Effect of duty cycle on pulsed discharge atmospheric pressure plasma: discharge volume and remnant electron density

Properties of atmospheric pressure plasmas sustained by a 5 kHz pulse power are investigated by adjusting the duty cycle from 10% to 80%. As a result of the decrease of the duty cycle, the upward trends are observed in the electron density and excitation temperature, however, the downward trend appears in the gas temperature. The spatially averaged model is applied to simulate the temporal evolutions of the electron density and temperature, further validated by the time-resolved experimental measurements. Since the discharge volume in the open-air conditions increases at higher duty cycles, the time-averaged electron density within the pulse-on period consequently declines. For shorter duty cycles, fewer charges remain for the next discharge, and a higher initial peak of the electron temperature appears. As a result, the time-averaged electron temperature within the pulse-on period increases. Both the experimental and simulation results suggest that the discharge volume of the atmospheric pressure plasma in the open air has a strong effect on the time-averaged electron density during the pulse-on period whereas the remnant electron density determines the time-averaged electron temperature within the pulse-on period. This work reveals the effective mechanisms for controlling the electron temperature and electron density of atmospheric pressure plasmas in open air by using short pulse driven discharges. (paper)