Cesium reference cell and optical cavity ring-down system

Abstract

This invention belongs to the field of optical measurement and atomic precision device technology, and discloses a cesium reference cell and an optical cavity ring-down system for use in an optical cavity ring-down system. The system includes: a cell body comprising an inner cell body and an outer cell body, the inner cell body being used to hold cesium elements and generate cesium vapor, and the outer cell body surrounding the inner cell body to provide a thermal environment; a temperature control component comprising a heating unit and a cooling unit, the heating unit being used to raise the temperature of the inner cell body, and the cooling unit being used to form a cold end on the inner cell body; an optical window disposed on opposite sides of the cell body for allowing a target beam to pass through the cesium vapor; and a control unit for determining the absolute cesium particle number concentration in the inner cell body based on the temperature of the inner cell body and the beam after passing through the cesium vapor.

Description

Technical Field

[0001] This application belongs to the field of optical measurement and atomic precision device technology, specifically relating to a cesium reference cell for an optical cavity ring-down system and an optical cavity ring-down system. Background Technology

[0002] In magnetic confinement fusion research, the negative ion concentration of the neutral beam ion source is a key parameter affecting plasma heating efficiency. Although cavity ring-down technology is the mainstream method for measuring this parameter, it faces many challenges. On the one hand, existing technologies lack a dedicated absolute concentration calibration benchmark adapted to fusion scenarios, and the system is susceptible to signal drift due to extreme environments, resulting in measurement results lacking traceability and reliability. On the other hand, traditional cesium cells have a simple structure, making it difficult to form a stable cesium vapor environment, and the vapor is prone to condensation at the optical window. Temperature control schemes also cannot achieve precise concentration adjustment. Some technologies can only measure the cesium evaporation rate offline and cannot provide online calibration support. These problems restrict the optimization of ion source performance and the advancement of fusion research. Therefore, a controllable cesium reference cell scheme adapted to the cavity ring-down system is urgently needed. Summary of the Invention

[0003] This application aims to address at least one of the technical problems existing in the prior art. To this end, this application proposes a cesium reference cell for an optical cavity ring-down system, which can solve the problems in the prior art of lacking a dedicated absolute concentration calibration benchmark adapted to the extreme environment of fusion, the easy condensation of cesium vapor in the optical window, and the difficulty in accurately controlling the concentration. It makes up for the deficiency of traditional offline measurement in providing real-time calibration for the optical cavity ring-down system, provides a stable and reliable concentration benchmark for the system, effectively improves the accuracy of negative ion concentration measurement, and provides key support for the performance optimization of neutral beam ion sources and plasma heating parameter optimization in magnetic confinement nuclear fusion.

[0004] To achieve the above objectives, a first aspect of the present invention provides a cesium reference cell for an optical cavity ring-down system, comprising a cell body including an inner cell body and an outer cell body. The inner cell body is used to hold cesium elements and generate cesium vapor, and the outer cell body surrounds the inner cell body to provide a thermal environment. A temperature control component includes a heating unit and a cooling unit. The heating unit is used to raise the temperature of the inner cell body, and the cooling unit is used to form a cold end on the inner cell body. An optical window is disposed on opposite sides of the cell body for allowing a target beam to pass through the cesium vapor. A control unit is used to determine the absolute cesium particle number concentration in the inner cell body based on the temperature of the inner cell body and the beam after passing through the cesium vapor.

[0005] In some embodiments, a first vacuum region is formed inside the inner pool, and a second vacuum region is formed between the inner pool and the outer pool.

[0006] In some embodiments, the inner pool is arranged in a T-shape, the heating unit includes a heating band disposed in the transverse region of the T-shape, and the cooling unit includes a cooling plate disposed in the longitudinal region of the T-shape and away from the transverse region to form a cold end in the longitudinal region.

[0007] In some embodiments, the optical window includes a first optical window and a second optical window. The first optical window is disposed on opposite sides of the outer pool body, and the second optical window is disposed on opposite sides of the inner pool body. The first optical window and the second optical window are arranged coaxially so that the target beam passes through the outer pool body, the inner pool body, and the cesium vapor in sequence.

[0008] In some embodiments, the heating unit further includes a first temperature sensor for detecting the temperature of the inner tank and sending a first detection signal to the control unit; the cooling unit further includes a second temperature sensor for detecting the cold end temperature and sending a second detection signal to the control unit; the control unit controls the heating belt and the cooling element to operate according to the first detection signal and the second detection signal, respectively, to achieve temperature control.

[0009] In some embodiments, the control unit is configured to perform the following steps: heating the inner pool to a first set temperature; adjusting the cold end to a second set temperature to establish a temperature gradient; determining the absorption signal of the target beam; and calculating the absolute particle number concentration by combining the first set temperature and the second set temperature.

[0010] In some embodiments, the absolute particle number concentration is expressed as:

[0011] in, Expressed as absolute particle number concentration, This is expressed as the saturated vapor pressure of cesium vapor. This is expressed as the temperature at the cold end. Expressed as Boltzmann constant, This represents the temperature of the inner pool.

