A method of characterizing the thickness of a thin film of an accelerator superconducting cavity

Abstract

The application relates to the technical field of spectrum measurement, and discloses a method for characterizing the thickness of a superconducting cavity film of an accelerator, which comprises the following steps: focusing a laser pulse on the surface of a superconducting cavity film to be detected to form an excited micro area on the surface of the superconducting cavity film to be detected; performing single-point ablation on the excited micro area by multiple laser pulses, and recording a LIBS spectrum corresponding to each laser pulse; selecting a tracer element for each recorded LIBS spectrum, and extracting to-be-detected characteristic information according to a fingerprint spectrum line of the tracer element; measuring the ablation depth corresponding to each laser pulse; establishing a corresponding relationship between the to-be-detected characteristic information and the ablation depth; and establishing a thickness prediction model, which represents the thickness of the superconducting cavity film to be detected. The application has the technical effect of realizing convenient and nearly nondestructive characterization of the thickness of the superconducting cavity film of the accelerator.

Description

Technical Field

[0001] This invention belongs to the field of spectroscopic measurement technology, and specifically relates to a method for characterizing the thickness of a thin film in an accelerator superconducting cavity. Background Technology

[0002] As the core accelerating component of a superconducting accelerator, the performance of the superconducting cavity determines the accelerator's energy efficiency and operational stability. Currently, superconducting cavities are mainly fabricated using low-temperature superconducting niobium to create radio frequency (RF) superconducting thin films, utilizing the zero-resistance characteristic in the superconducting state to reduce the surface resistance of the cavity. However, niobium-based superconducting cavities require immersion in liquid helium at 2K–4K for cooling, making operation complex. To overcome the limitations of liquid nitrogen and reduce the complexity and maintenance difficulty of superconducting accelerators while expanding their application range, RF superconducting cavity thin film materials such as Nb3Sn, MgB2, NbN, NbTiN, and iron-based superconductors can be selected. These RF superconducting cavity thin film materials possess high superconducting transition temperatures and high overheated magnetic fields, achieving RF performance at 4.2K or even higher, reaching the level of niobium-based superconducting cavities at 2K. Therefore, Nb3Sn thin-film superconducting cavities are a core technology for next-generation superconducting accelerators. Uneven tin content distribution in Nb3Sn films can easily lead to localized tin deficiency or excess, resulting in uneven thickness or defects. When the Nb3Sn film is too thin, interface defects may cause localized magnetic field penetration, triggering quench loss. Conversely, when the Nb3Sn film is too thick, increased grain boundary density or stress accumulation can reduce the critical current density, thus affecting the optimal balance between acceleration gradient and quality factor.

[0003] Currently, to ensure the superconducting performance of the superconducting cavity, the quantitative characterization of the thin film thickness of the radio frequency superconducting cavity is mainly based on energy dispersive X-ray spectroscopy (EDX) analysis technology. The principle is to inversely deduce the thickness value of the sample by combining the intensity and energy distribution of characteristic X-rays of the sample under test with the atomic layer decay model.

[0004] However, energy-dispersive X-ray spectroscopy analysis requires cutting the sample to be tested and then performing line or area scanning on the cut sample. This process introduces time-consuming and labor-intensive sampling and sample preparation procedures that are destructive and complex. In addition, it usually needs to be used in conjunction with scanning / transmission electron microscopy, which makes the process of measuring the thickness of radio frequency superconducting cavity films inconvenient. Summary of the Invention

[0005] To address the shortcomings of the prior art, this invention provides a method for characterizing the thickness of a superconducting cavity film in an accelerator. This method enables near-non-destructive quantitative characterization of the thickness of the superconducting cavity film, and the process does not require time-consuming and laborious sampling and sample preparation, making the measurement process convenient.

[0006] The technical effects to be achieved by this invention are realized through the following technical aspects:

[0007] This invention provides a method for characterizing the thickness of a thin film in an accelerator superconducting cavity, comprising the following steps:

[0008] A laser pulse is focused onto the surface of the superconducting cavity film under test, and laser pulse ablation is performed on the superconducting cavity film under test, forming an excitation micro-region on the surface of the superconducting cavity film under test.

