A pickling fixture for a 166MHz quarter-wavelength superconducting cavity

Abstract

This invention discloses an acid cleaning fixture for a 166MHz quarter-wavelength superconducting cavity. The acid cleaning fixture comprises a large-tube side fixture, a small-tube side combined fixture, and an acid flow guiding fixture. The large-tube side fixture serves as the acid inlet or outlet of the superconducting cavity system. One end of the fixture is sealed to the large-tube flange of the superconducting cavity system, and the other end is connected to the acid cleaning equipment via a first connecting flange and a connecting pipe. The small-tube side combined fixture also serves as the acid inlet or outlet of the superconducting cavity system. One end of the fixture is sealed to the small-tube flange, the coupler flange, and the flanges of each rinsing port of the superconducting cavity system. The other end is connected to the acid cleaning equipment via a second connecting flange and a pipeline. The acid flow guiding fixture is located inside the superconducting cavity system and communicates with the large-tube side fixture. It guides the flow of acid entering the superconducting cavity system through the large-tube side fixture and balances the acid flow rate. This invention significantly improves the acid cleaning effect of the superconducting cavity and ensures smooth bubble removal.

Description

Technical Field

[0001] This invention belongs to the fields of accelerator physics and superconducting high-frequency cavities, and relates to an acid washing fixture for a 166MHz quarter-wavelength superconducting cavity used for high-order mode depth suppression of high-energy synchrotron radiation sources. Background Technology

[0002] The superconducting cavity is the core component of a superconducting accelerator. During operation, the cavity is filled with a high-frequency electromagnetic field. The electromagnetic field interacts with the inner surface of the cavity, providing energy for the beam. Most superconducting cavities use high-purity niobium as the raw material. Ideally, the inner surface of the superconducting cavity should be smooth, flat, and free of impurities, and the peak magnetic field during operation should approach or even reach the superconducting theoretical limit of niobium. During the manufacturing process of the superconducting cavity, the niobium material undergoes rolling, stamping, machining, welding, and other manufacturing processes, resulting in scratches, pits, embeddings, welding spatter, and oil contamination on the surface. These defects on the inner surface of the superconducting cavity will lead to physical phenomena such as field emission, magnetoquench, and secondary electron multiplication, reducing the physical performance of the superconducting cavity, or even causing it to malfunction, ultimately leading to development failure.

[0003] To remove the contamination layer on the inner surface of a superconducting cavity, chemical polishing is typically employed. The buffered chemical polishing (BCP) process for a superconducting cavity involves preparing a BCP acid solution by mixing hydrofluoric acid (HF), nitric acid (HNO3), and phosphoric acid (H3PO4) in a volume ratio of 1:1:2. This BCP acid solution is injected into the cavity and circulated within it, causing an etching reaction between the acid and the niobium material on the cavity surface, removing a 100–150 μm contamination layer from the niobium material surface.

[0004] During the pickling process, the chemical reaction between niobium and acid is exothermic, causing the acid temperature to rise and further accelerating the chemical reaction, producing a large amount of hydrogen gas. This hydrogen gas can penetrate the niobium material and corrode the crystal lattice, potentially causing hydrogen poisoning in the superconducting cavity and reducing its testing performance. Therefore, a cooling system is necessary during pickling to control the acid temperature below 15°C. If the pickling fixture circuit is poorly designed, it will result in an unreasonable acid flow direction and ratio distribution. Air bubbles cannot be eliminated in time and accumulate on the inner surface of the cavity, hindering the etching reaction between the acid and the niobium material. This ultimately leads to uneven etching and various surface defects on the inner surface of the superconducting cavity, such as air cells, pits, bulges, and striped grooves. Therefore, a well-designed pickling fixture is crucial. A good pickling fixture can ensure sufficient acid circulation within the cavity, appropriate flow rate, and smooth bubble guidance.

[0005] A 166MHz quarter-wavelength superconducting cavity with high-order mode depth suppression has a relatively large volume due to its extremely low frequency. Even with a quarter-wavelength structure, which significantly reduces the size compared to an ellipsoidal cavity, the cavity size is still quite large. The outer conductor diameter is 400mm, the axial flange length is 880mm, and the volume is approximately 100L. A model of the 166MHz quarter-wavelength superconducting cavity with high-order mode depth suppression is shown below. Figure 1 As shown. According to engineering requirements, the cavity has seven openings of varying sizes, including: one large bundle tube with an inner diameter of 505 mm, one small bundle tube with an inner diameter of 80 mm, one coupler port with an inner diameter of 100 mm, and four rinsing ports with inner diameters of 30 mm. The inner diameter of the large bundle tube is 17 times that of the rinsing ports. The numerous superconducting cavity openings, the significant difference in aperture ratios (maximum / minimum ~ 17 times), and the inner conductor located inside the outer conductor opposite the large bundle tube directly affect the flow direction and flow rate distribution of the acid within the cavity, posing a significant challenge to the design of the superconducting cavity acid washing fixture. Given the complexity of the 166 MHz quarter-wavelength superconducting cavity structure with high-order mode depth suppression, the flow path of the acid within the cavity is extremely complex, and the acid flow velocity distribution is uneven, making uniform polishing of the cavity very difficult.

[0006] Acid cleaning of a 166MHz quarter-wavelength superconducting cavity with high-order mode depth suppression is very challenging. After acid cleaning using conventional equipment, linear groove defects were found on the large-beam tube transition section. Each groove is approximately 1mm wide and 60mm long, radiating outwards from the large-beam tube transition region. Since the performance of the superconducting cavity is extremely sensitive to the quality of its inner surface, these defects are unacceptable. Therefore, it is necessary to redesign the acid cleaning equipment to eliminate these defects, restore the smoothness, cleanliness, and defect-free nature of the cavity's inner surface, and ensure the testing performance of the superconducting cavity.

[0007] Internationally, Argonne National Laboratory in the United States has also discovered linear groove defects in spoke-shaped superconducting cavities. During the development of the spoke-shaped superconducting cavity, Argonne National Laboratory found similar linear groove acid imprints on the central inner conductor pillar. However, no solution has been found in the known field.

