A method for evaluating the acid flow rate and improving the tooling for buffered chemical polishing of superconducting cavities

Abstract

The present invention discloses an acid flow rate evaluation and tooling improvement method for buffered chemical polishing of a superconducting cavity, and the steps include: 1) inspecting a target superconducting cavity to be pickled; 2) designing a corresponding pickling tooling according to the structure of the target superconducting cavity and allocating the flow rate and flow rate of the acid at each inlet and outlet of the pickling tooling; 3) internally filling a target superconducting cavity model, a pickling tooling model and a connecting pipeline model through simulation software to generate an acid volume model; 4) using simulation software to simulate and analyze the acid volume model to obtain an optimized pickling tooling structure; 5) making a pickling tooling according to the pickling tooling structure and connecting it to the target superconducting cavity for buffered chemical polishing; 6) evaluating the buffered chemical polishing effect, if the standard is met, the optimized pickling tooling structure is used as the final pickling tooling structure of the target superconducting cavity, otherwise returning to step 1). The present invention provides a standardized and normalized pickling tooling preparation method.

Description

Technical Field

[0001] The invention belongs to the fields of accelerator physics and superconducting high-frequency technology, and relates to an acid flow rate evaluation and tooling improvement method for superconducting cavity buffer chemical polishing. Background Art

[0002] The superconducting accelerating cavity is the core component of the superconducting accelerator. The performance of the superconducting cavity directly determines the quality of the electron beam of the superconducting accelerator. The surface post-treatment of the superconducting cavity is one of the key factors that determine the performance of the superconducting cavity. Improving the inner surface quality of the superconducting cavity will make a significant contribution to improving the performance of the superconducting cavity.

[0003] Usually, superconducting cavities are made of high-purity niobium, and their performance is extremely sensitive to the quality of the inner surface of the cavity. In the manufacturing process of the superconducting cavity, a damage layer will be formed on the surface of the niobium after rolling, stamping, machining and electron beam welding. In addition, the contact between the niobium material and air, water, oil and other substances will also form pollutants. After the superconducting cavity is manufactured, cracks, scratches, pits, embeddings, oxides and adsorbed impurity particles may exist on the inner surface. These defects will cause thermal instability, field emission, secondary electron multiplication, residual resistance increase and other destructive mechanisms under high-frequency electromagnetic fields, which seriously affect the improvement of the performance of the superconducting cavity. Buffered chemical polishing is a cheap, simple, stable, effective and mature processing technology, and is widely used in major laboratories around the world. After the superconducting cavity is manufactured, the surface of the niobium material is removed by buffered chemical polishing by 150 to 200 μm, which can eliminate the damage layer on the surface of the niobium material and solve the above problems. The present invention is an improvement on the method proposed for buffered chemical polishing of superconducting cavities.

[0004] The buffered chemical polishing method is a commonly used superconducting cavity surface polishing method internationally. Its principle is to mix hydrofluoric acid (HF), nitric acid (HNO3), and phosphoric acid (H3PO4) in a certain volume ratio, and then react the mixed acid with niobium to chemically etch the inner surface of the niobium cavity. The specific chemical reaction process is: hydrofluoric acid removes the stable Nb2O5 on the surface of the niobium material to form water-soluble NbF5, which dissolves in the acid mixture; niobium has a strong ability to resist chemical corrosion, and nitric acid plays an oxidizing role, oxidizing the newly exposed niobium to generate stable Nb2O5; H3PO4 is used as a buffer, and adding different proportions of H3PO4 can control the reaction rate. The reaction process is as follows:

[0005] Nb2O5+10HF→2NbF5+5H2O

[0006] 2Nb+10HNO3→10NO2+5H+Nb2O5

[0007]

[0008] During the pickling process, in order to prevent the hydrogen produced by the reaction from penetrating into the corroded lattice boundaries, it is generally necessary to strictly control the ratio of the three acid solutions, optimize the circulation path of the acid solutions, and control the chamber temperature during the reaction not to exceed 15°C.

[0009] Traditional buffered chemical polishing methods such as Figure 1 shown.

[0010] (1) Check the inner and outer surfaces of the superconducting cavity. The surface needs to be kept clean, smooth and flat. If there are obvious defects on the inner surface of the cavity, they need to be removed by mechanical grinding.

[0011] (2) Design and manufacture pickling tooling. Use polyvinylidene fluoride (PVDF) and soluble polytetrafluoroethylene (PFA) to connect the pickling equipment and the superconducting cavity. Based on the experience of the pickling engineer, design the pickling tooling, plan the circulation path of the acid in the cavity and the flow rate distribution. The design quality of the pickling tooling is highly dependent on the experience of the pickling engineer.

