A Beam Current Intensity Control Method and System for a Small Cyclotron

Abstract

The present invention discloses a beam intensity control method and system for a small cyclotron. The method includes: Step 1, system initialization; Step 2, inserting an internal target and configuring the feedforward limit current I0 of the ion source high-voltage power supply; Step 3, establishing the accelerator high-frequency field, starting the ion source arc, and closing the loop of the target internal target beam intensity program; Step 4, after reaching the target internal target beam intensity, opening the loop of the target internal target beam intensity program, then pulling out the internal target, and starting a 1s delay for the program; Step 5, after the delay arrives, closing the loop of the target beam intensity program and waiting to reach the target beam intensity; during the implementation of any step from Step 1 to Step 5, if a device abnormality occurs, the system will return to the initialization state again. This method obtains the current cavity voltage through the communication between the accelerator control system controller and the accelerator high-frequency control system. After the ion source is normally started and the internal target is pulled out, the beam intensity information obtained by the beam intensity measurement system is used to control the arc current of the high-voltage power supply of the ion source to achieve the target extracted beam intensity.

Description

Technical Field

[0001] The present invention relates to the field of particle accelerators, and specifically to a beam intensity control method and system for a small cyclotron. Background Art

[0002] Cyclotrons have many uses, and among them, small medical cyclotrons are one of the special equipment for producing radioactive nuclear drugs. Currently, for some PET medical small cyclotrons internationally, the technical indicators are an energy range of 10 - 18 MeV and a beam current of 60 - 300 uA. The main components of a small cyclotron include an ion source system, a high-frequency system, a main magnet system, a beam extraction system, a vacuum system, a water-cooling and pneumatic system, a control system, a radiation protection system, a target system, etc.

[0003] The key technical indicator of the beam extraction energy of a small cyclotron is determined by physical design, and the extraction energy can be adjusted by changing the extraction position during extraction.

[0004] Another key technical indicator is the beam intensity. The beam intensity is related to multiple systems of the accelerator, mainly including the ion source system, the high-frequency system, the main magnet system, and the extraction system. The ion source system is the source of particle generation. Most small cyclotrons use an in-built ion source. After the physical and mechanical designs are completed, one of the main ways to control the particle energy and beam current is the ion source high-voltage power supply. After the particles are extracted by the ion source high-voltage power supply, they are accelerated by the Dee voltage of the high-frequency field. At the same time, the beam intensity is also related to the magnetic field. The magnetic field is fixedly set and not dynamically adjusted, so it cannot affect the beam intensity during operation. The beam intensity of a small cyclotron is mainly affected by factors such as the extraction of the ion source high-voltage power supply and the high-frequency field of the accelerator. Summary of the Invention

[0005] Object of the Invention: To provide a beam intensity control method and system for a small cyclotron to solve the above problems existing in the prior art.

[0006] Technical Solution: A beam intensity control method for a small cyclotron includes:

[0007] Step 1, system initialization;

[0008] Step 2, insert the internal target and configure the feedforward limit current I0 of the ion source high-voltage power supply;

[0009] Step 3, establish the high-frequency field of the accelerator, start the ion source to arc, and close the loop of the target internal target beam current program;

[0010] Step 4, after reaching the target internal target beam current, open the loop of the target internal target beam current program, then pull out the internal target, and start a 1s delay for the program;

[0011] Step 5: After the delay arrives, the target beam current program is closed-loop, and wait for the target beam current to be reached;

[0012] During the implementation of any step from Step 1 to Step 5, if a device anomaly occurs, the system returns to the initialization state.

[0013] This method is based on the accelerator control system. It does not require additional control devices. Only the operator needs to input the required output beam current intensity. The accelerator control system controller obtains the current cavity voltage by communicating with the accelerator high-frequency control system. After the ion source is normally arc-started and the internal target is extracted, the beam current intensity information obtained by the beam current intensity measurement system is used to control the arc current of the high-voltage power supply of the ion source, so as to achieve the target extracted beam current intensity.

