Composite superconducting cavity string reinforcing rib and bidirectional frequency modulation method of superconducting cavity string

Abstract

This invention discloses a composite superconducting cavity string reinforcing rib and a bidirectional frequency modulation method for the superconducting cavity string. The composite superconducting cavity string reinforcing rib of this invention is characterized by comprising two horizontal beams, two central vertical beams, four edge vertical beams, four connecting pressure plates, and four superconducting cavity lower flanges located in the same plane; a rectangular area is formed between the two horizontal beams by the two central vertical beams; two edge vertical beams are provided on the outer side of each horizontal beam; the four superconducting cavity lower flanges within the rectangular area are respectively connected and fixed to one side by a connecting pressure plate for connecting the superconducting cavity string; both ends of the horizontal beams have raised contact platforms as force points for contacting the end plate of the superconducting cavity liquid helium tank; the outer ends of the edge vertical beams have raised contact platforms as force points for connecting to the end plate of the superconducting cavity liquid helium tank; the superconducting cavity lower flanges have several threaded holes, the inner threaded holes for connection and fixation with the superconducting cavity small bundle tube flange, and the outer threaded holes for connection and fixation with the reinforcing ribs.

Description

Technical Field

[0001] This invention belongs to the fields of accelerator physics and superconducting high-frequency technology, and relates to a composite superconducting cavity string reinforcing rib and a bidirectional frequency modulation method for the superconducting cavity string. Background Technology

[0002] In the design of structural components, there may be situations where the overhang of the structure is too large or the span is too large. The connection surface of the structural component itself can only bear a limited load. The protrusions, ribs or plates added to it to enhance the performance of the structural component are called stiffeners. The main functions of stiffeners include: improving stiffness, dispersing stress, and optimizing material utilization.

[0003] Superconducting cavities are typically made of high-purity niobium and operate at ultra-low temperatures of 4.2K or 2K, immersed in liquid helium. Although niobium has zero electrical resistance in its superconducting state, the superconducting cavity still experiences slight energy loss under the influence of a strong radio frequency electromagnetic field, which is converted into heat. The heat generated on the inner surface of the superconducting cavity is conducted through the niobium cavity wall to the outer wall and then carried away by the liquid helium, thus maintaining the stability of the electromagnetic field inside the cavity.

[0004] At an ultra-low temperature of 4K, high-purity niobium has a thermal conductivity of 1.42 W / cmK, which is relatively poor. To improve the thermal conductivity of superconducting cavities, the wall thickness is generally no more than 4 mm. If the cavity wall is too thick, a significant temperature gradient will exist along the path of heat conduction from the inner wall to the outer wall, causing the inner wall temperature to rise to or even exceed the critical temperature (Tc≈9.2K) due to heat accumulation. This local area will then revert from the superconducting state to the normal conducting state. Once the superconductivity is lost, a large amount of heat will be generated instantaneously in this area, causing the superconducting region to expand rapidly. The entire cavity will lose its superconductivity and cannot function properly, exhibiting thermal instability. Therefore, superconducting cavities typically employ a thin-walled structure to reduce the temperature difference between the inside and outside of the cavity wall, ensuring that heat is rapidly dissipated into liquid helium, thereby maintaining the thermal stability of the superconducting cavity.

[0005] Superconducting cavities are hollow, thin-walled structures. While thin-walled structures offer advantages in maintaining thermal stability, their low overall stiffness presents significant challenges in terms of mechanical stability. During machining, welding, acid pickling, high-pressure water cleaning, assembly, transportation, and beam operation, any inappropriate external force can easily lead to plastic deformation and buckling of the cavity. Therefore, superconducting cavities require continuous structural optimization to improve their mechanical stability. Due to wall thickness limitations, to further enhance overall stiffness and stability, superconducting cavities often require the addition of reinforcing ribs to simultaneously achieve excellent thermal conductivity and mechanical stability.

[0006] Currently, conventional superconducting cavity reinforcing ribs, such as the sheet-like reinforcing ribs of a 325MHz half-wavelength superconducting cavity, the spoke-shaped vertical ribs of a 325MHz superconducting cavity, the annular reinforcing ribs of a 650MHz ellipsoidal superconducting cavity, and the bowl-shaped reinforcing ribs of a 166MHz quarter-wavelength superconducting cavity, have the following structures: Figure 1 As shown.

[0007] The aforementioned conventional superconducting cavity reinforcing ribs are introduced during the optimization of the superconducting cavity structure. Their main functions are to alleviate stress concentration within the cavity, reduce helium pressure sensitivity and Lorentz detuning coefficient, suppress microphone effects, improve tuning performance, and enhance buckling resistance. These reinforcing ribs are integrally connected to the superconducting cavity body using electron beam welding technology, typically permanently fixed to the cavity and inseparable. Therefore, this increases the manufacturing difficulty of the superconducting cavity to some extent. Furthermore, because the vacuum is visible during clean assembly of the superconducting cavity, it is necessary to ensure compliance with Class 10 cleanliness standards, increasing the difficulty of cleaning and assembly. Finally, the reinforcing ribs may obstruct liquid helium flow, leading to insufficient heat exchange, resulting in performance degradation or even quenching failure and malfunction of the superconducting cavity.

