A plasma three-dimensional optical diagnosis method based on depth of field constraint

Abstract

This invention discloses a three-dimensional optical diagnostic method for plasma based on depth-of-field constraints, belonging to the field of plasma diagnostics and optical measurement technology. The diagnostic structure includes an optical imaging unit and a plasma generation device. The optical imaging unit includes an imaging lens and an image sensor. The effective imaging space of the plasma is constrained by the depth-of-field characteristics of the imaging lens. Based on this depth-of-field constraint, at least one virtual detection plane is defined within the effective imaging space and / or at a position associated with the effective imaging space along the optical axis. This virtual plane characterizes the emission optical projection information of the plasma at the corresponding spatial position. By acquiring the projection information of the virtual detection plane at different observation angles, the diagnosis and reconstruction of the three-dimensional spatial distribution of the plasma are achieved. This invention does not require increasing the number of physical detectors and does not rely on the axisymmetric assumption of the plasma distribution, offering advantages such as simple system structure, low implementation cost, and wide applicability.

Description

Technical Field

[0001] This invention relates to the field of plasma diagnostic technology, and more specifically to a plasma three-dimensional diagnostic structure and method based on optical imaging. Background Technology

[0002] Plasma thrusters are widely used in spacecraft attitude control, orbit maintenance, and deep space exploration. The spatial distribution characteristics of the plasma plume generated during thruster operation directly affect propulsion efficiency, device lifespan, and the degree of contamination and interference to the spacecraft platform. Therefore, accurate three-dimensional spatial diagnosis of plasma plumes has significant engineering and scientific importance. Existing three-dimensional diagnostic methods for plasma plumes mainly include probe measurement methods and optical diagnostic methods. Among them, probe measurement methods usually require immersing a physical probe in the plasma, which easily disturbs the plasma and suffers from probe ablation and measurement reliability issues in high-temperature, high-energy particle environments, making them unsuitable for long-term stable measurements or acquisition of complex spatial distributions. Optical diagnostic methods, due to their advantages of non-contact operation and high spatial resolution, are widely used in the diagnostic research of plasma plumes. Common optical three-dimensional diagnostic methods include multi-camera synchronous imaging, multi-view array imaging, and tomographic imaging methods based on tomographic reconstruction. However, these methods usually rely on the arrangement of multiple physical imaging units or multiple physical probe planes, which places high demands on system structure, optical alignment accuracy, and synchronous control, resulting in high system complexity and implementation cost. Furthermore, some 3D reconstruction methods based on optical emission often introduce the axisymmetric assumption of plasma spatial distribution to reduce the complexity of the reconstruction problem. However, in actual operating conditions, influenced by factors such as thruster structure, electromagnetic field distribution, or changes in operating state, plasma plumes often exhibit significant asymmetric characteristics, rendering the axisymmetric assumption inapplicable and thus limiting the applicability and diagnostic accuracy of related methods. In optical imaging systems, the depth-of-field characteristics of the imaging lens affect the sharp imaging range of the imaged area. In existing technologies, depth of field is generally considered an inherent limiting factor of the imaging system, and imaging information in the out-of-focus area is often considered to lack effective spatial indicative significance; such information is typically not processed during 3D diagnostics. Current technologies have not yet proposed a solution that can simplify the optical system structure while effectively utilizing the depth-of-field characteristics of the imaging system to achieve accurate diagnosis of the 3D spatial distribution of plasma plumes. Summary of the Invention

[0003] This invention aims to address the problems existing in existing three-dimensional optical diagnostic methods for plasma plumes, such as complex system structure, high dependence on the arrangement of multiple physical detection planes or multiple cameras, difficulty in applying to non-axisymmetric plasma distributions, and ineffective utilization of the depth-of-field characteristics of the imaging system. It proposes a plasma three-dimensional optical diagnostic structure and method based on depth-of-field constraints.

[0004] This invention utilizes the depth-of-field characteristics of an optical imaging system to constrain the effective imaging space of plasma. Based on this depth-of-field constraint, it defines at least one virtual detection plane associated with the spatial position of the plasma. This allows for the diagnosis and analysis of the three-dimensional spatial distribution of plasma without increasing the number of physical detectors or relying on the assumption of plasma distribution axisymmetry. To achieve the above-mentioned objectives, this invention employs the following technical solution.

[0005] This invention provides a three-dimensional optical diagnostic structure for plasma based on depth-of-field constraints, including an optical imaging unit and a plasma generation device.

[0006] The optical imaging unit includes an imaging lens and an image sensor. The imaging lens has preset focal length, aperture parameters, and focus position, and is used to collect light signals generated by spontaneous emission of plasma.

[0007] The plasma generating device is used to generate the plasma to be diagnosed, and the plasma is located within the imaging field of view of the optical imaging unit.

