S. N. Stamenković

Study of relaxation kinetics in argon afterglow by the breakdown time delay measurements

In this paper the afterglow kinetics in argon is studied by the breakdown time delay measurements as a function of relaxation time t¯d(τ) (“memory curve”). Measurements were carried out at the pressure of 1.33mbar in a gas tube with gold-plated copper cathode and approximate and exact numerical models are developed to follow metastable and charged particle decay. It was found that the early afterglow kinetics is governed by the charged particle decay up to hundreds of milliseconds, extending from ambipolar to the free diffusion limit. Quenching processes reduce the effective lifetime of metastable states several orders of magnitude below that relevant for the time scale of the observations if realistic abundances and processes are included in the model. Nitrogen atoms originating from impurities and recombining on the cathode surface can determine the breakdown time delay down to that defined by the level of cosmic rays and natural radioactivity.

Metastable and charged particle decay in neon afterglow studied by the breakdown time delay measurements

Memory effect—the long time variation of the electrical breakdown time delay on the relaxation time td¯(τ) in neon—was explained by the Ne(P23) (1s5) metastable state remaining from the preceding glow [Dj. A. Bosan, M. K. Radovic, and Dj. M. Krmpotic, J. Phys. D 19, 2343 (1986)]. However, the authors neglected the quenching processes that reduce the effective lifetime of metastable states several orders of magnitude below that of the memory effect observations. In this paper the time delay measurements were carried out in neon at the pressure of 6.6mbar in a gas tube with gold-plated copper cathode, and the approximate and exact numerical models are developed in order to study the metastable and charged particle decay in afterglow. It was found that the metastable hypothesis completely failed to explain the afterglow kinetics, which is governed by the decay of molecular neon ions and molecular nitrogen ions produced in Ne2+ collisions with nitrogen impurities; i.e., Ne2++N2→N2++2Ne. Charged particle decay...

FLUCTUATIONS AND CORRELATIONS OF THE FORMATIVE AND STATISTICAL TIME DELAY IN NEON

The fluctuations and correlations of the formative tf and statistical time delay ts in neon are studied by electrical breakdown time delay measurements. The measurements were carried out at different preionization levels (afterglow periods) and the Gaussian distributions for the formative time were obtained to about 20?ms in afterglow. The formative time increases linearly with the afterglow period consistently with an exponential decay. After that, double-Gaussian (bi-normal) distributions for the formative time were obtained corresponding to and decay. For the statistical time delay Gaussian, Gauss-exponential and exponential distributions were obtained. It was found that the formative and statistical time delay are dependent variables for ts < tf and their correlations are estimated. The linear correlation coefficient is ? ? 1 at high electron yields (rates of electron production) and ? ? 0 at low electron yields.

New distributions of the statistical time delay of electrical breakdown in nitrogen

Two new distributions of the statistical time delay of electrical breakdown in nitrogen are reported in this paper. The Gaussian and Gauss-exponential distributions of statistical time delay have been obtained on the basis of thousands of time delay measurements on a gas tube with a plane-parallel electrode system. Distributions of the statistical time delay are theoretically founded on binomial distribution for the occurrence of initiating electrons and described by using simple analytical and numerical models. The shapes of distributions depend on the electron yields in the interelectrode space originating from residual states. It is shown that a distribution of the statistical time delay changes from exponential and Gauss-exponential to Gaussian distribution due to the influence of residual ionization.

Determination of correlation coefficient of the statistical and formative time delay in nitrogen

The determination of the correlation coefficient between the statistical and formative time delay of dc electrical breakdown in nitrogen is presented in this paper. Starting from a bivariate normal (Gaussian) distribution of two random variables, the analytical distribution of the electrical breakdown time delay is theoretically founded on correlation of the dependent statistical and formative time delay, contrary to convolution of independent variables. Within the limits, a Gaussian density distribution of the electrical breakdown time delay goes to a Gaussian of the formative time or to a Gaussian of the statistical time delay depending on electron yields (preionization level) in the interelectrode space, while the correlation coefficient is determined in the transition region from tf to ts dominated statistics.