[0008] The superconducting cavity reinforcing ribs described above lack frequency adjustment capabilities. The superconducting cavity frequency can only be pre-tuned after manufacturing. During processes such as vacuum sealing of the superconducting cavity string, integration of the superconducting cavity string and thermostat, and cooling, there is no means of frequency adjustment. Frequency adjustment can only be performed via a tuner after the module has cooled down sufficiently. Because the frequency changes of the superconducting cavity string during integration, post-processing, horizontal testing, transportation, and cooling are highly uncertain, if the frequency deviates from the expected range and cannot be compensated for by the tuner, the superconducting module will be unable to carry the beam, ultimately leading to development failure. Summary of the Invention

[0009] To address the problems existing in the prior art, the present invention aims to provide a composite superconducting cavity string reinforcing rib and a bidirectional frequency modulation method for superconducting cavity strings. The composite reinforcing rib involved in this application, which improves the mechanical stability of superconducting cavity strings and allows for bidirectional dynamic frequency adjustment, was 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 Facility (HERF), a major national science and technology infrastructure project. It can be widely applied to other superconducting cavity strings, especially those with limited frequency adjustable range, high stiffness, and requiring full-band frequency control.

[0010] The technical solution of this invention is as follows: A composite superconducting cavity string reinforcing rib, characterized in that it includes 2 horizontal beams, 2 central vertical beams, 4 edge vertical beams, 4 connecting pressure plates, and 4 superconducting cavity lower flanges located in the same plane; Two central vertical beams are provided between the two horizontal beams, with the central vertical beams perpendicular to the inner side of the horizontal beams, forming a rectangular area; two edge vertical beams are provided on the outer side of each horizontal beam, with the edge vertical beams perpendicular to the outer side of the horizontal beams; four superconducting cavity lower flanges are provided within the rectangular area, and each superconducting cavity lower flange is connected and fixed to the edge of the rectangular area by a connecting pressure plate. The four superconducting cavity lower flanges are spliced ​​end to end to form a complete circle, which is used to connect and fix the superconducting cavity string. The two ends of the crossbeam are provided with raised contact platforms, which are used as force points for contacting the end plate of the liquid helium tank in the superconducting cavity. The outer end of the edge vertical beam is provided with a protruding contact platform, which serves as a force point for connecting with the end plate of the superconducting cavity liquid helium tank; The lower flange of the superconducting cavity is provided with several threaded holes. The inner threaded holes are used to connect and fix with the small bundle tube flange of the superconducting cavity, and the outer threaded holes are used to connect and fix with the reinforcing ribs.

[0011] Preferably, the distance between the two central vertical beams is less than the distance between the two horizontal beams, in order to avoid interference during the assembly of the superconducting cavity string and the thermostat.

[0012] Preferably, the inner side of the superconducting cavity lower flange is a 90° arc structure, and the center of the complete flange after the four superconducting cavity lower flanges are spliced ​​end to end is a circle, and the outer edge is an octagonal structure.

[0013] Preferably, the three inner angles of the outer extension of the lower flange of the superconducting cavity are 78.75°, 135° and 56.25°, respectively; wherein, the tip of the 56.25° angle is removed to avoid contact with the crossbeam and the middle vertical beam in the non-stress area, to ensure that the applied force is smoothly transmitted from the composite reinforcing rib to the right end plate of the helium tank of the superconducting cavity, to achieve no interference between the composite reinforcing ribs and to avoid the forces canceling each other out inside the reinforcing ribs.

[0014] Preferably, the waist of the crossbeam has two sets of threaded holes adapted to M6 screws, each set of threaded holes including two threaded holes arranged along the narrow side of the crossbeam for connecting and fixing with the central vertical beam; each end face of the central vertical beam has a set of threaded holes adapted to M6 screws for fixing with the crossbeam by screws.

[0015] Preferably, the outer side of the connecting pressure plate is welded to the central vertical beam and the horizontal beam by argon arc welding.

[0016] Preferably, the connecting pressure plate is provided with multiple through holes on its upper and lower surfaces to accommodate M8 screws, for connecting the lower flange of the superconducting cavity by screws.

[0017] Preferably, the outer side of the lower flange of the superconducting cavity is provided with multiple threaded holes adapted to M8 screws for connection and fixation with the connecting pressure plate by screws.

[0018] A method for assembling the composite superconducting cavity string reinforcing rib and the superconducting cavity string, comprising the following steps: The lower flange of the superconducting cavity and the superconducting cavity are connected and fixed with screws and nuts; the screw tightening torque is in the order of cross-shaped tightening, and the final sealing torque of the lower flange of the superconducting cavity is 28 N.m; the torque increase steps are 6 N.m, 10 N.m, 16 N.m, 22 N.m, and 28 N.m respectively; When the final sealing torque of the lower flange of the superconducting cavity is 28 N·m, the connecting pressure plate and the lower flange of the superconducting cavity are initially connected and fixed with screws and nuts. At this time, the nuts are not tightened. The crossbeam and the central vertical beam are connected and fixed with screws and nuts; the sealing torque of the crossbeam and the central vertical beam is 10 N·m, and the torque increases in increments of 6 N·m, 8 N·m, and 10 N·m, respectively. The connecting pressure plate and the lower flange of the superconducting cavity are completely connected and fixed with screws and nuts. The nuts are tightened in sequence, with a sealing torque of 1 N·m and an adjustment step of the rotation of the adjusting nut. The frequency of the superconducting cavity is monitored at any time during the tightening process. As the frequency approaches the target frequency, the adjustment step is gradually reduced. When the contact platforms connecting the reinforcing ribs to the end plates of the superconducting cavity liquid helium tank are in a close fit, and the superconducting cavity string is close to the target frequency or within the target frequency setting range, it indicates that the superconducting cavity string frequency adjustment is in place and the installation is complete.