[0008] Currently, there is no known technical solution to address the linear groove defects that occur during the acid washing process of a 166MHz quarter-wavelength superconducting cavity to suppress the depth of higher-order modes.

[0009] During the pre-research phase of the high-energy synchrotron radiation source, the Institute of High Energy Physics successfully developed a 166MHz superconducting prototype cavity (166MHz PoP cavity). The acid washing process of this 166MHz PoP cavity is the closest technical solution to the present invention.

[0010] The pickling fixture for the 166MHz PoP chamber includes sealing flanges and connecting pipes. The sealing flanges used to seal the acid are made of acid-resistant polyvinylidene fluoride (PVDF), and the pipes used to connect the flanges are made of soluble polytetrafluoroethylene (PFA).

[0011] To ensure the uniformity of the wall thickness removal in the 166MHz PoP cavity, the superconducting cavity acid washing is divided into two steps.

[0012] The first step is acid etching via the large tube inlet. In the 166MHz PoP cavity, the large tube faces downwards, and acid enters the cavity through the large tube sealing flange. Chemical etching is completed within the cavity, and the acid flows out through the coupler sealing flange, signal extraction sealing flange, four rinse port sealing flanges, and the small tube sealing flange, finally exiting through the main pipe on the small tube. The model is as follows: Figure 2 As shown. The pickling time is 60 minutes.

[0013] The pickling fixture is divided into two parts: the first part is the fixture for the large bundle tube side (with an inner diameter of 44mm), and the second part is the fixture for the small bundle tube side.

[0014] The first part of the pickling fixture (44mm inner diameter): a 44mm inner diameter PVDF pipe serves as the inlet, and a 228mm outer diameter PVDF flange serves as the sealing flange for the large tube bundle. The PVDF pipe is connected to the PVDF flange, forming the first part of the pickling fixture for introducing acid.

[0015] The second part is the small bundle tube side assembly fixture: the coupler sealing flange, signal extraction sealing flange, four rinse port sealing flanges, and small bundle tube sealing flange are all made of PVDF material. A 44mm inner diameter PVDF pipe is installed on the upper side of the small bundle tube flange as the main outlet pipe. The small bundle tube sealing flange and the four rinse port sealing flanges are connected to the 44mm inner diameter PVDF outlet main pipe via 20mm inner diameter PVDF pipes. Because the coupler sealing flange and signal extraction sealing flange are far from the main outlet pipe, a certain degree of flexibility is required. Therefore, a 20mm inner diameter PFA hose is used to connect to the 44mm inner diameter PVDF outlet main pipe. The 44mm inner diameter PVDF outlet main pipe forms a 6-way connector.

[0016] The second step is acid etching via the small tube inlet. The 166MHz PoP cavity is inverted 180 degrees, with the small tube of the superconducting cavity facing downwards. Acid enters the main pipe from below the small tube, then passes through the small tube sealing flange, four rinsing flanges, the coupler sealing flange, and the signal extraction sealing flange into the cavity. Chemical etching is completed within the cavity, and the acid flows out through the large tube sealing flange. The model is as follows: Figure 3 As shown. The pickling time is 60 minutes.

[0017] The pickling fixture is divided into two parts: the first part is the fixture for the large bundle tube side (with an inner diameter of 20mm), and the second part is the fixture for the small bundle tube side assembly.

[0018] Part 1: Large Bundle Tube Side Fixture (20mm Inner Diameter): A 20mm inner diameter PVDF pipe serves as the outlet, and a 228mm outer diameter PVDF flange serves as the sealing flange for the large bundle tube. The PVDF pipe is connected to the PVDF flange. This part of the fixture serves as the outlet for the superconducting cavity acid solution and is connected to the pickling system.

[0019] Part Two: The small bundle tube side assembly fixture is the same as the small bundle tube side fixture from Part One, but reversed 180 degrees. This part of the fixture serves as the inlet for the superconducting cavity acid solution and is connected to the acid washing system.

[0020] Drawing on the acid washing process design of the 166MHz Point of Purchase (PoP) cavity during the pre-research phase of the High Energy Synchrotron Radiation Facility (HISF), acid washing was performed on the 166MHz quarter-wavelength superconducting cavity for high-order mode depth suppression (HEPDS). Although the 166MHz PoP cavity had a smooth inner surface and no acid washing defects after acid washing, meeting the requirements of buffered chemical polishing, the 166MHz quarter-wavelength superconducting cavity for high-order mode depth suppression has a more complex structure, more openings, and huge differences in aperture size (maximum / minimum ~ 17 times). This results in a complex flow path for the acid solution within the cavity and uneven distribution of acid flow velocity, making acid washing more difficult. For the 166MHz quarter-wavelength superconducting cavity for high-order mode depth suppression, linear groove defects were found on the transition section of the large-bundle tube after acid washing in the large-bundle tube. This damaged the morphology and quality of the inner surface of the superconducting cavity, which will lead to phenomena such as field emission, magnetoquench, and secondary electron multiplication during operation, reducing the physical performance of the superconducting cavity and even causing the development failure of the superconducting cavity. Therefore, it is necessary to explore an acid pickling fixture suitable for a 166MHz quarter-wavelength high-order mode depth suppression superconducting cavity to solve the problem of linear groove defects generated during the acid pickling process, improve the inner surface quality, and ensure the cavity's test performance. Summary of the Invention

[0021] To address the problems existing in the prior art, the purpose of this invention is to provide an acid washing fixture for a 166MHz quarter-wavelength superconducting cavity used for high-order mode depth suppression of high-energy synchrotron radiation sources.

[0022] The superconducting cavity buffer chemical polishing fixture involved in this application was developed to meet the high-performance requirements of the superconducting cavity acid washing equipment related to the storage ring high-frequency system of the High Energy Synchrotron Radiation Light Source Project, a major national science and technology infrastructure project. It can also provide a reference for the design of post-processing fixtures for other superconducting cavities, especially those with complex structures.