[0012] (3) Carry out buffered chemical polishing of the superconducting cavity. During this process, the acid inlet flow rate is set to 18 L / min and the acid temperature is controlled to be below 15°C.

[0013] (4) Evaluate the pickling effect of the superconducting cavity. If the etching amount of the superconducting cavity wall thickness is greater than 150um, and the inner surface of the superconducting cavity is smooth without air chambers, bulges and groove defects, then the pickling is completed. Otherwise, return to the superconducting cavity preparation stage.

[0014] The current pickling method has the following disadvantages.

[0015] (1) The pickling method currently used and the design quality of the pickling tooling largely depend on the experience of the pickling engineer. The pickling effect is closely related to the design ability of the pickling engineer.

[0016] (2) Designing the pickling tooling of the superconducting cavity based only on the designer's experience and planning the circulation path of the acid in the cavity is likely to lead to unreasonable circulation paths of the acid in the cavity. If the circulation path of the acid in the cavity is unreasonable, the acid and the niobium material of the superconducting cavity will react to produce a large amount of hydrogen. If the hydrogen cannot be removed in time by the circulating acid, the accumulated hydrogen will penetrate into the niobium lattice, which will reduce the performance of the cavity. At the same time, the accumulated gas will hinder the reaction between the acid and niobium, and the location will not be effectively etched and cleaned, which may result in the inability to completely remove the contamination layer on the surface of the superconducting cavity, affecting the test performance of the superconducting cavity.

[0017] (3) There is no basis for judging the effectiveness of pickling tools, and no method for identifying risk locations. During the pickling process, there may be unreasonable acid flow paths or sudden drops in acid flow rates on the cavity wall, resulting in pickling defects such as air chambers, pits, bulges, and groove-like stripes, which increase the time and economic costs of superconducting cavity processing. At the same time, pickling defects need to be polished away by mechanical polishing. If not handled properly, it may lead to excessive mechanical polishing of the superconducting cavity wall thickness, damage to the cavity wall, deterioration of mechanical properties, and degradation of microwave performance, increasing the risk of superconducting cavity development.

[0018] (4) For non-ellipsoidal superconducting cavities, especially those with complex structures, the uneven etching of the wall thickness is more serious because there is no means to monitor the acid flow rate in the cavity. In order to avoid insufficient local etching, the pickling time needs to be extended, which may lead to greater roughness of the local inner surface of the superconducting cavity, inconsistent frequency shift after pickling and increased difficulty in estimating changes in mechanical properties after pickling. Summary of the invention

[0019] In view of the problems existing in the prior art, the purpose of the present invention is to provide a method for evaluating the flow rate of acid liquid and improving tooling for buffered chemical polishing of superconducting cavities. The present invention is applicable to all superconducting cavities that require buffered chemical polishing, especially superconducting cavities with complex structures. In the design stage of the pickling tooling, the pickling process is evaluated, and the flow rate distribution of the acid liquid in the superconducting cavity is calculated through model creation, finite element simulation, result analysis, etc. The present invention proposes an evaluation criterion for the risk points of pickling defects, predicts the possibility of pickling defects in the superconducting cavity, and locates the position where defects may occur. According to needs, the design and improvement of the pickling tooling are guided to reduce the risk of defects such as pitting, grooves, and ripples on the inner surface after pickling, improve the quality of the inner surface of the superconducting cavity after pickling, and save the pickling cost and time cost of the superconducting cavity. At the same time, the method of the present invention is used to optimize the uniformity of the acid flow rate in the superconducting cavity, alleviate the unevenness of the wall thickness etching of non-ellipsoidal superconducting cavities, especially superconducting cavities with complex structures, improve the surface quality of the superconducting cavity, and avoid problems such as large local inner surface roughness caused by excessive etching, frequency offset after pickling that does not meet expectations, and increased difficulty in predicting changes in mechanical properties after pickling.

[0020] The acid flow rate evaluation and tooling improvement method for buffered chemical polishing of superconducting cavities involved in this application are developed to meet the high performance requirements of superconducting cavity equipment related to the storage ring high-frequency system of the high-energy synchrotron radiation light source project, a major national scientific and technological infrastructure project, and can be widely used in other superconducting cavities, especially low-frequency, complex-structured superconducting cavities that use buffered chemical polishing.

