The paper gives further development of the method of a plate single-sided probe, which makes it possible to reconstruct the total electron velocity distribution function in an axially symmetric nonequilibrium plasma with an arbitrary degree of anisotropy. The method is improved for plasma diagnostics without the assumption of any symmetry. The theory of the method is developed and analytical relations are obtained connecting the Legendre components of the second-order derivative of the probe current with respect to the potential of the probe and the electron distribution function. The method is experimentally tested in the plasma of a positive column of a helium glow discharge. New possibilities of the method for investigating plasma near the boundaries are demonstrated and non-traditional information is obtained on the processes of escape of charged particles from the plasma volume on the walls.
Flat one-sided probe was used for the first time to measure the first seven coefficients in the Legendre polynomial expansion of ion energy and angle distribution functions for He + in He and Ar + in Ar under the conditions when the ion velocity gained along its free run distance is comparable to the average thermal energy of atoms. Analytic solution of the Boltzmann kinetic equation is found for ions in their own gas for arbitrary tension of electric field in plasma when the dominating process is resonant charge exchange. The dependence of cross-section of resonant charge exchange on the relative velocity is accounted for. It is demonstrated that the ion velocity distribution function differs significantly from the Maxwell distribution and is defined by two parameters instead of just one. The results of computational and experimental data agree quite well, provided the spread function of measurement technique is taken into account.
The paper focuses on development of the analytical theory to assess spatial distribution of energy released during propagation of the fast electron beam in a gas, in particular in the air at electron energies of 1-100 keV. An approach adopted by authors [2, 3] to study inelastic deceleration of electrons in the air is further developed here. As the inelastic interaction in most cases leads to energy relaxation while elastic interaction causes distribution isotropization over directions, the first task solved in the paper is finding the electron distribution function including only elastic collisions. In the final part of this paper an analytical solution to this task is presented with account of both types of electron deceleration in the air. The calculations show that when elastic collisions are taken into account this leads to increased spatial density of energy release and to narrowing of the primary energy release region of the fast electrons, as compared to calculations accounting for only inelastic deceleration.
This work is dedicated to the formulation of an analytical theory for calculating the spacial distribution of energy release in a fast electron beam moving in gas and, particularly, in air, considering inelastic interaction. Electron energies of 1-100 keV are considered. Based on the analysis of data on the cross sections for inelastic and elastic interaction of electrons with gas molecules contained in air, it is concluded that inelastic collisions mainly cause energy relaxation, and elastic collisions cause mostly impulse relaxation. Solving Boltzmann’s kinetic equation for the electrons, it is used a model cross-section for the inelastic collisions of electrons with molecules, which guarantees a good description of the measured energy dependence of the mass stopping power of the electrons. Obtained results for de dependence of electrons´ mean energy on the number of inelastic collisions are in good compliance with the results obtained with the method of expanding distribution function in collision numbers and also with the results of Monte-Carlo simulation.
Experimental investigations of the ion velocity distribution function (IVDF) are of great importance to various kinds of application: plasma nanotechnology, surface treatment, nanoelectronics, etching processes et al. In this paper, we propose a new probe method for diagnostics of anisotropic IVDF. The possibilities of the method have been demonstrated in arbitrary electric field plasma under conditions when an ion acquires a velocity on its mean free path comparable with the average thermal velocity of atoms. The energy and angular dependency of seven IVDF Legendre components for He + in He and Ar + in Ar have been measured and polar diagrams of the ion motion have been plotted. In order to verify the reliability and accuracy of the method the analytic solution of the kinetic Boltzmann equation for ions in plasma of their own gas has been found. Conditions under which resonant charge exchange is the dominant process and the ambipolar field is arbitrary have been considered. For the ambipolar field the dependence of resonant charge cross-section on the relative velocity has been taken into account. It is shown that the form of the IVDF is significantly different from the Maxwellian distribution and defined by two parameters. The results of theoretical and experimental data taking into account the instrumental function of the probe method are in good agreement. Calculations of the drift velocity of Hg + ions in Hg, He + in He, Ar + in Ar, and mobility of N 2 + in N 2 are well matched with known experimental data in wide range of electric field values.
