Method for enhancing ionization degree of air plasma by metallic tin for air-breathing electric propulsion

Abstract

The invention discloses a method for enhancing the ionization degree of air plasma by metal tin for air-breathing electric propulsion, which comprises the following steps of: feeding in a cylindrical tin wire form at a reference electrode, and automatically controlling wire feeding through a feedback control circuit by adopting a mature automatic wire feeding technical scheme in the industrial welding field; the parameter for controlling wire feeding by the feedback control circuit is the intensity of current collected by the tin wire in the plasma; according to a global balance principle, obtaining the length l of the tin wire fed into the discharge chamber; and selecting a proper current intensity threshold value ISn, feeding the wire when the collected current I is less than the threshold value, and stopping feeding the wire when the collected current I is greater than the threshold value. The technical problem that air ionization is very difficult is solved by utilizing the four advantages that metallic tin is very low in chemical energy, easy to discharge, low in chemical activity, relatively easy to implement, solid, easy to store, relatively low in cost and convenient to carry.

Description

Technical Field

[0001] The invention belongs to the technical field of ultra-low orbit space electric propulsion, and in particular relates to a method for enhancing the ionization degree of air plasma using metal tin for air-breathing electric propulsion. Background Art

[0002] Novel applications in ultra-low orbit space are limited by the fact that existing electric propulsion technology has difficulty generating sufficient thrust, which is attributed to the difficult-to-ionize nature of air, the small number of ions used to generate thrust, and insufficient ionization.

[0003] Air-breathing electric propulsion technology is a very new technology. This technology has not yet been realized at home and abroad. The reason is that some key technologies have not yet been overcome. One of the key technologies is air ionization, which is very difficult. Summary of the invention

[0004] In view of the problems existing in the prior art, the present invention proposes a method for enhancing the ionization degree of air plasma by using metal tin for air-breathing electric propulsion, aiming to solve the difficult problems that air ionization is very difficult, there are few ions for generating thrust, and the ionization degree is insufficient.

[0005] The present invention proposes the following technical solutions to solve the problems existing in the prior art:

[0006] A method for enhancing the ionization degree of air plasma by using metal tin for air-breathing electric propulsion. The method is based on a device for enhancing the ionization degree of air plasma by using metal tin. The device comprises a plasma discharge chamber, a reference electrode, an insulating layer, an automatic tin wire feeding structure, and a feedback control circuit. The automatic tin 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 the tin wire to the plasma discharge chamber. The reference electrode and the insulating layer on the inner surface thereof are sleeved on the outer surface of the tin wire. The feedback control circuit is used to control the wire feeding movement, one end of which is connected to the reference electrode, and the other end is connected to the tin 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 required.

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

[0008] Step 1: Feed the reference electrode in the form of a cylindrical tin wire, and adopt the mature automatic wire feeding technology in the welding field of the industry, and automatically control the wire feeding through a feedback control circuit; the parameter of the feedback control circuit to control the wire feeding is the intensity of the current collected by the tin wire in the plasma;

[0009] Step 2: According to the global balance principle, the length l of the tin wire sent into the discharge chamber is obtained;

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

[0011] Furthermore, in step 2, the length l of the tin wire fed into the discharge chamber is obtained according to the global balance principle, and the specific process is as follows:

[0012] ⑴ Design the relationship between the threshold of the collection current and the size and length of the tin wire;

[0013] ⑵ According to the global balance principle that the rate of tin atomic vapor generated by sputtering on the surface of the tin wire is equal to the loss rate of tin atoms deposited on the wall, the length l of the tin wire sent into the discharge chamber is obtained.

[0014] Furthermore, the design of the step 2 process (1) collects the relationship parameters between the threshold of the current and the size and length of the tin wire, and the specific steps are as follows:

[0015] ① Design the concentration of tin atoms required to enhance discharge: n Sn ;

[0016] ② Design the electron concentration, electron temperature and ion temperature in 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 size of the exposed tin wire: diameter d, length l.

