High-precision current probe measuring device based on ion saturation principle and measuring method thereof

Abstract

The invention relates to a high-precision current probe measuring device based on an ion saturation principle and a measuring method thereof, the high-precision current probe measuring device comprises a tungsten electrode, the front end of the tungsten electrode is embedded into a ceramic thin tube, and the ceramic tube wraps a non-exposed section of the rear end of the tungsten electrode and is fixed on a stainless steel support rod; a platinum lead is welded at the tail part of the tungsten electrode, penetrates through the stainless steel support rod and then is connected to a coaxial cable core wire, the tail end of the stainless steel support rod is connected with the wall of the vacuum chamber through a metal-ceramic feed-through flange, and the coaxial cable core wire is directly connected with a metal shielding box in the vacuum chamber and then is connected into a high-resolution digitizer. And a metal flange is welded at the feed-through position of the coaxial cable outer-layer woven mesh. According to the invention, plasma density oscillation is measured, and the oscillation power spectrum, the dispersion relation and the group velocity of the ion sound wave can be finally obtained through data processing.

Description

Technical Field

[0001] This invention relates to the field of electric propulsion plasma diagnostics, and in particular to a high-precision current probe measuring device and its measuring method based on the principle of ion saturation. Background Technology

[0002] As humanity's exploration of interstellar space deepens, traditional chemical propulsion methods can no longer meet the demands for thruster performance, such as specific impulse and thrust. As a result, electric propulsion systems have come into focus and are gradually replacing chemical propulsion as the most popular propulsion method. Unlike traditional chemical propulsion, which uses the chemical energy of the propellant to generate a high-speed jet and thus a reaction force, electric propulsion primarily generates thrust through electromagnetic energy to accelerate ions. Furthermore, electric propulsion can produce higher exhaust velocities than chemical rocket propulsion. Therefore, electric propulsion can significantly reduce the propellant mass in specific space propulsion missions, thereby lowering propellant transportation costs and increasing satellite payload.

[0003] With the continuous maturation and application of electric propulsion technology, electric propulsion, with its high specific impulse, is becoming the preferred space propulsion method for deep space exploration missions. Among these, ion and Hall thrusters serve as the primary propulsion devices. Figure 1 Electric thrusters have been used in deep space probes such as Deep Space 1, Dawn, and Psyche, as well as in the binary asteroid reorientation experiment. To ensure the successful completion of deep space exploration missions that last for decades or even longer, electric thrusters must possess long lifespans and high reliability.

[0004] like Figure 1 As shown in (a)-(b), the core working principle of electric thrusters (ion thrusters, Hall thrusters) lies in the ionization of the working medium (such as xenon gas) to generate plasma, and then accelerating and ejecting the ions through an electrostatic field (ion thruster) or an electromagnetic field (Hall thruster) to generate thrust. This high specific impulse characteristic makes it an ideal power source for deep space exploration. However, it is precisely this core working mechanism, which relies on the complex state of plasma, that presents severe challenges to long lifespan and high reliability.

[0005] Driven by various factors such as electromagnetic fields, particle collisions, wall interactions, and flow shear, plasmas in electric thrusters commonly exhibit a variety of instabilities, turbulence, and wave phenomena. These phenomena manifest as continuous, random, or periodic spatiotemporal oscillations of key parameters such as plasma density, potential, and electron temperature. Among these, ion acoustic waves are a particularly common and influential collective oscillation mode in electric thruster plasmas. Essentially, they are compression-sparse waves of electron and ion density (and the corresponding changing electric field), with propagation speeds approaching the speed of sound of ions, and frequencies typically ranging from several kilohertz to several megahertz. The anomalous transport processes of ion acoustic waves and charged particles pose multiple potential threats to the performance and lifespan of the thruster.

[0006] Performance fluctuations and efficiency losses: The anomalous transport process of ion acoustic waves can induce ionization instability, which can cause large oscillations in plasma density and potential, directly affecting the stability of the ion acceleration electric field.

[0007] Intensified corrosion of critical components: The anomalous transport process between ion acoustic waves and charged particles leads to the formation of high-energy ions, causing sputtering corrosion of critical components such as the thruster discharge channel and cathode, significantly shortening the service life of the electric thruster.

