Method for enhancing air plasma ionization for air-breathing electric propulsion using metallic tin

Abstract

This invention discloses a method for enhancing the ionization degree of air plasma using metallic tin in air-breathing electric propulsion. The method includes the following steps: a cylindrical tin wire is fed into a reference electrode using an automated wire feeding technology mature in the industrial welding field, with automatic wire feeding controlled by a feedback control circuit; the parameter controlled by this feedback control circuit is the intensity of the current collected by the tin wire within the plasma; the length l of the tin wire fed into the discharge chamber is obtained according to the global balance principle; and a suitable current intensity threshold I is selected. Sn When the collected current I is less than the threshold, the wire is fed; when it is greater than the threshold, the wire feeding stops. This invention utilizes four advantages of metallic tin: very low chemical energy and easy discharge; relatively low chemical reactivity and easy implementation; solid state and easy storage; and relatively low cost and portability. It solves the technical problem of the great difficulty of air ionization.

Description

Technical Field

[0001] This invention belongs to the field of ultra-low orbit space electric propulsion technology, and particularly relates to a method for enhancing the ionization of air plasma with metallic tin for air-breathing electric propulsion. Background Technology

[0002] The novel application of ultra-low orbit space is limited by the fact that existing electric propulsion technology cannot generate enough thrust, due to the fact that air is difficult to ionize, there are few ions available to generate thrust, and the degree of ionization is insufficient.

[0003] Air-breathing electric propulsion technology is a very new technology that has not yet been realized domestically or internationally because some key technologies have not yet been overcome. One of these key technologies is air ionization, which is extremely difficult. Summary of the Invention

[0004] This invention addresses the problems existing in the prior art by proposing a method for enhancing the ionization degree of air plasma with metallic tin for air-breathing electric propulsion. The aim is to solve the problems of the difficulty in air ionization, the scarcity of ions for generating thrust, and insufficient ionization degree.

[0005] To address the problems existing in the prior art, the present invention proposes the following technical solution:

[0006] A method for enhancing the ionization degree of air plasma with metallic tin for air-breathing electric propulsion is disclosed. This method is based on a device for enhancing the ionization degree of air plasma with metallic tin. The device includes a plasma discharge chamber, a reference electrode, an insulating layer, an automatic solder wire feeding structure, and a feedback control circuit. The automatic solder wire feeding structure penetrates the plasma discharge chamber through the reference electrode and the insulating layer on the inner surface of the reference electrode, and automatically feeds solder wire into the plasma discharge chamber. The reference electrode and its inner insulating layer are fitted onto the outer surface of the solder wire. The feedback control circuit controls the wire feeding motion; one end is connected to the reference electrode, and the other end is connected to the solder wire. The circuit composed of the reference electrode and the feedback control circuit is a levitation system relative to the plasma, and the potential of this levitation system relative to the plasma is appropriately controlled as needed.

[0007] Its characteristics are: the method includes the following steps,

[0008] Step 1: At the reference electrode, a cylindrical solder wire is fed in, and a mature automatic wire feeding technology solution in the industrial welding field is adopted. The wire feeding is automatically controlled by a feedback control circuit. The parameter controlled by the feedback control circuit is the intensity of the current collected by the solder wire in the plasma.

[0009] Step 2: Based on the principle of global balance, obtain the length l of the solder wire fed into the discharge chamber;

[0010] Step 3: Select a suitable current intensity threshold ISn When the collected current I is less than the threshold, wire feeding is initiated; when it is greater than the threshold, wire feeding is stopped.

[0011] Furthermore, in step two, based on the principle of global balance, the length l of the solder wire fed into the discharge chamber is obtained. The specific process is as follows:

[0012] (1) Design parameters relating the threshold of the current collection to the size and length of the solder wire;

[0013] (2) Based on the global balance principle that the rate of tin atom vapor generated by sputtering on the tin wire surface is equal to the rate of loss of tin atoms deposited on the wall, the length l of the tin wire fed into the discharge chamber is obtained.

