A system and method for off-line measurement of cesium evaporation rate in a fusion device

Abstract

The present application provides a system and method for measuring cesium evaporation rate in a fusion device offline, comprising a vacuum chamber, a cesium crucible assembly, a heating assembly, a film thickness gauge, a laser absorption spectroscopy system and a vacuum pumping unit. The present application uses the vacuum pumping unit to provide an ultra-high vacuum environment for the whole device including the vacuum chamber; then uses the heating assembly to heat the cesium crucible and the transmission pipeline to ensure the effective evaporation of cesium and reduce the deposition of cesium on the pipeline wall; then uses the film thickness gauge and the laser absorption spectroscopy system to measure the deposition thickness of cesium and the concentration of cesium atoms, and cross-check the measurement results of the two diagnostic methods; realize the measurement of cesium evaporation rate and obtain the quantitative relationship between the cesium evaporation rate and the heating temperature; finally transplant the measurement system to the negative ion source to realize the real-time monitoring of the cesium injection amount in the vacuum stage. The present application provides effective data and technical support for cesium flow control in the magnetic confinement nuclear fusion negative neutral beam injection system.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of cesium deposition in a magnetic confinement nuclear fusion negative neutral beam system, and particularly relates to a system and method for measuring cesium evaporation rate off-line in a fusion device. BACKGROUND

[0002] Magnetic confinement nuclear fusion has become one of the important solutions to human energy problems due to its unique raw material abundance, huge energy and inherent safety, and has been valued by many developed and developing countries at home and abroad. However, the conditions for realizing the ignition condition of magnetic confinement nuclear fusion are very harsh, especially the core ion temperature needs to exceed 10keV. In order to realize the core particle temperature of magnetic confinement nuclear fusion exceeding 10keV, the negative neutral beam heating assembly with heating capacity has become one of the focuses of magnetic confinement nuclear fusion research. In the negative ion source system of the negative neutral beam heating assembly, it is difficult to produce enough negative ions due to the high electron work function of the conventional metal surface. 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 cesium is deposited on the surface of the plasma electrode, thereby reducing the metal work function of the plasma electrode surface, and then improving the negative hydrogen ion yield. 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 negative hydrogen ion yield. However, there are problems such as complex measurement system, high difficulty in operation, high-pressure sparking risk, etc. in the measurement of the cesium evaporation rate during the negative neutral beam experiment.

[0003] The complexity and limitations of on-line measurement make off-line measurement an important complementary means for cesium measurement. The off-line measurement system usually has high measurement accuracy and flexibility, and can quantitatively analyze the cesium evaporation rate under different environmental conditions. However, there is still a lack of off-line system for measuring the cesium evaporation rate, which leads to poor repeatability in the negative ion beam yield experiment, seriously affecting the stable operation of the high-performance negative neutral beam experiment. SUMMARY

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

[0005] To achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0006] A system for offline measurement of cesium evaporation rate in a fusion device includes a vacuum chamber, a cesium crucible assembly, a vacuum pumping unit, a heating assembly, a film thickness gauge, and a laser absorption spectroscopy system. The vacuum chamber includes interfaces for connecting to the cesium crucible assembly, film thickness gauge, laser absorption spectroscopy system, and vacuum pumping unit. The cesium crucible assembly, connected to the vacuum chamber via a metal sealing flange, includes a cesium crucible for storing liquid cesium, a transfer pipe, two control valves, and a cesium nozzle. The vacuum pumping unit communicates with the side of the vacuum chamber. The system 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 transfer pipe. The crystal oscillator probe of the film thickness gauge is fixed inside the vacuum chamber via a quick-connect adapter, with the crystal oscillator probe aligned directly below the cesium nozzle of the cesium crucible assembly, for measuring the cesium deposition thickness. The laser absorption spectroscopy system is connected to a transparent glass window on the side wall of the vacuum chamber via a laser for measuring the cesium atom concentration.

