System and method for off-line measurement of cesium evaporation rate in fusion device

Abstract

The invention provides a system and a method for off-line measurement of a cesium evaporation rate in a fusion device. The system comprises a vacuum chamber, a cesium crucible assembly, a heating assembly, a film thickness meter, a laser absorption spectrum system and a vacuum pumping unit. According to the invention, an ultrahigh vacuum environment is provided for the whole device including the vacuum chamber by using the vacuum pumping unit; then the cesium crucible and the conveying pipeline are heated through a heating assembly, so that effective evaporation of cesium is guaranteed, and deposition of cesium on the wall face of the pipeline is reduced; measuring the deposition thickness of cesium and the concentration of cesium atoms by using a film thickness meter and a laser absorption spectrum system, and checking the measurement results of the two diagnosis methods mutually; the cesium evaporation rate is measured, and the quantitative relation between the cesium evaporation rate and the heating temperature is obtained; and finally, a measurement system is transplanted into a negative ion source, and the cesium injection amount in the vacuum stage is monitored in real time. Effective data and technical support are provided for cesium flow control in the magnetic confinement nuclear fusion negative neutral beam injection system.

Description

Technical Field

[0001] The invention relates to the technical field of metal cesium deposition in a magnetic confinement nuclear fusion negative neutral beam system, and in particular to a system and method 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, the conditions are very harsh, especially the core ion temperature needs to exceed 10keV. In order to achieve a core particle temperature of magnetic confinement nuclear fusion exceeding 10keV, the negative neutral beam heating component has become one of the focuses of magnetic confinement nuclear fusion research with its significant heating capacity. In the negative ion source system of the negative neutral beam heating component, it is difficult to produce enough negative ions due to the high electron work function on the surface of conventional metals. Cesium, as the metal with the lowest surface work function, has been widely used in negative neutral beam high-yield negative ion beam experiments. Through the evaporation of cesium in the crucible, cesium enters the ion source and is deposited on the surface of the electrode that generates plasma, thereby reducing the metal work function on the surface of the plasma electrode, thereby increasing the yield of negative hydrogen ions. At the same time, in order to obtain uniform cesium conditions at the plasma electrode and avoid excessive cesium injection, accurate measurement of the cesium evaporation rate is crucial to the yield of negative hydrogen ions. However, the measurement of the cesium evaporation rate during the negative neutral beam experiment 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 an important supplement to cesium measurement. Offline measurement systems usually have high measurement accuracy and flexibility, and can quantitatively analyze the cesium evaporation rate under different environmental conditions. However, there is still a lack of offline systems for cesium evaporation rate measurement, which leads to poor repeatability in negative ion beam yield experiments, seriously affecting the stable operation of high-performance negative neutral beam experiments. Summary of the invention

[0004] In order to solve the above technical problems, realize the quantitative measurement of cesium evaporation rate, ensure stable and appropriate cesium injection, and obtain uniform cesium conditions at the plasma electrode, the present invention provides a system and method for offline measurement of cesium evaporation rate in a fusion device, which provides effective data and technical support for the precise control of cesium flow in the negative neutral beam heating system of magnetic confinement nuclear fusion. The system can simulate the evaporation rate of metallic cesium in the vacuum environment of the ion source, and cross-check the measurement results of different diagnoses to ensure the accuracy and reliability of the measurement results.

[0005] In order to achieve the above object, the present invention adopts the following technical scheme:

