering angle are used to evaluate and calculate the subsequent fine-tuning step size.

[0094] S4. Determine the current knob adjustment step size based on the necessary adjustment indicators and the adjustment correlation coefficient, and use the current knob adjustment step size to perform rotational fine-tuning of the medical cyclotron ion source.

[0095] During each fine-tuning of the ion source position after the knob has been coarsely set, if the necessary parameters are adjusted in real time to meet the preset rotation conditions, then fine-tuning is required. The suitability is then optimized to determine the optimal axial distance of the ion source position, and the matching degree is optimized to determine the optimal second setter adjustment, thereby determining the optimal centering adjustment angle of the ion source position, which in turn helps determine the adjustment step size of the fine-tuning process.

[0096] As an exemplary implementation, determining the current knob adjustment step size based on the adjustment necessity index and the adjustment correlation coefficient includes: The first step is to take the axial distance corresponding to the maximum fit as the optimal axial distance, and determine the axial correction coefficient based on the difference between the optimal axial distance and the commonly used preset axial distance.

[0097] It should be noted that the beam emittance is the smallest at the maximum suitability axial distance, and the overlap area of ​​the beam spot with the adjacent axial distance is the best at this position. Therefore, the optimal axial distance is determined by selecting the best suitability parameter.

[0098] In this embodiment, the absolute value of the difference between the optimal axial distance and the commonly used preset axial distance is calculated. The absolute value of the difference between two axial distances Perform negative correlation normalization and use the resulting normalized value as the axial correction coefficient.

[0099] As an example, the formula for calculating the axial correction factor can be: In the formula, This represents the zero-prevention coefficient, which can also be 0.1 or 0.001.

[0100] It should be noted that if the optimal axial distance is close to the commonly used axial distance, then the optimal axial distance is more suitable for the high-frequency real-time axial adjustment of medical cyclotrons. Therefore, the smaller the difference between the optimal axial distance and the commonly used axial distance, that is, the more negatively correlated they are, the larger the adjustment step size can be applied when fine-tuning the real-time knob, i.e., the larger the axial correction coefficient. The commonly used axial distance is set to 0.3mm, which can be adjusted according to the actual scenario.

[0101] The second step is to perform centering adjustment based on the matching degree between the beam axis and the transmission line during the initial set wire adjustment, so as to obtain the adjustment angle of each plane when the centering adjustment is completed.

[0102] In this embodiment, if the matching degree during the initial setter adjustment is greater than a preset matching threshold (e.g., 0.8), it indicates that the beam axis and transmission line are sufficiently matched, and the alignment adjustment is in place; conversely, if the matching degree during the initial setter adjustment is not greater than 0.8, the alignment adjustment is in place. The comparison is performed, and the plane with the larger value is prioritized as the dominant problem plane. For example, to correct a problem in the X plane (left-right deviation), the left set screw is tightened simultaneously while the right set screw is loosened by an equal amount (or vice versa); each adjustment is extremely small (e.g., 1 / 8 turn). After each adjustment, the value of the dominant problem plane |α| and the change in the beam spot are compared. When the value of |α| decreases significantly and the beam spot becomes more rounded, the adjustment direction is correct, and adjustment in this direction continues; otherwise, the direction is changed. This method is used to adjust the angle multiple times to achieve a more accurate centering. Finally, after the centering is achieved, the adjustment angles of each plane at the point of completion are obtained and used as the optimal centering angle.

[0103] The third step is to determine the centering correction coefficient based on the difference between the adjustment angle of each plane and the preset adjustment angle of the corresponding plane.

[0104] It should be noted that if the optimal centering angle is near the commonly used centering angle, it means that the optimal centering angle is more in line with the high-frequency real-time centering adjustment of the medical cyclotron. Therefore, if the difference between the optimal centering angle and the commonly used centering angle is smaller, that is, if they are more negatively correlated, then a higher adjustment step size can be applied when fine-tuning the knob in real time, that is, the centering correction coefficient is larger.

[0105] In this embodiment, upon completion of the centering adjustment, the absolute value of the difference between the adjustment angle of each plane and the preset adjustment angle of the corresponding plane is calculated and denoted as . and ;right and Data fusion processing is performed to obtain angle fusion values, and then the angle fusion values ​​are normalized by negative correlation. The obtained normalized values ​​are used as centering correction coefficients.

[0106] As an example, the formula for calculating the centering correction factor can be: ; In the formula for calculating the correction factor, if and The smaller the value, the smaller the difference between the optimal centering angle and the commonly used centering angle. This means that the optimal centering angle synchronization is more in line with the high-frequency real-time centering adjustment of medical cyclotrons, and a higher adjustment step can be applied when fine-tuning the knob in real time.

