Ion source current control device and system

Abstract

The invention discloses an ion source current control device and system, and relates to the field of circuits, the ion source current control device comprises a sampling circuit, a control circuit and a power supply circuit, the control circuit is connected with the sampling circuit, the ion source current of a neutron tube can be detected in real time, and power supply of a hot wire is controlled in real time by adopting a hardware circuit feedback mode. The current stability of the ion source is rapidly maintained, the calculation delay of a software mode is eliminated, and the control circuit can realize the adjustment of the duty ratio of the output pulse signal through the difference value between the first voltage value and the second voltage value, so as to realize the accurate control of the neutron tube hot wire power supply process. The whole control process is realized through a hardware circuit, the response speed is high, the output is stable, the stability of the output ion source current is ensured, the situations such as jitter are avoided, the application range of the neutron source is expanded, and wide popularization of the neutron source is facilitated.

Description

Technical Field

[0001] The present invention relates to the field of circuits, and particularly to a control device and system for ion source current. Background Art

[0002] With the continuous development of neutron sources, neutron tubes have played an important role in multiple application fields. In particular, they can be applied to the field of oilfield production logging. The neutron logging method is a logging method that is not restricted by casings and tubing, and is an important logging means during the oilfield development period. Neutrons are generated by neutron tubes. The interior of a neutron tube is divided into two main parts: an ion source and a target. The ion source generates deuterium ions, which are extracted through an extraction hole and accelerated in the gap between the ion source and the target. When a negative high voltage is applied to the target electrode, the deuterium ions obtain energy and bombard the tritium target of the target nucleus, resulting in a D-T nuclear reaction and releasing fast neutrons. The cathode of the neutron tube is grounded, and the anode of the ion source is powered by an external anode pulse transformer. When no power is applied to the anode of the ion source part, the deuterium gas is in a molecular or atomic state and does not conduct electricity. When a pulsed positive high voltage of a certain frequency is applied to the anode, during the duration of the pulsed high voltage, the positively charged deuterium ions in the deuterium ions collide with the cathode, generating electrons, and the electrons accelerate towards the anode, forming an avalanche discharge again and again. The neutron tube quickly enters the ionization state, and an ion current is formed between the anode and cathode circuits. When the frequency of the anode pulsed high voltage is constant, the higher the temperature of the heating filament, the higher the internal pressure of the neutron tube, and the higher the ion source current formed in the anode circuit. At this time, in order to avoid the situation where the excessive ion source current causes too large a load on the target electrode, resulting in target outgassing and damage to the neutron tube, it is necessary to maintain the stability of the ion source current. At this time, the supply of power to the heating filament can be controlled to control the amount of deuterium gas released by the heating filament, thereby maintaining the stability of the internal pressure of the neutron tube, keeping the ion source current stable, and realizing the stable operation of the neutron tube.

[0003] Please refer to Figure 1 , Figure 1A control circuit for the hot filament temperature of a neutron tube provided by the prior art. In the prior art, the current of the ion source is sampled through the ion source current circuit. There is a certain proportional relationship between the sampled voltage value and the magnitude of the ion source current. After the AD port of the single-chip microcomputer receives the sampled signal, the single-chip microcomputer will compare the sampled signal with the required ion source current value, and then output an analog voltage value obtained according to the comparison result through the DA port of the single-chip microcomputer. After passing through the voltage drive circuit, the conduction of the high-power triode N1 is controlled by the voltage after passing through the current-limiting resistor R to adjust the power supply to the hot filament, change the temperature of the hot filament, and thus maintain the stability of the neutron tube pressure. When the single-chip microcomputer determines that the sampled ion source current is less than the expected ion source current value, it increases the output of the DA, raises the power supply voltage, increases the temperature of the hot filament, releases more deuterium gas, and increases the pressure of the neutron tube. When the single-chip microcomputer determines that the sampled ion source current is greater than the expected ion source current value, it reduces the output of the DA, decreases the power supply voltage, reduces the temperature of the hot filament, reduces the number of free deuterium gas, and reduces the pressure of the neutron tube. However, this method uses the control method of the single-chip microcomputer. The single-chip microcomputer usually works in a cyclic and periodic manner, samples the ion source current value through software query, and controls the magnitude of the power supply voltage of the hot filament by judging the magnitude of the current value. The cycle of the whole process is about 50 milliseconds, there is a delay in time, it cannot sample in real time, and the ion source current after control fluctuates and there is a jitter situation. Summary of the Invention

[0004] The object of the present invention is to provide a control device and system for ion source current, which adopts the way of hardware circuit feedback to control the power supply of the hot filament in real time, quickly maintain the stability of the ion source current, eliminate the calculation delay of the software method, and the control circuit can adjust the duty cycle of the output pulse signal through the difference between the first voltage value and the second voltage value to achieve accurate control of the power supply process of the neutron tube hot filament. The whole control process is realized by the hardware circuit, with fast response speed and stable output, ensuring the stability of the output ion source current, avoiding the generation of jitter and other situations, expanding the application range of the neutron source, and being beneficial to the wide promotion of the neutron source.

[0005] To solve the above technical problems, the present invention provides a control device for ion source current. The ion source current is the discharge current formed between the anode and cathode of the neutron tube. The circuit includes:

[0006] A sampling circuit, with its input end connected to the neutron tube, for detecting the ion source current of the neutron tube and converting it into a corresponding first voltage value, and the first voltage value is linearly positively correlated with the ion source current;

[0007] A control circuit, with its first input terminal connected to the output terminal of the sampling circuit and its second input terminal receiving a second voltage value corresponding to the target ion source current, is configured to compare the first voltage value and the second voltage value to obtain a difference and output a pulse signal with a preset duty cycle. The preset duty cycle is positively linearly correlated with the difference between the first voltage value and the second voltage value.

[0008] A power supply circuit, with its input terminal connected to the output terminal of the control circuit and its output terminal connected to the filament of the neutron tube, is configured to turn on or off based on the pulse signal output by the control circuit to control the power supply to the filament, thereby controlling the ion source current.

[0009] Preferably, the sampling circuit includes an inverting proportional amplifier and a sampling resistor; the first end of the sampling resistor is connected to the anode transformer of the neutron tube, the second end is grounded and connected to the cathode of the neutron tube, and the input terminal of the inverting proportional amplifier is connected to the first end of the sampling resistor; the output terminal is connected to the first input terminal of the control circuit.

[0010] Preferably, the inverting proportional amplifier includes a first resistor, a second resistor, a third resistor, a fourth resistor, a first capacitor, a second capacitor, a third capacitor and an operational amplifier;

[0011] The first end of the first capacitor is grounded and connected to the second end of the sampling resistor, the second end is respectively connected to the first end of the sampling resistor and the first end of the first resistor, the second end of the first resistor is respectively connected to the first end of the second capacitor and the first end of the second resistor, the second end of the second capacitor is grounded, the second end of the second resistor is respectively connected to the first end of the third resistor and the first input terminal of the operational amplifier, the second input terminal of the operational amplifier is grounded, the output terminal is respectively connected to the second end of the third resistor and the first end of the fourth resistor, the second end of the fourth resistor is respectively connected to the first end of the third capacitor and the first input terminal of the control circuit, and the second end of the third capacitor is grounded.

