Method for representing thickness of thin film of superconducting cavity of accelerator

Abstract

The invention relates to the technical field of spectral 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 the superconducting cavity film to be detected, and forming an excitation micro-area on the surface of the superconducting cavity film to be detected; performing single-point ablation of multiple laser pulses on the excitation micro-area, and recording an LIBS spectrum corresponding to each laser pulse; for each recorded LIBS spectrum, selecting a tracer element, and extracting to-be-detected feature information according to a fingerprint spectral line of the tracer element; the ablation depth corresponding to each laser pulse is measured; establishing a corresponding relationship between the to-be-detected feature information and the ablation depth; and establishing a thickness prediction model, wherein the thickness prediction model represents the thickness of the superconducting cavity film to be detected. According to the invention, the technical effect of convenient and near-lossless characterization of the thickness of the superconducting cavity film of the accelerator is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of spectrum measurement, and in particular relates to a method for characterizing the thickness of an accelerator superconducting cavity film. Background Art

[0002] As the core acceleration component of a superconducting accelerator, the performance of the superconducting cavity determines the energy efficiency and operational stability of the accelerator. Currently, superconducting cavities mainly use low-temperature superconducting metal niobium to manufacture radio frequency superconducting cavity films, utilizing the zero resistance characteristics in the superconducting state to reduce the surface resistance of the cavity. However, since superconducting cavities made of metal niobium need to be immersed in liquid helium at 2K to 4K for cooling, the operation is complicated. In order to break free from the constraints of liquid nitrogen, reduce the complexity and operation and maintenance difficulty of superconducting accelerators, and expand the application range of superconducting accelerators, superconducting cavities can choose radio frequency superconducting cavity thin film materials such as Nb3Sn, MgB2, NbN, NbTiN, and iron-based superconductors. Such radio frequency superconducting cavity thin film materials have high superconducting transition temperatures and high superheat magnetic fields. The radio frequency performance at 4.2K or even higher temperatures reaches the level of niobium-based superconducting cavities at 2K. Therefore, Nb3Sn thin-film superconducting cavities are a key technology for next-generation superconducting accelerators. Uneven tin content distribution in Nb3Sn thin 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 can cause localized magnetic field penetration, leading to a quench. When the film is too thick, increased grain boundary density or stress accumulation can reduce the critical current density, affecting the optimal balance between the acceleration gradient and the quality factor.

[0003] At present, in order to ensure the superconducting performance of the superconducting cavity, the quantitative characterization of the thickness of the RF superconducting cavity film is mainly based on energy dispersive X-ray spectroscopy (EDX) analysis technology. Its principle is to infer the thickness value of the sample to be tested through the intensity and energy distribution of the characteristic X-rays of the sample to be tested, combined with the atomic layer attenuation model.

[0004] However, during the energy dispersive X-ray spectroscopy analysis process, the sample to be tested needs to be cut and then subjected to line scanning or surface scanning. This process introduces time-consuming and labor-intensive destructive procedures such as sampling and sample preparation, and usually needs to be used in conjunction with a scanning / transmission electron microscope. The thickness measurement process of the RF superconducting cavity film is inconvenient. Summary of the Invention

[0005] In order to address the shortcomings of the above-mentioned prior art, the present invention provides a method for characterizing the thickness of an accelerator superconducting cavity film, which can perform nearly non-destructive quantitative characterization of the thickness of the superconducting cavity film, and the process does not require time-consuming and labor-intensive destructive operations such as sampling and sample preparation, making the measurement process convenient.

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

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

[0008] The laser pulse is focused on the surface of the superconducting cavity film to be inspected, and the laser pulse ablation is performed on the superconducting cavity film to be inspected, so that an excitation micro-region is formed on the surface of the superconducting cavity film to be inspected;

[0009] Performing single-point ablation of the excitation microregion with multiple laser pulses, and recording the LIBS spectrum corresponding to each laser pulse;

[0010] For each recorded LIBS spectrum, a tracer element is selected and the characteristic information to be detected is extracted based on the fingerprint spectrum of the tracer element;

[0011] Measure the ablation depth corresponding to each laser pulse;

[0012] Establishing the corresponding relationship between the feature information to be inspected and the ablation depth;

[0013] The corresponding relationship between the characteristic information to be tested 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 superconducting cavity film to be tested.

[0014] In some implementations, when a single tracer element is selected in the LIBS spectrum, a fingerprint spectrum line of the tracer element is extracted, and the characteristic information to be detected of the fingerprint spectrum line is the spectrum line intensity or plasma parameters.

