Nonlocal Models Of Gas Discharge Low Temperature Plasma And Its Applications

Since the realization of gas discharge plasma in the laboratory at the beginning of the last century,the theory of gas discharge plasma and its applications have been fully developed.Gas discharge plasma has realized important applications in daily life as well as in military and national defense.It has made significant contributions to science and technology,and has created great social wealth.With the development of these technologies,the control requirements of gas discharge plasma has become more and more demanding and needs more sophisticated theories and methods.Currently,kinetic theory is a commonly used tool to describe gas discharge plasma.Many applicable theories based on the Boltzmann equation have been developed,among which the local approximation theory has been widely used.However,the local approximation theory ignores the spatial gradient term when describing the gas discharge plasma,which is difficult to apply under conditions such as low pressure.Therefore,the non-local approximation theory has been developed to solve the problems related to the spatial gradient,especially the influence of the spatial gradient on the plasma characteristics at low pressure.For the practical applications of gas discharge plasma,there are still some physical problems that need to be solved.Particularly,in the field of interaction between plasma and electromagnetic waves in aerospace field,this also has gradually developed into a large interdisciplinary research field.This thesis takes the gas discharge lowtemperature plasma as the research object,and mainly explores the non-local theoretical model,probe diagnosis,the absolute negative conductivity of the plasma and its interaction with electromagnetic waves.(1)The research on the non-local kinetic theory model of gas discharge lowtemperature plasma.Firstly,based on the kinetic theory of gas discharge plasma,using the spatially averaged Holstein-Tsendin non-local approximation of the Boltzmann equation,the effects of the metastable atoms in gas discharge plasma on the plasma electron distribution function and plasma-related reaction characteristics are studied;the superelastic collision between electrons and metastable atoms will strongly affect the shape of the electron distribution function and the reactions rate constant;The duplication of the electron distribution function will appear with the excitation threshold period;The effect of the ambipolar electric field in the non-local plasma on the plasma electron distribution function is explored,and the obtained results are compared with the results under the local approximation;Whether under low or medium-high pressure,when the ambipolar electric field exceeds the heating electric field,the influence of the ambipolar electric field on the formation of the electron distribution function cannot be ignored;(2)Generation and diagnosis of gas discharge low-temperature plasma.Using the developed program control software,the discharge characteristics of the hollow cathode in the laboratory are studied,and the characteristics of the hollow cathode with no normal glow or short normal glow are obtained experimentally.Based on the non-local plasma probe diagnosis theory and time synchronization circuit,the Langmuir probe diagnosis method is improved,and the accurate diagnosis of AC discharge plasma is realized.At the same time the microwave method is used to diagnose plasma as an auxiliary measurement;(3)The non-local theory to conduct theoretical analysis and electrical conductivity research in gas discharge plasma.By introducing a non-local ionization source,the typical DC glow discharge structure is more completely reproduced;the plasma parameters near the cathode region and the positive column region are accurately estimated;this model has the ability to quickly perform DC glow discharge simulation giving the longitudinal structure of the DC glow discharge and compare with the phenomenon observed in the experiment,which has important application value for the generation and diagnosis of plasma;The formation of the absolute negative conductivity of the plasma is studied.Through the corresponding theoretical modeling and analysis,the spatial gradient of the non-local plasma is used in the study to make the glow discharge plasma achieve two electric field inversions within a certain pressure range.Then the electron energy distribution function is reversed at a point greater than the second electric field reversal point;Finally,the characteristics of the Ramsauer minimum value of the momentum transfer section of heavier gases such as argon are used to produce a stable absolute negative conductivity of the plasma;(4)The research on the interaction of electromagnetic waves with local and non-local plasmas.By using numerical optimization methods,the dependence of the attenuation of electromagnetic waves on the plasma parameters in uniform plasma is studied;the relationship between plasma parameters and electromagnetic attenuation is not monotonous,and appropriate plasma parameters need to be selected for the problem to be solved;Considering the influence of inhomogeneous plasma on the transmission of electromagnetic waves in the presence of the sheath,based on the idea of potential wells,the "Tick" distribution is proposed to control the transmission of electromagnetic waves in the plasma;network analyzer and coaxial hollow cathodes are used in experiments.At a specific pressure,the absolute negative conductivity of the non-local plasma is discovered,and the plasma’s amplification effect on electromagnetic waves is realized.