[0006] A system for offline measurement of cesium evaporation rate in a fusion device, comprising a vacuum chamber, a cesium crucible assembly, a vacuum pumping unit, a heating assembly, a film thickness meter, and a laser absorption spectrometer system; the vacuum chamber comprises an interface connected to the cesium crucible assembly, the film thickness meter, the laser absorption spectrometer system, and the vacuum pumping unit; the cesium crucible assembly is connected to the vacuum chamber by a metal sealing flange, comprising a cesium crucible for storing liquid cesium, a transmission pipeline, two control valves, and a cesium nozzle; the vacuum pumping unit is connected to the side of the vacuum chamber, and the cesium crucible assembly is connected to the vacuum chamber by a metal sealing flange. The cesium crucible assembly is connected via a quick-connect flange and includes a molecular pump and a mechanical pump; the heating assembly is connected to the cesium crucible assembly via a heating wire and a thermocouple, and includes two sets of heating and temperature monitoring devices at the cesium crucible and the transmission pipeline; the crystal oscillator probe of the film thickness meter is fixed inside the vacuum chamber via a quick-connect adapter, and the crystal oscillator probe is aligned with the cesium nozzle of the cesium crucible assembly directly below, for measuring the cesium deposition thickness; the laser absorption spectroscopy system is connected to the transparent glass window on the side wall of the vacuum chamber via a laser, for measuring the cesium atomic concentration.

[0007] Furthermore, the vacuum chamber is made of stainless steel, and is 730 mm long, 320 mm wide, and 350 mm high.

[0008] Furthermore, a sealing flange with a diameter of 35 mm is opened on the top of the vacuum chamber, which is connected to the cesium crucible assembly. Two glass observation windows with a diameter of 16 mm are opened on the side wall of the chamber for connecting to the laser absorption spectroscopy system; a sealing flange with a diameter of 35 mm is connected to the film thickness meter; and a sealing flange with a diameter of 40 mm is connected to the vacuum exhaust unit.

[0009] Furthermore, the cesium crucible assembly includes a cylindrical stainless steel crucible with a length of 75 mm and a diameter of 16 mm, which can be loaded with 10 g of liquid metal cesium; a transmission pipeline with a length of 400 mm and a diameter of 12 mm; two control valves are installed on the transmission pipeline, one is located 60 mm away from the cesium crucible, and the other is located 170 mm away from the upper top surface of the vacuum chamber, which is used to ensure the vacuum sealing inside the cesium crucible during the installation of the cesium crucible to prevent oxidation of metal cesium. At the same time, the valve close to the crucible can be used to control the transmission of cesium vapor in the crucible, thereby determining the time of cesium injection, and the other can control the transmission of cesium vapor in the pipeline.

[0010] Furthermore, one end of the transmission pipe in the cesium crucible assembly is inserted into the cesium crucible in a 60° bend, and the other end is inserted into the vacuum chamber perpendicular to the top of the vacuum chamber. The length of the pipe in the vertical direction is 300 mm, and the length of the pipe in the inclined direction is 100 mm. The design purpose of this shape is to avoid the right-angle structure of the cesium crucible being unsuitable for cesium storage when installed vertically, causing liquid cesium to flow out of the liquid reservoir.

[0011] Furthermore, the vacuum pumping unit is connected to the vacuum chamber via a quick-connect vacuum sealing flange, and includes a molecular pump with a pumping speed of 300L / s and a mechanical pump with a pumping speed of 6L / s, which are used to provide an ultra-high vacuum experimental environment for the vacuum chamber.

[0012] Furthermore, the heating assembly includes a heating wire, a thermocouple and a heating power supply. The heating wire is divided into two groups, one group is wound around the cesium crucible, and the other group is wound around the transmission pipeline. Similarly, the thermocouple is also divided into two groups, one group measures the temperature at the cesium crucible, and the other group measures the temperature at the transmission pipeline. The heating power supply controls the temperature of the cesium crucible and the transmission pipeline through real-time feedback of the temperature monitored by the thermocouple.

[0013] Furthermore, the film thickness meter is connected to the vacuum chamber through a quick-connect vacuum sealing flange, and the crystal oscillator probe at one end of the film thickness meter is inserted from the side of the vacuum chamber through the sealing flange and fixed inside the vacuum chamber. The probe is about 100 mm directly below the cesium nozzle, and the oscillator at the other end of the film thickness meter is connected to the crystal oscillator probe through a cable, and the deposition thickness and deposition rate of cesium on the probe are displayed in real time on the display.

