Pulsed Regime of the Diffusive Mode of a Barrier Discharge in Helium

Periodic pulsations of the active current component are revealed experimentally in transversely homogeneous barrier discharges in helium at small values of the parameter Pd (below 500 torr mm) and moderate frequencies of the applied voltage (f < 100 kHz). The frequency of the current pulsations is higher than the frequency of the well-studied pulsations in a transversely inhomogeneous streamer barrier discharge in air by a factor of approximately 100. Numerical calculations show that the physical nature of the observed pulsations can be explained in terms of the negative differential resistance of the cathode fall region, which occupies essentially the entire interelectrode gap in each half-period of the applied voltage.     

Comparison of the AC barrier corona with DC positive and negative coronas and barrier discharge

Results are presented from experimental studies of ac corona discharges between a point electrode and a dielectric-coated plate in nitrogen, argon, helium, and air in the voltage frequency range f=50 Hz–50 kHz. The characteristic features of this type of discharge are compared with the well-known features of dc positive and negative coronas and a barrier discharge between plane electrodes. It is shown that the presence of a dielectric barrier on the plane electrode significantly changes the electric characteristics and spatial structure of the corona, whereas the main phases of the discharge evolution remain unchanged as the voltage increases. With a point electrode, the breakdown voltage of the barrier corona decreases substantially as compared to the breakdown voltage of a barrier discharge with plane electrodes. This leads to softer conditions for the streamer formation in a barrier corona, which becomes more stable against spark generation.     

Specificity of probe measurements in diffuse plasmas of dense gases in strong electric fields

The article is devoted to extending the applicability of the probe diagnostics to the range of higher pressures of the plasma-forming gas by taking into account the effect of the probe shadow on the anode. The probe current–voltage characteristic in the diffuse plasma of a dense gas in a strong electric field was measured, and the influence of the probe potential and probe current on the dimensions of the probe shadow on the anode was studied experimentally. The experiments were carried at different currents of a steady-state glow discharge and different velocities of the gas flow through the discharge. The plasma-forming gas was nitrogen at a pressure of P = 100 Torr.     

Various properties of immobilized terminal deoxynucleotidyl transferase from the cattle thymus

The effects of temperature, pH, and concentration of sodium cacodylate buffer on the activity of partially purified terminal deoxynucleotidyl transferase from cattle thymus immobilized on BrCN-Sepharose were studied. The enzyme retained at least 60% of the initial activity after 6 h of incubation at 30 degrees in 50 mM potassium phosphate buffer, pH 7.2 in the absence of substrate. Short-term activation of the enzyme during incubation was noticed. The maximum activity of the immobilized preparations was observed in 240-280 mM sodium cacodylate buffer in the reaction mixture, pH 7.5-7.9 at 37-40 degrees.     

Decomposition of toluene in a steady-state atmospheric-pressure glow discharge

Results are presented from experimental studies of decomposition of toluene (C₆H₅CH₃) in a polluted air flow by means of a steady-state atmospheric pressure glow discharge at different water vapor contents in the working gas. The experimental results on the degree of C₆H₅CH₃ removal are compared with the results of computer simulations conducted in the framework of the developed kinetic model of plasma chemical decomposition of toluene in the N₂: O₂: H₂O gas mixture. A substantial influence of the gas flow humidity on toluene decomposition in the atmospheric pressure glow discharge is demonstrated. The main mechanisms of the influence of humidity on C₆H₅CH₃ decomposition are determined. The existence of two stages in the process of toluene removal, which differ in their duration and the intensity of plasma chemical decomposition of C₆H₅CH₃ is established. Based on the results of computer simulations, the composition of the products of plasma chemical reactions at the output of the reactor is analyzed as a function of the specific energy deposition and gas flow humidity. The existence of a catalytic cycle in which hydroxyl radical OH acts a catalyst and which substantially accelerates the recombination of oxygen atoms and suppression of ozone generation when the plasma-forming gas contains water vapor is established.     

The Memory Effect of Microdischarges in the Barrier Discharge in Airflow

Plasma Physics Reports - The paper devoted to the research of the microdischarge dynamics in the dielectric barrier discharge. The discharge between rail electrodes in airflow along the electrodes...     

Pink splash of active nitrogen in the discharge afterglow

Results are presented from experimental studies of the glow dynamics of active nitrogen in the stage of its excitation by a current pulse and during the discharge afterglow. The mechanism is proposed for the generation of a light splash in a highly activated nitrogen after the end of its pulsed excitation. The key role in the generation of this splash is played by the D-V processes, by which the dissociation energy is transferred to the vibrational degrees of freedom in the course of recombination of nitrogen atoms, and the V-E processes, by which the vibrational energy of highly excited molecules N₂(X, v ≥ 25–27) is transferred to the emitting electronic states N₂(B, v) after the V-V delay. Results of simulations based on the mechanism proposed are also presented.     

Pulsed mode of a negative corona in nitrogen: II. Numerical calculations

A simplified model of a cathode sheath sustained by electron avalanches is presented. The model is used to calculate the pulsed mode of a negative corona in nitrogen in order to establish the physical picture of the processes occurring in a pulsed corona. The most important point is that, in the pulsed mode, both the averaged and dynamic current-voltage characteristics of a glow cathode sheath are found to have a negative slope. Lowering the degree to which the glow cathode sheath is subnormal (by sharply reducing the sheath area) or switching on additional ionization mechanisms (e.g., stepwise ionization) that force the cathode sheath to evolve into a prearc spot causes the negative slopes of the averaged and dynamic current-voltage characteristics of the sheath to become more gradual and even positive, thereby stabilizing the discharge current.     

Ultrahigh charging of dust grains by the beam−plasma method for creating a compact neutron source

Generation of high-voltage high-current electron beams in a low-pressure (P = 0.1–1 Torr) gas discharge is studied experimentally as a function of the discharge voltage and the sort and pressure of the plasma-forming gas. The density of the plasma formed by a high-current electron beam is measured. Experiments on ultrahigh charging of targets exposed to a pulsed electron beam with an energy of up to 25 keV, an electron current density of higher than 1 A/cm², a pulse duration of up to 1 μs, and a repetition rate of up to 1 kHz are described. A numerical model of ultrahigh charging of dust grains exposed to a high-energy electron beam is developed. The formation of high-energy positive ions in the field of negatively charged plane and spherical targets is calculated. The calculations performed for a pulse-periodic mode demonstrate the possibility of achieving neutron yields of higher than 10⁶ s^–1 cm^–2 in the case of a plane target and about 10⁹ s^–1 in the case of 10³ spherical targets, each with a radius of 250 μm.     

Effect of cold plasma on the E. coli cell wall and plasma membrane

The effect of cold plasma on E. coli cells was studied. It was shown that the treatment of E. coli cells with cold plasma caused partial or total disruption of the plasma membrane integrity, which was accompanied by a release of intracellular substances into the extracellular environment. A quantitative assessment of the extent of the damage to the cell membrane showed that a loss of no more than 23.6% of intracellular substances (calculated by the proportion of the intracellular nucleotide release) is sufficient to lead to cell death. The use of media with different ionic strength levels to create osmotic shock showed that the treatment of E. coli cells with cold plasma significantly decreased the cell wall strength.