A noise shielding system and method for measuring extremely weak plasma electrical signals of electric thrusters

Abstract

The present invention proposes a noise shielding system and method for measuring extremely weak plasma electrical signals of electric thrusters, which consists of an ion beam, an E×B probe main structure, a signal collection module, a coaxial cable shielding layer in the cabin, a coaxial cable signal line in the cabin, an aluminum foil protective layer, a vacuum cabin wall, a coaxial cable cabin joint, an outer coaxial cable shielding layer, an outer coaxial cable signal line, a picoammeter grounding wire, and a picoammeter. The scheme and signal collection module design of the present invention take into account the noise interference that may occur in the entire circuit, and shield and suppress the noise through the above-mentioned means, which greatly improves the signal-to-noise ratio of the E×B probe, and can suppress the background noise of the E×B probe signal measurement to the pA level. The signal collection module for receiving the current signal adopts a design based on the standard BNC connector, which is quick and convenient to process and install. Compared with the stable welding connection, it improves the robustness, replaceability and scalability of the entire set of equipment, has a wide applicability, and has a low system cost.

Description

Technical Field

[0001] The present invention belongs to the field of plasma diagnosis of electric propulsion technology, and in particular is a noise shielding system and method suitable for measuring extremely weak plasma electrical signals of electric thrusters. Background Art

[0002] Over the past century, electric propulsion has developed rapidly due to its advantages over chemical propulsion, such as high specific impulse, long life, and precise and adjustable thrust. It has been widely used in satellite position keeping, orbit transfer, deep space exploration, etc. As the source of thrust generated by electric thrusters, the measurement and diagnosis of plasma in thrusters is crucial to a deep understanding of the working mechanism of electric thrusters and improving their working performance.

[0003] Contact diagnosis is the longest-developed plasma diagnostic method. After decades of development, it has developed measuring instruments including Faraday probes, Langmuir probes, and retarding potential energy analyzers. It can perform steady-state or transient measurements of plasma electrical characteristic parameters (current, voltage, etc.), plasma characteristic parameters (plasma density, electron temperature, electric potential, etc.), and other parameters. It can achieve an in-depth understanding of plasma and has a wide range of applications in aerospace, material processing, food agriculture, and other fields. However, when contact diagnosis is applied to the plasma diagnosis of electric thrusters, it faces the problem of extremely weak electrical signals. Taking ion thrusters as an example, the total beam current of a thruster with a rated power of 200W may be only tens of milliamperes (10 -2 A), the signal measured by the Faraday probe for diagnosing beam current density is less than microampere level (10 -7 A). For the most sensitive E×B probe that measures the proportion of ions of different valence states, the typical peak value of the measured signal is about nanoampere level (10 -9 A), the signal of multivalent ions is not even at the nanoampere level (10 -10 A), if the background noise measured by the probe is too large, the real signal cannot be identified. In order to ensure that the plasma contact probe has a good signal-to-noise ratio, it is necessary to develop a method suitable for noise shielding of extremely weak plasma electrical signal measurements of electric thrusters. This method can be applied to electric thruster plasma contact diagnostic equipment represented by E×B probes.

[0004] At present, the most common electric thruster extremely weak plasma electrical signal measurement device is the E×B probe. For example, the typical E×B probe measurement system is as follows: Figure 5 The current signal is collected by using a Faraday collector made of metal with a low sputtering rate or a ceramic channel electron multiplier (CEM), and then converted into a voltage signal by a picoammeter, and the recorded data is read by a data acquisition card or an oscilloscope.

[0005] The Faraday collector used to collect current generally adopts a bowl-shaped Faraday cup design, such as Figure 6 As shown. Faraday collectors are generally made of materials such as tungsten and molybdenum, which have low secondary electron yields under xenon bombardment. The bowl-shaped structure is to collect as many secondary electrons as possible and improve measurement accuracy. Some research institutions have also proposed high aspect ratio concave collectors to better collect secondary electrons.

