CN111935893B - Electrostatic probe system with three-electrode structure - Google Patents
Electrostatic probe system with three-electrode structure Download PDFInfo
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- CN111935893B CN111935893B CN202010715223.1A CN202010715223A CN111935893B CN 111935893 B CN111935893 B CN 111935893B CN 202010715223 A CN202010715223 A CN 202010715223A CN 111935893 B CN111935893 B CN 111935893B
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Abstract
The invention discloses an electrostatic probe system with a three-electrode structure.A three-electrode probe unit collects electronic current and ion current and removes radio frequency noise through a high-voltage-resistant radio frequency noise reduction unit; the current after the radio frequency noise is removed is input into the power amplification unit through the sampling resistor, and forms a probe loop through the grounding end of the power amplification unit; the power amplification unit amplifies the periodic scanning voltage signal generated by the signal control and data processing unit and loads the amplified periodic scanning voltage signal to a probe pole of the three-electrode probe unit; the current acquisition unit acquires current signals of the probe electrode and the reference electrode at the same time, power frequency noise is actively eliminated through the power frequency interference suppressor, and the signals are input into the signal control and data processing unit through the isolator to be processed to obtain electronic density and electronic temperature data. The compensation of radio frequency noise and the active elimination of power frequency noise are realized, so that a volt-ampere characteristic curve with high signal-to-noise ratio is obtained, and the accurate measurement of the electron temperature and the electron density of plasma containing strong radio frequency noise and power frequency interference can be realized.
Description
Technical Field
The invention belongs to the technical field of plasma diagnosis, and particularly relates to an electrostatic probe system with a three-electrode structure.
Background
Electrostatic probe diagnosis is widely concerned due to its simple structure, low cost and diverse diagnostic parameters. The basic principle of electrostatic probe diagnosis is that a metal needle inserted into plasma attracts ions and electrons in the plasma under the action of voltage, so as to form current. A voltammetry characteristic curve containing information such as plasma electron density and electron temperature is obtained by measuring probe voltage and current, and then key parameters such as electron temperature, electron density and the like of the plasma can be obtained through calculation according to the curve and probe theory.
The problem that the existing electrostatic probe system has difficulty in diagnosing plasmas containing radio frequency noise and power frequency interference, the existence of the noise causes poor signal-to-noise ratio of a volt-ampere characteristic curve and electronic temperature and electronic density data cannot be obtained is particularly obvious in MW-level high-frequency induction wind tunnels which are very important in the field of high-power plasma equipment such as deep-space detection pneumatic heat protection, and therefore the elimination of the noise to obtain a high signal-to-noise ratio volt-ampere characteristic curve becomes the key for diagnosing plasma parameters. For the above noise problem treatment, the probe structure proposed in the article of Isaac D Sudit and Francis F Chen 1993 is mainly adopted at present, i.e. a choke coil is used to realize frequency-fixed limiting of radio frequency interference. However, the probe applying the technology can only be applied to a discharge system matched with a wave-limiting frequency, other discharge frequencies cannot be directly used, and noise generally presents an envelope distribution characteristic and is not an infinite narrow single frequency, so that the method cannot completely eliminate the noise, and the volt-ampere characteristic deformation caused by the problem is particularly obvious because the absolute value of the noise in a high-power device is large. In addition, low-frequency noise such as power frequency interference widely exists in laboratory plasma, especially for discharge of radio frequency, microwave and the like, a power supply can couple power frequency components, and the noise can cause the vibration of a volt-ampere characteristic curve. Because the power frequency is difficult to eliminate by a filtering method, the power frequency needs to be processed separately, and the parameter diagnosis is difficult. According to the published data of the existing electrostatic probe diagnosis, no technology for suppressing the interference of low-frequency noise such as power frequency and the like in the electrostatic probe diagnosis exists at present.
