A Faraday probe device

Abstract

A Faraday probe device includes a shielding electrode, a collecting electrode, a housing, an insulating component, and a base plate. The collecting electrode comprises a collecting cylinder and a collecting base. The collecting electrode is disposed within and covered by the housing, which is mounted on the base plate. One end of the collecting cylinder is closed and has an end hole, while the other end is open. The closed end of the collecting cylinder is located on the collecting base, which is mounted on the base plate. Vent holes are arranged on the collecting base and the base plate, with the end hole and vent holes staggered. Along the axial direction of the collecting cylinder, the insulating component, the shielding electrode, and the housing have coaxial through holes communicating with the open end of the collecting cylinder. The shielding electrode and the collecting electrode can be energized separately. The shielding electrode generates a repellent electron sheath and collects ions, while the collecting electrode collects reflected ions and secondary electrons generated by ions entering the collecting cylinder. This invention uses a housing to shield the sheath inside the probe, eliminating the problem of sheath expansion in traditional Faraday probes and improving measurement accuracy.

Description

Technical Field

[0001] This invention relates to the field of aerospace technology, and in particular to a Faraday probe device for diagnosing the ion current density of electric propulsion. Background Technology

[0002] Electric thrusters, such as Hall thrusters and ion thrusters, have the advantage of high specific impulse, which can greatly improve the payload rate of spacecraft and are suitable for missions such as position holding and orbit transfer. In Hall and ion thrusters, the working propellant is first ionized into plasma. The generated ions are ejected from the thruster outlet under the action of an accelerating electric field, thereby generating thrust. After the thruster plume is ejected from the thruster outlet at a certain angle, it will diffuse. The plume distribution is a key parameter of electric thrusters. On the one hand, it directly affects the thruster performance; plume divergence reduces acceleration efficiency. On the other hand, it imposes requirements on the placement of the thruster on the satellite; a proper placement can prevent corrosion of solar panels and satellite components.

[0003] The plume distribution is characterized by the ion current density distribution. A typical probe for measuring ion current density distribution is the Faraday probe. By scanning the Faraday probe along a semicircle (or a straight line), the spatial distribution of ion current density can be obtained, and parameters such as ion current, plume divergence angle, and propellant utilization rate can be calculated. The most commonly used Faraday probe consists of a collector electrode and a shield electrode. The collector electrode is a circular surface used to receive ions; the shield electrode consists of a ring surrounding the collector electrode to reduce sheath expansion of the collector electrode.

[0004] However, the accuracy of current Faraday probes is poor. First, even with shielding to constrain the collecting area, the probe sheath changes with plasma density. As plasma density decreases, the probe sheath expands, leading to more ions being collected. During probe scanning, the plasma density on both sides of the thruster is much lower than that along the thruster's centerline, resulting in more ion current being collected on the sides. When integrating the ion current density hemispherically, the weighting of the sides is greater, affecting the ion current and propellant utilization results; furthermore, the increased ion current on both sides leads to a larger calculated plume divergence angle. In actual tests, ion current, propellant utilization, and plume divergence angle are highly correlated—the more divergent the plume, the higher the ion current and propellant utilization—resulting in extremely poor Faraday data accuracy. Furthermore, at higher ion energies, high-energy ion bombardment of the collecting electrode surface causes ion reflection and the escape of secondary electrons. Ion reflection reduces the collected ion current, while secondary electrons increase it, both affecting measurement accuracy. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and propose a Faraday probe device to solve the problem of decreased measurement accuracy caused by sheath expansion, ion reflection and secondary electron escape in existing Faraday probes.

