A multi-point quasi-monochromatic soft x-ray spectrometer for plasma radiation measurements

Abstract

This invention discloses a multi-energy quasi-monoenergy soft X-ray spectrometer for plasma radiation measurement, belonging to the field of X-ray detection technology. It includes an aperture group, an objective lens unit, and an image plane detector array with time resolution. The aperture group is used to define the incident solid angle of each measurement channel and suppress stray radiation. The objective lens unit consists of multiple quasi-monoenergy multilayer mirrors, each mirror surface corresponding to an independent measurement channel and including a background channel. Multiple measurement channels share a single energy point. The image plane detector array corresponds one-to-one with each measurement channel, forming a soft X-ray detection system with time-resolved measurement capabilities. This invention, using the above spectrometer, effectively avoids measurement uncertainties caused by the convolution inversion of energy spectrum distribution and energy response function, and is suitable for online soft X-ray energy spectrum diagnosis of inertial confinement fusion plasmas such as lasers and Z-pinch.

Description

Technical Field

[0001] This invention relates to the field of X-ray detection technology, and in particular to a multi-energy point quasi-monoenergy soft X-ray spectrometer for plasma radiation measurement. Background Technology

[0002] Inertial confinement fusion is an important, efficient, clean, and safe future energy solution, significant for both energy supply and national security. Precise spectroscopic measurements of the fusion plasma radiation field in the soft X-ray band can accurately deduce key information such as radiation power, flux, and plasma electron temperature and density, playing a crucial role in scientifically assessing the fusion plasma state and effectively guiding fusion numerical simulations and program verification. Currently, commonly used diagnostic methods include crystal spectrometers, grating spectrometers, and Dante spectrometers. Crystal spectrometers and grating spectrometers offer high energy spectral resolution, but crystal spectrometers have fixed lattice constants, allowing operation only at specific energies and limiting the applicable crystal materials and orientations. While grating spectrometers offer continuous spectrum coverage, their response to different wavelengths is not uniform, and their efficiency is low in the short wavelength range. These spectrometers have narrow reflection bandwidths and low integrated reflectivity. Furthermore, the source intensity of the bremsstrahlung spectrum generated during the experiment is relatively weak, making it difficult to guarantee image brightness in diagnostics. This results in poor signal-to-noise ratios for spectrometer measurements, making them unsuitable for time-resolved soft X-ray energy spectrum detection.

[0003] Compared to the previous two types of spectrometers, Dante spectrometers offer advantages in high throughput and nanosecond-level time resolution, leading to their widespread application in laser installations and Z-pinch experimental platforms both domestically and internationally. Traditional Dante spectrometers typically consist of filters, single-layer mirrors, and X-ray detectors, achieving energy selection through a combination of low-energy cutoff filters and high-energy cutoff mirrors. Different channels employ different materials or grazing incidence angles to expand the overall spectral coverage. However, existing Dante spectrometers rely on filter-single-layer membrane combinations for energy selection, resulting in an integrated signal with a wide energy bandwidth, making it impossible to directly obtain the spectral distribution. To obtain the energy distribution, an ideal radiation model needs to be introduced, followed by spectral decomposition using an inversion algorithm. Although a calibrated Dante system can achieve high-precision response function fitting, the non-delta-type nature of the ERF and the discrepancy between the theoretical model and the actual radiation distribution still introduce significant measurement uncertainty. Foreign researchers have previously applied multilayer films with quasi-monoenergetic properties to X-ray imaging or energy dispersive spectroscopy diagnostics. However, the uncertainty in energy dispersive spectroscopy measurements remains significant. They have also proposed using aperiodic multilayer film structures with flat energy response characteristics to achieve more uniform reflectivity within a certain energy range, thereby weakening the coupling between the system response function and the spectral distribution. However, aperiodic multilayer films require extremely high fabrication precision; even slight fluctuations in layer thickness can lead to non-uniform reflectivity, introducing additional uncertainty. These factors result in the uncertainty of energy dispersive spectroscopy measurements in currently used Dante spectrometers being 7.8% or higher, and further improvements are difficult, especially in the low radiation temperature range. Summary of the Invention