[0012] In some embodiments, the outer pool body is further provided with a vacuum extraction port for evacuating the second vacuum region.

[0013] In some embodiments, the target beam is obtained based on the splitting of the probe laser by a coupler configured to provide a 50:50 splitting ratio.

[0014] According to an embodiment of the present invention, a cesium reference cell for a cavity ring-down system includes a cell body comprising an inner cell body and an outer cell body. The inner cell body is used to hold cesium elements and generate cesium vapor, while the outer cell body surrounds the inner cell body to provide a thermal environment. A temperature control component includes a heating unit and a cooling unit. The heating unit is used to raise the temperature of the inner cell body, and the cooling unit is used to form a cold end on the inner cell body. An optical window is disposed on opposite sides of the cell body for allowing a target beam to pass through the cesium vapor. A control unit is used to determine the absolute cesium particle number concentration in the inner cell body based on the temperature of the inner cell body and the beam after passing through the cesium vapor. Therefore, this application can solve the problems in the prior art of lacking a dedicated absolute concentration calibration benchmark adapted to the extreme environment of fusion, the easy condensation of cesium vapor in the optical window, and the difficulty in accurately controlling the concentration. It also overcomes the shortcomings of traditional offline measurements in providing real-time calibration for cavity ring-down systems, providing a stable and reliable concentration benchmark for the system, effectively improving the accuracy of negative ion concentration measurement, and providing key support for the performance optimization of neutral beam ion sources and plasma heating parameter optimization in magnetic confinement fusion.

[0015] To achieve the above objectives, a second aspect of the present invention provides a cavity ring-down system, comprising: a light source module for outputting a probe laser; a beam splitting module configured to split the probe laser into a measurement beam and a target beam, the measurement beam entering a cavity ring-down measurement channel and the target beam entering a cesium reference cell channel; a cavity ring-down measurement channel for receiving the measurement beam and performing ring-down absorption measurement on the target sample to obtain a sample measurement signal; a controllable cesium reference cell module disposed in the cesium reference cell channel, including the cesium reference cell as described in the first aspect for a cavity ring-down system, for receiving the target beam and outputting an absolute particle number concentration reference; and a data processing unit communicatively connected to the cavity ring-down measurement channel and the controllable cesium reference cell module, for real-time calibration of the sample measurement signal using the absolute particle number concentration reference to obtain the calibrated absolute concentration result of the target sample.

[0016] According to an embodiment of the present invention, an optical cavity ring-down system includes: a light source module for outputting a probe laser; a beam splitting module configured to split the probe laser into a measurement beam and a target beam, wherein the measurement beam enters an optical cavity ring-down measurement channel and the target beam enters a cesium reference cell channel; the optical cavity ring-down measurement channel for receiving the measurement beam and performing ring-down absorption measurement on the target sample to obtain a sample measurement signal; a controllable cesium reference cell module disposed in the cesium reference cell channel, including a cesium reference cell as described in the first aspect for an optical cavity ring-down system, for receiving the target beam and outputting an absolute particle number concentration reference; and a data processing unit communicatively connected to the optical cavity ring-down measurement channel and the controllable cesium reference cell module, for performing real-time calibration of the sample measurement signal using the absolute particle number concentration reference to obtain the calibrated absolute concentration result of the target sample. Therefore, this application can solve the problems in the prior art of lacking a dedicated absolute concentration calibration standard adapted to the extreme environment of fusion, the easy condensation of cesium vapor in the optical window and the difficulty in accurately controlling the concentration, make up for the deficiency of traditional offline measurement in providing real-time calibration for the optical cavity ring decay system, provide a stable and reliable concentration standard for the system, effectively improve the accuracy of negative ion concentration measurement, and provide key support for the performance optimization of the neutral beam ion source and the optimization of plasma heating parameters in magnetic confinement nuclear fusion.

[0017] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0018] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a schematic diagram of the internal structure of a cesium reference cell for an optical cavity ring-down system according to an embodiment of this application; Figure 2 This is a three-dimensional cross-sectional view of a cesium reference cell for an optical cavity ring-down system according to an embodiment of this application; Figure 3 This is a schematic diagram of the inner cell of a cesium reference cell for an optical cavity ring-down system according to an embodiment of this application; Figure 4 This is an overall three-dimensional view of a cesium reference cell for an optical cavity ring-down system according to an embodiment of this application; Figure 5 This is a schematic diagram of the beam splitting module of the cesium reference cell used in the optical cavity ring-down system in an embodiment of this application; Figure 6 This is a schematic diagram of the workflow of the control unit in the embodiments of this application; Figure 7 This is a schematic diagram of the optical cavity ring-down system in an embodiment of this application; Figure 8This is a schematic diagram of the working process of the cesium reference cell used in the optical cavity ring-down system in the embodiments of this application.