[0009] The excitation micro-region was subjected to single-point ablation by multiple laser pulses, and the LIBS spectrum corresponding to each laser pulse was recorded.

[0010] For each recorded LIBS spectrum, tracer elements are selected, and the feature information to be detected is extracted based on the fingerprint spectral lines of the tracer elements.

[0011] The ablation depth corresponding to each laser pulse was measured;

[0012] Establish the correspondence between the feature information to be inspected and the ablation depth;

[0013] The correspondence between the feature information to be inspected and the ablation depth is analyzed to establish a thickness prediction model. The results predicted by the thickness prediction model are used to characterize the thickness of the thin film in the superconducting cavity to be inspected.

[0014] In some implementations, when the LIBS spectrum selects a single tracer element, the fingerprint spectral line of the tracer element is extracted, and the detectable feature information of the fingerprint spectral line is the spectral line intensity or plasma parameters.

[0015] In some implementations, when different tracer elements are selected for the LIBS spectrum, fingerprint spectral lines of the tracer elements are extracted, and the detectable feature information of the fingerprint spectral lines is the spectral line intensity, intensity ratio, or plasma parameters.

[0016] In some implementations, the following steps are included: establishing a correspondence between the feature information to be inspected and the number of laser pulses; establishing a correspondence between the ablation depth and the number of laser pulses, wherein the feature information to be inspected is established through the correspondence between the number of laser pulses and the ablation depth.

[0017] In some implementations, the establishment of the thickness prediction model includes the following steps: normalizing the intensity of the feature information to be inspected for each fingerprint spectral line to obtain a normalized value I; establishing the correspondence between the normalized value I and the ablation depth, and analyzing the relationship between the normalized value I and the ablation depth to quantify the thickness of the superconducting cavity film to be inspected.

[0018] In this implementation, the superconducting cavity thin film to be inspected includes a superconducting cavity thin film layer and a superconducting cavity substrate layer. The normalized value I changes abruptly at the junction of the thin film layer and the substrate layer. The ablation depth corresponding to the location where the normalized value I changes abruptly is the thickness of the superconducting cavity thin film.

[0019] In some implementations, the establishment of the thickness prediction model includes the following steps:

[0020] Select a standard superconducting cavity thin film sample to obtain standard characteristic information of tracer elements;

[0021] The superconducting cavity thin film to be tested includes a superconducting cavity thin film layer and a superconducting cavity substrate layer. When extracting the feature information to be tested, substrate tracer elements and thin film tracer elements are selected according to each recorded LIBS spectrum. Substrate feature information is extracted according to the fingerprint spectral lines of the substrate tracer elements, and thin film feature information is extracted according to the fingerprint spectral lines of the thin film tracer elements.

[0022] The correlation coefficient between substrate feature information and standard feature information was calculated using the Pearson coefficient method and denoted as r1, and the correlation coefficient between film feature information and standard feature information was denoted as r2.

[0023] Establish the correspondence between correlation coefficient r1 and ablation depth, and the correspondence between r2 and ablation depth. The ablation depth value corresponding to the intersection of r1 and r2 is the thickness of the thin film of the superconducting cavity to be inspected.

[0024] In this implementation, the standard superconducting cavity thin film sample is subjected to laser pulse ablation to obtain a standard LIBS spectrum. Tracer elements are selected based on the standard LIBS spectrum, and standard feature information is extracted based on the fingerprint spectral lines of the tracer elements.

[0025] In some implementations, when the laser pulse is focused on the superconducting cavity film under test, the optimal laser flux range of the laser pulse needs to be determined based on the variation of the spectral characteristic parameters of the LIBS spectral signal with the number of pulses under different laser fluxes.

[0026] In this implementation, the spectral characteristic parameters of the LIBS spectral signal are any one of the following: spectral line intensity, intensity ratio, signal-to-background ratio, signal-to-noise ratio, and spectral line broadening of the tracer element.

