Variations in the electron energy distribution function in discharge plasma of a unipolar gas breakdown

It is experimentally demonstrated that the electron energy distribution function (EEDF) and electron density in plasma of a little-studied pulse discharge of a unipolar gas breakdown (UGB) significantly vary in time. The revealed behavior of its plasma parameters is explained based on the proposed physical model of a UGB discharge.     

Influence of second kind collisions on the electron distribution function in the positive column of low pressure nitrogen discharge

A numerical solution of the Boltzmann equation for the electron gas in the positive column of a DC discharge in nitrogen is presented. The Boltzmann equation was solved with the inclusion of the second kind (superelastic) collisions proceeding from the first six excited vibrational levels of molecular nitrogen. The vibrational level population is supposed to follow a Boltzmann distribution for a given vibrational temperatureT _v, with a possible deviation of the ground level, which can be overpopulated in a given ratio. Apart from the electron distribution functions, which were gained for various values ofE/p ₀,T _v and, the values of some production frequencies and kinetic coefficients are presented in form of tables and plots. It is found that the electron distribution (and also the corresponding production rates) depends above a certain energy limit onT _v and through the normalization constant only.     

气体放电中正柱区电场的光谱不介入诊断

基于速度调制分子离子光谱技术，提出并实现了分别通过研究分子离子光谱强度随母体分子气压变化以及光谱线宽随放电电流变化两条途径对气体放电等离子体中电场的两种光谱不介入诊断方法，两者所获得的电场吻合较好，表明速度调制分子离子光谱方法对等离子体诊断具有十分重要的意义。     

Radial distribution of plasma density in the positive column of thehigh-current stationary glow discharge

A model is presented which describes the radial distributions of the plasma density, electric potential, current density, and magnetic field in the positive column of a stationary glow discharge not in contact with the longitudinal walls of the discharge chamber. In this model, the compression of the positive column is provided by the azimuthal magnetic field created by the discharge current. The value of, the discharge current is obtained for the case where charged-particle diffusion is balanced by the actions of the radial electric field and the magnetic pinch effect. The radial distributions of plasma parameters are also calculated for the case of high-current glow discharges where charged-particle diffusion can be ignored     

Apparatus for the electron energy distribution function measurement in the afterglow discharge

A method for measuring the second derivative of the Langmuir probe characteristic in plasma with fast varying parameters is described. Discussion about its applicability and the results of measurements in the Ne afterglow are given.The author wishes to acknowledge the support afforded him by Doc. Dr. M.ícha, CSc. and J.Glosík.     

Contribution to the electron energy distribution function measurement in the afterglow discharge

The measurement of the higher energy part of the electron distribution function in the neon afterglow is presented. A simple theory which enables us to estimate the error which arises by applying the Druyvesteynian theory to the transition regime is given. The numerical calculations of this error are presented to illustrate the dependence on the various plasma parameters.The author wishes to express his thanks to Doc. dr. M.ícha CSc and Dr. V.Hrachová CSc, for many helpful remarks.     

Determination of the relaxation length of electron temperature in the positive column of a glow discharge

This paper presents a formula (14) for determining the reciprocal value of the relaxation length of the temperature of electrons,a ₁, by means of the phase shift of directly measurable curves, of the deviation of the intensity of radiated light and the concentration of the electrons from the equilibrium state. Furthermore, the average values of this phase shift are given as measured in Ne and He in the region of artificially excited moving striations as well as in the wave of stratification anda ₁ is calculated by means of (14).     

Beam electron energy distribution at a volume nanosecond discharge in atmospheric-pressure air

The energy distributions of beam electrons and x-ray photons in a volume nanosecond discharge on atmospheric-pressure air are studied. Several groups of elevated-energy electrons are found. It is shown that electrons with an energy from several tens to several hundreds of kiloelectronvolts (which is lower than a maximal voltage across the gap) make a major contribution to the beam current measured behind thin foils. It is corroborated that fast electrons (with an energy from several kiloelectronvolts to several tens of kiloelectron-volts) arise 100–150 ps before the basic peak of the beam current, elongating the current pulse and significantly increasing its amplitude. The contribution from electrons with an anomalously high energy (exceeding a maximal voltage across the gap) to the beam current is shown to be insignificant (less than 5%). The x-ray spectra in gas-filled diodes of different design are studied. Techniques of measuring the subnanosecond electron beam current and mechanisms generating fast and runaway electrons in volume high-pressure gas discharges are analyzed.     