[0019] Reference numerals in the figures: cesium reference cell 100 for the cavity ring-down system, heating belt 11, cooling element 12, inner cell 131, first vacuum region 132, outer cell 141, second vacuum region 142, first temperature sensor 15, second temperature sensor 16, control interface 17, first optical window 181, second optical window 182, heat-insulating vacuum cavity 19, heat sink 21, fan 22, screw hole 23, support foot 24, probe laser 501, measurement beam 502, target beam 503, cavity ring-down system 700, light source module 701, beam splitting module 702, cavity ring-down measurement channel 703, controllable cesium reference cell module 704, data processing unit 705. Detailed Implementation

[0020] Embodiments of this application will now be described in more detail with reference to the accompanying drawings. While some embodiments of this application are shown in the drawings, it should be understood that this application can be implemented in various forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of this application. It should be understood that the drawings and embodiments of this application are for illustrative purposes only and are not intended to limit the scope of protection of this application.

[0021] It should be understood that the steps described in the method embodiments of this application may be performed in different orders and / or in parallel. Furthermore, the method embodiments may include additional steps and / or omit the steps shown. The scope of this application is not limited in this respect.

[0022] As described in the background section, in magnetic confinement fusion research, the negative ion concentration of the neutral beam ion source is the core parameter determining the plasma heating efficiency and ion source performance. Cavity ring-down spectroscopy has become the core means of measuring this parameter due to its high sensitivity. However, in practical applications, existing cavity ring-down systems lack a dedicated cesium vapor standard reference cell adapted to the extreme environment of fusion, making it impossible to achieve absolute calibration of the negative ion concentration. Traditional cesium storage structures are mostly single cavities, making it difficult to form a stable cesium vapor environment, and the vapor is prone to condensation in the optical window. Temperature control schemes also cannot accurately regulate the vapor concentration. At the same time, some calibration techniques can only achieve offline measurement, which cannot match the online diagnostic requirements of the cavity ring-down system. This results in measurement results lacking traceability and being inefficient, easily leading to concentration misjudgments that affect the evaluation of ion source performance. Furthermore, parameter deviations may restrict the optimization of fusion plasma heating, making it difficult to meet the high-precision and real-time requirements of fusion devices for neutral beam diagnosis.

[0023] To address the shortcomings of existing cavity ring-down systems in negative ion concentration diagnosis, this invention utilizes a cesium reference cell within the cavity ring-down system. This cell, employing a double-layered vacuum structure consisting of an inner and outer cell, a coordinated hot and cold end temperature control component, a 50:50 split-beam dual-path design, and a concentration inversion process based on saturated vapor pressure, can stably generate controllable concentrations of cesium vapor and provide an absolute particle number concentration benchmark. This effectively solves the problems of lacking a dedicated calibration source, difficulty in controlling cesium vapor, and inability to perform online calibration. It achieves accurate, real-time measurement of negative ion concentration, improves the reliability and consistency of diagnostic results, and avoids the potential for misjudgment of ion source optimization direction or inaccurate fusion heating parameters due to measurement deviations. This provides crucial technical support for performance improvement of neutral beam ion sources in magnetic confinement fusion and for plasma physics research.

[0024] The following is for reference. Figures 1-5 This application describes a cesium reference cell for an optical cavity ring-down system, as provided in an embodiment of the present application.

[0025] refer to Figure 1 This is a schematic diagram of the internal structure of a cesium reference cell for an optical cavity ring-down system provided in an embodiment of this application.

[0026] like Figure 1 As shown, the cesium reference cell for the optical cavity ring-down system includes: a cell body comprising an inner cell body 131 and an outer cell body 141, wherein the inner cell body 131 is used to hold cesium elements and generate cesium vapor, and the outer cell body 141 surrounds the inner cell body 131 to provide a thermal environment; a temperature control assembly comprising a heating unit and a cooling unit, wherein the heating unit is used to raise the temperature of the inner cell body 131, and the cooling unit is used to form a cold end on the inner cell body 131; an optical window disposed on opposite sides of the cell body for allowing a target beam to pass through the cesium vapor; and a control unit for determining the absolute cesium particle number concentration in the inner cell body 131 based on the temperature of the inner cell body 131 and the beam after passing through the cesium vapor.

