Results 1 - 10 of 158
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[en] The kinetics of Townsend discharge is studied following the electronic processes of ionization in the gap and on the cathode surfaces. The main aim of this paper is to calculate the probability of the breakdown, assuming the appearence of lone electron near the cathode surface as a function of the electron multiplication factor of electron avalanche. The resulting formula describes well the phenomenon, but its parameters, the adequate values of elementary probabilities are to be calculated in an independent way. (D.Gy.)
[en] The effect of the grounded electrode diameter on the ignition voltage using 13.56 MHz in argon gas is studied experimentally. The results indicate a systematic decrease of the breakdown voltage with increasing electrode area for the same pd value. No multi-valued breakdown voltages are observed. The Paschen minimum is not affected by the electrode diameter as long as the parallel plane approximation is valid. A modified Paschen equation which takes into account indirect discharge via the chamber walls at high pd values gives reasonable fits to the experimental data
[en] We discuss the effect of electrode shape on Paschen curves and our ability to seal off microdischarges to prevent long path breakdown. It was found that for structured electrodes at high pressures and small gaps, the left-hand side of the Paschen curve is relatively flat, extending the minimum to lower pd values. At high pd values the curves are almost identical to those at standard pressures/gaps and the discharge runs between the top plane of the cathode and the anode. For intermediate pd values the higher electric field at the edge attracts most of the current and the discharge extends along the side wall maintaining the same low breakdown voltage. When the length of the discharge reaches the longest path the voltage starts a rapid increase. We have selected the dimension of the segmented electrode so as to have the same losses to the walls that block or allow the long path breakdown, thus being able to represent situations when the Paschen curve may be properly determined. In general, however, this shows that recording of the left-hand side for open structures (without enclosure by a dielectric) is impossible and conclusions about secondary emission should be focused on the well-defined conditions. (special)
[en] This paper contains measured breakdown voltage curves and calculated transport parameters for the dry air and gases included in the air composition. The breakdown voltage curves exhibit U-shaped form for the interelectrode separation of 100 μm and departure from the standard Paschen law for a few micrometers gap sizes. The results of calculations provide an insight into similarities and differences between the transport parameters for individual gases and the gas mixture.
[en] In this paper investigations of the voltage required to break down water vapor are reported for the region around the Paschen minimum and to the left of it. In spite of numerous applications of discharges in biomedicine, and recent studies of discharges in water and vapor bubbles and discharges with liquid water electrodes, studies of the basic parameters of breakdown are lacking. Paschen curves have been measured by recording voltages and currents in the low-current Townsend regime and extrapolating them to zero current. The minimum electrical breakdown voltage for water vapor was found to be 480 V at a pressure times electrode distance (pd) value of around 0.6 Torr cm (∼0.8 Pa m). The present measurements are also interpreted using (and add additional insight into) the developing understanding of relevant atomic and particularly surface processes associated with electrical breakdown.
[en] In this paper, we present data from experimental studies of the DC breakdown in ethanol vapour at low pressure as well as electrical and optical measurements of DC discharge parameters from low-current to high-current regimes. A Paschen curve and the corresponding distribution of emission intensities at low-current were recorded in the range of pd (pressure x electrode gap) from 0.10 Torr cm to 3.00 Torr cm, covering the region of Paschen minimum. Recorded axial profiles of emitted light from low-current discharge reveal that heavy particles make up a significant part in ethanol vapour breakdown in a wide range of values of pd i.e. E/N, for values E/N > 3 kTd they become dominant. Also, we recorded volt–ampere characteristics at working conditions close to the minimum of the Paschen curve, together with spatial profiles of low-current discharge. In the region of transition from normal to abnormal glow, sudden changes of the regime of operation were observed. (paper)
[en] The gas breakdown was experimentally investigated in dc electrical field in long discharge tubes. The measurements were performed in the tube of radius R=4 mm, whereas the inter-electrode gap values varied in the range L=2-230 mm. The conventional Paschen law was shown to hold in short discharge tubes for which L/R≤1. At L/R>1 the breakdown curves Udc(p) are shifted not only to lower pressure p values but also to higher dc voltage Udc values with the gap value increasing, i.e., one must employ the modified law of gas breakdown Udc(pL,L/R). However in long tubes the breakdown curve pattern experiences qualitative changes. At L/R>20 increasing L makes the dc breakdown curves to shift to higher Udc values, their minima being observed almost at the same gas pressure value. That is, for small gaps with increasing distance between the electrodes, the breakdown curves shift to the left on the scale of the gas pressure at a constant voltage at the minimum, and for long tubes with increasing distance between the electrodes, the breakdown curves shift upward on the scale of the voltage with the same gas pressure at the minimum. Theoretical treatment reveals that for gas breakdown in a long tube the rates of ionization via electron impact and diffusion loss to the tube wall must be equal. - Highlights: → The dc gas breakdown at different inter-electrode gap values in long discharge tubes. → The conventional Paschen law is valid only for short discharge tubes. → In long tubes breakdown curves shift to higher voltages at unchanged gas pressure. → For breakdown in long tubes the rates of ionization and diffusion loss must be equal.
[en] Coplanar discharges (CDs) appear in arrangements where pair(s) of electrodes are embedded in a solid dielectric. The ignition voltage of CDs is much higher than that in common dielectric barrier discharge arrangements with a gas gap comparable with the electrode distance of CD arrangements. From calculations of the initial field strength distributions the ignition voltage can be found for different electrode distances. In order to analyze the discharge structure an intensified CCD camera has been used. From highly resolved photographs follows that CDs consists of more or less parallel discharge channels on the surface similar to those in common arrangements with gas gaps. (author)
[en] This paper demonstrates that the similarity law for the rf gas breakdown has the form Urf = ψ(p.L, L/ R, f.L)( where Urf is the rf breakdown voltage, p is the gas pressure, L and R are the length and diameter of the discharge tube, respectively, f is the frequency of the rf electric field). It means that two rf breakdown curves registered for narrow inter-electrode gaps or in geometrically similar tubes and depicted in the Urf(p.L) graph will coincide only when the condition f.L = const is met. This similarity law follows from the rf gas breakdown equation and it is well supported by the results of measurements. (authors)
[en] A global model which includes the time-dependent evolution of spatially averaged plasma parameters is used for studying several different types of low-temperature plasma discharges such as the pseudospark discharge and the inductively coupled plasma discharges. The pulse effect of the applied power source to plasma including secondary electron emission and recombination is extensively investigated. These characteristics are compared (whenever possible) with those from particle-in-cell simulations with Monte-Carlo collisions which are also used for examining in detail the Paschen breakdown and self-oscillation (with period doubling) properties of a capacitively coupled discharge