Radial and axial electric field measurements in self-triggered multiperiodic AC plasma jets

Abstract

AC-driven atmospheric pressure plasma jets can produce both positive and negative ionization fronts (IFs). Non perturbative electric field (E-field) probe measurements based on Pockels effect have been used to capture the dynamic of IFs. Under specific conditions of applied voltage and frequency, and in the presence of a grounded ring electrode, IFs self-trigger in less than 100 ns jitter, every N voltage periods, defining the so-called multi-periodic (MP) regime. The grounded electrode additionally extends multiperiodic plasma bullet length by up to a factor of two in the 2P mode, and the inter-electrode gap is shown to host multiple short intragap discharges preceding the emission of long bullets every two periods. E-field probe measurements have been used to determine the polarity of inter-electrode discharges and plasma bullets, revealing that positive and negative bullets deposit distinct surface charge densities inside the capillary. A newly identified 1.5P mode is characterized alongside the 2P mode: it produces short-range secondary bullets every period while generating long-range major bullets of opposite polarity every two periods. Mode stability mapping as a function of gas impurity levels demonstrates that increasing nitrogen and oxygen concentrations suppress higher-order MP modes while broadening the stability domain of the 1.5P regime.