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

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

[0021] The left side of the equation (1) is the rate of tin atom vapor generated by sputtering on the tin wire surface, and the right side of the equation (1) is the loss rate of tin atoms deposited on the wall surface;

[0022] The parameters on the left side of the equal sign in formula (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 i is the ion number density in the sheath, and the Bohm velocity where k is the Boltzmann constant, T e is the electron temperature, m i is the mass of the ion;

[0023] The parameters on the right side of the equal sign in formula (1): D is the diameter of the plasma discharge chamber, L is the length of the plasma discharge chamber, n Sn is the tin ion density in the discharge chamber, and the thermal motion speed of the tin ions Where k is the Boltzmann constant, T i is the tin ion temperature, m Sn is the mass of tin ions,

[0024] ② Set the Bohm speed Thermal motion speed of tin ions Substituting into formula (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 is the ion number density in the sheath, k is the Boltzmann constant, T e is the electron temperature, m i is the ion mass, D is the diameter of the plasma discharge chamber, L is the length of the plasma discharge chamber, and n Sn is the tin ion density in the discharge chamber, T i is the tin ion temperature, m Sn is the mass of tin ions;

[0028] ③ Arrange formula (2) to obtain the length l of the tin wire sent into the discharge chamber:

[0029]

[0030] Furthermore, the step 3 selects a suitable current intensity threshold I 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 is stopped. 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 a probe equivalent to tin wire;

[0034] ② Add bias voltage to the tin wire to generate saturated ion current. By moving γ on 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 described by equation (4). The parameters on the right side of the transformed equation can be determined in the design and test stage and can be used as a criterion for controlling wire feeding. Therefore, the current criterion is:

[0035]

[0036] Among them, D, L, n Sn Given by the design solution, γ and v th Determine through testing, thereby determining the current criterion I Sn .

[0037] ③When 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 , retract some of the tin wire and reduce the current.

[0038] Furthermore, the potential of the suspension system relative to the plasma is appropriately controlled as follows: Scenario 1: The potential is made lower than the plasma potential, which can be used to collect tin ions in the plasma, thereby recovering the tin element and reducing tin loss, while reducing the tin vapor concentration at the lead end and reducing the short-circuit risk of electric field acceleration.

[0039] Furthermore, the appropriate control of the potential of the suspension system relative to the plasma, scenario two: making its potential higher than the plasma potential, can be used to enhance the tin ion concentration in the plasma, enhance the ionization intensity, and at the same time enhance the ion concentration in the plasma, which is beneficial to the efficiency of electric propulsion such as magnetic nozzles that rely on charge acceleration.

[0040] Furthermore, the wire feeding control includes the use of PID technology to optimize the control parameters through experimental adjustment; the amount of tin wire is evaluated using typical parameters: assuming that the electron temperature is ~1eV and the Bohm speed is ~10 3 m / s, electron density ~10 20 m -3 , the tin wire length is ~10mm and the diameter is ~1mm, then the loss rate is about (assuming γ≈1): The annual consumption is: The electron density is 10 20 m -3 That is: under 1Pa discharge pressure and 300K air temperature, 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 the commonly used electric propulsion medium xenon (the ionization energy of xenon is about 12.1 eV). It is easy to ionize and generate enough free electrons to participate in the ionization reaction;

[0043] 2. The chemical activity of metal tin is weak, it does not react violently with the air, it is reliable and easy to preserve;

[0044] 3. Metal tin is solid at room temperature and does not need to be stored in a compressed container, making it very suitable for carrying;

[0045] 4. Metallic tin is very commonly used in industry and has very low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 This is a flow chart of the method for enhancing the ionization degree of air plasma with metal tin for air-breathing electric propulsion of the present invention;

[0047] Figure 2 It is a schematic diagram of a metal tin enhanced air plasma ionization device for air-breathing electric propulsion of the present invention; DETAILED DESCRIPTION

[0048] Design principle of the present invention

[0049] 1. Innovation of the present invention: The innovation lies in overcoming traditional prejudices and adopting the technical means of using tin metal for air ionization that people have abandoned due to technical prejudices, thereby solving the technical problem that air ionization is very difficult. The present invention utilizes four advantages of tin metal: First, the chemical energy is very low and it is easy to discharge, which is a very core point. The chemical ionization energy of tin metal is only about 7.3eV, which is lower than the commonly used electric propulsion working fluid xenon (xenon gas ionization energy is about 12.1eV), so it is easy to ionize and produce enough free electrons to participate in the ionization reaction of air. Second, the chemical activity is not so strong and it is relatively easy to achieve. The chemical activity of metallic tin is weak, it does not react violently with the air, it has good reliability and is easy to preserve; third, it is solid, easy to store, and does not require high-pressure compression. Metallic tin is solid at room temperature and does not need to be stored in a compressed container, which is very suitable for carrying; fourth, the cost is relatively low and it is easy to carry. Metallic tin is very commonly used in industry and has very low cost. The relatively low cost and easy to carry refer to the annual consumption of metallic tin for air ionization: If air-breathing electric propulsion technology is used to sustain 10 years of flight in ultra-low orbit space, the amount of metal tin required to be carried is only 190g.