[0023] Based on the structural characteristics of a 166MHz quarter-wavelength superconducting cavity with high-order mode depth suppression, this invention designs an acid pickling fixture, rationally plans the flow path of the acid solution within the cavity, and designs the pipe diameter and flow rate distribution of the acid pickling fixture to balance the flow velocity of the acid solution at various positions within the superconducting cavity. This ensures sufficient circulation of the acid solution within the cavity and smooth removal of air bubbles, ultimately achieving a smooth inner surface of the superconducting cavity without defects such as linear grooves after acid pickling, with uniform etching amount on the inner surface, improving the acid pickling effect of the superconducting cavity, and meeting the requirements of post-processing of the superconducting cavity.

[0024] This invention proposes an acid-guiding cylinder design with an acid outlet hole. The acid outlet hole creates an impact interference on the acid collection area of ​​the large tube transition section, effectively increasing the acid flow rate in the large tube transition section, accelerating the acid flow at this location, and making it more conducive to the smooth discharge of bubbles, thereby disrupting the formation mechanism of pickling linear groove defects.

[0025] This invention proposes an annular disk design. By designing the position and outer diameter of the disk, the flow cross-section of the acid can be effectively reduced, guiding the acid to flow from the outside of the annular disk through the neck of the superconducting cavity into the superconducting cavity. This increases the flow velocity of the acid in the transition section of the large tube, balances the flow velocity relationship between the transition section of the large tube and the neck of the superconducting cavity, and helps to eliminate accumulated bubbles and disrupt the generation mechanism of strip-shaped groove defects in the transition section of the large tube.

[0026] The pickling fixture for the 166MHz quarter-wavelength superconducting cavity with high-order mode depth suppression is made of acid-resistant polyvinylidene fluoride (PVDF) and soluble polytetrafluoroethylene (PFA).

[0027] The pickling fixture consists of three parts: the first part is the fixture for the large bundle tube side, the second part is the fixture for the small bundle tube side combination, and the third part is the fixture for guiding acid flow inside the cavity.

[0028] The large bundle tube side tooling serves as the acid inlet or outlet of the superconducting cavity system. One end of it is sealed to the large bundle tube flange 1 of the superconducting cavity system, and the other end is connected to the acid washing equipment through the first connecting flange and the connecting pipe.

[0029] The small bundle tube side assembly tooling serves as the acid inlet or outlet of the superconducting cavity system. One end of it is sealed and connected to the cavity small bundle tube flange 2, cavity coupler flange 7 and each rinse port flange of the superconducting cavity system. The other end is connected to the acid washing equipment through the second connecting flange and pipeline.

[0030] The acid flow guiding fixture is located inside the superconducting cavity system and is connected to the large bundle tube side fixture. It is used to guide the flow of acid that is input into the superconducting cavity system through the large bundle tube side fixture and to balance the acid flow rate.

[0031] Part 1: Large Bundle Tube Side Fixture: Composed of a large bundle tube sealing flange, connecting pipe, and connecting flange. The large bundle tube sealing flange has an outer diameter of 571mm and a wall thickness of 25mm. It connects to the large bundle tube flange of the superconducting cavity, serving as the sealing point for the cavity's large bundle tube flange, the inlet or outlet for the acid, and providing sufficient strength to support the weight of the acid within the cavity. The large bundle tube sealing flange is connected to a connecting flange with an outer diameter of 140mm and a thickness of 25mm via a connecting pipe with inner and outer diameters of 44mm and 50mm respectively, forming a single unit. The connecting pipe is used for connection and acid flow guidance. The connecting flange connects the large bundle tube side fixture to the pickling equipment, serving as the acid inlet or outlet for the entire superconducting cavity pickling system, depending on the cavity's orientation.

[0032] The second part, the small tube side assembly tooling, consists of a small tube sealing flange, a rinse port sealing flange, a coupler sealing flange, a connecting flange, a main pipeline, and small pipelines. The small tube sealing flange has an outer diameter of 140mm, the rinse port sealing flange has an outer diameter of 70mm, and the coupler sealing flange has an outer diameter of 160mm. All flanges are 25mm thick. The small tube sealing flange is used for sealing the small tube flange of the cavity, the rinse port sealing flange is used for sealing the rinse port flange of the cavity, and the coupler sealing flange is used for sealing the coupler flange of the cavity. The connecting flange has an outer diameter of 140mm and a wall thickness of 25mm. One side connects to the main pipeline of the small tube side assembly tooling, and the other side connects to the pickling equipment. Depending on the orientation of the cavity, it serves as the acid inlet or outlet for the entire superconducting cavity pickling system. The main pipeline has an inner diameter of 44mm and an outer diameter of 50mm. It is used to connect the small bundle of pipe sealing flanges, connecting flanges, and four small pipelines leading from the shower port sealing flanges and one small pipeline leading from the coupler sealing flange, forming a 7-way connector. The small pipelines have inner diameters of 20mm and outer diameters of 25mm. They are used to connect the main pipeline to the four shower port sealing flanges and the main pipeline to the coupler sealing flange.

[0033] The third part consists of an acid-guiding fixture within the cavity: an acid-guiding cylinder with an inner diameter of 44 mm, an outer diameter of 50 mm, a total length of 324 mm, an open bottom, and a closed top, and an annular disk with an outer diameter of 140 mm and a thickness of 4 mm. This fixture is used only when the acid enters from the large tube bundle. Its purpose is to guide the acid flow, balance the acid flow rate, disrupt the formation mechanism of the strip-shaped groove defects in the transition section of the large tube bundle, prevent the conductor inside the superconducting cavity from being directly washed by the acid, and improve the problem of uneven etching in the superconducting cavity.

[0034] The bottom opening (inner diameter 44mm) of the acid-conducting cylinder is connected to the sealing flange (inner diameter 44mm) of the large bundle tube of the superconducting cavity to receive the input acid. The acid-conducting cylinder has 26 acid outlet holes with a diameter of 9mm. The position of the acid outlet holes is defined by the distance from the acid outlet hole to the bottom plane of the acid-conducting cylinder 18, the number of acid outlet holes, and the angle of the acid outlet holes when viewed from above.

