阅读说明：本技术 一种Nb3Sn超导加速腔的热处理方法 (Nb-shaped alloy3Heat treatment method of Sn superconducting accelerating cavity ) 是由 杨自钦 何源 郭浩 李春龙 宋玉堃 谭腾 牛小飞 张军辉 张生虎 于 2020-06-11 设计创作，主要内容包括：本发明公开了一种Nb-(3)Sn超导加速腔的热处理方法。该方法包括以下步骤：1)对Nb-(3)Sn超导加速腔进行洁净装配前的后处理,如超声波清洗、高压纯净水冲洗；2)Nb-(3)Sn超导加速腔的洁净装配；3)Nb-(3)Sn超导加速腔洁净装配后的真空检漏；4)Nb-(3)Sn超导加速腔的高真空低温烘烤。本发明的热处理工艺能够显著降低Nb-(3)Sn超导加速腔的表面电阻,从而降低Nb-(3)Sn超导加速腔的功率损耗；能够消除Nb-(3)Sn超导加速腔在加速梯度小于5MV/m时品质因子随梯度显著下降的问题,从而增大Nb-(3)Sn超导加速腔的有效加速梯度。(The invention discloses a Nb 3 A heat treatment method of a Sn superconducting accelerating cavity. The method comprises the following steps: 1) to Nb 3 Carrying out post-treatment, such as ultrasonic cleaning and high-pressure pure water washing, on the Sn superconducting acceleration cavity before clean assembly; 2) nb 3 Clean assembly of the Sn superconducting accelerating cavity; 3) nb 3 Vacuum leak detection is carried out after clean assembly of the Sn superconducting accelerating cavity; 4) nb 3 And (3) high-vacuum low-temperature baking of the Sn superconducting accelerating cavity. The heat treatment process can obviously reduce Nb 3 Surface resistance of Sn superconducting accelerating cavity, thereby reducing Nb 3 Power loss of the Sn superconducting accelerating cavity; can eliminate Nb 3 The quality factor of the Sn superconducting accelerating cavity follows the gradient when the acceleration gradient is less than 5MV/mProblem of significant drop, increasing Nb 3 Effective acceleration gradient of the Sn superconducting acceleration cavity.)

1. For Nb₃The heat treatment method of the Sn superconducting accelerating cavity comprises the following steps:

1) to Nb₃Cleaning the Sn superconducting acceleration cavity before clean assembly;

2) for cleaned Nb₃Cleaning Sn superconductive accelerating cavityPreparing;

3) for clean assembled Nb₃Performing vacuum leak detection on the Sn superconducting accelerating cavity;

4) for Nb after leakage detection₃The Sn superconducting accelerating cavity is baked at high vacuum and low temperature; wherein the baking temperature is 90-150 ℃, the baking time is 12-54 hours, and the Nb is₃The vacuum degree in the Sn superconducting acceleration cavity is better than 10^-6mbar。

2. The method of claim 1, wherein: in the step 4), the baking temperature is 100-120 ℃; the baking time is 24-48 hours.

3. The method according to claim 1 or 2, characterized in that: in the step 4), Nb is required to be treated in the whole baking process₃Continuously vacuumizing the Sn superconducting accelerating cavity;

the pump set used for vacuumizing needs to be completely provided with an oil-free pump; the Nb₃And the Sn superconducting accelerating cavity is connected with the oil-free pump set through an air exhaust pipeline.

4. The method according to any one of claims 1-3, wherein: in the step 1), the cleaning treatment includes sequentially subjecting the Nb to₃And the Sn superconducting accelerating cavity is subjected to ultrasonic cleaning and high-pressure pure water washing.

5. The method of claim 4, wherein: the water adopted for ultrasonic cleaning is ultrapure water, and a cleaning agent is not added; the water temperature of the ultrapure water is 50-60 ℃; the cleaning time of the ultrasonic cleaning is 30-60 minutes; the ultrasonic power density of the ultrasonic cleaning is 25-35W/gal; the ultrasonic cleaning is carried out in a clean environment of not less than ten thousand levels;

the pressure of the purified water adopted by the high-pressure purified water washing is 80-100 psi; the high-pressure pure water flushing is carried out in a clean environment not lower than hundred grades.

