CN112083295A - Experimental device and method based on pulse Thomson method - Google Patents
Experimental device and method based on pulse Thomson method Download PDFInfo
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- CN112083295A CN112083295A CN202010803557.4A CN202010803557A CN112083295A CN 112083295 A CN112083295 A CN 112083295A CN 202010803557 A CN202010803557 A CN 202010803557A CN 112083295 A CN112083295 A CN 112083295A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/12—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing
- G01R31/1227—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing of components, parts or materials
- G01R31/1263—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing of components, parts or materials of solid or fluid materials, e.g. insulation films, bulk material; of semiconductors or LV electronic components or parts; of cable, line or wire insulation
- G01R31/1281—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing of components, parts or materials of solid or fluid materials, e.g. insulation films, bulk material; of semiconductors or LV electronic components or parts; of cable, line or wire insulation of liquids or gases
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/12—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing
- G01R31/16—Construction of testing vessels; Electrodes therefor
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Abstract
The invention discloses an experimental device and method based on a pulse Thomson method, which comprises a vacuum cavity, an optical system, a vacuum system and a measuring system; the vacuum cavity consists of a vacuum cavity, a first film gauge barometer, a second film gauge barometer, a micro-water content detector, a micro-oxygen content detector, an electrode support, an electrode insulation connecting piece, a vacuum displacement table, a Rogowski electrode, photocathode coated glass, a high-voltage cable and an insulation sleeve; the optical system comprises a nanosecond laser, a spectroscope, a beam expander and a photodiode; the vacuum system comprises a mechanical pump, a molecular pump, a mass flow meter and an electromagnetic valve; the measuring system comprises a high-voltage direct-current power supply, a current-limiting resistor, a high-voltage probe, a voltage-stabilizing capacitor, a gain-adjustable trans-impedance amplifier, an oscilloscope and a computer; the invention can rapidly and accurately control the type of the measured gas, realize the accurate measurement of the discharge parameters of the gas, and determine the critical breakdown field strength of the gas through the effective ionization rate coefficient.
Description
[ technical field ] A method for producing a semiconductor device
The invention belongs to the field of plasma physics and gas discharge, and particularly relates to an experimental device and method based on a pulse Thomson method.
[ background of the invention ]
The sulfur hexafluoride gas has good insulation and arc extinguishing performance, and is widely applied to medium and high voltage gas insulation equipment; meanwhile, the gas is also a common gas medium in the field of plasma industry. However, sulfur hexafluoride is an extremely strong greenhouse gas, and thus its use is increasingly limited or replaced. In order to find the application of the novel insulating gas, it is an effective method to accurately measure the parameters of the electron group in the gas. The electronic group parameters in the gas are important characteristics of the discharge properties of single gas and mixed gas, and are statistical representation of each physical process in the low-temperature plasma.
Therefore, the accurate measurement of the electron group parameters in the gas has important significance for researching the basic properties of the gas, such as the insulation performance, the electron transport parameters, the collision cross section and the like.
The pulse soup-senescent Method (PT) is an experimental Method for accurately measuring discharge parameters in gas, and the PT experiment is an experimental Method for measuring electron group parameters in gas by measuring displacement current waveforms generated by the initial electrons moving in a uniform electric field and a gas environment to be measured based on the fact that a certain number of initial electrons are released by photoelectric effect on the surface of a photocathode focused by pulse laser.
The traditional PT experiment often adopts laser to incide to the photocathode surface from measuring observation window, and the laser access causes certain influence to the gas that awaits measuring like this to lead to the experiment precision to descend.
Secondly, the traditional PT experimental device usually adopts the traditional mechanical structure in the control of the electrode spacing, so that the accuracy and repeatability of the electrode spacing setting are not high, and the experimental accuracy is also influenced.
Moreover, the traditional PT experimental method adopts a relatively simple mathematical physical model to analyze the measured displacement current waveform, and cannot sufficiently extract information in the measured current signal to obtain complete parameter data of the electron group in the gas.
At present, no experimental device or experimental method can automatically and efficiently carry out experiments, and high-precision and complete gas discharge parameters can be obtained from experimental waveforms.
[ summary of the invention ]
The invention aims to solve the problems that the repeatability of electrode distance setting is not high and the experimental precision is affected because a traditional mechanical structure is usually adopted in the control of the electrode distance of a traditional PT experimental device in the prior art, and provides an experimental device and method based on a pulse Thomson method.