[0035] First row: Two acid outlet holes are evenly distributed 4mm from the bottom plane of the acid guide cylinder 18, located at 0° and 180°.

[0036] Second row: Two acid outlet holes are evenly distributed 70mm from the bottom plane of the acid guide cylinder 18, located at 0° and 180°.

[0037] The third row: There are two acid outlet holes, 75mm from the bottom plane of the acid guide cylinder 18, evenly distributed at 90° and 270° positions.

[0038] Fourth row: Four acid outlet holes are evenly distributed 105mm from the bottom plane of the acid guide cylinder 18, located at 45°, 135°, 225° and 315°.

[0039] Fifth row: The acid outlet holes are 145mm from the bottom plane of the acid guide cylinder 18, with 4 acid outlet holes evenly distributed at 0°, 90°, 180° and 270°.

[0040] Sixth row: Two acid outlet holes are evenly distributed 180mm from the bottom plane of the acid guide cylinder 18, located at 135° and 315°.

[0041] Seventh row: Two acid outlet holes are evenly distributed 195mm from the bottom plane of the acid guide cylinder 18, located at 45° and 225°.

[0042] Eighth row: The acid outlet is 215mm from the bottom plane of the acid guide cylinder 18, with two acid outlets evenly distributed at 90° and 270° positions.

[0043] The ninth row: There are two acid outlet holes, 240mm from the bottom plane of the acid guide cylinder 18, evenly distributed at 0° and 180°.

[0044] The tenth row: There are 4 acid outlet holes evenly distributed 295mm from the bottom plane of the acid guide cylinder 18, located at 0°, 90°, 180° and 270°.

[0045] The total area of ​​the 26 circular holes is slightly larger than the area of ​​the acid inlet cross-section, with a ratio of 1.3.

[0046] Between the large tube flange 1, the small tube flange 2, the first rinse port flange 3, the second rinse port flange 4, the third rinse port flange 5, the fourth rinse port flange 6, the cavity coupler flange 7, and the acid pickling fixture sealing flange, and between the acid inlet flange 20, the acid outlet flange 21, and the acid pickling fixture flange, PTFE sealing rings and fluororubber rings are placed and secured with screws. The acid guiding cylinder 18 and the annular disc 19 are welded together as a single unit using heat fusion welding. The acid guiding fixture in the third part of the cavity and the large tube sealing flange are also welded together using heat fusion welding.

[0047] The advantages of this invention are as follows:

[0048] The pickling fixture of the present invention rationally plans the flow path of acid in the superconducting cavity. By designing the pipe diameter of the pickling fixture, the flow rate of acid at each port is rationally distributed, so that the acid circulates fully in the cavity and the bubble flow is smooth.

[0049] A flow guiding device was employed to balance the acid flow rate distribution within the cavity, improving the uniformity of etching in the superconducting cavity and preventing excessive local etching and excessive frequency shift after acid washing. For the transition section of the large tube bundle, which is prone to strip-shaped groove defects, the acid flow rate in the large tube bundle transition section was significantly increased through the acid outlet hole on the acid guiding cylinder and the flow guidance of the annular disk; at the same time, the small end of the inner conductor of the superconducting cavity was protected, preventing the small end of the inner conductor from being directly washed by the acid, which would cause excessive etching and excessive frequency shift.

[0050] The 166MHz quarter-wavelength superconducting cavity with high-order mode depth suppression exhibits a smooth, flat inner surface free of defects such as striped grooves after acid washing, meeting the requirements for buffered chemical polishing. This successfully solves the problem of defects caused by acid washing in the large-beam transition section of the superconducting cavity. Attached Figure Description

[0051] Figure 1 A schematic diagram of a 166MHz quarter-wavelength superconducting cavity structure for high-order mode depth suppression.

[0052] Figure 2 This is a schematic diagram of the 166MHz PoP cavity pickling fixture during liquid inlet in a large bundle tube.

[0053] Figure 3 This is a schematic diagram of the 166MHz PoP cavity pickling fixture when liquid is introduced into a small bundle tube.

[0054] Figure 4 A 166MHz quarter-wavelength superconducting cavity model and tooling model for high-order mode depth suppression;

[0055] Among them, 1-large bundle tube flange, 2-small bundle tube flange, 3-first rinse port flange, 4-second rinse port flange, 5-third rinse port flange, 6-fourth rinse port flange, 7-cavity coupler flange, 8-large bundle tube transition section, 9-inner conductor, 10-outer conductor, 11-large bundle tube sealing flange, 12-small bundle tube sealing flange, 13-first rinse port sealing flange, 14-second rinse port sealing flange, 15-third rinse port sealing flange, 16-fourth rinse port sealing flange, 17-coupler sealing flange, 18-acid-conducting cylinder, 19-annular disc, 20-acid inlet connection flange, 21-acid outlet connection flange.

[0056] Figure 5This is a schematic diagram of the first part of the superconducting cavity acid washing fixture, specifically the large bundle tube side fixture.

[0057] (a) Structural diagram, (b) Dimensional diagram.

[0058] Figure 6 This is a schematic diagram of the small bundle tube side assembly tooling, which is the second part of the superconducting cavity acid washing tooling.

[0059] (a) Structural diagram, (b) Dimensional diagram.

[0060] Figure 7 A schematic diagram of the acid flow guide fixture in the third part of the superconducting cavity pickling fixture;

[0061] (a) Structural diagram, (b) Hole structure diagram, (c) Hole positional relationship diagram.

[0062] Figure 8 Acid washing process for a 166MHz quarter-wavelength superconducting cavity with high-order mode depth suppression.

[0063] Figure 9 A schematic diagram of a 166MHz quarter-wavelength superconducting cavity acid washing fixture during liquid inlet in a large bundle tube;

[0064] (a) Cross-sectional view, (b) 3D structural view.