[0014] Furthermore, the design of step two (1) involves collecting parameters relating the current threshold to the size and length of the solder wire. The specific steps are as follows:

[0015] ① The required tin atom concentration for enhanced discharge design: n Sn ;

[0016] ②Design the electron concentration, electron temperature, and ion temperature within the plasma discharge chamber: n e ,T e ,T i ;

[0017] ③ Design the dimensions of the plasma discharge chamber: diameter D, length L;

[0018] ④ Design the dimensions of the exposed solder wire: diameter d, length l.

[0019] Furthermore, in step two (2), based on the global balance principle that the rate of tin atom vapor generated by sputtering on the tin wire surface is equal to the loss rate of tin atoms deposited on the wall surface, the length l of the tin wire fed into the discharge chamber is obtained. The specific steps are as follows:

[0020] ①γπdl·n i u B =πDL·n Sn v th (1)

[0021] The left side of Equation (1) represents the rate of tin atom vapor generated by sputtering on the tin wire surface, and the right side of Equation (1) represents the rate of tin atom loss on the wall surface.

[0022] The parameters on the left side of equation (1) are: γ is the yield of tin atoms under sputtering, d is the diameter of the tin wire, l is the length of the tin wire fed into the discharge chamber, and n is the length of the tin wire fed into the discharge chamber. i It is the ion number density within the sheath, and the Bohm velocity. Where k is the Boltzmann constant, and T e It is the electron temperature, m i It is the mass of the ions;

[0023] The parameters on the right side of equation (1) are: D is the diameter of the plasma discharge chamber, L is the length of the plasma discharge chamber, and n Sn It refers to the tin ion density and the thermal velocity of tin ions within the discharge chamber. Where k is the Boltzmann constant, T i It is the tin ion temperature, m Sn It is the mass of tin ions.

[0024] ② Bohm speed Tin ion thermal motion velocity Substituting into equation (1), we get:

[0025]

[0026] Where γ is the yield of tin atoms under sputtering, d is the diameter of the tin wire, and l is the length of the tin wire extending into the discharge chamber.

[0027] Degree, n i T is the number density of ions within the sheath, k is the Boltzmann constant, and T is the number density of ions within the sheath. e It is the electron temperature, m i Where is the ion mass, D is the diameter of the plasma discharge chamber, L is the length of the plasma discharge chamber, and n is the ion mass. Sn It is the tin ion density in the discharge chamber, T i It is the tin ion temperature, m Sn It is the mass of tin ions;

[0028] ③ By rearranging formula (2), the length l of the tin wire fed into the discharge chamber can be obtained:

[0029]

[0030] Furthermore, in step three, a suitable current intensity threshold I is selected. sn When the collected current I is less than the threshold, wire feeding begins; when it is greater than the threshold, wire feeding stops. The specific steps are as follows:

[0031] ① Obtain the saturated ion current I collected by the probe

[0032] I=πdl·n i u B (4)

[0033] The probe is an equivalent probe made of tin wire;

[0034] ② Apply a bias voltage to the tin wire to generate a saturated ion current. By moving γ from the left side of equation (1) to the right side, it can be found that the left side of the transformed equation is the saturated ion current I collected by the probe as described by equation (4). The parameters on the right side of the transformed equation can be determined in the design and testing phase and can be used as the criteria for controlling wire feeding. Therefore, let the current criterion be:

[0035]

[0036] Where, D, L, n Sn As given in the design scheme, γ and v th The current criterion I is determined through testing. Sn .

[0037] ③ When the actual measured current I = πdl·n i u B <I Sn Feed the wire and increase the current; when the actual measured current I = πdl·n i u B >I Sn Some of the solder wire was retracted, and the current was reduced.

[0038] Furthermore, the appropriate control of the potential of the levitation system relative to the plasma is as follows: Scenario 1: Setting its potential lower than the plasma potential can be used to collect tin ions in the plasma, thereby recovering tin elements and reducing tin loss. At the same time, it reduces the tin vapor concentration at the lead-out end and lowers the short-circuit risk of electric field acceleration propulsion.