[0006] For electric thruster plasma contact diagnostic equipment represented by the E×B probe, the existing design shortcomings and problems are as follows:

[0007] 1. No consideration is given to shielding the noise of extremely weak plasma electrical signal measurements. For electric thruster plasma contact diagnostic equipment, the existing technology often uses a coaxial cable to connect the current collector to the final signal measurement equipment such as a source meter, and a flange is used in the middle to pass through the vacuum chamber. Although the shielding layer of the coaxial cable can greatly reduce the background noise of the signal based on the principle of electromagnetic shielding, it is found in experiments that if the shielding layer is suspended, the signal will still have noise of the order of 100pA. This noise is acceptable for probes with larger signals such as Faraday probes and Langmuir probes, but for equipment such as E×B probes that need to measure extremely weak plasma electrical signals, the required signal may be buried behind the messy noise.

[0008] The current collector and signal line of the existing electric thruster plasma contact diagnostic equipment represented by the E×B probe are often connected by a one-time connection method such as welding. On the one hand, it is difficult to ensure the quality of such a welding structure. Connecting the current collector and the signal line by soldering may cause air cavities or poor contact between the contact points of the two. When measuring plasma parameters in a vacuum environment, there is weak ionization, which makes the measuring equipment measure unexpected weak signals, and it is not robust. On the other hand, such a welding structure is disposable. When there is a problem with the connection, the structure can only be destroyed and re-welded. It is not replaceable, and the welding connection will cause the entire shielding layer to have breakpoints at the welding point. The lack of electromagnetic shielding here will introduce additional noise.

[0009] Literature about the E×B Probe Measurement System:

[0010] [1]Kim SW, Gallimore A D.Plume study of a 1.35-kW SPT-100 using an ExBprobe[J]. Journal of Spacecraft and Rockets, 2002, 39(6):904-909.

[0011] Literature on E×B probe collector structure:

[0012] [2]Liu L,Cai G,You F,et al.Improving the viability and versatility of the E×B probe with an active cooling system[J].Review of Scientific Instruments,2018,89(4):043502.

[0013] Literature on high aspect ratio concave collector structure of E×B probe:

[0014] [3]Reid B, Shastry R, ​​Gallimore A, et al. Angularly-Resolved ExB ProbeSpectra in the Plume of a 6-kW Hall Thruster[C] / / 44th AIAA / ASME / SAE / ASEEJoint Propulsion Conference&Exhibit.2008:5287. Summary of the invention

[0015] The technical problems to be solved by the present invention are:

[0016] 1. A full-circuit grounding shielding scheme for electric signal of electric thruster plasma contact diagnostic equipment represented by E×B probe is proposed to achieve electromagnetic wave noise shielding from current collector, coaxial signal line, vacuum chamber penetration to electric signal measurement equipment, so that the measurement signal can achieve pA-level background noise, greatly improving the signal-to-noise ratio of E×B probe;

[0017] 2. The design of the signal collection module of the E×B probe includes a rear collimator, a current collector, and an insulating end cap. Through the matching and design of standardized coaxial connectors, the one-time welding connection method is avoided, and a standardized and modular design is achieved, which is convenient for the repair of collector failures. In addition, the connection further reduces the disturbance of the electromagnetic signal to the E×B probe, thereby improving the signal-to-noise ratio of the E×B probe.

[0018] Technical solutions adopted to solve technical problems:

[0019] In order to achieve the goal of reducing the background noise of the electrical signal of the electric thruster plasma contact diagnostic equipment represented by the E×B probe, this technical solution designs the structure of the current collecting electrode to the current signal measurement equipment and the wiring shielding solution. This solution improves the sensitivity, robustness and replaceability of the probe system, and can stably suppress the background noise of the E×B probe signal measurement to the order of pA. Please refer to Figure 1-4shown.

[0020] The present invention provides a noise shielding system suitable for measuring extremely weak plasma electrical signals of electric thrusters, such as Figure 1-3 As shown, the main structure consists of an ion beam 1, an E×B probe main structure 2, a signal collection module 3, an in-cabin coaxial cable shielding layer 4, an in-cabin coaxial cable signal line 5, an aluminum foil protective layer 6, a vacuum cabin wall 7, a coaxial cable cabin joint 8, an out-cabin coaxial cable shielding layer 9, an out-cabin coaxial cable signal line 10, a picoammeter grounding wire 11, and a picoammeter 12. The present invention realizes noise shielding for extremely weak plasma electrical signal measurement through a full-line grounding shielding scheme and the design of a signal collection module.