[0015] In some implementations, when the LIBS spectrum selects different tracer elements, fingerprint spectral lines of the tracer elements are extracted, and the characteristic information to be detected of the fingerprint spectral lines is spectral line intensity, intensity ratio or plasma parameters.

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

[0017] In some implementations, the establishment of the thickness prediction model includes the following steps: normalizing the intensity of the characteristic information to be tested of each fingerprint spectrum line to obtain a normalized value I; establishing a corresponding relationship 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 tested.

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

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

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

[0021] The superconducting cavity thin film to be inspected includes a superconducting cavity thin film layer and a superconducting cavity substrate layer. When extracting the characteristic information to be inspected, a substrate tracer element and a thin film tracer element are selected according to each recorded LIBS spectrum. The substrate characteristic information is extracted according to the fingerprint spectrum of the substrate tracer element, and the thin film characteristic information is extracted according to the fingerprint spectrum of the thin film tracer element.

[0022] The correlation coefficient between the substrate characteristic information and the standard characteristic information is calculated by the Pearson coefficient method and recorded as r1, and the correlation coefficient between the film characteristic information and the standard characteristic information is recorded as r2;

[0023] The corresponding relationship between the correlation coefficient r1 and the ablation depth, as well as the corresponding relationship between r2 and the ablation depth, is established. The ablation depth value corresponding to the intersection of r1 and r2 is the thickness of the superconducting cavity film to be tested.

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

[0025] In some implementations, when the laser pulse is focused on the superconducting cavity thin film to be inspected, 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 pulse number under different laser fluxes.

[0026] In this implementation, the spectral characteristic parameter of the LIBS spectral signal is any one of the 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 benefits:

[0028] The method provided by the present invention for characterizing the thickness of accelerator superconducting cavity films uses laser pulses to ablate the superconducting cavity film to be tested. The emission spectrum of the microplasma generated in the excited microregion of the superconducting cavity film, i.e., the LIBS spectrum, is analyzed to obtain the elemental composition of the surface of the superconducting cavity film to be tested. Multiple laser pulse ablation operations establish a relationship between the characteristic information of the target tracer element and the ablation depth, thereby obtaining a well-resolved elemental distribution result. By then developing a thickness prediction model and processing the elemental depth distribution data, quantitative characterization of the thickness of the superconducting cavity film to be tested can be achieved.

[0029] This thickness characterization method, based on laser pulse ablation of the superconducting cavity film under test, eliminates the need for cutting or other sampling or sample preparation procedures, compared to traditional energy-dispersive X-ray spectroscopy analysis, offering near-nondestructive testing. Furthermore, laser pulses enable non-contact, in-situ testing of the superconducting cavity film under test, making it convenient to operate. This allows for analysis of the depth distribution of elements to characterize the thickness of the superconducting cavity film under test, while also enabling analysis of the effects of detecting a wider range of elements in the periodic table, from trace to constant amounts. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The flowchart of the method for characterizing the thickness of the accelerator superconducting cavity film according to a specific embodiment of the present invention is shown.

[0031] Figure 2 1 is a graph showing the corresponding relationship between the normalized values of the spectral line intensities of Nb, Sn and Cu and the number of laser pulses in the superconducting cavity film to be inspected in Example 2 of the present invention.

[0032] Figure 3 This is a graph showing the corresponding relationship between the normalized ratio of the spectral line intensities of Sn and Cu and the number of laser pulses in the superconducting cavity film to be inspected in Example 2 of the present invention. DETAILED DESCRIPTION

[0033] To make the purpose, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. The described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0034] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are also within the scope of protection of the present invention.

[0035] Example 1:

[0036] The method of the present invention for characterizing the thickness of the accelerator superconducting cavity film is described in detail in the following sections. Figure 1 , including the following steps:

[0037] The laser pulse is focused on the surface of the superconducting cavity film to be inspected, and the laser pulse ablation is performed on the superconducting cavity film to be inspected, so that 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 base layer. In the process of focusing the laser pulse on the surface of the superconducting cavity film to be inspected, the laser pulse can ablate the superconducting cavity film to be inspected on the surface of the film layer;

[0038] Perform single-point ablation of the excited microarea with multiple laser pulses, and record the LIBS spectrum corresponding to each laser pulse;

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

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

[0041] Establishing the corresponding relationship between the feature information to be inspected and the ablation depth;

[0042] In a preferred embodiment, by establishing a corresponding relationship between the characteristic information to be detected and the number of laser pulses, and establishing a corresponding relationship between the ablation depth and the number of laser pulses (a linear relationship within the superconducting cavity thin film layer), the characteristic information to be detected can establish a corresponding relationship between the number of laser pulses and the ablation depth.