In order to achieve the purpose, the invention adopts the following technical scheme to realize the purpose:
an experimental device based on a pulse Thompson method comprises a vacuum cavity, an optical system used for the vacuum cavity to receive initial electrons needed by a photoelectric effect release experiment, a vacuum system used for ensuring that the gas pressure and components in the vacuum cavity are unchanged, and a measuring system used for measuring the uniformity of an electric field in the vacuum cavity;
the vacuum cavity comprises a vacuum cavity, an electrode support, an electrode insulation connecting piece, a vacuum displacement table, a Rogowski electrode, photocathode coated glass, a high-voltage cable and an insulation sleeve;
the electrode holder is located within a vacuum chamber,
the lower part of the electrode support is connected with the lower part of the electrode support in a sliding way through a vacuum displacement table;
the rogowski electrodes comprise a static electrode and a dynamic electrode;
a vacuum servo motor used for enabling a moving electrode to do reciprocating motion is arranged on the vacuum displacement table;
a grating ruler for controlling the distance between the static electrode and the moving electrode is arranged on the vacuum servo motor;
the photocathode coated glass is connected with the static electrode, and the moving electrode is connected with the electrode insulation connecting piece;
the static electrode is connected with a high-voltage cable, the high-voltage cable is connected with an insulating sleeve, and the insulating sleeve is connected with a measuring system;
the optical system excites a light spot, the light spot irradiates on the photocathode coated glass, and initial electrons required by the experiment are released through a photoelectric effect.
The invention further improves the following steps:
the vacuum cavity further comprises a first film gauge barometer, a second film gauge barometer, a micro-water content detector and a micro-oxygen content detector;
one side of the vacuum chamber is sequentially connected with a first film gauge barometer, a second film gauge barometer, a micro-water content detector and a micro-oxygen content detector from top to bottom.
The optical system comprises a nanosecond laser, a spectroscope, a beam expander and a photodiode;
the nanosecond laser emits laser, one part of laser is reflected to the photodiode after passing through the spectroscope, the other part of laser enters the beam expander after passing through the spectroscope, light spots passing through the beam expander are incident through a window in the end cover of the vacuum chamber and irradiate on the photocathode coated glass, and initial electrons required by the experiment are released through a photoelectric effect.
The vacuum system comprises a molecular pump and a mechanical pump;
the molecular pump is connected with the bottom of the vacuum chamber;
one end of the mechanical pump is connected with the vacuum chamber through a pipeline, and the other end of the mechanical pump is connected with the molecular pump.
The measuring system comprises a direct-current high-voltage power supply, a current-limiting resistor, a high-voltage probe, a voltage-stabilizing capacitor, an amplifier, an oscilloscope and a computer;
the direct-current high-voltage power supply, the current-limiting resistor and the voltage-stabilizing capacitor are connected in series;
the high-voltage probe is positioned at the connection part of the current-limiting resistor and the voltage-stabilizing capacitor;
the current-limiting resistor and the voltage-stabilizing capacitor are connected in series and then are electrically connected with the insulating sleeve;
one end of the amplifier is electrically connected with the moving electrode, and the other end of the amplifier is electrically connected with the oscilloscope;
the oscilloscope is in communication connection with the computer.
The amplifier is a gain-adjustable trans-impedance amplifier.
The first body and the second body are made of aluminum.
The movable electrode and the static electrode are made of copper.
The invention also discloses an experimental processing method based on the pulse Thomson method, which comprises the following steps:
and 3, controlling the voltage, the inflation pressure and the electrode spacing during the experiment, and establishing the following expression form for the current waveform measured under the specific reduced electric field intensity:
wherein, IeIs a measured current, Ne(0) Is the initial number of electrons released at the moment of laser triggering, q0Is an electronic charge, veffFor effective ionization rate, TeFor electron transit time, τDIs the electron longitudinal diffusion characteristic time;
NτD＝N*τD
wherein k iseffRepresenting the effective ionization rate coefficient, N represents the population density of the gas,ωerepresents the electron drift velocity and d represents the electrode spacing.