[0039] Furthermore, appropriately controlling the potential of the levitation system relative to the plasma, in scenario two, allows the system to have a potential higher than the plasma potential. This can enhance the concentration of tin ions in the plasma, increase the ionization intensity, and simultaneously increase the ion concentration in the plasma, which is beneficial to the efficiency of electric propulsion systems such as magnetic nozzles that rely on charge acceleration.

[0040] Furthermore, the wire feeding control employs PID technology, with control parameters optimized through experimental tuning; the amount of solder wire used is evaluated using typical parameters: assuming an electron temperature of ~1 eV and a Bohm speed of ~10. 3 m / s, electron density ~10 20 m -3 If the solder wire is approximately 10mm long and 1mm in diameter, then the loss rate is approximately (assuming γ≈1): The annual consumption is: The electron density is ~10 20 m -3 That is, at a discharge pressure of 1 Pa and an air temperature of 300 K, the degree of ionization is close to 100%.

[0041] Advantages and effects of the present invention

[0042] 1. The chemical ionization energy of metallic tin is only about 7.3 eV, which is lower than that of xenon, a commonly used electric propulsion propellant (xenon has an ionization energy of about 12.1 eV). It is easy to ionize and generate enough free electrons to participate in the ionization reaction.

[0043] 2. Metallic tin has weak chemical activity, does not react violently with air, has good reliability, and is easy to store;

[0044] 3. Metallic tin is solid at room temperature and does not require compressed storage containers, making it very suitable for carrying.

[0045] 4. Tin is widely used in industry and is very inexpensive. Attached Figure Description

[0046] Figure 1 This is a flowchart of the method for enhancing the ionization degree of air plasma with metallic tin for air-breathing electric propulsion according to the present invention;

[0047] Figure 2 This is a schematic diagram of the tin-enhanced air plasma ionization device for air-breathing electric propulsion of the present invention. Detailed Implementation

[0048] Design principle of the invention

[0049] 1. Innovation of this invention: The innovation lies in overcoming traditional biases and employing the technique of using tin metal for air ionization, a method often abandoned due to technological prejudice, thus solving the very difficult technical problem of air ionization. This invention utilizes four advantages of tin metal: First, its chemical energy is very low, making it easy to discharge—a crucial point. Tin metal's chemical ionization energy is only about 7.3 eV, lower than that of xenon gas, a commonly used electric propulsion propellant (xenon's ionization energy is about 12.1 eV), making it easy to ionize and generate enough free electrons to participate in the air ionization reaction. Second, its chemical reactivity is not so strong, making it relatively easy to implement. Tin metal has weak chemical reactivity, does not react violently with air, has good reliability, and is easy to store. Third, it is solid, making it easy to store and requiring no high-pressure compression. Tin metal is solid at room temperature, requiring no compressed containers for storage, making it very suitable for portability. Fourth, it has relatively low cost and is convenient to carry. Tin metal is widely used in industry, and its cost is very low. The aforementioned relatively low cost and portability refer to the annual consumption of tin metal for air ionization: If air-breathing electric propulsion technology is used to sustain flight in ultra-low Earth orbit for 10 years, the amount of tin metal required would only be 190g.

[0050] 2. The difference between the air-breathing electric propulsion of this invention and existing technologies: Existing electric propulsion does not inhale air; it carries its own working fluid. Therefore, the working fluid it carries is generally easily ionized, such as xenon. The air-breathing technology of this invention inhales air, which is not easily ionized. Therefore, metallic tin is used to enhance the ionization degree of the air plasma.