6. According to any one of claims 1 to 5The method is characterized in that: after the cleaning treatment in the step 1) is finished, the method also comprises the following steps before the cleaning assembly in the step 3): the cleaned Nb is added₃Placing the Sn superconducting accelerating cavity in a hundred-grade clean room for airing; the airing time is not less than 12 hours.

7. The method according to any one of claims 1-6, wherein: the cleaning assembly in the step 2) is carried out in a hundred-grade clean room.

8. The method according to any one of claims 1-7, wherein: the leak rate required for vacuum leak detection needs to be lower than 1x10^-10mbar.L/s; in the vacuum leak detection process, slow vacuum pumping is needed, and the vacuum pump needs an oil-free pump set.

9. The method according to any one of claims 1-8, wherein: after the step 3), the method needs to perform the following treatment before performing the step 4): mixing Nb with₃Closing an angle valve of the Sn superconducting accelerating cavity to ensure that the cavity is in a vacuum state, and then adding Nb₃Placing the Sn superconducting accelerating cavity on a baking platform to continue vacuumizing until Nb₃The vacuum degree in the Sn superconducting acceleration cavity is better than 10^-6mbar, then Nb₃The outside of the Sn superconducting accelerating cavity is wound by a heating belt, and the heating belt and the Nb are wound by tinfoil₃The outer surface of the Sn superconducting accelerating cavity is integrally wrapped.

Technical Field

The invention relates to the technical field of superconduction, in particular to a superconducting Nb-doped high-temperature-resistant high-temperature-resistant material₃A post-processing method of a Sn superconducting accelerating cavity.

Background

The large scientific device based on the radio frequency superconducting accelerator has large scale and high cost, and the economic reason is often the limiting factor. Nb₃The radio frequency performance of the Sn superconducting accelerating cavity at 4.2K can reach the level of the pure niobium superconducting accelerating cavity at 2-K, and the Sn superconducting accelerating cavity has the potential of operating at twice the gradient of the pure niobium superconducting accelerating cavity. Thus, Nb₃The Sn superconducting accelerating cavity not only can greatly reduce the construction cost of the superconducting accelerator, but also can greatly reduce the running cost of the superconducting accelerator, is a key technology of the next generation of superconducting accelerator, and has bright application prospect.

However, Nb₃The post-processing technology of the Sn superconducting accelerating cavity is still in an initial exploration stage, and the radio frequency performance of the superconducting accelerating cavity is directly determined by the post-processing technology level of the superconducting accelerating cavity. At present, Nb₃The effective post-treatment method of the Sn superconducting accelerating cavity only comprises high-pressure pure water washing, which limits Nb₃The radio frequency performance of the Sn superconducting accelerating cavity is improved.

Disclosure of Invention

In view of the above problems, it is an object of the present invention to provide a Nb₃The post-processing method of the Sn superconducting accelerating cavity can effectively improve Nb₃Radio frequency performance of Sn superconducting accelerating cavity, thereby solving Nb₃The problem of lack of effective post-processing technology of the Sn superconducting accelerating cavity.

In order to achieve the purpose, the invention is realized by adopting the following technical scheme:

for Nb₃The heat treatment method of the Sn superconducting accelerating cavity comprises the following steps:

1) to Nb₃Cleaning the Sn superconducting acceleration cavity before clean assembly;

2) for cleaned Nb₃Clean assembly is carried out on the Sn superconducting accelerating cavity;

3) for clean assembled Nb₃Performing vacuum leak detection on the Sn superconducting accelerating cavity;

4) for Nb after leakage detection₃The Sn superconducting accelerating cavity is baked at high vacuum and low temperature; wherein the baking temperature is 90-150 ℃, the baking time is 12-54 hours, and the Nb is₃The vacuum degree in the Sn superconducting acceleration cavity is better than 10^-6mbar。

In step 1), the cleaning treatment comprises sequentially subjecting Nb to Nb₃And the Sn superconducting accelerating cavity is subjected to ultrasonic cleaning and high-pressure pure water washing.