Compared with the prior art, the invention has the following beneficial effects:
the invention is based on the pulse Thomson experiment principle, builds a high-precision experiment platform suitable for measuring the parameters of electronic groups in various environment-friendly insulating gases, and provides a corresponding data processing method. The invention can realize high-precision gas distribution of any single gas and binary and ternary gases with any mixing proportion by the multi-path mass flowmeter and the high-precision barometer, and has safe and reliable operation, high analysis speed and high efficiency. For the gas with unknown insulation strength and discharge parameters, the method can realize rapid measurement and evaluate the insulation performance of the gas, and effectively meets the defects of the traditional breakdown experiment. Meanwhile, the vacuum cavity and the vacuum system used by the invention can ensure that the air is pumped to 5 multiplied by 10 before the experiment-4Pa, greatly improving the purity of the experimental gas.
Furthermore, the invention uses a high-precision vacuum displacement platform, controls the electrode spacing through a vacuum servo motor, measures the actual distance by using a Renyshao grating ruler and introduces feedback control, thereby realizing the high-precision and high-repeated positioning accuracy control of the electrode spacing from 0-40mm in the experiment.
Furthermore, the invention uses the glass plated with a 15nm palladium film as a photocathode, and is matched with a 266nm wavelength laser to excite and release initial electrons, so that the quantum efficiency is extremely high; meanwhile, the repetition frequency of the laser is adjusted to be 20Hz, so that the experimental efficiency can be greatly improved. In addition, the invention also discloses that the parallel laser beam reflected by the beam splitter passes through the photodiode, and the signal of the parallel laser beam is used as a trigger signal of the oscilloscope, so that the accuracy of the experiment is improved.
Furthermore, the high-stability direct-current power supply is fed into the experiment cavity through the current-limiting resistor and the voltage-stabilizing capacitor, so that the voltage drop caused by the displacement current in the experiment process can not influence the experiment precision. And meanwhile, the high-voltage probe is used for measuring the voltage actually fed into the experimental cavity, so that the electric field intensity in the experiment can be accurately measured.
[ description of the drawings ]
In order to more clearly explain the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention, and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained according to the drawings without inventive efforts.
FIG. 1 is a schematic structural diagram of the whole experimental apparatus of the present invention;
FIG. 2 is a graph showing the measured current waveform of the present invention with an 8Td reduced electric field strength, an electrode spacing of 25mm, and pure carbon dioxide at 10kPa, and the fitting results thereof;
FIG. 3 shows the measured current waveform of 125Td reduced electric field, 20mm electrode spacing, 10kPa pure carbon dioxide and the fitting result thereof according to the present invention;
FIG. 4 shows 10kPa pure CO according to the invention2Effective ionization coefficient measurement of (a);
FIG. 5 shows 10kPa pure CO according to the invention2Electron drift velocity measurements of (a);
FIG. 6 shows 10kPa pure CO according to the invention2(ii) density-reduced electron longitudinal diffusion characteristic time measurements;
FIG. 7 is a flow chart of the operation of the multimode fiber LIBS detector in the spectrum collection process of the present invention;
FIG. 8 is a flow chart of the multimode fiber LIBS detector processing and analyzing process according to the present invention.
Wherein, A-the vacuum cavity part of the experimental device; b-the optical system of the experimental setup; c-vacuum system of experimental apparatus; d-a control and measurement system of the experimental device; 1-a vacuum chamber; 2-a first film gauge barometer; 3-a second film gauge barometer; 4-micro water content detector; 5-micro oxygen content detector; 6-electrode support; 7-electrode insulation connecting piece; 8-a vacuum displacement table; 9-rogowski electrodes; 10-photocathode coated glass; 11-high voltage cables; 12-an insulating sleeve; a 13-nanosecond laser; 14-a beam splitter; 15-a beam expander; 16-a photodiode; 17-a mechanical pump; 18-a molecular pump; 19-mass flow meter; 20-an electromagnetic valve; 21-a direct current high voltage power supply; 22-current limiting resistor; 23-a high voltage probe; 24-a voltage stabilizing capacitor; 25-an amplifier; 26-an oscilloscope; 27-computer.
[ detailed description ] embodiments
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. The components of embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations.
Thus, the following detailed description of the embodiments of the present invention, presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It should be noted that: like reference numbers and letters refer to like items in the following figures, and thus, once an item is defined in one figure, it need not be further defined and explained in subsequent figures.
In the description of the embodiments of the present invention, it should be noted that if the terms "upper", "lower", "horizontal", "inner", etc. are used for indicating the orientation or positional relationship based on the orientation or positional relationship shown in the drawings or the orientation or positional relationship which is usually arranged when the product of the present invention is used, the description is merely for convenience and simplicity, and the indication or suggestion that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and thus, cannot be understood as limiting the present invention. Furthermore, the terms "first," "second," and the like are used merely to distinguish one description from another, and are not to be construed as indicating or implying relative importance.