[0006] A Faraday probe device includes a shielding electrode, a collecting electrode, a housing, an insulator A, an insulator B, and a base plate. The collecting electrode includes a collecting cylinder and a collecting base. The collecting electrode is disposed inside the housing and covered by the housing. The housing is mounted on the base plate. One end of the collecting cylinder is closed and has an end hole, while the other end of the collecting cylinder is open. The closed end of the collecting cylinder is disposed on the collecting base, which is disposed on the base plate. Vent holes are arranged on the collecting base and the base plate. The end hole and the vent holes are staggered. From bottom to top, the open end of the collecting cylinder has insulator B, the shielding electrode, and insulator A arranged sequentially. On the axial direction of the collecting cylinder, insulator B, the shielding electrode, insulator A, and the housing have coaxial through holes that communicate with the open end of the collecting cylinder. The shielding electrode and the collecting electrode can be energized respectively. The shielding electrode is used to generate repulsive electrons and collect ion sheaths. The collecting electrode is used to collect ions entering the collecting cylinder and to recollect reflected ions and secondary electrons generated by the ions entering the collecting cylinder.

[0007] The surface of the insulating component A facing the shielding electrode is provided with an annular groove.

[0008] The surface of the insulating component B facing the collecting cylinder is provided with an annular groove.

[0009] In use, different plasma environments can be adapted by changing the potentials of shielding electrode 1 and collecting electrode.

[0010] The advantages of this invention compared to the prior art are:

[0011] This application employs an outer shell to shield the sheath inside the probe, eliminating the problem of sheath expansion in traditional Faraday probes and improving measurement accuracy; the collecting electrode uses a long collecting tube to recollect reflected ions and secondary electrons, further improving measurement accuracy.

[0012] The present application will be further described below with reference to the accompanying drawings and embodiments: Attached Figure Description

[0013] Figure 1 This is a perspective view of the Faraday probe device of the present invention;

[0014] Figure 2 for Figure 1 A bottom view;

[0015] Figure 3 for Figure 1 Top view;

[0016] Figure 4 A perspective view of the Faraday probe apparatus after removing its outer casing;

[0017] Figure 5 This is a schematic diagram of insulating component A;

[0018] Figure 6 This is a schematic diagram of insulating component B;

[0019] Figure 7 Comparative images of the sheath collected by the Faraday probe;

[0020] Figure 8 Comparison of the collecting pole structure of the Faraday probe;

[0021] Figure 9 This is a comparison chart of the actual measurement results. Detailed Implementation

[0022] The embodiments of the technical solution of the present invention will now be described in detail with reference to the accompanying drawings. Unless otherwise stated, the technical or scientific terms used in this application have the ordinary meaning as understood by those skilled in the art.

[0023] Figures 1-6 A Faraday probe device is shown, which includes a shielding electrode 1, a collecting electrode, a housing 4, an insulating component A5, an insulating component B6, and a base plate 7;

[0024] The collecting electrode includes a collecting cylinder 2 and a collecting base 3. The collecting electrode is disposed inside and covered by the outer shell 4, which is mounted on a base plate 7. One end of the collecting cylinder 2 is closed and has an end hole, while the other end of the collecting cylinder 2 is open. The closed end of the collecting cylinder 2 is disposed on the collecting base 3, which is disposed on the base plate 7. Vent holes are arranged on the collecting base 3 and the base plate 7, with the end hole and vent holes staggered. From bottom to top, the open end of the collecting cylinder 2 is provided with an insulating component B6, a shielding electrode 1, and an insulating component A5. In the axial direction of the collecting cylinder 2, the insulating component B6, the shielding electrode 1, the insulating component A5, and the outer shell 4 are provided with coaxial through holes that communicate with the open end of the collecting cylinder 2. The shielding electrode 1 and the collecting electrode can be energized respectively. The shielding electrode 1 is used to generate repulsive electrons and collect ion sheaths. The collecting electrode is used to collect ions entering the collecting cylinder 2 and to recollect reflected ions and secondary electrons generated by the ions entering the collecting cylinder 2.

[0025] This embodiment improves upon the shortcomings of the Faraday probe in the background and proposes a novel high-precision Faraday probe device.

[0026] Combination Figure 5 and Figure 6The insulating components A5 and B6 are designed with a ring structure. The surface of insulating component A5 facing the shielding electrode 1 has a ring-shaped groove; the surface of insulating component B6 facing the collecting cylinder 2 also has a ring-shaped groove. Arranging the ring-shaped grooves on the insulating components increases the insulation distance between the conductive components. The probe insulation structure only fails after all surfaces are coated, thus significantly improving probe lifespan.