[0012] Preferably, the power supply circuit includes a switching tube, a power supply capacitor and a power supply resistor; the first end of the power supply capacitor is connected to the output terminal of the control circuit, the second end is respectively connected to the first end of the power supply resistor and the control terminal of the switching tube, the second end of the power supply resistor is grounded, the first end of the switching tube is connected to a power supply, and the second end is connected to the filament of the neutron tube.

[0013] Preferably, the control circuit includes a differential circuit and a signal conversion circuit; a first input end of the differential circuit is connected to an output end of the sampling circuit, a second input end is connected to a second voltage value corresponding to a target ion source current, a third input end is connected to a first output end of the signal conversion circuit, an output end is connected to an input end of the signal conversion circuit, and a second output end of the signal conversion circuit is connected to an input end of the power supply circuit;

[0014] The differential circuit is configured to compare the first voltage value with the second voltage value to obtain a difference value, and output a voltage signal based on the difference value and a reference voltage, and the voltage signal is linearly positively correlated with the difference value and the reference voltage respectively;

[0015] The signal conversion circuit is configured to output the reference voltage to the differential circuit through the first output end, calculate a preset duty ratio by using the voltage signal, and convert the voltage signal into a pulse signal with the preset duty ratio, and the preset duty ratio is linearly negatively correlated with the voltage signal.

[0016] Preferably, the differential circuit includes a first voltage dividing resistor, a second voltage dividing resistor, a reference voltage circuit and a differential amplifier; a first end of the first voltage dividing resistor is connected to an output end of the sampling circuit, a second end is connected to a first input end of the differential amplifier, a first end of the second voltage dividing resistor is connected to the second voltage value corresponding to the target ion source current, a second end is connected to a second input end of the differential amplifier, a third input end of the differential amplifier is connected to an output end of the reference voltage circuit, an output end is connected to an input end of the signal conversion circuit, and an input end of the reference voltage circuit is connected to a first output end of the signal conversion circuit.

[0017] Preferably, the reference voltage circuit includes a third voltage dividing resistor and a fourth voltage dividing resistor; a first end of the third voltage dividing resistor is connected to a first output end of the signal conversion circuit, a second end is respectively connected to a first end of the fourth voltage dividing resistor and a third input end of the differential amplifier, and a second end of the fourth voltage dividing resistor is grounded.

[0018] Preferably, the signal conversion circuit includes a controller and a frequency circuit; an input end of the controller is connected to an output end of the differential circuit, a first output end is respectively connected to a third input end of the differential circuit and a first end of the frequency circuit, a second output end is connected to an input end of the power supply circuit, and a second end of the frequency circuit is connected to a timing port of the controller;

[0019] The controller is configured to output the reference voltage to the differential circuit and the frequency circuit through a first output terminal, calculate a preset duty cycle by using the voltage signal, convert the voltage signal into a pulse signal with the preset duty cycle, and the preset duty cycle is negatively linearly correlated with the voltage signal.

[0020] The frequency circuit is configured to control the frequency of the pulse signal output by the controller.

[0021] Preferably, the frequency circuit includes a fifth resistor, a fourth capacitor, and a fifth capacitor; a first end of the fifth resistor is respectively connected to a third input terminal of the differential circuit, a first end of the fifth capacitor, and a first output terminal of the controller, and a second end is respectively connected to a timing port of the controller and a first end of the fourth capacitor, and a second end of the fifth capacitor and a second end of the fourth capacitor are grounded.

[0022] To solve the above technical problems, the present invention further provides a control system for an ion source current, including a neutron tube and the control device for the ion source current as described above, and the neutron tube is connected to the control device for the ion source current.

[0023] The present invention provides a control device for an ion source current, including a sampling circuit, a control circuit, and a power supply circuit. The control circuit is connected to the sampling circuit and can detect the ion source current of the neutron tube in real time. By means of the feedback of the hardware circuit, the power supply of the hot filament is controlled in real time, the stability of the ion source current is quickly maintained, the calculation delay of the software method is eliminated, and the control circuit can adjust the duty cycle of the output pulse signal through the difference between the first voltage value and the second voltage value to achieve accurate control of the power supply process of the neutron tube hot filament. The entire control process is implemented by a hardware circuit, with a fast response speed and stable output, ensuring the stability of the output ion source current, avoiding the occurrence of jitter and other situations, expanding the application range of the neutron source, and being conducive to the wide promotion of the neutron source.

[0024] The present invention further provides a control system for an ion source current, which has the same beneficial effects as the above control device for the ion source current. Description of the Drawings

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the prior art and the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0026] Figure 1 A control circuit for the temperature of the hot filament of a neutron tube provided by the prior art;

[0027] Figure 2 Schematic structural diagram of a control device for ion source current provided by the present invention;

[0028] Figure 3 Schematic internal structure diagram of a neutron tube provided by the present invention;

[0029] Figure 4 Schematic signal diagram of a control device for ion source current provided by the present invention;

[0030] Figure 5 Schematic structural diagram of another control device for ion source current provided by the present invention;

[0031] Figure 6 Schematic structural diagram of a control system for ion source current provided by the present invention. Specific embodiments

[0032] The core of the present invention is to provide a control device and system for ion source current. By means of hardware circuit feedback, the power supply of the hot filament is controlled in real time, the ion source current is quickly stabilized, the calculation delay of the software method is eliminated, and the control circuit can adjust the duty cycle of the output pulse signal through the difference between the first voltage value and the second voltage value to accurately control the power supply process of the neutron tube hot filament. The entire control process is implemented by a hardware circuit, with fast response speed and stable output, ensuring the stability of the output ion source current, avoiding jitter and other situations, expanding the application range of the neutron source, and being conducive to the wide promotion of the neutron source.

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0034] In the field of oilfield production logging, the neutron logging method is a logging method that is not restricted by casings and tubing. It can be used for tasks such as dividing oil, gas, and water layers; finding oil and gas layers that have been overlooked in interpretation; judging the migration of the oil-gas-water interface; evaluating the plugging effect of waterflooded layers; and measuring the remaining oil and residual oil saturation. It is an important logging means during the oilfield development period. Neutron sources used in neutron logging such as PNN are controllable pulsed neutron sources. Neutrons are generated by neutron tubes. When the control circuit of the neutron tube does not work, no neutrons are generated, and neutron radiation will not be caused to on-site workers.