It has been demonstrated, that cylindrical probe in anisotropic plasma allows to measure only the even components of the electron velocity distribution expansion. For the first time the method for determining the odd moments of the distribution function by solving a system of ki-netic Boltzmann equations, connecting the even and odd moments ( f 0 , f 1 ); ( f 0 , f 1 , f 2 ) etc. has been developed. The method was tested in plasma of low-voltage beam discharge in helium. The experimental probe I- V traces for different orientations of a cylindrical probe with respect to the axis of symmetry of the plasma has been obtained. The moments of f 0 and f 2 has been cal-culated, f 1 moment is defined by solving the «vector» kinetic equation. The accuracy of f 1 calculation controlled by coincidence of calculated and measured values of discharge current. Theoretical and experimental values are in a good agreement.
This paper deals with the further development of the probe method for the investigation of the anisotropic plasma. The theoretical basis of the method for determining the full electron velocity distribution function in the mirror-symmetric plasma has been developed. For probes of different geometries the analytical expressions, which connects the second derivative of probe current with respect to the potential with the multipole moments of the electron velocity distribution function has been obtained.
Theoretical consideration of collision electron spectroscopy (CES) for gaseous media analysis and experimental results on CES detector are presented. It is demonstrated that a diffusion path confinement for characteristic electrons provides a possibility to measure electrons energy distribution function and to find characteristic spectra of species at high (up to atmospheric) gas pressure. Simple micro-plasma CES detector of two plane parallel electrode configuration with current-voltage measurement in afterglow of helium glow discharge may be designed to operate at a high gas pressure up to atmospheric one. Experimental electron energy spectra of pair He metastables collisions in dependence of interelectrode gap are discussed.
The method of local anisotropic plasma has been developed. The mathematical apparatus of the method for rapid analysis of the degree of anisotropy electron distribution function, as one of the main characteristics of anisotropic plasma has been proposed. It has been demonstrated that the degree of anisotropy of the plasma can be determined only by the form of the IU curve (the second derivative of probe current to the probe potential). The possibilities of the method in area of reconstruction of the full distribution function have been illustrated.
Fundamental research in the field of plasma energetics provides a new opportunity to achieve high efficiency of thermionic converters (TIC). The interelectrode gap of such TICs contains the condensate of excited states (CES), consisting of up to 1000 excited Cs atoms in the form of a plasma crystal (Rydberg matter). In a laboratory TIC with Cs CES the efficiency of ~25 % was registered by emitter’s tem- perature ТЕ ~1600 К and collector’s temperature ТС ~700 К. A unique combination of low TE and high efficiency of the system provides a prospect to implement such systems in small nuclear energetics. The results were obtained with SSC RF – Institute for Physics and Power Engineering (Obninsk).
This article deals with the diagnostic method of emission parameters of thermo emission cathodes by the transverse magnetic field. The knudsen Cs-Ba-diode with the surface ionization are investigated.
Various modes of resistance welding between steel and Ni-Ti-extracting electrodes and fractures of endodontic files were investigated. It was demonstrated that in close to real clinical situations there is most suitable a sequence of a number of pulses of a steepened welding current. As a result, detachment force limit of 15-50 N is achievable which is sufficient for the fracture extraction in most cases.
In this work a device for measurement on a constant voltage of the basic electric characteristics of high-resistance dielectric materials and products from – their electric capacitance and resistance – is developed. The principle of work of the device is based on use of transients in connected in sereies elements having electric capacity and resistance. In the electric circuit of the device the MOSFET with high entrance resistance is used. The device on the basis of the MOSFET for measurement of surface potential of dielectrics is considered also. Use of this device is especially effective at measurement of electret surface potential. Results of research of electrets on a basis of silicon dioxide are discussed.
There is presented a multiprocessor photometric CCD-system for a wide range of spectrometers and for various spectral analysis methods implementation.
Emission parameters and coefficients of reflection of heat electrons from tungsten thermo cathodes were investigated under nontraditional for emission electronic conditions, when the surface contacts with highly ionized plasma. For measurements plasma diode electron current-magnetic field strength relations were used. Parameter Dj, which characterizes cathode heterogeneity by work function, and coefficient of reflection for policrystallic tungsten and for face 110 tungsten single crystal were measured. Proportion entering in effective reflection coefficient of electrons, reflected immediately from the surface and from potential barrier of spots field was determinate.
