Low-frequency current oscillations in a linear hot-cathode discharge

Low-frequency (ω ⪡ ω_pi) plasma oscillations in the transition regime between the high and the low current mode of a thermionic hot-cathode discharge are investigated experimentally. This type of current oscillation often shows chaotic dynamics. The current oscillations are related to nonlinear short wavelength potential structures which are identified as ion bunches formed by a fluctuating ionization front. These ion bunches are separated by ion holes and move at ion thermal speed rather than ion acoustic speed. By entering the negative space charge region of the cathode sheath, the ion bunches trigger electron current fluctuations that provide the required feedback mechanism for the observed wave train formation.     

Low-frequency oscillations in Hall thrusters

In this paper, we summarize the research development of low-frequency oscillations in the last few decades. The findings of physical mechanism, characteristics and stabilizing methods of low-frequency oscillations are discussed. It shows that it is unreasonable and incomplete to model an ionization region separately to analyze the physical mechanism of low-frequency oscillations. Electro-dynamics as well as the formation conditions of ionization distribution play an important role in characteristics and stabilizing of low-frequency oscillations. Understanding the physical mechanism and characteristics of low- frequency oscillations thoroughly and developing a feasible method stabilizing this instability are still important research subjects.     

Glow discharge in low-pressure excilamps

This paper presents a review of the principal publications devoted to the study of the spontaneous radiation sources operating in the uv region and discusses the properties of a low-pressure glow discharge in binary mixtures of inert gases with halides. It has been demonstrated that for variation of the excitation parameters over a wide range more than 10% emission efficiencies are realized for exciplex molecules and thatXeCl ^* andKrCl ^* molecules are formed in the main by the harpoon reaction. The current-voltage characteristics of glow discharges in cylindrical, coaxial, and planar excilamps and the parameters of the radiation ofXeCl ^*,KrCl ^*, andXeF ^* molecules generated on excitation of inert-gas-halide mixtures by normal and high-voltage glow discharges are presented. It is pointed out that low-pressure glow-discharge excilamps enable one to use simple power supplies. Institute of High Current Electronics. Siberian Branch of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 50–66, June, 1999.     

Generation of homogeneous plasma in a low-pressure glow discharge

The possibility of producing homogeneous plasma in a low-pressure discharge with the use of a hollow anode or hollow cathode is analyzed. It is shown that, in contrast to the high-pressure discharge, where uniform ionization is needed to produce homogeneous plasma, in the low-pressure discharge, nearly uniform radial distribution of the plasma parameters can be achieved under nonuniform ionization conditions by increasing the ionization probability at the system periphery and reducing it near the system axis. It is shown that the magnetic field can facilitate generation of the homogeneous plasma instead of interfering with it.     

Interaction of a low-pressure mercury discharge with the discharge tube wall

The darkening of soda-lime glass envelopes of low-pressure mercury discharge tubes has nothing to do with the formation of sodium amalgam on the inner surface of the tube. It is, however, connected with the diffusion of mercury ions into the glass of the tube. By applying a high negative voltage to part of the outer surface of a burning tube a sodium depleted region is created at the corresponding part of the inner surface. After removal of the high-voltage electrode and continued normal operation the rate of darkening of the sodium-depleted part of the tube is about 50 times larger than the rate observed for the normal parts of the same tube.     

The pulsed optogalvanic effect in a low-pressure mercury discharge

Experiments are described in which a low-pressure mercury discharge is irradiated with a 10 ns dye laser pulse tuned resonant to one of 6 ³P-7 ³S₁ transitions. The time behaviour of the induced optogalvanic effect is found to be dependent on the value of the ballast resistance in the discharge circuit. The qualitative explanation for this phenomenon is that the ratio of the relative change in the electron temperature and the relative change in electron density depends on the value of the ballast resistance.     

Low-frequency longitudinal oscillations in a plasma with a relativistic electron component

Ion-sound oscillations in a three-dimensional plasma with relativistic electron component are studied. It is established that in this case ion-sound oscillations can exist only at electron and ion temperatures much less than the rest mass of the ions. In particular, it is shown that for an electron-positron plasma at relativistic temperatures ion-sound is impossible. The problem of ion-sound excitation by a charged particle beam is considered. Corresponding increments in beam instability are calculated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 24–27, December, 1985.     

The positive column of a low-pressure discharge in a toroidal tube

The positive column of a low-pressure glow discharge in a toroid is investigated. The radial distribution of charged particles, the distribution of the electric fild and the course of the equipotentials are derived from theory. Assuming the curvature of the walls in the direction of the toroid axis to be negligible one can solve the problem as that of a positive column between concentric circular cylinders.Presented at the conference of the German Physical Society at Leipzig, April 1966.     

