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.
The paper presents an analysis of electrical characteristics of streamer-to-spark transition discharge in air at atmospheric pressure named transient spark (TS). The TS is applicable for flue gas cleaning or bio-decontamination and has potential in plasma shielding, combustion and flow control applications. Despite the dc applied voltage, TS has a pulsed character with short (∼10-100 ns) high current (>1 A) pulses, with repetitive frequencies 1-20 kHz. Estimation of the temporal evolution of electron density shows that n e ≈ 10 16 cm −3 at maximum and ∼10 11 cm −3 on average are reached using relatively low power delivered to the plasma (0.2-3 W). Thanks to the high repetition frequency, n e between two current pulses does not fall below a critical value and therefore plasma exists during the whole time. A detailed analysis of the TS control by electrical circuit parameters is presented. With appropriate circuit components, the current pulse tail (>1 mA) can be extended and the electron density can be held above ∼10 13 cm −3 for several tens of µs.
Generation of microdischarges inside porous ceramics by AC high voltage was explored. The physical properties of the microdischarges were investigated by electrical measurements, photographic visualization, and optical emission spectroscopy. The effects of pore size, discharge power, and gas mixture composition on the discharge properties and its development are described. The optimum generation and distribution of the microdischarges was observed with pore sizes of 50 and 80 µm. The emission spectra of the microdischarges indicated their strongly non‐equilibrium character. A theoretical analysis of the microdischarge mechanism is provided, accounting for the pore size and the elementary processes such as ionization, recombination, and ambipolar diffusion.
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