[0051] 3. Design difficulties and key points of this method: ① The difficulty lies in how to maintain the best feeding of the solder wire and maintain an optimal feeding state. ② In order to maintain an optimal feeding state, this invention adopts the theory of a probe (the probe is equivalent to a probe made of solder wire), applies a bias voltage to the probe, and uses the voltage current to detect when the feeding is optimal. Formula (1) is used to explain the design idea of ​​the probe theory. Formula (1) utilizes the global balance principle, which is that the rate of tin atom vapor generated by sputtering on the surface of the solder wire is equal to the loss rate of tin atoms deposited on the wall. When the two are equal, global balance is achieved. ③ The ultimate purpose of formula (1) is to obtain the feeding length l and d of the solder wire. The appropriate setting of the feeding length l and diameter d of the solder wire is related to the parameters set in advance. The design parameters are the design requirements of electric propulsion. The l and d of the solder wire are designed according to the requirements. That is, the design is based on the previous constraints. ④ d and l cannot be arbitrarily chosen because there is a certain dependency between d and l. This dependency is formula (1). Formula (1) tells us that when you choose a known design parameter d, d will correspond to a l, and at the same time, the assumption that l is much larger than d must be met, so this formula (1) should be used. d is a design value in the design stage. Based on this d, we can deduce l, thus obtaining a design diameter d and a l derived from formula (1). Although theoretically, we can also deduce d from l in the design stage using formula (1), the wire feeding structure controls the length l, not the diameter d, and it is more convenient to determine d and then deduce l. ⑤ The bias voltage can be positive or negative, depending on the actual process. If recycling is required, negative bias is appropriate; if recycling is not required, positive bias is appropriate. ⑥ Feasibility analysis of the scheme, that is, demonstration, refers to whether the tin consumption is particularly large. For example, if the amount of tin required is particularly large, it is not feasible. After demonstration, it is found that 19 grams of tin are used per year, and only 190 grams are used in 10 years. Therefore, the scheme is feasible.

[0052] Based on the above principles, this invention relates to a method for enhancing the ionization degree of air plasma using metallic tin in air-breathing electric propulsion, such as... Figure 1 , Figure 2 As shown, this method is based on a device for enhancing the ionization degree of air plasma using metallic tin. Figure 1As shown, the device includes a plasma discharge chamber, a reference electrode, an insulating layer, an automatic solder wire feeding structure, and a feedback control circuit. The automatic solder wire feeding structure passes through the reference electrode and the insulating layer on the inner surface of the reference electrode into the plasma discharge chamber, and automatically feeds solder wire into the plasma discharge chamber. The reference electrode and the insulating layer on its inner surface are fitted onto the outer surface of the solder wire. The feedback control circuit is used to control the wire feeding movement, with one end connected to the reference electrode and the other end connected to the solder wire. The circuit composed of the reference electrode and the feedback control circuit is a suspension system relative to the plasma, and the potential of the suspension system relative to the plasma is appropriately controlled as needed.

[0053] Supplementary Note 1

[0054] like Figure 2 As shown, ① the reference electrode is a cylindrical reference electrode with an insulating layer on its inner surface. The reference electrode and the insulating layer are fitted onto the outer surface of the solder wire; ② the solder wire and the plasma discharge chamber are at the same potential, both being the negative potential terminals of the feedback control circuit, while the reference electrode is the positive potential terminal of the feedback control circuit.

[0055] Its characteristics are: the method includes the following steps,

[0056] Step 1: At the reference electrode, a cylindrical solder wire is fed in, and a mature automatic wire feeding technology solution in the industrial welding field is adopted. The wire feeding is automatically controlled by a feedback control circuit. The parameter controlled by the feedback control circuit is the intensity of the current collected by the solder wire in the plasma.

[0057] Step 2: Based on the principle of global balance, obtain the length l of the solder wire fed into the discharge chamber;

[0058] Supplementary Note 2

[0059] like Figure 2 As shown, the length l of the solder wire fed into the discharge chamber is not unique, but is related to the diameter d of the solder wire. If the length l of the solder wire is longer, the diameter d will be relatively smaller, and if the diameter d is smaller, the length l will be relatively longer.

[0060] Step 3: Select a suitable current intensity threshold I Sn When the collected current I is less than the threshold, wire feeding is initiated; when it is greater than the threshold, wire feeding is stopped.

[0061] Furthermore, in step two, based on the principle of global balance, the length l of the solder wire fed into the discharge chamber is obtained. The specific process is as follows:

[0062] (1) Design parameters relating the threshold of the current collection to the size and length of the solder wire;

[0063] (2) Based on the global balance principle that the rate of tin atom vapor generated by sputtering on the tin wire surface is equal to the rate of loss of tin atoms deposited on the wall, the length l of the tin wire fed into the discharge chamber is obtained.