[0065] Figure 10 A schematic diagram of a 166MHz quarter-wavelength superconducting cavity acid washing fixture during liquid inlet in a small bundle tube;

[0066] (a) Cross-sectional view, (b) 3D structural view. Detailed Implementation

[0067] The present invention will now be described in further detail with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0068] The 166MHz quarter-wavelength superconducting cavity with high-order mode depth suppression is the main accelerating cavity on the storage ring of a high-energy synchrotron radiation source. This cavity has a complex structure with numerous openings of varying diameters (maximum / minimum ~17 times). The inner diameter of the large-beam tube is 505mm, the inner diameter of the outer conductor is 400mm, the total length is 880mm, and the cavity volume is 100 liters. The complex cavity structure and large cavity size pose significant challenges to buffered chemical polishing of the superconducting cavity. This invention designs an acid cleaning fixture suitable for the 166MHz quarter-wavelength superconducting cavity structure with high-order mode depth suppression. Using this acid cleaning fixture, the inner surface of the 166MHz quarter-wavelength superconducting cavity with high-order mode depth suppression is smooth, flat, and defect-free after acid cleaning, meeting the requirements of buffered chemical polishing.

[0069] The 166MHz quarter-wavelength superconducting cavity model, acid pickling fixture model, and component names for high-order mode depth suppression are as follows: Figure 4 As shown. The pickling fixture for the 166MHz quarter-wavelength superconducting cavity with high-order mode depth suppression is made of acid-resistant polyvinylidene fluoride (PVDF) and soluble polytetrafluoroethylene (PFA). PTFE sealing rings and fluororubber rings are placed between the cavity large bundle flange 1, cavity small bundle flange 2, first rinse port flange 3, second rinse port flange 4, third rinse port flange 5, fourth rinse port flange 6, cavity coupler flange 7, and the pickling fixture sealing flange; and between the acid inlet connection flange 20, the acid outlet connection flange 21, and the pickling fixture flange, and are secured with screws for sealing. The acid-conducting cylinder 18 and the annular disk 19, and the acid-conducting cylinder 18 and the large bundle sealing flange 11 are integrally welded together by hot-melt welding.

[0070] Based on their location and function, the pickling fixture is divided into three parts: the first part is the fixture for the large bundle of tubes, the second part is the combined fixture for the small bundle of tubes, and the third part is the acid flow guiding fixture inside the cavity. These will be described in detail below.

[0071] The first part of the large tube side fixture consists of a large tube sealing flange 11, a connecting flange, and a connecting pipe. The large tube sealing flange 11 has an outer diameter of 571 mm and connects to the large tube flange 1 in the cavity, used to seal the large tube flange 1. The connecting flange has an outer diameter of 140 mm and connects to the acid inlet or outlet pipeline, serving as the acid inlet or outlet for the superconducting cavity system, connecting the entire superconducting cavity to the acid washing equipment. The connecting pipe has an inner diameter of 44 mm and an outer diameter of 50 mm, used to connect the large tube sealing flange 11 and the connecting flange, and to guide the acid flow. Both flanges are 25 mm thick to provide sufficient strength to support the 155 kg weight of 100 liters of acid inside the cavity. The first part of the large tube side fixture is made of polyvinylidene fluoride (PVDF). The model and dimensions of the first part of the fixture are as follows... Figure 5 As shown.

[0072] The second part of the small tube side assembly tooling consists of a small tube sealing flange 12, a first rinse port sealing flange 13, a second rinse port sealing flange 14, a third rinse port sealing flange 15, a fourth rinse port sealing flange 16, a coupler sealing flange 17, a connecting flange, a main pipeline, and a small pipeline. The outer diameter of the small bundle tube sealing flange 12 is 140mm, and it is connected to the cavity small bundle tube flange 2 to seal the cavity small bundle tube flange; the outer diameters of the first rinse port sealing flange 13, the second rinse port sealing flange 14, the third rinse port sealing flange 15, and the fourth rinse port sealing flange 16 are 70mm, and they are connected to the first rinse port flange 3, the second rinse port flange 4, the third rinse port flange 5, and the fourth rinse port flange 6 to seal the cavity rinse port flange; the outer diameter of the coupler sealing flange 17 is 160mm, and it is connected to the cavity coupler flange 7 to seal the cavity coupler flange; the outer diameter of the connecting flange is 140mm, and it is connected to the acid inlet or outlet pipeline, serving as the acid inlet or outlet of the superconducting cavity system, so that the entire superconducting cavity is connected to the acid washing equipment. The main pipeline has an inner diameter of 44mm and an outer diameter of 50mm, used to connect the small bundle tube sealing flange 12, the connecting flange, and five small pipelines. The small pipelines have inner diameters of 20mm and outer diameters of 25mm, used to connect the main pipeline, the first rinse port sealing flange 13, the second rinse port sealing flange 14, the third rinse port sealing flange 15, the fourth rinse port sealing flange 16, and the coupler sealing flange 17. The main pipeline forms a 7-way system to effectively guide acid from or into the coupler sealing flange 17, the small bundle tube sealing flange 12, and the first to fourth rinse port sealing flanges (when the small bundle tubes are facing down, the main pipeline acts as the acid inlet; otherwise, it guides the acid out), forming a reasonable acid flow distribution ratio and uniformly etching various areas of the superconducting cavity's inner surface. At the same time, hydrogen generated during the etching process is promptly discharged through pipelines distributed around the cavity wall to avoid the existence of blind spots for hydrogen emission within the cavity, which could lead to hydrogen accumulation and damage to the cavity's performance. In the second part of the small bundle tube side assembly fixture, the thickness of the six sealing flanges (corresponding to numbers 12-17) and the connecting flanges is 25mm, which is intended to provide sufficient strength to support the weight of 155 kg of 100 liters of acid solution inside the cavity. The seven sealing flanges, the main pipeline, and the four small pipelines connected to the main pipeline and the four rinse port sealing flanges in the second part of the small bundle tube side assembly fixture are made of polyvinylidene fluoride (PVDF). Because the coupler sealing flange 17 is far from the main pipeline, the connecting small pipelines require a certain degree of flexibility and are made of soluble polytetrafluoroethylene (PTFE) flexible tubing. The model and dimensions of the second part of the fixture are as follows: Figure 6 As shown.

