Results 1 - 10 of 1028
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[en] We present a study of the streamer-to-spark transition in a self-pulsing dc-driven discharge called a transient spark (TS). The TS is a streamer-to-spark transition discharge with short spark duration (∼10–100 ns), based on charging and discharging of the internal capacity of the electric circuit with repetition frequency 1–10 kHz. The TS can be maintained under relatively low energy conditions (0.1–1 mJ pulse−1). It generates a very reactive non-equilibrium air plasma applicable for flue gas cleaning or bio-decontamination. Thanks to the short spark current pulse duration, the steady-state gas temperature, measured at the beginning of the streamers initiating the TS, increases from an initial value of ∼300 K only up to ∼550 K at 10 kHz. The streamer-to-spark transition is governed by the subsequent increase in the gas temperature in the plasma channel up to ∼1000 K. This breakdown temperature does not change with increasing repetition frequency f. The heating after the streamer accelerates with increasing f, leading to a decrease in the average streamer-to-spark transition time from a few µs to less than 100 ns. (paper)
[en] A method is described for the characterization and counting of discharges in MSGCs. It is shown that the technique is sensitive enough to detect the micro-discharges which occur prior to full sparking, with a detection efficiency of 0.8. Some example results are presented, showing the variation of micro-discharge rate with gain. (orig.)
[en] A positive leader in air at gap lengths of up to 8 m was studied experimentally on an open experimental stand. The voltage source was a 6-MV pulsed voltage generator or an artificial charged aerosol cloud. The dependence of the leader velocity on the current in the range 0.2-8 A was determined by simultaneously recording the optical picture and electric parameters of the discharge. Particular attention was paid to the final-jump phase of the discharge, when the gap was completely bridged by the streamer zone of the leader. It is shown that the character of the dependence of the leader velocity on the current in this phase remains unchanged; hence, the final-jump phase can be used in experiments in which the current has to be varied within a wide range. For this purpose, one can use a damping resistance, which is inefficient in the initial phase. The parameters of the power-law dependence of the leader velocity on the current at currents of a few amperes are established reliably. It is found that the power-law dependence with constant parameters is inapplicable to calculate the leader velocity at currents of about 0.1 A, which correspond to the lower limit of the leader viability.
[en] The glow-to-spark transition in a pin-to-water anode electrode system is investigated and compared with a pin-to-metal-plate system with 20 ns time resolution by fast imaging and corresponding current and voltage measurements. A contraction of the anode spot and cathode spot of the glow is observed in the pin-metal-plate system leading to a narrow filamentary spark, while the anode spot on the water anode electrode remains diffuse. In the latter case only a significant radial constriction of the glow in the bulk and near the metal cathode of the discharge gap is observed which causes a broadening of the spark near the water anode. Constriction of this broadened spark channel occurs several 100 ns after spark ignition. Additionally, the influence of the conductivity of the liquid electrode on the glow-to-spark transition is investigated.
[en] The new ion source that has three spark electrodes, was described. It can give Iα of 100∼300A at Us=10∼15kV and Uα=1∼2kV. Several spark electrodes that circularly operate, were arranged along the surface of a cylindrical ceramic insulator, resulting in significant increase of the life-time of this source. The new neutron tube that has been proofed to 200 kV, was developed and a pulsed yield of the tube was 1.2x107 neutrons. (author)
[en] Recently measurement methods are becoming available to study the corona discharge in more detail. One of the most promising methods is laser-induced fluorescence to determine radical density. Recent improvements in CCD cameras makes it now possible to improve measurements of the discharge structure to a resolution of 1 ns in time and 10 μm in space. This paper shows the first results of the spontaneous emission of a point-to-plane corona discharge in air using such a camera. It clearly indicates that the 2-D approach for streamer propagation under these conditions is insufficient
[en] A numerical model of a spark discharge propagating along the ground surface from the point at which an ∼100-kA current pulse is input into the ground has been developed based on experiments in which the velocity of a long leader was measured as a function of the leader current. The results of numerical simulations are in good agreement with the measured characteristics of creeping discharges excited in field experiments by using a high-power explosive magnetic generator. The reason why the length of a spark discharge depends weakly on the number of simultaneously developing channels is found. Analysis of the influence of the temporal characteristics of the current pulse on the parameters of the creeping spark discharge shows that actual lighting may exhibit similar behavior.
[en] The expansion of a spark produced plasma was studied with a simple model and compared to experiments. The model and experiments were performed using a 11.2 nF capacitor bank charged up to 10kV corresponding to a total energy of 0.6 J. The nanosecond shadow pictures revealed detail structure of the shock waves, giving trajectory, speed and blast wave pressure ratios. Conversions of energy into motion and light wave were estimated