[0027] Specifically, the cesium reference cell core used in the aforementioned optical cavity ring-down system comprises four main modules: the cell body, the temperature control component, the optical window, and the control unit. The cell body is divided into an inner cell body 131 and an outer cell body 141. The inner cell body 131 adopts a T-shaped structure design, possessing a highly airtight structure. The lower part of the inner cell body 131 (i.e., the longitudinal region of the T-shaped structure) is used to hold the cesium solution, while the transverse region provides ample space for vapor diffusion. After heating, the temperature in the transverse region is uniform, and the cesium vapor distribution is also more uniform, while effectively separating the cold end and the hot end. The inner tank 131 is designed to create a convection environment, allowing cesium vapor to move smoothly. The outer tank 141 tightly surrounds the outer side of the inner tank 131, effectively isolating it from external temperature fluctuations and providing a stable heat preservation environment for the inner tank 131. The temperature control assembly includes a heating unit and a cooling unit. The heating element 11 of the heating unit is located in the transverse region of the inner tank 131 to heat the cavity. The cooling element 12 of the cooling unit is installed below the inner tank 131, in the longitudinal region of the T-shaped structure, ensuring the cesium vapor is in circulation. The outer cell 141 is equipped with a heat sink 21 and a fan 22 to dissipate the heat generated by the cooling element 12. A temperature detection component monitors the temperature of the inner cell 131 and the cold end in real time, providing data support for precise temperature control. Furthermore, optical windows are positioned on opposite sides of the cell, employing a double-layer coaxial design corresponding to the optical paths of the outer cell 141 and the inner cell 131 respectively. This ensures that the target beam passes through the outer cell 141, the inner cell 131, and the cesium vapor within them without deviation or loss, effectively carrying the beam absorption signal output. The control unit performs core control and calculation functions. On one hand, it receives signals from the temperature detection component to precisely control the operating state of the heating and cooling units, maintaining a stable temperature in the inner cell 131. On the other hand, it receives the beam absorption signal and, combined with the temperature data of the inner cell 131, performs preset logic calculations to ultimately determine the absolute cesium particle number concentration in the inner cell 131, providing a reliable concentration calibration benchmark for the optical cavity ring-down system.

[0028] As an optional embodiment, a first vacuum region 132 is formed inside the inner pool 131, and a second vacuum region 142 is formed between the inner pool 131 and the outer pool 141.

[0029] As an optional embodiment, the outer pool 141 is also provided with a vacuum port for evacuating the second vacuum region 142.

[0030] Specifically, after the inner pool 131 is sealed, it is evacuated to form a first vacuum region 132, which completely isolates the contact between air (such as oxygen and water vapor) and cesium, preventing cesium from reacting due to its chemical reactivity and generating impurities. This ensures that the generated cesium vapor is pure and interference-free, and does not affect the accuracy of the subsequent beam absorption signal. The annular space between the inner pool 131 and the outer pool 141 is evacuated through a vacuum port on the outer pool 141, forming a second vacuum region 142. Since a vacuum is a poor conductor of heat, this region can significantly reduce the heat exchange between the inner pool 131 and the external environment. When the external temperature fluctuates by ±5℃ due to equipment operation, the second vacuum region 142 can control the temperature fluctuation of the inner pool 131 within ±0.1℃, avoiding sudden temperature changes that could lead to unstable cesium vapor concentration. In actual operation, the vacuum level of the second vacuum region 142 is first evacuated to 10. -3 Keep the pressure below 10 Pa, then evacuate the sealed inner tank 131 to 10 Pa. -4 Pa, after loading a quantitative amount of cesium, reseals the first vacuum region 132, ultimately providing a reliable cavity environment for the temperature control component to precisely regulate the cesium vapor concentration and for the optical window to stably transmit the beam.

[0031] As an optional embodiment, the inner pool 131 is arranged in a T-shape. The heating unit includes a heating band 11, which is disposed in the transverse region of the T-shape. The cooling unit includes a cooling plate 12, which is disposed in the longitudinal region of the T-shape and away from the transverse region, so as to form a cold end in the longitudinal region.

[0032] Heating belt setting method: winding, the winding density of the heating belt can be controlled according to actual needs.

[0033] When the temperature control component is activated, the heating band 11 located in the T-shaped transverse region of the inner tank 131 releases heat to uniformly heat the transverse region, providing the energy required for the evaporation of cesium in the inner tank 131 and causing cesium to be converted into stable vapor. At the same time, the cooling plate 12 installed in the T-shaped longitudinal region and far away from the transverse region will continuously cool, forming a low-temperature cold end in the longitudinal region. This transverse heating and longitudinal cooling layout can build a stable temperature gradient inside the inner tank 131. Cesium vapor will slowly circulate from the transverse region to the longitudinal region driven by the temperature difference, avoiding uneven vapor concentration due to local temperature changes, and preventing vapor from condensing and accumulating in the optical window, ultimately achieving stable control of cesium vapor concentration.

[0034] Furthermore, the heating unit also includes a first temperature sensor 15, which is used to detect the temperature of the inner pool and send a first detection signal to the control unit; the cooling unit also includes a second temperature sensor 16, which is used to detect the cold end temperature and send a second detection signal to the control unit; the control unit controls the heating belt 11 and the cooling element 12 to work according to the first detection signal and the second detection signal, so as to achieve temperature control.