[0019] A method for bidirectional frequency modulation of a superconducting cavity string equipped with the aforementioned composite superconducting cavity string reinforcing ribs, comprising the following steps: The superconducting cavity string and the vector network analyzer are connected via microwave cables to monitor the frequency of the superconducting cavity string in real time. The temperature, humidity and ambient atmospheric pressure of the superconducting cavity string are also recorded, and the measured frequency is normalized to the frequency under standard conditions. Each superconducting cavity lower flange is connected and fixed to the connecting pressure plate by a number of screws and nuts; all the adjusting nuts on the four superconducting cavity lower flanges are rotated in a set step size; when the superconducting module frequency is higher than expected, each adjusting nut is loosened in a set step size, and the frequency of the superconducting cavity string is observed to decrease; if the expected frequency is not reached, the adjusting nuts are loosened again until the frequency is adjusted to the target frequency; when the superconducting module frequency is lower than expected, each adjusting nut is tightened in a set step size, and the frequency of the superconducting cavity string is observed; if the expected frequency is not reached, the adjusting nuts are tightened again until the frequency is adjusted to the target frequency; Once the superconducting module frequency matches the expected frequency, frequency adjustment is complete, and the vector network analyzer is turned off.

[0020] This invention can effectively alleviate the peak stress of a large-size, high-mass, and structurally complex 166MHz superconducting cavity string, enabling it to meet the stress safety and mechanical stability requirements throughout the entire process from clean assembly to beam operation.

[0021] The reinforcing ribs introduced in this invention do not affect the flow of liquid helium, nor do they affect the heat exchange capacity of the superconducting cavity and liquid helium, and they do not increase the difficulty of processing and welding the cavity and liquid helium tank.

[0022] The composite reinforcing rib design of this invention enables dynamic frequency adjustment of a 166MHz superconducting cavity string in all stages and in both directions. This greatly alleviates the contradiction between the limited tuning range of the superconducting cavity string and the huge uncertainty of frequency changes, and plays a key role in the precise frequency control of the superconducting cavity string.

[0023] The composite reinforcing rib of the present invention, when installed after the cavity string is cleanly assembled and vacuum sealed, reduces the difficulty of cleaning and assembling the superconducting cavity string without affecting the cleanliness of the inner surface of the cavity string.

[0024] This invention provides a method for bidirectional frequency modulation of a superconducting cavity string based on composite reinforcing ribs.

[0025] The advantages of this invention are as follows: (1) The composite reinforcing rib design of the present invention can effectively alleviate the peak stress of the large-size, high-mass, and complex 166MHz superconducting cavity string, so that it meets the stress safety and mechanical stability requirements of the entire process from clean assembly to beam operation.

[0026] (2) The composite reinforcing rib design of the present invention can realize the dynamic frequency adjustment function of the 166MHz superconducting cavity string in all stages and bidirectional adjustment, which greatly alleviates the contradiction between the limited tuning range of the superconducting cavity string and the huge uncertainty of frequency change, and plays a key role in the precise frequency control of the superconducting cavity string.

[0027] (3) The composite reinforcing rib design of the present invention, while realizing module safety and dynamic frequency adjustment, fully considers the ultra-high requirements of vacuum sealing and cleanliness of the superconducting cavity string. It is designed to be located outside the superconducting cavity string and assembled after the module is vacuum sealed, which greatly avoids the increase in the difficulty of superconducting cavity development, does not affect the flow of liquid helium in the liquid helium tank of the superconducting cavity, and greatly reduces the risk of introducing additional pollution during the assembly stage and causing the performance of the superconducting cavity string to decline. Attached Figure Description

[0028] Figure 1 Diagram of a conventional superconducting cavity reinforcing rib structure; (a) Sheet-shaped reinforcing ribs of a 325MHz half-wavelength superconducting cavity, (b) Ring-shaped reinforcing ribs of a 650MHz ellipsoidal superconducting cavity, (c) Vertical reinforcing ribs of a 325MHz spoke-shaped superconducting cavity, (d) Bowl-shaped reinforcing ribs of a 166MHz quarter-wavelength superconducting cavity.

[0029] Figure 2 This is a diagram of a composite reinforcing rib structure. (a) Schematic diagram of composite reinforcing rib structure, (b) exploded view.

[0030] Figure 3 Here is a diagram showing the parameters of the crossbeam; (a) Oblique view of the beam structure, (b) Front view of the beam structure.

[0031] Figure 4 Figure showing the parameters of the edge vertical beam; (a) Oblique view of the edge vertical beam, (b) Front view of the edge vertical beam.

[0032] Figure 5 This is a parameter diagram for the central vertical beam; (a) Oblique view of the central vertical beam structure, (b) Side view of the central vertical beam structure.

[0033] Figure 6 Diagram showing the parameters for connecting the pressure plate; (a) Isometric view of the connecting pressure plate structure from below, (b) Isometric view of the connecting pressure plate structure from above.