[0021] The present invention proposes for the first time to apply simulation software tools to superconducting cavity pickling in simulation. Based on the pickling equipment and previous superconducting cavity pickling experience, a series of superconducting cavity pickling parameters required to be set in the simulation of special application scenarios of superconducting cavity pickling are summarized, which has guiding significance for future superconducting cavity pickling and is one of the protection points of the present invention. Establishing a basis for judging risk points, evaluating whether the pickling tooling is effective based on the criteria, predicting the possibility and risk location of possible pickling defects, and optimizing the pickling tooling according to needs also has protective significance and is one of the protection points of the present invention.

[0022] The technical solution of the present invention is:

[0023] A method for evaluating the flow rate of acid solution and improving tooling for buffered chemical polishing of a superconducting cavity, comprising the following steps:

[0024] 1) inspecting the target superconducting cavity to be pickled, and if it does not meet the set requirements, processing the target superconducting cavity to make it meet the set requirements;

[0025] 2) designing a corresponding pickling tool according to the structure of the target superconducting cavity and allocating the flow rate and flow rate of the acid solution at each inlet and outlet of the pickling tool;

[0026] 3) Modeling the target superconducting cavity and the pickling tooling to obtain a target superconducting cavity model and a pickling tooling model; internally filling the target superconducting cavity model, the pickling tooling model and the connecting pipeline model through simulation software to generate an acid liquid volume model;

[0027] 4) Using simulation software to perform simulation analysis on the acid volume model:

[0028] 41) Set the dynamic viscosity, density and specific heat of the acid solution, the reaction heat of niobium and the acid solution, the temperature of the acid solution, the inlet flow rate of the acid, the temperature and flow rate of the cavity cooling water; then calculate the pickling path and the distribution cloud map of the acid solution flow rate under the current pickling tooling through simulation;

[0029] 42) Select multiple structural mutation areas on the inner wall of the target superconducting cavity, and set a monitoring point in each structural mutation area, take the monitoring point close to the side where the acid flows in as the starting point, and the monitoring point close to the side where the acid flows out as the end point, and connect the acid flow rate values ​​of each pair of starting point and end point and the monitoring points between them according to the flow direction of the acid to obtain a flow rate distribution curve for observing the change trend of the acid flow rate. If the ratio of the flow rate of the monitoring point i to the surrounding flow rate is lower than the set value, the monitoring point i is marked as a risk point;

[0030] 43) Modify the pickling tooling structure according to the location of the risk point to increase the acid flow rate at the risk point;

[0031] 44) Repeat steps 42 to 43) until there is no risk point; and obtain the pickling tooling structure after simulation optimization;

[0032] 5) manufacturing a pickling tool according to the pickling tool structure optimized by simulation and connecting it to the target superconducting cavity that meets the set requirements, and performing buffered chemical polishing on the target superconducting cavity;

[0033] 6) Evaluate the buffered chemical polishing effect. If the set standard is met, use the simulated optimized pickling tooling structure as the final pickling tooling structure of the target superconducting cavity. Otherwise, return to step 1).

[0034] Furthermore, when the structure of the pickling tooling is modified according to the location of the risk point, a flow guide device is provided in the pickling tooling to extend into the target superconducting cavity to increase the flow rate of the acid at the location of the structural mutation in the target superconducting cavity; in step 43), the flow rate of the acid at the risk point is increased by modifying the structure of the flow guide device.

[0035] Furthermore, by adding guide columns, discs or guide holes to the guide device, the flow rate of the acid at the risk point is increased.

[0036] Furthermore, if the flow velocity at monitoring point i is 2 orders of magnitude lower than the surrounding flow velocity, the monitoring point i is marked as a risk point.

[0037] Furthermore, the dynamic viscosity, density and specific heat capacity of the acid solution are 0.022Ns / m 2 、1545Kg / m 3 and 2090J / kg / K; the heat of reaction between niobium and acid solution is 1200W / m 2 ; The acid temperature is 15°C and the acid inlet flow rate is <18L / min; the cavity cooling water temperature and flow rate are 6°C and 18L / min respectively.

[0038] Furthermore, in step 5), during the buffered chemical polishing of the target superconducting cavity, the acid liquid inlet flow rate is set to 18 L / min and the temperature is set to be lower than 15°C.

[0039] Furthermore, the acid inlet and outlet ports of the pickling tooling and the diameter of each port are determined according to the number of cavity ports of the target superconducting cavity and the relative positions of the ports.

[0040] Furthermore, polyvinylidene fluoride and soluble polytetrafluoroethylene are used to make a pickling tool, as well as a connecting pipeline between the pickling tool and the target superconducting cavity.

[0041] Furthermore, the setting requirement is that the inner surface of the target superconducting cavity is neat, smooth and flat.