Wherein the water adopted by the ultrasonic cleaning is ultrapure water; the temperature of the ultrapure water is 50-60 ℃ (preferably 55 ℃), and no cleaning agent is added; the cleaning time of the ultrasonic cleaning is 30-60 minutes; the ultrasonic power density of the ultrasonic cleaning is 25-35W/gal. The ultrasonic cleaning is carried out in a clean environment of not less than ten thousand levels.

The pressure of the purified water adopted by the high-pressure purified water flushing is 80-100 psi. The high-pressure pure water flushing is carried out in a clean environment not lower than hundred grades.

After the washing treatment, before clean assembly, the method further comprises the following steps: the cleaned Nb is added₃And placing the Sn superconducting accelerating cavity in a hundred-grade clean room for airing. The airing time is not less than 12 hours.

The cleaning assembly in step 2) above is performed in a hundred-grade clean room.

In the step 3), the leak rate required by vacuum leak detection needs to be lower than 1x10^-10mbar L/s. In the vacuum leak detection process, slow vacuum pumping is needed, and the vacuum pump needs an oil-free pump set.

After the vacuum leakage is detected in the step 3), the following processing is required before the step 4): mixing Nb with₃Closing an angle valve of the Sn superconducting accelerating cavity to ensure that the cavity is in a vacuum state, and then adding Nb₃Sn superconducting accelerating cavity amplifierPlacing on a baking platform, and continuously vacuumizing until Nb₃The vacuum degree in the Sn superconducting acceleration cavity is better than 10^-6mbar, then Nb₃The outside of the Sn superconducting accelerating cavity is wound by a heating belt, and the heating belt and the Nb are wound by tinfoil₃The outer surface of the Sn superconducting accelerating cavity is integrally wrapped so as to achieve the effect of uniform heating.

In the step 4), the baking temperature is preferably 100-120 ℃, and specifically may be 100 ℃; the baking time is preferably 24 to 48 hours, and specifically may be 48 hours. The whole baking process needs to be carried out on Nb₃And continuously vacuumizing the Sn superconducting accelerating cavity. The pump set used for vacuumizing needs to be completely provided with an oil-free pump. The Nb₃And the Sn superconducting accelerating cavity is connected with the oil-free pump set through an air exhaust pipeline.

And Nb₃Compared with the prior treatment after pure high-pressure pure water washing, the Sn superconducting accelerating cavity has the following beneficial effects:

the invention can obviously reduce Nb₃The surface resistance Rs of the Sn superconducting accelerating cavity obviously improves the Nb₃Quality factor Q value of Sn superconducting accelerating cavity and elimination of Nb₃The quality factor of the Sn superconducting accelerating cavity is obviously reduced along with the gradient when the accelerating gradient is less than 5MV/m, so that the Nb is reduced₃Low-temperature loss of Sn superconducting accelerating cavity and increase of Nb₃Effective acceleration gradient of the Sn superconducting acceleration cavity.

Drawings

FIG. 1 is a 1.3GHz Nb₃Comparing test results of the Sn superconducting accelerating cavity (before and after low-temperature baking);

FIG. 2 is a flow chart of the method of the present invention.

Detailed Description

The following examples are provided to more clearly illustrate the technical solutions of the present invention, and should not be construed as limiting the scope of the present invention.

The flow of the present invention is shown in FIG. 2, and the following description of the Nb is made with reference to FIG. 2₃The post-processing method of the Sn superconducting accelerating cavity is described in detail.

Nb3Sn superconducting accelerator cavity used in the following examplesThe preparation can be carried out according to the methods in the following documents: sam Posen, unrestanceting and overlapping limitations mechanisms in Nb₃Sn superconducting RF vitamins, Ph doctor paper, university of Cornell, USA, 2015; or s.posen, m.liepe and y.xie, Cornell SRF New Materials Program, Proceedings of IPAC2011.

In the following embodiments, the quality factors are all default to unloaded quality factors, and the Q value represents the power loss of the superconducting cavity wall under a certain energy storage condition.

