No abstract

Streamer-to-spark transition in a self-pulsing positive transient spark (TS) discharge was investigated at different repetition frequencies. The temporal evolution of the TS was recorded, showing the primary streamer and the secondary streamer phases. A streak camera-like images were obtained using spatio-temporal reconstruction of the discharge emission detected by a photomultiplier tube with light collection system placed on a micrometric translation stage. With increasing TS repetition frequency f (from ~1 to 6 kHz), the increase of the propagation velocity of both the primary and the secondary streamer was observed. Acceleration of the primary and secondary streamers, and shortening of streamer-to-spark transition time τ with increasing f was attributed to the memory effect composed of pre-heating and gas composition changes induced by the previous TS pulses. Fast propagation of the secondary streamer through the entire gap and fast gas heating could explain the short τ (~100 ns) at f above ~3 kHz.

This paper deals with an optical emission spectroscopy study of a diffuse coplanar surface barrier discharge (DCSBD) in air at atmospheric pressure. The main aim of this study was to verify the areal homogeneity of the generated plasma, which is important for many applications like treatment of nonwoven fabrics, glass, metals, polymers, foils, and so on. Optical emission spectra of DCSBD plasma in air were measured for three different frequencies (15, 30, and 50 kHz) of the applied voltage. Comparison of the calculated rotational and vibrational temperatures was carried out, and areal homogeneity of plasma was proved. Electrical parameters of discharge such as the plasma power using the area of the Lissajous figures and energy transfer efficiency to the discharge were also investigated. The effective thickness of plasma layer as a function of the input power was measured.

Nowadays hydrogel materials are being used in medical practice for wound dressing purposes. Hydrogel/textile composites can be formed to increase the mechanical strength and handling capability of hydrogel materials. Nonwoven textiles are optional for such applications, however, it is often necessary to improve their surface properties. Here plasma activation/grafting of polypropylene (PP) nonwoven fabric with an acrylate layer to improve its adhesive properties is reported. A diaphragm discharge was used for the plasma treatment of the PP fabric. The discharge was burnt in a solution of acrylic acid (AAc), which resulted in a single step process of plasma activation and plasma grafting of the fabric. Results of wettability testing and ATR-FTIR measurements showed the existence of a thin poly(acrylic acid) (PAAc) layer grafted on the fabric surface. Peel strength measurements showed a 4.7 fold increase in the peel strength when compared with untreated PP fabric.

We present an experimental study of negative corona pulses in short point-to-plane geometry measured with nanosecond time resolution in air and in air with admixture of terpene vapours at atmospheric pressure. The aim of this work is to explain observed differences in the discharge on trees and plants and standard negative corona burning on a metal cathode. To this goal we have compared the waveform of the first negative corona current pulses in pure air with those in air with admixture of terpene vapours. The observed difference has been explained by the growth of thin polymeric layer on the cathode surface, which changes the cathode surface properties and the discharge mechanism.PACS: 52.80.Hc