開放空間低氣壓微波脈沖放電氮氣等離子體電子行為研究
發(fā)布時間：2018-10-17 12:30
【摘要】：微波產(chǎn)生等離子體的技術(shù)很早就應用在工業(yè)生產(chǎn)中,并且最近人們對微波放電產(chǎn)生的等離子體特性也進行了深入的討論。但是人們大多關(guān)注微波產(chǎn)生等離子體之后的穩(wěn)定狀態(tài)的作用,并不關(guān)注放電過程中等離子體形成的過程及此時等離子體狀態(tài)的變化。另一方面,微波氣體擊穿的研究在很多微波傳輸或者微波器件的研究都有涉及,但是大多數(shù)針對微波氣體擊穿的研究的目標在于防止微波產(chǎn)生擊穿(打火)的效果,所以該類研究大多關(guān)注微波擊穿時微波本身的參數(shù)和環(huán)境因素,對微波擊穿之后的形態(tài)并不詳細討論和研究。本文研究的主要目的是詳細討論從微波擊穿開始,到產(chǎn)生等離子體,最后形成穩(wěn)定的等離子體的全過程。而研究這整個過程的核心點在于研究電子在微波電場的作用如何得到能量,損失能量以及如何產(chǎn)生更多的電子最終形成穩(wěn)定等離子體。由于該過程是相當復雜的過程,所以簡化該過程中的非重要因素是非常必須的。在實驗中本文選擇開放空間的條件去除了電子與容器壁的相互作用,并且背景氣體的狀態(tài)更加穩(wěn)定,同時使得電子的擴散效應占據(jù)主導地位,但是該開放空間的條件也導致了微波放電過程中等離子體的形成將是一個電子運動遠快于離子運動的過程。同時在實驗中選擇低氣壓氮氣作為背景氣體將使得電子與氮分子的碰撞過程更加重要,這樣避免了在極低的氣壓下電子與電子和電子與離子的碰撞過程會產(chǎn)生劇烈的影響或者在極高的氣壓下氮分子之間碰撞作為主要碰撞過程出現(xiàn)。本文采取脈沖式微波進行放電可以清晰和直觀地分辨放電過程中從擊穿到產(chǎn)生等離子體到最終形成穩(wěn)定等離子體的過程。脈沖式微波放電也為測量和診斷提供了清晰的參考。在理論上,本文首先從單電子運動模型出發(fā),導出擴散效應下單電子在微波電場中運動的流體方程,并討論該方程的適用條件和注意事項。然后詳細討論電子與氮分子的各個碰撞過程,氮分子之間的碰撞行為、電子與電子和電子與離子的碰撞行為以及電子的自擴散行為。并針對開放空間低氣壓的條件對各類碰撞行為進行討論,分析其適用條件,最后就電子的碰撞行為對單電子模型進行補充說明。最后從統(tǒng)計的角度出發(fā),將單電子模型拓展到全域模型(Global Model)中,并采用統(tǒng)計的觀點對電子的碰撞行為進行具體分析,討論該模型適用的條件。最后通過實驗測量結(jié)果與理論計算的結(jié)果進行對比,分析和討論開放空間低氣壓條件下,微波脈沖放電產(chǎn)生等離子體中電子溫度和電子密度的變化過程及其受影響的因素。實驗中采用氣壓300Pa,氣體溫度300K氮氣作為背景氣體進行放電。放電微波采用C波段5.3GHz的微波聚焦產(chǎn)生等離子體,脈沖寬度為1μs,重復頻率為500Hz,峰值功率為600-800kW。在診斷上主要采用X波段的連續(xù)波進行微波透射診斷以得到電子密度的變化,同時采用發(fā)射光譜診斷對氮分子的振動和轉(zhuǎn)動溫度進行測量。最后通過實驗結(jié)果與理論結(jié)果對比發(fā)現(xiàn)在微波擊穿到形成穩(wěn)定等離子體的過程中,電子溫度會率先迅速上升達到一個較高的值,然后較高的電子溫度促使電離過程劇烈發(fā)生,形成雪崩效應,此時電子密度開始急劇上升。在電子密度上升至放電微波頻率對應的臨界密度的時候,等離子體開始對放電微波的進入產(chǎn)生阻礙,這導致進入等離子體的微波電場開始衰減,而微波電場的衰減將導致電子從微波電場中吸收的能量減少,從而使電子溫度下降。電子溫度的下降又會導致電離率下降,從而導致電子密度的增長速度下降。最終在電子數(shù)目的得失與電子能量的得失上達到一個平衡,即形成穩(wěn)定的等離子體。整個放電過程是一個非平衡和非線性的過程,但是究其物理本質(zhì)是等離子體態(tài)本身與微波相互作用的結(jié)果,這也是等離子體態(tài)相對于其它三種狀態(tài)的特性。
[Abstract]:The technology of microwave generating plasma has been widely used in industrial production, and the plasma characteristics of microwave discharge have been discussed in depth recently. However, most attention is paid to the stabilization of plasma after microwave generation, and it is not concerned about the process of plasma formation during the discharge process and the change of plasma state at this time. On the other hand, the research on the breakdown of microwave gas is related to many microwave transmission or microwave devices, but most of the research on the breakdown of microwave gas is to prevent the effect of microwave generating breakdown (sparking). Therefore, most attention is paid to the parameters and environmental factors of the microwave itself at the time of microwave breakdown, and the morphology after microwave breakdown is not discussed and studied in detail. The main purpose of this paper is to discuss the whole process of generating plasma and finally forming stable plasma from the beginning of microwave breakdown. The core point of this process is to study how electrons gain energy, loss of energy, and how to generate more electrons eventually form stable plasma in the microwave electric field. Since the process is a quite complex process, it is very necessary to simplify the non-important factors in the process. in the experiment, the condition of the open space is selected to remove the interaction between the electrons and the wall of the container, and the state of the background gas is more stable, and meanwhile, the diffusion effect of the electrons is dominant, However, the condition of the open space also results in the formation of the plasma in the process of microwave discharge will be the process of electron motion much faster than the ion motion. meanwhile, selecting low-pressure nitrogen