[0027] In summary, the present invention has at least the following advantages:

[0028] The method for characterizing the thickness of a superconducting cavity film provided by this invention involves ablating the superconducting cavity film under test with a laser pulse. The superconducting cavity film under test generates a micro-plasma emission spectrum (LIBS spectrum) in the excitation micro-region. Analyzing the LIBS spectrum reveals the elemental composition of the surface of the superconducting cavity film under test. By performing multiple pulse ablations with the laser pulse, a correlation between the target tracer elements and the ablation depth can be established to obtain elemental distribution results with good depth resolution. Furthermore, by establishing a thickness prediction model to process the elemental depth distribution data, quantitative characterization of the thickness of the superconducting cavity film under test can be achieved.

[0029] The laser pulse ablation method for characterizing the thickness of superconducting cavity films under test offers a near-non-destructive testing advantage compared to traditional energy-dispersive X-ray spectroscopy. It eliminates the need for sampling and preparation operations such as cutting the superconducting cavity film. Furthermore, the laser pulse allows for non-contact, in-situ detection of the superconducting cavity film, making it convenient to operate. This method enables the analysis of elemental depth distribution to characterize the film's thickness, while simultaneously analyzing the detection of a wider range of elements from trace amounts to constant amounts within the periodic table. Attached Figure Description

[0030] Figure 1 This is a flowchart illustrating a method for characterizing the thickness of a superconducting cavity film in an accelerator, according to a specific embodiment of the present invention.

[0031] Figure 2 This is a graph showing the normalized values ​​of the spectral intensities of Nb, Sn, and Cu in the superconducting cavity film under test in Embodiment 2 of the present invention, and their correspondence with the number of laser pulses.

[0032] Figure 3 This is a graph showing the relationship between the normalized ratio of the spectral intensities of Sn and Cu in the superconducting cavity film under test and the number of laser pulses in Example 2 of the present invention. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. The described embodiments are some, but not all, of the embodiments of the present invention.

[0034] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0035] Example 1:

[0036] For the method of characterizing the thickness of a superconducting cavity film in an accelerator according to this invention, please refer to [link to relevant documentation]. Figure 1 This includes the following steps:

[0037] A laser pulse is focused onto the surface of the superconducting cavity film to be inspected, and the superconducting cavity film to be inspected is ablated by the laser pulse. An excitation micro-region is formed on the surface of the superconducting cavity film to be inspected. Specifically, the superconducting cavity film includes a superconducting cavity film layer and a superconducting cavity substrate layer. During the process of focusing the laser pulse onto the surface of the superconducting film to be inspected, the laser pulse can ablate the superconducting cavity film to be inspected on the surface of the film layer.

[0038] The excited micro-region was subjected to single-point ablation by multiple laser pulses, and the LIBS spectrum corresponding to each laser pulse was recorded.

[0039] For each recorded LIBS spectrum, a tracer element is selected, and the feature information to be detected is extracted based on the fingerprint spectral line of the tracer element. When a single tracer element is selected for the LIBS spectrum, the fingerprint spectral line of the tracer element is extracted. The feature information to be detected for the fingerprint spectral line is the spectral line intensity or plasma parameters. When different tracer elements are selected for the LIBS spectrum, the fingerprint spectral lines of different tracer elements are extracted. The feature information to be detected for the fingerprint spectral line is the spectral line intensity, intensity ratio, or plasma parameters. Among them, the plasma parameters can be selected as plasma temperature, electron density, or atomic number density.

[0040] The ablation depth corresponding to each laser pulse is measured. Specifically, the laser pulse bombards the excitation micro-region of the superconducting cavity film under test to form an ablation pit, and the ablation depth is the depth of the ablation pit.

[0041] Establish the correspondence between the feature information to be inspected and the ablation depth;

[0042] In a preferred embodiment, by establishing a correspondence between the feature information to be inspected and the number of laser pulses, and establishing a correspondence between the ablation depth and the number of laser pulses (which is linear within the thin film layer of the superconducting cavity), a correspondence can be established between the feature information to be inspected and the ablation depth via the number of laser pulses.