[0008] By utilizing the depth-of-field characteristics of the imaging lens, the effective imaging space of the plasma is constrained. Based on this depth-of-field constraint, at least one virtual detection plane is defined within the effective imaging space and / or at a position associated with the effective imaging space along the optical axis. The virtual detection plane is used to characterize the emission optical projection relationship of the plasma at the corresponding spatial position, thereby achieving three-dimensional spatial diagnosis of the plasma.

[0009] Preferably, the effective imaging space is defined by adjusting at least one of the aperture parameters, focus position, and imaging distance of the imaging lens.

[0010] Preferably, the virtual detection plane may be located at the far boundary of the effective imaging space, at the optical axis position outside the far boundary, or be a detection plane determined by equivalent mapping, extrapolation or inversion based on the depth constraint relationship.

[0011] Preferably, the virtual detection plane is a non-physical detection plane, which is not composed of physical detectors, but is an equivalent detection surface used to describe the optical projection relationship of plasma emission.

[0012] Furthermore, the diagnostic structure also includes a rotation drive device, which is used to drive the plasma generating device to rotate relative to the optical imaging unit around a predetermined rotation axis, so that the optical imaging unit can acquire corresponding emission optical image data at different rotation angles to obtain projection information of at least one virtual detection plane at multiple angles.

[0013] This invention also provides a three-dimensional optical diagnostic method for plasma based on depth-of-field constraints, comprising the following steps:

[0014] The optical parameters of the optical imaging unit are set, including the focal length, aperture parameters and focus position of the imaging lens, in order to form a depth constraint on the effective imaging space of the plasma.

[0015] Based on the depth-of-field constraint relationship, at least one virtual detection plane is defined within the effective imaging space and / or at a position associated with the effective imaging space along the optical axis.

[0016] The optical imaging unit is used to collect the light signal generated by the spontaneous emission of plasma, and the emission optical projection information of the plasma is obtained based on the virtual detection plane;

[0017] Based on the acquired projection information, a three-dimensional spatial distribution analysis of the plasma is performed.

[0018] Preferably, during the acquisition of the emission optical projection information, the plasma generating device is driven to rotate relative to the optical imaging unit to obtain projection information corresponding to at least one virtual detection plane at multiple angles, thereby realizing the three-dimensional reconstruction of the non-axisymmetric plasma distribution.

[0019] The beneficial effects of this invention are:

[0020] (1) The present invention uses the depth-of-field characteristics of the optical imaging system to constrain the plasma imaging space, ensuring the correspondence and determinism between the plasma spatial light intensity and the diagnostic optical path.

[0021] (2) This invention does not rely on the axisymmetric assumption of plasma distribution and can be applied to the three-dimensional diagnosis of asymmetric plasma plumes, thus improving the applicability and accuracy of the diagnostic method.

[0022] (3) The present invention is based on passive optical emission for measurement, which avoids the disturbance of plasma by physical probes and is suitable for plasma diagnosis under complex working conditions;

[0023] (4) The present invention has the advantages of simple system structure, low implementation cost and strong scalability, and is suitable for promotion and application in plasma thrusters and other plasma diagnostic fields. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the structure of an embodiment of the present invention;

[0025] Figure 2 The figure shows the experimental results of this invention; Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described below in conjunction with specific embodiments.

[0027] Example 1

[0028] This embodiment provides a plasma three-dimensional optical diagnostic method based on depth-of-field constraints, and its diagnostic process includes the following steps.

[0029] First, determine the three-dimensional spatial range of the plasma to be photographed, identify the nearest and farthest points of the plasma along the optical axis, and use the distance between these points as the basis for determining the near and far boundaries of the depth of field in the imaging system. Figure 1 As shown, a three-dimensional mesh model is established in the space to be diagnosed, and the center of the three-dimensional mesh is defined as the origin of the coordinate system.

[0030] Based on the three-dimensional spatial dimensions of the plasma to be detected, combined with the target surface size and working distance of the imaging system, the focal length of the imaging lens is calculated and selected to meet the imaging requirements that the entire plasma is within the imaging field of view.

[0031] Furthermore, based on the focal length and related optical parameters of the selected imaging lens, the depth of field of the imaging system is adjusted by regulating the aperture size of the imaging lens, so that the plasma space to be measured is included within the depth of field. For example... Figure 1 As shown, the far boundary of the depth range is defined as a virtual detection plane.

[0032] Subsequently, the position and orientation of the optical imaging device are adjusted so that the plasma to be generated is within the effective imaging range of the imaging system.

[0033] After completing the above settings, the plasma generation device is started for the experiment. During the experiment, the plasma generation device is driven to rotate relative to the optical imaging device around a predetermined rotation axis, and the emission optical images of the plasma are acquired at different rotation angles. Preferably, a narrowband filter can be set in front of the imaging lens to filter the emission light of the plasma by wavelength, thereby achieving the separation and acquisition of the emission intensity information of ions or neutral atoms.

[0034] After acquiring images from multiple angles, the obtained two-dimensional optical images are equivalently mapped onto the virtual detection plane along the optical axis. Based on the aperture parameters, the optical geometric relationship between the plasma spatial position and the virtual detection plane, the contribution weight of each voxel in the three-dimensional mesh to the corresponding pixel on the virtual detection plane is calculated, thereby establishing a projection relationship model.

