Electronegativity effects on plasma dynamics in He/O$_2$ RF microplasma jets at atmospheric pressure

Abstract: This work investigates the transitions between ohmic mode and Penning-Gamma mode in a capacitively coupled radio frequency micro atmospheric pressure plasma jets (CCRF $\mu$APPJ) operated in He/O$_2$ mixtures by comparing phase-resolved optical emission spectroscopy (PROES) measurements of helium excitation with numerical simulations. The simulations employ a hybrid model that treats electrons kinetically via PIC/MCC, while ions and neutrals are modeled fluid dynamically. These results reveal that increasing electronegativity causes inhomogeneities in the bulk electric field, consequently modulating electron impact excitation dynamics. A good agreement was found between experiments and simulations.