[0027] The collecting cylinder 2 and the collecting base 3 together form the collecting electrode, while the shielding electrode 1 and the collecting electrode can be energized separately. In use, different plasma environments can be adapted by changing the potentials of the shielding electrode 1 and the collecting electrode.

[0028] The shielding electrode 1 generates a sheath that repels electrons and collects ions. The shielding electrode 1 is covered by an open outer shell 4. The sheath formed inside the probe is shielded by the outer shell. Figure 7 As shown in the left figure, the sheath layer a represents the collection area of ​​the Faraday probe device in this embodiment, which is the area of ​​the opening above the probe housing 5; while a conventional Faraday sheath layer, such as... Figure 7 As shown in the right figure, the traditional Faraday collector 8 and the traditional shielding electrode 9 are as follows: Figure 7 As shown in the right figure. When the plasma density is high (e.g., at the center of the thruster), the sheath is collected as... Figure 7 As shown in the middle layer b of the right figure, when the plasma density is low (such as on both sides of the thruster), the collection sheath is as follows: Figure 7 As shown in the middle layer c of the right figure; that is, the traditional Faraday probe collects sheaths that change with the environment, affecting measurement accuracy. However, the Faraday probe device of this embodiment can eliminate the influence of plasma density on sheath expansion, greatly improving measurement accuracy.

[0029] The collecting cylinder 2 and the collecting bottom 3 together form the collecting electrode. After ions enter, the reflected ions and secondary electrons generated will be collected again by the elongated cylinder structure, such as... Figure 8 As shown in the left figure, this improves measurement accuracy. The end holes of the collecting cylinder 2 and the bottom vent holes of the collecting base 3 are staggered to reduce the atomic density inside the probe (atoms are expelled from the end holes and vent holes) without ion leakage, thus reducing the impact of secondary ionization; while traditional Faraday probes collect electrodes... Figure 8 As shown in the right figure, the ion reflection generated after high-energy ions bombard the collecting electrode will reduce the collected ion current, while the generated secondary electrons will increase the collected ion current, affecting the measurement accuracy. The Faraday device of this embodiment can eliminate the effects of ion reflection and secondary electrons.

[0030] For example, this embodiment selects the best material for the Faraday probe. The shielding electrode 1, the collecting cylinder 2, the collecting base 3, and the outer shell 4 are gates that come into contact with high-energy ions. Therefore, the materials of the above components are preferably selected from materials that are resistant to sputtering and easy to process, such as pure titanium.

[0031] The shielding electrode 1 is made of pure titanium.

[0032] The collecting cylinder 2 is made of pure titanium.

[0033] The collection base 3 is made of pure titanium.

[0034] The outer shell 4 is made of pure titanium.

[0035] The insulating component A5 between the outer shell 4 and the shielding electrode 1, the insulating component B6 between the shielding electrode 1 and the collecting cylinder 2, and the base plate 7 must simultaneously ensure insulation and strength. Therefore, alumina material is preferred for the above components.

[0036] The insulating component A5 is made of aluminum oxide.

[0037] The insulating component B6 is made of aluminum oxide.

[0038] This embodiment is a practical application result of the Faraday probe device of the present invention, combined with... Figure 9 This implementation method is described below.

[0039] This implementation method was verified using Hall thruster. A Hall thruster is an electric propulsion device that uses orthogonal electromagnetic fields to ionize and accelerate the working gas to generate thrust, primarily used in aerospace propulsion. The Hall thruster creates orthogonal electromagnetic fields inside the channel. Electrons emitted from the cathode are constrained by the magnetic field as they reach the anode at the bottom of the channel, undergoing Larmor cyclotron motion around the magnetic field lines. Propellant is injected from the bottom of the channel, where neutral atoms collide with electrons, ionizing them and generating a large number of ions and electrons. These ions are ejected at high speed under the influence of the axial electric field, forming a plume that generates thrust. In Hall thruster, the distribution of ion current density represents the degree of plume divergence, and parameters such as ion current, plume divergence angle, and working propellant utilization can be calculated. These parameters reflect the ionization effect and provide a basis for the installation of the thruster on a satellite, making them crucial parameters.