[0043] The corresponding relationship between the characteristic information to be tested and the ablation depth is analyzed, and a thickness prediction model is established. The prediction results of the thickness prediction model can be used to characterize the thickness of the superconducting cavity film to be tested.

[0044] In preferred embodiments, the laser pulse flux range is determined based on how the spectral characteristic parameters of the LIBS spectral signal change with pulse number at different laser fluxes. The spectral characteristic parameters of the LIBS spectral signal can be any one of the following: spectral line intensity, intensity ratio, signal-to-background ratio, signal-to-noise ratio, and line broadening of the tracer element. By comprehensively considering these various spectral characteristic parameters, the laser pulse flux is adjusted to achieve the optimal laser pulse flux. In some specific embodiments, for low concentrations of tracer elements, where the spectral line intensity is low, the laser flux corresponding to the highest spectral line intensity is preferred. For high concentrations of tracer elements, the laser flux corresponding to the highest signal-to-background ratio is preferred, facilitating data acquisition and presentation.

[0045] The superconducting cavity film to be inspected is ablated by laser pulses, and the superconducting cavity film to be inspected undergoes material micro-plasma ablation in the excited micro-region. With multiple single-point ablation by laser pulses, ablation pits are formed in the excited micro-region.

[0046] During the laser pulse ablation process, the LIBS spectrum of each laser pulse and the ablation depth are recorded. The LIBS spectrum is then used to extract the characteristic information of the tracer element to be tested. This reveals the elemental composition and distribution along the thickness of the superconducting cavity film to be tested, providing both qualitative and quantitative information about the elements. By analyzing the relationship between the characteristic information and the ablation depth and establishing a thickness prediction model, quantitative characterization of the thickness of the superconducting cavity film to be tested can be achieved.

[0047] The thickness of the superconducting cavity film to be inspected is characterized by analyzing its elemental composition. Compared to traditional quantitative characterization methods, laser pulses perform multiple single-point ablation to form micron-scale ablation pits. This eliminates the need for cutting, sampling, and sample preparation of the superconducting cavity film to be inspected, minimizing damage and enabling near-nondestructive testing and saving time. Furthermore, laser pulse ablation of the superconducting cavity film to be inspected enables non-contact, in-situ testing, eliminating the need for an electron microscope. This makes it suitable for both online and on-site testing, and improves detection 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] Normalize the intensity of the feature information to be detected of each fingerprint spectrum line to obtain the normalized value I;

[0051] The corresponding relationship between the normalized value I and the ablation depth is established, and the relationship between the normalized value I and the ablation depth is analyzed to quantify the thickness of the superconducting cavity film to be tested.

[0052] In some specific embodiments, the superconducting cavity film to be inspected includes a superconducting cavity film layer and a superconducting cavity base layer, the normalized value I mutates at the junction of the base layer and the film layer, and the ablation depth value corresponding to the position where the normalized value I mutates is the thickness of the superconducting cavity film.

[0053] Specifically, the superconducting cavity film to be tested is a sample obtained by magnetron sputtering bronze on a niobium substrate and annealing to generate a Nb3Sn film. The superconducting cavity film to be tested contains a composite layer structure of bronze-Nb3Sn-Nb.

[0054] The method for characterizing the thickness of the Nb3Sn film of the superconducting cavity to be inspected comprises the following steps:

[0055] The laser pulse is focused on the surface of the superconducting cavity film to be tested. Specifically, the laser pulse is emitted by the LIBS device. To make the ablation depth of the laser pulse uniform, the pulsed laser emitted by the LIBS can be expanded by a beam expander and focused on the surface of the superconducting cavity film to be tested, and the surface is ablated 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 spectrum signal. Specifically, the laser energy of the pulsed laser can be 30 to 100 mJ, and the corresponding laser flux can be 24 to 39 J / cm 2 .

[0056] The excited micro-area was ablated by laser pulses 200 times, and the LIBS spectrum corresponding to each laser pulse was recorded and marked in sequence as S1, S2, S3, S4...S 200 It is understandable that those skilled in the art can select an appropriate number of laser pulses according to actual measurement conditions.

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

[0058] The above three spectral line intensities are normalized to obtain the normalized intensity values of the above three fingerprint spectral lines, which are respectively recorded as I Cu1 , I Sn1 , I Nb1 .