Kinetic modeling of positive ions in a low-pressure RF discharge

The evolution of the ion-velocity distribution function in a planar RF discharge is computed by numerically solving the Boltzmann equation in phase space. The electric field in this equation is computed with regard to the ion density, assuming Maxwellian electrons with a given uniform temperature. The collision term in the Boltzmann equation contains creation of ions by electron-impact ionization of the background gas and the effect of charge-exchange collisions. Examples are given of the behavior of discharges in argon at RF frequencies of 50 kHz, 300 kHz, and 15 MHz at a very low pressure and at a pressure of approximately 40 Pa. A good agreement is found with published experimental observations of the time-dependent behavior of the electric field profile in the RF sheath     

Self-consistent mechanism for sustaining ionization waves in a low-pressure discharge

The possibility of constructing a self-consistent model for the sustaining of ionization waves is demonstrated for a low-pressure discharge in an inert gas. The model is based on the combined solution of the kinetic equation of the electrons and the equation of motion of the ions in a spatially periodic field. The distribution function is constructed in an experimentally measured field and then used to calculate the spatial distributions of the plasma density and the ionization rate. The solution of the equation of motion of the ions makes it possible to reconstruct a field similar to the original one. One specific feature of the mechanism considered is the pronounced nonlocal character of the formation of the electron distribution function by the entire nonuniform potential profile of the ionization wave. Zh. Tekh. Fiz. 67, 24–30 (February 1997)     

A planar XeCl-exilamp pumped by a low-pressure glow discharge

The energy characteristics of an XeCl exciplex lamp with planar construction pumped by a low-pressure gas discharge are investigated experimentally. When a discharge gap of width 2 cm and a Xe-Cl₂ mixture were used, average radiation powers up to 20 mW were obtained in the wavelength interval 200–380 nm at efficiencies of ∼0.4%. In this case the total efficiency of radiation into an angle of 4π exceeded 4%. It is shown that increasing the working pressure and using low discharge currents can lead to “point” radiation sources. Zh. Tekh. Fiz. 67, 43–46 (December 1997)     

Low-frequency dielectric-barrier discharge in the Townsend mode

An analytic model is proposed of a dielectric-barrier discharge in the Townsend mode, in which the space charge is small compared to the charge accumulated on the dielectric surface. The discharge mode depends substantially on the ratio between the frequency of the external voltage and the ion drift time through the gap. A low-frequency case is investigated, in which the space charge can be ignored. The analytic expressions obtained agree well with experiments and numerical simulations. The physical mechanism for the onset of relaxation oscillations in the Townsend mode is revealed. The time behavior of a dielectric-barrier discharge is qualitatively described, and its basic scaling parameters are determined.     

Mixed-mode oscillations and chaos in a glow discharge

We present results from numerical simulations on mixed-mode oscillations and chaos excited in a glow discharge, where a model of one-dimensional fluid equations coupled with an external circuit is used. Long duration of high ion and electron densities and fast recharge of a capacitor after a breakdown contribute to the generation of mixed-mode oscillations. The chaotic behavior is characterized by a one-dimensional multibranched map.     

Radial inhomogenity of plasma parameters in a low-pressure inductive RF discharge

This work is devoted to systematic investigation into the radial dependence of the plasma parameters of a low-pressure inductive radio-frequency (RF) discharge on pressure within a wide range of 0.8–1 Torr. Experimental results that were obtained under the considered pressures make it possible to analyze the patterns of the changes in plasma parameters upon both a nonlocal mode of discharge and a transition from a nonlocal to local mode of the RF power input. Discharges in helium, neon, argon, and krypton were considered. Experimental data were compared to the results of the numerical simulation of the inductive RF discharge using the particle-in-cell (PIC) method.     

Characteristics of surface glow discharge in a low-pressure supersonic gas flow

Kinetic particle-in-cell simulations are performed to examine the characteristics of the surface glow discharge in a supersonic nitrogen flow. The gas pressure is varied between 100 and 500 mTorr; the applied voltage, between −500 and −1000 V. The analysis focuses on the effect of boundary conditions at the dielectric barrier surrounding the electrodes on the electron energy distribution function. The potential on the dielectric is found by using a local balance condition for the electron and ion currents to the surface. The results of self-consistent simulations show that a negative potential on the dielectric substantially reduces the rate of high-energy electron loss from the bulk plasma and thus significantly changes the ionization rate, as well as plasma parameters and configuration.     

Characteristics of the discharge of a charged dielectric in low-pressure air

A charged dielectric generates a series of discharges in the surrounding air when the pressure is steadily reduced from near atmospheric to fractions of a torr. The dielectrics here employed were Mylar and Teflon. With positive polarity different discharge regimes were observed as the pressure varied: spark and long streamers at relatively high pressure; diffuse cloud-like discharges below 266 Pa (2 torr). With negative polarity it is difficult to induce a discharge, due to the absence of an electron-emitting surface. Similarities between our results and some of the features of mesospheric and stratospheric discharges are discussed.