[0034] Figure 7 This is a diagram showing the parameters of the lower flange of the superconducting cavity.

[0035] Figure 8 This diagram shows the sequence of sealing and tightening the lower flange of the superconducting cavity and the connecting screws of the superconducting cavity.

[0036] Figure 9 This diagram shows the connection and fixation of the lower flange and the superconducting cavity.

[0037] Figure 10 This diagram shows the connection between the composite reinforcing rib connecting plate and the lower flange of the superconducting cavity.

[0038] Figure 11 This diagram shows the connection and fixing between the horizontal beam and the central vertical beam of the composite reinforcing rib.

[0039] Figure 12 This is a frequency monitoring diagram of a superconducting cavity string.

[0040] Figure 13 This is a diagram showing the tightening sequence of the adjusting nut.

[0041] Figure 14 A diagram showing the fit of the eight contact platforms connected to the end plate of the liquid helium tank in the superconducting cavity.

[0042] Figure 15 This is a structural diagram of the superconducting cavity string and composite reinforcing ribs after installation.

[0043] Figure 16 This is a flowchart of bidirectional frequency adjustment for a superconducting cavity. Detailed Implementation

[0044] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0045] A 166MHz superconducting cavity, used as a fundamental frequency accelerating cavity, is employed in the storage ring of a high-energy synchrotron radiation source to accelerate the electron beam. It achieves low-frequency resonance and high-order mode depth suppression within a compact longitudinal length constraint. During the development of the superconducting module, due to the large size, large mass, and complex structure of the superconducting cavity string, reasonable reinforcing ribs need to be designed to reduce peak stress and meet the stress safety and mechanical stability requirements throughout the entire process from clean assembly to beam operation. The composite reinforcing ribs of this invention, acting on the superconducting cavity string, are an effective supplement to the existing superconducting cavity reinforcing ribs. They effectively alleviate the peak stress under vacuum conditions, reducing it from 140 MPa to 49 MPa, thus achieving the stress safety and mechanical stability requirements of the superconducting cavity string.

[0046] (1) Structure and material of composite reinforcing ribs The superconducting cavity's reinforcing rib structure includes: 2 horizontal beams, 2 central vertical beams, 4 edge vertical beams, 4 connecting pressure plates, 16 adjusting nuts, and 4 lower flanges for the superconducting cavity; (e.g.) Figure 2 As shown.

[0047] The crossbeam is the main supporting structure for the reinforcing ribs. Both ends of the crossbeam have raised contact platforms, which serve as the force points for contact with the end plate of the superconducting cavity's liquid helium tank. The outer middle section of the crossbeam and the two edge vertical beams are welded together as a whole. The outer ends of the edge vertical beams also have raised contact platforms, serving as the force points for connection with the end plate of the superconducting cavity's liquid helium tank. The inner middle section of the crossbeam is welded together with a connecting pressure plate, used for fixing to a lower flange of the superconducting cavity via the connecting pressure plate. The waist of the crossbeam has two sets of threaded holes for M6 screws. Each set of threaded holes includes two holes arranged along the narrow side of the crossbeam, with a 16 mm spacing between the two holes, a 7.5 mm distance from the long side of the crossbeam to the hole's center, and a 102.5 mm distance from the nearest narrow side of the crossbeam to the hole's center. The total distance between the two sets of holes is 195 mm. The crossbeam is 400 mm long, 15 mm wide, and 30 mm thick; the raised contact platforms are 40 mm long, 15 mm wide, and 0.5 mm thick. Dimensions are as follows. Figure 3 As shown.

[0048] Edge vertical beams: These are the main supporting structure for the reinforcing ribs. The inner end of the edge vertical beam is welded to the crossbeam using argon arc welding to form a single unit, serving as an integral connection with the reinforcing rib. During welding, filler wire is applied to the bevel, and the fillet weld is stacked high. The outer end of the edge vertical beam has a raised contact platform, serving as the force point for connection to the end plate of the superconducting cavity liquid helium tank. The edge vertical beam is 92 mm long, 15 mm wide, and 30 mm thick; the raised contact platform is 40 mm long, 15 mm wide, and 0.5 mm thick; the height of the raised portion of the welded structure is 3 mm; dimensions are as follows. Figure 4 As shown.

[0049] The central vertical beam is the main supporting structure for the reinforcing ribs. Both ends of the central vertical beam are fixed to the horizontal beam via bolts. The inner side of the central vertical beam is welded to the connecting pressure plate to form a single unit, used for connection to the lower flange of a superconducting cavity. The central vertical beam is 180 mm long, 15 mm wide, and 29.5 mm thick. Each end face of the central vertical beam has a set of M6 threaded holes for fixing to the horizontal beam via bolts. Dimensions are as follows... Figure 5 As shown.

[0050] Connecting pressure plate: This is the main connecting structure for the reinforcing ribs. The outer side of the connecting pressure plate is welded to the central vertical / horizontal beam as a whole using argon arc welding. During welding, filler wire is applied to the bevel, and the fillet weld is built up. The connecting pressure plate has four through holes on both the top and bottom for M8 threaded rods, used to connect the superconducting cavity lower flange via screws. The connecting pressure plate is 100 mm long, 16 mm wide, and 12 mm thick. The height of the raised portion of the welded structure is 2 mm. Dimensions are as follows... Figure 6 As shown.

