Surface ionization probe system for off-line measurement of cesium evaporation rate in fusion device

Abstract

The invention relates to the technical field of metal cesium deposition in a magnetic confinement nuclear fusion negative neutral beam injection system, in particular to a surface ionization probe system for off-line measurement of the cesium evaporation rate in a fusion device. According to the technical scheme, the device comprises a vacuum chamber, a cesium crucible assembly, a vacuum air extractor set, a heating assembly and a surface ionization probe system, the vacuum chamber is a cuboid chamber made of stainless steel, the top of the vacuum chamber is provided with a sealing flange connected with a cesium evaporation channel, and the side wall of the vacuum chamber is provided with a quick-connection flange connected with the vacuum air extractor set. According to the invention, the evaporation rate of cesium in a vacuum environment can be calculated, and real-time monitoring of the evaporation rate of cesium in a vacuum stage is realized by transplanting an off-line measurement system into a negative ion source. And through the quantized cesium injection amount, the good coverage rate of cesium at the plasma electrode is determined, and generation of negative ions of the negative ion source is facilitated.

Description

Technical Field

[0001] The invention relates to the technical field of metal cesium deposition in a magnetic confinement nuclear fusion negative neutral beam injection system, and in particular to a surface ionization probe system for off-line measurement of cesium evaporation rate in a fusion device. Background Art

[0002] Magnetic confinement nuclear fusion has become one of the important solutions to human energy problems with its unique rich raw materials, huge energy and inherent safety properties, and has attracted the attention of many developed and developing countries at home and abroad. However, in order to achieve fusion ignition conditions for magnetic confinement nuclear fusion, its conditions are very harsh, especially the core ion temperature needs to exceed 10keV. In order to achieve a core particle temperature of more than 10keV for magnetic confinement nuclear fusion, the neutral beam injection system has become one of the focuses of magnetic confinement nuclear fusion research with its significant heating capacity. In principle, the core component of the neutral beam injection system, the ion source, can be a positive ion source or a negative ion source, but as the beam energy is higher than 200keV, the neutralization efficiency of positive ions decreases to less than 20%, while the neutralization efficiency of negative ion sources remains at around 60% when the energy is as high as 1MeV. To optimize the use of negative ion sources, it is necessary to increase the generation of negative ions in the negative ion source. The most efficient way to increase the yield of negative ions is to inject cesium into the negative ion source. However, cesium will react with impurities in the ion source to generate compounds that are difficult to remove. This part of cesium cannot participate in the cesium distribution process. After the ion source has been running for a period of time, there will not be enough cesium accumulation at the PG. Therefore, it is necessary to evaporate liquid cesium into the ion source continuously through the cesium injection system, which requires accurate measurement of the cesium evaporation rate. However, in the negative ion source experiment, the measurement of the cesium evaporation rate has problems such as complex measurement system, difficult operation, and high-voltage ignition risk.

[0003] The complexity and limitations of online measurement make offline measurement methods an important supplementary means of cesium measurement. Offline measurement systems usually have high measurement accuracy and flexibility, and can quantitatively analyze the cesium evaporation rate under different temperature conditions. In addition, the offline measurement system can be well transplanted into the negative ion source of the fusion device to achieve real-time monitoring of the cesium evaporation amount during the experiment. However, there is still a lack of offline systems for cesium evaporation rate measurement, which makes it impossible to intuitively judge the impact of cesium on the beam yield in negative ion source experiments, seriously affecting the stable operation of high-performance negative neutral beam experiments.

[0004] Therefore, the present application proposes a surface ionization probe system for off-line measurement of cesium evaporation rate in a fusion device. Summary of the invention

[0005] The purpose of the present invention is to solve the problem that the cesium evaporation rate cannot be quantitatively measured in the background technology, and to propose a surface ionization probe system for off-line measurement of the cesium evaporation rate in a fusion device.