[0040] The high-precision Faraday probe of this embodiment was validated on a 300W Hall thruster with a rated flow rate of 15 sccm. Relevant data are as follows: Figure 9 As shown in the left figure, it can be seen that the plume divergence gradually decreases with increasing working fluid flow rate (circled curve in the figure). The working fluid utilization rate also gradually increases from less than 80% at 5 sccm to over 90% (asterisk curve in the figure), and decreases slightly at high flow rates. At low flow rates, ionization and acceleration performance are poor, and insufficient ionization leads to some atoms remaining undionized, thus exhibiting plume divergence and low working fluid utilization. The relevant data are consistent with the common knowledge of Hall thrusters.

[0041] The conventional Faraday probe was validated on a 1.35 kW Hall thruster with a rated flow rate of 50 sccm. Relevant data are as follows: Figure 9 As shown in the right figure (the circled curve represents the relationship between the plume divergence angle and the flow rate, and the asterisked curve represents the relationship between the working fluid utilization rate and the flow rate), although the thruster models measured by the two methods are different, the traditional Faraday method, due to sheath collisions, shows a high correlation between ion current, working fluid utilization rate, and plume divergence angle; that is, the more divergent the plume, the higher the ion current and working fluid utilization rate. At the lowest flow rate, the plume divergence angle is the largest, while the working fluid utilization rate is very high, generally exceeding 100%, which reflects the poor accuracy of the traditional Faraday method.

[0042] The present invention has been disclosed above with reference to preferred embodiments, but it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed structure and technical content to create equivalent embodiments without departing from the scope of the present invention, and all such modifications or alterations shall still fall within the scope of the present invention.

Claims

1. A Faraday probe device, characterized in that: It includes a shielding electrode (1), a collecting electrode, a housing (4), an insulating component A (5), an insulating component B (6), and a base plate (7); The collecting electrode includes a collecting cylinder (2) and a collecting base (3); the collecting electrode is disposed inside and covered by the outer shell (4), the outer shell (4) is mounted on the base plate (7), one end of the collecting cylinder (2) is closed and has an end hole, the other end of the collecting cylinder (2) is open, the closed end of the collecting cylinder (2) is disposed on the collecting base (3), the collecting base (3) is disposed on the base plate (7), and air outlets are arranged on the collecting base (3) and the base plate (7), the end hole and the air outlet are staggered, and the open end of the collecting cylinder (2) is arranged from bottom to top with Insulator B (6), shielding electrode (1) and insulating element A (5) are provided with coaxial through holes on the axial direction of the collecting cylinder (2). The through holes are connected to the opening of the collecting cylinder (2). The shielding electrode (1) and the collecting electrode can be energized respectively. The shielding electrode (1) is used to generate repulsive electrons and collect ion sheaths. The collecting electrode is used to collect ions entering the collecting cylinder (2) and to recollect the reflected ions and secondary electrons generated by the ions entering the collecting cylinder (2).

2. The Faraday probe device according to claim 1, characterized in that: The surface of the insulating component A (5) facing the shielding electrode (1) is provided with an annular groove.

3. The Faraday probe device according to claim 1, characterized in that: The insulating component B (6) has an annular groove on its surface facing the collecting cylinder (2).

4. The Faraday probe device according to claim 1, characterized in that: The shielding electrode (1) is made of pure titanium.

5. The Faraday probe device according to claim 1, characterized in that: The material of the collection tube (2) is pure titanium.

6. The Faraday probe device according to claim 1, characterized in that: The collection base (3) is made of pure titanium.

7. The Faraday probe device according to claim 1, characterized in that: The outer shell (4) is made of pure titanium.

8. The Faraday probe device according to claim 1, characterized in that: The insulating component A(5) is made of aluminum oxide.

9. The Faraday probe device according to claim 1, characterized in that: The insulating component B(6) is made of aluminum oxide.

10. The Faraday probe device according to claim 1, characterized in that: When in use, different plasma environments can be adapted by changing the potentials of the shielding electrode (1) and the collecting electrode.

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