[0043] The correspondence between the feature information to be inspected and the ablation depth is analyzed, and a thickness prediction model is established. The results predicted by the thickness prediction model can be used to characterize the thickness of the thin film in the superconducting cavity to be inspected.

[0044] In a preferred embodiment, the laser pulse's laser flux range needs to be determined based on the variation of spectral characteristic parameters of the LIBS spectral signal with the number of pulses under different laser fluxes. The spectral characteristic parameters of the LIBS spectral signal can be any one of the tracer element's spectral line intensity, intensity ratio, signal-to-background ratio, signal-to-noise ratio, or spectral line broadening. By comprehensively considering different spectral characteristic parameters, the laser pulse's laser flux is adjusted to obtain the optimal laser flux. In some specific embodiments, for low-concentration tracer elements with low spectral line intensities, the laser flux corresponding to the highest spectral line intensity is preferred. Conversely, when analyzing high-concentration tracer elements, the laser flux corresponding to the highest signal-to-background ratio is preferred, which is beneficial for data acquisition and representation.

[0045] The superconducting cavity film under test is ablated by laser pulses. The superconducting cavity film under test undergoes ablation by micro-plasma in the excitation micro-region. With repeated single-point ablation by laser pulses, ablation pits are formed in the excitation micro-region.

[0046] During laser pulse ablation, the LIBS spectrum and ablation depth of each laser pulse are recorded. The tracer element characteristics are extracted from the LIBS spectrum, reflecting the elemental composition and distribution of the superconducting cavity film in the thickness direction, thus obtaining qualitative and quantitative information about the elements. By analyzing the relationship between the tracer characteristics and the ablation depth, and establishing a thickness prediction model, the quantitative characterization of the superconducting cavity film thickness can be achieved.

[0047] The thickness of the superconducting cavity thin film under test is characterized by analyzing its elemental composition. Compared with traditional quantitative characterization methods, laser pulses ablate the film at multiple single points, forming micron-sized ablation pits. This eliminates the need for cutting, sampling, and sample preparation of the superconducting cavity thin film, reducing damage and enabling near-non-destructive testing while saving time. Furthermore, laser pulse ablation of the superconducting cavity thin film allows for non-contact, in-situ testing, eliminating the need for an electron microscope. This adapts to online or on-site testing scenarios and improves testing accuracy.

[0048] Example 2:

[0049] The difference between this embodiment and Embodiment 1 is that the establishment of the thickness prediction model in this embodiment includes the following steps:

[0050] The intensity of the feature information to be detected for each fingerprint spectral line is normalized to obtain the normalized value I;

[0051] Establish the correspondence between the normalized value I and the ablation depth, and analyze the relationship between the normalized value I and the ablation depth to quantify the thickness of the thin film in the superconducting cavity under test.

[0052] In some specific embodiments, the superconducting cavity thin film to be tested includes a superconducting cavity thin film layer and a superconducting cavity substrate layer. The normalized value I changes abruptly at the junction of the substrate layer and the thin film layer. The ablation depth corresponding to the location where the normalized value I changes abruptly is the thickness of the superconducting cavity thin film.

[0053] Specifically, the superconducting cavity film to be tested was selected as a sample in which bronze was deposited on a niobium substrate by magnetron sputtering and then annealed to form a Nb3Sn film. The superconducting cavity film to be tested contained a composite layer structure of bronze-Nb3Sn-Nb.

[0054] The method for characterizing the thickness of the Nb3Sn thin film in the superconducting cavity under test includes the following steps:

[0055] The laser pulse is focused onto the surface of the thin film in the superconducting cavity under test. Specifically, a laser pulse is emitted through a LIBS (Liquidity-Induced Broadband) device. To ensure uniform ablation depth, the pulsed laser emitted from the LIBS is expanded by a beam expander and focused onto the surface of the thin film, ablating the surface to form an excitation micro-region. The laser flux of the pulsed laser is selected based on the signal-to-noise ratio and spectral line intensity of the LIBS spectral signal. Specifically, the laser energy of the pulsed laser can be 30–100 mJ, corresponding to a laser flux of 24–39 J / cm². 2 .