[0050] 2. The difference between the air-breathing electric propulsion of the present invention and the prior art: the electric propulsion of the prior art does not breathe air, but carries its own working fluid, so the working fluid it carries is generally easy to ionize, such as xenon. The air-breathing described in the present invention breathes air, which is not easy to ionize, so metal tin is used to enhance the ionization degree of air plasma.

[0051] 3. The design difficulties and key points of this method are as follows: ① The difficulty lies in how to keep the tin wire fed as best as possible and maintain an optimal feeding state. ② In order to maintain an optimal feeding state, the present invention adopts a probe theory (the probe is a probe equivalent to tin wire), gives the probe a bias voltage, and uses the voltage current to detect when the feeding is best. Formula (1) is used to illustrate the design concept of the probe theory. Formula (1) utilizes the global balance principle. The global balance principle is that the rate of tin atom vapor generated by sputtering on the surface of the tin 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 goal of formula (1) is to obtain the feeding length l and d of the tin wire. The appropriate setting of the feeding length l and diameter d of the tin wire is related to the parameters set in advance. The design parameters are the design requirements of the electric propulsion, and the l and d of the tin wire are designed according to the requirements. That is, it is designed according to the previous constraints. ④ d and l cannot be taken arbitrarily, because d and l have a certain dependence relationship. This dependence relationship is formula (1). Formula (1) tells us that when you select a known design parameter d, d will correspond to an l, and at the same time, the assumption that l is much greater than d must be satisfied, so this formula (1) must be used. d is a design value in the design stage. Based on this d, an l is obtained by reverse calculation, thereby obtaining a designed diameter d and an l obtained by reverse calculation using formula (1). Although in theory, d can be reversed using formula (1) based on the l in the design stage, the wire feeding structure controls the length l rather than the diameter d, and it is more convenient to determine d and then reverse calculate l. ⑤ The bias voltage can be positive or negative, depending on the actual process. If recycling is required, a negative bias voltage is appropriate. If recycling is not required, a positive bias voltage is appropriate. ⑥ Feasibility analysis of the scheme, that is, demonstration. The feasibility analysis is whether the consumption of tin is particularly large. For example, if the amount of tin consumed is particularly large, it is not feasible. After demonstration, 19 grams of tin is used per year, and only 190 grams is used in 10 years, so the scheme is feasible.

[0052] Based on the above principle, the present invention relates to a method for enhancing the ionization degree of air plasma by metal tin for air-breathing electric propulsion, such as Figure 1 , Figure 2 As shown, the method is based on a device for enhancing the ionization degree of air plasma by metal tin. Figure 1As shown, the device includes a plasma discharge chamber, a reference electrode, an insulating layer, an automatic tin wire feeding structure, and a feedback control circuit; the automatic tin 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 the tin wire to the plasma discharge chamber; the reference electrode and the insulating layer on the inner surface thereof are sleeved on the outer surface of the tin wire; the feedback control circuit is used to control the wire feeding movement, one end of which is connected to the reference electrode, and the other end is connected to the tin 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, the inner surface of the reference electrode is an insulating layer, and the reference electrode and the insulating layer are sheathed on the outer surface of the tin wire; ② the tin wire and the plasma discharge chamber have the same potential, both are the negative potential end of the feedback control circuit, and the reference electrode is the positive potential end of the feedback control circuit.

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

[0056] Step 1: Feed the reference electrode in the form of a cylindrical tin wire, and adopt the mature automatic wire feeding technology in the welding field of the industry, and automatically control the wire feeding through a feedback control circuit; the parameter of the feedback control circuit to control the wire feeding is the intensity of the current collected by the tin wire in the plasma;

[0057] Step 2: According to the global balance principle, the length l of the tin wire sent into the discharge chamber is obtained;

[0058] Supplementary Note 2

[0059] like Figure 2 As shown, the length l of the tin wire fed into the discharge chamber is not unique, but is related to the diameter d of the tin wire. The longer the length l of the tin wire is, the smaller the diameter d is, and the smaller the diameter d is, the longer the length l is.

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

[0061] Furthermore, in step 2, the length l of the tin wire fed into the discharge chamber is obtained according to the global balance principle, and the specific process is as follows:

[0062] ⑴ Design the relationship between the threshold of the collection current and the size and length of the tin wire;

[0063] ⑵ According to the global balance principle that the rate of tin atomic vapor generated by sputtering on the surface of the tin wire is equal to the loss rate of tin atoms deposited on the wall, the length l of the tin wire sent into the discharge chamber is obtained.

[0064] Furthermore, the design of the step 2 process (1) collects the relationship parameters between the threshold of the current and the size and length of the tin wire, and the specific steps are as follows:

[0065] ① Design the concentration of tin atoms required to enhance discharge: n Sn ;

[0066] ② Design the electron concentration, electron temperature and ion temperature in 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 size of the exposed tin wire: diameter d, length l.