[0014] Furthermore, the laser absorption spectrum transmits the laser with a wavelength of 852.1nm generated by the laser through two 16mm diameter glass observation windows on the side wall of the vacuum chamber through optical fiber. The laser path passes through 30mm directly below the cesium nozzle. When cesium atoms pass through, they absorb the 852.1nm characteristic wavelength laser, thereby realizing the collection of cesium atom concentration.

[0015] The present invention also provides a method for off-line measurement of cesium evaporation rate in a fusion device, comprising: firstly sealing the vacuum chamber, turning on a mechanical pump to start pumping, then keeping a valve in the cesium crucible assembly near the top of the chamber open, and when it is observed that the vacuum condition in the chamber meets the start-up condition of the molecular pump, turning on the molecular pump, continuously observing the vacuum condition, and then opening a control valve in the cesium crucible assembly near the cesium crucible to continue pumping, and when the vacuum degree reaches When the temperature is on the Pa level, the system meets the ultra-high vacuum environment requirements required for the experiment; then the heating wire and thermocouple are divided into two groups, one group is wound around the cesium crucible, and the other group is wound around the transmission pipe. The heating power is turned on, and the temperature of the cesium crucible and the transmission pipe is controlled by real-time feedback of the temperature monitored by the thermocouple. The temperature setting of the cesium crucible and the transmission pipe is determined according to the experimental requirements to ensure that the temperature of the transmission pipe is at least 20°C higher than that of the cesium crucible; the crystal oscillator probe at one end of the film thickness meter deposits cesium vapor in the vacuum chamber, and the other end displays the deposition thickness and deposition rate of cesium on the crystal oscillator probe in real time through a display; the laser absorption spectroscopy system transmits the laser with a wavelength of 852.1nm generated by the laser through two 16mm diameter glass observation windows on the side wall of the vacuum chamber through optical fiber. When cesium atoms pass through, they absorb the 852.1nm characteristic wavelength laser, thereby realizing the collection of cesium atom concentration.

[0016] Beneficial effects:

[0017] The present invention provides a simple and effective system and method for measuring the cesium evaporation rate in a fusion device, which can calculate the cesium evaporation rate in a vacuum environment, and realize real-time monitoring of the cesium evaporation rate in the vacuum stage by transplanting the measurement system into the negative ion source. 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

[0018] Figure 1 The present invention is a schematic structural diagram of a system for measuring cesium evaporation rate in a fusion device.

[0019] In the figure, the reference numerals are: 1-vacuum chamber; 2-cesium crucible; 3-transmission pipeline; 4-mechanical pump; 5-molecular pump; 6-heating wire; 7-thermocouple; 8-heating power supply; 9-film thickness meter; 10-crystal oscillator probe; 11-laser absorption spectroscopy system. DETAILED DESCRIPTION

[0020] The purpose of the present invention is to design a cesium evaporation rate measurement system that can be transplanted into a negative ion source for fusion experiments, and to ensure the accuracy of the system by utilizing the flexibility of measurement. The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0021] like Figure 1As shown, the present invention implements a system for off-line measurement of cesium evaporation rate in a fusion device, including a vacuum chamber 1, a cesium crucible 2, a transmission pipeline 3, a mechanical pump 4, a molecular pump 5, a heating wire 6, a thermocouple 7, a heating power supply 8, a film thickness meter 9, a crystal oscillator probe 10, and a laser absorption spectroscopy system 11.