Disclosure of Invention
Aiming at the problems in the prior art, the invention aims to provide an electrostatic probe system with a three-electrode structure, which uses a three-electrode probe comprising a probe electrode, a compensation electrode and a reference electrode, and combines a noise suppression circuit to realize the suppression of noise in probe current, can obtain a high signal-to-noise ratio volt-ampere characteristic curve, and solves the problem of accurate diagnosis of key parameters of plasma with radio frequency noise and power frequency interference. The compensation electrode is connected with the probe electrode through a blocking capacitor, so that the space potential vibration of the plasma around the probe electrode is effectively compensated; the high-voltage-resistant radio frequency suppression unit realizes effective suppression of noise in a radio frequency band range; the reference pole is combined with the current acquisition unit to realize active elimination of power frequency noise, and meanwhile, the circuit system of the whole set of probe is placed in the metal shielding box to avoid interference of a space electromagnetic field.
The technical scheme adopted by the invention is as follows:
an electrostatic probe system of a three-electrode structure, comprising: the three-electrode probe unit is a three-electrode probe composed of a probe pole P1, a reference pole P2 and a compensation pole P3;
the three-electrode probe unit collects the electron current and the ion current, and radio frequency noise is removed through the high-voltage-resistant radio frequency noise reduction unit;
the current after the radio frequency noise is removed is input into the power amplification unit through the sampling resistor, and forms a probe loop through the grounding end of the power amplification unit; meanwhile, the power amplification unit amplifies the periodic scanning voltage signal generated by the signal control and data processing unit and loads the periodic scanning voltage signal to a probe pole P1 of the three-electrode probe unit;
the current acquisition unit acquires current signals of the probe electrode P1 and the reference electrode P2 at the same time, power frequency noise is eliminated actively through the power frequency interference suppressor, and the signals are input to the signal control and data processing unit through the isolator to be processed to obtain electronic density and electronic temperature data.
Further, the three-electrode probe unit comprises a three-electrode probe head and a blocking capacitor C, a probe pole P1, a reference pole P2 and a compensation pole P3 are arranged at the input end of the three-electrode probe head, the compensation pole P3 is connected to the probe pole P1 through the blocking capacitor C, and the input end of the high-voltage-resistant radio-frequency noise reduction unit is connected with the output ends of the probe pole P1 and the reference pole P2 of the three-electrode probe unit.
Furthermore, the probe pole P1 of the three-electrode probe unit collects electron current and ion current under the action of scanning voltage, the reference pole P2 is a signal source for eliminating power frequency interference, the electron current and the ion current of plasma noise are collected under the action of the plasma on ground potential, and the compensation pole P3 is the probe pole P1 for compensating the space potential vibration of the plasma.
Further, the probe pole P1 and the reference pole P2 of the three-electrode probe unit are identical in structure and made of metal, and charged particles in plasma are collected through the probe pole P1; the reference pole P2 is used as a signal source for power frequency interference elimination, and the reference pole P2 is used for providing an input signal for eliminating power frequency interference for a power frequency interference suppressor of the current acquisition unit; the compensation pole P3 is made of metal with an area more than 5 times larger than that of the probe pole P1, and the compensation pole P3 compensates the space potential vibration of the plasma.
Furthermore, the high-voltage-resistant radio frequency noise reduction unit is provided with two sets of high-voltage-resistant passive filters and a preprocessing circuit which are completely the same, the attenuation coefficient of a stop band of each filter is larger than 60dB, the maximum amplitude of the stop band of each filter is 100V, the requirement on noise attenuation of a high-power discharge system can be met, the preprocessing circuit is greatly simplified due to the high-voltage-resistant characteristic, and the reliability of the system is improved; the RF noise is removed by the filter through the impedance matching of the preprocessing circuit and the protection filter.
