Neutron generator based on radio frequency discharge for neutron logging

Abstract

The neutron generator comprises a neutron generator shell, a power supply module and a neutron tube, the power supply module and the neutron tube are arranged in the shell, and the neutron tube adopts a sealing design and comprises a radio frequency ion source, a plasma electrode, an extraction electrode, a target seat and an air suction heater; the radio frequency ion source is of an external capacitance coupling structure composed of a dielectric tube, a coupling ring and a permanent magnet ring. Through the design of the external capacitance coupling structure, radio frequency power can be coupled into the medium tube to excite and generate plasma, low-power discharge is achieved, meanwhile, the monatomic ion proportion and the neutron yield are improved, and the working performance of the neutron tube can be adjusted through the adjusting technology of the capacitance coupling structure. In addition, based on the target end grounding design, the heat dissipation capability of the target can be effectively improved, the neutron yield and the working stability of the neutron generator are further improved, and the high application effect is achieved in the field of small-size neutron generators.

Description

Technical Field

[0001] This application relates to the field of accelerator neutron sources, and particularly to a radio-frequency discharge-based neutron generator for neutron logging. Background Art

[0002] The thermal neutron logging method (compensated logging method) has important applications in the field of petroleum logging. Currently, the Am-Be neutron source is mainly used. This source is a radioactive source with a relatively long half-life, and the reaction cannot be started and stopped at any time. There are safety and management risks during transportation and use, and the cost is high. Currently, the petroleum logging tool based on the deuterium-tritium neutron tube that is under development has the advantage of being able to be started and stopped at any time, and its safety is higher than that of the Am-Be neutron source. However, the tritium material used in it is still a radioactive material, which limits its management and use in many aspects. Moreover, the neutron energy of the neutron tube based on the deuterium-tritium reaction is as high as 14.5 MeV, and the γ signal generated by the inelastic reaction will interfere with the measurement. When performing thermal neutron logging, other logging methods need to be combined to correct the data, making the measurement process complicated.

[0003] The deuterium-deuterium neutron generator is a nuclear technology device that uses deuterium nuclear fusion reaction to generate neutrons. The neutrons generated by the deuterium-deuterium reaction have an energy of 2.45 MeV, which is closer to the neutron energy of the Am-Be. At the same time, it has the advantages of being able to be started and stopped at any time, having no radioactive materials, small interference signals, and high sensitivity, and is the best choice for future thermal neutron logging methods. The reaction used in the current commercial neutron tube is the deuterium-tritium reaction, and the ion source in it is a Penning ion source, which has the defect of a low proportion of single atomic ions. The life of the target limits the improvement of the deuterium ion beam intensity. Therefore, when the commercial neutron tube is directly used to generate deuterium-deuterium neutrons, the yield is lower than 1×10 6 n / s, which will result in a long measurement time and severely limit the application of the deuterium-deuterium neutron tube. Therefore, it is necessary to develop other high-performance neutron tubes different from the discharge principle of the current commercial neutron tube to adapt to the application of the deuterium-deuterium neutron generator. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a radio-frequency discharge-based neutron generator for neutron logging to solve the problems of low neutron yield and insufficient safety of the current neutron generator for logging.

[0005] To solve the above problems, the present invention adopts the following technical solutions:

[0006] A radio-frequency discharge-based neutron generator for neutron logging, comprising a neutron generator housing 19 and a power supply module and a neutron tube arranged inside the housing;

[0007] The power supply module includes a high-voltage power supply module 13, a radio frequency power source module 12, and an getter heater power supply module 14; the high-voltage power supply module 13 is connected to the high-voltage feed-in electrode 1; the radio frequency power source module 12 is connected to the coupling ring 3; the getter heater power supply module 14 supplies power to the getter heater 9;