[0035] The interaction between neutrons and the formation is the physical basis of neutron logging and pulsed neutron logging methods. During formal operation, the neutron generator intermittently emits fast neutrons with an energy of 14 MeV. The fast neutrons enter the formation and interact with the formation materials, generating various nuclear reactions. The key to neutron logging is to control the operation of the neutron tube. The specific implementation method is described in detail below.

[0036] Please refer to Figure 2 , Figure 2 FIG. [0000102] is a schematic structural diagram of a control device for ion source current provided by the present invention; to solve the above technical problems, the present invention provides a control device 31 for ion source current. The ion source current is the discharge current formed between the anode and the cathode of the neutron tube 4. The circuit includes:

[0037] A sampling circuit 1, the input end of which is connected to the neutron tube 4, is used to detect the ion source current of the neutron tube 4 and convert it into a corresponding first voltage value. The first voltage value is positively linearly correlated with the ion source current;

[0038] A control circuit 2, the first input end of which is connected to the output end of the sampling circuit 1, and the second input end is connected to the second voltage value corresponding to the target ion source current, is used to compare the first voltage value and the second voltage value to obtain a difference, and output a pulse signal with a preset duty cycle. The preset duty cycle is positively linearly correlated with the difference between the first voltage value and the second voltage value;

[0039] A power supply circuit 3, the input end of which is connected to the output end of the control circuit 2, and the output end is connected to the heating filament of the neutron tube 4, is used to conduct or cut off based on the pulse signal output by the control circuit 2 to control the power supply of the heating filament, thereby controlling the ion source current.

[0040] Specifically, the control circuit 2 detects the current ion source current of the neutron tube 4 according to the first voltage value output by the sampling circuit 1, and uses the obtained second voltage value corresponding to the target ion source current to obtain the gap between the current ion source current and the target ion source current, so as to determine how large a duty cycle of the pulse signal needs to be output to control the power supply of the heating filament through the power supply circuit 3, so that the current ion source current can reach the target ion source current.

[0041] Please refer to Figure 3 , Figure 3Schematic diagram of the internal structure of a neutron tube provided by the present invention; the interior of the neutron tube 4 is divided into two major parts: an ion source and a target, and the two are distributed at both ends. One end of the neutron tube 4 leads to connect the heating filament, anode and ground, and the other end is connected to the target electrode lead and ground. The sealed neutron tube 4 is essentially a small electrostatic accelerator-type neutron source. Deuterium ions are generated by the ion source, extracted through the extraction hole, and accelerated in the acceleration gap. When a negative high voltage of up to -100 KV is applied to the target electrode, the deuterium ions obtain an energy of up to 100 kev, bombard the tritium target on the target nucleus, and a D-T nuclear reaction occurs, releasing fast neutrons. The nuclear reaction formula is:

[0042] The ion source therein includes two parts: a heating filament and anode high voltage. Deuterium gas is stored on the heating filament. The resistance value of the heating filament is approximately around 4 ohms. When the heating filament is not heated, deuterium ions are adsorbed on the heating filament. The neutron tube 4 is in a high-vacuum state, and the air pressure is approximately 10 -3 Pa. Then, the ion source control circuit 2 supplies voltage to the heating filament to heat the heating filament, and the temperature rises. The heating filament releases deuterium gas, and the air pressure is generated inside the neutron tube 4. The air pressure inside the neutron tube 4 is approximately (1 - 5×10 -2 Pa). When the air pressure is balanced, the air pressure magnitude is related to the temperature of the heating filament. Different heating filament temperatures release different amounts of deuterium gas, and the air pressure inside the neutron tube 4 is different.

[0043] The cathode of the neutron tube 4 is grounded, and the anode of the ion source is powered by an external anode pulse transformer. When no power is applied to the anode of the ion source part, deuterium gas is in a molecular or atomic state and does not conduct electricity. When a pulsed positive high voltage of approximately 2400 V with a certain frequency is applied to the anode, during the duration of the pulsed high voltage, the positively charged accelerated deuterium ions in the deuterium ions collide with the cathode to generate electrons, and the electrons are accelerated towards the anode again and again, forming an avalanche discharge. The neutron tube 4 quickly enters the ionization state, and an ion current is formed between the anode and cathode circuits. The ion source current is the discharge current of a certain intensity formed between the anode and cathode of the neutron tube 4 when a positive high voltage pulse with a certain frequency and duty cycle is applied to the anode of the neutron tube 4 and the heating filament is heated to a certain extent. When the frequency of the anode pulsed high voltage is constant, the higher the temperature of the heating filament, the higher the air pressure inside the neutron tube 4, and the higher the ion source current formed in the anode circuit. However, the ion source current cannot be too high, which will cause excessive load on the target electrode, resulting in outgassing of the target electrode and damage to the neutron tube 4. Therefore, when the neutron tube 4 is working, the stability of the ion source current must be maintained.

[0044] When a negative voltage of up to nearly one million volts is applied to the target electrode, the deuterium ions are accelerated in the acceleration gap between the anode and cathode, obtaining an energy of up to one million kev, hitting the tritium target, generating a D-T nuclear reaction, and releasing fast neutrons. Usually, a tritium target is used in the neutron tube 4. The tritium target is a target with radioactive material tritium, which can withstand the bombardment of high-energy deuterium ions to produce nuclear reactions to generate neutrons.

[0045] As can be seen from the working principle of the neutron tube 4, as the storage medium for deuterium gas, the hot wire, by controlling the power supply to the hot wire, can control the amount of deuterium gas released, so as to generate a stable air pressure inside the neutron tube 4, automatically adjust the power supply to the hot wire, and keep the ion source current stable, which is very important. The hot wire is the storage medium for deuterium gas inside the neutron tube 4. It is made of a tungsten wire with a layer of insulating AI2O3 electrophoresed on its surface, and a getter metal titanium with a special adsorption capacity for deuterium gas is installed around it. The adsorption capacity of metal titanium for deuterium gas is different at different temperatures. By controlling the temperature of the hot wire through electric heating, the gas absorption and release of titanium are controlled to maintain the stability of the air pressure inside the neutron tube 4. This is the premise for the stable operation of the neutron tube 4. The present invention aims to design a new method for generating a hot wire temperature control circuit to control the power supply to the hot wire in real time, control the temperature of the hot wire, keep the ion source current stable, and reduce the circuit volume and circuit heat loss.

[0046] It can be understood that for the specific circuit structures and implementation manners of the sampling circuit 1, the control circuit 2, and the power supply circuit 3, no special limitations are made in this application; there are multiple options for the detection method of the ion source current of the neutron tube 4 by the sampling circuit 1. It can be realized by devices such as sensors, or a sampling resistor can be added to reflect the situation of the ion source current through the electrical characteristics of the sampling resistor; the comparison process of the first voltage value and the second voltage value by the control circuit 2 can be realized by a comparator or a differential module, etc. The output pulse signal can be in the form of a PWM (Pulse Width Modulation) wave, or in the form of other square waves, etc.; there are also multiple options for the determination method of the duty cycle. The mapping relationship between the difference value and the duty cycle can be preset in the control circuit 2 in advance, or it can be calculated by a control chip such as a PWM controller; the power supply process of the hot wire by the power supply circuit 3 can be realized by switching devices such as relays and MOS tubes (Metal Oxide Semiconductor Field Effect Transistor).

