Primary and secondary discharges in an atmospheric pressure plasma jet fed with helium and tetrafluoromethane mixtures

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The primary and secondary discharge phenomenon in an atmospheric pressure plasma jet fed with helium and tetrafluoromethane (CF4) mixtures is reported in this letter. The two discharges are observed one after the other in discharge current waveforms and nanosecond images. The influence of the gap distance, applied voltage, and CF4 volume fraction on this phenomenon is studied. According to the results, the formation reason and mechanism of the phenomenon are discussed. The primary discharge is quenched by CF4 molecules which have strong electron affinities. The residual species remain in the primary discharge channel, which promote the occurrence of the secondary discharge. In conclusion, the primary and secondary discharges are involved with the processes of discharge quenching and re-ignition.