Furthermore, the term "horizontal", if present, does not mean that the component is required to be absolutely horizontal, but may be slightly inclined. For example, "horizontal" merely means that the direction is more horizontal than "vertical" and does not mean that the structure must be perfectly horizontal, but may be slightly inclined.
In the description of the embodiments of the present invention, it should be further noted that unless otherwise explicitly stated or limited, the terms "disposed," "mounted," "connected," and "connected" should be interpreted broadly, and may be, for example, fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.
The invention is described in further detail below with reference to the accompanying drawings:
example 1
Referring to fig. 1, the experimental device based on the pulse thomson method includes a vacuum chamber a, an optical system B, a vacuum system C, and a measurement system D.
The vacuum cavity A is respectively connected with the optical system B and the vacuum system C. The optical system B is connected to the measurement system D.
The vacuum cavity A comprises a vacuum cavity 1, a first film gauge barometer 2, a second film gauge barometer 3, a micro-water content detector 4, a micro-oxygen content detector 5, an electrode support 6, an electrode insulation connecting piece, a vacuum displacement table 8, a rogowski electrode 9, photocathode coated glass 10, a high-voltage cable 11 and an insulation sleeve 12.
The vacuum chamber 1 is a stainless steel chamber having a length and a diameter of 55cm and a volume of about 130 liters.
A first film gauge barometer 2, a second film gauge barometer 3, a micro-water content detector 4 and a micro-oxygen content detector 5 are sequentially arranged on one side of the vacuum chamber 1 from top to bottom.
The first film gauge barometer 2 and the second film gauge barometer 3 are respectively connected with the vacuum cavity A through flanges.
The range of the first film gauge barometer 2 is 1.3 Pa-13.3 kPa, the range of the second film gauge barometer 3 is 13.3 Pa-133.3 kPa, in order to realize accurate measurement of the inflation pressure p, the whole range from 1.3Pa to the atmospheric pressure is covered, and the accurate measurement of the typical experimental inflation pressure of 100 Pa-10 kPa is ensured.
The micro water content detector 4 and the micro oxygen content detector 5 are respectively connected with the vacuum cavity A through flanges, so that the measurement of the water content of 0-1000ppm and the oxygen content of 0-20% is realized.
The electrode holder 6 is located in the vacuum chamber 1 and comprises a first body and a second body, and an electrode insulation connecting piece is connected to the top of the second body.
First body and second body pass through vacuum displacement platform 8 sliding connection, and vacuum displacement platform 8 is connected with the bottom one side of first body.
A gap is arranged between the top of the first body and the top of the second body.
The first body and the second body are made of aluminum, so that the load of the vacuum displacement table 8 is reduced while the mechanical strength is ensured.
The electrode insulation connecting piece is made of polyformaldehyde materials, and meanwhile, the connecting strength and the insulation performance between the electrode supports 6 are guaranteed.
In addition, the first body and the second body can be finely adjusted through a bottom screw, so that the parallelism of the electrodes after the electrodes are installed is ensured.
The Rogowski electrode 9 comprises a static electrode and a moving electrode, and the photocathode coated glass 10 is connected with the static electrode.
A vacuum servo motor used for enabling the moving electrode to do reciprocating motion is arranged on the vacuum displacement table 8.
And a grating ruler for controlling the distance between the static electrode and the moving electrode is arranged on the vacuum servo motor.
The vacuum displacement table 8 is an AML high-vacuum low-temperature displacement table which is driven by a vacuum servo motor and can realize the repeated positioning precision of 1 micron; in addition, a Renysha Tonic series grating ruler is additionally arranged, so that the measurement accuracy of 0.5 mu m is realized, and the control and measurement accuracy of the distance between the moving electrode and the static electrode are greatly improved.
The moving electrode and the static electrode are both made of copper, the diameters of the moving electrode and the static electrode are 170mm, and the curved surface parameters of the moving electrode and the static electrode are designed according to an ideal distance of 20 mm.
The movable electrode and the static electrode are not in contact with the side wall of the vacuum chamber 1, and the movable electrode and the static electrode are not in contact with the end cover of the vacuum chamber 1, so that the electrodes are not influenced by inflation pressure.
A hole with the diameter of 30mm is reserved on the static electrode applying the negative high voltage for mounting the photocathode coated glass 10, so that the surface is flush with the central surface of the static electrode and has good electric contact.