[0051] The lower flange of the superconducting cavity is the main connecting structure of the reinforcing rib. The four threaded holes on the inner side of the lower flange, adapted for M10 screws, are used for fixing to the small bundle tube flange of the superconducting cavity; the four threaded holes on the outer side of the lower flange, adapted for M8 screws, are used for fixing to the connecting pressure plate. The lower flange is 10 mm thick. Four identical lower flanges can be joined end-to-end to form a complete circumference. The lower flange has various dimensions, which are marked on [the diagram / reference needed]. Figure 7 The 4.9 mm notch in the lower flange of the superconducting cavity further prevents contact with the horizontal and vertical beams in non-stressed areas, ensuring that the applied force is smoothly transmitted from the composite reinforcing ribs to the right end plate of the helium tank in the superconducting cavity. There is no interference between the composite reinforcing ribs, and the forces are prevented from canceling each other out inside the reinforcing ribs.

[0052] Adjusting nuts: These are the main connecting structure for the reinforcing ribs, and the nut specification is M8. There are 4 nuts in each set, for a total of 16 nuts across four sets. The adjusting nuts are fixed to the connecting pressure plate via M8 stainless steel screws. The adjusting nuts are one of the main components for adjusting the frequency.

[0053] The composite reinforcing ribs (including adjusting nuts) are all made of titanium. The reasons for choosing titanium for the composite reinforcing ribs are as follows: 1) Titanium has high rigidity, meeting the mechanical performance requirements of the reinforcing ribs; 2) Since the superconducting cavity's liquid helium tank is made of titanium, the reinforcing ribs and the liquid helium tank are made of the same material and have the same coefficient of thermal expansion. This ensures that during the cooling process of the superconducting cavity, the contraction and expansion amplitudes of the composite reinforcing ribs and the liquid helium tank are as consistent as possible, avoiding gaps caused by different coefficients of thermal expansion that would ultimately reduce the effectiveness of the reinforcing ribs; 3) The M8 nut is made of titanium, unlike the stainless steel screw used in its production. This is to prevent the screw and nut of the same material from seizing after thermal cycling, making them difficult to remove.

[0054] (2) Installation of composite reinforcing ribs After the 166MHz superconducting cavity and components such as the large insulating tube, small insulating tube, coupler, high-order mode absorber, tapered tube, gate valve, and extraction flange are cleanly assembled and before the cavity string is evacuated, the composite reinforcing rib is installed.

[0055] 1) Preparations before installation: a) Trial fitting The composite reinforcing rib and the superconducting cavity are combined together, and the fit is checked to ensure that the composite reinforcing rib hole positions are accurate, the fit is good, the assembly is smooth, and there are no interference problems.

[0056] b) Cleaning The cleaning was carried out in a Class 100 cleanroom (ISO5).

[0057] First, the composite reinforcing ribs are degreased outside the cleanroom.

[0058] Then, fill the ultrasonic bath with deionized water, add Liquinox cleaning agent at a concentration of 5%, and then put in the components of the composite reinforcing ribs. Set the temperature to 50°C and sonicate for 30 minutes.

[0059] Then, rinse with pure water for 3 to 5 minutes.

[0060] Finally, air dry in a Class 100 cleanroom.

[0061] 2) Installation process: a) Connection and fixation between the lower flange of the superconducting cavity and the superconducting cavity The lower flange of the superconducting cavity and the superconducting cavity are connected and fixed by 16 M10 stainless steel bolts, each 65 mm long, and 16 M10 titanium nuts. The final sealing torque of the lower flange of the superconducting cavity is 28 N·m. This final sealing torque of 28 N·m is calculated based on parameters such as bolt size, number of bolts, and bolt material, which can prevent vacuum leakage at low temperatures (-269℃).

[0062] Screw tightening sequence and torque increment: Tighten the screws in a crisscross pattern, increasing the torque as needed. Figure 8 As shown, the torque increase steps are 6 N·m, 10 N·m, 16 N·m, 22 N·m, and 28 N·m, respectively. The screw tightening sequence and torque increase step size can improve the success rate of vacuum sealing and reduce the risk of vacuum cold leakage.

[0063] When vacuum sealing the small bundle tube flange of the superconducting cavity, the lower flange of the superconducting cavity is required. Its purpose is to connect with the composite reinforcing rib to achieve its corresponding functions. This position is carefully selected based on electromagnetic field performance and mechanical performance. Other positions cannot achieve the desired purpose. The screw sealing tightening sequence is designed for sealing the small bundle tube flange and the lower flange of the superconducting cavity.

[0064] The structure of the superconducting cavity lower flange and the superconducting cavity after installation is as follows: Figure 9 As shown.

[0065] b) Initially connect and fix the composite reinforcing rib connecting plate and the lower flange of the superconducting cavity (note the installation direction). The composite reinforcing rib connecting plate and the lower flange of the superconducting cavity are connected by 16 M8 stainless steel screws, each 40 mm long, and 16 M8 titanium nuts. These 16 M8 titanium nuts are adjusting nuts, which are only lightly turned on by hand and are not tightened.

