Magnetic field enhanced discharge and water activation of atmospheric pressure plasma jet: effect of assistance region and underlying physico-chemical mechanism

Magnetic field-assistance holds the promise of becoming a new or complementary approach to enhance the efficiency of atmospheric pressure plasma jet (APPJ), but there is currently a lack of research on the effect of the assistance region between magnetic field and plasma on application of APPJ. Herein, using a 130 mT perpendicular magnetic field to assist APPJ in treating deionized water to prepare plasma activated water (PAW) as a model, we studied the effect of magnetic field-assisted region on the performance of PAW produced by APPJ, and found that introducing a magnetic field could always enhance the performance of the prepared PAW with higher concentrations of H₂O₂, NO₃^-, and NO₂^- and lower concentrations of O₃ and lower pH values, but this enhancement effect was related to the magnetic field-assisted region relative to the APPJ, where the optimized PAW performance was achieved when the magnetic field did not act on the jet tube wall (only assisting plasma plume). To reveal the underlying physico-chemical mechanism behind the differences in the enhanced performance of PAW under different magnetic field-assisted regions, a plasma reaction network involving physical parameters and chemical products was considered. The results showed that the magnetic field-assisted region modulated the equilibrium between the confinement effect and the recombination loss of magnetized electrons, and subsequently altered the reactive species in PAW via plasma reaction network mediated by electron density n_e and electron excitation temperature T_exc which without remarkable changing the discharge intensity, discharge power, plasma plume, and gas temperature T_gas. These insights contribute to understanding the mechanism of magnetic field-assisted region effect on APPJ which provide guidance for optimizing discharge activity and promote the development of applications.