CN103048062B - Method for measuring temperature of pulse discharge plasma sheath - Google Patents

Abstract

The invention belongs to the technical field of optical measurement and relates to a method for measuring a temperature of a pulse discharge plasma sheath. The method combines a spectrum method and wave velocity measurement of a shock wave and comprises the following steps of: firstly, accurately measuring a gas temperature of a positive column by utilizing the spectrum method; then accurately measuring a wave velocity of the discharged shock wave by utilizing a pore diaphragm shadow method; and calculating the temperature of the sheath by the temperature of the positive column and the wave velocity of the shock wave. The invention overcomes the defects that the discharge plasma sheath has a small thickness and weak total luminous quantity and cannot be directly measured; the method utilizes the characteristics that the positive column has a large volume and strong luminescence and is beneficial to collection and the wave velocity of the shock wave is constant and is easy to measure; and by applying an approximation principle of a shock tube, the gas temperature of the discharge plasma sheath is accurately measured.

Description

A kind of method of ranging pulse discharge plasma sheath layer temperature

Technical field

The invention belongs to field of optical measuring technologies, what relate to is the method for ranging pulse plasma discharging sheath layer temperature, the shock wave that particularly utilizes sheath layer and positive column temperature difference to produce, indirectly measure the temperature of plasma sheath, the method is particularly useful for the gas thermometry of the thin sheath layer of gas discharge plasma in transverse-discharge excitation's pulsed gas laser.

Background technology

The fields such as pulsed gas discharge is applied in pulsed gas laser pumping widely, plasma immersion ion injection.In pulsed gas discharge process, sheath layer has shielding external electric field, and sustain discharge stability prevents that glow discharge is to effects such as arc light conversions.Particularly, in high repetition pulsed discharge application, discharge stability transforms and seems particularly important to arc light with preventing glow discharge.So the plasma sheath gas temperature of ranging pulse electric discharge device is not only conducive to study the mechanism of pulsed gas discharge, more the raising of discharge stability is had to very big realistic meaning.

Temperature sensing for discharge plasma has spectroscopic methodology, interferometric method and sonde method conventionally.

Mostly spectroscopic methodology is to utilize the molecular spectrum of discharge plasma self transmitting.Want fast because the rotation of molecule and translational energy transfer ratio it and electron energy shift, conventionally adopt the rotational temperature of molecule to be equivalent to isoionic gas temperature.This method adopts the most extensively in plasma temperature is measured.Although sheath layer is luminous often slightly strong than positive column, sheath layer thickness is much smaller than positive column, thus the luminous total amount of sheath layer much smaller than positive column luminous total amount.And plasma luminescence is isotropic, be difficult to shielding positive column for body discharge plasma luminous and only gather the emission spectrum of sheath layer.

Interferometric method is to utilize plasma temperature to change the variable density causing, and then changes the refractive index of plasma area, measures the distribution of refractive index by interferometric method, and then obtains plasma temperature distribution.Interferometric method can directly be measured the space distribution of temperature.But be because sheath layer thickness is very thin equally, and detecting light beam is serious in the hard-edge diffraction effect of negative electrode annex, so directly use interferometric method observation sheath layer very difficult.On the other hand, pulse discharging energy is to inject moment, has little time to be converted into density gradient by thermograde, thereby cannot from index distribution, obtain the information of Temperature Distribution in the time that electric discharge completes toward contact.

Sonde method is the most traditional plasma measurement means.It can derive the temperature of plasma, density feature according to the volt-ampere characteristic of probe.But probe must be deep into plasma inside, will there is strong interaction with plasma in it like this, thereby affect flash-over characteristic.So it is especially not suitable for the measurement of sheath layer temperature.

Summary of the invention

The object of the present invention is to provide a kind of method of ranging pulse discharge plasma sheath layer temperature, the method adopts contactless measuring method, by measuring shock wave velocity of wave and the positive column gas temperature of sheath layer and the generation of positive column interphase, measure accurately the temperature of plasma sheath.

The method of a kind of ranging pulse discharge plasma sheath layer temperature provided by the invention, the method comprises the steps:

The 1st step is utilized the molecular spectrum of spectrometer measurement plasma discharging transmitting, utilizes the molecular spectrum data of measuring, and matching obtains the molecule rotation temperature of discharge gas as the gas temperature of positive column;

The 2nd step utilizes aperture shadowing method to obtain the distribution of shock-wave figure between discharge plasma sheath layer and positive column, and utilizes enhancement type charge coupling imaging part to gather the image obtaining, and obtains the sequential chart picture of Dark cavity; The sequential chart obtaining is looked like to carry out level and smooth and denoising, then carry out binaryzation and thinning processing, obtain shock-wave spot, then carry out linear fit and obtain shock wave velocity of wave W;

The 3rd step is calculated plasma sheath temperature by positive column gas temperature and shock wave velocity of wave.