[0008] Therefore, real-time and high-precision monitoring of plasma density oscillation characteristics in key areas of the thruster (especially downstream of the discharge chamber, grid gap, and plume near field), particularly the intensity, frequency distribution (power spectrum), propagation characteristics (dispersion relation), and energy propagation direction (group velocity) of ion acoustic waves, is crucial for understanding the internal physical processes of the thruster, diagnosing potential problems, assessing erosion risks, validating numerical models, optimizing thruster design, and ultimately ensuring its lifespan and reliable operation.

[0009] Moreover, traditional probes suffer from insufficient spatial resolution, inadequate high-frequency response, poor environmental adaptability, and weak noise immunity. Summary of the Invention

[0010] To address the problems existing in the prior art, the present invention aims to provide a high-precision current probe measurement device and its measurement method based on the ion saturation principle, for measuring plasma density oscillations. Through data processing, the oscillation power spectrum, dispersion relation, and group velocity of the ion acoustic wave can be obtained.

[0011] To achieve the above objectives, the present invention provides the following solution:

[0012] A high-precision current probe measurement device based on the ion saturation principle includes:

[0013] A tungsten electrode, wherein a ceramic tube is embedded at the front end of the tungsten electrode, the ceramic tube covers the non-exposed section at the rear end of the tungsten electrode, and is fixed to a stainless steel support rod;

[0014] The tungsten electrode has a platinum lead welded to its tail, which passes through the ceramic tube and connects to the coaxial cable core. The coaxial cable core passes through the stainless steel support rod and connects to the vacuum feedthrough connector. The flange of the vacuum feedthrough connector is sealed to the vacuum chamber wall. At the same time, the output end of the vacuum feedthrough connector is connected to an external coaxial cable, which is connected to the signal processing system.

[0015] Optionally, the non-exposed section of the tungsten electrode encapsulated by the ceramic tube includes: encapsulating the non-exposed section of the tungsten electrode with a stepped alumina ceramic tube, and transitioning to a thicker ceramic tube at the end of the non-exposed section.

[0016] Optionally, the signal processing system includes: a bias circuit and a low-noise acquisition chain, wherein the bias circuit and the low-noise acquisition chain constitute a measurement loop, the target battery and the target metal foil resistor are connected in series in the measurement loop, and the double-shielded coaxial cable in the measurement loop is directly connected to the metal shielding box in the vacuum chamber, and then connected to a 16-bit high-resolution digitizer.

[0017] To achieve the above objectives, the present invention also provides a measurement method for a high-precision current probe measurement device based on the ion saturation principle, comprising:

[0018] A high-precision current probe is obtained, and the target data is acquired using the high-precision current probe.

[0019] Acquiring the target data includes: performing Fourier transform analysis based on the high-precision current probe to determine the amplitude, frequency, and wave number; determining the potential fluctuations at different locations using the high-precision current probe; and performing a Fourier transform on the potential fluctuations with respect to time to estimate the wave dispersion.

[0020] Optionally, determining the amplitude includes:

[0021] A Fourier transform is performed based on a single ion saturated probe in the high-precision current probe to determine the plasma oscillation intensity of the frequency function, and the plasma oscillation intensity is analyzed to determine the amplitude.

[0022] Determining the plasma oscillation intensity of the frequency function includes:

[0023]

[0024] Where, |δn f | represents the oscillation amplitude at frequency f, i represents the phase relationship of the oscillation, and ft represents the product of frequency and time.

[0025] Optionally, determining the frequency includes:

[0026]

[0027] in, k is the frequency. f Let f be the wave number at frequency f, and k be the wave number at frequency f. f x represents the phase difference between the signals measured at two locations x1 and x2.

[0028] Optionally, determining the wave number includes:

[0029] The wavenumber is determined by calculating the signals in multiple ion-saturated probes using cross-correlation and combining the signals with the distances between the multiple ion-saturated probes.

[0030]

[0031] Where Δx is the distance between ion-saturated probes, and k f Let θ be the wave number. f1 Let θ be the phase angle of the first probe signal at frequency f. f2 Let f be the phase angle of the second probe signal at frequency f.