[0007] Furthermore, the vacuum chamber is made of stainless steel and measures 730mm in length, 320mm in width, and 350mm in height.

[0008] Furthermore, a 35mm diameter sealing flange is installed at the top of the vacuum chamber to connect to the cesium crucible assembly. Two 16mm diameter glass observation windows are installed on the side wall of the chamber for connection to the laser absorption spectroscopy system; a 35mm diameter sealing flange is connected to the film thickness gauge; and a 40mm diameter sealing flange is connected to the vacuum pump unit.

[0009] Furthermore, the cesium crucible assembly includes a cylindrical stainless steel crucible, 75mm long and 16mm in diameter, capable of holding 10g of liquid cesium metal; a 400mm long and 12mm in diameter transfer pipe; and two control valves installed on the transfer pipe, one located 60mm from the cesium crucible and the other 170mm from the top surface of the vacuum chamber, to ensure the vacuum seal inside the cesium crucible during installation and prevent oxidation of the metallic cesium. Simultaneously, the valve near the crucible controls the transfer of cesium vapor within the crucible, thus determining the timing of cesium injection, while the other valve controls the transfer of cesium vapor within the pipe.

[0010] Furthermore, in the cesium crucible assembly, one end of the transfer pipe is inserted into the cesium crucible at 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 vertical pipe is 300 mm, and the length of the inclined pipe is 100 mm. The purpose of this design is to avoid the right-angle structure of the cesium crucible being unsuitable for cesium storage when installed vertically, which would cause liquid cesium to flow out of the 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 300 L / s and a mechanical pump with a pumping speed of 6 L / s, used to provide an ultra-high vacuum experimental environment for the vacuum chamber.

[0012] Furthermore, the heating assembly includes a heating wire, thermocouples, 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 pipe. Similarly, the thermocouples are also divided into two groups: one group measures the temperature at the cesium crucible, and the other group measures the temperature at the transmission pipe. The heating power supply controls the temperature of the cesium crucible and the transmission pipe in real time through the temperature monitored by the thermocouples.

[0013] Furthermore, the film thickness gauge is connected to the vacuum chamber via a quick-connect vacuum sealing flange. The crystal oscillator probe at one end of the film thickness gauge is inserted from the side of the vacuum chamber through the sealing flange and fixed inside the vacuum chamber. The probe is positioned approximately 100 mm directly below the cesium nozzle. The oscillator at the other end of the film thickness gauge is connected to the crystal oscillator probe via a cable. 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 is transmitted through an optical fiber to two 16mm diameter glass observation windows on the side wall of the vacuum chamber. The laser path passes 30mm directly below the cesium nozzle. When cesium atoms pass through, they absorb the characteristic wavelength of 852.1nm laser light, thereby achieving the collection of cesium atom concentration.

[0015] This invention also provides a method for offline measurement of cesium evaporation rate in a fusion device, comprising: first, sealing a vacuum chamber, starting a mechanical pump to begin evacuation, then keeping a valve near the top of the chamber in the cesium crucible assembly open; when the vacuum condition in the chamber meets the starting conditions of the molecular pump, starting the molecular pump, continuously observing the vacuum condition, and then opening a control valve near the cesium crucible in the cesium crucible assembly to continue evacuation until the vacuum level reaches a certain value. At the Pa level, the system meets the ultra-high vacuum environment requirements of the experiment. The heating wire and thermocouples are then divided into two groups: one group is wound around the cesium crucible, and the other group is wound around the transfer pipe. The heating power is turned on, and the temperature of the cesium crucible and transfer pipe is controlled in real time by the temperature monitored by the thermocouples. The temperature settings for the cesium crucible and transfer pipe are determined according to experimental requirements, ensuring that the temperature of the transfer pipe is at least 20°C higher than that of the cesium crucible. A crystal oscillator probe at one end of the film thickness gauge deposits cesium vapor in the vacuum chamber, while the other end displays the deposition thickness and deposition rate of cesium on the crystal oscillator probe in real time. The laser absorption spectroscopy system transmits a 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 via optical fiber. When cesium atoms pass through, they absorb the characteristic wavelength of 852.1 nm laser light, thus achieving cesium atom concentration acquisition.