As the improvement of technique scheme, in the 3rd step, plasma sheath temperature T ₁computing formula be:

${\mathrm{<figure-callout\; id="1"\; label="T"\; filenames="HDA00002541378900011.png"\; state="\{\{state\}\}">T</figure-callout>}}_1=\frac{{[a_5+(\mathrm{\&gamma;}-1)u/2]}^2}{\mathrm{\&gamma;}{R}_g},$ $u=W(1-\frac{(\mathrm{\&gamma;}+1){M_s}^2}{(\mathrm{\&gamma;}-1){{\mathrm{<figure-callout\; id="2"\; label="M\; s"\; filenames="HDA00002541378900011.png"\; state="\{\{state\}\}">M</figure-callout>}}_s}^2+2})$

Wherein, a ₅for local velocity of sound, the specific heat ratio that γ is discharge gas, W is the shock wave velocity of wave obtaining in the 2nd step, R _gfor the gas law constant of discharge gas, M _sfor shock wave local Mach number.

In technique scheme, the execution sequence of the 1st step and the 2nd step can exchange or carry out simultaneously.

The present invention combines spectroscopic methodology and shock wave velocity of wave is measured, first utilize spectroscopic methodology to measure accurately the gas temperature of positive column, recycling aperture shadowing method, measures the velocity of wave of electric discharge rear shock accurately, then calculates thin sheath layer temperature with positive column temperature and shock wave wave-velocity meter.

The present invention has overcome the shortcoming that thin, the luminous total amount of plasma discharging sheath layer thickness is weak, cannot directly measure, utilized positive column volume large, luminous strong, be beneficial to collection, and shock wave velocity of wave is constant, be easy to the feature of measuring, by using the approximate principle of shock tube, measure accurately the gas temperature of plasma discharging sheath layer.

Brief description of the drawings

Fig. 1 is (a) electric discharge region of discharge schematic diagram while just having completed; (b) the rear shock region of discharge schematic diagram while having grown up that discharged;

Fig. 2 is sheath layer temperature survey process flow diagram;

Fig. 3 is the measurement mechanism schematic diagram of plasma molecular spectrum;

Fig. 4 is that aperture shadowing method is measured shock wave device schematic diagram.

Embodiment

Below in conjunction with accompanying drawing, the specific embodiment of the present invention is described further.It should be noted that at this, be used for helping to understand the present invention for the explanation of these embodiments, but do not form limitation of the invention.In addition,, in each embodiment of described the present invention, involved technical characterictic just can combine mutually as long as do not form each other conflict.

Region of discharge plasma when being depicted as pulsed discharge and just having completed as Fig. 1 (a) distributes.Because the difference of Implantation Energy forms sheath layer 1 and region, 2 two of positive columns.Between two regions because the difference of Implantation Energy exists temperature difference.Due to pulse discharge time very short (nanosecond order), energy is to inject moment, so form precipitous thermograde on the interphase 3 of sheath layer 1 and positive column 2, this thermograde can cause the generation of shock wave.Region of discharge state when being depicted as the rear shock that discharged and having grown up as Fig. 1 (b).After having discharged, interfacial thermograde causes the shock wave 6 of propagating to positive column 2 directions and the expansion wave group 4 of propagating to sheath layer 1 direction, and between sheath layer 1 and positive column 2, forms a transitional region 5.Meanwhile, in discharge process, positive column 2 can produce a strong aura, is measured and can be obtained positive column gas temperature by molecular spectrum.

The present invention by measuring the velocity of propagation of shock wave 6 and the temperature of positive column 2, uses the theory of shock tube to obtain the gas temperature of sheath layer 1 just.

Sheath layer 1 temperature survey process flow diagram as shown in Figure 2, comprises following step:

1) measurement of plasma emission spectroscopy:

Utilize the molecular spectrum of spectrometer measurement plasma discharging transmitting.

As shown in Figure 3, the measurement mechanism of plasma emission spectroscopy comprises lens focus system 8, optical fiber 9, spectrometer 10 and an ICCD camera 11.One end of optical fiber 9 is positioned in the focus of lens focus system 8, and the other end is connected with spectrometer 10, and spectrometer 10 is connected with an ICCD camera 11.