as a background gas in the experiment will make the collision process of electrons and nitrogen molecules more important, This avoids dramatic effects on the collision of electrons with electrons and electrons and ions at very low pressures or collisions between nitrogen molecules as a major impact process at very high gas pressures. In this paper, pulsed microwave discharge can clearly and intuitively distinguish the process from breakdown to generation of plasma to stable plasma in the process of discharge. Pulse microwave discharge also provides a clear reference for measurement and diagnosis. In this paper, based on the single-electron motion model, the fluid equation of the electron in the microwave electric field is derived by the diffusion effect, and the applicable conditions and precautions of the equation are discussed. The collision behavior between electrons and nitrogen molecules, the collision behavior between electrons and electrons and ions, and the self-diffusion behavior of electrons are discussed in detail. According to the condition of the open space low air pressure, the collision behavior is discussed, the applicable conditions are analyzed, and finally the single electronic model is supplemented by the collision behavior of the electrons. At last, from the statistical point of view, the single electronic model is extended to the Global Model, and the collision behavior of the electrons is analyzed in a statistical way to discuss the applicable conditions of the model. Finally, the change of electron temperature and electron density in plasma generated by microwave pulse discharge and its influence factors were analyzed and discussed by comparing the experimental results with the results of theoretical calculation. In the experiment, a gas pressure of 300Pa and a gas temperature of 300K were used as background gas to discharge. The plasma has a pulse width of 1. m u.m, a repetition frequency of 500Hz and a peak power of 600-800kW. In the diagnosis, the X-band continuous wave is mainly used for microwave transmission diagnosis to obtain the change of electron density, and the vibration and rotation temperature of nitrogen molecules are measured by emission spectrum diagnosis. Finally, by comparing the experimental results with the theoretical results, it is found that in the process of microwave breakdown to the stable plasma, the electron temperature will rise rapidly to a higher value, then the higher electron temperature will cause the ionization process to occur violently, forming the avalanche effect. At this time, the electron density begins to rise sharply. when the electron density rises to a critical density corresponding to the discharge microwave frequency, the plasma starts to interfere with the entry of the discharge microwave, which causes the microwave electric field entering the plasma to begin to decay, and the attenuation of the microwave electric field will result in a reduction in the energy absorbed by the electrons from the microwave electric field, thereby lowering the electronic temperature. The decrease in the electron temperature will also cause the ionization rate to drop, resulting in a decrease in the growth rate of the electron density. and finally achieving a balance on the gain and loss of the electronic number and the gain and loss of the electronic energy, namely forming a stable plasma. The whole discharge process is a non-equilibrium and non-linear process, but its physical nature is the result of the interaction between the plasma state itself and the microwave, which is also the characteristic of the plasma state with respect to the other three states.