[0073] The third part of the cavity acid guiding fixture consists of an acid guiding cylinder 18 and an annular disk 19. This fixture is only used when the acid enters from the large bundle tube. Its purpose is to guide the flow of acid, balance the acid flow rate, destroy the generation mechanism of the strip-shaped groove defects in the transition section 8 of the large bundle tube, avoid the conductor 9 in the superconducting cavity being directly washed by the acid, and improve the problem of uneven etching in the superconducting cavity.

[0074] The acid-conducting cylinder 18 has an inner diameter of 44 mm, an outer diameter of 50 mm, and a total length of 324 mm, and is connected to the large bundle tube sealing flange 11. The acid-conducting cylinder 18 has 26 acid outlet holes with a diameter of 9 mm, of which 22 are located at the long end (below the annular disc 19) and 4 are located at the short end (above the annular disc 19), used to guide the flow of acid. The position of the acid outlet holes is defined by the distance from the outlet hole to the bottom plane of the acid-conducting cylinder 18, the number of outlet holes, and the angle of the outlet holes when viewed from above.

[0075] First row: Two acid outlet holes are evenly distributed 4mm from the bottom plane of the acid guide cylinder 18, located at 0° and 180°.

[0076] Second row: Two acid outlet holes are evenly distributed 70mm from the bottom plane of the acid guide cylinder 18, located at 0° and 180°.

[0077] The third row: There are two acid outlet holes, 75mm from the bottom plane of the acid guide cylinder 18, evenly distributed at 90° and 270° positions.

[0078] Fourth row: Four acid outlet holes are evenly distributed 105mm from the bottom plane of the acid guide cylinder 18, located at 45°, 135°, 225° and 315°.

[0079] Fifth row: The acid outlet holes are 145mm from the bottom plane of the acid guide cylinder 18, with 4 acid outlet holes evenly distributed at 0°, 90°, 180° and 270°.

[0080] Sixth row: Two acid outlet holes are evenly distributed 180mm from the bottom plane of the acid guide cylinder 18, located at 135° and 315°.

[0081] Seventh row: Two acid outlet holes are evenly distributed 195mm from the bottom plane of the acid guide cylinder 18, located at 45° and 225°.

[0082] Eighth row: The acid outlet is 215mm from the bottom plane of the acid guide cylinder 18, with two acid outlets evenly distributed at 90° and 270° positions.

[0083] The ninth row: There are two acid outlet holes, 240mm from the bottom plane of the acid guide cylinder 18, evenly distributed at 0° and 180°.

[0084] The tenth row: There are 4 acid outlet holes evenly distributed 295mm from the bottom plane of the acid guide cylinder 18, located at 0°, 90°, 180° and 270°.

[0085] The total area of ​​the 26 circular holes is slightly larger than the area of ​​the acid inlet cross-section, with a ratio of 1.3, to ensure that the acid inlet efficiency of the entire cavity does not decrease even with the addition of the third tooling section. The top end of the acid-conducting cylinder 18 is a sealed structure, while the bottom end is an open structure, connected to the sealing flange 11 of the large bundle tube. On the long end side of the acid-conducting cylinder 18, near the annular disk 19, eight acid outlet holes are opened adjacent to the large bundle tube transition section 8 (located on the sixth to ninth rows), with each of the eight holes spaced 45° apart when viewed from above. The acid outlet holes at this location create impact interference to the acid collection area of ​​the large bundle tube transition section 8, effectively increasing the acid flow rate of the large bundle tube transition section 8 and disrupting the formation mechanism of the linear groove defects in the pickling process. On the short end side of the acid-conducting cylinder 18, four evenly distributed acid outlet holes can increase the pickling volume of the superconducting cavity end cap and the inner conductor side, improving the uniformity of the acid flow rate.

[0086] The annular disk 19 has an outer diameter of 140 mm and a thickness of 4 mm. Its distances from the bottom and top surfaces of the acid-conducting cylinder 18 are 250 mm and 70 mm, respectively. Located at the neck of the superconducting cavity, the annular disk 19 reduces the acid flow cross-section and guides the acid flow from the outside of the disk through the neck into the superconducting cavity. The distance from the outer surface of the annular disk 19 to the straight section of the neck is 50 mm. The annular disk can increase the acid flow velocity in the large-tube transition section 8, balance the flow velocity relationship between the large-tube transition section 8 and the neck of the superconducting cavity, and disrupt the generation mechanism of the strip-shaped groove defects in the large-tube transition section 8. Since the frequency of the 166MHz quarter-wavelength superconducting cavity with high-order mode depth suppression is very sensitive to the wall thickness change of the small end of the conductor 9 inside the superconducting cavity, with a frequency sensitivity as high as 330kHz / mm, an annular disk 19 is used to avoid the acid liquid directly impacting the small end of the conductor 9 inside the superconducting cavity, thereby improving the problems of excessive etching of the inner conductor wall thickness and excessive frequency shift after acid washing.

[0087] The third part of the tooling is made of polyvinylidene fluoride. The acid-conducting cylinder 18 and the annular disk 19 are welded together as a single unit. The model and dimensions of the third part of the tooling are as follows: Figure 7 As shown.

[0088] To ensure uniform and consistent wall thickness removal in the 166MHz quarter-wavelength superconducting cavity for high-order mode depth suppression, two liquid inlet methods (large-tube inlet and small-tube inlet) are used for acid etching to eliminate etching inhomogeneities caused by the cavity placement orientation. The acid etching process is as follows: Figure 8 As shown.

[0089] (1) Acid washing with liquid introduced from the large bundle tube.

[0090] With the large bundle tube of the 166MHz quarter-wavelength superconducting cavity, designed for high-order mode depth suppression, facing downwards, an acid pickling fixture (comprising three parts) is installed on the superconducting cavity. Acid enters through the large bundle tube flange via the acid inlet flange and piping, then flows into the superconducting cavity through the acid guide fixture. After chemical etching within the cavity, the acid passes through the coupler sealing flange, the first to fourth rinse port sealing flanges, and the small bundle tube sealing flange into the main pipeline, finally exiting through the upper acid outlet flange and piping. The acid pickling time is 60 minutes.