Furthermore, the power amplifier unit is provided with an operational amplifier U, U 'and an isolation transformer T, T' which are completely the same, an operational amplifier U of the power amplifier unit firstly primarily amplifies the scanning voltage signal, the primarily amplified signal is secondarily amplified through the isolation transformer T, and the amplitude of the scanning voltage reaches 100V at most after two-stage amplification, so as to obtain a complete volt-ampere characteristic curve; meanwhile, the isolation of the probe scanning voltage and the input voltage of the power amplification unit is realized through an isolation transformer; the reference electrode circuit does not load a scanning voltage signal, the load of the reference electrode and the load of the probe electrode circuit are kept the same through the operational amplifier U 'and the isolation transformer T', and new noise caused by device difference is avoided.
Furthermore, the current acquisition unit comprises high-performance sampling resistors Rs and Rs ', operational amplifiers U1 and U1', a power frequency interference suppressor and an isolation circuit,
an operational amplifier U1 collects common mode voltage signals S1 at two ends of a sampling resistor of a probe P1, wherein the S1 signals comprise effective current signals and power frequency noise interference signals; obtaining a voltage signal S2 at two ends of a reference electrode sampling resistor through an operational amplifier U1', wherein S2 only contains power frequency noise signals and is used as a signal source for eliminating power frequency noise interference signals in S1; the voltage signal S1 and the voltage signal S2 are simultaneously input into the power frequency interference suppressor.
Furthermore, the power frequency interference suppressor comprises an operational amplifier U2 and a feedback circuit,
the operational amplifier U2 and the external resistance electronic device form a subtracter, the voltage signal S2 component in the voltage signal S1 is subtracted by the subtracter, and the signal size of the voltage signal S2 is actively adjusted by a feedback circuit, so that the voltage signal S2 component in the voltage signal S1 is optimally eliminated.
Further, the isolation circuit comprises a voltage-current conversion circuit, an isolator H1 and a current-voltage conversion circuit,
the signal output by the power frequency interference suppressor is firstly converted into a current signal through the voltage-current conversion circuit and then input into the isolator H1 after being subjected to certain bias, the current acquisition unit and the signal control and data processing unit are isolated through the isolator H1, possible strong noise signals (such as impact disturbance generated when power is converted in the discharging process or strong disturbance generated by a pulse excitation source in the diagnosis of pulse radio frequency discharging) are avoided, and the current passing through the isolator H1 is converted into a voltage signal through the current-voltage conversion circuit and is recorded and processed by the signal control and data processing unit.
Furthermore, the signal control and data processing unit is responsible for controlling scanning signals and processing the volt-ampere characteristic curve to obtain electron density and electron temperature data, and comprises an industrial personal computer, a board card, a D/A converter, an A/D converter and probe data processing software,
the industrial personal computer is controlled by software to generate a scanning voltage signal, the scanning voltage signal is converted by the board card and the D/A converter and then input to a power amplification circuit connected with the probe electrode in the power amplification unit for amplification, the analog current signal of the current acquisition unit is converted into a digital current signal by the A/D converter and then recorded by the industrial personal computer, and then the digital current signal is processed by the probe data processing software to obtain electronic density and electronic temperature data.
The invention has the beneficial effects that:
the invention can realize the compensation of radio frequency noise and the active elimination of power frequency noise based on the unique three-electrode probe structure idea and the design scheme of combining the radio frequency noise suppression circuit and the power frequency interference suppressor, thereby obtaining the volt-ampere characteristic curve with high signal-to-noise ratio and realizing the accurate measurement of the plasma electron temperature and the electron density containing strong radio frequency noise and power frequency interference.
(1) The invention comprehensively considers the problems of radio frequency interference, power frequency noise and the like, provides a brand-new three-electrode probe structure, designs a circuit scheme combining a radio frequency noise suppression circuit and a power frequency interference suppressor, and can realize the compensation of the radio frequency noise and the active elimination of the power frequency noise.
(2) The active power frequency noise elimination circuit comprises a power frequency and other low-frequency noise active elimination circuit, wherein a reference pole signal is used as an input signal, and the whole active elimination of power frequency noise and some low-frequency noise is realized through automatic scaling operation.