[0008] The neutron tube adopts a sealed design and includes a radio frequency ion source, a plasma electrode 5, an extraction electrode 6, a target seat, and a getter heater 9; the radio frequency ion source includes a dielectric tube 2, a coupling ring 3, and a permanent magnet ring 4; the dielectric tube 2 forms a sealed outer shell main body, which is integrally welded with the high-voltage feed-in electrode 1, the plasma electrode 5, and the target seat. The high-voltage feed-in electrode 1 is located at the head of the dielectric tube 2, the plasma electrode 5 is located inside the middle of the dielectric tube 2, and the target seat is located at the tail of the dielectric tube 2; the coupling ring 3 and the permanent magnet ring 4 are arranged outside the dielectric tube 2 and close to the plasma electrode 5. The coupling ring 3 is a single coil, and the permanent magnet ring 4 is connected to the neutron generator housing 19; the target seat is composed of a target piece 7, a heat dissipation base 8, an electron suppression magnet 10, and a heat dissipation adapter seat 11. The target piece 7 is arranged on the heat dissipation base 8, the heat dissipation base 8 is arranged on the heat dissipation adapter seat 11, and an electron suppression magnet 10 is embedded at the contact end of the heat dissipation adapter seat 11 and the heat dissipation base 8. The heat dissipation adapter seat 11 is connected to the neutron generator housing 19; the extraction electrode 6 is installed on the target seat; the getter heater 9 is embedded inside the heat dissipation adapter seat 11 and can store and release the deuterium gas required for the radio frequency ion source discharge.

[0009] Preferably, the material of the dielectric tube 2 is one of glass, quartz, and ceramic.

[0010] Preferably, the distance between the permanent magnet ring 4 and the coupling ring 3 is 5 - 25 mm.

[0011] Preferably, the permanent magnet ring 4 is located 0 - 10 mm above the plasma electrode 5.

[0012] Preferably, the extraction electrode 6 is threadedly connected to the target seat.

[0013] Preferably, the getter heater 9 stores deuterium-tritium mixed gas or tritium gas.

[0014] Preferably, the target piece 7 is a light target without pre-stored gas.

[0015] Preferably, the gas pre-stored in the target piece 7 is one of deuterium gas, deuterium-tritium mixed gas, and tritium gas.

[0016] Preferably, the target end is connected to a negative potential

[0017] The beneficial effects of the neutron generator based on radio frequency discharge for neutron logging of the present invention include:

[0018] (1) Adopting a capacitive coupling radio frequency discharge design can make the beam current intensity greater than 100 μA, the proportion of single atomic ions greater than 50%, and the deuterium-deuterium neutron yield reach 1×10 7 n / s. Compared with the existing inductive coupling method and Penning discharge method, in the field of small-sized neutron generators, it can effectively achieve low-power discharge, increase the proportion of single atomic ions, and thus increase the neutron yield;

[0019] (2) Adopting an external design for the ion source power supply system simplifies the internal structure of the neutron tube, can effectively improve the working stability of the neutron tube, and reduce the risk of neutron tube failure caused by ion source problems in the neutron tube; The working performance of the neutron tube can also be adjusted in a timely manner through the adjustment of the capacitive coupling structure;

[0020] (3) Adopting a target-end grounding design enables the target to be directly connected to the neutron generator housing, improving the heat dissipation capacity of the target, reducing the target surface temperature, increasing the deuterium storage capacity of the target surface, and increasing the neutron yield and the working stability of the neutron generator. Description of the Drawings

[0021] Figure 1 It is a schematic structural diagram of a radio frequency discharge-based neutron generator for neutron logging according to the present invention.

[0022] In the figure, 1. High-voltage feeding electrode; 2. Dielectric tube; 3. Coupling ring; 4. Permanent magnet ring; 5. Plasma electrode; 6. Extraction electrode; 7. Target piece; 8. Heat dissipation base; 9. Getter hot cathode; 10. Electron suppression magnet; 11. Heat dissipation adapter; 12. Radio frequency power source module; 13. High-voltage power source module; 14. Getter hot cathode power supply module; 15. High-voltage power source module output line; 16. Radio frequency power source module output line; 17. Connection line between the permanent magnet ring and the neutron generator housing; 18. Getter hot cathode power supply module output line; 19. Neutron generator housing. Detailed Embodiments

[0023] To make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the present invention will be further described below in conjunction with embodiments and drawings. The illustrative embodiments and descriptions of the present invention are only used for detailed explanation of the present invention and cannot be used to limit the present invention.