[0014] In a further embodiment, the system initialization includes the upper computer sending of Table 1 and Table 2, the sending of target beam current information, and the open-loop setting of the loop;

[0015] Table 1 is the arc power and internal target beam current table;

[0016] Table 2 is the cavity voltage and beam transmission efficiency table.

[0017] In a further embodiment, the obtaining of the arc power and internal target beam current table:

[0018] Limit and change the current value output by the high-voltage power supply of the ion source, calculate the arc power output by the high-voltage power supply, so as to obtain different beam current values on the internal target of the accelerator;

[0019] Integrate the output arc power and beam current values to obtain the arc power and internal target beam current table.

[0020] In a further embodiment, the obtaining of the cavity voltage and beam transmission efficiency table:

[0021] Change the closed-loop cavity voltage set value of the high-frequency control system to obtain the beam transmission efficiency corresponding to different cavity voltages, and obtain the cavity voltage and beam transmission efficiency table.

[0022] In a further embodiment, the obtaining of the feedforward limit current I0 of the high-voltage power supply of the ion source:

[0023] After obtaining Table 1 and Table 2, given that the target beam current is I set , the cavity voltage is V dee , through Table 2 and V dee obtain the beam transmission efficiency as η;

[0024] The target beam current I set corresponds to the internal target beam current as I set / η, and the arc power obtained through Table 1 is P;

[0025] Set the feedforward limit current I0 of the ion source high-voltage power supply to I0 = P / 300V.

[0026] A beam intensity control system for a small cyclotron, comprising:

[0027] An accelerator control system controller, and a high-frequency control system and a beam intensity measurement system connected to the accelerator control system controller;

[0028] The accelerator control system controller is connected to an ion source high-voltage power supply;

[0029] The accelerator control system controller includes a PLC controller;

[0030] The accelerator control system controller obtains information from the high-frequency control system and extracts the current cavity voltage information therefrom;

[0031] The accelerator control system controller obtains the current beam intensity transmitted from the beam intensity measurement system and performs fitting to obtain the current actual beam intensity.

[0032] Beneficial effects: The present invention discloses a beam intensity control method and system for a small cyclotron. The method is based on an accelerator control system and does not require additional control equipment. Only the operator needs to input the beam intensity that needs to be output currently. The accelerator control system controller obtains the current cavity voltage through communication with the accelerator high-frequency control system. After the ion source is normally arc-started and the inner target is pulled out, the beam intensity information obtained by the beam intensity measurement system is used to control the arc current of the high-voltage power supply of the ion source, so as to achieve the target extracted beam intensity.

[0033] The present invention can control the beam generated by a medical small cyclotron to have a dynamically adjustable beam intensity, thereby providing a stable and accurate beam intensity for the backend application. Based on this method, a larger beam current can be extracted compared with the traditional method, thereby improving the beam power level and acceleration efficiency of the accelerator and enhancing the beam stability. Description of the Drawings

[0034] Figure 1 is a schematic structural diagram of the system of the present invention.

[0035] Figure 2 is a schematic diagram of the relationship between the arc power and the inner target beam current of the present invention.

[0036] Figure 3 is a schematic diagram of the relationship between the accelerator cavity voltage and the beam transmission efficiency of the present invention.

[0037] Figure 4 is a schematic block diagram of the software implementation principle for approaching the target inner target beam current of the present invention.

[0038] Figure 5It is the principle block diagram of the software implementation for the present invention to approximate the target beam intensity.

[0039] Figure 6 It is the schematic diagram of the method flow of the present invention. Specific implementation manners

[0040] This application relates to a beam intensity control method and system for a small cyclotron, which will be explained in detail through specific implementation manners below.

[0041] The embodiment of the present invention provides a beam intensity control method and system for a small cyclotron. Based on the accelerator control system, without the need to add additional control devices, only the operator needs to input the currently required output beam intensity. The controller of the accelerator control system obtains the current cavity voltage by communicating with the accelerator high-frequency control system. After the ion source is normally arc-started and the internal target is pulled out, the beam intensity information obtained by the beam intensity measurement system is used to control the arc current of the high-voltage power supply of the ion source, so as to achieve the target extracted beam intensity.