(3) The radio frequency noise suppression unit can attenuate high frequency noise such as radio frequency of 2 MHz-50 MHz by more than 65dB, can bear voltage interference of 100V, reduces a pretreatment circuit, improves the reliability of the system, and greatly improves the universality of the system without a plasma source.
(4) The plasma processing device comprises an integrated electronic circuit module, is arranged outside the plasma, does not need a thermal protection system, and simultaneously avoids interference caused by a thermal effect; the independently developed data processing software can process multi-path data at the same time, and is convenient to be connected in parallel and expanded into a multi-probe system.
(5) The invention can realize a plurality of waveforms and output forms of 10 Hz-10 kHz scanning signals, the scanning voltage can be adjusted in a multi-waveform range of +/-30- +/-100V, the volt-ampere characteristic curve can be rapidly acquired in a plurality of periods, and the processing such as filtering and the like is carried out, so that the data such as high-precision electron density, electron temperature and the like can be obtained.
Drawings
FIG. 1 is a schematic diagram of an electrostatic probe system with a three-electrode configuration;
FIG. 2 is a schematic cross-sectional view of a three-electrode probe head of an electrostatic probe system with a three-electrode structure according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of an overall structure of a three-electrode probe head of an electrostatic probe system with a three-electrode structure according to an embodiment of the present invention;
FIG. 4 is a plot of current-voltage characteristics measured by an electrostatic probe system with a three-electrode structure according to an embodiment of the present invention;
FIG. 5 shows the diagnostic results of an embodiment of an electrostatic probe system with a three-electrode structure according to an embodiment of the present invention: electron density;
FIG. 6 shows the diagnostic results of an embodiment of an electrostatic probe system with a three-electrode structure according to an embodiment of the present invention: electron temperature;
wherein, 1, three electrode probe unit; 2. a high-voltage-resistant radio frequency noise reduction unit; 3. a power amplifier unit; 4. a current collection unit; 5. and the signal control and data processing unit.
Detailed Description
For better clarity of the description of the technical advantages and objectives of the present invention, the following analysis is made in conjunction with the accompanying drawings and examples. The specific devices, elements and parameters used in the examples are illustrative only and not intended to be limiting.
The invention relates to an electrostatic probe system with a three-electrode structure, which solves the problem of interference of radio frequency noise and power frequency noise in plasma on probe data, obtains a volt-ampere characteristic curve with high signal-to-noise ratio as shown in figure 4, and finally obtains high-precision electronic temperature and electronic density data as shown in figures 5 and 6.
As shown in fig. 1, 2 and 3, an electrostatic probe system with a three-electrode structure includes: the device comprises a three-electrode probe unit 1, a high-voltage-resistant radio frequency noise reduction unit 2, a power amplifier unit 3, a current acquisition unit 4 and a signal control and data processing unit 5, wherein the three-electrode probe unit is used for collecting electronic current and ionic current and comprises a three-electrode probe and a blocking capacitor C.
The input end of the three-electrode probe comprises a probe pole P1, a reference pole P2 and a compensation pole P3, wherein the probe pole P1 and the reference pole P2 are respectively connected with a noise suppression unit pole, the compensation pole P3 is connected with a DC blocking capacitor C1, and the probe pole P1 is made of metal and used for collecting charged particles in plasma; the reference pole P2 is used as a signal source for power frequency interference elimination, has the same structure and material as the probe pole P1, and provides an input signal for eliminating power frequency interference for the power frequency interference suppressor of the current acquisition unit 4; the compensation electrode P3 is a metal with an area more than 5 times larger than that of the probe electrode P1, is connected to the probe electrode P1 through a blocking capacitor C, and is used for compensating the space potential vibration of the plasma.