[0016] Beneficial effects:

[0017] This invention provides a simple and effective system and method for measuring the cesium evaporation rate in fusion devices. It can calculate the evaporation rate of cesium in a vacuum environment. By adapting the measurement system to a negative ion source, real-time monitoring of the cesium evaporation rate in the vacuum stage is achieved. Quantifying the cesium injection amount allows for determining the optimal cesium coverage at the plasma electrodes, which is beneficial for the generation of negative ions in the negative ion source. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of a system for measuring the cesium evaporation rate in a fusion device according to the present invention.

[0019] In the figure, the labels are as follows: 1-vacuum chamber; 2-cesium crucible; 3-transfer pipe; 4-mechanical pump; 5-molecular pump; 6-heating wire; 7-thermocouple; 8-heating power supply; 9-film thickness gauge; 10-crystal oscillator probe; 11-laser absorption spectroscopy system. Detailed Implementation

[0020] The purpose of this invention is to design a cesium evaporation rate measurement system that can be ported to a negative ion source for fusion experiments, ensuring the system's accuracy through measurement flexibility. The invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of the 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 offline measurement of cesium evaporation rate in a fusion device, comprising a vacuum chamber 1, a cesium crucible 2, a transmission pipe 3, a mechanical pump 4, a molecular pump 5, a heating wire 6, a thermocouple 7, a heating power supply 8, a film thickness gauge 9, a crystal oscillator probe 10, and a laser absorption spectroscopy system 11.

[0022] The vacuum chamber 1 is the main body for experiments in this invention, with multiple sealing flanges on its surface. The cesium crucible assembly is connected to the vacuum chamber 1 and fixed to the top of the vacuum chamber 1 by a 35mm diameter metal sealing flange. The vacuum pump unit is connected to the side of the vacuum chamber 1 via a quick-connect flange to achieve an ultra-high vacuum environment in the vacuum chamber. The vacuum pump unit mainly includes a mechanical pump 4 and a molecular pump 5. The heating assembly uses a heating power supply 8 to heat and monitor the cesium crucible 2 and the transmission pipe 3 of the cesium crucible assembly via a heating wire 6 and a thermocouple 7. The crystal oscillator probe 10 of the film thickness gauge 9 is fixed inside the vacuum chamber 1 via 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 both sides of the vacuum chamber 1 via a laser.

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

[0024] The cesium crucible assembly consists of four parts: a cesium crucible 2, a transmission pipe 3, control valves, and a cesium nozzle. It is vertically fixed to the top of the vacuum chamber 1 via a metal sealing flange. After the vacuum chamber 1 reaches an ultra-high vacuum environment, heating wire 6 and thermocouple 7 are used to heat and monitor the temperature of the cesium crucible 2 and the transmission pipe 3, respectively. Two control valves are opened, allowing cesium vapor in the crucible to pass through the transmission pipe 3 and enter the vacuum chamber 1 through the cesium nozzle. Simultaneously, the valves ensure the vacuum seal inside the cesium crucible during installation, preventing oxidation of the metallic cesium.

[0025] Preferably, the vacuum pumping unit mainly comprises a molecular pump 5 with a pumping speed of 300 L / s and a mechanical pump 4 with a pumping speed of 60 L / s. When using the vacuum pumping unit to evacuate the vacuum chamber 1, the mechanical pump 4 is turned on first. Once it is observed that the vacuum conditions in the vacuum chamber 1 meet the starting conditions of the molecular pump 5, the molecular pump 5 is turned on to continue evacuating until the ultra-high vacuum environment required for the experiment is reached.