[0059] Repeat the above operation to perform intensity normalization on the remaining LIBS spectrum line intensity, and record the remaining normalized values obtained in order as I Cu2 , I Sn2 , I Nb2 / I Cu3 , I Sn3 , I Nb3 / …… / I Cu200 , I Sn200 , I Nb200 , see Figure 2 , establish the corresponding relationship between the above normalized value and the ablation depth.

[0060] The ablation depth corresponding to each laser pulse is measured. Specifically, a profilometer can be used to measure the ablation depth corresponding to different numbers of laser pulses, and a corresponding relationship between the ablation depth and the number of laser pulses is established. Finally, a corresponding relationship between the normalized values of the tracer elements Cu, Sn, and Nb and the ablation depth is established to realize the establishment of a thickness prediction model.

[0061] 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 have similar trends, in order to facilitate the correct judgment of the normalized value trends of Cu and Sn, the normalized ratio of Sn and Cu can be calculated, such as I Sn1 / I Cu1 , see Figure 3 Before the 51st laser pulse, the normalized value of Sn was significantly higher than that of Cu, that is, the normalized ratio of Sn to Cu was greater than 1.05; between the 51st laser pulse and the 109th laser pulse, the normalized ratio of Sn to Cu was basically 1; and 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, because the normalized value mutated at the junction of the Nb3Sn layer and the Nb layer. At this time, the laser pulse had penetrated the Nb3Sn layer to the Nb layer.

[0063] The ablation depth corresponding to the mutation position of the normalized Nb value can be used to characterize the thickness of the bronze layer, while the ablation depth corresponding to the mutation position of the normalized ratio of Sn to Cu can be used to characterize the thickness of the bronze layer and the Nb3Sn layer. Specifically, the ablation depth corresponding to the 15th laser pulse is the thickness of the bronze layer. The ablation depth of the 15th laser pulse is 23.08 μm, and the bronze layer thickness is 23.08 μm. The ablation depth corresponding to the 109th pulse is 27.28 μm. The total thickness of the bronze layer and the Nb3Sn layer is 27.28 μm. Based on this calculation, the thickness of the Nb3Sn layer is 4.20 μm. By measuring the thickness of the bronze-Nb3Sn-Nb film to be tested, the thickness of the bronze layer and the total thickness of the Nb3Sn layer and the bronze layer can be calculated separately, ultimately characterizing the thickness of the Nb3Sn film in the superconducting cavity to be tested. This calculation process is known to those skilled in the art and is achievable, and is not described in detail in this embodiment.

[0064] When the layer structure of the superconducting cavity film to be tested is different, the method of characterizing the thickness of the accelerator superconducting cavity film can be based on the specific location where the normalized value suddenly changes. It is not limited to characterizing the thickness of the base layer and the film layer, but can also further calculate and characterize 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] Selecting a standard superconducting cavity thin film sample to obtain standard characteristic 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 based on the standard LIBS spectrum, and the standard characteristic information is extracted based on the fingerprint spectrum of the tracer element.

[0068] For the bronze-Nb3Sn-Nb thin film to be tested, when extracting the characteristic information, the tracer elements of each layer are selected based on each recorded LIBS spectrum, and the characteristic information is extracted 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 intensity;

[0069] The correlation coefficient between the bronze layer characteristic information and the standard characteristic information is calculated by the Pearson coefficient method and recorded as r1, the correlation coefficient between the Nb3Sn characteristic information and the standard characteristic information is recorded as r2, and the correlation coefficient between the Nb characteristic information and the standard characteristic information is recorded as r3. The calculation formula of the Pearson correlation coefficient is as follows:

[0070]

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

[0072] The corresponding relationships between the correlation coefficient r1 and the ablation depth, the corresponding relationship between r2 and the ablation depth, and the corresponding relationship between r3 and the ablation depth are established. The ablation depth value corresponding to the intersection of r1 and r2 is the thickness of the bronze layer, and the ablation depth value corresponding to the intersection of r2 and r3 is the total thickness of the bronze layer and the Nb3Sn layer, thereby obtaining the thickness of the Nb3Sn layer, and realizing the characterization of the thickness of the Nb3Sn film in the superconducting cavity to be tested.

[0073] In the present invention, unless otherwise expressly specified or limited, the terms "mounted," "connected," "connect," "fixed," etc. should be understood broadly. For example, they may refer to fixed connection, detachable connection, or integration; mechanical connection or electrical connection; direct connection or indirect connection through an intermediate medium; internal communication between two components or interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0074] In the description of the present invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer" and the like indicate positions or locations based on the positions shown in the accompanying drawings, or the positions or locations in which the inventive product is typically placed when in use. These terms are intended solely to facilitate the description of the present invention and to simplify the description, and are not intended to indicate or imply that the devices or components referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on the present invention. Furthermore, the terms "first," "second," and "third," etc., are used solely to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0075] Furthermore, terms such as "horizontal," "vertical," and "overhanging" do not necessarily imply that a component must be absolutely horizontal or overhanging, but rather that it can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but rather that it can be slightly tilted.