[0066] Installation Instructions: During installation, pay attention to the relative positions of the reinforcing ribs. The horizontal beams should be placed horizontally, and the vertical beams vertically. After installation, the distance between the vertical beams should be small, and the distance between the horizontal beams should be large. This is to avoid interference during future assembly of the superconducting cavity string and the thermostat. The structure after installation is as follows: Figure 10 As shown.

[0067] c) Connection and fixing of the composite reinforcing ribs to the horizontal beams and the central vertical beams. The composite reinforcing ribs of the crossbeam and the central vertical beam are connected by eight 35mm long M6 stainless steel bolts and eight M6 titanium nuts. The final sealing torque at this location is 10 N·m. The torque increases in increments of 6 N·m, 8 N·m, and 10 N·m. The structure after installation is as follows. Figure 11 As shown.

[0068] d) The connecting pressure plate and the lower flange of the superconducting cavity are fully connected and fixed (installation conditions and installation completion evaluation criteria) After the connecting screws between the crossbeam and the central vertical beam of the composite reinforcing rib are tightened to the final torque, the adjusting nuts are tightened to completely connect and fix the connecting pressure plate and the lower flange of the superconducting cavity. The purpose is to avoid deformation of the composite reinforcing rib structure, especially at the contact platform position at the far end of the crossbeam and the edge vertical beam, and to ensure that the contact platform and the end plate of the liquid helium tank of the superconducting cavity are in the same state.

[0069] Installation conditions and tightening sequence of adjusting nuts Before adjusting the torque on the adjusting nut, a coaxial adapter needs to be installed on the superconducting cavity coupler side, and then connected to the vector network analyzer outside the clean room via a high-frequency cable, such as... Figure 12 As shown. Throughout the entire torque application process, the frequency of the superconducting cavity string is monitored. It is particularly important to note that during frequency measurement, the temperature, humidity, and ambient atmospheric pressure of the superconducting cavity string must also be recorded. The measured frequency is then normalized to the standard temperature and pressure (STP) level to reduce error interference. When the superconducting cavity string approaches the target frequency, or is within 5 kHz of the target frequency, it indicates that the superconducting cavity string frequency adjustment is in place.

[0070] Tightening sequence of adjusting nuts: When applying torque, to ensure that the force of the composite reinforcing rib is evenly applied to the liquid helium tank of the superconducting cavity, tighten the adjusting nuts on each connecting pressure plate sequentially. The tightening torque is 1 N·m, and the step size for each tightening is one revolution of the nut. As the superconducting cavity frequency gradually approaches the target frequency, the step size can be gradually reduced, for example, adjusted to 1 / 2 revolution, 1 / 6 revolution, etc. The tightening sequence of adjusting nuts is as follows: Figure 13 As shown. Specifically, after tightening every four, i.e., after tightening 4, 8, and 12 adjusting nuts, tighten all loose screws by hand again; after all 16 adjusting nuts have been tightened to torque, check them again by applying a torque of 1 N·m for each full turn. The torque applied to each adjusting nut is 1 N·m.

[0071] Installation completion evaluation criteria In the composite reinforcing rib, the superconducting cavity lower flange and the superconducting cavity string are connected by M10 stainless steel bolts and titanium nuts, with a torque of up to 28 N·m.

[0072] In the composite reinforcing rib, the crossbeam and the central vertical beam are connected by M6 stainless steel bolts and titanium nuts, with a torque of up to 10 N·m.

[0073] In the composite reinforcing rib, the connecting pressure plate and the lower flange of the superconducting cavity are connected by M8 stainless steel bolts and titanium nuts. Tightening is performed step-by-step using a torque of 1 N·m in a prescribed sequence, with the superconducting cavity frequency monitored using a vector network analyzer during torque increase. This continues until it is confirmed that the eight contact platforms connected to the liquid helium tank end plate of the superconducting cavity are in a close fit. Figure 14 As shown.

[0074] The vector network analyzer indicates that when the superconducting cavity string approaches the target frequency or is within 5kHz of the target frequency, it means that the superconducting cavity string frequency adjustment is in place and the installation is complete.

[0075] e) Post-installation structure After installation, the overall structure after the superconducting cavity string and composite reinforcing ribs are installed is as follows: Figure 15 As shown.

[0076] 3) Two-way frequency modulation method for composite reinforcing ribs throughout the entire process Quarter-wavelength (QWR) superconducting cavities are characterized by a narrow frequency modulation range, typically less than 1 MHz. This narrow frequency modulation range is incompatible with the significant frequency variation uncertainties during fabrication, post-processing, and cooling processes.

[0077] Typically, frequency modulation is not available during the vacuum sealing of the superconducting cavity string, integration of the superconducting cavity string and the thermostat, and cooling processes. Frequency adjustment can only be performed via a tuner after the module has cooled down sufficiently. Because the frequency changes of the superconducting cavity string during integration, post-processing, horizontal testing, transportation, and cooling are highly uncertain, if the frequency deviates from the expected range and cannot be compensated for by the tuner, the superconducting module will be unable to carry the beam, ultimately leading to development failure.