[0026] Preferably, the cesium crucible 2 and the transfer pipe 3 of the cesium crucible assembly are heated and their temperatures monitored using heating wire 6 and thermocouples 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 transfer pipe 3. Similarly, the thermocouples 7 are also divided into two groups: one group measures the temperature at the cesium crucible 2, and the other group measures the temperature at the transfer pipe 3. The heating power supply 8 controls the temperatures of the cesium crucible 2 and the transfer pipe 3 in real time based on the temperature monitored by the thermocouples 7.

[0027] Preferably, the crystal oscillator probe 10 of the film thickness gauge 9 is inserted from the side and fixed inside the vacuum chamber 1 through a sealing flange. The oscillator at one end of the film thickness gauge 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 852.1nm wavelength laser generated by the laser through two 16mm diameter glass observation windows on the side wall of the vacuum chamber via optical fiber. The laser path passes 30mm directly below the cesium nozzle. When cesium atoms pass through, they absorb the 852.1nm characteristic wavelength laser, thereby achieving cesium atom concentration acquisition.

[0029] The specific workflow of this invention is as follows: First, seal the vacuum chamber 1, turn on the mechanical pump 4 to start evacuation, then keep the valve near the top of the chamber in the cesium crucible assembly open. When the vacuum condition in the chamber meets the starting conditions of the molecular pump 5, turn on the molecular pump 5, continue to observe the vacuum condition, then turn on the control valve near the cesium crucible 2 in the cesium crucible assembly to continue evacuation. When the vacuum degree reaches... At the Pa level, the system meets the ultra-high vacuum environment requirements of the experiment. The heating wire 6 and thermocouple 7 are then 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 in real time by the temperature monitored by the thermocouple 7. The temperature settings for the cesium crucible 2 and the transmission pipe 3 are determined according to the experimental requirements, ensuring that the temperature of the transmission pipe 3 is at least 20°C higher than the temperature of the cesium crucible 2. A crystal oscillator probe 10 at one end of the film thickness gauge 9 deposits cesium vapor in the vacuum chamber 1, while the other end displays the deposition thickness and deposition rate of cesium on the crystal oscillator probe 10 in real time via a monitor. The laser absorption spectroscopy system 11 transmits a 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 1 via optical fiber. When cesium atoms pass through, they absorb the characteristic wavelength laser light of 852.1 nm, thus achieving cesium atom concentration acquisition. By cross-checking the two diagnostic methods, the reliability of the experimental data can be ensured.

[0030] Those skilled in the art will readily understand that the above description is merely 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 within the scope of protection of the present invention.

Claims

1. A system for offline measurement of cesium evaporation rate in a fusion device, characterized in that: The system includes a vacuum chamber, a cesium crucible assembly, a vacuum pumping unit, a heating assembly, a film thickness gauge, and a laser absorption spectroscopy system. The vacuum chamber includes interfaces connecting to the cesium crucible assembly, film thickness gauge, laser absorption spectroscopy system, and vacuum pumping unit. The cesium crucible assembly, connected to the vacuum chamber via a metal sealing flange, includes a cesium crucible for storing liquid cesium, a transfer pipe, two control valves, and a cesium nozzle. The vacuum pumping unit, connected to the side of the vacuum chamber via a quick-connect flange, includes a molecular pump and a mechanical pump. The heating assembly, connected to the cesium crucible assembly via heating wires and thermocouples, includes two sets of heating and temperature monitoring devices at the cesium crucible and the transfer pipe. The film thickness gauge's crystal oscillator probe is fixed inside the vacuum chamber via a quick-connect adapter, with the probe aligned directly below the cesium nozzle of the cesium crucible assembly, for measuring the cesium deposition thickness. The laser absorption spectroscopy system, connected to a transparent glass window on the side wall of the vacuum chamber via a laser, is used to measure the cesium atom concentration. The crystal oscillator probe at one end of the film thickness gauge is inserted from the side of the vacuum chamber through a sealing flange and fixed inside the vacuum chamber. The crystal oscillator probe is 100mm directly below the cesium nozzle. The oscillator at the other end of the film thickness gauge is connected to the crystal oscillator probe through a cable. The deposition thickness and deposition rate of cesium on the probe are displayed in real time on the display. The laser absorption spectroscopy system transmits an 852.1nm wavelength laser generated by the laser through two 16mm diameter glass observation windows on the side wall of the vacuum chamber via optical fiber. The laser path passes 30mm directly below the cesium nozzle. When cesium atoms pass through, they absorb the 852.1nm characteristic wavelength laser, thereby achieving cesium atom concentration acquisition.