The compensating pole P3 is connected with the probe pole P1 through a blocking capacitor C, the input end of the high-voltage resistant radio frequency noise reduction unit 2 is connected with the reference pole P2 of the three-electrode probe unit 1 and the output end of the probe pole P1, the output current is subjected to noise reduction through two sets of identical preprocessing circuits and high-voltage resistant passive filters F, F ', the sampling resistors Rs1 and Rs 1' through which the radio frequency noise is removed are input into the operational amplifier U, U 'and the isolation transformer T, T' of the power amplification unit, and the power amplification unit 3 forms a probe loop through the grounding end; the current acquisition unit 4 acquires current signals of a probe pole P1 and a reference pole P2 through sampling resistors Rs1 and Rs 1', eliminates power frequency noise through a power frequency interference suppressor, inputs the current signals into an A/D converter of the signal control and data processing unit 5 through an isolator, converts analog current signals of the current acquisition unit 4 into digital current signals, and processes the digital current signals by an industrial personal computer to obtain electronic density and electronic temperature data; the software controls the industrial personal computer to generate a scanning voltage signal, and the scanning voltage signal is input to a power amplification circuit connected with the probe pole in the power amplification unit 3 after being converted by the board PC & B and the D/A.
The probe pole P1 of the three-electrode probe unit collects electron current and ion current under the action of scanning voltage, the reference pole P2 is used as a signal source for power frequency interference elimination, the electron current and the ion current of plasma noise are collected under the action of the plasma on ground potential, and the compensation pole P3 is connected with the probe pole P1 through a blocking capacitor to compensate the space potential vibration of the plasma for the probe pole P1; the high-voltage-resistant radio frequency noise reduction unit 2 is used for removing radio frequency noise; the current after removing the radio frequency noise is input into the power amplification unit 3 after passing through the sampling resistor, and forms a probe loop through the grounding end of the power amplification unit 3; meanwhile, the power amplification unit 3 amplifies the periodic scanning voltage signal generated by the signal control and data processing unit 5 and loads the amplified periodic scanning voltage signal to a probe P1 of the three-electrode probe unit; the current acquisition unit 4 acquires current signals of the probe pole P1 and the reference pole P2 at the same time, power frequency noise is eliminated actively through the power frequency interference suppressor, and the signals are input to the signal control and data processing unit 5 through the isolator to be processed to obtain electronic density and electronic temperature data.
The three-electrode probe in the three-electrode probe unit in the embodiment of the invention comprises a probe electrode P1, a compensation electrode P2, a reference electrode P3 and an insulating ceramic tube, wherein the probe electrode P1 and the reference electrode P2 are tungsten wires with the size of phi 0.3 multiplied by 8mm, the compensation electrode P3 is prepared by using a stainless steel sheet with the size of 3 multiplied by 8mm, and the compensation electrode is connected with the probe electrode P1 through a DC blocking capacitor C with the frequency of 30pF to compensate the plasma space potential oscillation around the probe electrode P1.
The high-voltage-resistant radio frequency noise reduction unit 2 is used for removing radio frequency band noise, is two sets of completely same high-voltage-resistant passive filters and pretreatment circuits, meets the requirement on noise attenuation of a high-power discharge system, greatly simplifies the pretreatment circuits due to high-voltage resistance, and improves the reliability of the system; the pre-processing circuit is mainly used for impedance matching and protecting a filter, and the filter is used for removing radio frequency noise.
In the embodiment of the present invention, the high voltage resistant radio frequency noise reduction unit 2 specifically includes: the filter has the advantages that the attenuation coefficient of a stop band of the filter is larger than 60dB, the filter can bear the maximum peak voltage of 100V and has the cutoff frequency of 2MHz, the ripple wave of a pass band is smaller than 1dB, the attenuation is more than 60dB after 1MHz, the cutoff frequency of the stop band is larger than 120MHz, and the RC circuit matches a probe pole load with the filter.