[0056] The excited micro-region was subjected to 200 laser pulse ablations. The LIBS spectrum corresponding to each laser pulse was recorded and sequentially labeled as S1, S2, S3, S4...S 200 It is understandable that those skilled in the art can select an appropriate number of laser pulses based on the actual measurement conditions.

[0057] For each recorded LIBS spectrum, a tracer element is selected, and the feature information to be detected is extracted based on the fingerprint spectral lines of the tracer element. Specifically, for the LIBS spectrum corresponding to the first ablation by the laser pulse, Cu, Sn, and Nb are selected as tracer elements, and the integrated area of ​​the three fingerprint spectral lines—Cu I 324.7 nm (a characteristic spectral line emitted by neutral Cu atoms at a wavelength of 324.7 nm), Sn I 217.5 nm, and Nb I 316.3 nm—is extracted as the spectral line intensity, i.e., the feature information to be detected.

[0058] The intensities of the three spectral lines were normalized to obtain the normalized intensity values ​​of the three fingerprint lines, which were denoted as I. Cu1 I Sn1 I Nb1 .

[0059] Repeat the above operation to normalize the intensity of the spectral lines in each remaining LIBS spectrum, and denote the resulting remaining normalized values ​​as I in sequence. Cu2 I Sn2 I Nb2 / I Cu3 I Sn3 I Nb3 / …… / I Cu200 I Sn200 I Nb200 Please see Figure 2 Establish the correspondence between the above normalized values ​​and the ablation depth.

[0060] The ablation depth corresponding to each laser pulse is measured. Specifically, a profilometer can be used to determine the ablation depth corresponding to different laser pulse numbers to establish the correspondence between ablation depth and laser pulse number. Finally, the normalized values ​​of tracer elements Cu, Sn and Nb are established respectively to establish the correspondence between ablation depth and thickness prediction model.

[0061] Please see Figure 2 The normalized value of Nb increases significantly when the number of laser pulses is 15, that is, the 15th laser pulse. At this time, the laser pulse acts on the Nb3Sn layer through the bronze layer.

[0062] Since the normalized values ​​of Cu and Sn show similar trends, to facilitate accurate judgment of their trends, the normalized ratio of Sn and Cu can be calculated, such as I. Sn1 / I Cu1 Please see Figure 3 Before the 51st laser pulse, the normalized value of Sn was significantly higher than that of Cu, meaning the normalized ratio of Sn to Cu was greater than 1.05. Between the 51st and 109th laser pulses, the normalized ratio of Sn to Cu was approximately 1. After the 109th laser pulse, the normalized value of Sn was significantly lower than that of Cu, and the normalized ratio of Sn to Cu was less than 0.95. This is because the normalized value changed abruptly at the boundary between the Nb3Sn and Nb layers, indicating that the laser pulse had already penetrated from the Nb3Sn layer to the Nb layer.

[0063] The thickness of the bronze layer can be characterized by the ablation depth corresponding to the abrupt change in the normalized Nb value, while the thickness of both the bronze and Nb3Sn layers can be characterized by the ablation depth corresponding to the abrupt change in the normalized ratio of Sn and Cu. Specifically, the ablation depth corresponding to the 15th laser pulse is the thickness of the bronze layer, which is 23.08 μm. The thickness of the bronze layer is also 23.08 μm. The ablation depth corresponding to the 109th pulse is 27.28 μm, and the total thickness of the bronze and Nb3Sn layers is 27.28 μm. Therefore, the thickness of the Nb3Sn layer is calculated to be 4.20 μm. By measuring the thickness of the bronze-Nb3Sn-Nb thin film under test, the thickness of the bronze layer and the total thickness of the Nb3Sn and bronze layers can be calculated separately, ultimately achieving the characterization of the thickness of the Nb3Sn thin film in the superconducting cavity under test. This calculation process is known to those skilled in the art and is achievable; therefore, it will not be described in detail in this embodiment.

[0064] When the layer structure of the superconducting cavity film under test is different, the method of characterizing the thickness of the superconducting cavity film of the accelerator can be based on the specific location where the normalized value changes abruptly. It is not limited to characterizing the thickness of the base layer and the film layer, but can also be further calculated and characterized for the specific thickness of each layer in different layer structures.