[0032] Optionally, determining the potential fluctuation includes:

[0033] The high-precision current probe is used to characterize the properties of fluctuations in the plasma, thereby determining potential fluctuations at different locations:

[0034]

[0035] Where k(ω) is the wave number at frequency ω, φ1(ω) is the complex amplitude at position x1 at frequency ω, e is the complex exponential function, t is time, φ2(ω) is the complex amplitude at position x2 at frequency ω, and x is the spatial position.

[0036] Optionally, characterizing the wave properties in the plasma includes:

[0037]

[0038] Where φ is the potential fluctuation signal, φ(ω) is the complex amplitude of the wave with frequency w, and x is the spatial position.

[0039] Optionally, estimating the wave dispersion includes:

[0040]

[0041] Where S(ω) is the wave frequency spectrum at angular frequency ω, and F(φ1(t)) and F(φ2(t)) refer to the Fourier transforms of the potential fluctuations at the two probe positions, respectively.

[0042] The beneficial effects of this invention are as follows:

[0043] Traditional probes suffer from insufficient spatial resolution. This invention utilizes a dual-probe design and cross-correlation analysis to directly calculate the wavenumber k and construct the dispersion relation. Traditional probes also suffer from insufficient high-frequency response. This invention employs tungsten electrodes (high-temperature resistant), low-capacitance coaxial cables, and a high-speed digitizer to capture microsecond-level transients. Traditional probes exhibit poor environmental adaptability. This invention, through stepped alumina ceramic encapsulation and support rods, can operate stably under ultra-high vacuum. Traditional probes have weak noise immunity. This invention, through double-shielded cables and cross-power spectrum phase averaging, can suppress random noise and extract coherent wave signals.

[0044] This invention is made by encapsulating a thin metal wire (such as tungsten or molybdenum) or metal rod in an insulating ceramic tube, with only the tip exposed. The structure is extremely simple, the material cost is low, and the processing technology is relatively simple. It is small in size and can be easily inserted into the observation window, port, or specially designed probe driving mechanism of the plasma chamber. It has relatively little interference with the plasma (especially for single probes) and can even be used in harsh environments such as the divertor of some large devices (such as tokamak).

[0045] This invention is itself a resistive element (ignoring the small sheath capacitance), whose current response time is mainly limited by the time it takes for ions to cross the sheath (typically on the order of microseconds or less). This allows the ion-saturated probe to capture rapid transient phenomena and high-frequency fluctuations in plasma, such as plasma turbulence, instabilities (e.g., Langmuir waves, ion acoustic waves), and pulsed discharge behavior. Combined with a high-speed data acquisition system and FFT analysis, the spectral characteristics (frequency, amplitude, and mode) of plasma fluctuations can be studied.

[0046] In magnetized plasma, the cyclotron radius of ions in a magnetic field is typically larger than the probe size (depending on the magnetic field strength). When plasma flow exists parallel to the magnetic field lines, the flux of ions reaching the probe varies with the angle of the probe relative to the magnetic field and the flow direction. By using a probe installed at a specific angle (e.g., tilted) or comparing the currents of probes in different directions, the plasma flow velocity in the magnetic field can be inferred. This is an important means of diagnosing plasma rotation and transport. Attached Figure Description

[0047] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0048] Figure 1The diagram below shows the working principle of a thruster in the background technology; where (a) is a diagram of the working principle of a thruster, and (b) is a diagram of the working principle of an electron bombardment ion thruster.