[0006] The technical solution of the present invention is a surface ionization probe system for off-line measurement of cesium evaporation rate in a fusion device, comprising: The vacuum chamber is a rectangular chamber made of stainless steel, with a sealing flange connected to the cesium evaporation channel on the top and a quick-connect flange connected to the vacuum pumping unit on the side wall; The cesium crucible assembly is fixed in the cesium evaporation channel at the top of the vacuum chamber through a metal sealing flange, and includes a cylindrical cesium crucible for storing liquid cesium, a transmission pipeline, a control valve and a cesium nozzle; one end of the transmission pipeline is bent and inserted into the cesium crucible, and the other end extends vertically into the cesium evaporation channel; A vacuum pumping unit, including a mechanical pump and a molecular pump, is connected to the side wall flange of the vacuum chamber through a bellows to provide an ultra-high vacuum environment; A heating assembly, including a heating wire, a thermocouple and a heating power supply wound around the cesium crucible and the transmission pipe, for heating and real-time temperature monitoring; The surface ionization probe system is fixed inside the cesium evaporation channel and includes an ionization probe, an ohmic heating control system and a bias voltage. The ionization probe includes two high-temperature tungsten wire rings, which are heated to more than a thousand degrees by the ohmic heating control system, and a bias voltage is applied to detect the ion current generated by the ionization of cesium vapor, thereby calculating the cesium evaporation rate.

[0007] Optionally, the dimensions of the vacuum chamber are 730 mm in length, 320 mm in width, and 350 mm in height; the diameter of the top sealing flange is 35 mm, and the diameter of the side wall quick-connect flange is 40 mm.

[0008] Optionally, the cesium crucible is made of cylindrical stainless steel, 75 mm long, 16 mm in diameter, and has a capacity of 10 g of liquid cesium; the transmission pipeline is 400 mm long and 12.7 mm in diameter, with the bent end inserted into the cesium crucible at 60° and the vertical end fixed in the cesium evaporation channel.

[0009] Optionally, the control valve is installed in the transmission pipeline at a distance of 60 mm from the cesium crucible, and is used to maintain the vacuum sealing of the cesium crucible and control the transmission of cesium vapor.

[0010] Optionally, the molecular pump of the vacuum pumping unit has a pumping speed of 300 L / s, and the mechanical pump has a pumping speed of 60 L / s; the molecular pump is turned on after the mechanical pump is pre-pumped to a starting condition, so that the vacuum chamber reaches 10 -5 Ultra-high vacuum of Pa order.

[0011] Optionally, the heating wires are divided into two groups, which are respectively wound around the cesium crucible and the transmission pipe; the thermocouples are divided into two groups, which respectively monitor the temperatures of the cesium crucible and the transmission pipe, and achieve temperature closed-loop control through a heating power supply.

[0012] Optionally, the ionization probe is fixed in the cesium evaporation channel through a CF35 flange interface, and its tungsten wire ring is located directly below the cesium nozzle; the ohmic heating control system controls the temperature of the tungsten wire ring, and the bias voltage range is 10-100V, which is used to drive ion current detection.

[0013] Optionally, the terminals of the ionization probe are arranged in a 5 cm×5 cm square on the CF35 flange, the tungsten wire is fixed through an M2 threaded hole, and the ionization wire and the collection wire are respectively connected to the positive and negative electrodes of the bias voltage.

[0014] Optionally, the heating temperature of the transfer pipe is at least 20° C. higher than the temperature of the cesium crucible to avoid deposition of cesium vapor in the pipe.

[0015] Optionally, the system is transplanted into a negative ion source to achieve online feedback control of the cesium evaporation rate by real-time monitoring of the ion current.

[0016] Compared with the prior art, the present invention has at least one of the following beneficial technical effects: The dual heating wire and dual thermocouple independent temperature control system is used to achieve temperature gradient control of the cesium crucible and the transmission pipeline, ensuring that the liquid cesium evaporates at a stable rate. The control valve design can achieve micro-flow regulation to avoid the pulse phenomenon of traditional gravity feeding; The high-temperature tungsten wire ring improves the ionization efficiency of cesium atoms, and the double tungsten wire ring structure forms a uniform electric field, with high ion collection efficiency and low detection limit.

[0017] The combination of molecular pump and mechanical pump achieves ultra-high vacuum, and the all-metal sealing structure avoids interference from rubber parts degassing and shortens the vacuum response time.

[0018] The present invention can calculate the evaporation rate of cesium in a vacuum environment, and by transplanting the offline measurement system into the negative ion source, the real-time monitoring of the cesium evaporation rate in the vacuum stage is realized. By quantifying the cesium injection amount, the better coverage of cesium at the plasma electrode is determined, which is beneficial to the generation of negative ions in the negative ion source. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the structure of the surface ionization probe system used for off-line measurement of cesium evaporation rate in fusion devices.