[0042] Furthermore, the target superconducting cavity and the pickling tooling are modeled using the three-dimensional drawing software SolidWorks to obtain a target superconducting cavity model and a pickling tooling model; the target superconducting cavity model and the pickling tooling model are connected through a simulated connecting pipeline to obtain an acid volume model.

[0043] By adopting the method provided by the present invention, the high dependence of pickling tool design on engineer experience can be eliminated, and a more standardized and normalized pickling tool preparation method can be established. The key points of the present invention specifically include:

[0044] (1) During the design stage of the superconducting cavity pickling tooling, the acid flow rate simulation calculation is added. Simulation method: Finite element analysis software is used to model the superconducting cavity, initial pickling tooling, connecting pipelines and other structures and the pickling volume inside the structure. The parameters of the acid are: the dynamic viscosity of the acid is 0.022Ns / m 2 , the density of acid is 1545Kg / m 3 The specific heat capacity of the acid is 2090 J / kg / K, and the heat of reaction between niobium and acid is 1200 W / m 2 , the acid temperature is 15℃, the acid flow rate is <18L / min, the cavity cooling water temperature is 6℃, and the cooling water flow rate is 18L / min. The acid inlet flow rate and the cooling water flow rate are adjustable. The acid path and acid flow rate distribution in the simulation cavity.

[0045] (2) During the analysis of simulation results, key points on the inner wall of the superconducting cavity at the location of the structural mutation are selected as flow velocity monitoring points, and the flow velocity distribution curve from one side of the cavity wall to the other side is calculated. The change in the flow velocity of the cavity inner wall corresponding to the location of the structural mutation is analyzed to evaluate the possibility of pickling defects and determine the location of the defects.

[0046] (3) Risk point assessment criteria:

[0047] For the location where the superconducting cavity structure changes, if the flow velocity at the monitoring point at that location is 2 orders of magnitude lower than that of the surrounding area, the monitoring point is identified as a risk point. Pickling defects may occur at the risk point, and the pickling tooling needs to be improved.

[0048] If the acid flow rate on the cavity wall is uniform, and the acid flow rate at the location of the structural mutation differs from that at the adjacent location by less than one order of magnitude, the tooling design is considered effective and the manufacture of the pickling tooling can be carried out.

[0049] (4) According to simulation prediction or experimental results, if there are pickling defects on the inner surface of the cavity, the finite element simulation calculation of the improved tooling using this method can provide quantitative data parameters of the acid on the cavity wall, which can guide the improvement direction of the pickling tooling in a targeted manner and evaluate the improvement effect of the pickling tooling.

[0050] The present invention can greatly reduce the dependence on the experience of pickling engineers. On the basis of the existing superconducting cavity pickling process, simulation calculations are added in the tooling design stage, focusing on the position of the acid liquid flow velocity mutation, and combining the structure of the superconducting cavity to calculate the flow velocity distribution of the acid liquid in the superconducting cavity, propose risk point assessment criteria, predict the possibility of pickling defects in the superconducting cavity, and locate the position where defects may occur. Through the design and improvement of the pickling tooling, such as adding guide columns, punching holes, discs and other devices, the circulation path of the acid liquid in the superconducting cavity is optimized, the acid liquid flow velocity in key areas and the uniformity of the overall acid liquid flow velocity are improved, the improvement effect of the pickling tooling is predicted, and guidance is provided for optimizing the pickling process to avoid the occurrence of pickling defects. At the same time, the method of the present invention is adopted to improve the uniformity of the acid liquid flow velocity in the superconducting cavity and alleviate the problem of uneven etching of the wall thickness of non-ellipsoidal superconducting cavities.

[0051] (1) Analyze the acid flow path through simulation and predict the rationality of the acid flow path in the cavity.

[0052] (2) Analyze the location of structural mutation according to the structure of the cavity. Perform a simulation of the acid flow rate of the superconducting cavity and set monitoring points at the location of structural mutation. The side close to the acid inflow is the starting point and the side close to the acid outflow is the end point. According to the flow direction of the acid, the acid flow rate values ​​of each pair of starting points and end points and the monitoring points between them are connected to obtain a flow rate distribution curve, which is used to observe the change trend of the acid flow rate and evaluate the monitoring points. Evaluation criteria for risk points: For the location of structural mutation of the superconducting cavity, if the flow rate of the monitoring point is 2 orders of magnitude lower than that of the surrounding area, then the monitoring point is determined as a risk point and pickling defects may occur at this location. If the flow rate of the monitoring point at the location of structural mutation of the superconducting cavity is less than 1 order of magnitude different from the flow rate of the adjacent location, it is considered that the circulation path of the acid in the cavity is reasonable and the design of the pickling tooling is effective.