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

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

[0071] The left side of the equation (1) is the rate of tin atom vapor generated by sputtering on the tin wire surface, and the right side of the equation (1) is the loss rate of tin atoms deposited on the wall surface;

[0072] The parameters on the left side of the equal sign in formula (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 i is the ion number density in the sheath, and the Bohm velocity where k is the Boltzmann constant, T e is the electron temperature, m i is the mass of the ion;

[0073] The parameters on the right side of the equal sign in formula (1): D is the diameter of the plasma discharge chamber, L is the length of the plasma discharge chamber, n Sn is the tin ion density in the discharge chamber, and the thermal motion speed of the tin ions Where k is the Boltzmann constant, T i is the tin ion temperature, m Sn is the mass of tin ions,

[0074] ② Set the Bohm speed Thermal motion speed of tin ions Substituting into formula (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 is the ion number density in the sheath, k is the Boltzmann constant, T e is the electron temperature, m i is the ion mass, D is the diameter of the plasma discharge chamber, L is the length of the plasma discharge chamber, and n Sn is the tin ion density in the discharge chamber, T i is the tin ion temperature, m Sn is the mass of tin ions;

[0077] ③ Arrange formula (2) to obtain the length l of the tin wire sent into the discharge chamber:

[0078]

[0079] Furthermore, the step 3 selects a suitable current intensity threshold I 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 is stopped. 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 a probe equivalent to tin wire;

[0083] ② Add bias voltage to the tin wire to generate saturated ion current. By moving γ on 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 described by equation (4). The parameters on the right side of the transformed equation can be determined in the design and test stage and can be used as a criterion for controlling wire feeding. Therefore, the current criterion is:

[0084]

[0085] Among them, D, L, n Sn Given by the design solution, γ and v th Determine through testing, thereby determining the current criterion I Sn .

[0086] ③When 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 , retract some of the tin wire and reduce the current.

[0087] Furthermore, the potential of the suspension system relative to the plasma is appropriately controlled as follows: Scenario 1: The potential is made lower than the plasma potential, which can be used to collect tin ions in the plasma, thereby recovering the tin element and reducing tin loss, while reducing the tin vapor concentration at the lead end and reducing the short-circuit risk of electric field acceleration.

[0088] Furthermore, the appropriate control of the potential of the suspension system relative to the plasma, scenario two: making its potential higher than the plasma potential, can be used to enhance the tin ion concentration in the plasma, enhance the ionization intensity, and at the same time enhance the ion concentration in the plasma, which is beneficial to the efficiency of electric propulsion such as magnetic nozzles that rely on charge acceleration.

[0089] Furthermore, the wire feeding control includes the use of PID technology to optimize the control parameters through experimental adjustment; the amount of tin wire is evaluated using typical parameters: assuming that the electron temperature is ~1eV, the Bohm velocity is ~103m / s, and the electron density is ~10 20 m -3 , the tin wire length is ~10mm and the diameter is ~1mm, then the loss rate is about (assuming γ≈1): The annual consumption is: The electron density is 10 20 m -3 That is: under 1Pa discharge pressure and 300K air temperature, 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 they are not limitations of the present invention. After reading this specification, those skilled in the art can make modifications to the above embodiments without any creative contribution as needed, 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 by using metal tin for air-breathing electric propulsion, the method is based on a device for enhancing the ionization degree of air plasma by using metal tin, the device comprising a plasma discharge chamber, a reference electrode, an insulating layer, an automatic tin wire feeding structure, and a feedback control circuit; the automatic tin 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 the tin wire to the plasma discharge chamber; The reference electrode and the insulating layer on its inner surface are sheathed on the outer surface of the tin wire; The feedback control circuit is used to control the wire feeding motion, one end of which is connected to the reference electrode and the other end is connected to the tin 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 required; The method is characterized in that: Step 1: Feed the reference electrode in the form of a cylindrical tin wire, and adopt the mature automatic wire feeding technology in the welding field of the industry, and automatically control the wire feeding through a feedback control circuit; the parameter of the feedback control circuit to control the wire feeding is the intensity of the current collected by the tin wire in the plasma; Step 2: According to the global balance principle, the length l of the tin wire sent into the discharge chamber is obtained; Step 3: Select a suitable current intensity threshold I Sn When the collected current I is less than the threshold, wire feeding starts; when it is greater than the threshold, wire feeding stops.