[0047] The control device 31 for the ion source current provided by this application adopts a hardware circuit feedback method to control the duty cycle of the output pulse signal in real time and quickly. When the temperature of the heating filament is low, fewer deuterium ions are released, and the sampled value of the ion current is relatively low. At this time, the duty cycle of the pulse signal output by the control circuit 2 is large, and the heating time of the heating filament is long. As the temperature of the heating filament increases, the released deuterium ions also increase, and the sampled value of the ion current also increases. The duty cycle of the pulse signal output by the control circuit 2 becomes lower, and the heating time of the heating filament decreases. When the ion current is equal to the required current value, the duty cycle of the pulse signal output by the control circuit 2 is zero, and the heating filament stops heating. When the temperature of the heating filament decreases again, the sampled value of the ion current also decreases relatively, and the control circuit 2 outputs a pulse signal with a duty cycle, and the heating filament of the neutron tube 4 is reheated. All controls are automatically controlled by hardware, with fast response and stability. The hardware circuit feedback method can control the power supply of the heating filament in real time, quickly maintain the stability of the ion source current, and eliminate the calculation delay of the software method.

[0048] The present invention provides a control device 31 for an ion source current, including a sampling circuit 1, a control circuit 2, and a power supply circuit 3. The control circuit 2 is connected to the sampling circuit 1 and can detect the ion source current of the neutron tube 4 in real time. By adopting a hardware circuit feedback method, it can control the power supply of the heating filament in real time, quickly maintain the stability of the ion source current, eliminate the calculation delay of the software method, and the control circuit 2 can adjust the duty cycle of the output pulse signal through the difference between the first voltage value and the second voltage value to accurately control the power supply process of the heating filament of the neutron tube 4. The entire control process is implemented by a hardware circuit, with a fast response speed and stable output, ensuring the stability of the output ion source current, avoiding jitter and other situations, expanding the application range of the neutron source, and being conducive to the wide promotion of the neutron source.

[0049] Based on the above embodiments, please refer to Figure 4 and Figure 5 , Figure 4 is a signal schematic diagram of a control device for an ion source current provided by the present invention. In the figure, Via represents the second voltage value corresponding to the target ion source current value, Vout represents the first voltage value output by the sampling circuit 1, Vpwm represents the voltage signal output by the differential circuit 21, and DRV represents the pulse signal output by the control circuit 2 to the power supply circuit 3; Figure 5 is a structural schematic diagram of another control device for an ion source current provided by the present invention;

[0050] As a preferred embodiment, the sampling circuit 1 includes an inverting proportional amplifier and a sampling resistor R7; the first end of the sampling resistor R7 is connected to the anode transformer of the neutron tube 4, the second end is grounded and connected to the cathode of the neutron tube 4, and the input end of the inverting proportional amplifier is connected to the first end of the sampling resistor R7; the output end is connected to the first input end of the control circuit 2.

[0051] Specifically, in order to better sample the ion source current, a sampling resistor R7 connected between the anode transformer and the cathode is additionally provided in the circuit of the neutron tube 4. The sampling resistor R7 converts the ion source current into a voltage signal, enabling the inverting proportional amplifier to monitor the ion source current through the sampling resistor R7.

[0052] It can be understood that the function of the sampling circuit 1 is to measure the value of the ion current Ia of the neutron tube 4. One end of the anode transformer of the neutron tube 4 is connected to the anode in the ion source part of the neutron tube 4 through a diode, providing a pulsed high voltage of 2000 - 2400V with a certain frequency and duty cycle to the anode. It is connected to the other end VJ of the anode transformer through the cathode ground and the sampling resistor R7 to form a power supply loop. The electron flow formed by avalanche discharge flies from the cathode ground to the anode. Therefore, the voltage value VJ of the sampling resistor R7 with respect to the ground represents the value of the ion source current Ia, and the relationship between them is: VJ = R7 × Ia.

[0053] In practical applications, generally, Ia selected is between 70 - 100 microamperes. R7 can be a high-temperature chip resistor with a 0805 package and a size of 20K. When Ia is 100 microamperes, the corresponding VJ is -2V. Since the ion source current flows from the cathode ground to the anode, the voltage of VJ is negative. Therefore, it is also necessary to use an inverting proportional amplifier to convert this voltage value into a positive value. The main function of the inverting proportional amplifier is to make the voltage converted by the sampling resistor R7 positive for subsequent operations such as comparison and difference calculation by the control circuit 2. The specific types and parameter values of the sampling resistor R7 and the inverting proportional amplifier are not particularly limited in this application. The sampling resistor R7 can be implemented by a fixed resistor or a variable resistor, etc.; there are also various choices for the specific circuit structure of the inverting proportional amplifier.

[0054] Specifically, the sampling circuit 1 includes an inverting proportional amplifier and a sampling resistor R7; the sampling resistor R7 converts the ion source current into a voltage signal, and the inverting proportional amplifier makes this voltage signal positive, ensuring that the subsequent control circuit 2 can accurately compare and calculate the difference between the first voltage signal and the second voltage signal, guaranteeing the accurate implementation of the entire ion source current control device 31.

[0055] As a preferred embodiment, the inverting proportional amplifier includes a first resistor R8, a second resistor R9, a third resistor R10, a fourth resistor R11, a first capacitor E1, a second capacitor C4, a third capacitor C5, and an operational amplifier U3;

[0056] The first terminal of the first capacitor E1 is grounded and connected to the second terminal of the sampling resistor R7. The second terminal is respectively connected to the first terminal of the sampling resistor R7 and the first terminal of the first resistor R8. The second terminal of the first resistor R8 is respectively connected to the first terminal of the second capacitor C4 and the first terminal of the second resistor R9. The second terminal of the second capacitor C4 is grounded. The second terminal of the second resistor R9 is respectively connected to the first terminal of the third resistor R10 and the first input terminal of the operational amplifier U3. The second input terminal of the operational amplifier U3 is grounded. The output terminal is respectively connected to the second terminal of the third resistor R10 and the first terminal of the fourth resistor R11. The second terminal of the fourth resistor R11 is respectively connected to the first terminal of the third capacitor C5 and the first input terminal of the control circuit 2. The second terminal of the third capacitor C5 is grounded.