[0091] When the large bundle tube is filled with liquid, the pickling fixture includes: a first part of the large bundle tube side fixture, a second part of the small bundle tube side combined fixture, and a third part of the acid flow guiding fixture in the cavity.

[0092] The first part, the large tube side tooling, is used to seal the large tube flange, connect to the acid inlet flange and pipeline, and connect the cavity to the pickling system.

[0093] The second part, the small bundle tube side assembly tooling, is used to seal the small bundle tube flange, the first rinse port flange, the second rinse port flange, the third rinse port flange, the fourth rinse port flange, and the coupler flange, guiding the acid flow. The main pipeline forms a 7-way system, which can effectively discharge the acid from the cavity, forming a reasonable acid flow distribution ratio, and uniformly etching various areas of the superconducting cavity's inner surface; at the same time, it can promptly discharge the hydrogen gas generated during the etching process, avoiding hydrogen accumulation and causing a decrease in the superconducting cavity's performance. It also connects to the acid outlet flange and pipeline for connection to the acid washing system.

[0094] The third part of the cavity is an acid flow guiding device used to guide the flow of acid, balance the acid flow rate, disrupt the generation mechanism of strip-shaped groove defects in the transition section of the large bundle tube, and improve the problem of uneven etching in the superconducting cavity.

[0095] A schematic diagram of the 166MHz quarter-wavelength superconducting cavity acid washing fixture for high-order mode depth suppression during liquid injection in a large-bundle tube is shown below. Figure 9 As shown.

[0096] (2) Acid washing with liquid entering through the small tube

[0097] With the small bundle tube of the 166MHz quarter-wavelength superconducting cavity, designed for high-order mode depth suppression, facing downwards, an acid etching fixture (comprising two parts) is installed on the superconducting cavity. Acid enters through the inlet flange and piping, starting from the small bundle tube flange, then passes through the small bundle tube sealing flange, the first to fourth rinse port sealing flanges, and the coupler sealing flange into the superconducting cavity. After chemical etching is completed within the cavity, the acid flows out through the large bundle tube flange, then through the outlet flange and piping. The acid etching time is 60 minutes.

[0098] When the small bundle of tubes is fed with liquid, the pickling fixture includes: a first part, the fixture on the large bundle of tubes side, and a second part, the fixture combined with the fixture on the small bundle of tubes side. The pickling fixture does not include the third part, the acid flow guiding fixture inside the cavity.

[0099] The first part, the large tube side tooling, is used to seal the large tube flange, connect to the acid outlet flange and pipeline, and is used to connect to the pickling system.

[0100] The second part, the small bundle tube side assembly tooling, is used to seal the small bundle tube flange, the first rinse port flange, the second rinse port flange, the third rinse port flange, the fourth rinse port flange, and the coupler flange, guiding the acid flow. The main pipeline forms a 7-way system, which can effectively introduce acid into the cavity, forming a reasonable acid flow path and flow distribution ratio, promoting the uniformity of etching on the inner surface of each region of the superconducting cavity; and timely removing hydrogen generated during the etching process to avoid hydrogen accumulation and degradation of the superconducting cavity performance. Simultaneously, it connects to the acid inlet flange and pipeline for connection to the acid washing system, such as... Figure 10 As shown.

[0101] (3) Determine the pickling effect

[0102] To determine the etching amount of the cavity wall thickness and the quality of the inner surface, if the average etching amount of the cavity wall thickness reaches 150 micrometers and the inner surface of the cavity is smooth and free of defects such as air chambers and groove-shaped acid marks, then the pickling is completed; if the requirements are not met, the defects are treated and then returned to (1) pickling from the large bundle tube.

[0103] (4) Pickling is complete.

[0104] Following the above process, using the pickling fixture of this invention, after pickling, the inner surface of the 166MHz quarter-wavelength superconducting cavity with high-order mode depth suppression is smooth and flat, without strip-shaped groove defects, meeting the chemical polishing requirements of the 166MHz superconducting cavity. This successfully solves the problem of defects caused by pickling on the transition section 8 of the large bundle tube of the superconducting cavity.

[0105] Electrochemical polishing (EP) is another chemical polishing technique. Because EP is insensitive to grain boundary defects, the surface of the superconducting cavity after treatment is smoother, and it is considered a key technology for the development of superconducting cavities with higher acceleration gradients (>40 MV / m).

[0106] For ellipsoidal cavities, electrochemical polishing can be an alternative. However, electrochemical polishing equipment is complex, and the installation, debugging, and disassembly of the equipment are complicated and difficult; compared with buffered chemical polishing, electrochemical polishing is more expensive and has a longer processing cycle; electrochemical polishing contains hydrofluoric acid, which causes more serious environmental pollution. Currently, electrochemical polishing is still in the research and development and small-scale use stage and has not been widely used in major laboratories around the world.

[0107] Electrochemical polishing techniques are generally not applicable to non-ellipsoidal superconducting cavities. This is because the internal structure of non-ellipsoidal superconducting cavities is complex and irregular, making it impossible for electrodes to penetrate and for a uniform electric field to be established on the inner surface of the cavity. Therefore, electrochemical polishing techniques cannot be used in 166MHz quarter-wavelength superconducting cavities with high-order mode depth suppression and similar complex cavity structures.

[0108] Although specific embodiments of the invention have been disclosed for illustrative purposes to aid in understanding and implementing the invention, those skilled in the art will understand that various substitutions, variations, and modifications are possible without departing from the spirit and scope of the invention and the appended claims. Therefore, the invention should not be limited to the content disclosed in the preferred embodiments, and the scope of protection claimed by the invention is defined by the claims.