[0020] Figure numerals: 1. vacuum chamber; 2. cesium crucible; 3. transmission pipeline; 4. cesium evaporation channel; 5. heating wire; 6. thermocouple; 7. heating power supply; 8. mechanical pump; 9. molecular pump; 10. tungsten wire ring; 11. ohmic heating control system; 12. bias voltage. DETAILED DESCRIPTION

[0021] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0022] Example 1

[0023] like Figure 1 As shown, the surface ionization probe system for offline measurement of cesium evaporation rate in a fusion device proposed by the present invention includes a vacuum chamber 1, a cesium crucible assembly, a vacuum pumping unit, a heating assembly, and a surface ionization probe system. Each part is described in detail below.

[0024] In this embodiment, the vacuum chamber 1 is a rectangular chamber made of stainless steel, which is the main body of the experiment of the present invention. A sealing flange with a diameter of 35 mm is provided on the top for connecting with the cesium evaporation channel 4; and a quick-connect flange with a diameter of 40 mm is provided on the side wall for connecting with the vacuum pumping unit.

[0025] The cesium crucible assembly is fixed in the cesium evaporation channel 4 at the top of the vacuum chamber 1 through a metal sealing flange. The assembly consists of a cylindrical cesium crucible 2 for storing liquid cesium, a transmission pipeline 3, a control valve and a cesium nozzle. One end of the transmission pipeline 3 is bent and inserted into the cesium crucible 2, and the other end extends vertically into the cesium evaporation channel 4.

[0026] In addition, the vacuum pumping unit includes a molecular pump 8 with a pumping speed of 300L / s and a mechanical pump 9 with a pumping speed of 60L / s, which are connected to the quick-connect flange on the side wall of the vacuum chamber 1 through a bellows to provide an ultra-high vacuum environment for the vacuum chamber 1. When the unit is used to pump air for the vacuum chamber 1, the mechanical pump 9 is turned on first, and when it is observed that the vacuum condition in the vacuum chamber 1 meets the start-up condition of the molecular pump 8, the molecular pump 8 is turned on to continue pumping until the ultra-high vacuum environment required for the experiment is reached.

[0027] It is worth noting that the heating assembly includes a heating wire 5, a thermocouple 6 and a heating power supply 7 wound around the cesium crucible 2 and the transmission pipeline 3, which are used for heating and real-time temperature monitoring. The heating wire 5 is divided into two groups, one group is wound around the cesium crucible 2, and the other group is wound around the transmission pipeline 3; the thermocouple 6 is also divided into two groups, one group measures the temperature at the cesium crucible 2, and the other group measures the temperature at the transmission pipeline 3. The heating power supply 7 controls the temperature of the cesium crucible 2 and the transmission pipeline 3 through real-time feedback of the temperature monitored by the thermocouple 6. After the vacuum chamber 1 reaches an ultra-high vacuum environment, the heating wire 5 and the thermocouple 6 are used to heat and monitor the temperature of the cesium crucible 2 and the transmission pipeline 3 respectively. Opening the control valve allows the cesium vapor in the crucible to enter the cesium evaporation channel 4 through the transmission pipeline 3. At the same time, during the installation process of the cesium crucible 2, the control valve can ensure the vacuum sealing inside the cesium crucible to avoid oxidation of metallic cesium.

[0028] In this embodiment, the surface ionization probe system is fixed inside the cesium evaporation channel 4, including an ionization probe, an ohmic heating control system 11 and a bias voltage 12. The ionization probe includes two high-temperature tungsten wire rings 10, which are placed directly below the cesium nozzle. The tungsten wire rings 10 on the ionization probe are heated to a high temperature of thousands of degrees by the ohmic heating control system 11. When the cesium vapor evaporated into the channel touches the high-temperature tungsten wire rings 10, surface ionization will occur. The bias voltage 12 between the two tungsten wire rings 10 will form an ion current. By detecting the ion current, the evaporation rate of cesium can be calculated.

[0029] The specific working process of the present invention is as follows: first, the vacuum chamber 1 is sealed, and the mechanical pump 8 is turned on to start pumping. When it is observed that the vacuum condition in the chamber meets the starting condition of the molecular pump 9, the molecular pump 9 is turned on, and the vacuum condition is continuously observed. Then, the control valve in the cesium crucible assembly is opened to continue pumping. When the vacuum degree reaches At the same time, the system meets the ultra-high vacuum environment requirements required for the experiment. Then, the heating wire 5 and the thermocouple 6 are divided into two groups, one group is wound around the cesium crucible 2, and the other group is wound around the transmission pipe 3. The heating power supply 7 is turned on, and the temperature of the cesium crucible 2 and the transmission pipe 3 is controlled by real-time feedback of the temperature monitored by the thermocouple 6. The temperature setting of the cesium crucible 2 and the transmission pipe 3 is determined according to the experimental requirements to ensure that the temperature of the transmission pipe 3 is at least 20°C higher than that of the cesium crucible 2. The tungsten wire ring 10 on the ionization probe is heated to a high temperature of thousands of degrees by the ohmic heating control system 11. When the cesium vapor evaporated into the channel touches the high-temperature tungsten wire ring 10, surface ionization will occur. Applying a bias voltage 12 between the two tungsten wire rings 10 will form an ion current. The evaporation rate of cesium is calculated by detecting the ion current.