[0065] Example 3:

[0066] The difference between this embodiment and Embodiment 2 is that the establishment of the thickness prediction model in this embodiment includes the following steps:

[0067] A standard superconducting cavity thin film sample is selected to obtain standard feature information of the tracer element. In a preferred embodiment, the superconducting cavity thin film sample is subjected to laser pulse ablation to obtain a standard LIBS spectrum. The tracer element is selected according to the standard LIBS spectrum, and the standard feature information is extracted according to the fingerprint spectral lines of the tracer element.

[0068] The bronze-Nb3Sn-Nb thin film to be inspected involves extracting the characteristic information by selecting tracer elements for each layer based on the recorded LIBS spectrum, and then extracting the characteristic information based on the fingerprint spectral lines of the tracer elements. Specifically, the tracer elements can be Cu, Nb, and Sn, and the standard characteristic information and the characteristic information of each layer can be selected from the spectral line intensities.

[0069] The correlation coefficients between bronze layer feature information and standard feature information are calculated using the Pearson coefficient method and denoted as r1, Nb3Sn feature information and standard feature information are denoted as r2, and Nb feature information and standard feature information are denoted as r3. The formula for calculating the Pearson correlation coefficient is as follows:

[0070]

[0071] Specifically, in the calculation of r1, r1 represents the Pearson correlation coefficient. Representative at the Characteristic information of tracer elements in the bronze layer during each laser pulse. Representative at the Standard characteristic information of tracer elements during each laser pulse. represent The mean value of the bronze layer feature information of the next laser pulse. represent The mean of the standard feature information of each laser pulse, where n represents the number of laser pulses. Similarly, the correlation coefficient r2 between the feature information of the Nb3Sn layer and the standard feature information, and the correlation coefficient r3 between the feature information of the Nb layer and the standard feature information, can also be obtained using the above Pearson correlation coefficient calculation formula. It can be understood that when establishing the Pearson correlation coefficient, the Pearson correlation coefficient is calculated between the feature information of the bronze layer and the standard feature information of the corresponding tracer element, the Pearson correlation coefficient is calculated between the feature information of the Nb3Sn layer and the standard feature information of the corresponding tracer element, and the Pearson correlation coefficient is calculated between the feature information of the Nb layer and the standard feature information of the corresponding tracer element.

[0072] The correlation coefficients r1 and r2, r3 and r3 are established. The ablation depth at the intersection of r1 and r2 is the thickness of the bronze layer, and the ablation depth at the intersection of r2 and r3 is the total thickness of the bronze layer and the Nb3Sn layer. Thus, the thickness of the Nb3Sn layer is obtained, which means that the thickness of the Nb3Sn thin film in the superconducting cavity under test is characterized.

[0073] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0074] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. In addition, the terms "first," "second," "third," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0075] Furthermore, terms such as "horizontal," "vertical," and "sag" do not imply that components must be absolutely horizontal or suspended, but rather that they can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal relative to "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0076] In this invention, unless otherwise expressly specified and limited, "above or below" a first feature may include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on" the first feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the first feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0077] Although the description of the invention has been given in conjunction with the specific embodiments described above, it will be apparent to those skilled in the art that many substitutions, modifications, and variations can be made based on the foregoing. Therefore, all such substitutions, modifications, and variations are included within the spirit and scope of the appended claims.