[0057] Specifically, as Figure 5 shown, the first resistor R8, the second resistor R9, the third resistor R10, the fourth resistor R11, the first capacitor E1, the second capacitor C4, the third capacitor C5 and the operational amplifier U3 form an inverting amplifier. At this time, the relationship between VJ and the first voltage value Vout output by the sampling circuit 1 is: For the specific types and parameter values of the first resistor R8, the second resistor R9, the third resistor R10, the fourth resistor R11, the first capacitor E1, the second capacitor C4, the third capacitor C5 and the operational amplifier U3, this application does not make special limitations here. The resistor device can be implemented by a fixed resistor or a variable resistor, etc.; the capacitor device can be implemented by an electrolytic capacitor or a common capacitor, etc.

[0058] As a specific embodiment, the third resistor R10 can be selected as a high-temperature chip resistor with an 0805 package, with a size of 20K; the first resistor R8 and the second resistor R9 can be selected as high-temperature chip resistors with an 0805 package, with a size of 10K; at this time, Vout = -VJ. When the ion current Ia is 100 microamperes, the output Vout of the ion current circuit is 2V. Therefore, the relationship between the output Vout of the ion source current circuit and the actual current of the ion source is: Vout = 20×10 3 ×Ia = 2×10 4 ×Ia; the unit of Vout is volts, and the unit of Ia is microamperes. When Ia is equal to 100 microamperes, it can be calculated that Vout is 2V. U3 can be selected as a CA3140M high-temperature operational amplifier with an SO-8 chip package. The first capacitor E1 can be selected as a chip TPSB package, a high-temperature tantalum capacitor of 10UF / 50V; the second capacitor C4 and the third capacitor C5 can be selected as high-temperature chip capacitors with an 0805 package, with a size of 0.1UF. E1, C4 and C5 all have a filtering effect. The fourth resistor R11 can be selected as a high-temperature chip resistor with an 0805 package, with a size of 100 ohms, which plays an output protection role and can protect U3.

[0059] Specifically, the inverting proportional amplifier includes a first resistor R8, a second resistor R9, a third resistor R10, a fourth resistor R11, a first capacitor E1, a second capacitor C4, a third capacitor C5, and an operational amplifier U3; the inverting proportional amplifier is implemented through the operational amplifier U3, resistor devices, and capacitor devices. The circuit structure is simple, easy to implement, the devices are simple, the cost is low, the output is accurate, which is conducive to the wide promotion of the entire device.

[0060] As a preferred embodiment, the power supply circuit 3 includes a switching transistor N2, a power supply capacitor C6, and a power supply resistor R2; the first end of the power supply capacitor C6 is connected to the output end of the control circuit 2, the second end is respectively connected to the first end of the power supply resistor R2 and the control end of the switching transistor N2, the second end of the power supply resistor R2 is grounded, the first end of the switching transistor N2 is connected to the power supply, and the second end is connected to the filament of the neutron tube 4.

[0061] It can be understood that the power supply control of the filament by the power supply circuit 3 is achieved by the on or off of the switching transistor N2. At the same time, in order to further ensure the accurate conduction of the switching transistor N2, the power supply capacitor C6 and the power supply resistor R2 are provided to play an isolation role to ensure the accurate control of the switching transistor N2 by the control circuit 2. For the switching transistor N2, the specific types and implementation methods of the power supply capacitor C6 and the power supply resistor R2 are not particularly limited in this application. The power supply resistor R2 can be implemented by a fixed resistor or a variable resistor, etc.; the power supply capacitor C6 can be implemented by an electrolytic capacitor or a common capacitor, etc.; the switching transistor N2 can be implemented by a switching device such as a MOS transistor or an IGBT (Insulated Gate Bipolar Transistor).

[0062] Considering the prior art, the method of controlling the heating of the filament by an analog voltage control requires a high-power triode N1 to drive, and a high-power current-limiting resistor R is added. Both the triode N1 and the current-limiting resistor R itself consume a large part of the power. The triode N1 and the current-limiting resistor R are large in volume and prone to heat, and are prone to damage during long-term operation. Since the filament resistance of the neutron tube 4 is only about 4 ohms, the supply current is relatively large and fluctuates. Generally, when the ion source current reaches the normal working condition, the normal filament working current If is between 0.25 - 0.3A. However, at the starting state of operation, since the filament is cold, it takes some time for the deuterium gas to be released, and the supply voltage is the maximum, about half a minute. So the filament working current is relatively large at this time and can reach about 0.8A. Therefore, in the prior art, the power supply to the filament is through a 5V voltage supplied by a high-power current-limiting resistor R and a high-power composite triode N1. Generally, the current-limiting resistor R is selected as a 2-ohm and 2W high-temperature resistor. Under normal circumstances, the current-limiting resistor R consumes a part of the power, and the consumed power is P R , then P R = IR 2 ×R, the voltage V across the high-power current-limiting resistor R R is: V R = I R ×R; I R represents the current value flowing through the current-limiting resistor R. When the power supply is 5V, the voltage drop across the high-power triode N1 is V N , and V N = 5 - V R ; the power P consumed by the high-power triode N1 N , and P N = V N ×I R ; the power consumed by the current-limiting resistor R and the high-power triode N1 is wasted, and the resistor R and the triode N1 will also get hot. Moreover, due to the large working current, the 5V working voltage will be pulled down. Generally, the diameter of the instrument shell is 38 mm, with single-core DC power supply. The smaller the current required, the smaller the components, and the smaller the circuit board size. However, due to the large power, the package of the current-limiting resistor R in the above circuit is large. For safety reasons, a 2-ohm and 2W power resistor is generally used, with an AXIAL0.8 through-hole package, 20 mm long and 4.5 mm wide. The triode N1 uses a high-power composite triode with a TO-247 package, 26 mm long and 16 mm wide. Therefore, not only does it get hot and have a large volume, but it also consumes the power of the power supply in vain. Therefore, in practical applications, the switching tube N2 usually selects a MOS tube to implement.

[0063] Specifically, please refer to Figure 5 , the power supply circuit 3 consists of a power supply capacitor C6, a power supply resistor R2, and a switching tube N2 of an N-channel MOS tube. A diode D1 is also added. The power supply circuit 3 is connected to the hot wire. The ultimate purpose of the power supply circuit 3 is to supply power to the hot wire, control the temperature of the hot wire, reduce the thermal loss of the circuit, and reduce the circuit volume. The pulse signal DRV output by the control circuit 2 passes through the power supply capacitor C6 and then controls the on and off of the MOS tube to intermittently supply power to the hot wire. The power supply capacitor C6 can select a 0805 package high-temperature chip capacitor with a capacitance value of 1UF; the power supply resistor R2 can select a 0805 package high-temperature chip resistor with a resistance value of 100K; the diode D1 can select a high-temperature chip diode IN4148, whose function is to protect the MOS tube. The N-channel MOS tube can select a TO-252 package chip MOS tube IRFR430, 10.6 mm long and 5.69 mm wide, with a breakdown voltage of 500V and a current that can reach 3A. The high-power current-limiting resistor is removed, and a small-volume, large-current MOS tube replaces the large-volume triode. By using the switching function of the MOS tube with a small on-resistance and a large on-current, and adopting the method of intermittently controlling the MOS tube to heat the hot wire of the neutron tube 4 with a pulse signal, the useless thermal loss of the circuit is greatly reduced.

