Physical and chemical properties of a magnetic-assisted DC superimposed nanosecond-pulsed streamer discharge plasma

In the present work, a magnetic-assisted DC superimposed nanosecond-pulsed streamer discharge (DC-NPSD) with a 0.4 T parallel magnetic field is developed that achieves good performance for ozone production and toluene degradation. The influence of the assisted parallel magnetic field on the electrical characteristics, streamer propagation behavior, reactive species generation and plasma chemical properties of the DC-NPSD are systematically investigated. The experimental results indicate that better impedance matching of a nanosecond pulsed power supply and a discharge reactor can be realized by superimposing DC voltage (U-DC), which facilitates reactive species production and toluene degradation. The discharge current, input energy and reactive species production can be further enhanced by the application of a parallel magnetic field under different pulse and DC voltage conditions. There are two distinct streamer phases in the DC-NPSD: a primary streamer (PS) with longer propagation distance and higher propagation velocity and a secondary streamer (SS) with shorter propagation distance and lower propagation velocity. The propagation velocities of both the PS and the SS increase with increasing U-DC. Only PS propagation velocity is accelerated by a parallel magnetic field; however, that of the SS remains almost constant with or without a magnetic field. Both ozone generation and toluene degradation performance are improved by a magnetic field, which is attributed to the lengthened electron motion path under the action of Lorentz force and the constraint effect on energetic electrons in the presence of a parallel magnetic field.