[0053] (3) According to the prediction results, the pickling tooling is improved according to the location of the risk point, such as designing guide columns, holes, discs, etc. to improve the uniformity of the acid flow rate. The pickling tooling structure with the guide device is simulated again, the acid flow rate on the inner wall of the cavity is analyzed, the monitoring points are set again and a flow rate distribution curve is generated. The monitoring points in the superconducting cavity structure mutation area where the risk point exists are consistent with those in step (2) and verified. If the flow rate at the risk point position is increased and the flow rate difference with the adjacent position is only less than 1 order of magnitude, the tooling design is considered to be effective. If it is not satisfied, it is necessary to continue to improve the pickling tooling until all risk points are eliminated. Ultimately, the purpose of improving the overall uniformity of the acid flow rate is achieved.

[0054] (4) Make pickling tools and apply them to pickling, and combine the pickling results to verify the pickling effect.

[0055] (5) Improving the uniformity of the pickling flow rate can also improve the problem of uneven pickling of the superconducting cavity wall thickness, making the overall etching amount of the cavity more uniform and consistent.

[0056] This method uses simulation to guide the improvement of the superconducting cavity pickling process, effectively reducing the occurrence of pickling defects, improving the quality of the superconducting cavity inner surface, and saving the pickling cost and time cost of the superconducting cavity. After the pickling defects occur, this method can be used to guide the improvement direction of the pickling tooling, improve the efficiency of the improvement, and avoid the risks of excessive local mechanical polishing, cavity wall damage, and mechanical property deterioration on the surface of the superconducting cavity due to multiple trials and errors. For superconducting cavities with complex structures, the unevenness of the etching on the inner surface of the cavity can be improved to avoid problems such as large local inner surface roughness due to excessive etching, inconsistent frequency offset after pickling, and increased difficulty in estimating changes in mechanical properties after pickling.

[0057] The advantages of the present invention are as follows:

[0058] (1) This method can greatly reduce the reliance on the experience of pickling engineers and establish a standardized pickling process and evaluation method.

[0059] (2) Based on the existing superconducting cavity pickling process, simulation calculations are added in the early stage of tooling design to propose risk point assessment criteria, predict the possibility of pickling defects and the location of defects, and evaluate the pickling effect. This will greatly reduce the probability of pickling defects, save the pickling cost and time cost increased by defects, and improve the surface quality of the superconducting cavity.

[0060] (3) When pickling defects occur, this method is used to simulate and quantify the pickling flow rate data to design pickling tools, such as guide columns, holes, and discs, to provide improvement directions and quantitative basis for optimizing the pickling process. This will avoid blind trial and error, which may cause excessive mechanical grinding of the superconducting cavity wall thickness, damage to the cavity wall, deterioration of mechanical properties, and degradation of microwave performance, thereby increasing the risk of superconducting cavity development.

[0061] (4) This method can improve the uniformity of the acid flow rate and alleviate the problem of uneven etching of the superconducting cavity. It is especially suitable for non-ellipsoidal superconducting cavities caused by complex structures. It can avoid problems such as excessive etching amount causing large local inner surface roughness, frequency shift after pickling not meeting expectations, and increased difficulty in estimating changes in mechanical properties after pickling.

[0062] This method has been successfully applied to the pickling of multi-band superconducting cavities such as 166MHz quarter-wavelength superconducting cavities and 500MHz ellipsoidal cavities with high-order mode depth suppression, and has achieved good pickling results. In addition, this pickling method is applicable to all superconducting cavities using buffered chemical polishing, and has broad application prospects. It is an innovative and meaningful attempt. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Figure 1 Flow chart of buffered chemical polishing method.

[0064] Figure 2 Flow chart for the buffered chemical polishing method with acid flow rate evaluation and tooling improvements.

[0065] Figure 3 It is the acid path and flow velocity distribution diagram;

[0066] (a) 500MHz superconducting cavity acid path and flow velocity distribution diagram, (b) 166MHz quarter-wavelength superconducting cavity acid path and flow velocity distribution diagram.

[0067] Figure 4 Flow rate monitoring results and dangerous point determination for the initial pickling tooling of a 166MHz quarter-wavelength superconducting cavity.

[0068] Figure 5 Flow rate monitoring results and dangerous point determination of the improved pickling tooling for the 166MHz quarter-wavelength superconducting cavity. DETAILED DESCRIPTION

[0069] The present invention is further described in detail below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention but not to limit the scope of the present invention.