[0064] Specifically, the power supply circuit 3 includes a switching transistor N2, a power supply capacitor C6, and a power supply resistor R2; the control of the power supply process to the heating wire is achieved by the on or off of the switching transistor N2. The circuit structure is simple and easy to implement. Generally, a MOS transistor is used as the switching transistor N2. By controlling the on and off of the MOS transistor in the heating wire power supply circuit 3, the power supply to the heating wire is controlled. The MOS transistor functions as a switch. When it is off, the resistance value between the source and the drain is very large. When it is on, the resistance value between the source and the drain is very small, generally only a few tenths of an ohm. Therefore, when the MOS transistor works, the power consumption is very small. In addition, under the same volume, the current passing through the MOS transistor is much larger than that of a triode. There is no need for a high-power triode and a current-limiting resistor, which can reduce the circuit volume and circuit heat loss and save the instrument circuit design space.

[0065] As a preferred embodiment, the control circuit 2 includes a differential circuit 21 and a signal conversion circuit 22; the first input terminal of the differential circuit 21 is connected to the output terminal of the sampling circuit 1, the second input terminal is connected to the second voltage value corresponding to the target ion source current, the third input terminal is connected to the first output terminal of the signal conversion circuit 22, the output terminal is connected to the input terminal of the signal conversion circuit 22, and the second output terminal of the signal conversion circuit 22 is connected to the input terminal of the power supply circuit 3;

[0066] The differential circuit 21 is used to compare the first voltage value and the second voltage value to obtain a difference value, and output a voltage signal based on the difference value and a reference voltage. The voltage signal is positively linearly related to the difference value and the reference voltage respectively;

[0067] The signal conversion circuit 22 is used to output a reference voltage to the differential circuit 21 through the first output terminal, calculate a preset duty cycle using the voltage signal, and convert the voltage signal into a pulse signal with the preset duty cycle. The preset duty cycle is negatively linearly related to the voltage signal.

[0068] It can be understood that the differential circuit 21 realizes the comparison function of the control circuit 2 for the first voltage value and the second voltage value, and the signal conversion circuit 22 realizes the function of the control circuit 2 to output a pulse signal with a preset duty cycle. The specific circuit structure and implementation method of the differential circuit 21 and the signal conversion circuit 22 are not particularly limited in this application. The differential circuit 21 can be implemented by a differential amplifier or an instrumentation amplifier, etc. An instrumentation amplifier is a closed-loop gain unit with differential input and single-ended output relative to a reference terminal. The signal conversion circuit 22 can be implemented by a control chip such as a PWM controller. The specific type and implementation method of the voltage signal output by the differential circuit 21 and the pulse signal with a variable duty cycle output by the signal conversion circuit 22 are not particularly limited in this application. The voltage signal output by the differential circuit 21 can be implemented by a PWM wave. The duty cycle of the pulse signal DRV output by the signal conversion circuit 22 can be set to automatically adjust from 0 to 50%, or can be set to a pulse signal with an adjustable duty cycle in other ranges, and can be specifically selected according to actual application requirements.

[0069] The differential circuit 21 and the signal conversion circuit 22 adopt the method of hardware circuit feedback to control the power supply of the hot wire in real time, maintain the stability of the ion source current, and input the first voltage value Vout corresponding to the ion source current value sampled by the sampling circuit 1 and the second voltage value Via corresponding to the target ion source current value required for the neutron tube 4 to be stable into the differential circuit 21 at the same time. According to the comparison result of the two, the differential circuit 21 sends the output voltage signal Vpwm to the signal conversion circuit 22 to control the signal conversion circuit 22 to output a pulse signal DRV with a variable duty cycle of 0 - 50%. Because it is usually necessary to supply power to the hot wire when the current ion source current is less than the target ion source current to meet the demand, the pulse signal DRV is usually set to have a variable duty cycle of 0 - 50%. The smaller Vout is, the larger the duty cycle is, and the longer the conduction time of the MOS tube is. The closer Vout is to Via, the smaller the duty cycle is, and the shorter the conduction time of the MOS tube is. When Vout is greater than Via, the duty cycle is zero and the MOS tube is cut off. Due to the hardware processing method of circuit sampling, the circuit response is very fast, belonging to the nanosecond level, and the Vout output is stable.

[0070] Specifically, the control circuit 2 includes a differential circuit 21 and a signal conversion circuit 22. The differential circuit 21 determines the gap between the current ion source current and the target ion source current. Then, the signal conversion circuit 22 calculates and outputs a pulse signal with a variable duty cycle by using the voltage signal corresponding to the difference, controls the conduction and cut-off of the switching tube N2 in the hot wire power supply circuit 3, and thus supplies power to the wire of the neutron tube 4 through the output pulse signal to control the power supply of the hot wire. The function of the control circuit 2 is effectively realized, ensuring the accurate implementation of the ion source current control device 31. Using a MOS tube as the switching tube N2 can further reduce the circuit volume and circuit heat loss.

[0071] As a preferred embodiment, the differential circuit 21 includes a first voltage dividing resistor R12, a second voltage dividing resistor R13, a reference voltage circuit, and a differential amplifier U2. The first end of the first voltage dividing resistor R12 is connected to the output end of the sampling circuit 1, and the second end is connected to the first input end of the differential amplifier U2. The first end of the second voltage dividing resistor R13 is connected to the second voltage value corresponding to the target ion source current, and the second end is connected to the second input end of the differential amplifier U2. The third input end of the differential amplifier U2 is connected to the output end of the reference voltage circuit, and the output end is connected to the input end of the signal conversion circuit 22. The input end of the reference voltage circuit is connected to the first output end of the signal conversion circuit 22.

[0072] It can be understood that the differential circuit 21 can be implemented by the differential amplifier U2. Considering that the magnitude relationship between the first voltage value and the second voltage value is not clear, a reference voltage circuit is set to provide a reference for the output signal of the differential amplifier U2, avoiding the situation where the output is negative due to the first voltage value being less than or greater than the second voltage value, and thus unable to correctly output a voltage signal. At the same time, considering that directly connecting the voltage signal may cause an impact on the input end of the differential amplifier U2 and other situations, the first voltage dividing resistor R12 and the second voltage dividing resistor R13 are set to protect the circuit. The specific types and implementation methods of the first voltage dividing resistor R12, the second voltage dividing resistor R13, the reference voltage circuit, and the differential amplifier U2 are not particularly limited in this application.

[0073] Specifically, the differential circuit 21 includes a first voltage dividing resistor R12, a second voltage dividing resistor R13, a reference voltage circuit, and a differential amplifier U2. The circuit structure is simple, easy to implement, the components used are simple, the cost is low, and the volume is small, which is conducive to the simple implementation and application promotion of the entire device.