The power amplifier unit 3 is used for amplifying the periodic scanning voltage signal generated by the signal control and data processing unit 5, and is loaded on the probe P1 of the three-electrode probe unit, and includes an identical operational amplifier U, U 'and an isolation transformer T, T'.
The operational amplifier U of the power amplifier unit 3 primarily amplifies the scan voltage signal, and the primarily amplified signal is secondarily amplified by the isolation transformer T, so that the maximum amplitude of the scan voltage can reach 100V after two-stage amplification, and a complete volt-ampere characteristic curve can be obtained (as shown in fig. 4). Meanwhile, the isolation transformer realizes the isolation of the probe scanning voltage and the input voltage of the power amplification unit 3; the circuit of the reference pole P2 is not loaded with the scanning voltage signal, and the operational amplifier U 'and the isolation transformer T' are used for keeping the circuit load of the reference pole P2 and the circuit load of the probe pole P1 the same, so that new noise caused by device difference is avoided.
In the embodiment of the invention, the power amplification unit 3 comprises U and U' consisting of an operational amplifier OPA445 and an OPA541 high-power operational amplifier, the bandwidth of a device is 0-1 MHz, the maximum gain is 40dB, the maximum power supply voltage is +/-45V, and the maximum allowable current is 5A; the isolation transformer T, T' realizes 5 times of amplification and isolates the probe unit and the power amplifier unit.
The current acquisition unit 4 is used for acquiring probe current and comprises high-performance sampling resistors Rs and Rs ', operational amplifiers U1 and U1', a power frequency interference suppressor and an isolation circuit.
An operational amplifier U1 collects a common-mode voltage signal S1 at two ends of a sampling resistor of a probe P1, wherein the signal comprises an effective current signal and a power frequency noise interference signal; u1' is used for obtaining voltage signals S2 at two ends of a reference electrode P2 sampling resistor, and S2 only contains power frequency noise signals and is used as a signal source for eliminating power frequency noise in S1; and S1 and S2 are simultaneously input into the power frequency interference suppressor.
The power frequency interference suppressor comprises an operational amplifier U2 and a feedback circuit.
The operational amplifier U2 and electronic devices such as an external resistor and the like form a subtracter for subtracting the S2 component in the S1, and the feedback circuit is used for actively adjusting the signal size of the S2 so as to realize the optimal elimination of the S2 component in the S1.
The isolation circuit includes a voltage-to-current conversion circuit, an isolator H1, and a current-to-voltage conversion circuit.
The signal output by the power frequency interference suppressor is firstly converted into a current signal through the voltage-current conversion circuit and then input into the isolator after a certain bias, the isolator realizes the isolation of the current acquisition unit 4 and the signal control and data processing unit 5, avoids possible strong noise signals from damaging the acquisition card, and the current passing through the isolator is converted into a voltage signal through the current-voltage conversion circuit and is recorded and processed by the signal control and data processing unit 5.
In the embodiment of the present invention, the current collection unit 4 includes: high performance resistance Rs ═ Rs' ═ 1k Ω (0.1% error); u1, U1' and U2 represent an operational amplifier AD810AN, the bandwidth of the amplifier is 1MHz, and the current is 20 mA; the isolator adopts a photoelectric isolator HCNR201 with the linearity of 0.01 percent, the bandwidth of 1MHz and the current of 20mA, and a corresponding current-voltage conversion circuit.
As shown in fig. 4, 5 and 6, the signal control and data processing unit 5 is responsible for controlling the scanning signal and processing the current-voltage characteristic curve to obtain the electron density and electron temperature data. The system comprises an industrial personal computer, a board card, a D/A converter, an A/D converter and probe data processing software which is developed autonomously.
The industrial personal computer is controlled by software to generate a scanning voltage signal, and the scanning voltage signal is input to a power amplification circuit connected with the probe electrode P1 in the power amplification unit 3 for amplification after being converted by a board card and D/A. The A/D converter converts the analog current signal of the current acquisition unit into a digital current signal, records the digital current signal by the industrial personal computer, and then processes the digital current signal by the independently developed probe data processing software to obtain the electron density and electron temperature data (as shown in figures 5 and 6).