针一板介质阻挡放电中电子能量空间分布研究

测量了大气压环境下氩气空心针-板放电等离子体中原子与分子谱线强度的空间分布,分析了等离子体中电子能量的空间分布.实验利用空心针-板放电装置,得到了约3 cm长的放电等离子体弧.在300～800 nm范围内采集发射光谱,发现了强度较高的Ar I谱线、N2第二正带系谱线C 3Ⅱu(v=o)→B 3皿(v=0)以及强度较弱的...     

On the Coulomb energy of a finite-temperature electron gas

We rederive the Coulomb expansion of the electron gas average energy at finite temperature, starting from scratch, i.e., using only the framework of the grand canonical ensemble and not the finite-T Green's function formalism. We recover the analytical expressions of the exchange and correlation energy in both the high-T and theT=0 limits. We explicitly show the origin of the crossover of the correlation energy leading term frome ⁴ lne ² at zero temperature toe ³ at finiteT. We also discuss the relative importance of exchange and correlation in both limits.     

Low frequency waves in a positive column of discharge

The propagation of longitudinal low frequency waves in the plasma of the positive column of a d.c. glow discharge is studied theoretically. The dispersion characteristics are obtained for conduction, ion acoustic and neutral acoustic waves. Equations are solved numerically and the results are compared with other theories and measurements.     

Nonlocal phenomena in the positive column of a medium-pressure glow discharge

Commercial CFDRC software () is used to self-consistently simulate the plasma of the positive column (PC) of a medium-pressure dc discharge in argon. The software allows simulations in an arbitrary 3D geometry by using Poisson’s equation for the electric potential and fluid equations for the heavy components and by solving a nonlocal kinetic equation for electrons. It is shown that, in calculating the electron distribution function, the local approximation is almost always inapplicable not only at relatively low pressures (pR<1 cm Torr), but also at relatively high pressures (pR<10 cm Torr), i.e., under the real conditions of a diffuse PC usually met in practice. The use of the local approximation in solving the kinetic equation for electrons leads to significant errors in determining the main parameters of the PC. A paradoxical effect has been revealed: the peaks of the profiles of the excitation rates shift from the discharge axis toward the periphery as the pressure increases from low to medium values (1 cm Torr<pR<10 cm Torr). It is shown that the effect is related to the nonlocal character of the electron distribution function.     

The influence of metastable atoms and the effect of the nonlocal character of the electron distribution on the characteristics of the positive column in an argon discharge

Commercial CFDRC software () is used to self-consistently simulate the plasma of the positive column (PC) of a dc discharge in argon. The software allows simulations in an arbitrary 3D geometry by using Poisson’s equation for the electric potential and fluid equations for the heavy components and by solving a nonlocal kinetic equation for electrons. It is shown that, in calculating the electron distribution function, the local approximation is almost always inapplicable under real conditions of a diffuse PC usually met in practice (pR<(5–10) cm Torr). The influence of metastable atoms, which can substantially affect the parameters of the PC plasma, is considered. It is shown that superelasic collisions play an important role in enriching the fast component of the electron distribution function and that the Penning ionization can result in an ascending volt-ampere characteristic of the positive column.     

Mechanisms for formation of the electron distribution function in the positive column of discharges under Langmuir-paradox conditions

The form of the electron distribution function in the positive column of low-pressure discharges is examined under conditions such that the electron mean free path exceeds the vessel radius. Its formation is analyzed taking all major factors into account, including elastic and inelastic collisions, radial and axial electric fields, and the loss of fast electrons to the wall. It is shown that the main mechanism controlling the fast part of the distribution function is the loss of electrons to the wall, which is determined by the scattering of electrons into a comparatively small loss cone that depends on the relationship between the axial and radial components of the velocity. Since the elastic collision rate for all elements has a weak dependence on the energy beyond the ionization threshold, ultimately the high-energy part of the electron energy distribution function in the positive column of low-pressure discharges is nearly Maxwellian. The subthreshold portion of the distribution function, in turn, is determined by the energy diffusion, in a comparatively strong field, of Maxwellian electrons which arrive after inelastic collisions. The final electron distribution function is well approximated by an exponential with a single slope over the entire energy range. Only within a narrow range of scattering angles is the electron distribution function strongly depleted by the loss of electrons to the vessel walls. In the end, it is concluded that this phenomenon, like the Langmuir paradox, may be related to aspects of the physics of the formation of the electron distribution function owing to a combination of already known mechanisms, rather than to a hypothetical mechanism for thermalization of the electrons, as assumed up to now in the literature. A comparison of solutions of the model kinetic equation given here with published Monte Carlo calculations and experimental data shows that they are in good agreement. Zh. Tekh. Fiz. 69, 34–41 (November 1999)