[0064] Furthermore, the design of step two (1) involves collecting parameters relating the current threshold to the size and length of the solder wire. The specific steps are as follows:

[0065] ① The required tin atom concentration for enhanced discharge design: n Sn ;

[0066] ②Design the electron concentration, electron temperature, and ion temperature within the plasma discharge chamber: n e ,T e ,T i ;

[0067] ③ Design the dimensions of the plasma discharge chamber: diameter D, length L;

[0068] ④ Design the dimensions of the exposed solder wire: diameter d, length l.

[0069] Furthermore, in step two (2), based on the global balance principle that the rate of tin atom vapor generated by sputtering on the tin wire surface is equal to the loss rate of tin atoms deposited on the wall surface, the length l of the tin wire fed into the discharge chamber is obtained. The specific steps are as follows:

[0070] ①γπdl·n i u B =πDL·n Sn v th (1)

[0071] The left side of Equation (1) represents the rate of tin atom vapor generated by sputtering on the tin wire surface, and the right side of Equation (1) represents the rate of tin atom loss on the wall surface.

[0072] The parameters on the left side of equation (1) are: γ is the yield of tin atoms under sputtering, d is the diameter of the tin wire, l is the length of the tin wire fed into the discharge chamber, and n is the length of the tin wire fed into the discharge chamber. i It is the ion number density within the sheath, and the Bohm velocity. Where k is the Boltzmann constant, and T e It is the electron temperature, m i It is the mass of the ions;

[0073] The parameters on the right side of equation (1) are: D is the diameter of the plasma discharge chamber, L is the length of the plasma discharge chamber, and n Sn It refers to the tin ion density and the thermal velocity of tin ions within the discharge chamber. Where k is the Boltzmann constant, T i It is the tin ion temperature, m Sn It is the mass of tin ions.

[0074] ② Bohm speed Tin ion thermal motion velocity Substituting into equation (1), we get:

[0075]

[0076] Where γ is the yield of tin atoms under sputtering, d is the diameter of the tin wire, l is the length of the tin wire extending into the discharge chamber, and n i T is the number density of ions within the sheath, k is the Boltzmann constant, and T is the number density of ions within the sheath. e It is the electron temperature, m i Where is the ion mass, D is the diameter of the plasma discharge chamber, L is the length of the plasma discharge chamber, and n is the ion mass. Sn It is the tin ion density in the discharge chamber, T i It is the tin ion temperature, m Sn It is the mass of tin ions;

[0077] ③ By rearranging formula (2), the length l of the tin wire fed into the discharge chamber can be obtained:

[0078]

[0079] Furthermore, in step three, a suitable current intensity threshold I is selected. sn When the collected current I is less than the threshold, wire feeding begins; when it is greater than the threshold, wire feeding stops. The specific steps are as follows:

[0080] ① Obtain the saturated ion current I collected by the probe

[0081] I=πdl·n i u B (4)

[0082] The probe is an equivalent probe made of tin wire;

[0083] ② Apply a bias voltage to the tin wire to generate a saturated ion current. By moving γ from the left side of equation (1) to the right side, it can be found that the left side of the transformed equation is the saturated ion current I collected by the probe as described by equation (4). The parameters on the right side of the transformed equation can be determined in the design and testing phase and can be used as the criteria for controlling wire feeding. Therefore, let the current criterion be:

[0084]

[0085] Where, D, L, n Sn As given in the design scheme, γ and v th The current criterion I is determined through testing. Sn .

[0086] ③ When the actual measured current I = πdl·n i u B <ISn Feed the wire and increase the current; when the actual measured current I = πdl·n i u B >I Sn Some of the solder wire was retracted, and the current was reduced.

[0087] Furthermore, the appropriate control of the potential of the levitation system relative to the plasma is as follows: Scenario 1: Setting its potential lower than the plasma potential can be used to collect tin ions in the plasma, thereby recovering tin elements and reducing tin loss. At the same time, it reduces the tin vapor concentration at the lead-out end and lowers the short-circuit risk of electric field acceleration propulsion.