[0035] Finally, based on the projection relationship model, a three-dimensional reconstruction algorithm is used to reconstruct the spatial distribution of the plasma. The reconstruction algorithm may include an iterative reconstruction algorithm or an analytical reconstruction algorithm, preferably including the Feldkamp–Davis–Kress (FDK) algorithm, so as to obtain the three-dimensional spatial distribution result of the plasma.

[0036] The specific reconstruction results are as follows: Figure 2 As shown, the method used in this invention is applicable to three-dimensional diagnosis of plasma light intensity.

Claims

1. A plasma three-dimensional optical diagnostic method based on depth-of-field constraints, characterized in that, include: • Optical imaging unit, which is disposed on one side of the rotating support device, includes an imaging lens and an image sensor; the imaging lens is configured with adjustable aperture parameters, and is used to acquire optical images of plasma emission at multiple angles when the plasma generating device rotates; • Structural design relationship, which cooperates with the optical imaging unit, including a mapping unit for establishing the geometric relationship of the virtual detection plane, a parameter determination unit for determining the depth range of the imaging system, and a reconstruction unit for realizing three-dimensional spatial reconstruction based on the projection relationship; The mapping unit is configured to define at least one virtual detection plane at a spatial position associated with the plasma generating device along the optical axis, and to establish an equivalent projection relationship between the virtual detection plane and the image sensor. The parameter determination unit, based on the aperture parameters and focal length of the imaging lens, is used to limit the depth of field range of the imaging system so that the depth of field range covers the space region to be measured of the plasma generating device. The reconstruction unit is configured to reconstruct the spatial emission distribution of plasma in three dimensions based on the projection relationship under multiple rotation angles. • A plasma generating device configured to generate plasma for carrying the plasma to be diagnosed, and to drive the plasma generating device to rotate about a predetermined rotation axis. The effective imaging space of the plasma is constrained by the depth-of-field characteristics of the imaging lens, and based on the depth-of-field constraint relationship, at least one virtual detection plane is defined within the effective imaging space and / or at a position associated with the effective imaging space along the optical axis. Each equivalent detection position on the virtual detection plane corresponds to an equivalent ray path along the optical axis or a predetermined projection direction. The emission intensity distribution of the plasma along this ray path forms corresponding linear integral projection data, thereby making the projection information on the virtual detection plane geometrically equivalent to the projection data in computed tomography, thus realizing the three-dimensional spatial diagnosis of the plasma.

2. The diagnostic method as described in claim 1, characterized in that, The effective imaging space is defined by adjusting the aperture parameters of the imaging lens, at least one of the focus position and imaging distance, so that the acquired emission optical image satisfies the linear integral projection condition.

3. The diagnostic method as described in claim 1 or 2, characterized in that, When the data processing module maps the emitted optical image onto the virtual detection plane model, the virtual detection plane is located at the far boundary of the depth of field, at the optical axis direction position outside the far boundary, or is a detection plane determined by equivalent mapping, extrapolation or inversion based on the depth of field constraint relationship.

4. The diagnostic method according to any one of claims 1-3, characterized in that, The virtual detection plane is a non-physical detection plane. It is not composed of physical detectors, but is an equivalent detection surface used to describe the optical projection relationship of plasma emission.

5. The diagnostic method according to any one of claims 1–4, characterized in that, The optical imaging unit is used to acquire the light signals generated by the spontaneous emission of the plasma.

6. The diagnostic method according to any one of claims 1–5, characterized in that, Also includes: A rotation drive device is provided for driving the plasma generating device to rotate about a predetermined rotation axis relative to the optical imaging unit.

7. The diagnostic method as described in claim 6, characterized in that, The optical imaging unit acquires corresponding emission optical image data when the plasma generating device is at different rotation angles, so as to obtain projection information of at least one virtual detection plane at multiple angles.

8. The diagnostic method as described in claim 7, characterized in that, Based on the projection information obtained from multiple angles, the three-dimensional spatial distribution of the plasma is reconstructed, and the three-dimensional spatial distribution reconstruction process does not depend on the axisymmetric assumption of the plasma distribution.

9. The plasma three-dimensional optical diagnostic method based on depth-of-field constraints as described in claim 1, characterized in that, include: • Set the optical parameters of the optical imaging unit to form a depth constraint on the effective imaging space of the plasma. • Based on the depth-of-field constraint relationship, at least one virtual detection plane is defined within the effective imaging space and / or at a position associated with the effective imaging space along the optical axis; • The emission optical projection information of the plasma is collected using the virtual detection plane; • Based on the collected projection information, a three-dimensional spatial distribution analysis of the plasma is performed.

10. The diagnostic method as described in claim 9, characterized in that, During the acquisition of the emission optical projection information, the plasma generating device is driven to rotate relative to the optical imaging unit to obtain projection information corresponding to at least one virtual detection plane at multiple angles.

Images