[0035] Specifically, the first temperature sensor 15 of the heating unit is tightly attached to the inner wall of the T-shaped transverse region of the inner tank 131, which can capture the overall temperature of the inner tank in real time and accurately transmit the first detection signal (e.g., the current measured temperature is 48°C) to the control unit. The second temperature sensor 16 of the cooling unit (the material can be a thermistor) is fixed near the cold end of the longitudinal region, which synchronously collects the cold end temperature and sends the second detection signal (e.g., the current measured temperature is 22°C). The control unit will first retrieve the preset target parameters, assuming that the inner tank 131 needs to be maintained at 50°C to ensure stable evaporation of cesium and the cold end needs to be controlled at 20°C to construct... By using a reasonable temperature gradient, the real-time detection signal is compared and analyzed with the target value. When the first detection signal is below 50°C, the control unit will immediately output a command to increase the heating power of the heating belt until the temperature of the inner tank 131 rises to 50°C and remains stable. When the second detection signal is above 20°C, the control unit will enhance the cooling intensity of the cooling element and gradually reduce the cold end temperature to 20°C. Through such continuous feedback and fine-tuning, it can be ensured that the inner tank 131 always provides suitable heat for the generation of cesium vapor, stabilizes the temperature gradient of horizontal heat and vertical cold, and effectively avoids the problem of uneven concentration of cesium vapor due to temperature fluctuations.

[0036] As an optional embodiment, the optical window includes a first optical window 181 and a second optical window 182. The first optical window 181 is disposed on opposite sides of the outer pool 141, and the second optical window 182 is disposed on opposite sides of the inner pool 131. The first optical window 181 and the second optical window 182 are arranged coaxially so that the target beam passes through the outer pool, the inner pool and the cesium vapor in sequence.

[0037] The second optical window 182 is made of ruby ​​because ruby ​​has high transmittance for infrared lasers, which can effectively reduce energy loss during beam transmission and provide stable optical path conditions for accurate detection of subsequent beam absorption signals.

[0038] refer to Figure 2This is a three-dimensional cross-sectional view of a cesium reference cell for a cavity ring-down system in this embodiment of the application. The first optical window 181 is installed on opposite sides of the outer cell 141 to initially guide the beam into the cell. The second optical window 182 is closely fitted to opposite sides of the inner cell 131 and directly faces the cesium vapor in the inner cell 131. Through precise calibration, the central axes of the first optical window 181 and the second optical window 182 are completely aligned. When the target beam of the cavity ring-down system is emitted, it first passes through the first optical window 181 of the outer cell, and then enters the inner cell 131 without any offset by aligning with the second optical window 182 of the inner cell. Finally, it passes smoothly through the cesium vapor. This coaxial layout can minimize the offset and energy loss in beam transmission, allowing the beam to fully carry the absorption characteristics of the cesium vapor and output them, providing a stable optical path basis for the control unit to calculate the absolute cesium particle number concentration through the absorption signal.

[0039] refer to Figure 3 This is a schematic diagram of the inner cell of a cesium reference cell for an optical cavity ring-down system in an embodiment of this application.

[0040] The cesium element cell adopts a T-shaped vacuum chamber structure. Position A in the inner chamber 131 stores cesium. When heated by the heating device, the cesium evaporates and diffuses towards the optical path, ensuring uniform vapor distribution in the transverse region. Ruby windows are used at positions B at both ends of the transverse region of the inner chamber 131, providing high infrared laser transmittance, reducing beam transmission loss, and ensuring stable transmission of the target beam carrying the cesium vapor absorption signal. A first temperature sensor 15 (material can be a thermocouple) is installed at position C. The thermocouple directly contacts the internal environment, capturing real-time temperature changes of the internal cesium vapor and synchronously transmitting the temperature data to the control system. To ensure a vacuum environment within the chamber, a valve is installed at position D. This valve connects to an external evacuation device, allowing the T-shaped chamber to be evacuated to a vacuum level better than 10. -3 The high vacuum state of Pa isolates the air from contact with cesium, preventing cesium from oxidizing due to its chemical reactivity or reacting with water vapor, thus ensuring the purity of cesium vapor.

[0041] refer to Figure 4 This is an overall three-dimensional view of a cesium reference cell for an optical cavity ring-down system in an embodiment of this application.

[0042] The outer chamber 141 adopts a low-vacuum cylindrical cavity to provide a stable constant temperature environment for the inner chamber 131. By maintaining the low vacuum state inside the cavity and reducing heat exchange caused by air convection, the influence of external temperature fluctuations on the inner chamber 131 can be effectively isolated. At the same time, the outer chamber 141 is designed with two pairs of observation windows with different functions. One pair uses sapphire windows as the optical path channel for external light beams to enter the outer chamber 141. It is coaxially aligned with the ruby ​​windows of the inner chamber 131 to ensure that the light beam is transmitted without deviation. The other pair uses ordinary glass windows, which allows operators to directly observe the state of cesium vapor inside the cavity and the operation of various components. In addition, the upper end of the outer chamber 141 integrates the internal control and signal line feedthrough flange interface and the vacuum port. The former can realize the signal transmission of thermocouples, controllers and other equipment while ensuring the airtightness of the outer chamber 141. The latter is connected to the external vacuum equipment to maintain the low vacuum state of the outer chamber 141. Together, they provide environmental protection for the stable generation and precise control of cesium vapor.