[0024] A radio frequency discharge-based neutron generator for neutron logging, as Figure 1As shown in the figure, it includes a neutron generator housing and a power supply module and a neutron tube disposed inside the housing. Among them, the power supply module includes a high-voltage power supply module, a radio frequency power source module, and an getter heater power supply module. The high-voltage power supply module is connected to the high-voltage feed-in electrode, the radio frequency power source module is connected to the coupling ring, and the getter heater power supply module supplies power to the getter heater. By applying a direct current, the getter heater can release a certain amount of deuterium gas; the neutron tube adopts a sealed design and includes a radio frequency ion source, a plasma electrode, an extraction electrode, a target seat, and a getter heater. The radio frequency ion source in the neutron tube is composed of a dielectric tube, a coupling ring, and a permanent magnet ring. The dielectric tube forms the main sealed housing body, which is integrally welded with the high-voltage feed-in electrode, the plasma electrode, and the target seat. The high-voltage feed-in electrode is located at the head of the dielectric tube, the plasma electrode is located inside the middle of the dielectric tube, and the target seat is located at the tail of the dielectric tube; the coupling ring and the permanent magnet ring are disposed outside the dielectric tube and close to the plasma electrode. The coupling ring is a single coil, which is used to couple the radio frequency power into the dielectric tube, and the permanent magnet ring is connected to the neutron generator housing. Through the design of this permanent magnet ring, on the one hand, it can confine the plasma generated by the discharge, reduce the wall loss, and increase the proportion of single atomic ions. On the other hand, it can form a capacitive coupling structure together with the coupling ring, and can couple the radio frequency power into the dielectric tube with an outer diameter of 25 mm, and then ionize the deuterium gas released by the getter heater to generate plasma. The target seat in the neutron tube is composed of a target piece, a heat dissipation base, an electron suppression magnet, and a heat dissipation adapter seat. Among them, the target piece is disposed on the heat dissipation base, the heat dissipation base is disposed on the heat dissipation adapter seat, the electron suppression magnet is embedded at the contact end of the heat dissipation adapter seat and the heat dissipation base, and the heat dissipation adapter seat is connected to the neutron generator housing. The electron suppression magnet is used to suppress the secondary electrons generated when the target piece is bombarded by the beam current; the heat dissipation adapter seat can effectively conduct the heat generated by the beam current bombarding the target piece to the outside, ensuring that the surface temperature of the target piece will not be too high. The extraction electrode in the neutron tube is installed on the target seat and forms a beam extraction structure together with the plasma electrode. When the positive high voltage of the high-voltage feed-in electrode from the head of the dielectric tube reaches the plasma, the positive ions in the plasma are extracted through the beam extraction structure to achieve the bombardment of the target piece after the acceleration electrode; the getter heater is embedded inside the heat dissipation adapter seat and can store and release the deuterium gas required for the discharge of the radio frequency ion source.

[0025] Through the structural design of the present invention, when a positive high voltage greater than 80 kV is applied to the head of the dielectric tube, the proportion of single atomic ions in the deuterium ion beam extracted by the beam extraction structure will exceed 50%. The deuterium ion beam bombards the deuterium target, and neutrons of 2.45 MeV can be generated through the deuterium-deuterium reaction, and it can achieve greater than 1×10 7The deuterium-deuterium neutron yield of n / s replaces the Am-Be neutron source used in the current logging tube and the deuterium-tritium neutron source in some oil logging tools, which can effectively improve the safety of the neutron source and the efficiency and accuracy of thermal neutron logging. In addition, through the design of grounding the target end, on the one hand, the target can be directly connected to the outer cylinder of the generator, improving the heat dissipation capacity of the target and greatly extending the service life of the target; on the other hand, the neutron generation position can be located at the end of the generator, closer to the detector, thereby improving the neutron logging efficiency.

[0026] In a preferred embodiment, the dielectric tube is made of one of glass, quartz, and ceramic.

[0027] To further improve the discharge efficiency, the proportion of single atomic ions, and the neutron yield, the distance between the permanent magnet ring and the coupling ring can be set to 5-25 mm.

[0028] Further preferably, the permanent magnet ring 4 is located 0-10 mm above the plasma electrode 5, so that the magnetic field can more effectively confine the plasma above the plasma electrode and improve the beam extraction efficiency.

[0029] Further preferably, a threaded connection is adopted between the extraction electrode and the target seat to better press the target piece, the heat dissipation base, and the electron suppression magnet on the heat dissipation adapter seat, improving the heat dissipation efficiency.

[0030] The neutron generator of the present invention can be used not only for deuterium-deuterium reactions but also for deuterium-tritium reactions. Therefore, the getter hot cathode can also store deuterium-tritium mixed gas or tritium gas to achieve deuterium-tritium neutron reactions and increase their neutron yield.