[0042] This device is based on the accelerator control system, and the main devices involved are the high-voltage power supply of the ion source, the high-frequency control system, and the beam intensity measurement system.

[0043] A beam intensity control method for a small cyclotron includes:

[0044] Step 1, system initialization;

[0045] Step 2, insert the internal target and configure the feedforward limit current I0 of the high-voltage power supply of the ion source;

[0046] Step 3, establish the accelerator high-frequency field, start the arc of the ion source, and close the loop of the target internal target beam intensity program;

[0047] Step 4, after reaching the target internal target beam intensity, open the loop of the target internal target beam intensity program, then pull out the internal target, and start a 1s delay of the program;

[0048] Step 5, after the delay arrives, close the loop of the target beam intensity program and wait to reach the target beam intensity;

[0049] During the implementation of steps 1-5, if equipment abnormalities occur in any step, the system will return to the initialization state again.

[0050] The system initialization includes the upper computer sending of Table 1 and Table 2, the sending of target beam intensity information, and the open-loop setting of the loop;

[0051] Table 1 is the arc power and internal target beam intensity table;

[0052] Table 2 is the cavity voltage and beam transmission efficiency table.

[0053] Obtaining the arc power and internal target beam intensity table:

[0054] Limit and change the current value output by the ion source high-voltage power supply, calculate the arc power output by the high-voltage power supply, so as to obtain different beam current intensity values on the target in the accelerator;

[0055] Integrate the output arc power and beam current intensity values to obtain the arc power and the target in-beam current intensity table.

[0056] Obtaining the cavity voltage and beam transmission efficiency table:

[0057] Change the closed-loop cavity voltage setting value of the high-frequency control system to obtain the beam transmission efficiency corresponding to different cavity voltages, and obtain the cavity voltage and beam transmission efficiency table.

[0058] Obtaining the feed-forward limit current I0 of the ion source high-voltage power supply:

[0059] After obtaining Table 1 and Table 2, given that the target beam current intensity is I set , the cavity voltage is V dee , through Table 2 and V dee obtain the beam transmission efficiency as η;

[0060] The target beam current intensity I set corresponds to the target beam current intensity on the target in the beam as I set / η, and the arc power obtained through Table 1 is P;

[0061] Set the feed-forward limit current I0 of the ion source high-voltage power supply = P / 300V.

[0062] A beam current intensity control system for a small cyclotron, comprising:

[0063] An accelerator control system controller, and a high-frequency control system and a beam current intensity measurement system connected to the accelerator control system controller;

[0064] The accelerator control system controller is connected to an ion source high-voltage power supply;

[0065] The accelerator control system controller includes a PLC controller;

[0066] The accelerator control system controller is used to obtain information of the high-frequency control system and extract the current cavity voltage information therefrom;

[0067] The accelerator control system controller obtains the current beam current intensity conveyed from the beam current intensity measurement system and performs fitting to obtain the current actual beam current intensity.

[0068] Embodiment 1:

[0069] As shown in the appendix Figure 1 The implementation of beam current intensity control is based on the accelerator control system controller, and here the controller is generally a PLC controller.

[0070] The PLC obtains all the information of the current high-frequency control system through communication, extracts the current cavity voltage information from it, obtains the current beam intensity sent from the beam intensity measurement system through the analog input module, and performs fitting to obtain the current actual beam intensity.

[0071] The target beam intensity, cavity voltage, and beam intensity are used to calculate and output the current limiting value for controlling the output current of the current ion source high-voltage power supply through operations to obtain the target extracted beam intensity.

[0072] The ion source high-voltage power supply operates in the constant voltage mode when the ion source has not started to arc, and operates in the constant current mode after the ion source starts to arc normally.

[0073] By restricting and changing the current value output by the ion source high-voltage power supply, different beam intensity values can be obtained on the internal target of the accelerator.

[0074] The smaller the arc power (arc power P = V * I) output by the ion source high-voltage power supply after the ion source starts to arc, the smaller the beam intensity obtained on the internal target, and the larger the arc power output by the ion source high-voltage power supply, the larger the beam intensity obtained on the internal target.