[0076] In the present invention, unless otherwise expressly specified or limited, a first feature being above or below a second feature may include the first and second features being in direct contact, or may include the first and second features being in contact not directly but through another feature between them. Furthermore, a first feature being above, above, and above the second feature includes the first feature being directly above and obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being below, below, and below the second feature includes the first feature being directly below and obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

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

Claims

1. A method for characterizing the thickness of an accelerator superconducting cavity film, characterized in that: The following steps are involved: The laser pulse is focused on the surface of the superconducting cavity film to be inspected, and the laser pulse ablation is performed on the superconducting cavity film to be inspected, so that an excitation micro-region is formed on the surface of the superconducting cavity film to be inspected; Performing single-point ablation of the excitation microregion with multiple laser pulses, and recording the LIBS spectrum corresponding to each laser pulse; For each recorded LIBS spectrum, a tracer element is selected and the characteristic information to be detected is extracted based on the fingerprint spectrum of the tracer element; Measure the ablation depth corresponding to each laser pulse; Establishing the corresponding relationship between the feature information to be inspected and the ablation depth; The corresponding relationship between the characteristic information to be tested 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 superconducting cavity film to be tested.

2. The method for characterizing the thickness of an accelerator superconducting cavity film according to claim 1, characterized in that: When a single tracer element is selected in the LIBS spectrum, a fingerprint spectrum line of the tracer element is extracted, and the characteristic information to be detected of the fingerprint spectrum line is the spectrum line intensity or plasma parameters.

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

4. The method for characterizing the thickness of an accelerator superconducting cavity film according to claim 1, characterized in that: The following steps are involved: Establishing the corresponding relationship between the characteristic information to be detected and the number of laser pulses; A corresponding relationship between the ablation depth and the number of laser pulses is established, and a corresponding relationship is established between the characteristic information to be detected through the number of laser pulses and the ablation depth.

5. The method for characterizing the thickness of an accelerator superconducting cavity film according to claim 1, characterized in that: The establishment of the thickness prediction model comprises the following steps: Normalize the intensity of the feature information to be detected of each fingerprint spectrum line to obtain the normalized value I; The corresponding relationship between the normalized value I and the ablation depth is established, and the relationship between the normalized value I and the ablation depth is analyzed to quantify the thickness of the superconducting cavity film to be tested.

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

7. The method for characterizing the thickness of an accelerator superconducting cavity film according to claim 1, characterized in that: The establishment of the thickness prediction model comprises the following steps: Select standard superconducting cavity film samples to obtain standard characteristic information of tracer elements; The superconducting cavity thin film to be inspected includes a superconducting cavity thin film layer and a superconducting cavity substrate layer. When extracting the characteristic information to be inspected, a substrate tracer element and a thin film tracer element are selected according to each recorded LIBS spectrum. The substrate characteristic information is extracted according to the fingerprint spectrum of the substrate tracer element, and the thin film characteristic information is extracted according to the fingerprint spectrum of the thin film tracer element. The correlation coefficient between the substrate characteristic information and the standard characteristic information is calculated by the Pearson coefficient method and recorded as r1, and the correlation coefficient between the film characteristic information and the standard characteristic information is recorded as r2; The corresponding relationship between the correlation coefficient r1 and the ablation depth, as well as the corresponding relationship between r2 and the ablation depth, is established. The ablation depth value corresponding to the intersection of r1 and r2 is the thickness of the superconducting cavity film to be tested.

8. The method for characterizing the thickness of an accelerator superconducting cavity film according to claim 7, characterized in that: The standard superconducting cavity thin film sample is subjected to laser pulse ablation to obtain a standard LIBS spectrum, a tracer element is selected according to the standard LIBS spectrum, and standard characteristic information is extracted according to the fingerprint spectrum line of the tracer element.

9. The method for characterizing the thickness of an accelerator superconducting cavity film according to claim 1, characterized in that: When the laser pulse is focused on the superconducting cavity thin film to be inspected, 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 pulse number under different laser fluxes.

10. The method for characterizing the thickness of an accelerator superconducting cavity film according to claim 9, characterized in that: The spectral characteristic parameter of the LIBS spectral signal is any one of the 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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