[0021] The present invention solves the problem that the measurement noise of the EB probe cannot be stably suppressed at the pA level. The ion beam 1 is generally a conical beam structure, which comes from the plasma plume of an electric thruster (such as an ion thruster, a Hall thruster, etc.), which contains ions of different valence states. As the measurement object for subsequent diagnosis, it is generally composed of inert gas ions such as xenon ions and krypton ions. The EB probe main structure 2 is consistent with the existing conventional EB probe main structure, generally containing orthogonal electric fields and magnetic fields inside, and screening ions with specific speeds through the balance of electric power and Lorentz force. The ion beam 1 and the EB probe main structure 2 are matched by direct contact. The signal collection module 3 plays the role of collecting the aforementioned screened ion current and transmitting the signal to the subsequent coaxial cable. The specific structure of the signal collection module 3 is described in detail later. The EB probe main structure 2 is matched with the signal collection module 3 through a bolt connection, and the signal collection module 3 is matched with the coaxial cable shielding layer 4 and the coaxial cable signal line 5 in the cabin through a standard BNC connector. The coaxial cable shielding layer 4 in the cabin and the coaxial cable shielding layer 9 outside the cabin generally use a metal mesh woven with copper wire or silver wire, and the coaxial cable signal line 5 in the cabin and the coaxial cable signal line 10 outside the cabin generally use a wire core twisted into a strand of multiple copper wires. The coaxial cable shielding layer 4 in the cabin and the coaxial cable signal line 5 in the cabin are coaxially matched to form a coaxial cable. Specifically, the metal woven mesh coaxial cable shielding layer 4 in the cabin is coated on the outside of the coaxial cable signal line 5 in the cabin, which has the function of transmitting current signals and shielding noise. The aluminum foil protective layer 6 is a thin sheet of aluminum foil or aluminum foil tape, which is wrapped and covered on the outside of the coaxial cable shielding layer 4 in the cabin, which plays a role in isolating the plasma interference in the space and further reducing the measurement noise. The vacuum cabin wall surface 7 is part of the vacuum environment simulation system. It is a metal wall surface that isolates the atmospheric environment and is connected to the ground wire. The coaxial cable cabin connector 8 is a standard BNC connector, which is bolted on the vacuum cabin wall surface 7 and has the function of transmitting the current signal from the cabin to the outside. The coaxial cable shielding layer 4 and the coaxial cable signal line 5 in the cabin are connected to the coaxial cable cabin penetration joint 8 through a standard BNC connector, and the coaxial cable cabin penetration joint 8 is connected to the coaxial cable shielding layer 9 and the coaxial cable signal line 10 outside the cabin through a standard BNC connector. The coaxial cable shielding layer 9 and the coaxial cable signal line 10 outside the cabin are connected to the picoammeter 12 through a standard BNC connector, and the coaxial cable shielding layer 9 outside the cabin is grounded. The picoammeter 12 is a standard current measuring device that can measure current signals at a minimum level of pA. The picoammeter 12 is connected to the ground wire through the picoammeter grounding wire 11, and the picoammeter grounding wire 11 is generally a thicker copper wire.

[0022] In order to make the connection between the Faraday probe for collecting current and the coaxial cable more robust and reliable, and to further reduce the spatial electromagnetic interference introduced by the connection here, the present invention designs a standardized and modular signal collection module 3. The rear collimator 301 has a wine glass-shaped structure, which is used to further screen the velocity direction of the ion beam, and is generally made of 304 stainless steel. The Faraday collector 302 has a bowl-shaped structure, which is used to receive and generate current signals. It is generally made of metals such as tungsten, molybdenum, and aluminum with a low secondary electron sputtering rate. The bowl-shaped structure can better absorb the sputtered secondary electrons. The Faraday insulating device 303 has a cylindrical structure, which is used to isolate the rear collimator 301 from the Faraday collector 302 to prevent signal dissipation. It is generally made of insulating materials such as polytetrafluoroethylene and ceramics. The BNC female connector 304 and the BNC male connector 305 are standard parts. The Faraday collector 302 is connected to the BNC female connector 304 through a mechanical interference fit, and the BNC female connector 304 is connected to the Faraday insulating device 303 through a threaded fit. The Faraday insulating device 303 extends into the interior of the rear collimator 301 and is matched with the rear collimator 301 through a bolt fit. The BNC female connector 304 and the BNC male connector 305 are matched through a standard bayonet. The Faraday plug 306 is a cylindrical structure that serves to isolate the interference of the plasma atmosphere and is generally made of insulating materials such as polytetrafluoroethylene and ceramics. The Faraday plug 306 is connected to the rear collimator 301 through a mechanical interference fit and is blocked at the end of the rear collimator 301, serving to isolate the interference of the space plasma as much as possible. The coaxial cable 307 includes a total of 4 layers, which are coaxial columnar structures, and from the inside to the outside are a metal (copper) inner conductor for transmitting signals, an insulating layer made of polytetrafluoroethylene, a metal (copper wire or silver wire) braided layer for electromagnetic shielding, and an outer sheath made of rubber. The coaxial cable 307 is mated with the BNC male connector 305 by welding or mechanical clamping.