Claims

1. A pickling fixture for a 166 MHz quarter-wavelength superconducting cavity, characterized in that, This includes tooling for the large bundle tube side, combined tooling for the small bundle tube side, and acid flow guiding tooling; The large bundle tube side tooling serves as the acid inlet or outlet of the superconducting cavity system. One end of it is sealed to the large bundle tube flange (1) of the superconducting cavity system, and the other end is connected to the acid washing equipment through the first connecting flange and the connecting pipe. The small bundle tube side assembly tooling serves as the acid inlet or outlet of the superconducting cavity system. One end of it is sealed and connected to the cavity small bundle tube flange (2), cavity coupler flange (7) and each rinse port flange of the superconducting cavity system, and the other end is connected to the acid washing equipment through the second connecting flange and pipeline. The acid flow guiding device is located inside the superconducting cavity system and is connected to the large bundle tube side device. It is used to guide the flow of acid entering the superconducting cavity system through the large bundle tube side device and balance the acid flow rate. The acid flow guiding device includes an acid guiding cylinder (18) and an annular disc (19). The bottom end of the acid guiding cylinder (18) is sealed to the large bundle tube side device through the cavity large bundle tube flange (1), and the top end is closed. The annular disc (19) is fitted on the acid guiding cylinder (18), and the acid guiding cylinder (18) is provided with multiple acid outlet holes.

2. The pickling fixture according to claim 1, characterized in that, The acid-conducting cylinder (18) has 22 acid outlet holes between its bottom end and the annular disk (19), and 4 acid outlet holes between its top end and the annular disk (19); the acid outlet holes are divided into multiple rows according to their position from the bottom end of the acid-conducting cylinder (18). in The first row of acid outlet holes is 4 mm from the bottom end, with 2 acid outlet holes evenly distributed at 0° and 180° positions; The second row of acid outlet holes is 70 mm from the bottom, with two acid outlet holes evenly distributed at 0° and 180° positions; The third row of acid outlet holes is 75 mm from the bottom, with two acid outlet holes evenly distributed at 90° and 270° positions; The fourth row of acid outlet holes is 105mm from the bottom, with four acid outlet holes evenly distributed at 45°, 135°, 225° and 315° azimuths; The fifth row of acid outlet holes is 145mm from the bottom, with 4 acid outlet holes evenly distributed at 0°, 90°, 180° and 270° positions; The sixth row of acid outlet holes is 180mm from the bottom, with two acid outlet holes evenly distributed at 135° and 315° azimuths; The seventh row of acid outlet holes is 195mm from the bottom, with two acid outlet holes evenly distributed at 45° and 225° azimuths; The eighth row of acid outlet holes is 215mm from the bottom, with two acid outlet holes evenly distributed at 90° and 270° positions; The ninth row of acid outlet holes is 240mm from the bottom, with two acid outlet holes evenly distributed at 0° and 180° positions; The tenth row of acid outlet holes is 295mm from the bottom, with four acid outlet holes evenly distributed at 0°, 90°, 180° and 270°.

3. The pickling fixture according to claim 2, characterized in that, The diameter of the acid outlet hole is 9 mm; the inner diameter of the acid-conducting cylinder (18) is 44 mm, the outer diameter is 50 mm, and the total length is 324 mm; the eight acid outlet holes in the sixth, seventh, eighth, and ninth rows are opposite to the position of the large bundle tube transition section (8) of the superconducting cavity system, which are used to increase the acid flow rate at the position of the large bundle tube transition section (8) and destroy the acid washing linear grooves formed at the position of the large bundle tube transition section (8).

4. The pickling fixture according to claim 2, characterized in that, The annular disk (19) has an outer diameter of 140 mm and a thickness of 4 mm. It is 250 mm away from the bottom of the acid-conducting cylinder (18) and 70 mm away from the top of the acid-conducting cylinder (18).

5. The pickling fixture according to claim 1 or 2, characterized in that, The sum of the opening areas of all the acid outlet holes is greater than the cross-sectional area of ​​the acid inlet of the acid guide cylinder (18).

6. The pickling fixture according to claim 5, characterized in that, The sum of the opening areas of each of the acid outlet holes is 1.3 times the cross-sectional area of ​​the acid inlet of the acid guide cylinder (18).

7. The pickling fixture according to claim 1, characterized in that, The large bundle tube side tooling includes a large bundle tube sealing flange (11), a first connecting flange and a connecting pipe; one end of the large bundle tube sealing flange (11) is sealed to the cavity large bundle tube flange (1), and the other end is connected to the pickling equipment through the first connecting flange and the connecting pipe.

8. The pickling fixture according to claim 1, characterized in that, The superconducting cavity system's flushing port flanges include a first flushing port flange (3), a second flushing port flange (4), a third flushing port flange (5), and a fourth flushing port flange (6); the small bundle tube side assembly tooling includes a small bundle tube sealing flange (12), a first flushing port sealing flange (13), a second flushing port sealing flange (14), a third flushing port sealing flange (15), a fourth flushing port sealing flange (16), a coupler sealing flange (17), a second connecting flange, a main pipeline, and a small pipeline; the small bundle tube sealing flange (12) is sealed to the cavity small bundle tube flange (2), and the first flushing port sealing flange (13), the second flushing port sealing flange (14), the third flushing port sealing flange (15), and the fourth flushing port sealing flange (16) are respectively connected to the corresponding first flushing port flange (3), second flushing port flange (4), and third flushing port flange (5). The fourth rinse port flange (6) is sealed and connected; the coupler sealing flange (17) is sealed and connected to the cavity coupler flange (7); the second connecting flange is connected to the pickling equipment; the main pipeline is connected to the small bundle tube sealing flange (12) and the second connecting flange respectively; the first rinse port sealing flange (13), the second rinse port sealing flange (14), the third rinse port sealing flange (15), the fourth rinse port sealing flange (16) and the coupler sealing flange (17) are respectively connected to the main pipeline through a small pipeline, for exporting or importing acid from the coupler sealing flange (17), the small bundle tube sealing flange (12) and the first rinse port sealing flange (13), the second rinse port sealing flange (14), the third rinse port sealing flange (15) and the fourth rinse port sealing flange (16), and exporting hydrogen generated during the etching process.

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