[0031] Furthermore, the target piece can be a bare target without pre-stored gas, or it can pre-store one of deuterium gas, deuterium-tritium mixed gas, and tritium gas, so that when the plasma after beam extraction bombards the target piece, it can react with the pre-stored deuterium (or tritium) in the target piece to generate neutrons, increasing the neutron yield in the initial stage of the reaction.

[0032] In another embodiment, the target end is connected to a negative potential.

[0033] The present invention has been described in detail above in combination with specific embodiments and exemplary examples. The above description is exemplary and not exhaustive, and is not limited to the disclosed embodiments; the above description should not be construed as a limitation of the present invention. Those skilled in the art understand that without departing from the spirit and scope of the present invention, various equivalent substitutions, modifications, or improvements can be made to the technical solutions and their implementation manners of the present invention, and these all fall within the scope of the present invention; the protection scope of the present invention is subject to the appended claims.

Claims

1. A neutron generator based on radio frequency discharge for neutron logging, characterized in that: It comprises a neutron generator housing (19) and a power supply module and a neutron tube arranged in the housing; The power supply module comprises a high-voltage power supply module (13), a radio frequency power source module (12) and an air-intake heater power supply module (14); the high-voltage power supply module (13) is connected to the high-voltage feed-in electrode (1); the radio frequency power source module (12) is connected to the coupling ring (3); the air-intake heater power supply module (14) supplies power to the air-intake heater (9); The neutron tube adopts a sealed design and comprises a radio frequency ion source, a plasma electrode (5), an extraction electrode (6), a target seat and an air intake heater (9); the radio frequency ion source comprises a dielectric tube (2), a coupling ring (3) and a permanent magnet ring (4); the dielectric tube (2) constitutes a sealed shell body and is integrally welded with the high-voltage feed electrode (1), the plasma electrode (5) and the target seat, the high-voltage feed electrode (1) being located at the head of the dielectric tube (2), the plasma electrode (5) being located in the middle of the dielectric tube (2), and the target seat being located at the tail of the dielectric tube (2); the coupling ring (3) and the permanent magnet ring (4) being arranged outside the dielectric tube (2) and close to the plasma electrode (5); The coupling ring (3) is a single coil, and the permanent magnet ring (4) is connected to a neutron generator housing (19); the target seat is composed of a target piece (7), a heat dissipation base (8), an electron suppression magnet (10) and a heat dissipation adapter (11); the target piece (7) is arranged on the heat dissipation base (8), the heat dissipation base (8) is arranged on the heat dissipation adapter (11), the heat dissipation adapter (11) and the contact end of the heat dissipation base (8) are embedded with the electron suppression magnet (10), and the heat dissipation adapter (11) is connected to the neutron generator housing (19); the extraction electrode (6) is installed on the target seat; the air-intake heater (9) is embedded in the heat dissipation adapter (11) and can store and release deuterium gas required for the discharge of the radio frequency ion source.

2. The neutron generator based on radio frequency discharge for neutron logging according to claim 1, characterized in that: The material of the medium tube (2) is one of glass, quartz and ceramic.

3. The neutron generator based on radio frequency discharge for neutron logging according to claim 1, characterized in that: The distance between the permanent magnetic ring (4) and the coupling ring (3) is 5 to 25 mm.

4. The neutron generator based on radio frequency discharge for neutron logging according to claim 1, characterized in that: The permanent magnetic ring (4) is located 0 to 10 mm above the plasma electrode (5).

5. The neutron generator based on radio frequency discharge for neutron logging according to claim 1, characterized in that: The lead-out electrode (6) is threadedly connected to the target seat.

6. The neutron generator based on radio frequency discharge for neutron logging according to claim 1, characterized in that: The air-intake heater (9) stores deuterium-tritium mixed gas or tritium gas.

7. The neutron generator based on radio frequency discharge for neutron logging according to claim 6, characterized in that: The target piece (7) is a light target without pre-stored gas.

8. The neutron generator based on radio frequency discharge for neutron logging according to claim 6, characterized in that: The gas pre-stored in the target piece (7) is one of deuterium gas, deuterium-tritium mixed gas, and tritium gas.

9. The neutron generator based on radio frequency discharge for neutron logging according to claim 1, characterized in that: The target is terminated at a negative potential.

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