In order to release initial electrons required by experiments through a photoelectric effect under the induction of laser with a wavelength of 266nm, Pd is selected as a coating material on the photocathode coated glass 10, the thickness of the Pd is 15nm, and the long service life and the high quantum efficiency of photoelectron conversion are both considered.
The optical system B includes a nanosecond laser 13, a beam splitter 14, a beam expander 15, and a photodiode 16.
The nanosecond laser 13 emits laser, a part of the laser after passing through the spectroscope 14 is reflected to the photodiode 16, the other part of the laser is transmitted through the spectroscope 14 and then enters the beam expander 15, light spots passing through the beam expander 15 are incident through a window on an end cover of the vacuum chamber 1 and irradiate on the photocathode coated glass 10, and initial electrons required by an experiment are released through a photoelectric effect.
The nanosecond laser 13 is placed on the lifting displacement table, the nanosecond laser 13 is a Cyrlas FQSS266-200 laser, the laser wavelength is 266nm, the pulse width is 1.5ns, the pulse energy is 200 muJ, the repetition frequency is 20Hz, the spot diameter is 0.8mm, after the laser is emitted, the laser passes through a spectroscope 14 with the diameter of 50.8mm, wherein 5 percent of the laser is reflected and then irradiates on a photodiode to form a trigger signal of the oscilloscope 26; and transmitting the remaining 95% of laser energy, then entering a beam expander 15, expanding the laser energy ten times to form a light spot with the diameter of 8mm, irradiating the light spot through a window on an end cover of the vacuum chamber 1 onto a Pd coating of the photocathode coated glass 10, and releasing initial electrons required by the experiment through a photoelectric effect.
The vacuum system C includes a molecular pump 18 and a mechanical pump 17.
Firstly, the cavity is vacuumized to below 8Pa by the mechanical pump 17, and the molecular pump 18 is started for subsequent work. The FF200/1200 type molecular pump 18 is fixedly connected with the bottom of the vacuum chamber 1 through a connecting piece, and is controlled to be switched on and off with the vacuum chamber 1 by an ultrahigh vacuum inserting plate valve.
The TRP-36 mechanical pump 17 is connected to the vacuum chamber 1 through a rubber hose and a quick-connect coupling, and is connected to the molecular pump 18 through a stainless steel bellows.
The maximum flow of the two mass flowmeters 19 is 500cc/min, the vacuum chamber 1 is connected with a quick connector by adopting a rubber hose, and the electromagnetic valve 20 is used for controlling the on-off, so that the accurate control of the inflation pressure and the ratio of single or mixed gas can be realized.
The experiment is carried out indoors, the room temperature control is stable, the experiment is started after the experiment is carried out for a period of time after the experiment is carried out, and the temperature in the cavity can be considered as the room temperature.
The vacuum chamber 1 of the invention has no electrode, support and electric translation table inside when no load, the ultimate vacuum is better than 10-5Pa, and the vacuum degree better than 5 multiplied by 10-4Pa can be realized after the corresponding parts are put in; meanwhile, after all valves are closed after the inflation is finished, the leakage rate of the vacuum chamber 1 is lower than 0.8Pa/h, and the gas pressure and components in the chamber can be ensured to be hardly changed in the experimental process.
The measuring system D comprises a direct-current high-voltage power supply 21, a current-limiting resistor 22, a high-voltage probe 23, a voltage-stabilizing capacitor 24, an amplifier 25 and an oscilloscope 26.
The measurement system D adopts a Heinzinger ultrahigh-stability direct-current high-voltage power supply 21 to provide bias voltage, the maximum power is 40W, the maximum voltage is 40kV for the Rogowski electrode 9 in the vacuum chamber 1, and the voltage can be continuously adjusted through a thickness adjusting knob on a power panel to realize the electric field intensity required by an experiment; the voltage deviation of the power supply is less than 0.001% of the maximum voltage within 8 hours, and the power supply ripple is less than 0.001% of the maximum voltage +/-50 mV.
The dc high-voltage power supply 21 uses a negative polarity, and is connected to the electrostatic pole via the insulating sleeve 12 and the high-voltage cable 11 after being connected to the current-limiting resistor 22 and the voltage-stabilizing capacitor 24 via the high-voltage cable 11.
The resistance value of the current limiting resistor 22 is selected to be 1 MOmega, and the voltage stabilizing capacitor 24 is selected to be 4nF, so that the high-frequency ripple waves of the power supply can be filtered, and meanwhile, the voltage drop caused by the generation of displacement current in an experiment can be prevented.