[0049] Figure 2 This is a schematic diagram of an ion-saturated probe according to an embodiment of the present invention;

[0050] Figure 3 This is a schematic diagram of the ion saturation probe circuit according to an embodiment of the present invention;

[0051] Figure 4 The ion saturation current I measured by the two-channel ion saturation probes in this embodiment of the invention. sat,1 and I sat,2 Schematic diagram;

[0052] Figure 5 The following are natural logarithmic plots of the power spectrum characteristic curves according to embodiments of the present invention: (a) is a natural logarithmic plot of the power spectrum characteristic curves for different discharge currents Id, and (b) is a natural logarithmic plot of the power spectrum characteristic curves for different Q (gas flow rates). Detailed Implementation

[0053] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0054] To further investigate the properties of ion acoustic wave propagation, ion saturation probes can measure time-varying parameters such as the power spectrum of spatial potential oscillations and ion density. This allows them to capture the rapid density oscillations caused by ion acoustic waves and electron drift instability (EDI), obtaining the oscillation power spectrum, dispersion relation, and group velocity of the ion acoustic waves. Ion saturation probes can not only capture minute fluctuations in potential and ion density, but also provide in-depth analysis of more complex phenomena in plasmas, such as the nonlinear effects and multi-frequency mode interactions of ion acoustic waves.

[0055] like Figure 2 As shown, this embodiment discloses a high-precision current probe measurement device based on the principle of ion saturation, comprising: a tungsten electrode, the front end of which is embedded in a ceramic tube, the ceramic tube wrapping around the non-exposed section of the rear end of the tungsten electrode and fixed on a stainless steel support rod; a platinum lead wire is welded to the tail end of the tungsten electrode, which passes through the ceramic tube and is connected to a coaxial cable core wire, the coaxial cable core wire passes through the stainless steel support rod and is connected to a vacuum feedthrough connector, the flange of the vacuum feedthrough connector is sealed to the vacuum chamber wall, and the output end of the vacuum feedthrough connector is connected to an external coaxial cable, the external coaxial cable being connected to a signal processing system;

[0056] The non-exposed section of the tungsten electrode encapsulated by the ceramic tube includes: the non-exposed section of the tungsten electrode is encapsulated by a stepped alumina ceramic tube, and the non-exposed section transitions to a thicker ceramic tube at the end;

[0057] The signal processing system includes a bias circuit and a low-noise acquisition chain. The bias circuit and the low-noise acquisition chain form a measurement loop. The target battery and the target metal foil resistor are connected in series in the measurement loop. The double-shielded coaxial cable in the measurement loop is directly connected to the metal shielding box in the vacuum chamber and then connected to a 16-bit high-resolution digitizer.

[0058] Specifically, this embodiment discloses a high-precision current probe measurement device based on the principle of ion saturation. It is a highly sensitive diagnostic tool, mainly composed of three parts: a probe head, an insulating support structure, and a signal transmission system (e.g., ...). Figure 2 (As shown).

[0059] The probe tip is composed of a cylindrical electrode made of high-purity tungsten. Tungsten's extremely high melting point allows it to withstand high-temperature plasma exceeding 1000K in the Hall thruster plume, while its low sputtering rate prevents material contamination of the plasma. The electrode surface is electrolytically polished to a mirror finish to eliminate the risk of micro-tip discharge. Each tip is 1.5 mm long and 0.3 mm in diameter, and the measurable ion saturation current range is approximately 10–100 mA.

[0060] The insulating portion of the insulating support structure (plasma isolation layer) utilizes a stepped alumina ceramic tube to encapsulate the probe tip. The near-electric end is a thin tube to minimize plasma obstruction; the rear end transitions to a thicker tube. The ceramic material was chosen based on its ultra-high vacuum compatibility (outgassing rate <10%). -10 Torr·L / s·cm 2 The probe has a dielectric strength (>15kV / mm). The probe is fixed by a stainless steel support rod, with coaxial signal cables running internally. External signal transmission is achieved through a metal-ceramic feedthrough flange, ensuring the system operates within 10... -8 Reliability of sealing and electrical isolation under Torr-level vacuum.

[0061] The signal transmission system (bias and acquisition module) includes a bias circuit and a low-noise acquisition chain. The bias circuit and the low-noise acquisition chain together with the probe itself form a complete measurement loop. The function of the low-noise acquisition chain is to accurately and with low noise measure the weak ion saturation current generated by the probe and flowing through the bias circuit, and convert it into a voltage signal suitable for digitization or recording.

