CN103048062A - 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

Pulsed gas discharge is applied in the pulsed gas laser pumping widely, the fields such as plasma immersion ion injection.In the pulsed gas discharge process, the sheath layer has the 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 was used, discharge stability seemed particularly important with preventing glow discharge to the arc light conversion.So the plasma sheath gas temperature of ranging pulse electric discharge device not only is conducive to study the mechanism of pulsed gas discharge, more the raising of discharge stability there is very big realistic meaning.

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

Mostly spectroscopic methodology is to utilize the molecular spectrum of discharge plasma self emission.Because it shifts the rotation of molecule and translational energy transfer ratio with electron energy and want fast, usually adopt the rotational temperature of molecule equivalent is isoionic gas temperature.This method adopts the most extensively in plasma temperature is measured.Although the sheath layer is luminous often slightly strong than the positive column, the sheath layer thickness is much smaller than the positive column, thus the luminous total amount of sheath layer much smaller than the positive column luminous total amount.And plasma luminescence is isotropic, is difficult to the shielding positive column for the 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 that causes, and then changes the refractive index of plasma area, measures the distribution of refractive index by interferometric method, and then obtains the plasma temperature distribution.Interferometric method can directly be measured the space distribution of temperature.But be because the 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 toward contact when discharge is finished, thereby can't obtain the information of Temperature Distribution from index distribution.

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, and it will strong interaction occur with plasma like this, thereby affects flash-over characteristic.So it especially is 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 the generation of sheath layer and 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 molecular spectrum that the 1st step was utilized the emission of spectrometer measurement plasma discharging utilizes the molecular spectrum data of measuring, and match obtains the molecule rotation temperature of discharge gas as the gas temperature of positive column;

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

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

As improvement of the technical scheme, in the 3rd step, the 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 ₅Be local velocity of sound, γ is the specific heat ratio of discharge gas, and W is the shock wave velocity of wave that obtains in the 2nd step, R _gBe the gas law constant of discharge gas, M _sBe the shock wave local Mach number.

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

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

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

Description of drawings

Fig. 1 is (a) discharge region of discharge schematic diagram when just having finished; Region of discharge schematic diagram when (b) discharge is finished rear shock and grown up;

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 the 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.Need to prove at this, understand the present invention for the explanation of these embodiments for helping, but do not consist of limitation of the invention.In addition, below in each embodiment of described the present invention involved technical characterictic just can mutually not make up as long as consist of each other conflict.

Region of discharge plasma when being depicted as pulsed discharge and just having finished such as Fig. 1 (a) distributes.Owing to the difference of Implantation Energy forms 2 two zones of sheath layer 1 and positive column.There is temperature difference in difference owing to Implantation Energy between two zones.Because pulse discharge time very short (nanosecond order), energy are to inject moment, so in the precipitous thermograde of sheath layer 1 and interphase 3 formation of positive column 2, this thermograde can cause the generation of shock wave.Region of discharge state when being depicted as discharge and finishing rear shock and grown up such as Fig. 1 (b).After discharge was finished, interfacial thermograde caused the shock wave 6 that 2 directions are propagated to the positive column and the expansion wave group 4 of propagating to sheath layer 1 direction, and formed a transitional region 5 between sheath layer 1 and positive column 2.Meanwhile, in discharge process, positive column 2 can produce a strong aura, measures by molecular spectrum and can obtain the positive column gas temperature.

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

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

1) measurement of plasma emission spectroscopy:

Utilize the molecular spectrum of spectrometer measurement plasma discharging emission.

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 on 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.

Discharge plasma 7 luminous scioptics focusing systems 8 are 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 just be with rotation spectrum, gather the spectroscopic data that spectrometer obtains by an ICCD camera 11 again.It should be noted that for most of pulsed discharges, all contain at least the nitrogen of trace in the gas composition, and the second positive band spectrum luminous intensity of nitrogen molecular is large, very easily gather; Even the actual requirement electric discharge device can not contain nitrogen fully, in experimental stage, also can use the present invention to obtain sheath layer gas temperature by sneak into the mode of trace nitrogen gas in discharge gas, the nitrogen that adds trace can be ignored for the impact of flash-over characteristic.