[0107] The fourth step involves using the necessary adjustment indicators, the axial correction coefficient, and the centering correction coefficient to correct the preset initial knob adjustment step size and determine the current knob adjustment step size.

[0108] As an example, the formula for calculating the current knob adjustment step size can be: In the formula, This indicates the current knob adjustment step size, where 'r' represents the preset initial knob adjustment step size. This represents the maximum and minimum value normalization function. This indicates adjustments to necessary indicators. Indicates the axial correction factor. This represents the centering correction factor.

[0109] In the current formula for calculating the adjustment step size of the knob, if the necessary adjustment index is larger, the urgency of the adjustment requirement is higher, and the adjustment step size should be larger. At the same time, when the optimal centering angle and the optimal axial distance are closer to the commonly used values, the optimal state satisfies the real-time requirements of high-frequency applications. This indicates that the confidence level of the optimal centering angle and the optimal axial distance is higher, and a higher adjustment step size can be set at this time.

[0110] It should be noted that when the axial or alignment condition is poor, a single rotation adjustment may be difficult to converge. Therefore, this embodiment uses the rotation step size to increase or decrease in order to coordinate with the overall debugging strategy.

[0111] In this embodiment, after obtaining the current knob adjustment step size, the medical cyclotron ion source is rotated and fine-tuned using the current knob adjustment step size.

[0112] It should be noted that after determining the adjustment step size, the direction of rotation adjustment needs to be determined. This embodiment adopts a trial-and-error adjustment strategy: first, control the ion source to rotate clockwise by a small trial step of 0.1 degrees in the preset direction; if the necessary adjustment parameters are not found, the adjustment will be recalculated. If the direction decreases, then the direction is confirmed as correct; if If the value increases, then clockwise is confirmed as the correct direction.

[0113] It should be noted that after completing the rotational fine-tuning of the ion source of the medical cyclotron accelerator, based on the ion source position of the medical cyclotron accelerator after rotational fine-tuning, and based on the calculation process of the necessary adjustment indicators in step S2 above, the necessary adjustment indicators for the rotational operation of the ion source position of the medical cyclotron accelerator in the current state are obtained again. If the necessary adjustment indicators still do not meet the preset rotation conditions, the axial adjustment and centering adjustment steps are returned to be executed until the necessary adjustment indicators corresponding to the medical cyclotron accelerator in the current state do not meet the preset rotation conditions or the maximum number of iterations is reached. The maximum number of iterations is set to 30 times. If the setting is too high, the ion source position adjustment process will be subject to too much control within a small range, reducing the control efficiency.

[0114] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions 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 invention, and should all be included within the protection scope of the present invention.

Claims

1. A method for adjusting the position of an ion source in a medical cyclotron accelerator to improve discharge stability, characterized in that, Includes the following steps: Acquire arc signal data and beam signal data of the medical cyclotron during the current monitoring period; the arc signal data includes arc voltage curve and arc flow curve, and the beam signal data includes beam emittance and beam spot morphology. Based on the multidimensional fluctuation characteristics of the arc signal data, the necessary adjustment indicators for rotating the ion source position of the medical cyclotron accelerator under the current state are determined; the necessary adjustment indicators are at least used to characterize the degree of influence of the current rotation position on the abnormal electric field between the electrodes. The preset rotation conditions are determined based on the necessary adjustment indicators. When the necessary adjustment indicators meet the preset rotation conditions, the adjustment correlation coefficient of the medical cyclotron under the current state is determined based on the emission characteristics and multidimensional beam pattern of the electric beam signal data. The adjustment correlation coefficient includes suitability and matching degree. The suitability is used to determine the optimal axial distance of the ion source knob, and the matching degree is used to adjust the knob centering. The current knob adjustment step size is determined based on the necessary adjustment indicators and the adjustment correlation coefficient; the medical cyclotron accelerator ion source is then finely rotated using the current knob adjustment step size. Based on the multidimensional fluctuation characteristics of the electric arc signal data, the necessary adjustment indicators for the medical cyclotron accelerator in its current state are determined, including: Based on the analysis of the curve fitting deviation of the arc pressure curve, the arc pressure distance factor is determined; The arc flow fluctuation factor is determined by analyzing the curve fluctuation based on the arc flow curve. Based on the arc pressure distance factor and the arc flow fluctuation factor, the necessary adjustment indicators for the medical cyclotron in the current state are determined; the arc pressure distance factor, the arc flow fluctuation factor, and the necessary adjustment indicators are positively correlated. Based on the emittance characteristics and multidimensional beam pattern of the beam signal data, the adjustment correlation coefficient of the medical cyclotron under the current state is determined, including: A first suitable factor is determined based on the beam emittance under different axial step sizes; the beam emittance is negatively correlated with the first suitable factor. Based on the analysis of the beam spot morphology diagram, the overlap area of ​​the beam spot shape under different axial step size changes is determined to identify the second suitable factor. The suitability is determined for each axial distance based on the first suitability factor and the second suitability factor; Based on the analysis of the beam spot morphology diagram, the first matching factor is determined; The second matching factor is determined based on the elliptic symmetry of the beam emittance analysis. The degree of matching between the beam axis and the transmission line is determined based on the first matching factor and the second matching factor. The current knob adjustment step size is determined based on the necessary adjustment indicators and the adjustment correlation coefficient, including: The axial distance corresponding to the maximum fit is taken as the optimal axial distance, and the axial correction coefficient is determined by the difference between the optimal axial distance and the commonly used preset axial distance. The centering adjustment is performed based on the matching degree between the beam axis and the transmission line during the initial set wire adjustment, and the adjustment angle of each plane when the centering adjustment is completed is obtained. Based on the difference between the adjustment angle of each plane and the preset adjustment angle of the corresponding plane, determine the centering correction coefficient; Using the necessary adjustment indicators, the axial correction coefficient, and the centering correction coefficient, the preset initial knob adjustment step size is corrected to determine the current knob adjustment step size.