[0078] The composite reinforcing rib ensures the safety of the superconducting cavity string under stress, while also providing full-stage, bidirectional frequency tuning capabilities without disrupting the vacuum of the superconducting cavity string. This effectively expands the frequency tuning range of the superconducting cavity, compensates for the inherent limitations of the QWR cavity type, and allows for adjustment throughout the entire process, from after the superconducting cavity string is vacuum-sealed until the module is fully developed. This plays a crucial role in the precise frequency control of the superconducting cavity string. Furthermore, the composite reinforcing rib has a simple structure and does not introduce any additional complex tuning mechanisms or devices, making it easy to operate and use.

[0079] After the superconducting cavity string is cleanly assembled, it undergoes a series of processes including vacuuming the cavity string, baking, collimation adjustment, integration with the thermostat, installation of the temperature sensor, installation of multi-layer insulation and cold shield, connection of cryogenic pipelines, vacuuming, installation of the tuner, thermostat cooling, and transportation. Throughout this process, the resonant frequency of the superconducting cavity string is monitored. If the frequency differs significantly from the expected frequency, bidirectional frequency adjustment can be achieved using composite reinforcing ribs. This effectively prevents excessive deviation of the superconducting cavity string frequency, ensuring that the resonant frequency is within the tuner's operating range after the superconducting module cools to 4K inside the tunnel, thus ensuring the module can resonate and operate.

[0080] Frequency modulation is achieved by adjusting the tightness of the 16 adjusting nuts in the composite reinforcing rib. The specific method is as follows: The superconducting cavity string and vector network analyzer are connected via microwave cables to monitor the frequency of the superconducting cavity string in real time. During the frequency measurement process, it is also necessary to record the temperature, humidity, and ambient atmospheric pressure of the superconducting cavity string, and normalize the measured frequency to the standard state (STP) frequency to reduce errors.

[0081] When the superconducting module frequency is higher than expected, loosen the adjusting nut. Figure 13 The nuts are adjusted in the following sequence: loosen each nut by 1 / 6 of its face, with an adjustment torque of 1 N·m, and observe the change in the frequency reduction of the superconducting cavity. If the frequency does not decrease to the target frequency after all 16 nuts have been loosened by 1 / 6 of their faces, continue adjusting in this manner. Figure 13 The nuts are adjusted in sequence, loosening the second 1 / 6 face of each nut sequentially, observing the frequency decrease of the superconducting cavity string until the frequency is adjusted to the target frequency. When the adjusting nuts are loosened, the composite reinforcing ribs drive the superconducting cavity small bundle tube to move inward, increasing the conductor length inside the superconducting cavity. At the same time, the acceleration gap of the superconducting cavity decreases, and the frequency of the superconducting cavity decreases accordingly.

[0082] When the superconducting module frequency is lower than expected, tighten the adjusting nut. Figure 13 The nuts are adjusted in the following sequence: tighten each nut one-sixth of its face, with an adjustment torque of 1 N·m, and observe the change in the frequency increase of the superconducting cavity string. If the frequency does not rise to the target frequency after all 16 nuts have been tightened one-sixth of their faces, continue adjusting in this manner. Figure 13 The nuts are adjusted in sequence, tightening the second 1 / 6 face of each nut in turn, observing the frequency increase of the superconducting cavity string until the frequency is adjusted to the target frequency. When the adjusting nuts are tightened, the composite reinforcing ribs drive the superconducting cavity small bundle tube to move outward, the conductor length inside the superconducting cavity decreases, and at the same time the acceleration gap of the superconducting cavity increases, and the frequency of the superconducting cavity increases accordingly.

[0083] Once the superconducting module frequency matches the expected frequency, frequency adjustment is complete, and the vector network analyzer is turned off.

[0084] The bidirectional frequency adjustment process of the superconducting cavity is as follows: Figure 16 As shown.

[0085] This invention effectively alleviates the peak stress under vacuum conditions in the cavity string, reducing it from 140 MPa to 49 MPa, thus meeting the mechanical stability requirements of the cavity string during vacuuming. The newly added reinforcing rib is not located within the liquid helium tank, therefore it does not affect liquid helium flow. While effectively reducing peak stress, it does not increase the difficulty of machining or welding the cavity and liquid helium tank. By adjusting the tightness of the adjusting nut on the reinforcing rib, the module's bidirectional frequency modulation function can be achieved. The reinforcing rib is installed after the cavity string is cleanly assembled and vacuum-sealed, without affecting the cleanliness of the cavity string's inner surface, greatly reducing the assembly difficulty of the superconducting cavity string.

[0086] The above are preferred embodiments of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A composite superconducting cavity string reinforcing rib, characterized in that, It includes two horizontal beams, two central vertical beams, four edge vertical beams, four connecting pressure plates, and four superconducting cavity lower flanges located in the same plane; Two central vertical beams are provided between the two horizontal beams, with the central vertical beams perpendicular to the inner side of the horizontal beams, forming a rectangular area; two edge vertical beams are provided on the outer side of each horizontal beam, with the edge vertical beams perpendicular to the outer side of the horizontal beams; four superconducting cavity lower flanges are provided within the rectangular area, and each superconducting cavity lower flange is connected and fixed to the edge of the rectangular area by a connecting pressure plate. The four superconducting cavity lower flanges are spliced ​​end to end to form a complete circle, which is used to connect and fix the superconducting cavity string. The two ends of the crossbeam are provided with raised contact platforms, which are used as force points for contacting the end plate of the liquid helium tank in the superconducting cavity. The outer end of the edge vertical beam is provided with a protruding contact platform, which serves as a force point for connecting with the end plate of the superconducting cavity liquid helium tank; The lower flange of the superconducting cavity is provided with several threaded holes. The inner threaded holes are used to connect and fix with the small bundle tube flange of the superconducting cavity, and the outer threaded holes are used to connect and fix with the reinforcing ribs.