[0023] The present invention provides a noise shielding method for measuring extremely weak plasma electrical signals of an electric thruster, comprising the following steps:

[0024] 1. First, build the noise shielding system for measuring the extremely weak plasma electrical signal of the electric thruster as described above. During the construction process, it should be noted that it should start from the picoammeter 12, and connect in the order of the picoammeter grounding wire 11, the vacuum cabin wall surface 7 grounding, the outer coaxial cable shielding layer 9 and the outer coaxial cable signal line 10, the coaxial cable through the cabin connector 8, the inner coaxial cable shielding layer 4 and the inner coaxial cable signal line 5, the signal collection module 3, the E×B probe main structure 2, the aluminum foil protective layer 6, and the ion beam 1, and each connected part should read the current signal of the background noise through the picoammeter 12 to ensure efficient suppression of noise at the pA level.

[0025] 2. The Faraday probe and the coaxial cable are connected using a standard BNC connector. The Faraday probe is composed of a Faraday collector 302, a Faraday insulating device 303, and a BNC female connector 304. The coaxial cable 307 is connected to the BNC female connector 304 through a BNC male connector 305 and matched with a standard bayonet. The existing E×B probes are basically in the laboratory use stage and have not yet been applied on a large scale in industry. Therefore, a relatively simple welding method is generally selected between the connection between the Faraday probe and the coaxial cable. This will bring about a one-time problem that the connection cannot be disassembled, and welding may cause the weak ionization of the air cavity to introduce additional noise. In addition, welding cannot guarantee the robustness of the line connection, which may cause poor line contact. The method of the present invention can achieve rapid disassembly and assembly and stable connection between the Faraday probe and the coaxial cable, thereby improving the robustness and replaceability of the system.

[0026] 3. After the system is built, strictly check whether the aluminum foil protective layer 6 completely covers the coaxial cable shielding layer 4 in the vacuum chamber to completely isolate the noise of the space plasma bombardment on the current signal; strictly check whether the vacuum chamber wall 7, the coaxial cable shielding layer 9 outside the chamber, and the picoammeter grounding wire 11 are in common ground to prevent the occurrence of virtual ground. The current collection module of the traditional E×B probe continues the design of the Faraday probe, so the grounding shielding of the signal noise is not taken seriously. Even if the coaxial cable is used to suppress the electromagnetic interference in the space, the noise suppression effect is not good enough because there is no common grounding, the grounding position is incorrect, or there is no full line shielding, so the background noise of the signal measurement cannot be reduced to a satisfactory range.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. The full-circuit grounding shielding scheme and signal collection module design of the electric thruster plasma contact diagnostic equipment represented by the E×B probe designed in the present invention take into account the noise interference that may occur in the entire circuit, and shield and suppress the noise through the above-mentioned means, which greatly improves the signal-to-noise ratio of the E×B probe and can suppress the background noise of the E×B probe signal measurement to the pA level.

[0029] 2. The signal collection module for receiving current signals adopts a design based on the standard BNC connector, which is quick and easy to process and install. Compared with the stable welding connection, it improves the robustness, replaceability and scalability of the whole equipment, has wide applicability and low system cost.

[0030] 3. The electrical signal full-circuit grounding shielding scheme and signal collection module of the electric thruster plasma contact diagnostic equipment represented by the E×B probe designed by the present invention can also be used as a reference and promoted in other electric thruster plasma contact diagnostic equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic diagram of the overall structure of the present invention.

[0032] Figure 2 Schematic diagram of the signal collection module.