[0074] As a preferred embodiment, the reference voltage circuit includes a third voltage dividing resistor R14 and a fourth voltage dividing resistor R15. The first end of the third voltage dividing resistor R14 is connected to the first output end of the signal conversion circuit 22, and the second end is respectively connected to the first end of the fourth voltage dividing resistor R15 and the third input end of the differential amplifier U2. The second end of the fourth voltage dividing resistor R15 is grounded.

[0075] It can be understood that the reference voltage circuit can be implemented by a voltage dividing circuit. The specific types and parameter values of the third voltage dividing resistor R14 and the fourth voltage dividing resistor R15 are not particularly limited in this application and can be implemented by fixed resistors or variable resistors, etc.

[0076] Specifically, as Figure 5As shown, the differential amplifier U2, the first voltage-dividing resistor R12, the second voltage-dividing resistor R13, the third voltage-dividing resistor R14, the fourth voltage-dividing resistor R15, and the resistor RL form a differential circuit 21. The differential amplifier U2 is an instrumentation amplifier AD620 with differential input and relative reference terminal, implemented in a surface mount SO-8 package. The relationship between its input and output is as follows: In the formula, Vpwm represents the voltage signal output by the differential amplifier U2, Vout represents the first voltage value corresponding to the current ion source current output from the sampling circuit 1, and Via represents the second voltage value corresponding to the target ion source current required for the operation of the neutron tube 4. The relationships between Vout and Via and the ion source current both satisfy the descriptions in the above embodiments. For example, when Vout is 2V, it represents that the ion source current at this time is 100 microamps, and when Vout is 1V, it represents that the ion source current at this time is 50 microamps; This is the calculation formula for the amplification factor of this type of instrumentation amplifier. Vref is the reference voltage terminal of the differential amplifier U2, which is the value of the reference voltage output by the reference voltage circuit. When the input voltage difference is zero, the output voltage Vref of the amplifier is We can take R14 = R15, so Vref = 2.5V.

[0077] In practical applications, RL connected to the differential amplifier U2 is usually disconnected, that is, RL is infinite, and 49.4K / RL is approximately zero. Then Vpwm = Vout - Via + Vref, and Vref = 2.5V; The first voltage-dividing resistor R12 and the second voltage-dividing resistor R13 can be selected as high-temperature surface mount resistors in 0805 package, with a size of 10K. The third voltage-dividing resistor R14 and the fourth voltage-dividing resistor R15 can be selected as high-temperature surface mount resistors in 0805 package, with a size of 1K.

[0078] Specifically, the reference voltage circuit includes the third voltage-dividing resistor R14 and the fourth voltage-dividing resistor R15, which is implemented through a voltage-dividing circuit. The circuit structure is simple and effective, easy to implement, the devices used have low cost and small volume, which is beneficial to the simple implementation and application promotion of the entire device.

[0079] As a preferred embodiment, the signal conversion circuit 22 includes a controller and a frequency circuit; The input end of the controller is connected to the output end of the differential circuit 21. The first output end is respectively connected to the third input end of the differential circuit 21 and the first end of the frequency circuit. The second output end is connected to the input end of the power supply circuit 3. The second end of the frequency circuit is connected to the timing port of the controller;

[0080] The controller is used to output a reference voltage to the differential circuit 21 and the frequency circuit through the first output end, calculate a preset duty cycle using the voltage signal, and convert the voltage signal into a pulse signal with a preset duty cycle. The preset duty cycle is negatively linearly correlated with the voltage signal;

[0081] The frequency circuit is used to control the frequency of the pulse signal output by the controller.

[0082] Specifically, the function of the controller is to receive the voltage signal Vpwm output by the differential circuit 21, and output a pulse signal with a corresponding duty cycle according to the value of the voltage signal to control the conduction and cut-off of the power supply circuit 3. The specific circuit structure and connection method of the controller and the frequency circuit are not particularly limited in this application, and can be selected and adjusted according to factors such as the type of the specifically selected controller. The core device controller U1 of the signal conversion circuit 22 can select a PWM controller of UC1844 high-temperature patch. The 8-pin VREF can provide a reference voltage of 5V. When a pulse signal with a variable duty cycle of 0-50% is to be output, when the voltage signal received at the input terminal of pin 2 is greater than or equal to 2.5V, the device is cut off and there is no output at pin 6. When the voltage at pin 2 is less than 2.5V, pin 6 outputs a pulse signal with adjustable pulse width. The pulse width changes with the voltage at pin 2. The smaller the voltage at pin 2, the larger the duty cycle of the output pulse signal, but the maximum duty cycle is less than 50%.

[0083] When a pulse signal with a variable duty cycle of 0-50% is to be output, the duty cycle D of the controller output signal is: where D represents the duty cycle, Vpwm represents the input voltage signal received by the controller. When the input is zero, the duty cycle is the largest, which is 50%. When the input is 2.5 volts, the duty cycle is 0. In practical applications, a resistor R1 and a capacitor C1 can also be set to play roles such as filtering and isolation; when the controller is in use, the TSEN pin can be grounded through a resistor R6 to ensure the normal operation of the controller. R1 can select a 0805 package high-temperature patch resistor with a resistance value of 51K; R6 can select a 0805 package high-temperature patch resistor with a resistance value of 1K; C1 can select a 0805 package high-temperature patch capacitor with a capacitance value of 100P.

[0084] Specifically, the signal conversion circuit 22 includes a controller and a frequency circuit. The controller is used to implement the output of a pulse signal with a variable duty cycle, and the frequency circuit assists in controlling the frequency of the output pulse signal, effectively realizing the function of the signal conversion circuit 22. The circuit structure is simple and easy to implement.

[0085] As a preferred embodiment, the frequency circuit includes a fifth resistor R7, a fourth capacitor C2, and a fifth capacitor C3; the first end of the fifth resistor R7 is respectively connected to the third input terminal of the differential circuit 21, the first end of the fifth capacitor C3, and the first output terminal of the controller, and the second end is respectively connected to the timing port of the controller and the first end of the fourth capacitor C2. The second ends of the fifth capacitor C3 and the fourth capacitor C2 are grounded.

[0086] Specifically, the frequency circuit includes a fifth resistor R7, a fourth capacitor C2, and a fifth capacitor C3. Under the control of the peripheral frequency circuit, the frequency F of the signal output by the controller is: In a specific circuit, RT = R7, CT = C2. R7 can be a 0805 package high-temperature chip resistor with a resistance value of 10K. C2 can be a 0805 package high-temperature chip capacitor with a capacitance value of 0.6UF; C3 can be a 0805 package high-temperature chip capacitor with a capacitance value of 0.1U; at this time, the frequency F of the output signal is approximately 2.5K.

[0087] Specifically, the frequency circuit includes a fifth resistor R7, a fourth capacitor C2, and a fifth capacitor C3, effectively realizing the function of the frequency circuit. The circuit structure is simple and easy to implement.