[0075] We can insert the internal target, change the current limiting value of the high-voltage power supply after the ion source starts to arc, calculate the arc power output by the high-voltage power supply, and different ion source extraction beam intensity values can be obtained on the internal target.

[0076] In this way, we can obtain the arc power and the internal target beam intensity table Table 1 (Table 1).

[0077] The relationship between the ion source arc power and the internal target beam intensity is as shown in the appendix Figure 2 as follows;

[0078] From the appendix Figure 2 it can be seen that the arc power and the internal target beam intensity do not show a linear relationship, and we can obtain the internal target beam intensity corresponding to any arc power through the method of looking up the table and linear interpolation.

[0079] For example, if we hope to obtain a beam intensity of I x on the internal target, then through looking up the table, we obtain that the beam intensity I x is between the beam intensity I0 and the beam intensity I1. Then the arc power corresponding to the voltage I0 is P0, and the arc power corresponding to the voltage I1 is P1. Then the arc power corresponding to I x can be interpolated and calculated as:

[0080] Different accelerator cavity voltages will cause different beam transmission efficiencies. If the accelerator cavity voltage is too small, it will cause too much beam loss.

[0081] If the accelerator cavity voltage is too high, it will cause frequent arcing in the cavity, resulting in extremely unstable beam current. We can fix the output current of the ion source high-voltage power supply, insert the inner target, measure the beam current intensity on the inner target to obtain the ion source output current intensity value I1, and set the closed-loop cavity voltage V of the high-frequency control system dee1 , remove the inner target, and the beam current intensity I2 can be measured on the stripping target. Then the cavity voltage V dee1 corresponding beam transmission efficiency

[0082] By changing the set value of the closed-loop cavity voltage of the high-frequency control system, the beam transmission efficiency corresponding to different cavity voltages can be obtained.

[0083] In this way, we can obtain the cavity voltage and beam transmission efficiency table Table2 (Table 2).

[0084] The relationship between the accelerator cavity voltage and the beam transmission efficiency is as shown in the appendix Figure 3 as follows;

[0085] From the appendix Figure 3 it can be seen that the beam transmission efficiency and the accelerator cavity voltage do not show a linear relationship. We can obtain the beam transmission efficiency corresponding to any accelerator cavity voltage by looking up the table and using linear interpolation.

[0086] Typically, we obtain the current cavity voltage as V through the high-frequency control system x , then through looking up the table, we get that the voltage V x is between the voltage V0 and the voltage V1.

[0087] Then the beam transmission efficiency corresponding to the voltage V0 is η0, and the beam transmission efficiency corresponding to the voltage V x is η1. Then the beam transmission efficiency corresponding to V1

[0088] After obtaining Table1 and Table2, we know that the target current intensity is I set , and the cavity voltage is V dee . Then the beam transmission efficiency η can be obtained through Table2 and V dee . Then the target current intensity I set corresponds to the target current intensity on the inner target as I set / η, and further the arc power P obtained through Table1.

[0089] Since the ion source high-voltage power supply operates in a constant current mode after the ion source arcs, and the voltage after arcing is generally about 300V, then set the ion source high-voltage power supply limit current I0 = P / 300V.

[0090] In order to obtain the target beam intensity more quickly, we can preset a current value of the ion source high-voltage power supply near the target beam intensity. This current value is the limit current I0 of the ion source high-voltage power supply that we set after the ion source arcs normally.

[0091] In order to obtain a stable beam intensity, when the ion source has not arced, we insert the inner target. At this time, the accelerator ion source arcs normally. After the accelerator ion source arcs normally and the high-frequency field is established normally, we use the beam intensity information on the inner target obtained by the beam intensity measurement system to compare and feedback with the converted target beam intensity of the inner target in real time. After PID operation, we adjust the current limit value of the ion source high-voltage power supply in real time, so as to obtain a stable target inner target beam intensity. At this time, the feedback operation is stopped. The operation principle of this process is as shown in the appendix Figure 4 as follows.