The high voltage probe 23 is directly hung at the junction of the current limiting resistor 22 and the voltage stabilizing capacitor 24, and can measure the real voltage applied to the rogowski electrode 9 and record the real voltage through the oscilloscope 26.
A BNC joint is arranged behind the moving electrode and is connected with the amplifier 25 through a high-frequency cable.
The amplifier 25 is a FEMTODHPCA-100 gain-adjustable trans-impedance amplifier, and can convert a current signal in an experiment into a voltage signal and multiply amplify the voltage signal.
The gain-adjustable trans-impedance amplifier can realize 102-108 times of adjustable gain, and each step of gain multiple has a response bandwidth; the bandwidth of a frequently used 103 gear in the experiment is 175MHz, so that the real acquisition of the experimental waveform is ensured.
The converted and amplified voltage signal is collected and recorded by an oscilloscope 26, and typical waveforms are shown in fig. 2 and 3.
The oscilloscope 26 and the computer 27 communicate through a LAN port, directly transmit the acquired waveform to the computer 27, and process the experimental data by using a program written by a client.
The invention programs a computer 27 for fitting the parameters of the electron population in the gas, including the effective ionization rate coefficient keffElectron drift velocity ωeAnd a density-reduced electron longitudinal diffusion characteristic time Nτ D.
Firstly, for the voltage U and the electrode distance d adopted in measurement, the current electric field strength E can be determined as U/d; secondly, for the temperature T and the inflation pressure p during measurement, the gas population density N at the time of experiment can be obtained by using an ideal gas state equation, wherein the gas population density N is equal to RT/p, and the reduced electric field intensity (E/N) at the time of experiment can be obtained, wherein the unit is Td (1Td is equal to 10)-21Vm2)。
And the voltage, the inflation pressure and the electrode spacing during the experiment are controlled, so that the measurement of the electronic group parameters of the gas under different reduced electric field strengths is realized. For a current waveform measured at a certain reduced electric field strength, the following expression is established:
wherein IeIs a measured current, Ne(0) Is the initial number of electrons released at the moment of laser triggering, q0Is an electronic charge, veffFor effective ionization rate, Teτ D is the electron transit time and the electron longitudinal diffusion characteristic time. After fitting is carried out through a computer program to obtain parameters in the formula, the required electronic group parameters can be obtained according to the following relation:
keff＝veff/N
ωe＝d/Te
NτD＝N*τD
by changing the experimental conditions (voltage U, electrode spacing d and inflation pressure p) continuously, the data of the change of the electron group parameters in the gas along with the intensity of the reduced electric field can be measured.
The effective ionization rate coefficient keff, the electron drift velocity ω e and the density-reduced electron longitudinal diffusion characteristic time Nτ D for pure carbon dioxide at 10kPa are given with reference to FIGS. 4, 5 and 6, respectively.
Example 2
A method for processing experimental data based on a pulse Thomson method comprises the following specific working procedures (taking the experiment on 10kPa pure carbon dioxide as an example):
1. and setting parameters.
As shown in the working flow chart of the parameter setting link in fig. 6, the cavity end cover is opened to replace the photocathode glass, and then the moving electrode is controlled to move towards the static electrode until the moving electrode is closed and conducted through the multimeter test, and at this time, the distance is reset to zero.
Then, the vacuum displacement stage 8 is controlled to move the movable electrode to a desired set pitch position, and then the power supply to the vacuum displacement stage 8 is cut off.
Starting the mechanical pump 17 to pump the cavity to below 8Pa, starting the molecular pump 18 and opening the gate valve, and vacuumizing the vacuum chamber 1 to below 5 x 10 < -5 >.
And closing the gate valve and the side pumping valve at the mechanical pump 17, opening the mass flow meter 19 and the electromagnetic valve 20 to pump carbon dioxide into the cavity, and gradually reducing the flow of the mass flow meter 19 when the readings of the first film gauge pressure gauge 2 and the second film gauge pressure gauge 3 are close to the target pressure of 10kPa until the target pressure of 10kPa is aerated, and closing the electromagnetic valve 20 and the mass flow meter 19. The high voltage power supply is started and the knob is adjusted until the voltage measured by the high voltage probe 23, which is displayed by the oscilloscope 26, is the target voltage. The voltage U, the electrode spacing d and the inflation pressure p required for the experiment and the gas type have been set up.