Luminous discharge plasma 7 scioptics focusing system 8 is focused on optical fiber 9 end faces of spectrometer 10, by optical fiber 9, light beam is passed to spectrometer 10 again, obtain nitrogen molecular second and be just with rotation spectrum, then gather by an ICCD camera 11 spectroscopic data that spectrometer obtains.It should be noted that for most of pulsed discharges, in gas composition, all at least contain micro-nitrogen, and the second positive band spectrum luminous intensity of nitrogen molecular is large, very easily gather; Even if actual requirement electric discharge device can not contain nitrogen completely, in experimental stage, also can be by sneak into the mode of trace nitrogen gas in discharge gas, use the present invention to obtain sheath layer gas temperature, add micro-nitrogen negligible for the impact of flash-over characteristic.

2) simulate positive column temperature:

Utilize the molecular spectrum data of measuring, matching obtains the molecule rotation temperature of discharge gas as the gas temperature of positive column;

First a default temperature range, then simulates the curve of spectrum that each temperature value is corresponding, then the spectroscopic data obtaining taking the experiment variance that is the benchmark matching curve of spectrum, obtains the temperature value corresponding to matching spectrum of variance minimum.If this temperature value is not the border of temperature range, this temperature value is molecule rotation temperature; If this temperature value is the upper (lower) border of temperature range, again get the temperature range of former temperature range higher (low), repeat above-mentioned fit procedure, finally obtain molecule rotation temperature.Because plasma overwhelming majority region is positive column, and luminous intensity is large, so can assert that this molecular rotation spectrum is positive column molecular rotation spectrum.And want fast because the rotation of molecule and translational energy transfer ratio it and electron energy shift, adopt the molecule rotation temperature of positive column as the gas temperature of positive column.

3) measurement of plasma shock wave

Utilize aperture shadowing method to obtain the distribution of shock-wave figure between discharge plasma sheath layer and positive column, and utilize enhancement mode electric charge coupling (ICCD) image device to gather the image obtaining, obtain the sequential chart picture of Dark cavity.

Its concrete measurement can adopt the device of aperture method measurement shock wave velocity of wave as shown in Figure 4, and this device comprises probe source 12, beam-expanding system 13, simple lens 14, aperture 15, ground glass 16 and the 2nd ICCD camera 17.

First detection light probe source 12 being sent expands by beam-expanding system 13, parallel by discharge plasma 7, recycle afterwards simple lens 14 by its focusing, and aperture 15 is set at focus place carries out spatial filtering, filtered divergent beams are incident upon on ground glass 16, and recycling the 2nd ICCD camera 17 gathers.Wherein the 2nd ICCD camera 17 adopts the electromagnetic interference (EMI) of pulsed discharge moment of discharge plasma 7 as synchronous triggering signal, controller by ICCD camera carries out trigger pip time delay, obtain the time delayed signal sequence of one group of constant duration, do not gather in the same time after electric discharge by this burst control the 2nd ICCD camera 17, obtain the sequential chart picture that shock wave 6 develops.

4) data processing obtains shock wave velocity of wave

To step 3) sequential chart that obtains looks like to carry out level and smooth and denoising, then carries out binaryzation and thinning processing, and obtain shock-wave spot, then use the method for linear fit to obtain shock wave velocity of wave.

Due to the unevenness of detecting light beam self, and the factors such as the disturbance of rear other flow field changes to detection light of discharging, can make the image obtaining have certain ground unrest.By the image obtaining is carried out to level and smooth and denoising, shock wave 6 images comparatively uniformly be can obtain, then binaryzation and thinning processing adopted, obtain shock wave 6 wave fronts.Again the position of discharge centers region (being equal to or less than electrode width) shock wave 6 wave fronts is extracted, average and obtain the not mean place in the same time in discharge centers region.Adopt first-order linear fit equation y=y ₀+ Wt, utilizes least square method to solve shock wave 6 velocity of wave W, and wherein t is time (using the moment of discharging as time zero), and y is the shock wave 6 wave front positions that moment t is corresponding, and W is shock wave velocity of wave, y ₀for initial time (t=0) shock wave 6 wave front positions (sheath layer and positive column interphase 3 positions).In order to obtain accurate result, measure number of times and should be greater than 10 groups, thereby reduce the error that the factors such as noise and discharge instability produce.

Above-mentioned steps 1) to 2) with step 3) to 4) and order can walk abreast.

5) calculate plasma sheath temperature by positive column gas temperature and shock wave velocity of wave

Utilize the positive column gas temperature and the shock wave velocity of wave that have recorded, use the theoretical calculate of shock tube to go out the gas temperature of plasma sheath.