[0043] Furthermore, the target beam is obtained based on the splitting of the probe laser by a coupler configured to provide a 50:50 splitting ratio.

[0044] Specifically, refer to Figure 5 This is a schematic diagram of the beam splitting module of the cesium reference cell used in the cavity ring-down system in this embodiment of the application. First, the probe laser 501 output by the cavity ring-down system enters a dedicated coupler, which distributes the beam at a splitting ratio of 50:50. When the total power of the probe laser 501 is 10... -2 When W, it will be evenly divided into two 5×10 paths. -3 The light beam has two paths: one as the measurement beam 502, which enters the cavity ring-down measurement channel, and the other as the target beam 503, which is directed towards the optical window of the cesium reference cell. The target beam 503 first contacts the first optical windows 181 on opposite sides of the outer cell 141. Since the first optical windows 181 and the second optical windows 182 on opposite sides of the inner cell 131 are precisely calibrated to ensure their central axes are completely aligned, the beam can smoothly pass through the first optical windows 181 without needing to adjust its direction. It then smoothly enters the second optical windows 182 and penetrates the cesium vapor in the inner cell. During this process, the double-layered optical windows isolate external interference factors such as dust and temperature fluctuations, preventing beam deflection or scattering, while simultaneously controlling the energy loss of the beam transmission to an extremely low level (e.g., 5 × 10⁻⁶). -3 After the target beam 503 of W passes through the two windows, the power loss can be controlled within 2×10. -4 Within W), ensuring that the beam can fully carry the absorption signal of cesium vapor and continue to transmit, providing accurate and reliable optical path signal support for the subsequent control unit to invert the absolute cesium particle number concentration through the absorption signal.

[0045] refer to Figure 6 This is a schematic diagram of the working process of the control unit in the embodiments of this application.

[0046] like Figure 6 As shown, in this embodiment of the application, the control unit is configured to perform the following steps: Step S601: Heat the inner pool to the first set temperature.

[0047] Step S602: Adjust the cold end to the second set temperature to establish a temperature gradient.

[0048] Step S603: Determine the absorption signal of the target beam and calculate the absolute particle number concentration by combining the first set temperature and the second set temperature.

[0049] Specifically, firstly, the control unit sends a command to the heating unit according to preset parameters, driving the heating component to heat the inner pool to a first set temperature (e.g., 50°C), providing sufficient energy for the evaporation of cesium in the inner pool and promoting the generation of stable cesium vapor. Next, the control unit synchronously regulates the cooling unit to precisely adjust the cold end temperature to a second set temperature (e.g., 20°C), establishing a stable temperature gradient inside the inner pool by utilizing the temperature difference between the inner pool and the cold end, ensuring that the cesium vapor is evenly distributed and does not easily condense. Furthermore, the control unit receives the target beam absorption signal after passing through the cesium vapor, and combines the stabilized first and second set temperatures, using physical models such as the saturated vapor pressure formula and the beam absorption law to calculate the absolute cesium particle number concentration in the inner pool, providing a traceable concentration calibration benchmark for the optical cavity ring-down system.

[0050] Furthermore, the absolute particle number concentration is expressed as:

[0051] in, Expressed as absolute particle number concentration, This is expressed as the saturated vapor pressure of cesium vapor. This is expressed as the temperature at the cold end. Expressed as Boltzmann constant, This represents the temperature of the inner pool.

[0052] Specifically, the control unit drives the heating unit to stabilize the inner tank at a first set temperature (i.e., (e.g., 50℃ is equivalent to 323.15K), while simultaneously adjusting the refrigeration unit to maintain the cold end at the second set temperature (i.e. (e.g., 20℃ is equivalent to 293.15K) to ensure a stable temperature gradient. Next, the control unit will collect these two temperature parameters and, based on... Retrieve the corresponding value from the built-in cesium vapor saturated vapor pressure database (e.g., at 293.15 K). Approximately 1.3 × 10 - ³Pa), further, , , and the known Boltzmann constant ( ≈1.38×10 - Substituting ²³J / K into the above formula for calculating absolute particle number concentration, the absolute particle number concentration of cesium vapor in the inner pool can be obtained through calculation (e.g., by substituting the above values, we can obtain...). ≈2.8×10 17 m -3 Finally, the control unit combines the absorption signal of the target beam after passing through the cesium vapor to verify and fine-tune the calculated concentration value, ensuring the accuracy and reliability of the results.