[0022] The vacuum chamber 1 is the main body of the experiment of the present invention, and a plurality of sealing flanges are provided on the surface; the cesium crucible assembly is connected to the vacuum chamber 1 and fixed to the top of the vacuum chamber 1 through a metal sealing flange with a diameter of 35 mm; the vacuum pumping unit is connected to the side of the vacuum chamber 1 through a quick-connect flange to achieve an ultra-high vacuum environment in the vacuum chamber. The vacuum pumping unit mainly includes a mechanical pump 4 and a molecular pump 5; the heating component uses a heating power supply 8 to perform two groups of heating and temperature monitoring on the cesium crucible 2 and the transmission pipeline 3 of the cesium crucible assembly through a heating wire 6 and a thermocouple 7; the crystal oscillator probe 10 of the film thickness meter 9 is fixed inside the vacuum chamber 1 through a quick-connect adapter, and the crystal oscillator probe 10 is located directly below the cesium nozzle; the laser absorption spectroscopy system 11 is connected to the transparent glass windows on the side walls of the vacuum chamber 1 through a laser.

[0023] Preferably, a sealing flange with a diameter of 35 mm is provided on the top of the vacuum chamber 1, which is connected to the cesium crucible assembly. Two glass observation windows with a diameter of 16 mm are provided on the side wall of the vacuum chamber 1, which are connected to the laser absorption spectrometer system 11, a sealing flange with a diameter of 35 mm is connected to the film thickness meter 9, and a sealing flange with a diameter of 40 mm is connected to the vacuum exhaust unit.

[0024] The cesium crucible assembly is divided into four parts: cesium crucible 2, transmission pipeline 3, control valve, and cesium nozzle, which are fixed in the vertical direction of the top of the vacuum chamber 1 through a metal sealing flange. After the vacuum chamber 1 reaches an ultra-high vacuum environment, the heating wire 6 and the thermocouple 7 are used to heat and monitor the temperature of the cesium crucible 2 and the transmission pipeline 3 respectively, and the two control valves are opened to allow the cesium vapor in the crucible to pass through the transmission pipeline 3 and enter the vacuum chamber 1 from the cesium nozzle. At the same time, during the installation of the cesium crucible 2, the valve can ensure the vacuum sealing inside the cesium crucible to prevent oxidation of metallic cesium.

[0025] Preferably, the vacuum pumping unit mainly comprises a molecular pump 5 with a pumping speed of 300L / s and a mechanical pump 4 with a pumping speed of 60L / s. When the vacuum pumping unit is used to pump air into the vacuum chamber 1, the mechanical pump 4 is first turned on, and when it is observed that the vacuum condition in the vacuum chamber 1 has met the start-up condition of the molecular pump 5, the molecular pump 5 is turned on again to continue pumping until the ultra-high vacuum environment required for the experiment is reached.

[0026] Preferably, the cesium crucible 2 and the transmission pipe 3 of the cesium crucible assembly are heated and the temperature is monitored by the heating wire 6 and the thermocouple 7. The heating wire 6 is divided into two groups, one group is wound around the cesium crucible 2, and the other group is wound around the transmission pipe 3. Similarly, the thermocouple 7 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 pipe 3. The heating power supply 8 controls the temperature of the cesium crucible 2 and the transmission pipe 3 through real-time feedback of the temperature monitored by the thermocouple 7.

[0027] Preferably, the crystal oscillator probe 10 of the film thickness meter 9 is inserted from the side and fixed inside the vacuum chamber 1 through a sealing flange, and the oscillator at one end of the film thickness meter 9 is connected to the crystal oscillator probe 10 through a cable, and the deposition thickness and deposition rate of cesium on the crystal oscillator probe 10 are displayed in real time on the display.

[0028] Preferably, the laser absorption spectroscopy system 11 transmits the laser with a wavelength of 852.1 nm generated by the laser through two 16 mm diameter glass observation windows on the side wall of the vacuum chamber through an optical fiber. The laser path passes through 30 mm directly below the cesium nozzle. When cesium atoms pass through, they absorb the 852.1 nm characteristic wavelength laser, thereby realizing the collection of cesium atom concentration.