[0070] The present invention proposes a method for evaluating the acid flow rate and improving tooling for buffered chemical polishing of superconducting cavities. Based on the traditional buffered chemical polishing method for superconducting cavities, this method proposes a method for evaluating the acid flow rate and a criterion for the generation of pickling defects. Designers can quantitatively evaluate the pickling effect during the design stage of pickling tooling, predict the location of pickling defects, and iteratively design pickling tooling to reduce the risk of pickling defects such as air chambers, pits, bulges, grooves, etc., alleviate the uneven etching of the superconducting cavity wall thickness, greatly improve the rationality of the pickling tooling, improve the quality of the inner surface of the superconducting cavity after pickling, save time for improving the pickling tooling, and reduce economic expenditure.

[0071] The flow chart of the acid flow rate evaluation and tooling improvement method for superconducting cavity buffered chemical polishing is shown in the figure. Figure 2 shown.

[0072] (1) Check the inner and outer surfaces of the target superconducting cavity to be pickled, and keep the inner surface of the cavity clean, smooth and flat. If there are obvious defects on the inner surface of the cavity, they need to be removed by mechanical grinding.

[0073] (2) Pickling tooling design: Acid flow rate evaluation and tooling improvement design for the target superconducting cavity pickling were carried out.

[0074] a) Initial tooling design

[0075] According to the number of cavity ports of the target superconducting cavity and the relative positions of the ports, the acid inlet and outlet and the diameter of each port are selected, and the flow rate and flow velocity of the acid at each inlet and outlet are allocated. If the pickling tooling needs to be improved, a flow guide device can be added to the pickling tooling to extend into the target superconducting cavity to increase the acid flow rate at the location of the structural mutation in the target superconducting cavity; the area of ​​structural mutation on the inner wall of the superconducting cavity is determined according to the structure of the superconducting cavity, such as the shrinkage position of the large beam tube of the 166MHz superconducting cavity, such as the connection position of the right end cover and the rinsing port of the 166MHz superconducting cavity, such as the position of the beam tube and the cavity connection port of the 500MHz superconducting cavity. According to experience, the acid flow rate will generally decrease at the location of the structural mutation, and pickling defects may occur; so the simulation should focus on the flow rate on the inner wall of the cavity at these locations.

[0076] b) Mechanical model creation

[0077] The target superconducting cavity, pickling tooling and connecting pipelines are modeled by three-dimensional drawing software to obtain target superconducting cavity models, pickling tooling models and connecting pipeline models; the target superconducting cavity model, pickling tooling model and connecting pipeline models are filled with the internal filling function of the three-dimensional drawing software to generate an acid volume model.

[0078] c) Finite element software analysis

[0079] Finite element software such as ANSYS and Comsol were used to import the acid volume model, and the dynamic viscosity, density and specific heat capacity of the acid were set to 0.022Ns / m 2 、1545Kg / m 3 and 2090J / kg / K; the heat of reaction between niobium and acid solution is 1200W / m 2 The acid temperature is 15°C, and the acid inlet flow rate is <18L / min. The cavity cooling water temperature and flow rate are 6°C and 18L / min, respectively. Since the acid inlet flow rate and cooling water flow rate are adjustable, the actual simulation can be adjusted at any time according to the actual parameters.

[0080] Table 1 Some data required for simulation.

[0081] parameter Numeric unit Dynamic viscosity of acid 0.022 <![CDATA[Ns / m 2 ]]> Density of acid 1545 <![CDATA[kg / m 3 <!-- 6 -->]]> Specific heat capacity of acid 2090 J / kg / K Reaction heat of niobium and acid solution 1200 <![CDATA[W / m 2 ]]> Acid temperature 15 ℃ Acid flow <18, adjustable L / min Cavity cooling water temperature 6 ℃ Cooling water flow Adjustable L / min

[0082] Through simulation, the pickling path and the distribution cloud map of the acid flow rate under the initial pickling tooling are calculated. The simulation results of 500MHz ellipsoidal cavity and 166MHz quarter-wavelength superconducting cavity are taken as examples. Figure 3 (a) shows the acid circulation path and acid flow rate distribution cloud diagram obtained from the 500MHz ellipsoid cavity pickling simulation. The acid enters from the liquid inlet pipe at the bottom of the superconducting cavity, enters the superconducting cavity through the guide holes of the pickling tooling, and finally flows out from the ducts on the top and sides of the superconducting cavity. Figure 3(b) The acid circulation path and acid flow rate distribution cloud diagram obtained from the 166MHz quarter-wavelength superconducting cavity pickling simulation are given. The acid enters the superconducting cavity from the liquid inlet pipe at the bottom, enters the cavity through the guide hole of the pickling tooling, and finally flows out from the guide pipe at the top of the cavity.