[0004] The purpose of this invention is to provide a multi-energy quasi-monoenergy soft X-ray spectrometer for plasma radiation measurement, and to provide detailed system assembly and adjustment methods as well as uncertainty evaluation methods and means to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides a multi-energy quasi-monoenergy soft X-ray spectrometer for plasma radiation measurement, comprising an aperture group, an objective lens unit, and an image plane detector array with time-resolved capability. The aperture group is used to define the incident solid angle of each measurement channel and suppress stray radiation. The objective lens unit is composed of multiple quasi-monoenergy multilayer mirrors, which are fabricated and assembled into a whole. Each mirror of the quasi-monoenergy multilayer mirror corresponds to an independent measurement channel and includes a background channel for subtracting stray signals. Multiple measurement channels share a single energy point to verify the consistency of the energy spectrum measurement signal. The image plane detector array corresponds one-to-one with each measurement channel, constituting a soft X-ray detection system with time-resolved measurement capability.

[0006] Preferably, multiple measurement channels are arranged sequentially according to the energy distribution law, and different measurement channels use different Bragg angles and multilayer film materials to achieve multi-energy point measurement.

[0007] Preferably, each measurement channel Measurement signal strength and Energy spectrum distribution of plasma radiation source at any time and energy response function It can be written as:

[0008] ;

[0009] in, For measurement channel i Maximum energy response, For measurement channel i The lowest energy response, For energy, For measurement channel The corresponding peak energy point of Bragg diffraction for multilayer films.

[0010] Preferably, the quasi-monoenergy multilayer film reflector is made of a material with high reflectivity in the corresponding wavelength band, and the multilayer film thickness ratio is 0.5.

[0011] Preferably, the quasi-monoenergetic multilayer mirror with a large Bragg angle forms a near-the-Bragg diffraction energy peak. The quasi-monoenergetic narrowband energy response function of the function , represented as:

[0012] ;

[0013] in, The reflectivity corresponds to the peak energy point. denoted as the energy spectral bandwidth of the energy response function.

[0014] Preferably, the quasi-monoenergy multilayer reflector, the background channel substrate, and the image plane detector are respectively mounted on a high-precision machined support structure. The support structure includes multiple mutually fixed reference mounting surfaces, which are used to define the relative positional relationship between each measurement channel and serve as a geometric reference for angle and position calibration during the assembly and adjustment process. By establishing an optical axis reference corresponding to the position of the radiation source, the aperture group, objective lens unit, and image plane detector array are axially aligned. During the assembly and adjustment process, by setting a visible light point source at the position of the radiation source, the position of the light spot formed by each measurement channel on the detector plane is observed. Based on the positional deviation of the light spot relative to the center of the detector, the mounting angle of the quasi-monoenergy multilayer reflector is adjusted to form a determined grazing incidence angle state.

[0015] Preferably, any measurement channel energy spectrum measurement uncertainty Based on the detector signal input and energy response function peak reflectivity and spectral bandwidth The uncertainty is assessed and conforms to the following relationship:

[0016] ;

[0017] in, Indicates measurement channel The measurement signal, Indicates uncertainty, Represents relative values. u r This indicates relative uncertainty.

[0018] Preferably, by separating the energy spectrum distribution and energy response function The convolution of the energy sources yields the radiation intensity at multiple energy points. satisfy:

[0019] .

[0020] Preferably, each measurement channel Quasi-monoenergy narrowband measurements were performed on soft X-ray radiation at different Bragg diffraction energy peaks to obtain the radiation intensity at multiple energy points. Finally, by interpolating and fitting the soft X-ray radiation intensity at multiple Bragg diffraction energies, the energy spectrum distribution of the entire plasma radiation source was reconstructed.