Claims

1. A method for characterizing the thickness of a thin film in an accelerator superconducting cavity, characterized in that, Includes the following steps: A laser pulse is focused onto the surface of the superconducting cavity film under test, and laser pulse ablation is performed on the superconducting cavity film under test, forming an excitation micro-region on the surface of the superconducting cavity film under test. The excitation micro-region was subjected to single-point ablation by multiple laser pulses, and the LIBS spectrum corresponding to each laser pulse was recorded. For each recorded LIBS spectrum, tracer elements are selected, and the feature information to be detected is extracted based on the fingerprint spectral lines of the tracer elements. The ablation depth corresponding to each laser pulse was measured; Establish the correspondence between the feature information to be inspected and the ablation depth; The correspondence between the feature information to be inspected and the ablation depth is analyzed, and a thickness prediction model is established. The results predicted by the thickness prediction model are used to characterize the thickness of the thin film in the superconducting cavity to be inspected. The establishment of the thickness prediction model includes the following steps: The intensity of the feature information to be detected for each fingerprint spectral line is normalized to obtain the normalized value I; Establish the correspondence between the normalized value I and the ablation depth, and analyze the relationship between the normalized value I and the ablation depth to quantify the thickness of the thin film in the superconducting cavity under test.

2. The method for characterizing the thickness of a superconducting cavity film in an accelerator according to claim 1, characterized in that, When selecting a single tracer element in the LIBS spectrum, the fingerprint spectral line of the tracer element is extracted. The detectable feature information of the fingerprint spectral line is the spectral line intensity or plasma parameters.

3. The method for characterizing the thickness of a superconducting cavity film in an accelerator according to claim 1, characterized in that, When different tracer elements are selected for the LIBS spectrum, the fingerprint spectral lines of the tracer elements are extracted. The detectable feature information of the fingerprint spectral lines is the spectral line intensity, intensity ratio, or plasma parameters.

4. The method for characterizing the thickness of a superconducting cavity film in an accelerator according to claim 1, characterized in that, Includes the following steps: Establish the correspondence between the feature information to be inspected and the number of laser pulses; A correspondence is established between ablation depth and the number of laser pulses, wherein the feature information to be inspected is established through a correspondence between the number of laser pulses and the ablation depth.

5. The method for characterizing the thickness of a superconducting cavity film in an accelerator according to claim 1, characterized in that, The superconducting cavity film to be inspected includes a superconducting cavity film layer and a superconducting cavity substrate layer. The normalized value I changes abruptly at the junction of the film layer and the substrate layer. The ablation depth corresponding to the location where the normalized value I changes abruptly is the thickness of the superconducting cavity film.

6. The method for characterizing the thickness of a superconducting cavity film in an accelerator according to claim 1, characterized in that, The establishment of the thickness prediction model includes the following steps: Select a standard superconducting cavity thin film sample to obtain standard characteristic information of tracer elements; The superconducting cavity thin film to be tested includes a superconducting cavity thin film layer and a superconducting cavity substrate layer. When extracting the feature information to be tested, substrate tracer elements and thin film tracer elements are selected according to each recorded LIBS spectrum. Substrate feature information is extracted according to the fingerprint spectral lines of the substrate tracer elements, and thin film feature information is extracted according to the fingerprint spectral lines of the thin film tracer elements. The correlation coefficient between substrate feature information and standard feature information was calculated using the Pearson coefficient method and denoted as r1, and the correlation coefficient between film feature information and standard feature information was denoted as r2. Establish the correspondence between correlation coefficient r1 and ablation depth, and the correspondence between r2 and ablation depth. The ablation depth value corresponding to the intersection of r1 and r2 is the thickness of the thin film of the superconducting cavity to be inspected.

7. The method for characterizing the thickness of a superconducting cavity film in an accelerator according to claim 6, characterized in that, The standard superconducting cavity thin film sample was subjected to laser pulse ablation to obtain a standard LIBS spectrum. Tracer elements were selected based on the standard LIBS spectrum, and standard feature information was extracted based on the fingerprint spectral lines of the tracer elements.

8. The method for characterizing the thickness of a superconducting cavity film in an accelerator according to claim 1, characterized in that, When the laser pulse is focused on the superconducting cavity film under test, the optimal laser flux range of the laser pulse needs to be determined based on the change of spectral characteristic parameters of the LIBS spectral signal with the number of pulses under different laser fluxes.

9. The method for characterizing the thickness of a superconducting cavity film in an accelerator according to claim 8, characterized in that, The spectral characteristic parameters of the LIBS spectral signal are any one of the following: spectral line intensity, intensity ratio, signal-to-background ratio, signal-to-noise ratio, and spectral line broadening of the tracer element.

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