[0062] A battery connected in series provides a -30V voltage (far below the plume float potential of -5 to -10V), forcing the probe to operate in the ion saturation region. A 100Ω metal foil resistor is connected in series in the circuit to convert the ion current into a voltage drop V. R The double-shielded coaxial cable (capacitance <50pF) in the circuit is directly connected to the metal shielding box inside the vacuum chamber, and then connected to the 16-bit high-resolution digitizer.

[0063] Between the probe head and the insulating support structure: The tungsten electrode is embedded in the front end of a ceramic capillary tube and fixed with high-temperature ceramic adhesive. The adhesive layer thickness is <0.1mm. The ceramic tube completely covers the non-exposed section of the electrode, ensuring that only the head contacts the plasma. The lateral insulation distance is >5mm. The tungsten-ceramic interface (boron nitride coating) is coated with a boron nitride thermally conductive layer to conduct the electrode heat to the support rod.

[0064] A tungsten electrode is inserted into and bonded to the front end hole of a ceramic tube. A thin and uniform hexagonal boron nitride thermal conductive layer is pre-coated on the outer surface of the tungsten electrode embedding section and the inner surface of the ceramic tube hole. The end of the ceramic tube is connected to a support tube. Finally, the support tube is connected to the cooling system and the vacuum chamber wall.

[0065] Between the insulation support structure and the signal transmission system: Platinum leads are welded to the tail of the tungsten electrode, threaded through a ceramic tube, and connected to the coaxial cable core. The end of the stainless steel support rod is connected to the vacuum chamber wall via a metal-ceramic feedthrough flange, and a gold wire sealing ring ensures 10... -8 Torr seal, coaxial cable outer braided mesh welded to metal flange at feedthrough to achieve bulkhead grounding:

[0066] The coaxial cable must be connected to the signal transmission system. First, the tungsten electrode is connected to the coaxial cable core. The coaxial cable enters from the rear end of the ceramic tube, extends through the internal cavity of the support rod to the outside of the vacuum chamber, and is suspended and fixed throughout its length or secured by a ceramic insulating bracket to avoid contact with the inner wall of the metal support rod. It is then connected to the vacuum feedthrough connector (core interface). Internal end: The coaxial core inside the support rod is soldered or crimped to the center conductor input end of the feedthrough. Grounding end: The metal casing of the feedthrough is tightly connected to the end of the support rod and grounded (to achieve electromagnetic shielding continuity). Vacuum seal: The feedthrough flange is sealed to the vacuum chamber wall via a copper gasket or welding. External end: The output end of the feedthrough (with a coaxial SMA connector) connects to an external coaxial cable. Finally, the external coaxial cable is connected to the signal processing system.

[0067] This embodiment discloses a measurement method for a high-precision current probe measurement device based on the principle of ion saturation, including: acquiring a high-precision current probe, and using the high-precision current probe to acquire target data; acquiring the target data includes: performing Fourier transform analysis based on the high-precision current probe to determine the amplitude, frequency and wavenumber, determining the potential fluctuations at different locations through the high-precision current probe, and performing a Fourier transform on the potential fluctuations with respect to time to estimate the wave dispersion.

[0068] Specifically, the basic working principle of the probe is as follows: When the electrode is exposed to plasma, a certain amount of ion current and electron current are collected. The current collected for each type of particle is proportional to several plasma parameters and the potential applied to the electrode. By analyzing the relationship between the collected current and the applied voltage, various parameters can be separated and calculated. When a strong negative bias voltage is applied to the probe, all electrons are repelled, and the probe only collects an ion current equal to the ion saturation current. In this ion saturation state, ions collide with the probe at Bohm velocity. Therefore, the collected ion current is a function of electron temperature, plasma density, and collection surface area.

[0069]

[0070] Where, n i0 A represents the background plasma density. s This represents the probe surface area. It is a correction factor based on the probe sheath assumption, that is, the main assumption is that the probe radius is much larger than the Debye length, e is the elementary charge, and n i0 As the background plasma density, A s T represents the effective surface area of ​​the probe exposed to the plasma. e For electron temperature, m i Let be the ion mass. If we assume that the electron temperature oscillation is small, then the oscillation of the ion saturation current is proportional to the plasma density oscillation, and therefore:

[0071]

[0072] in, This represents the oscillatory component (perturbation term) of the plasma ion density. Background plasma density (steady-state average), This represents the oscillating component of the ion saturation current. This represents the steady-state average value of the ion saturation current.