[0021] Preferably, the time-resolved measurement of the multi-energy quasi-monoenergy soft X-ray spectrometer is achieved by using a time-resolved X-ray detector; and the time-integrating X-ray camera or film is used to achieve time-integrated energy spectrum recording.

[0022] Therefore, the present invention employs the above-mentioned multi-energy quasi-monoenergy soft X-ray spectrometer for plasma radiation measurement, which has the following beneficial effects: by utilizing the delta-like characteristics of the quasi-monoenergy multilayer film, and by analyzing the sources of the corresponding uncertainty and the corresponding high-precision energy response function calibration methods, the measurement uncertainty caused by the convolution inversion of the energy spectrum distribution and the energy response function is effectively avoided, and the uncertainty of the entire reconstructed energy spectrum is significantly reduced.

[0023] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0024] Figure 1 This is an embodiment of the overall optical path structure of a multi-energy quasi-monoenergy soft X-ray spectrometer for plasma radiation measurement according to an embodiment of the present invention;

[0025] Figure 2 The diagram shows the energy response curve of the quasi-monoenergetic multilayer membrane and the filter transmittance curve of an embodiment of the present invention.

[0026] Figure 3 The energy response function of this invention embodiment Line graph;

[0027] Figure 4 This is a graph of the synchrotron radiation calibration energy response function according to an embodiment of the present invention.

[0028] Figure 5 This is a graph showing the simulation evaluation of the uncertainty of the reconstructed energy spectrum distribution in an embodiment of the present invention.

[0029] Figure 6 A graph showing the spectrometer reconstruction energy spectrum results of an embodiment of the present invention;

[0030] Figure Labels

[0031] 1. Radiation source; 2. Aperture; 3. Multilayer film; 4. X-ray detector. Detailed Implementation

[0032] 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. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. 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 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 present invention without inventive effort are within the scope of protection of the present invention.

[0033] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0034] Example

[0035] This embodiment addresses the diagnostic needs of Z-pinch device plasma soft X-ray energy spectrum analysis. Preliminary experimental results indicate that the plasma temperature is approximately 299-313 eV, and the expected soft X-ray radiation energy range is below 1 keV. Therefore, a multi-energy quasi-monoenergy soft X-ray spectrometer with eight measurement channels for plasma radiation measurement below 1 keV is provided. This spectrometer mainly includes an aperture group, an objective lens unit, and an image plane detector array with time resolution. (Refer to...) Figure 1 The aperture group is used to define the incident solid angle of each measurement channel and suppress stray radiation; the objective lens unit consists of multiple quasi-monoenergetic multilayer mirrors, which are assembled into a whole through high-precision machining. Each quasi-monoenergetic multilayer mirror corresponds to an independent measurement channel and includes a background channel for subtracting stray signals. Multiple measurement channels share a single energy point to verify the consistency of the energy spectrum measurement signal; the image plane detector array corresponds one-to-one with each measurement channel, forming a soft X-ray detection system with time-resolved measurement capabilities.

[0036] The aperture assembly, objective lens unit, and image plane detector array are assembled and adjusted using high-precision methods to match the incident light path, reflection geometry, and image plane receiving position of each measurement channel. Furthermore, the working angle of the corresponding quasi-monoenergetic multilayer reflector is aligned with the preset measurement energy point, thus establishing a defined measurement optical path structure and energy correspondence within the system. This spectrometer, combined with high-precision mechanical assembly, can further reduce the uncertainty in soft X-ray radiation intensity measurements. The optical structural parameters of this spectrometer are shown in Table 1.