The acceleration gradient Eacc in the following examples characterizes the energy gain that can be obtained per unit length of a charged particle.

The quality factor-Eacc test curve in the following examples is tested by a superconducting cavity low-temperature vertical test method, and the specific test method is as follows: the method comprises the steps of suspending a superconducting cavity into a vertical shaft, wherein the vertical shaft needs to effectively shield earth residual magnetism and has good heat shielding capacity, then filling cold helium into the vertical shaft until liquid helium solution appears in the vertical shaft, the liquid level of the liquid helium solution is over the superconducting cavity, then feeding power into the superconducting cavity from one end through a cable, extracting signals from the other end of the cavity, and analyzing the signals to obtain cavity wall loss (quality factor representation) of the superconducting cavity under different field strengths (Eacc representation) so as to obtain a quality factor-Eacc test curve.

Example 1, p-Nb₃Post-processing of Sn superconducting accelerating cavity

One, Nb₃Post-treatment before clean assembly of Sn superconducting accelerating cavity, mainly removing Nb₃The Sn superconduction accelerating cavity is prepared and then transported to a clean room to cause possible pollution to the inner surface and the outer surface, and the main process comprises the following steps:

and (3) a visual inspection stage: nb₃Nb at each position of inner surface of Sn superconducting accelerating cavity₃The Sn film needs to grow uniformly without macroscopic uneven distribution;

and (3) a purified water ultrasonic cleaning stage: using non-woven fabric wet by absolute ethyl alcohol to mix Nb₃Carefully scrubbing the outer surface of the Sn superconducting accelerating cavity, and then adding Nb₃The Sn superconducting accelerating cavity is integrally arranged in an ultrasonic cleaning pool (not less than ten thousand grade clean environment), and is cleaned by ultrapure water for 30-60 minutesThe water temperature is about 55 ℃, and the ultrasonic power density is as follows: 25-35W/gal, and then adding Nb with ultrapure water₃And cleaning the inner surface and the outer surface of the Sn superconducting acceleration cavity, and then airing the Nb3Sn superconducting acceleration cavity.

High-pressure purified water washing stage: to Nb₃High-pressure pure water washing is carried out on the inner surface of the Sn superconducting accelerating cavity for removing Nb₃Sn superconductivity accelerates particles adsorbed on the inner surface of the cavity, the cleaning water pressure is 80-100Psi, 2-4 cycles are cleaned (one cycle refers to that a high-pressure water nozzle moves from the bottom of the cavity to the top of the cavity at a certain rising rate and rotating rate and then moves from the top to the bottom), the cleaning environment is a hundred-grade clean environment, and then Nb is cleaned by high-pressure pure water₃And the Sn superconducting accelerating cavity is placed in an airing area of a hundred-grade clean room and aired for at least 10 hours.

II, Nb₃The clean assembly of the Sn superconducting accelerating cavity needs to be carried out under a correct assembly environment and an assembly process, and the main process comprises the following steps:

1. the assembly needs to be carried out in a non-disturbance hundred-grade clean environment, all parts except the angle valve need to be ultrasonically cleaned before preassembling, and parts subjected to ultrasonic cleaning are dried and moved into a hundred-grade clean room.

2. In a hundred-grade clean room, the surfaces of all the parts to be assembled and the vacuum surface are firstly wiped by methanol and then are purged by high-purity nitrogen until the indication of a particle counter within 10 seconds is 0.

3. The assembling process needs to be slow, each assembling flange opening is protected by a clean cover plate, each flange opening needs to be turned to the opening as far as possible and assembled downwards, and after the assembling is finished, the angle valve needs to be Nb₃And the Sn superconductivity accelerates the lower part of the cavity to prevent particles in the angle valve from being hung into the cavity.

III, Nb₃The leak hunting after the superconductive chamber assembly of Sn needs to be gone on in hundred grades of clean environment, ensures mainly that 4.2K and 2K low temperature down liquid helium can not leak into the superconductive chamber, and correct leak hunting can prevent the secondary pollution to the superconductive chamber, and its main flow includes:

1. before air exhaust, the main valve for quick air exhaust is confirmed to be in a closed state, the slow air exhaust valve is in an open state, the flow controller is in a closed gearMinimize its flow and then turn on Nb₃An angle valve on the Sn superconducting accelerating cavity is opened, and a dry pump is started.