[0033] Figure 3 This is an exploded diagram of the signal collection module.

[0034] Figure 4 This is a noise diagram measured using the method of the present invention.

[0035] Figure 5 This is Kim's document, a typical E×B probe measurement system.

[0036] Figure 6 It is Liu's document, E×B probe structure.

[0037] The numbers in the figure are explained as follows:

[0038] Ion beam 1 E×B probe main structure 2 Signal collection module 3

[0039] In-cabin coaxial cable shielding layer 4 In-cabin coaxial cable signal line 5 Aluminum foil protective layer 6

[0040] Vacuum cabin wall 7 Coaxial cable cabin joint 8 Coaxial cable shielding layer outside cabin 9

[0041] Coaxial cable signal line outside the cabin 10 Picoammeter ground wire 11 Picoammeter 12

[0042] Back collimator 301 Faraday collector 302 Faraday insulator 303 BNC Female connector 304 BNC male connector 305 Faraday plug 306 Coaxial cable 307 DETAILED DESCRIPTION

[0043] The present invention is characterized in that the design realizes the full circuit grounding shielding of the electric signal of the electric thruster plasma contact diagnostic equipment represented by the E×B probe. The following substitutions can be made:

[0044] 1. The line grounding position can be changed. Possible solutions are to ground the coaxial cable shielding layer 4 in the cabin, and to ground the coaxial cable shielding layer 4 in the cabin and the coaxial cable shielding layer 9 outside the cabin at the same time. According to experimental determination, the existing solution of grounding the coaxial cable shielding layer 9 outside the cabin is the most stable, because if the cabin is grounded, the ground wire will be exposed to the plasma atmosphere, deviate from the real ground or produce oscillation.

[0045] The present invention is applicable to electric thruster plasma contact diagnostic equipment represented by E×B probes. To ensure that the current signal can pass through the coaxial cable smoothly and the bending radius of the cable is not too large, the core diameter of the coaxial cable is generally between 0.3 mm and 2 mm. In order to ensure strict common grounding, the core diameter of the grounding wire should not be less than 1 mm.

[0046] The system's working process:

[0047] Ion beam 1 is the object that the E×B probe needs to measure. It contains ion beams of different valence states flowing to the entrance of the E×B probe. They are generally rare gas ions such as xenon ions and krypton ions. The ion beam size is generally in the range of 1mA to 1A. It passes through the E×B probe main structure 2. This part is the same as the conventional design of the E×B probe. The length is generally 20 to 40cm, the width and height are 10 to 20cm, and the weight is 5 to 15kg. Through the screening effect of the orthogonal electromagnetic field, the magnetic field size is 0.1 to 0.3T, and the ion current of a specific speed reaches the signal collection module 3 of the E×B probe. The length of the signal collection module 3 is generally about 10cm. The signal collection module 3 transmits the current signal to the current signal measurement device through a coaxial cable. The current signal size is generally 1pA to 1nA, and the core diameter of the coaxial cable is generally between 0.3mm and 2mm. In the vacuum chamber, the vacuum degree is generally 0.001Pa. The coaxial cable shielding layer 4 in the chamber plays a role in suppressing the interference of electromagnetic waves on the current signal. The current signal is transmitted to the outside of the vacuum chamber through the coaxial cable signal line 5 in the chamber. The entire section of the coaxial cable in the chamber needs to be coated with an aluminum foil protective layer 6 to suppress the interference of the plasma atmosphere on the line current signal. The thickness of the aluminum foil protective layer 6 is generally 0.05-0.2mm. The current signal passes through the coaxial cable through the cabin connector 8 on the vacuum chamber wall 7. The coaxial cable through the cabin connector 8 is generally a BNC standard connector. Outside the vacuum chamber, the coaxial cable shielding layer 9 outside the chamber plays a role in suppressing the interference of electromagnetic waves on the current signal. The current signal is transmitted to the current signal measuring device picoammeter 12 through the coaxial cable signal line 10 outside the chamber. The picoammeter 12 can measure the current of the order of pA at the lowest. Among them, the picoammeter 12, the vacuum chamber wall 7, and the coaxial cable shielding layer 9 outside the chamber need to be connected to the same ground to prevent the occurrence of virtual ground. The diameter of the grounding wire core is about 1mm.