2) simulate the positive column temperature:

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

Then at first default temperature range simulates the curve of spectrum corresponding to each temperature value, and the spectroscopic data that obtains take experiment again is the variance of the benchmark match curve of spectrum, obtains the temperature value corresponding to match spectrum of variance minimum.If this temperature value is not the border of temperature range, then this temperature value is the molecule rotation temperature; If this temperature value is upper (descending) border of temperature range, then again get the temperature range of former temperature range higher (low), repeat above-mentioned fit procedure, finally obtain the molecule rotation temperature.Because plasma overwhelming majority zone is the positive column, and luminous intensity is large, is the positive column molecular rotation spectrum so can assert this molecular rotation spectrum.And since the rotation of molecule and translational energy transfer ratio it shift with electron energy and want soon, the molecule rotation temperature of employing positive column is as the gas temperature of positive column.

3) measurement of plasma shock wave

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

Its concrete measurement can be adopted 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.

The detection light that at first probe source 12 is sent expands by beam-expanding system 13, parallel by discharge plasma 7, recycle afterwards simple lens 14 with its focusing, and at the focus place aperture 15 is set and carries out spatial filtering, filtered divergent beams are incident upon on the ground glass 16, recycle the 2nd ICCD camera 17 and gather.Wherein the 2nd ICCD camera 17 adopts the electromagnetic interference (EMI) of pulsed discharge moment of discharge plasmas 7 as synchronous triggering signal, controller by the ICCD camera carries out the trigger pip time-delay, obtain the time delayed signal sequence of one group of constant duration, control the 2nd ICCD camera 17 different constantly collection after discharge by this burst, obtain the sequential chart picture that shock wave 6 develops.

4) data are processed and are obtained the 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, obtains shock-wave spot, uses the method for linear fit to obtain the shock wave velocity of wave again.

Because the unevenness of detecting light beam self, and other flow field changes can make the image of acquisition that certain ground unrest is arranged to surveying the factors such as disturbance of light after the discharge.By the image that obtains is carried out level and smooth and denoising, can obtain comparatively uniformly shock wave 6 images, adopt again binaryzation and thinning processing, obtain shock wave 6 wave fronts.Position with discharge centers zone (being equal to or less than electrode width) shock wave 6 wave fronts extracts again, averages to obtain the different mean places constantly in discharge centers zone.Adopt first-order linear fit equation y=y ₀+ Wt utilizes least square method to find the solution shock wave 6 velocity of wave W, wherein t be the time (with discharge moment as time zero), y be moment shock wave 6 wave front positions corresponding to t, W is the shock wave velocity of wave, y ₀Be initial time (t=0) shock wave 6 wave front positions (sheath layer and positive column interphase 3 positions).In order to obtain accurate result, measuring number of times should be greater than 10 group, thus the error that noise reduction disturbs and the factor such as discharge instability produces.

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

5) calculate the 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, the theoretical calculate of utilization shock tube goes out the gas temperature of plasma sheath.

Utilize the positive column gas temperature and the shock wave velocity of wave that have recorded, the theoretical calculate of utilization shock tube goes out the gas temperature of plasma sheath 1.Because the discharge transient energy is injected, gas has little time to expand, so hypothesis positive column gas density is constant.Temperature T by 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 zone 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, can't directly measure, utilized the positive column volume large, luminous strong, be beneficial to collection, and the shock wave velocity of wave is constant, and the characteristics that are easy to measure are measured the gas temperature of the thin sheath layer of plasma discharging accurately.

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.So everyly do not break away from the equivalence of finishing under the spirit disclosed in this invention or revise, all fall into the scope of protection of the invention.

Claims (4)

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

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

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

The 3rd step was calculated the 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 the plasma sheath temperature T ₁Computing formula be:

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

Wherein, a ₅Be local velocity of sound, γ is the specific heat ratio of discharge gas, and W is the shock wave velocity of wave that obtains in the 2nd step, R _gBe the gas law constant of discharge gas, M _sBe the 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 carry out simultaneously.

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