[0073] The primary analytical technique for measuring the waveform of ion saturation current is the Discrete Fourier Transform (DFT or FFT), given a waveform of length N: x k For k = 0...N-1, FFT produces a new complex vector y. mm = 0...N-1, where the time-domain current sequence is mapped to a frequency-domain complex vector through complex exponential basis decomposition, the magnitude corresponds to the oscillation intensity, and the phase characterizes the wave time shift. The plasma density oscillation spectrum characteristics (such as ion acoustic waves) are analyzed.

[0074]

[0075] Among them, y m The complex output after Fourier transform represents the complex amplitude (including amplitude and phase information) with frequency component m, where N is the number of discrete data points in the waveform, k is the position of the signal on the time axis, and x... k is the sampled value of the ion saturation current at time point k, where i is the imaginary unit and m is the frequency index.

[0076] Here Indicates about the average value Disturbance: Where x is the total amount, For disturbance quantity, This is the average value.

[0077] For a purely digital input waveform, the vector y m It follows these properties: Where * denotes complex conjugate, and if N is even, then y0 and y N2 Values ​​higher than m = N / 2 are purely real and are ignored due to their redundancy, and for sampling rate f s The collected time-dependent input waveforms, each value at index m representing a given f m =mf s / N,m=0...N / 2, assuming plasma oscillations consist of linear combinations, then the FFT is related to physical properties:

[0078]

[0079] |δn f | is the oscillation amplitude at frequency f. Based on this assumption, y m The relationship between the value and the oscillation amplitude is as follows:

[0080]

[0081] Where, δ n The plasma density oscillation signal in the time domain represents the instantaneous fluctuation of plasma density with time t. ft is the product of frequency and time; this term describes the phase evolution of the oscillation with frequency f over time t. mThe result is a Fourier transform, containing the amplitude and phase information (complex number) of the frequency component mm, where f is the frequency, representing the specific frequency component of the plasma oscillation, and t is the time, representing the variable of oscillation that changes over time.

[0082] This synthesized vector can be considered as the power spectrum of the oscillations, although the definitions of power spectrum (and power spectral density) are slightly different, strictly speaking. Nevertheless, by performing an FFT on a single ion-saturated probe, the intensity of the plasma oscillations as a function of frequency can be determined.

[0083] By using two ion-saturated probes, the wavelength can also be calculated using FFT, extending the position and time variations of equation (4):

[0084]

[0085] Where, k f It is the wave number at frequency f, and the term k f x can be considered as the phase difference (θ) between the signals measured at two locations x1 and x2. f ): θ f2 -θ f1 =k f (x2-x1).

[0086] Using the properties of the Fourier transform, cross-correlation can be used to calculate two signals n1 and n2:

[0087]

[0088] Among them, y m1 It is the FFT of probe 1, y m2 This is the FFT of probe 2. If the distance between the two probes is known (Δx), the wavenumber can be calculated using the following formula:

[0089]

[0090] This can also be viewed as measuring the delay between a specific phase of the oscillation passing through probe 1 and subsequently arriving at probe 2. Since the phase is between -π and π, this method can only measure k. max =π / Δx, the maximum wavenumber. If a wavenumber greater than the limit is observed during measurement, then through k measured =k true -nk max It is aliased into a measurable wavenumber box, where is an integer representing 2k. max The multiples can be divided by the true wavenumber; where k measured To measure the wavenumber, k true For the true wavenumber, k max This represents the maximum wave number.

[0091] For example, if the maximum wavenumber that can be directly measured is 100 rad / m, and there is a wave with a wave number of 125 rad / m, then the FFT analysis will produce a calculated wavenumber of -75 rad / m, and a wave with a wave number of 275 rad / m will produce a wavenumber of 75 rad / m.