[0092] After pulling out the inner target for 1 s, we perform real-time comparison and feedback between the target beam intensity and the actual extracted beam intensity. After PID operation, we adjust the current limit value of the ion source high-voltage power supply in real time. During the real-time feedback period, if abnormal conditions such as an accelerator cavity discharge or an ion source high-voltage power supply discharge occur, the feedback is stopped. After the system recovers, the feedback is restarted. The principle block diagram of this process is shown in the appendix Figure 5 as follows.

[0093] Description of the working principle:

[0094] Step 1: System initialization;

[0095] Step 2: Insert the inner target and configure the feedforward limit current I0 of the ion source high-voltage power supply;

[0096] Step 3: Establish the accelerator high-frequency field, the ion source arcs, and the target inner target beam intensity program is closed-loop;

[0097] Step 4: After reaching the target inner target beam intensity, the target inner target beam intensity program is open-loop, then the inner target is pulled out, and a 1 s delay of the program is started;

[0098] Step 5: After the delay arrives, the target beam intensity program is closed-loop and waits to reach the target beam intensity;

[0099] When equipment abnormalities occur in any step during the implementation of Steps 1-5, the system returns to the initialization state again.

[0100] The preferred specific embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the specific details in the above specific embodiments. Within the scope of the technical concept of the present invention, various equivalent transformations can be made to the technical solutions of the present invention, and these equivalent transformations all belong to the protection scope of the present invention.

Claims

1. A method for controlling the beam intensity of a small cyclotron accelerator, characterized in that: include: Step 1: System initialization; Step 2: Insert the inner target and configure the ion source high voltage power supply to limit the current ; Step 3: The accelerator high frequency field is established, the ion source arc is started, and the target current intensity program is closed; Step 4: After reaching the target internal current intensity, the target internal current intensity program is opened, and then the internal target is pulled out, and the program is started with a 1s delay; Step 5: After the delay is reached, the target flow intensity program is closed and waits for the target flow intensity to be reached; The system initialization includes sending Table 1 and Table 2 to the host computer, sending the target flow intensity information, and setting the loop open loop; Table 1 is a table of arc power and internal target current intensity; Table 2 is a table of cavity voltage and beam transmission efficiency If an equipment abnormality occurs in any step during the implementation of steps 1-5, the system will return to the initialization state; the ion source high voltage power supply feedforward limits the current Obtaining: After obtaining Table 1 and Table 2, it is known that the target flow intensity is , the cavity voltage is , through Table 2 and The beam transmission efficiency is obtained as η; Target flow intensity The corresponding flow intensity to the internal target is / η, the arc power obtained from Table 1 is P; Set the ion source high voltage power supply feedforward limit current =P / 300.

2. The beam intensity control method of a small cyclotron accelerator according to claim 1, characterized in that: How to obtain the arc power and internal target current intensity table: Limit and change the current value output by the high voltage power supply of the ion source, calculate the arc power output by the high voltage power supply, so as to obtain different current intensity values ​​on the target in the accelerator; The output arc power and current intensity values ​​are integrated to obtain the arc power and internal target current intensity table.

3. The beam intensity control method of a small cyclotron accelerator according to claim 1, characterized in that: Obtaining the table of cavity voltage and beam transmission efficiency: The closed-loop cavity voltage setting value of the high-frequency control system is changed to obtain the beam transmission efficiency corresponding to different cavity voltages, and a cavity voltage and beam transmission efficiency table is obtained.

4. A beam intensity control system for a small cyclotron accelerator, characterized in that: include: An accelerator control system controller, and a high-frequency control system and a beam intensity measurement system connected to the accelerator control system controller; The accelerator control system controller is connected to the ion source high voltage power supply; The accelerator control system controller includes a PLC controller; The accelerator control system controller acquires information of the high-frequency control system and extracts current cavity voltage information therefrom; The accelerator control system controller acquires the current beam intensity transmitted from the beam intensity measurement system, and performs fitting to obtain the current actual beam intensity.

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