[0048] In order to make the connection between the Faraday probe for collecting current and the coaxial cable more robust and reliable, and to further reduce the spatial electromagnetic interference introduced by the connection here, the present invention designs a standardized and modular signal collection module 3. After the ion beam 1 passes through the E×B probe main structure 2, it enters the wine glass-shaped back collimator 301, which is generally made of 304 stainless steel, with a maximum diameter of generally about 2.5 cm and a length of generally about 10 cm. After that, the ion beam 1 reaches the bowl-shaped Faraday collector 302 and is received to generate a current signal. The Faraday insulation device 303 is used to isolate the back collimator 301 from the Faraday collector 302 to prevent signal dissipation. The Faraday collector 302 is generally made of metals such as tungsten, molybdenum, and aluminum with a low secondary electron sputtering rate, with a diameter of 5 to 8 mm and a bowl-shaped structure depth of 5 mm. The Faraday insulation device 303 is generally made of polytetrafluoroethylene or ceramics, with a diameter of generally 2 cm and a height of generally 2 cm. The BNC female connector 304 is connected to the Faraday insulating device 303 by threading, and the Faraday collector 302 is fixed to the wire core of the BNC female connector 304 by mechanical interference fit to transmit the current signal. The BNC male connector 305 is connected to the BNC female connector 304 by a standard bayonet, and transmits the current signal to the coaxial cable 307 through the Faraday plug 306. The Faraday plug 306 is generally made of insulating materials such as polytetrafluoroethylene and ceramics, and plays a role in isolating the interference of the plasma atmosphere. The size matches the back collimator 301, and the thickness is generally 2 mm.

Claims

1. A noise shielding system for measuring extremely weak plasma electrical signals of electric thrusters. Features: It consists of an ion beam, an E×B probe main structure, a signal collection module, a coaxial cable shielding layer in the cabin, a coaxial cable signal line in the cabin, an aluminum foil protective layer, a vacuum cabin wall, a coaxial cable cabin joint, an outer coaxial cable shielding layer, an outer coaxial cable signal line, a picoammeter grounding wire, and a picoammeter; wherein the ion beam cooperates with the E×B probe main structure through direct contact; the E×B probe main structure cooperates with the signal collection module through bolt connection, and the signal collection module is connected to the coaxial cable shielding layer and The coaxial cable signal line in the cabin is matched; the aluminum foil protective layer is wrapped around the outside of the coaxial cable shielding layer in the cabin; the vacuum cabin wall is part of the vacuum environment simulation system, and as a metal wall that isolates the atmospheric environment, it is connected to the ground wire; the coaxial cable cabin connector is connected to the coaxial cable shielding layer and the coaxial cable signal line outside the cabin through a standard BNC connector outside the cabin; the coaxial cable shielding layer and the coaxial cable signal line outside the cabin are connected to the picoammeter through a standard BNC connector; the picoammeter is connected to the ground wire through the picoammeter grounding wire; Among them, the signal collection module consists of a rear collimator, a Faraday collector, a Faraday insulating device, a BNC female head, a BNC male head, a Faraday plug and a coaxial cable; among them, the rear collimator is used to further screen the speed direction of the ion beam; the Faraday collector is used to receive the generated current signal; the Faraday insulating device is used to isolate the rear collimator and the Faraday collector to prevent signal dissipation; the Faraday collector is connected to the BNC female head through a mechanical interference fit, the BNC female head is connected to the Faraday insulating device through a threaded fit, the Faraday insulating device extends into the rear collimator, and is matched with the rear collimator through a bolt fit; the Faraday plug is connected to the rear collimator through a mechanical interference fit, blocked at the end of the rear collimator, and isolated from space plasma interference; the coaxial cable is matched with the BNC male head through welding or mechanical clamping.

2. According to claim 1, a noise shielding system for measuring extremely weak plasma electrical signals of electric thrusters, Features: Ion beam 1 is a cone-shaped beam structure that comes from the plasma plume of the electric thruster. It contains ions of different valence states and is the measurement object for subsequent diagnosis. It is composed of inert gas ions, including xenon ions and krypton ions.

3. According to claim 1, a noise shielding system for measuring extremely weak plasma electrical signals of electric thrusters, Features: The signal collection module collects the screened ion current and transmits the signal to the subsequent coaxial cable.