The signal control and data processing unit 5 in the embodiment of the invention comprises a porphyry industrial personal computer, an NI board card, a Labview program, an A/D converter and a D/A converter, and the scanning voltage frequency adopted in the embodiment is 500 Hz.
The above description is not meant to be limiting, it being noted that: it will be apparent to those skilled in the art that various changes, modifications, additions and substitutions can be made without departing from the true scope of the invention, and these improvements and modifications should also be construed as within the scope of the invention.
Claims (7)
1. An electrostatic probe system of a three-electrode structure, comprising: the device comprises a three-electrode probe unit (1), a high-voltage-resistant radio-frequency noise reduction unit (2), a power amplifier unit (3), a current acquisition unit (4) and a signal control and data processing unit (5), wherein the three-electrode probe unit (1) is a three-electrode probe composed of a probe pole P1, a reference pole P2 and a compensation pole P3;
the three-electrode probe unit (1) collects electron current and ion current, and radio frequency noise is removed through the high-voltage-resistant radio frequency noise reduction unit (2);
the current after the radio frequency noise is removed is input into the power amplification unit (3) through the sampling resistor, and forms a probe loop through the grounding end of the power amplification unit (3); meanwhile, the power amplification unit (3) amplifies the periodic scanning voltage signal generated by the signal control and data processing unit (5) and loads the periodic scanning voltage signal to a probe pole P1 of the three-electrode probe unit (1);
the current acquisition unit (4) acquires current signals of the probe electrode P1 and the reference electrode P2 at the same time, power frequency noise is eliminated actively through a power frequency interference suppressor, and the signals are input to the signal control and data processing unit (5) through an isolator to be processed to obtain electronic density and electronic temperature data;
the three-electrode probe unit (1) comprises a three-electrode probe and a blocking capacitor C, a probe pole P1, a reference pole P2 and a compensation pole P3 are arranged at the input end of the three-electrode probe, the compensation pole P3 is connected to the probe pole P1 through the blocking capacitor C, and the input end of the high-voltage-resistant radio-frequency noise reduction unit (2) is connected with the output ends of the probe pole P1 and the reference pole P2 of the three-electrode probe unit (1);
the probe pole P1 of the three-electrode probe unit (1) collects electron current and ion current under the action of scanning voltage, the reference pole P2 is a signal source for eliminating power frequency interference, the electron current and the ion current of plasma noise are collected under the action of the plasma on ground potential, and the compensation pole P3 is the probe pole P1 for compensating the space potential vibration of the plasma;
the probe pole P1 and the reference pole P2 of the three-electrode probe unit (1) are identical in structure and made of metal, and charged particles in plasma are collected through the probe pole P1; a reference pole P2 signal is used as a signal source for power frequency interference elimination, and an input signal for eliminating power frequency interference is provided for a power frequency interference suppressor of the current acquisition unit (4); the compensation electrode P3 is made of metal with an area more than 5 times larger than that of the probe electrode P1, and compensates the space potential vibration of the plasma.
2. The electrostatic probe system with the three-electrode structure is characterized in that the high-voltage-resistant radio-frequency noise reduction unit (2) is provided with two sets of completely same high-voltage-resistant passive filters and pretreatment circuits, the attenuation coefficient of the stop band of each filter is larger than 60dB, and the maximum withstand voltage of the amplitude is 100V; the impedance matching and the protection of the filter are realized through the preprocessing circuit, and the radio frequency noise is removed through the filter.