【學位授予單位】：華中科技大學
【學位級別】：博士
【學位授予年份】：2016
【分類號】：O53
[Abstract]:The technology of microwave generating plasma has been widely used in industrial production, and the plasma characteristics of microwave discharge have been discussed in depth recently. However, most attention is paid to the stabilization of plasma after microwave generation, and it is not concerned about the process of plasma formation during the discharge process and the change of plasma state at this time. On the other hand, the research on the breakdown of microwave gas is related to many microwave transmission or microwave devices, but most of the research on the breakdown of microwave gas is to prevent the effect of microwave generating breakdown (sparking). Therefore, most attention is paid to the parameters and environmental factors of the microwave itself at the time of microwave breakdown, and the morphology after microwave breakdown is not discussed and studied in detail. The main purpose of this paper is to discuss the whole process of generating plasma and finally forming stable plasma from the beginning of microwave breakdown. The core point of this process is to study how electrons gain energy, loss of energy, and how to generate more electrons eventually form stable plasma in the microwave electric field. Since the process is a quite complex process, it is very necessary to simplify the non-important factors in the process. in the experiment, the condition of the open space is selected to remove the interaction between the electrons and the wall of the container, and the state of the background gas is more stable, and meanwhile, the diffusion effect of the electrons is dominant, However, the condition of the open space also results in the formation of the plasma in the process of microwave discharge will be the process of electron motion much faster than the ion motion. meanwhile, selecting low-pressure nitrogen as a background gas in the experiment will make the collision process of electrons and nitrogen molecules more important, This avoids dramatic effects on the collision of electrons with electrons and electrons and ions at very low pressures or collisions between nitrogen molecules as a major impact process at very high gas pressures. In this paper, pulsed microwave discharge can clearly and intuitively distinguish the process from breakdown to generation of plasma to stable plasma in the process of discharge. Pulse microwave discharge also provides a clear reference for measurement and diagnosis. In this paper, based on the single-electron motion model, the fluid equation of the electron in the microwave electric field is derived by the diffusion effect, and the applicable conditions and precautions of the equation are discussed. The collision behavior between electrons and nitrogen molecules, the collision behavior between electrons and electrons and ions, and the self-diffusion behavior of electrons are discussed in detail. According to the condition of the open space low air pressure, the collision behavior is discussed, the applicable conditions are analyzed, and finally the single electronic model is supplemented by the collision behavior of the electrons. At last, from the statistical point of view, the single electronic model is extended to the Global Model, and the collision behavior of the electrons is analyzed in a statistical way to discuss the applicable conditions of the model. Finally, the change of electron temperature and electron density in plasma generated by microwave pulse discharge and its influence factors were analyzed and discussed by comparing the experimental results with the results of theoretical calculation. In the experiment, a gas pressure of 300Pa and a gas temperature of 300K were used as background gas to discharge. The plasma has a pulse width of 1. m u.m, a repetition frequency of 500Hz and a peak power of 600-800kW. In the diagnosis, the X-band continuous wave is mainly used for microwave transmission diagnosis to obtain the change of electron density, and the vibration and rotation temperature of nitrogen molecules are measured by emission spectrum diagnosis. Finally, by comparing the experimental results with the theoretical results, it is found that in the process of microwave breakdown to the stable plasma, the electron temperature will rise rapidly to a higher value, then the higher electron temperature will cause the ionization process to occur violently, forming the avalanche effect. At this time, the electron density begins to rise sharply. when the electron density rises to a critical density corresponding to the discharge microwave frequency, the plasma starts to interfere with the entry of the discharge microwave, which causes the microwave electric field entering the plasma to begin to decay, and the attenuation of the microwave electric field will result in a reduction in the energy absorbed by the electrons from the microwave electric field, thereby lowering the electronic temperature. The decrease in the electron temperature will also cause the ionization rate to drop, resulting in a decrease in the growth rate of the electron density. and finally achieving a balance on the gain and loss of the electronic number and the gain and loss of the electronic energy, namely forming a stable plasma. The whole discharge process is a non-equilibrium and non-linear process, but its physical nature is the result of the interaction between the plasma state itself and the microwave, which is also the characteristic of the plasma state with respect to the other three states.
【學位授予單位】：華中科技大學
【學位級別】：博士
【學位授予年份】：2016
【分類號】：O53
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