2. And (6) data acquisition.
As shown in the work flow diagrams of the data acquisition segment of fig. 7 and 8, the nanosecond laser 13 is first started and the repetition frequency is adjusted to 20Hz, and the output of the photodiode 16 is used as a trigger signal of the oscilloscope 26. The light path is finely adjusted to ensure that the expanded laser is correctly incident into the cavity, and then the amplifier 25 is adjusted to a proper gear, so that the typical waveform shown in fig. 2 and 3 can be acquired in the oscilloscope 26. By using a mathematical operation channel of the oscilloscope 26, 400 waveforms under the same condition are superposed and averaged, and the averaged waveform is stored and transmitted to the computer 27 for storage.
3. Data processing
For data processing, the current waveforms at different reduced electric field strengths were fitted using a program programmed in computer 27 as follows
And converted according to the following relation
keff＝veff/N
ωe＝d/Te
NτD＝N*τD
The measured gas effect ionization rate coefficient k can be obtainedeffElectron drift velocity ωeAnd the law of three discharge parameters of density reduced electron longitudinal diffusion characteristic time Nτ D along with the change of the intensity of the reduced electric field, as shown in FIGS. 4 and 5And shown in fig. 6.
And determining the reduced electric field intensity when the effective ionization coefficient is 0 according to the change rule of the effective ionization coefficient, namely the critical reduced breakdown field intensity of the single gas or the mixed gas with a specific proportion, and can be used for evaluating the insulation performance of the gas.
The principle of the invention is as follows:
the vacuum chamber 1 is provided with a Rogowski electrode 9 whose distance can be adjusted by a vacuum displacement table 8, and the Rogowski electrode and a high-voltage power supply together provide a uniform electric field.
The vacuum chamber 1 provides the experimental gas atmosphere by controlling the inflation type and pressure by the mass flow meter 19. The invention can adjust the electrode spacing, voltage and inflation pressure according to the requirements, and provides changeable reduced electric field intensity E/N for experiments.
The invention utilizes the expanded 266nm laser to irradiate the photocathode arranged at the center of the Rogowski electrode 9, and generates a certain amount of initial electrons through the photoelectric effect. The initial electrons move to the anode in a directional manner under the action of an electric field between the electrodes, collide with gas molecules to be detected filled in the chamber in various types and are balanced, and displacement current is formed in the period, converted into a voltage signal through an amplifier 25 and collected and recorded through an oscilloscope 26.
The vacuum chamber 1 is connected with two paths of mass flowmeters 19 through electromagnetic valves 20, and the type of experimental gas can be adjusted by changing the gas connected into the mass flowmeters 19. The inflation ratio and pressure of the mixed gas can be controlled by detecting the pressure at the time of inflation by the first gauge 2 and the second gauge 3.
The oscilloscope 26 superposes and averages 400 waveforms under the same condition through a mathematical operation channel, so that the interference of noise in an experiment can be effectively counteracted, and the statistical significance of experimental data can be better embodied. The oscilloscope 26 communicates with the computer 27 through the LAN port, and can quickly transmit the waveform acquired by the experiment to the computer 27 for storage and processing.
The invention compiles a set of data processing program on the computer 27, processes the data collected in the experiment quickly and accurately, and draws a curve of the discharge parameter changing along with the intensity of the reduced electric field for further analysis.
The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and various modifications and changes will occur to those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (9)
1. An experimental device based on a pulse Thomson method is characterized by comprising a vacuum cavity (A), an optical system (B) used for releasing initial electrons required by an experiment by receiving a photoelectric effect in the vacuum cavity (A), a vacuum system (C) used for ensuring that the gas pressure and components in the vacuum cavity (A) are unchanged, and a measuring system (D) used for measuring the uniformity of an electric field in the vacuum cavity (A);
the vacuum cavity (A) comprises a vacuum cavity (1), an electrode support (6), an electrode insulation connecting piece (7), a vacuum displacement table (8), a rogowski electrode (9), photocathode coated glass (10), a high-voltage cable (11) and an insulation sleeve (12);
the electrode holder (6) is located within the vacuum chamber (1),
the lower part of the electrode support (6) is connected with the lower part of the electrode support in a sliding way through a vacuum displacement table (8);
the rogowski electrodes (9) comprise a static electrode and a dynamic electrode;
a vacuum servo motor used for enabling a moving electrode to do reciprocating motion is arranged on the vacuum displacement table (8);
a grating ruler for controlling the distance between the static electrode and the moving electrode is arranged on the vacuum servo motor;
the photocathode coated glass (10) is connected with a static electrode, and the dynamic electrode is connected with an electrode insulation connecting piece (7);
the static electrode is connected with a high-voltage cable (11), the high-voltage cable (11) is connected with an insulating sleeve (12), and the insulating sleeve (12) is connected with a measuring system (D);
the optical system (B) excites light spots, the light spots irradiate on the photocathode coated glass (10), and initial electrons required by the experiment are released through a photoelectric effect.