Utilize the positive column gas temperature and the shock wave velocity of wave that have recorded, use the theoretical calculate of shock tube to go out the gas temperature of plasma sheath 1.Because electric discharge transient energy is injected, gas has little time to expand, so hypothesis positive column gas density is constant.By the temperature T of positive column 2 gases ₂, shock wave velocity of wave W and shock wave local Mach number M _s, can calculate the temperature T of transitional region 5 ₅, and the flow velocity u of former sheath layer and positive column interphase 3:

${\mathrm{<figure-callout\; id="5"\; label="T"\; filenames="HDA00002541378900011.png"\; state="\{\{state\}\}">T</figure-callout>}}_5=T_2[1+\frac{2(\mathrm{\&gamma;}-1)}{{(\mathrm{\&gamma;}+1)}^2}\frac{\mathrm{\&gamma;}{{\mathrm{<figure-callout\; id="2"\; label="M\; s"\; filenames="HDA00002541378900011.png"\; state="\{\{state\}\}">M</figure-callout>}}_s}^2+1}{{M_s}^2}({M_s}^2-1)]---\left(1\right)$

$u=W(1-\frac{(\mathrm{\&gamma;}+1){M_s}^2}{(\mathrm{\&gamma;}-1){M_s}^2+2})---\left(3\right)$

Wherein γ, R _gbe respectively discharge gas specific heat ratio and gas law constant, they are all only relevant with gas composition, all have nothing to do with the residing region of gas, state.Again by the local velocity of sound of transitional region 5

and the flow velocity u of former sheath layer and positive column interphase 3, calculate sheath layer temperature T ₁:

${\mathrm{<figure-callout\; id="1"\; label="T"\; filenames="HDA00002541378900011.png"\; state="\{\{state\}\}">T</figure-callout>}}_1=\frac{{[a_5+(\mathrm{\&gamma;}-1)u/2]}^2}{\mathrm{\&gamma;}{R}_g}---\left(4\right)$

The present invention has overcome the shortcoming that thin, the luminous total amount of plasma discharging sheath layer thickness is weak, cannot directly measure, utilized positive column volume large, luminous strong, be beneficial to collection, and shock wave velocity of wave is constant, be easy to the feature of measurement, measure accurately the gas temperature of the thin sheath layer of plasma discharging.

The above is preferred embodiment of the present invention, but the present invention should not be confined to the disclosed content of this embodiment and accompanying drawing.Do not depart from the equivalence or the amendment that under spirit disclosed in this invention, complete so every, all fall into the scope of protection of the invention.

Claims (4)

1. a method for ranging pulse discharge plasma sheath layer temperature, the method comprises the steps:

The 1st step is utilized the molecular spectrum of spectrometer measurement discharge plasma transmitting, utilizes the molecular spectrum data of measuring, and matching obtains the molecule rotation temperature of discharge gas as the gas temperature of positive column;

The 2nd step utilizes aperture shadowing method to obtain the distribution of shock-wave image between discharge plasma sheath layer and positive column, and utilizes enhancement type charge coupling imaging part to gather the image obtaining, and obtains the sequential chart picture of Dark cavity; The sequential chart obtaining is looked like to carry out level and smooth and denoising, then carry out binaryzation and thinning processing, obtain shock-wave spot, then carry out linear fit and obtain shock wave velocity of wave W;

The 3rd step is calculated plasma sheath temperature by positive column gas temperature and shock wave velocity of wave.

2. the method for a kind of ranging pulse discharge plasma sheath layer temperature according to claim 1, is characterized in that, in the 3rd step, and plasma sheath temperature T ₁, and the computing formula of former sheath layer and the interfacial flow velocity u in positive column is:

$T_1=\frac{{[a_5+(\mathrm{\&gamma;}-1)u/2]}^2}{{\mathrm{\&gamma;R}}_g},u=W(1-\frac{(\mathrm{\&gamma;}+1){M_s}^2}{(\mathrm{\&gamma;}-1){M_s}^2+2})$

Wherein, a ₅for local velocity of sound, the specific heat ratio that γ is discharge gas, W is the shock wave velocity of wave obtaining in the 2nd step, R _gfor the gas law constant of discharge gas, Ms is shock wave local Mach number.

3. the method for a kind of ranging pulse discharge plasma sheath layer temperature according to claim 1, is characterized in that, the 1st step and the 2nd step execution sequence exchange.

4. the method for a kind of ranging pulse discharge plasma sheath layer temperature according to claim 1, is characterized in that, the 1st step and the 2nd step are carried out simultaneously.

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