2. The system for offline measurement of cesium evaporation rate in a fusion device according to claim 1, characterized in that: The vacuum chamber is made of stainless steel and measures 730mm in length, 320mm in width, and 350mm in height. A 35mm diameter sealing flange is installed on the top of the vacuum chamber, which is connected to the cesium crucible assembly. Two 16mm diameter glass observation windows are installed on the side wall of the vacuum chamber, which are connected to the laser absorption spectroscopy system. A 35mm diameter sealing flange is installed on the side wall of the vacuum chamber, which is connected to the film thickness gauge. A 40mm diameter sealing flange is installed on the side wall of the vacuum chamber, which is connected to the vacuum pumping unit.

3. The system for offline 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 that is 75 mm long and 16 mm in diameter, capable of holding 10 g of liquid cesium metal; the cesium crucible assembly includes a transfer pipe that is 400 mm long and 12.7 mm in diameter, with one end bent at 60° and inserted into the cesium crucible, and the other end inserted into the vacuum chamber perpendicular to the top of the vacuum chamber.

4. A system for offline 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 300 L / s and a mechanical pump with a pumping speed of 60 L / s. It is connected to the pumping flange on the side wall of the vacuum chamber through a bellows and is used to provide an ultra-high vacuum environment for the vacuum chamber.

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

6. A system for offline 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 located 60 mm from the cesium crucible and the other located 170 mm from the top surface of the vacuum chamber. These valves are used to ensure the vacuum seal inside the cesium crucible during installation and to prevent oxidation of the metallic cesium.

7. A system for offline measurement of cesium evaporation rate in a fusion device according to claim 5, characterized in that: 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 pipe. 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 pipe. The heating power supply controls the temperature of the cesium crucible and the transmission pipe in real time by providing feedback on the temperature detected by the thermocouples.

8. A method for offline measurement of cesium evaporation rate applied to a system for offline measurement of cesium evaporation rate in a fusion device as described in any one of claims 1-7, characterized in that, include: First, seal the vacuum chamber and start evacuation with the mechanical pump. Then, keep the valve near the top of the vacuum chamber in the cesium crucible assembly open. When the vacuum level in the chamber meets the starting conditions for the molecular pump, start the molecular pump and continue observing the vacuum level. Then, open the control valve near the cesium crucible in the cesium crucible assembly to continue evacuation until the vacuum level reaches ~10. -5 At the Pa level, the system meets the ultra-high vacuum environment requirements of the experiment. The heating wire and thermocouples are then divided into two groups: one group is wound around the cesium crucible, and the other group is wound around the transfer pipe. The heating power is turned on, and the temperature of the cesium crucible and transfer pipe is controlled in real time by the temperature monitored by the thermocouples. The temperature settings for the cesium crucible and transfer pipe are determined according to experimental requirements, ensuring that the temperature of the transfer pipe is at least 20°C higher than that of the cesium crucible. A crystal oscillator probe at one end of the film thickness gauge deposits cesium vapor in the vacuum chamber, while the other end displays the deposition thickness and deposition rate of cesium on the crystal oscillator probe in real time. The laser absorption spectroscopy system transmits a 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 via optical fiber. When cesium atoms pass through, they absorb the characteristic wavelength of 852.1 nm laser light, thus achieving cesium atom concentration acquisition.

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