2. The method for enhancing the ionization degree of air plasma using metal tin for air-breathing electric propulsion according to claim 1, characterized in that: In step 2, the length l of the tin wire sent into the discharge chamber is obtained according to the global balance principle. The specific process is as follows: ⑴ Design the relationship between the threshold of the collection current and the size and length of the tin wire; ⑵ According to the global balance principle that the rate of tin atomic vapor generated by sputtering on the surface of the tin wire is equal to the loss rate of tin atoms deposited on the wall, the length l of the tin wire sent into the discharge chamber is obtained.

3. The method for enhancing the ionization degree of air plasma using metal tin for air-breathing electric propulsion according to claim 2, characterized in that: The design of the process (1) of step 2 collects the relationship parameters between the threshold of the current and the size and length of the tin wire. The specific steps are as follows: ① Design the concentration of tin atoms required to enhance discharge: n Sn ; ② Design the electron concentration, electron temperature and ion temperature in 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 size of the exposed tin wire: diameter d, length l.

4. The method for enhancing the ionization degree of air plasma using metal tin for air-breathing electric propulsion according to claim 2, characterized in that: The process (2) of step 2 is based on the global balance principle that the rate of tin atom vapor generated by sputtering on the surface of the tin wire is equal to the loss rate of tin atoms deposited on the wall surface, and the length l of the tin wire sent 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 the equation (1) is the rate of tin atom vapor generated by sputtering on the tin wire surface, and the right side of the equation (1) is the loss rate of tin atoms deposited on the wall surface; The parameters on the left side of the equal sign in formula (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 i is the ion number density in the sheath, and the Bohm velocity where k is the Boltzmann constant, T e is the electron temperature, m i is the mass of the ion; The parameters on the right side of the equal sign in formula (1): D is the diameter of the plasma discharge chamber, L is the length of the plasma discharge chamber, n Sn is the tin ion density in the discharge chamber, and the thermal motion speed of the tin ions Where k is the Boltzmann constant, T i is the tin ion temperature, m Sn is the mass of tin ions, ② Set the Bohm speed Thermal motion speed of tin ions Substituting into formula (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 is the ion number density in the sheath, k is the Boltzmann constant, T e is the electron temperature, m i is the ion mass, D is the diameter of the plasma discharge chamber, L is the length of the plasma discharge chamber, and n Sn is the tin ion density in the discharge chamber, T i is the tin ion temperature, m Sn is the mass of tin ions; ③ Arrange formula (2) to obtain the length l of the tin wire sent into the discharge chamber:

5. The method for enhancing the ionization degree of air plasma using metal tin for air-breathing electric propulsion according to claim 2, characterized in that: The step 3 of selecting a suitable current intensity threshold I 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 is stopped. 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 a probe equivalent to tin wire; ② Add bias voltage to the tin wire to generate saturated ion current. By moving γ on 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 described by equation (4). The parameters on the right side of the transformed equation can be determined in the design and test stage and can be used as a criterion for controlling wire feeding. Therefore, the current criterion is: Among them, D, L, n Sn Given by the design solution, γ and v th Determine through testing, thereby determining the current criterion I Sn ; ③When 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 , retract some of the tin wire and reduce the current.

6. The method for enhancing the ionization degree of air plasma using metal tin for air-breathing electric propulsion according to claim 1, characterized in that: The appropriate control of the potential of the suspension system relative to the plasma is as follows: Scenario 1: Making its potential lower than the plasma potential can be used to collect tin ions in the plasma, thereby recovering the tin element and reducing tin loss, while reducing the tin vapor concentration at the lead end and reducing the short-circuit risk of electric field acceleration electric propulsion.

7. The method for enhancing the ionization degree of air plasma using metal tin for air-breathing electric propulsion according to claim 1, characterized in that: The appropriate control of the potential of the suspension system relative to the plasma, scenario two: making its potential higher than the plasma potential, can be used to enhance the tin ion concentration in the plasma, enhance the ionization intensity, and at the same time enhance the ion concentration in the plasma, which is beneficial to the efficiency of electric propulsion such as magnetic nozzles that rely on charge acceleration.

8. The method for enhancing the ionization degree of air plasma using metal tin for air-breathing electric propulsion according to claim 1, characterized in that: Wire feeding control includes the use of PID technology to optimize control parameters through experimental adjustment; the amount of tin wire is evaluated using typical parameters: assuming that the electron temperature is ~1eV and the Bohm speed is ~10 3 m / s, electron density ~10 20 m -3 , the tin wire length is ~10mm and the diameter is ~1mm, then the loss rate is about (assuming γ≈1): The annual consumption is: The electron density is 10 20 m -3 That is: under 1Pa discharge pressure and 300K air temperature, the degree of ionization is close to 100%.

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