4. According to claim 1, a noise shielding system for measuring extremely weak plasma electrical signals of electric thrusters, Features: The shielding layer of the coaxial cable inside the cabin and the shielding layer of the coaxial cable outside the cabin are made of metal mesh woven with copper wire or silver wire.

5. According to claim 1, a noise shielding system for measuring extremely weak plasma electrical signals of electric thrusters, Features: The in-cabin coaxial cable signal line and the out-cabin coaxial cable signal line use a wire core made of multiple copper wires twisted into one strand; the in-cabin coaxial cable shielding layer and the in-cabin coaxial cable signal line are coaxially matched to form a coaxial cable. Specifically, the in-cabin coaxial cable shielding layer of the metal woven mesh is coated on the outside of the in-cabin coaxial cable signal line, which has the function of transmitting current signals and shielding noise.

6. A noise shielding system for measuring extremely weak plasma electrical signals of electric thrusters according to claim 1, Features: The aluminum foil protective layer is a thin sheet of aluminum foil paper or aluminum foil tape, which plays a role in isolating the plasma interference in the space and further reducing the measurement noise.

7. According to claim 1, a noise shielding system for measuring extremely weak plasma electrical signals of electric thrusters, Features: The coaxial cable penetration connector is bolted to the vacuum cabin wall surface to transmit the current signal from inside the cabin to outside the cabin; the coaxial cable shielding layer and the coaxial cable signal line inside the cabin are connected to the coaxial cable penetration connector through a standard BNC connector.

8. According to claim 1, a noise shielding system for measuring extremely weak plasma electrical signals of electric thrusters, Features: The rear collimator has a wine glass-shaped structure and is made of 304 stainless steel; the Faraday collector has a bowl-shaped structure and is made of tungsten, molybdenum and aluminum; the Faraday insulator has a cylindrical structure and is made of polytetrafluoroethylene and ceramic insulating materials; the Faraday plug is a cylindrical structure and is made of polytetrafluoroethylene and ceramic insulating materials; the coaxial cable contains a total of 4 layers, which is a coaxial columnar structure, and from the inside to the outside are a metal inner conductor for transmitting signals, an insulating layer made of polytetrafluoroethylene, a metal braided layer for electromagnetic shielding, and an outer sheath made of rubber.

9. A shielding method for a noise shielding system for measuring extremely weak plasma electrical signals of an electric thruster as claimed in any one of claims 1 to 8, comprising the following steps: Step 1. System construction: During the construction process, start from the picoammeter and connect in the order of picoammeter grounding wire, vacuum cabin wall grounding, coaxial cable shielding layer and coaxial cable signal line outside the cabin, coaxial cable cabin joint, coaxial cable shielding layer and coaxial cable signal line inside the cabin, signal collection module, E×B probe main structure, aluminum foil protective layer, and ion beam. The current signal of the background noise should be read through the picoammeter for each connected part to ensure that the noise is suppressed at the pA level. in, The signal collection module is composed of a rear collimator, a Faraday collector, a Faraday insulating device, a BNC female head, a BNC male head, a Faraday plug and a coaxial cable; wherein the rear collimator is used to further screen the velocity direction of the ion beam; the Faraday collector is used to receive and generate current signals; the Faraday insulating device is used to isolate the rear collimator and the Faraday collector to prevent signal dissipation; the Faraday collector is connected to the BNC female head through a mechanical interference fit, the BNC female head is connected to the Faraday insulating device through a threaded fit, the Faraday insulating device extends into the rear collimator and is matched with the rear collimator through a bolt fit; the Faraday plug is connected to the rear collimator through a mechanical interference fit, plugged at the end of the rear collimator to isolate the interference of space plasma; the coaxial cable is matched with the BNC male head through welding or mechanical clamping; Step 2. The Faraday probe is composed of a Faraday collector, a Faraday insulator, and a BNC female connector. The coaxial cable is connected to the BNC female connector through a BNC male connector and matched with a standard bayonet. Step 3. After the system is built, check whether the aluminum foil protective layer completely covers the coaxial cable shielding layer in the vacuum chamber to completely isolate the noise of the space plasma bombardment on the current signal; check whether the vacuum chamber wall, the coaxial cable shielding layer outside the chamber, and the picoammeter grounding wire are in the same ground to prevent the occurrence of virtual ground.

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