[0053] In summary, this application provides a cesium reference cell for a cavity ring-down system, comprising: a cell body, including an inner cell body and an outer cell body, the inner cell body being used to hold cesium elements and generate cesium vapor, and the outer cell body surrounding the inner cell body to provide a thermal environment; a temperature control component, including a heating unit and a cooling unit, the heating unit being used to raise the temperature of the inner cell body, and the cooling unit being used to form a cold end on the inner cell body; an optical window, disposed on opposite sides of the cell body, for allowing a target beam to pass through the cesium vapor; and a control unit for determining the absolute cesium particle number concentration in the inner cell body based on the temperature of the inner cell body and the beam after passing through the cesium vapor. Therefore, this application can solve the problems in the prior art of lacking a dedicated absolute concentration calibration benchmark adapted to the extreme environment of fusion, the easy condensation of cesium vapor in the optical window, and the difficulty in accurately controlling the concentration. It also overcomes the shortcomings of traditional offline measurements in providing real-time calibration for cavity ring-down systems, providing a stable and reliable concentration benchmark for the system, effectively improving the accuracy of negative ion concentration measurement, and providing key support for the performance optimization of neutral beam ion sources and plasma heating parameter optimization in magnetic confinement fusion.

[0054] It should be noted that the above description describes some embodiments of the present invention. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps described in the claims may be performed in a different order than that shown in the above embodiments and still achieve the desired results. Furthermore, the processes depicted in the drawings do not necessarily require a specific or sequential order to achieve the desired results. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0055] Corresponding to the above embodiments, the present invention also proposes an optical cavity ringback system.

[0056] refer to Figure 7 This is a schematic diagram of the optical cavity ring-down system in an embodiment of this application.

[0057] The cavity ring-down system 700 includes: a light source module 701, a beam splitting module 702, a cavity ring-down measurement channel 703, a controllable cesium reference cell module 704, and a data processing unit 705.

[0058] A light source module 701 is used to output a probe laser; a beam splitting module 702 is configured to split the probe laser into a measurement beam and a target beam, with the measurement beam entering the cavity ring-down measurement channel and the target beam entering the cesium reference cell channel; a cavity ring-down measurement channel 703 is used to receive the measurement beam and perform ring-down absorption measurement on the target sample to obtain a sample measurement signal; a controllable cesium reference cell module 704 is disposed in the cesium reference cell channel and includes a cesium reference cell 100 for the cavity ring-down system as described in the first aspect, used to receive the target beam and output an absolute particle number concentration reference; a data processing unit 705 is communicatively connected to the cavity ring-down measurement channel and the controllable cesium reference cell module, and uses the absolute particle number concentration reference to perform real-time calibration of the sample measurement signal to obtain the calibrated absolute concentration result of the target sample.

[0059] The spectral splitter module 702 is also configured as follows: The target beam is obtained by splitting the probe laser using a coupler configured to provide a 50:50 splitting ratio.

[0060] The cavity ringback measurement channel 703 is also configured as follows: The heating unit also includes a first temperature sensor, which is used to detect the temperature of the inner tank and send a first detection signal to the control unit; the cooling unit also includes a second temperature sensor, which is used to detect the cold end temperature and send a second detection signal to the control unit; the control unit controls the heating belt and the cooling plate to work according to the first detection signal and the second detection signal, respectively, so as to achieve temperature control.

[0061] The controllable cesium reference pool module 704 is also configured as follows: Heat the inner tank to the first set temperature; Adjust the cold end to the second set temperature to establish a temperature gradient; The absorption signal of the target beam is determined, and the absolute particle number concentration is calculated by combining the first set temperature and the second set temperature.

[0062] Optionally, the controllable cesium reference cell module 704 is also configured as follows: The absolute particle number concentration is expressed as:

[0063] in, Expressed as absolute particle number concentration, This is expressed as the saturated vapor pressure of cesium vapor. This is expressed as the temperature at the cold end. Expressed as Boltzmann constant, This represents the temperature of the inner pool.

[0064] Further, refer to Figure 8 This is a schematic diagram of the working process of the cesium reference cell used in the optical cavity ring-down system in this embodiment of the application.

[0065] First, the light source module 701 stably outputs a probe laser, providing the basic optical signal for the entire measurement process. This probe laser then enters the beam splitter module 702, which provides a 50:50 beam split according to system functional requirements, dividing the laser into two beams with different tasks. One beam serves as the measurement beam, directed into the cavity ring-down measurement channel 703. After receiving this measurement beam, the cavity ring-down measurement channel 703 performs detection on the target sample based on the ring-down absorption principle. By analyzing the interaction between the beam and the sample, it generates a sample measurement signal reflecting the sample characteristics. The other beam serves as the target beam, directed along the cesium reference beam... The data is transmitted from the cell channel to the controllable cesium reference cell module 704. This module has a built-in cesium reference cell adapted to the optical cavity ring-down system. After receiving the target beam and completing the interaction between the beam and cesium vapor, it calculates and outputs the absolute particle number concentration reference. The data processing unit 705, which maintains real-time communication with the optical cavity ring-down measurement channel 703 and the controllable cesium reference cell module 704, will synchronously retrieve the sample measurement signal and the absolute particle number concentration reference. Using the concentration reference as a reference, the sample measurement signal is dynamically calibrated, and finally the calibrated absolute concentration result of the target sample is obtained. This realizes the complete process of each module from signal generation and function execution to data processing.

