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Non-stationary charging of a dust grain in decaying streamer-channel plasma

The process of a dust grain charging in non-stationary (decaying) air plasma in external electric fields typical of a streamer channel at atmospheric air pressure is investigated numerically using two-dimensional spherical coordinates. The characteristic timescale on which the grain acquires maximal electric charge is found to be determined by the rate of electron attachment. For zero external field, the process of charging in decaying air plasma is compared with the analogous process in nitrogen (non-attaching gas). For non-zero external electric fields in air plasma, the correlation between the charging time and the field dependence of the attachment rate is revealed. For high values of external electric fields, a streamer discharge starting from the dust grain is observed, analogous to Trichel pulses in a negative corona.