[0037] Table 1 Overall optical path structure parameters of the spectrometer

[0038]

[0039] The quasi-monoenergy multilayer reflector, background channel substrate, and image plane detector are mounted on a high-precision fabricated support structure. The support structure includes multiple mutually fixed reference mounting surfaces, which define the relative positional relationship between each measurement channel and serve as the geometric reference for angle and position calibration during assembly and adjustment. By establishing an optical axis reference corresponding to the radiation source position, the aperture group, objective lens unit, and image plane detector array are axially aligned. During assembly and adjustment, a visible light point source is set at the radiation source position, and the position of the light spot formed by each measurement channel on the detector plane is observed. Based on the positional deviation of the light spot relative to the detector center, the mounting angle of the quasi-monoenergy multilayer reflector is adjusted to form a definite grazing incidence angle.

[0040] In this embodiment, the multiple measurement channels of the spectrometer are arranged sequentially according to the energy distribution law. Different measurement channels use different Bragg angles and multilayer film materials to achieve multi-energy point measurement. As shown in Table 2, measurement channel three and measurement channel four are set with the same energy to compare the consistency of the spectrometer's spectral measurement signal.

[0041] Each measurement channel Measurement signal strength The energy spectrum distribution of the plasma radiation source at that moment and energy response function It can be written as:

[0042] ;

[0043] in, For measurement channel i Maximum energy response, For measurement channel i The lowest energy response, For energy, For measurement channel The corresponding peak energy point of Bragg diffraction for multilayer films.

[0044] Quasi-monoenergetic multilayer mirrors are fabricated using materials with high reflectivity in the corresponding wavelength band (such as Co / C, Cr / Sc, W / Si, etc.), and the multilayer thickness ratio (the thickness of the high atomic number material layer divided by the total thickness) is selected to be 0.5 to suppress high-order harmonic reflections. By using quasi-monoenergetic multilayer mirrors, precise measurement of a single energy point and simultaneous measurement of multiple energy points can be achieved, solving the problems of limited measurement accuracy and insufficient spectral resolution in current soft X-ray energy spectroscopy diagnostic methods.

[0045] Using a quasi-monoenergetic multilayer mirror with a large Bragg angle (by adjusting the Bragg angle (10°-20°) and period thickness), a mirror-like structure is formed near its corresponding Bragg diffraction energy peak. The quasi-monoenergetic narrowband energy response function of the function , refer to Figure 2 This can be represented as:

[0046] ;

[0047] in, The reflectivity corresponds to the peak energy point. denoted as the energy spectral bandwidth of the energy response function.

[0048] Through optimized selection of material combinations, working Bragg angles, and thickness ratios in multilayer films, varying degrees of variation are achieved to match the optimal reflectivity of different soft X-ray energy regions and improve spectral performance. Each measurement channel is paired with filter assemblies of different materials and thicknesses (specific materials and thicknesses are given in Table 2), which improves the spectral purity of quasi-monoenergy narrowband measurements and effectively reduces the impact of low-energy and high-harmonic X-rays on measurement accuracy. The energy response function after stacking the filter assemblies is shown in the figure. like Figure 3 As shown, peak reflectivity Between 8% and 15%, the energy spectrum bandwidth Less than 50 eV.

[0049] Table 2. Structural parameters and filter materials of the multilayer film device for this spectrometer.

[0050]

[0051] In this embodiment, any measurement channel in the spectrometer energy spectrum measurement uncertainty Based on the detector signal input and energy response function peak reflectivity and spectral bandwidth The uncertainty is assessed and conforms to the following relationship:

[0052] ;

[0053] in, Indicates measurement channel The measurement signal, Indicates uncertainty, Represents relative values. u r This represents relative uncertainty. The three types of uncertainty mentioned above can be directly calibrated experimentally using a standard source, thereby effectively reducing the uncertainty of energy spectrum measurements.