[0083] In the result analysis, the focus should be on the area with structural mutation on the inner wall of the superconducting cavity. Monitoring points should be set, and the monitoring point close to the side where the acid flows in is used as the starting point and the monitoring point close to the side where the acid flows out is used as the end point. According to the flow direction of the acid, the acid flow rate values ​​of each pair of starting points and end points and the monitoring points between them are connected to obtain a flow rate distribution curve, which is used to observe the change trend of the acid flow rate, observe the flow rate of the cavity wall corresponding to the structural mutation position, and evaluate the monitoring point. If the flow rate of the monitoring point is 2 orders of magnitude lower than that of the surrounding area, the monitoring point is determined as a risk point. Specifically, if the flow rate of the monitoring point is 2 orders of magnitude lower than that of the adjacent monitoring points, the monitoring point is determined as a risk point; or the flow rate of the monitoring point is the bottom of the flow rate distribution diagram of the area where the monitoring point is located, and the flow rate of the monitoring point is 2 orders of magnitude lower than the flow rate peak of the flow rate distribution diagram of the area, then the monitoring point is determined as a risk point. Take the simulation results of a 166MHz quarter-wavelength superconducting cavity as an example. Flow rate monitoring points are set on the large beam tube, large beam tube transition section and neck position of the superconducting cavity. Figure 4 The flow rate monitoring results and dangerous point determination of the initial pickling tooling of the 166MHz quarter-wavelength superconducting cavity. Figure 4 It can be seen that the flow velocity at the transition section of the superconducting cavity large beam tube is 2 orders of magnitude lower than that at the adjacent position. According to the assessment criteria of the risk point, pickling defects may occur at this position, and the pickling tooling design needs to be improved.

[0084] d) Risk point judgment criteria

[0085] For the location of the superconducting cavity structure mutation, if the flow rate at the monitoring point is 2 orders of magnitude lower than that of the surrounding area, the monitoring point is determined as a risk point, and the risk point may produce pickling defects. It is necessary to improve the pickling tooling.

[0086] If the acid flow rate of the cavity wall is uniform, and the difference between the acid flow rate at the structural mutation position and the flow rate at the adjacent position is only less than one order of magnitude, it is considered that the circulation path of the acid in the cavity is reasonable and the design of the pickling tooling is effective. The manufacture of the pickling tooling can be carried out.

[0087] e) Improvement of pickling tooling

[0088] If the simulation predicts that pickling defects may occur, then it is necessary to further improve the design of the pickling tooling according to the location of the risk point, such as adding guide columns, holes, discs, etc., to improve the uniformity of the acid flow rate. Figure 5The flow rate monitoring results and dangerous point determination of the improved pickling tooling for the 166MHz quarter-wavelength superconducting cavity. Figure 5 It can be seen that after the pickling tooling was improved, the flow rate at each monitoring point on the inner wall of the superconducting cavity was greatly improved compared with that before the improvement. The difference between the flow rate at the monitoring point located at the transition section of the large beam tube of the superconducting cavity and the flow rate at the adjacent position was only less than one order of magnitude. According to the evaluation criteria of the risk point, this position will not produce pickling defects. The design of the improved pickling tooling is reasonable and effective.

[0089] f) Evaluate the improved pickling tooling, set monitoring points again and generate a velocity distribution curve through software simulation analysis. The monitoring points of the superconducting cavity structure mutation area with risk points are consistent with those in step c). Set reasonable monitoring points for the acid flow rate of the cavity inner wall, and judge the improvement effect of the pickling tooling according to the risk point criterion; if it is not satisfied, continue to iterate and improve the pickling tooling until the velocity criterion is met; finally, the purpose of improving the uniformity of the overall acid flow rate is achieved.

[0090] (3) Making pickling tooling

[0091] Polyvinylidene fluoride (PVDF) and soluble polytetrafluoroethylene (PFA) are used to make the pickling tooling and the pipeline connecting the tooling and the cavity.

[0092] (4) Buffered chemical polishing of the superconducting cavity was carried out. During this process, the acid inlet flow rate was set to 18 L / min and the temperature was controlled to be below 15°C.

[0093] (5) Evaluate the pickling effect of the superconducting cavity. The etching amount of the superconducting cavity wall thickness should be greater than 150um. At the same time, the inner surface of the superconducting cavity should be smooth, without air chambers, bulges and groove defects. If the above requirements are met, the pickling is completed, otherwise it returns to the superconducting cavity preparation stage.