[0029] The specific working process of the present invention is as follows: first, the vacuum chamber 1 is sealed, and the mechanical pump 4 is turned on to start pumping. Then, the valve near the top of the chamber in the cesium crucible assembly is kept open. When it is observed that the vacuum condition in the chamber meets the starting condition of the molecular pump 5, the molecular pump 5 is turned on, and the vacuum condition is continuously observed. Then, the control valve near the cesium crucible 2 in the cesium crucible assembly is opened to continue pumping. When the vacuum degree reaches When the temperature is at the Pa level, the system meets the ultra-high vacuum environment requirements required for the experiment. Then, the heating wire 6 and the thermocouple 7 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 8 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 7. The temperature setting of the cesium crucible 2 and the transmission pipe 3 is determined according to the experimental requirements to meet the temperature of the transmission pipe 3 at least 20°C higher than the temperature of the cesium crucible 2. The crystal oscillator probe 10 at one end of the film thickness meter 9 deposits cesium vapor in the vacuum chamber 1, and the other end displays the deposition thickness and deposition rate of cesium on the crystal oscillator probe 10 in real time through the display. The laser absorption spectroscopy system 11 transmits the laser with a wavelength of 852.1nm generated by the laser through the two glass observation windows with a diameter of 16mm on the side wall of the vacuum chamber 1 through the optical fiber. When the cesium atoms pass through, they will absorb the 852.1nm characteristic wavelength laser, thereby realizing the collection of cesium atomic concentration. The two diagnostic methods are used to check each other to ensure the reliability of the experimental data.

[0030] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A system for off-line measurement of cesium evaporation rate in a fusion device, characterized in that: The invention comprises a vacuum chamber, a cesium crucible assembly, a vacuum pumping unit, a heating assembly, a film thickness meter, and a laser absorption spectrum system; the vacuum chamber comprises an interface connected with the cesium crucible assembly, the film thickness meter, the laser absorption spectrum system, and the vacuum pumping unit; the cesium crucible assembly is connected with the vacuum chamber by a metal sealing flange, and comprises a cesium crucible for storing liquid cesium, a transmission pipeline, two control valves, and a cesium nozzle; the vacuum pumping unit is connected with the side of the vacuum chamber by a quick-connect flange, and comprises a molecular pump and a mechanical pump; the heating assembly is connected with the cesium crucible assembly by a heating wire and a thermocouple, and comprises two sets of heating and temperature monitoring devices at the cesium crucible and the transmission pipeline; the crystal oscillator probe of the film thickness meter is fixed inside the vacuum chamber by a quick-connect adapter, and the crystal oscillator probe is aligned with the cesium nozzle of the cesium crucible assembly to measure the cesium deposition thickness; the laser absorption spectrum system is connected with the transparent glass window on the side wall of the vacuum chamber by a laser to measure the cesium atomic concentration.

2. A system for off-line measurement of cesium evaporation rate in a fusion device according to claim 1, characterized in that: The vacuum chamber is made of stainless steel, with a length of 730 mm, a width of 320 mm, and a height of 350 mm; a sealing flange with a diameter of 35 mm is provided on the top of the vacuum chamber, which is connected to the cesium crucible assembly; two glass observation windows with a diameter of 16 mm are provided on the side wall of the vacuum chamber, which are connected to the laser absorption spectrum system; a sealing flange with a diameter of 35 mm is provided on the side wall of the vacuum chamber, which is connected to the film thickness meter; a sealing flange with a diameter of 40 mm is provided on the side wall of the vacuum chamber, which is connected to the vacuum exhaust unit.

3. A system for off-line measurement of cesium evaporation rate in a fusion device according to claim 1, characterized in that: The cesium crucible assembly includes a cylindrical stainless steel cesium crucible with a length of 75 mm and a diameter of 16 mm, which can load 10 g of liquid metal cesium; the cesium crucible assembly includes a transmission pipe with a length of 400 mm and a diameter of 12.7 mm, one end of which is inserted into the cesium crucible in a 60° bend, and the other end is inserted into the vacuum chamber perpendicular to the top of the vacuum chamber.