2. The experimental device based on the pulse Thomson method according to claim 1, wherein the vacuum chamber (A) further comprises a first film gauge barometer (2), a second film gauge barometer (3), a micro water content detector (4) and a micro oxygen content detector (5);
one side of the vacuum chamber (1) is sequentially connected with a first film gauge barometer (2), a second film gauge barometer (3), a micro-water content detector (4) and a micro-oxygen content detector (5) from top to bottom.
3. The experimental set-up based on the pulse thomson method according to claim 1, characterized in that the optical system (B) comprises a nanosecond laser (13), a beam splitter (14), a beam expander (15) and a photodiode (16);
the nanosecond laser (13) emits laser, one part of laser after passing through the spectroscope (14) is reflected to the photodiode (16), the other part of laser enters the beam expander (15) after being transmitted through the spectroscope (14), light spots passing through the beam expander (15) are incident through a window on an end cover of the vacuum chamber (1) and irradiate on the photocathode coated glass (10), and initial electrons required by an experiment are released through a photoelectric effect.
4. A pulse thomson-based experimental setup according to claim 1, characterized in that the vacuum system (C) comprises a molecular pump (18) and a mechanical pump (17);
the molecular pump (18) is connected with the bottom of the vacuum chamber (1);
one end of the mechanical pump (17) is connected with the vacuum chamber (1) through a pipeline, and the other end of the mechanical pump (17) is connected with the molecular pump (18).
5. The experimental facility based on the pulse thomson method according to claim 1, wherein the measuring system (D) comprises a dc high voltage power supply (21), a current limiting resistor (22), a high voltage probe (23), a voltage stabilizing capacitor (24), an amplifier (25), an oscilloscope (26) and a computer (27);
the direct-current high-voltage power supply (21), the current-limiting resistor (22) and the voltage-stabilizing capacitor (24) are connected in series;
the high-voltage probe (23) is positioned at the joint of the current-limiting resistor (22) and the voltage-stabilizing capacitor (24);
the current limiting resistor (22) and the voltage stabilizing capacitor (24) are connected in series and then are electrically connected with the insulating sleeve (12);
one end of the amplifier (25) is electrically connected with the moving electrode, and the other end of the amplifier is electrically connected with the oscilloscope (26);
the oscilloscope (26) is in communication connection with the computer (27).
6. An experimental arrangement based on the pulse thomson method according to claim 5, characterized in that said amplifier (25) is a gain adjustable transimpedance amplifier.
7. The PULSO-Thson-method-based experimental device as claimed in claim 1, wherein said first body and said second body are made of aluminum.
8. The experimental setup based on the pulse thomson method as claimed in claim 1, wherein the moving electrode and the static electrode are made of copper.
9. An experimental processing method based on a pulse Thomson method is characterized by comprising the following steps:
step 1, determining the current electric field intensity
U is the voltage used in the measurement, and d is the electrode spacing;
step 2, obtaining the gas particle number density in the experiment by using an ideal gas state equation
The reduced electric field strength at the time of the experiment was obtained in Td, where 1Td is 10-21Vm2And T is the temperature at the time of measurement,p is the inflation pressure;
and 3, controlling the voltage, the inflation pressure and the electrode spacing during the experiment, and establishing the following expression form for the current waveform measured under the specific reduced electric field intensity:
wherein, IeIs a measured current, Ne(0) Is the initial number of electrons released at the moment of laser triggering, q0Is an electronic charge, veffFor effective ionization rate, TeFor electron transit time, τDIs the electron longitudinal diffusion characteristic time;
step 4, obtaining parameters in the formula through fitting, and then obtaining the parameters of the required electronic group according to the following relation:
NτD＝N*τD
wherein k iseffRepresenting the effective ionization rate coefficient, N representing the particle number density of the gas, ωeRepresents the electron drift velocity and d represents the electrode spacing.
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