3. The electrostatic probe system of claim 1, wherein the power amplification unit (3) is configured with an operational amplifier U, U 'and an isolation transformer T, T' that are identical, the operational amplifier U of the power amplification unit (3) first primarily amplifies the scan voltage signal, and the primarily amplified signal is secondarily amplified by the isolation transformer T, and the amplitude of the scan voltage reaches up to 100V after two-stage amplification, so as to obtain a complete volt-ampere characteristic curve; meanwhile, the probe scanning voltage is isolated from the input voltage of the power amplification unit (3) through an isolation transformer; the reference electrode circuit does not load a scanning voltage signal, and the load of the reference electrode and the load of the probe electrode circuit are kept the same through an operational amplifier U 'and an isolation transformer T'.
4. The electrostatic probe system of a three-electrode structure according to claim 1, wherein the current collection unit (4) comprises high-performance sampling resistors Rs and Rs ', operational amplifiers U1 and U1', a power frequency interference suppressor, and an isolation circuit,
an operational amplifier U1 collects common mode voltage signals S1 at two ends of a sampling resistor of a probe P1, wherein the S1 signals comprise effective current signals and power frequency noise interference signals; obtaining a voltage signal S2 at two ends of a reference electrode sampling resistor through an operational amplifier U1', wherein S2 only contains power frequency noise signals and is used as a signal source for eliminating power frequency noise interference signals in S1; the voltage signal S1 and the voltage signal S2 are simultaneously input into the power frequency interference suppressor.
5. The electrostatic probe system of claim 4, wherein the power frequency interference suppressor comprises an operational amplifier U2 and a feedback circuit,
the operational amplifier U2 and the external resistance electronic device form a subtracter, the voltage signal S2 component in the voltage signal S1 is subtracted by the subtracter, and the signal size of the voltage signal S2 is actively adjusted by a feedback circuit, so that the voltage signal S2 component in the voltage signal S1 is optimally eliminated.
6. The electrostatic probe system of claim 4, wherein the isolation circuit comprises a voltage-to-current conversion circuit, an isolator H1 and a current-to-voltage conversion circuit,
the signal output by the power frequency interference suppressor is firstly converted into a current signal through a voltage-current conversion circuit and then input into an isolator H1 after being subjected to certain bias, the current acquisition unit (4) and the signal control and data processing unit (5) are isolated through the isolator H1, and the current through the isolator H1 is converted into a voltage signal through the current-voltage conversion circuit and is recorded and processed by the signal control and data processing unit (5).
7. The electrostatic probe system of claim 1, wherein the signal control and data processing unit (5) is responsible for controlling scanning signals and processing voltammetry curves to obtain electron density and electron temperature data, and comprises an industrial personal computer, a board card, a D/A converter, an A/D converter and a computer,
the industrial personal computer is controlled by software to generate a scanning voltage signal, the scanning voltage signal is converted by the board card and the D/A converter and then input to a power amplification circuit connected with the probe electrode in the power amplification unit (3) for amplification, the analog current signal of the current acquisition unit is converted into a digital current signal by the A/D converter and then recorded by the industrial personal computer, and then the digital current signal is processed by the computer to obtain electronic density and electronic temperature data.
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| CN114071848B (en) * | 2021-09-29 | 2024-02-23 | 太原市华纳方盛科技有限公司 | Plasma diagnostic circuit and method |
| CN114900934B (en) * | 2022-06-08 | 2024-04-26 | 山东大学 | Langmuir probe with compensation electrode and detection method |
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| JP2002216998A (en) * | 2001-01-23 | 2002-08-02 | Nisshin:Kk | Plasma density information measuring method and its equipment, and probe for plasma density information measurement, plasma processing method and its equipment |
| CN1157103C (en) * | 2002-04-19 | 2004-07-07 | 大连理工大学 | Composite probe for plasma diagnosis |
| CN104994672B (en) * | 2015-06-01 | 2018-04-10 | 北京航空航天大学 | A kind of cylindrical type probe for the measurement of magnetic plasma propeller plume |
| CN111263503B (en) * | 2019-12-11 | 2021-04-27 | 厦门大学 | Plasma pneumatic probe and measurement system thereof |
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