4. A system for off-line measurement of cesium evaporation rate in a fusion device according to claim 1, characterized in that: The vacuum pumping unit includes a molecular pump with a pumping speed of 300L / s and a mechanical pump with a pumping speed of 60L / s, which are connected to the pumping flange on the side wall of the vacuum chamber through a bellows to provide an ultra-high vacuum environment for the vacuum chamber.

5. A system for off-line measurement of cesium evaporation rate in a fusion device according to claim 1, characterized in that: The heating assembly comprises a heating and temperature testing device and a heating power supply.

6. A system for off-line measurement of cesium evaporation rate in a fusion device according to claim 1, characterized in that: The crystal oscillator probe at one end of the film thickness meter is inserted from the side of the vacuum chamber through a sealing flange and fixed inside the vacuum chamber. The crystal oscillator probe is about 100 mm directly below the cesium nozzle. The oscillator at the other end of the film thickness meter is connected to the crystal oscillator probe through a cable, and the deposition thickness and deposition rate of cesium on the probe are displayed in real time on the display.

7. A system for off-line measurement of cesium evaporation rate in a fusion device according to claim 1, characterized in that: The laser absorption spectroscopy system transmits the laser with a wavelength of 852.1 nm generated by the laser through two 16 mm diameter glass observation windows on the side wall of the vacuum chamber through optical fiber. The laser path passes through 30 mm directly below the cesium nozzle. When cesium atoms pass through, they absorb the 852.1 nm characteristic wavelength laser, thereby realizing the collection of cesium atom concentration.

8. A system for off-line measurement of cesium evaporation rate in a fusion device according to claim 3, characterized in that: Two control valves are installed on the transmission pipeline, one is located 60 mm away from the cesium crucible, and the other is located 170 mm away from the top surface of the vacuum chamber. They are used to ensure the vacuum tightness inside the cesium crucible during the installation of the cesium crucible and avoid oxidation of metallic cesium.

9. A system for off-line measurement of cesium evaporation rate in a fusion device according to claim 5, characterized in that: The heating wires are divided into two groups, one group is wound around the cesium crucible, and the other group is wound around the transmission pipeline; the thermocouples are divided into two groups, one group measures the temperature at the cesium crucible, and the other group measures the temperature at the transmission pipeline; the heating power supply controls the temperature of the cesium crucible and the transmission pipeline through real-time feedback of the temperature detected by the thermocouples.

10. A method for off-line measurement of cesium evaporation rate in a fusion device, characterized in that: include: First, seal the vacuum chamber, turn on the mechanical pump to start pumping, then keep the valve near the top of the vacuum chamber in the cesium crucible assembly open. When the vacuum condition in the vacuum chamber meets the start-up conditions of the molecular pump, turn on the molecular pump, continue to observe the vacuum condition, and then open the control valve near the cesium crucible in the cesium crucible assembly to continue pumping. When the vacuum degree reaches When the temperature is on the Pa level, the system meets the ultra-high vacuum environment requirements required for the experiment; then the heating wire and thermocouple are divided into two groups, one group is wound around the cesium crucible, and the other group is wound around the transmission pipe. The heating power is turned on, and the temperature of the cesium crucible and the transmission pipe is controlled by real-time feedback of the temperature monitored by the thermocouple. The temperature setting of the cesium crucible and the transmission pipe is determined according to the experimental requirements to ensure that the temperature of the transmission pipe is at least 20°C higher than that of the cesium crucible; the crystal oscillator probe at one end of the film thickness meter deposits cesium vapor in the vacuum chamber, and the other end displays the deposition thickness and deposition rate of cesium on the crystal oscillator probe in real time through a display; the laser absorption spectroscopy system transmits the laser with a wavelength of 852.1nm generated by the laser through two 16mm diameter glass observation windows on the side wall of the vacuum chamber through optical fiber. When cesium atoms pass through, they absorb the 852.1nm characteristic wavelength laser, thereby realizing the collection of cesium atom concentration.

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