[0094] Although the specific embodiments of the present invention are disclosed for the purpose of illustration, the purpose is to help understand the content of the present invention and implement it accordingly, those skilled in the art will understand that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the present invention should not be limited to the content disclosed in the best embodiment, and the scope of the present invention is subject to the scope defined in the claims.

Claims

1. A method for evaluating the acid flow rate and improving the tooling for buffered chemical polishing of a superconducting cavity, comprising the following steps: 1) inspecting the target superconducting cavity to be pickled, and if it does not meet the set requirements, processing the target superconducting cavity to make it meet the set requirements; 2) designing a corresponding pickling tool according to the structure of the target superconducting cavity and allocating the flow rate and flow rate of the acid solution at each inlet and outlet of the pickling tool; 3) Modeling the target superconducting cavity and the pickling tooling to obtain a target superconducting cavity model and a pickling tooling model; internally filling the target superconducting cavity model, the pickling tooling model and the connecting pipeline model through simulation software to generate an acid liquid volume model; 4) Using simulation software to perform simulation analysis on the acid volume model: 41) Set the dynamic viscosity, density and specific heat of the acid solution, the reaction heat of niobium and the acid solution, the temperature of the acid solution, the inlet flow rate of the acid, the temperature and flow rate of the cavity cooling water; then calculate the pickling path and the distribution cloud map of the acid solution flow rate under the current pickling tooling through simulation; 42) Select multiple structural mutation areas on the inner wall of the target superconducting cavity, and set a monitoring point in each structural mutation area, take the monitoring point close to the side where the acid flows in as the starting point, and the monitoring point close to the side where the acid flows out as the end point, and connect the acid flow rate values ​​of each pair of starting point and end point and the monitoring points between them according to the flow direction of the acid to obtain a flow rate distribution curve for observing the change trend of the acid flow rate. If the ratio of the flow rate of the monitoring point i to the surrounding flow rate is lower than the set value, the monitoring point i is marked as a risk point; 43) Modify the pickling tooling structure according to the location of the risk point to increase the acid flow rate at the risk point; 44) Repeat steps 42 to 43) until there is no risk point; and obtain the pickling tooling structure after simulation optimization; 5) manufacturing a pickling tool according to the pickling tool structure optimized by simulation and connecting it to the target superconducting cavity meeting the set requirements, and performing buffered chemical polishing on the target superconducting cavity; 6) Evaluate the buffered chemical polishing effect. If the set standard is met, use the simulated optimized pickling tooling structure as the final pickling tooling structure of the target superconducting cavity. Otherwise, return to step 1).

2. The method according to claim 1, characterized in that When the structure of the pickling tooling is modified according to the location of the risk point, a flow guide device is provided in the pickling tooling to extend into the target superconducting cavity to increase the acid flow rate at the location of the structural mutation in the target superconducting cavity; in step 43), the acid flow rate at the risk point is increased by modifying the structure of the flow guide device.

3. The method according to claim 2, characterized in that By adding guide columns, discs or guide holes to the guide device, the flow rate of the acid at the risk point is increased.

4. The method according to claim 1, characterized in that: If the flow velocity at monitoring point i is 2 orders of magnitude lower than the surrounding flow velocity, the monitoring point i is marked as a risk point.

5. The method according to claim 1, characterized in that The dynamic viscosity, density and specific heat capacity of the acid solution are 0.022Ns / m 2 、1545Kg / m 3 and 2090J / kg / K; the heat of reaction between niobium and acid solution is 1200W / m 2 ; The acid temperature is 15°C, and the acid inlet flow rate is <18L / min; the cavity cooling water temperature and flow rate are 6°C and 18L / min respectively.

6. The method according to claim 5, characterized in that In step 5), during the buffered chemical polishing of the target superconducting cavity, the acid liquid inlet flow rate is set to 18 L / min and the temperature is set to be lower than 15°C.

7. The method according to claim 1, characterized in that The acid inlet and outlet ports of the pickling tool and the diameter of each port are determined according to the number of cavity ports of the target superconducting cavity and the relative positions of the ports.

8. The method according to claim 1, characterized in that Polyvinylidene fluoride and soluble polytetrafluoroethylene are used to make a pickling tool, as well as a connecting pipeline between the pickling tool and a target superconducting cavity.

9. The method according to claim 1, characterized in that: The setting requirement is that the inner surface of the target superconducting cavity is neat, smooth and flat.

10. The method according to claim 1, characterized in that The target superconducting cavity and the pickling tooling are modeled by using the three-dimensional drawing software SolidWorks to obtain a target superconducting cavity model and a pickling tooling model; the target superconducting cavity model and the pickling tooling model are connected through a simulated connecting pipeline to obtain an acid volume model.

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