[0054] The absolute response and energy response function of the image detector in this embodiment Precise calibration was performed at a synchrotron radiation source. The absolute response of the experimental detector was precisely calibrated, as were the multilayer mirror and filters. Taking measurement channel one as an example, a step size of 1-5 eV was selected near the peak energy, and a step size of 5-20 eV was used for the peak energy range. The energy response function was synthesized and fitted to obtain the result. , refer to Figure 4 The uncertainty of the absolute response of the corresponding image plane detector is 0.4%, and the peak reflectivity is... and spectral bandwidth The relative uncertainties are 1.11% and 0.21%, respectively. Based on the formula, the final corresponding... It can also calculate the relative uncertainty of energy spectrum measurements for other measurement channels. and the corresponding extended relative uncertainty As shown in Table 3. Expanded relative uncertainty for each measurement channel. All are within 3%, and the expanded relative uncertainty varies depending on the measurement channel. The expanded uncertainty curve of the entire reconstructed energy spectrum was simulated, with reference to... Figure 5 The final expansion of the reconstructed energy spectrum relative uncertainty Below 3.2%, a relatively smooth and small level of uncertainty was maintained.

[0055] Table 3 Relative uncertainty of energy spectrum measurement for each measurement channel

[0056]

[0057] In this embodiment, to ensure a stable measurement optical path structure for the multi-energy quasi-single-energy soft X-ray spectrometer under experimental conditions, the spectrometer underwent mechanical assembly and system adjustment. Multiple quasi-single-energy multilayer mirrors and background channel reflectors are mounted on the same support body and fixed as a whole to the main mounting flange, thus forming the spectrometer's objective lens unit. The image plane detector array is mounted on the main mounting flange via multiple branch flanges, creating a one-to-one spatial correspondence between the measurement channels. The support body, main mounting flange, and branch flanges are manufactured using high-precision five-axis machining to define the relative positional relationships between the measurement channels. During system adjustment, an optical axis reference corresponding to the plasma radiation source position is first established, and the aperture group and objective lens unit are axially aligned. Subsequently, by setting a visible light point source at the radiation source position and observing the position of the light spots formed by each measurement channel at the image plane position, the installation angle of the single-energy multilayer mirror is adjusted based on the positional deviation of the light spots relative to the corresponding detector center.

[0058] Finally, an offline Z-pinch physics experiment was conducted on the spectrometer of this embodiment to obtain the radiation intensity signal that varies with time. And by separating the energy spectrum distribution and energy response function The convolution of the energy sources yields the radiation intensity at multiple energy points. satisfy:

[0059] ;

[0060] Each measurement channel Quasi-monoenergy narrowband measurements were performed on soft X-ray radiation at different Bragg diffraction energy peaks to obtain the radiation intensity at multiple energy points. Finally, by interpolating and fitting the soft X-ray radiation intensity at multiple Bragg diffraction energies, the energy spectrum distribution of the entire plasma radiation source was reconstructed, with reference to... Figure 6 .

[0061] The time-resolved measurements of this spectrometer can be achieved using X-ray detectors such as time-resolved X-ray diodes and phototubes; time-integrated energy spectrum recording can also be achieved using time-integrating X-ray cameras or films.

[0062] Therefore, the present invention employs a multi-energy quasi-monoenergy soft X-ray spectrometer for plasma radiation measurement, which can simultaneously measure multiple soft X-ray energy points and obtain quasi-monoenergy signals with narrow energy spectrum bandwidth. Furthermore, through high-precision calibration, the uncertainty of energy spectrum measurement can be significantly reduced, thereby providing more accurate and time-resolved radiation intensity data for soft X-ray energy spectrum diagnosis and reducing the impact of system assembly and adjustment factors on measurement accuracy.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A multi-point quasi-monochromatic soft X-ray spectrometer for plasma radiation measurements, characterized by: It includes an aperture group, an objective lens unit, and an image plane detector array with time resolution capability; the aperture group is used to define the incident solid angle of each measurement channel and suppress stray radiation; the objective lens unit is composed of multiple quasi-monoenergetic multilayer mirrors, which are processed and assembled into a whole. Each mirror of the quasi-monoenergetic multilayer mirror corresponds to an independent measurement channel and includes a background channel for subtracting stray signals. Multiple measurement channels share a single energy point to verify the consistency of the energy spectrum measurement signal. The image plane detector array corresponds one-to-one with each of the measurement channels, forming a soft X-ray detection system with time-resolved measurement function; Multiple measurement channels are arranged sequentially according to the energy distribution law, and different measurement channels use different Bragg angles and multilayer film materials to achieve multi-energy point measurement.