[0088] Furthermore, appropriately controlling the potential of the levitation system relative to the plasma, in scenario two, allows the system to have a potential higher than the plasma potential. This can enhance the concentration of tin ions in the plasma, increase ionization intensity, and simultaneously increase the ion concentration in the plasma, which is beneficial to the efficiency of electric propulsion systems such as magnetic nozzles that rely on charge acceleration.

[0089] Furthermore, the wire feeding control employs PID technology, with control parameters optimized through experimental tuning. The amount of solder wire used is evaluated using typical parameters: assuming an electron temperature of ~1 eV, a Bohm velocity of ~10³ m / s, and an electron density of ~10... 20 m -3 If the solder wire is approximately 10mm long and 1mm in diameter, then the loss rate is approximately (assuming γ≈1): The annual consumption is: The electron density is ~10 20 m -3 That is, at a discharge pressure of 1 Pa and an air temperature of 300 K, the degree of ionization is close to 100%.

[0090] It should be emphasized that the above specific embodiments are merely explanations of the present invention and are not intended to limit the present invention. After reading this specification, those skilled in the art can make modifications to the above embodiments without contributing any inventive step, but as long as they are within the scope of the claims of the present invention, they are protected by patent law.

Claims

1. A method for enhancing the ionization degree of air plasma with metallic tin for air-breathing electric propulsion, the method being based on a device for enhancing the ionization degree of air plasma with metallic tin, the device comprising a plasma discharge chamber, a reference electrode, an insulating layer, an automatic solder wire feeding structure, and a feedback control circuit; the automatic solder wire feeding structure penetrates into the plasma discharge chamber through the reference electrode and the insulating layer on the inner surface of the reference electrode and automatically feeds solder wire into the plasma discharge chamber. The reference electrode and its inner surface insulating layer are fitted onto the outer surface of the tin wire; This feedback control circuit is used to control the wire feeding motion. One end of it is connected to the reference electrode, and the other end is connected to the solder wire. The circuit consisting of the reference electrode and the feedback control circuit is a suspended system relative to the plasma. The potential of the suspended system relative to the plasma is appropriately controlled as needed. The method is characterized by the following steps: Step 1: At the reference electrode, a cylindrical solder wire is fed in, and the wire feeding is automatically controlled by a feedback control circuit. The parameter controlled by the feedback control circuit is the intensity of the current collected by the solder wire in the plasma. Step 2: Based on the principle of global balance, obtain the length l of the solder wire fed into the discharge chamber; Step 3: Select a suitable current intensity threshold I Sn When the collected current I is less than the threshold, wire feeding is started; when it is greater than the threshold, wire feeding is stopped. Step two, based on the principle of global balance, determines the length l of the solder wire fed into the discharge chamber. The specific process is as follows: (1) Design parameters to collect the relationship between the current intensity threshold and the size and length of the solder wire; (2) Based on the global balance principle that the rate of tin atom vapor generated by sputtering on the tin wire surface is equal to the rate of loss of tin atoms deposited on the wall, the length l of the tin wire fed into the discharge chamber is obtained; The appropriate control of the potential of the suspension system relative to the plasma is as follows: Scenario 1: Setting its potential lower than the plasma potential can be used to collect tin ions in the plasma, thereby recovering tin elements and reducing tin loss. At the same time, it reduces the tin vapor concentration at the lead-out end and reduces the short-circuit risk of electric field acceleration propulsion. The appropriate control of the potential of the suspension system relative to the plasma, in scenario two, allows the system to have a potential higher than that of the plasma. This can be used to increase the concentration of tin ions in the plasma, thereby increasing the ionization intensity. It can also increase the ion concentration in the plasma, which is beneficial to the efficiency of electric propulsion systems such as magnetic nozzles that rely on charge acceleration.

2. The method for enhancing the ionization degree of air plasma with metallic tin for air-breathing electric propulsion according to claim 1, characterized in that: Step two, process (1), involves designing and collecting parameters relating the current intensity threshold to the size and length of the solder wire. The specific steps are as follows: ① The required tin atom concentration for enhanced discharge design: n Sn ; ②Design the electron concentration, electron temperature, and ion temperature within the plasma discharge chamber: n e ,T e ,T i ; ③ Design the dimensions of the plasma discharge chamber: diameter D, length L; ④ Design the dimensions of the exposed solder wire: diameter d, length l.