And (3) driving the mass flow meter to a valve control gear, regulating the flow to 0.6slm (liter per minute), slowly vacuumizing the system, opening the quick air exhaust valve when the reading of the mass flow meter is reduced to 0.01slm or the vacuum of the system is reduced to below 10mbar, closing the slow air exhaust valve, switching the mass flow meter to a closing gear, and starting to quickly vacuumize the system, wherein the purpose is to prevent impurity particles in the pipeline from entering a cavity due to the fact that turbulent flow is formed in the vacuumized pipeline. When the vacuum of the system is lower than 0.1mbar, the molecular pump is turned on, and the system is continuously vacuumized.

2. When the system is vacuumized to 10^-6And when mbar is below, starting leak detection: spraying helium gas from top to bottom at each sealing port by using the gas amount of continuous bubbles, wherein each sealing port is 2 minutes, and when the leakage rate is less than 1x10^-10mbar L/s, can ensure that the super-flow helium can not leak into the superconducting cavity at the low temperature of 2K.

IV, Nb₃The low-temperature baking of the Sn superconducting accelerating cavity comprises the following specific processes:

1.Nb₃the Sn superconducting accelerating cavity needs to be continuously vacuumized in the whole low-temperature baking process, all pump sets used for vacuumizing need to adopt oil-free pumps, the interior of a vacuumizing pipeline connected with the cavity needs to be very clean, and the leakage rate is lower than 1x10^-10mbar·L/s。

2. After the leakage detection of the superconducting cavity is finished, the angle valve is closed to enable the cavity to be in a vacuum state, the cavity is placed on a low-temperature baking platform (the angle valve is noted to be downward), and the cavity is connected with an oil-free pump set through an air exhaust pipeline.

3. Ensuring that the superconducting cavity angle valve is in a closed state, starting a pump set to begin to vacuumize the pipeline, and when the vacuum of the pipeline is lower than 10 DEG C^-6When mbar occurs, the cavity angle valve is opened slowly, and the pump set begins to vacuumize the whole system formed by the superconducting cavity pipelines.

4. When the vacuum of the system is again lower than 10^-6mbar in Nb₃Winding a heating tape on the outer surface of the Sn superconducting accelerating cavity, and then winding Nb with tinfoil₃The outer surface of the Sn superconducting accelerating cavity and the heating belt are uniformly wrapped, and the heating temperature is set to be 90-150 DEG CHeating for 12-54 hr, starting to heat Nb₃And the Sn superconducting accelerating cavity is used for carrying out low-temperature baking. After the heating time is over, the power supply and the cavity angle valve are closed, and Nb pair is completed₃And (5) carrying out low-temperature baking post-treatment on the Sn superconducting accelerating cavity.

And (3) performance testing:

firstly, the invention is to a 1.3GHz Nb₃The Sn superconducting acceleration cavity (only washed by high-pressure pure water, namely the processing method from the first step to the third step) is tested under 4.2K, and the test curves of the quality factor and the Eacc are shown in figure 1; then, for this Nb₃The Sn superconducting accelerating cavity continues to perform the low-temperature baking treatment (low-temperature baking at 100 ℃ for 48 hours) of the fourth step, the test is performed under the same test condition at 4.2K, and the test result is compared with that before the low-temperature baking, as shown in figure 1;

as can be seen from FIG. 1, Nb after low-temperature baking at 100 ℃ for 48 hours₃The quality factor of the Sn superconducting acceleration cavity is improved by 8 times at most, and the phenomenon that the quality factor is remarkably reduced along with the acceleration gradient when the acceleration gradient is less than 5MV/m is eliminated. Therefore, the method provided by the invention can obviously improve Nb₃And a post-processing method of the radio frequency performance of the Sn superconducting accelerating cavity.

Although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that changes may be made in the embodiments and/or equivalents thereof without departing from the spirit and scope of the invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.