[0030] The above specific embodiments are only several optional embodiments of the present invention. Based on the technical solutions of the present invention and the relevant inspirations of the above embodiments, those skilled in the art can make various alternative improvements and combinations to the above specific embodiments.

Claims

1. A surface ionization probe system for off-line measurement of cesium evaporation rate in a fusion device, characterized in that: include: The vacuum chamber has a sealing flange connected to the cesium evaporation channel on the top and a quick-connect flange connected to the vacuum pumping unit on the side wall; The cesium crucible assembly is fixed in the cesium evaporation channel at the top of the vacuum chamber, and includes a cylindrical cesium crucible for storing liquid cesium, a transmission pipeline, a control valve and a cesium nozzle; one end of the transmission pipeline is bent and inserted into the cesium crucible, and the other end extends vertically into the cesium evaporation channel; A vacuum pumping unit, including a mechanical pump and a molecular pump, is connected to a flange of a vacuum chamber side wall through a bellows; A heating assembly, including a heating wire wound around the cesium crucible and the transmission pipe, a thermocouple and a heating power supply; The surface ionization probe system is fixed inside the cesium evaporation channel and includes an ionization probe, an ohmic heating control system and a bias voltage; the ionization probe includes two high-temperature tungsten wire rings, which are heated to more than a thousand degrees by the ohmic heating control system, and a bias voltage is applied to detect the ion current generated by the ionization of cesium vapor.

2. The surface ionization probe system for off-line measurement of cesium evaporation rate in a fusion device according to claim 1, characterized in that: The dimensions of the vacuum chamber are 730 mm in length, 320 mm in width, and 350 mm in height, with a top sealing flange diameter of 35 mm and a side wall quick-connect flange diameter of 40 mm.

3. The surface ionization probe system for off-line measurement of cesium evaporation rate in a fusion device according to claim 1, characterized in that: The cesium crucible is made of cylindrical stainless steel, 75 mm long and 16 mm in diameter. The transmission pipeline is 400 mm long and 12.7 mm in diameter. The bent end is inserted into the cesium crucible at an angle of 60°, and the vertical end is fixed in the cesium evaporation channel.

4. The surface ionization probe system for off-line measurement of cesium evaporation rate in a fusion device according to claim 1, characterized in that: The control valve is installed in the transmission pipeline at a distance of 60 mm from the cesium crucible, and is used to maintain the vacuum sealing of the cesium crucible and control the transmission of cesium vapor.

5. The surface ionization probe system for off-line measurement of cesium evaporation rate in a fusion device according to claim 1, characterized in that: The molecular pumping speed of the vacuum pumping unit is 300L / s, and the mechanical pumping speed is 60L / s.

6. The surface ionization probe system for off-line measurement of cesium evaporation rate in a fusion device according to claim 1, characterized in that: The heating wires are divided into two groups, which are respectively wound around the cesium crucible and the transmission pipeline; the thermocouples are divided into two groups, which respectively monitor the temperature of the cesium crucible and the transmission pipeline, and are used for temperature closed-loop control through the heating power supply.

7. The surface ionization probe system for off-line measurement of cesium evaporation rate in a fusion device according to claim 1, characterized in that: The ionization probe is fixed in the cesium evaporation channel through a CF35 flange interface, and its tungsten wire ring is located directly below the cesium nozzle; the ohmic heating control system controls the temperature of the tungsten wire ring.

8. The surface ionization probe system for off-line measurement of cesium evaporation rate in a fusion device according to claim 1, characterized in that: The terminals of the ionization probe are arranged in a 5 cm×5 cm square on the CF35 flange, and the ionization wire and the collection wire are connected to the positive and negative electrodes of the bias voltage respectively.

9. The surface ionization probe system for off-line measurement of cesium evaporation rate in a fusion device according to claim 1, characterized in that: The heating temperature of the transfer pipe is at least 20° C. higher than the temperature of the cesium crucible.

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