2. The method for adjusting the position of a medical cyclotron ion source to improve discharge stability according to claim 1, characterized in that, Based on the analysis of the curve fitting deviation of the arc pressure curve, the arc pressure distance factor is determined, including: The least squares fitted straight line of the arc pressure curve is determined based on the arc pressure curve; The arc pressure distance factor is determined based on the proximity of the arc pressure point position at each monitoring moment on the arc pressure curve to the least squares fitted straight line.

3. The method for adjusting the position of a medical cyclotron ion source to improve discharge stability according to claim 1, characterized in that, Based on the arc pressure distance factor and the arc flow fluctuation factor, determine the necessary adjustment indicators for the medical cyclotron in its current state, including: The overall dispersion of the arc flow is determined based on the difference between the maximum and minimum values ​​on the arc flow curve. The arc pressure distance factor, the arc flow fluctuation factor, and the overall dispersion of the arc flow are fused together, and the determined fusion value is used as a necessary indicator for adjusting the medical cyclotron in the current state.

4. The method for adjusting the position of a medical cyclotron accelerator ion source to improve discharge stability according to claim 1, characterized in that, Determine the preset rotation conditions based on the necessary adjustment indicators, including: If the necessary adjustment index is not less than the preset adjustment threshold, it is considered that the necessary adjustment index meets the preset rotation conditions, and the position of the medical cyclotron accelerator ion source after rough adjustment needs to be fine-tuned. If the necessary adjustment index is lower than the preset adjustment threshold, the current adjustment state of the medical cyclotron ion source will be retained.

5. The method for adjusting the position of a medical cyclotron ion source to improve discharge stability according to claim 1, characterized in that, Based on the analysis of the beam spot morphology diagram, the overlap area of ​​the beam spot shape under different axial step sizes is determined to identify the second suitable factor, including: The two beam spot morphology images obtained by adjacent axial distances are aligned according to the image registration algorithm, and the difference in beam spot area and the overlap area of ​​beam spot area of ​​the two beam spot morphology images after alignment are determined. Based on the difference in the area of ​​the beam spot region and the overlap area of ​​the beam spot region at each axial distance, a second suitable factor is determined for each axial distance; the second suitable factor is positively correlated with the overlap area of ​​the beam spot region and negatively correlated with the difference in the area of ​​the beam spot region.

6. The method for adjusting the position of a medical cyclotron accelerator ion source to improve discharge stability according to claim 1, characterized in that, Based on the analysis of the beam spot morphology diagram, the beam spot contour is determined to identify the first matching factor, including: The beam spot contour is fitted to the beam spot morphology image obtained after the initial top wire adjustment by a circular fitting algorithm, and the fitted circle of the beam spot contour is determined. In the bundle spot profile fitting circle, the first matching factor is determined based on the overall distance fluctuation from each bundle spot profile edge point to the center of the bundle spot profile fitting circle; the first matching factor is negatively correlated with the overall distance fluctuation.

7. The method for adjusting the position of a medical cyclotron ion source to improve discharge stability according to claim 6, characterized in that, The second matching factor is determined based on the emittance elliptic symmetry analysis, including: The emittance ellipse corresponding to the beam emittance after the initial topwire adjustment is obtained by processing the beam emittance of the medical cyclotron ion source position after the initial topwire adjustment using the emittance ellipse extraction algorithm. The α function value and axis ratio value of the emission ellipse in the X and Y horizontal planes are determined by the emission ellipse processing algorithm. The second matching factor is determined based on the α function value and axial ratio value of the emission ellipse in the transverse plane; the second matching factor is negatively correlated with both the α function value and the axial ratio value.

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