2. The multi-energy quasi-monoenergy soft X-ray spectrometer for plasma radiation measurement according to claim 1, characterized in that: Each measurement channel Measurement signal strength and Energy spectrum distribution of plasma radiation source at any time and energy response function writing: ； in, For measurement channel i Maximum energy response, For measurement channel i The lowest energy response, For energy, For measurement channel The corresponding peak energy point of Bragg diffraction for multilayer films.

3. A multi-energy quasi-monoenergy soft X-ray spectrometer for plasma radiation measurement according to claim 2, characterized in that: The quasi-monoenergy multilayer film mirror is made of a material with high reflectivity in the corresponding wavelength band, and the multilayer film thickness ratio is 0.

5.

4. A multi-energy quasi-monoenergy soft X-ray spectrometer for plasma radiation measurement according to claim 3, characterized in that: The quasi-monoenergetic multilayer mirror with the large Bragg angle forms a near-single-energy multilayer mirror at its corresponding Bragg diffraction energy peak. The quasi-monoenergetic narrowband energy response function of the function , is represented as: ； in, The reflectivity corresponds to the peak energy point. denoted as the energy spectral bandwidth of the energy response function.

5. A multi-energy quasi-monoenergy soft X-ray spectrometer for plasma radiation measurement according to claim 1, characterized in that: The quasi-monoenergy multilayer reflector, the background channel substrate, and the image plane detector are respectively mounted on a high-precision machined support structure. The support structure includes multiple mutually fixed reference mounting surfaces, which are used to define the relative positional relationship between each measurement channel and serve as a geometric reference for angle and position calibration during the assembly and adjustment process. By establishing an optical axis reference corresponding to the position of the radiation source, the aperture group, objective lens unit, and image plane detector array are axially aligned. During the assembly and adjustment process, a visible light spot source is set at the radiation source location to observe the position of the light spot formed on the detector plane by each measurement channel. Based on the positional deviation of the light spot relative to the detector center, the installation angle of the single-energy multilayer film reflector is adjusted to form a definite grazing incidence angle state.

6. A multi-energy quasi-monoenergy soft X-ray spectrometer for plasma radiation measurement according to claim 4, characterized in that: Any measurement channel energy spectrum measurement uncertainty Based on the detector signal input and energy response function peak reflectivity and spectral bandwidth The uncertainty is assessed and conforms to the following relationship: ； in, Indicates measurement channel The measurement signal, Indicates uncertainty, Represents relative values. u r This indicates relative uncertainty.

7. A multi-energy quasi-monoenergy soft X-ray spectrometer for plasma radiation measurement according to claim 6, characterized in that: By separating the energy spectrum distribution and energy response function The convolution of the energy sources yields the radiation intensity at multiple energy points. satisfy: 。 8. A multi-energy quasi-monoenergy soft X-ray spectrometer for plasma radiation measurement according to claim 7, characterized in that: Each measurement channel Quasi-monoenergy narrowband measurements were performed on soft X-ray radiation at different Bragg diffraction energy peaks to obtain the radiation intensity at multiple energy points. Finally, by interpolating and fitting the soft X-ray radiation intensity at multiple Bragg diffraction energies, the energy spectrum distribution of the entire plasma radiation source was reconstructed.

9. A multi-energy quasi-monoenergy soft X-ray spectrometer for plasma radiation measurement according to claim 1, characterized in that: The time-resolved measurement of the multi-energy quasi-monoenergy soft X-ray spectrometer is achieved through a time-resolved X-ray detector; time-integrating X-ray cameras or films are used to achieve time-integrated energy spectrum recording.

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