[0088] Please refer to Figure 6 , Figure 6 FIG.

[0089] It can be understood that specific types of the neutron tube 4 and the specific connection relationship between it and the ion source current control device 31 are not particularly limited in this application and can be adjusted according to the specific circuit structure in actual applications.

[0090] For the introduction of a control system for ion source current provided by the present invention, please refer to the embodiments of the ion source current control device 31 described above, and details will not be repeated herein.

[0091] In this specification, each embodiment is described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The same or similar parts among the embodiments can be referred to each other. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the description of the method part.

[0092] It should also be noted that in this specification, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, such that a process, method, article or device comprising a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article or device. Without further limitation, an element defined by the phrase "comprising an..." does not exclude the presence of additional identical elements in the process, method, article or device comprising the element.

[0093] The foregoing description of the disclosed embodiments enables those skilled in the art to practice or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A device for controlling ion source current, characterized in that: The ion source current is a discharge current formed between the anode and cathode of the neutron tube. The circuit includes: A sampling circuit, whose input end is connected to the neutron tube, is used to detect the ion source current of the neutron tube and convert it into a corresponding first voltage value, wherein the first voltage value is positively linearly correlated with the ion source current; A control circuit, wherein a first input end is connected to an output end of the sampling circuit, and a second input end is connected to a second voltage value corresponding to a target ion source current, and is used to compare the first voltage value with the second voltage value to obtain a difference, and output a pulse signal of a preset duty cycle, wherein the preset duty cycle is positively linearly correlated with the difference between the first voltage value and the second voltage value; A power supply circuit, whose input end is connected to the output end of the control circuit and whose output end is connected to the hot wire of the neutron tube, is used to control the power supply of the hot wire by turning it on or off based on the pulse signal output by the control circuit, thereby controlling the ion source current.

2. The ion source current control device according to claim 1, characterized in that: The sampling circuit includes an inverse proportional amplifier and a sampling resistor; a first end of the sampling resistor is connected to the anode transformer of the neutron tube, a second end is grounded and connected to the cathode of the neutron tube, an input end of the inverse proportional amplifier is connected to the first end of the sampling resistor; and an output end is connected to the first input end of the control circuit.

3. The ion source current control device according to claim 2, characterized in that: The reverse proportional amplifier comprises a first resistor, a second resistor, a third resistor, a fourth resistor, a first capacitor, a second capacitor, a third capacitor and an operational amplifier; The first end of the first capacitor is grounded and connected to the second end of the sampling resistor, the second end is respectively connected to the first end of the sampling resistor and the first end of the first resistor, the second end of the first resistor is respectively connected to the first end of the second capacitor and the first end of the second resistor, the second end of the second capacitor is grounded, the second end of the second resistor is respectively connected to the first end of the third resistor and the first input end of the operational amplifier, the second input end of the operational amplifier is grounded, the output end is respectively connected to the second end of the third resistor and the first end of the fourth resistor, the second end of the fourth resistor is respectively connected to the first end of the third capacitor and the first input end of the control circuit, and the second end of the third capacitor is grounded.

4. The ion source current control device according to claim 1, characterized in that: The power supply circuit includes a switching tube, a power supply capacitor and a power supply resistor; the first end of the power supply capacitor is connected to the output end of the control circuit, and the second end is respectively connected to the first end of the power supply resistor and the control end of the switching tube, the second end of the power supply resistor is grounded, the first end of the switching tube is connected to the power supply, and the second end is connected to the hot wire of the neutron tube.

5. The ion source current control device according to any one of claims 1 to 4, characterized in that: The control circuit includes a differential circuit and a signal conversion circuit; a first input end of the differential circuit is connected to an output end of the sampling circuit, a second input end is connected to a second voltage value corresponding to a target ion source current, a third input end is connected to a first output end of the signal conversion circuit, an output end is connected to an input end of the signal conversion circuit, and a second output end of the signal conversion circuit is connected to an input end of the power supply circuit; The differential circuit is used for comparing the first voltage value and the second voltage value to obtain a difference, and outputting a voltage signal based on the difference and a reference voltage, wherein the voltage signal is positively linearly correlated with the difference and the reference voltage respectively; The signal conversion circuit is used to output the reference voltage to the differential circuit through the first output terminal, calculate a preset duty cycle using the voltage signal, and convert the voltage signal into a pulse signal with a preset duty cycle, wherein the preset duty cycle is negatively linearly correlated with the voltage signal.

6. The ion source current control device according to claim 5, characterized in that: The differential circuit includes a first voltage-dividing resistor, a second voltage-dividing resistor, a reference voltage circuit and a differential amplifier; the first end of the first voltage-dividing resistor is connected to the output end of the sampling circuit, and the second end is connected to the first input end of the differential amplifier; the first end of the second voltage-dividing resistor is connected to the second voltage value corresponding to the target ion source current, and the second end is connected to the second input end of the differential amplifier; the third input end of the differential amplifier is connected to the output end of the reference voltage circuit, and the output end is connected to the input end of the signal conversion circuit; the input end of the reference voltage circuit is connected to the first output end of the signal conversion circuit.

7. The ion source current control device according to claim 6, characterized in that: The reference voltage circuit includes a third voltage-dividing resistor and a fourth voltage-dividing resistor; the first end of the third voltage-dividing resistor is connected to the first output end of the signal conversion circuit, and the second end is respectively connected to the first end of the fourth voltage-dividing resistor and the third input end of the differential amplifier, and the second end of the fourth voltage-dividing resistor is grounded.

8. The ion source current control device according to claim 5, characterized in that: The signal conversion circuit includes a controller and a frequency circuit; the input end of the controller is connected to the output end of the differential circuit, the first output end is respectively connected to the third input end of the differential circuit and the first end of the frequency circuit, the second output end is connected to the input end of the power supply circuit, and the second end of the frequency circuit is connected to the timing port of the controller; The controller is used to output the reference voltage to the differential circuit and the frequency circuit through the first output terminal, calculate a preset duty cycle using the voltage signal, and convert the voltage signal into a pulse signal of a preset duty cycle, wherein the preset duty cycle is negatively linearly correlated with the voltage signal; The frequency circuit is used to control the frequency of the pulse signal output by the controller.

9. The ion source current control device according to claim 8, characterized in that: The frequency circuit includes a fifth resistor, a fourth capacitor and a fifth capacitor; the first end of the fifth resistor is respectively connected to the third input end of the differential circuit, the first end of the fifth capacitor and the first output end of the controller, the second end is respectively connected to the timing port of the controller and the first end of the fourth capacitor, and the second end of the fifth capacitor and the second end of the fourth capacitor are grounded.

10. A control system for ion source current, characterized in that: The invention comprises a neutron tube and the ion source current control device as claimed in any one of claims 1 to 9, wherein the neutron tube is connected to the ion source current control device.

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