[0066] For ease of description, the above system is described by dividing it into various modules based on their functions. Of course, in implementing this invention, the functions of each module can be implemented in one or more software and / or hardware components.

[0067] The system described in the above embodiments is used to implement the corresponding method in any of the foregoing embodiments and has the beneficial effects of the corresponding method embodiments, which will not be repeated here.

[0068] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element. Furthermore, it should be noted that the scope of the methods and apparatuses in the embodiments of this application is not limited to performing functions in the order shown or discussed, but may also include performing functions substantially simultaneously or in the reverse order, depending on the functions involved. For example, the described methods may be performed in a different order than described, and various steps may be added, omitted, or combined. Additionally, features described with reference to certain examples may be combined in other examples.

[0069] From the above description of the embodiments, those skilled in the art can clearly understand that the methods of the above embodiments can be implemented by means of computer software products plus necessary general-purpose hardware platforms, and of course, they can also be implemented by hardware. The computer software product is stored in a storage medium (such as ROM, RAM, magnetic disk, optical disk, etc.) and includes several instructions to cause the terminal or network-side device to execute the methods described in the various embodiments of this application.

[0070] The embodiments of this application have been described above with reference to the accompanying drawings. However, this application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other implementations under the guidance of this application without departing from the spirit and scope of the claims. All of these implementations are within the protection scope of this application.

Claims

1. A cesium reference cell for an optical cavity ring-down system, characterized in that, include: The pool body includes an inner pool body (131) and an outer pool body (141), wherein the inner pool body (131) is used to hold cesium element and generate cesium vapor, and the outer pool body (141) surrounds the inner pool body (131) to provide a heat-insulating environment; The temperature control assembly includes a heating unit and a cooling unit, wherein the heating unit is used to raise the temperature of the inner pool (131) and the cooling unit is used to form a cold end on the inner pool (131); Optical windows are located on opposite sides of the pool body to allow the target beam to pass through the cesium vapor; A control unit is configured to determine the absolute cesium particle number concentration in the inner pool (131) based on the temperature of the inner pool (131) and the light beam passing through the cesium vapor. The inner pool (131) is arranged in a T-shape. The heating unit includes a heating band (11) which is disposed in the transverse region of the T-shape. The cooling unit includes a cooling plate (12) which is disposed in the longitudinal region of the T-shape and away from the transverse region, so as to form the cold end in the longitudinal region. The heating unit further includes a first temperature sensor (15), which is used to detect the temperature of the inner pool (131) and send a first detection signal to the control unit; the cooling unit further includes a second temperature sensor (16), which is used to detect the cold end temperature and send a second detection signal to the control unit; the control unit controls the heating belt (11) and the cooling chip (12) to work according to the first detection signal and the second detection signal, so as to achieve temperature control.

2. The cesium reference cell according to claim 1, characterized in that, A first vacuum region (132) is formed inside the inner pool (131), and a second vacuum region (142) is formed between the inner pool (131) and the outer pool (141).

3. The cesium reference cell according to claim 1, characterized in that, The optical window includes a first optical window (181) and a second optical window (182). The first optical window (181) is disposed on opposite sides of the outer pool body (141), and the second optical window (182) is disposed on opposite sides of the inner pool body (131). The first optical window (181) and the second optical window (182) are arranged coaxially so that the target beam passes through the outer pool (141), the inner pool (131) and the cesium vapor in sequence.

4. The cesium reference cell according to claim 1, characterized in that, The control unit is configured to perform the following steps: The inner pool (131) is heated to a first set temperature; Adjust the cold end to the second set temperature to establish a temperature gradient; The absorption signal of the target beam is determined, and the absolute particle number concentration is calculated by combining the first set temperature and the second set temperature.

5. The cesium reference cell according to claim 2, characterized in that, The outer pool body (141) is also provided with a vacuum port for evacuating the second vacuum region (142).

6. The cesium reference cell according to claim 1, characterized in that, The target beam is obtained by splitting the probe laser using a coupler configured to provide a 50:50 splitting ratio.

7. An optical cavity ring-down system, characterized in that, include: The light source module is used to output the detection laser; The beam splitting module is configured to split the probe laser into a measurement beam and a target beam, wherein the measurement beam enters the optical cavity ring-down measurement channel and the target beam enters the cesium reference cell channel; The optical cavity ring-down measurement channel is used to receive the measurement beam and perform ring-down absorption measurement on the target sample to obtain the sample measurement signal; A controllable cesium reference cell module is disposed in the cesium reference cell channel, including the cesium reference cell as described in any one of claims 1-6, for receiving the target beam and outputting an absolute particle number concentration reference; The data processing unit is communicatively connected to the optical cavity ring-down measurement channel and the controllable cesium reference cell module. It uses the absolute particle number concentration benchmark to calibrate the sample measurement signal in real time to obtain the absolute concentration result of the target sample after calibration.

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