For the first time magnetic and probe technique for diagnostics of anisotropic plasma have been worked out. Contemporary digital measuring methods, plasma plants and new generation devices of plasma energetics as well as special mathematical programs for fundamental investigations of anisotropic plasma were created. The inventions of Saint Petersburg Mining Institute are used for solving of plasma energetic problems.
Для оценки основных параметров коротких тлеющих разрядов предложена аналитическая модель, учитывающая как рождение электронов в катодном слое, так и нелокальную ионизацию в плазме отрицательного свечения. В отличие от традиционного, данная модель использует подход, в котором разрядный промежуток разделяется на слои объемного заряда и квазинейтральную плазму. Плазменная область включает в себя часть отрицательного свечения, фарадеево темное пространство и положительный столб. Представлены простые выражения для основных характеристик тлеющего разряда (вольт-амперных характеристик, ширины прикатодного слоя, положения точки обращения электрического поля и т.п.), а также профили распределения концентрации плазмы при отсутствии объемной рекомбинации. Полученные результаты удовлетворительно согласуются с экспериментальными данными, в то время как локальные приближения, основанные на классической модели Энгеля – Штеенбека, приводят к существенным расхождениям.
A comparative analysis of plasma chemical processes in high-pressure and low-pressure glow discharges is presented. Based on the results of numerical modeling, the processes determining the parameters of the glow discharge are determined. Correlations between the spatial distribution of the main characteristics of the glow discharge and the distribution of the main plasma chemical processes are presented.
A simple model has been developed to construct the volt-ampere characteristic for obstructed negative glow discharges, taking into account nonlocal ionization in negative glow discharges. Scale dependences allowing prediction of the main parameters of obstructed glow discharges are obtained. The basic expressions for calculating the electron density distribution along the gap in the negative glow plasma, the distribution of potential and electric field strength (including the electric field reversal point) are also presented. Comparison of the obtained results with in-situ modeling data showed satisfactory agreement. Conducting preliminary evaluations with the help of the presented model based on reliable physical principles allows us to better formulate the problem for in-situ modeling.
A comprehensive analysis of modern methods used for diamond identification has been carried out. It is shown that high thermal conductivity cannot unambiguously testify to the authenticity of a diamond, since synthetic imitations of silicon carbide have recently appeared. It is shown that electrical methods of gemstone diagnostics are promising but not yet sufficiently developed. A set of innovative electrocalcium methods for diamond identification is proposed. Techniques for measuring high resistivity, dielectric permittivity and surface potentials, which can be used in the procedure of diamond identification, are developed. An operational model has been tested in the study of new and traditional dielectric materials. The possibility of detecting differences in electrical and physical properties of externally identical materials using this method is shown.
Magnetic and probe techniques for diagnostics of anisotropic plasma were developed for the first time. Modern digital measurement methods, plasma installations and new generation plasma energy devices, as well as special mathematical programs for fundamental studies of anisotropic plasma were created. Inventions of the St. Petersburg Mining Institute are used to solve problems of plasma power engineering.
The electron distribution function in anisotropic plasma has been studied by probe method and Hanle magnetic polarization method. Moments of the anisotropic electron distribution function were measured in helium plasma - beam discharge, the rate constant of alignment decay for helium atoms in the 41D2 state as a result of collisions with charged particles was determined. A new method for diagnosing the anisotropic properties of inaccessible plasma objects has been experimentally tested; electron distribution functions, the degree of electron pressure anisotropy, and the alignment cross section of the total angular momentum of excited helium atoms in electron collisions have been measured. The advantage of the new method is the direct measurement of anisotropic parameters of inaccessible plasmas, the estimation of which was previously carried out only theoretically.
A method for recovering the full electron velocity distribution function and its angular components in a plasma with an arbitrary degree of anisotropy has been developed. The method is based on the measurement of the second derivative of the probe current with respect to the potential for different orientations of a flat one-sided probe with respect to the plasma symmetry axis. The optimal angles of the probe orientation are determined and the number of probe orientations necessary to recover the angular components of the electron velocity distribution of a given rank is estimated. The operability of the proposed method for determining the electron velocity distribution in a plasma with an arbitrary degree of anisotropy is demonstrated in a model experiment.
The kinetic equation for the motion of ions in the intrinsic gas is solved. It is shown that the ion velocity distribution differs significantly from the equilibrium (Maxwellian) distribution. The probe method was used to study the ion velocity distribution function in a low-temperature helium plasma.