[0092] FFT analysis yielded three crucial characteristics of instability: amplitude, frequency, and wavenumber (wavelength), which can be obtained by extending equation (4). Equation (6) explicitly defines the quantization method for frequency, and... Figure 5 The actual analysis results are presented. In principle, this information can be used to identify the dispersion relation of any instabilities present in the plasma plume, but it is limited in some respects. A major limitation of this simple analysis is that due to the noisy environment encountered in the plasma, which distorts the measured waveforms, it does not produce clear results on its own. To filter out noise, any recorded waveform is subdivided into a set of several smaller waveforms. Fourier analysis is applied to each sub-waveform, and the results are averaged together to obtain the statistically averaged power spectrum and cross-correlation / wavenumber.

[0093] like Figure 3 As shown, the probe consists of two exposed tungsten tips arranged axially, each 1.5 mm long and 0.3 mm in diameter. The selected measurement object is hollow cathode plume plasma. The probe design balances spatial resolution and mechanical stability while ensuring high-sensitivity diagnostics of hollow cathode plume plasma. The distance between the two probes is Δx = 2 mm, and both probes are set with a DC bias voltage of -30 V to reliably capture local plasma characteristics.

[0094] This device is designed to measure the ion saturation current I. sat The fluctuation of this current can also be used as an indicator of plasma potential, as shown in equation (9):

[0095]

[0096] Where φ is the time-varying spatial plasma potential, n i n is the time-varying ion density. i0 T is the time-averaged ion density. e Let q be the electron temperature and q be the elementary charge.

[0097] Because of I sat =αn i α is a constant that depends on the electron temperature and the probe size. Therefore, equation (3) can be simplified to:

[0098]

[0099] Among them, I sat0This is the time-averaged value of the ion saturation current. Therefore, by measuring the fluctuations in the ion saturation current, the fluctuations in the potential can be further inferred. To ensure the comparability of comparative conditions within the same experimental section, the same probe needs to be used to capture its changes. Therefore, in studying the power spectrum φ of ion acoustic waves... 2 When considering the relationship between dispersion and ion saturation, ion saturation probes are used for measurement.

[0100] An ion-saturated probe consists of two probes, such as... Figure 4 It is given that the two ion-saturated probes oscillate almost synchronously (the probe closer to the cathode measures the saturation current as I). sat,1 The saturation current measured away from the cathode probe is I. sat,2 In solving the power spectrum φ 2 Measurements are performed using a probe located close to the cathode, such as... Figure 4 As shown.

[0101] Furthermore, using this relationship (4), the properties of the wave in the plasma can be characterized by the signal from the relevant probe tip:

[0102]

[0103] Where k(ω) represents the wave number at frequency ω, and φ(ω) represents the complex amplitude of the wave at frequency ω. Therefore, the potential fluctuations measured at two different locations at spatial position x are:

[0104]

[0105] By taking the Fourier transform of these two signals with respect to time, the following relationship can be found:

[0106]

[0107] In the formula, Δx = x2 - x1; Δx is the distance between the two probes, x2 and x1 are the two spatial positions of the two probes, F[φ2(t)] is the Fourier transform of the potential fluctuations φ1(t) and φ2(t) measured by probe 2, and F * [φ1(t)] represents the Fourier transform of the potential fluctuations φ1(t) and φ2(t) measured by probe 1. This expression provides a method for measuring the wavenumber k(ω), which is along the vector direction between the two probe tips, where the resolvable wavenumber range is determined by the distance between the probes, |k| < π / Δx; |k| is the number of periods or phase change of the wave oscillation per unit length.

[0108] like Figure 5As shown in (a)-(b), the ion saturation currents collected by the two probes are used to estimate the wave dispersion S(ω). To achieve this, a cross-correlation technique (Equation (15)) is employed. F(φ1(t)) and F(φ2(t)) are obtained by Fourier decomposition of the measurements from the two ion saturation probes. The dispersion power is then calculated, and the propagation characteristics of the ion acoustic wave are derived, including its group velocity, wavelength range, and interaction with different wave modes.