3. The method for enhancing the ionization degree of air plasma with metallic tin for air-breathing electric propulsion according to claim 1, characterized in that: In step two (2), based on the global balance principle that the rate of tin atom vapor generated by sputtering on the tin wire surface is equal to the rate of loss of tin atoms deposited on the wall surface, the length l of the tin wire fed into the discharge chamber is obtained. The specific steps are as follows: ①γπdl·n i u B =πDL·n Sn v th (1) The left side of Equation (1) represents the rate of tin atom vapor generated by sputtering on the tin wire surface, and the right side of Equation (1) represents the rate of tin atom loss on the wall surface. The parameters on the left side of equation (1) are: γ is the yield of tin atoms under sputtering, d is the diameter of the tin wire, l is the length of the tin wire fed into the discharge chamber, and n is the length of the tin wire fed into the discharge chamber. i It is the ion number density within the sheath, and the Bohm velocity. Where k is the Boltzmann constant, and T e It is the electron temperature, m i It is the mass of the ions; The parameters on the right side of equation (1) are: D is the diameter of the plasma discharge chamber, L is the length of the plasma discharge chamber, and n Sn It refers to the tin ion density and the thermal velocity of tin ions within the discharge chamber. Where k is the Boltzmann constant, T i It is the tin ion temperature, m Sn It is the mass of tin ions. ② Bohm speed Tin ion thermal motion velocity Substituting into equation (1), we get: Where γ is the yield of tin atoms under sputtering, d is the diameter of the tin wire, l is the length of the tin wire extending into the discharge chamber, and n i T is the number density of ions within the sheath, k is the Boltzmann constant, and T is the number density of ions within the sheath. e It is the electron temperature, m i Where is the ion mass, D is the diameter of the plasma discharge chamber, L is the length of the plasma discharge chamber, and n is the ion mass. Sn It is the tin ion density in the discharge chamber, T i It is the tin ion temperature, m Sn It is the mass of tin ions; ③ By rearranging formula (2), the length l of the tin wire fed into the discharge chamber can be obtained:

4. The method for enhancing the ionization degree of air plasma with metallic tin for air-breathing electric propulsion according to claim 1, characterized in that: In step three, a suitable current intensity threshold I is selected. sn When the collected current I is less than the threshold, wire feeding begins; when it is greater than the threshold, wire feeding stops. The specific steps are as follows: ① Obtain the saturated ion current I collected by the probe I=πdl·n i u B (4) The probe is an equivalent probe made of tin wire; ② Apply a bias voltage to the tin wire to generate a saturated ion current. By moving γ from the left side of equation (1) to the right side, it can be found that the left side of the transformed equation is the saturated ion current I collected by the probe as described by equation (4). The parameters on the right side of the transformed equation can be determined in the design and testing phase and can be used as the criterion for controlling wire feeding. Therefore, let the current intensity threshold be: Where, D, L, n Sn As given in the design scheme, γ and v th The current intensity threshold I was determined through testing. Sn ; ③ When the actual measured current I = πdl·n i u B <I Sn Feed the wire and increase the current; when the actual measured current I = πdl·n i u B >I Sn Some of the solder wire was retracted, and the current was reduced.

5. The method for enhancing the ionization degree of air plasma with metallic tin for air-breathing electric propulsion according to claim 1, characterized in that: Wire feeding control employs PID technology, with control parameters optimized through experimental tuning. The amount of solder wire used is evaluated using typical parameters: assuming an electron temperature of approximately 1 eV and a Bohm speed of approximately 10... 3 m / s, electron density ~10 20 m -3 The solder wire is approximately 10mm long and 1mm in diameter. Assuming γ≈1, the loss rate is approximately: The annual consumption is: The electron density is ~10 20 m -3 That is, at a discharge pressure of 1 Pa and an air temperature of 300 K, the degree of ionization is close to 100%.

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