2. The composite superconducting cavity string stiffener of claim 1, wherein, The distance between the two central vertical beams is less than the distance between the two horizontal beams, in order to avoid interference during the assembly of the superconducting cavity string and the thermostat.

3. The composite superconducting cavity string stiffener of claim 1, wherein, The inner side of the superconducting cavity lower flange is a 90° arc structure. The complete flange after the four superconducting cavity lower flanges are spliced ​​end to end is a circle at the center and an octagonal structure at the outer edge.

4. The composite superconducting cavity string reinforcing rib according to claim 3, characterized in that, The three inner angles of the outer extension of the lower flange of the superconducting cavity are 78.75°, 135° and 56.25°, respectively. The tip of the 56.25° angle is removed to avoid contact with the crossbeam and the middle vertical beam in the non-stressed area, ensuring that the applied force is smoothly transmitted from the composite reinforcing rib to the right end plate of the helium tank of the superconducting cavity, achieving no interference between the composite reinforcing ribs and avoiding mutual cancellation of forces inside the reinforcing ribs.

5. The composite superconducting cavity string reinforcing rib according to claim 1, 2, or 3, characterized in that, The crossbeam has two sets of threaded holes adapted to M6 screws at its waist. Each set of threaded holes includes two threaded holes arranged along the narrow side of the crossbeam for connection and fixation with the central vertical beam. The central vertical beam has a set of threaded holes adapted to M6 screws on each end face for fixation with the crossbeam by screws.

6. The composite superconducting cavity string reinforcing rib according to claim 1, 2, or 3, characterized in that, The outer side of the connecting pressure plate is welded to the central vertical beam and the horizontal beam by argon arc welding.

7. The composite superconducting cavity string reinforcing rib according to claim 1, 2, or 3, characterized in that, The connecting pressure plate has multiple through holes on its upper and lower surfaces that are adapted to M8 screws, for connecting the lower flange of the superconducting cavity with screws.

8. The composite superconducting cavity string reinforcing rib according to claim 7, characterized in that, The outer side of the lower flange of the superconducting cavity is provided with multiple threaded holes adapted to M8 screws, which are used to connect and fix it to the connecting pressure plate by screws.

9. A method for assembling the composite superconducting cavity string reinforcing rib and the superconducting cavity string as described in claim 1, comprising the following steps: The lower flange of the superconducting cavity and the superconducting cavity are connected and fixed using screws and nuts; among them... The screw tightening torques are arranged in a crisscross pattern, and the final sealing torque of the lower flange of the superconducting cavity is 28 N·m. The torque increases in increments of 6 N·m, 10 N·m, 16 N·m, 22 N·m, and 28 N·m, respectively. When the final sealing torque of the lower flange of the superconducting cavity is 28 N·m, the connecting pressure plate and the lower flange of the superconducting cavity are initially connected and fixed with screws and nuts. At this time, the nuts are not tightened. The crossbeam and the central vertical beam are connected and fixed with screws and nuts; the sealing torque of the crossbeam and the central vertical beam is 10 N·m, and the torque increases in increments of 6 N·m, 8 N·m, and 10 N·m, respectively. The connecting pressure plate and the lower flange of the superconducting cavity are completely connected and fixed with screws and nuts; the adjusting nuts are tightened in sequence, with a sealing torque of 1 N·m and an adjustment step of the range of rotation of the adjusting nuts; During the tightening process, the frequency of the superconducting cavity is monitored at all times. As it gradually approaches the target frequency, the adjustment step size is gradually reduced. When the contact platforms connecting the reinforcing ribs to the end plates of the superconducting cavity liquid helium tank are in a close fit, and the superconducting cavity string is close to or within the target frequency setting, it indicates that the frequency adjustment of the superconducting cavity string is in place and the installation is complete.

10. A method for bidirectional frequency modulation of a superconducting cavity string equipped with the composite superconducting cavity string reinforcing ribs as described in claim 1, comprising the following steps: The superconducting cavity string and the vector network analyzer are connected via microwave cables to monitor the frequency of the superconducting cavity string in real time. Furthermore, the temperature, humidity, and ambient atmospheric pressure of the superconducting cavity string are recorded, and the measured frequency is normalized to the frequency under standard conditions. Each superconducting cavity lower flange is connected and fixed to the connecting pressure plate by a number of screws and nuts; all the adjusting nuts on the four superconducting cavity lower flanges are rotated in a set step size; when the superconducting module frequency is higher than expected, each adjusting nut is loosened in a set step size, and the frequency of the superconducting cavity string is observed to decrease; if the expected frequency is not reached, the adjusting nuts are loosened again until the frequency is adjusted to the target frequency; when the superconducting module frequency is lower than expected, each adjusting nut is tightened in a set step size, and the frequency of the superconducting cavity string is observed; if the expected frequency is not reached, the adjusting nuts are tightened again until the frequency is adjusted to the target frequency; Once the superconducting module frequency matches the expected frequency, frequency adjustment is complete, and the vector network analyzer is turned off.

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