[0109]

[0110] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A high-precision current probe measuring device based on the principle of ion saturation, characterized in that, include: A tungsten electrode, wherein a ceramic tube is embedded at the front end of the tungsten electrode, the ceramic tube covers the non-exposed section at the rear end of the tungsten electrode, and is fixed on a stainless steel support rod; The tungsten electrode has a platinum lead welded to its tail, which passes through the ceramic tube and connects to the coaxial cable core. The coaxial cable core passes through the stainless steel support rod and connects to the vacuum feedthrough connector. The flange of the vacuum feedthrough connector is sealed to the vacuum chamber wall. At the same time, the output end of the vacuum feedthrough connector is connected to an external coaxial cable, which is connected to the signal processing system.

2. The high-precision current probe measuring device based on the ion saturation principle according to claim 1, characterized in that, The non-exposed section of the tungsten electrode encapsulated by the ceramic tube includes: the non-exposed section of the tungsten electrode is encapsulated by a stepped alumina ceramic tube, and the non-exposed section transitions to a thicker ceramic tube at the end.

3. The high-precision current probe measuring device based on the ion saturation principle according to claim 1, characterized in that, The signal processing system includes a bias circuit and a low-noise acquisition chain. The bias circuit and the low-noise acquisition chain form a measurement loop. The target battery and the target metal foil resistor are connected in series in the measurement loop. The double-shielded coaxial cable in the measurement loop is directly connected to the metal shielding box in the vacuum chamber and then connected to a 16-bit high-resolution digitizer.

4. A measurement method for a high-precision current probe measuring device based on the principle of ion saturation, characterized in that, include: A high-precision current probe is obtained, and the target data is acquired using the high-precision current probe. Acquiring the target data includes: performing Fourier transform analysis based on the high-precision current probe to determine the amplitude, frequency, and wave number; determining the potential fluctuations at different locations using the high-precision current probe; and performing a Fourier transform on the potential fluctuations with respect to time to estimate the wave dispersion.

5. The measurement method of the high-precision current probe measuring device based on the ion saturation principle according to claim 4, characterized in that, Determining the amplitude includes: A Fourier transform is performed based on a single ion saturated probe in the high-precision current probe to determine the plasma oscillation intensity of the frequency function, and the plasma oscillation intensity is analyzed to determine the amplitude. Determining the plasma oscillation intensity of the frequency function includes: Where, |δn f | represents the oscillation amplitude at frequency f, i represents the phase relationship of the oscillation, and ft represents the product of frequency and time.

6. The measurement method of the high-precision current probe measurement device based on the ion saturation principle according to claim 4, characterized in that, Determining the frequency includes: in, k is the frequency. f Let f be the wave number at frequency f, and k be the wave number at frequency f. f x represents the phase difference between the signals measured at two locations x1 and x2.

7. The measurement method of the high-precision current probe measurement device based on the ion saturation principle according to claim 4, characterized in that, Determining the wave number includes: The wavenumber is determined by calculating the signals in multiple ion-saturated probes using cross-correlation and combining the signals with the distances between the multiple ion-saturated probes. Where Δx is the distance between ion-saturated probes, and k f Let θ be the wave number. f1 Let θ be the phase angle of the first probe signal at frequency f. f2 Let f be the phase angle of the second probe signal at frequency f.

8. The measurement method of the high-precision current probe measuring device based on the ion saturation principle according to claim 4, characterized in that, Determining the potential fluctuation includes: The high-precision current probe is used to characterize the properties of fluctuations in the plasma, thereby determining potential fluctuations at different locations: Where k(ω) is the wave number at frequency ω, φ1(ω) is the complex amplitude at position x1 at frequency ω, e is the complex exponential function, t is time, φ2(ω) is the complex amplitude at position x2 at frequency ω, and x is the spatial position.

9. The measurement method of the high-precision current probe measuring device based on the ion saturation principle according to claim 8, characterized in that, The properties characterizing the waves in the plasma include: Where φ is the potential fluctuation signal, φ(ω) is the complex amplitude of the wave with frequency w, and x is the spatial position.

10. The measurement method of the high-precision current probe measuring device based on the ion saturation principle according to claim 4, characterized in that, Estimating the wave dispersion includes: Where S(ω) is the wave frequency spectrum at angular frequency ω, and F(φ1(t)) and F(φ2(t)) refer to the Fourier transforms of the potential fluctuations at the two probe positions, respectively.

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