Experiment for measurements of the gas breakdown statistics by ramp voltage pulses

In the first part of this article the electronic automatic system for the measurements of dynamic breakdown voltages Ub with linearly rising (ramp) pulses is presented. It generates the sequence of ramp pulses with subvoltage level Usub≈0 during the relaxation time τ of the tube, and the ramp pulses start from the static breakdown voltage Us, thus enabling the correct study of electrical breakdowns and relaxation in gases. In the second part the measurements in argon with and without a voltage during the off period of the pulse are analyzed. The influence of the subvoltage on the mean value of the breakdown voltage Ub¯ as a function of the rise rate k, on the statistical Ub distributions and on the afterglow kinetics is also discussed.

The Applicability of Fluid Model to Electrical Breakdown and Glow Discharge Modeling in Argon

The simple fluid model, an extended fluid model, and the fluid model with nonlocal ionization are applied for the calculations of static breakdown voltages, Paschen curves and current-voltage characteristics. The best agreement with the experimental data for the Paschen curve modeling is achieved by using the model with variable secondary electron yield. The modeling of current-voltage characteristics is performed for different inter-electrode distances and the results are compared with the experimental data. The fluid model with nonlocal ionization shows an excellent agreement for all inter-electrode distances, while the extended fluid model with variable electron transport coefficients agrees well with measurements at short inter-electrode distances when ionization by fast electrons can be neglected.

The validity of the one-dimensional fluid model of electrical breakdown in synthetic air at low pressure

In this letter the validity of the fluid model used to simulate the electrical breakdown in air at low pressure is discussed. The new method for the determination of the ionization source term for the mixed gases is proposed. Paschens curve obtained by the fluid model is compared to the available experimental data. The electron and ions density profiles calculated by the fluid model are presented. Based on Ohms law, the current and voltage waveforms are calculated and compared to the ones measured by the oscilloscope in the synthetic-air filled tube with stainless-steel electrodes. It is shown that the one-dimensional fluid model can be used for modeling the electrical breakdown at pd values higher than Paschens minimum and to determine stationary values of electron and ions densities.

Conversion of an atomic to a molecular argon ion and low pressure argon relaxation

The dominant process in relaxation of DC glow discharge between two plane parallel electrodes in argon at pressure 200 Pa is analyzed by measuring the breakdown time delay and by analytical and numerical models. By using the approximate analytical model it is found that the relaxation in a range from 20 to 60 ms in afterglow is dominated by ions, produced by atomic-to-molecular conversion of Ar+ ions in the first several milliseconds after the cessation of the discharge. This conversion is confirmed by the presence of double-Gaussian distribution for the formative time delay, as well as conversion maxima in a set of memory curves measured in different conditions. Finally, the numerical one-dimensional (1D) model for determining the number densities of dominant particles in stationary DC glow discharge and two-dimensional (2D) model for the relaxation are used to confirm the previous assumptions and to determine the corresponding collision and transport coefficients of dominant species and processes.

The glow discharge inception and post-discharge relaxation of charged and neutral active particles in synthetic air at low pressure

The study of dc glow discharge inception and post-discharge relaxation of charged and neutral active particles in synthetic air at low pressure is presented. The breakdown time delay dependence as a function of relaxation time (the memory curve) is measured and modelled from milliseconds to the saturation region determined by the cosmic rays and natural radioactivity level. Due to fast conversion , relaxation of dc discharge in synthetic air in the time interval from one to about ninety milliseconds is dominated by the diffusion decay of molecular oxygen ions. The change of regimes, from ambipolar to the free diffusion limit, is investigated and the variation of effective diffusion coefficients is determined. The late relaxation is explained by the kinetics of nitrogen atoms, recombining on the surfaces of gas discharge tube and stainless steel electrodes and relevant surface recombination coefficients are determined.