Influence of Pulse Modulation on Atmospheric Pressure RF Plasma Jet Shape

In recent days, atmospheric pressure cold plasma jets are gaining attention due to their suitability for various biomedical and industrial applications. Usually, these plasma jets are formed in a regular conical shape and are generally influenced by the input parameters viz., excitation source characteristics, feed gas type, and flow rate, etc. In the present work, we demonstrate the excitation of a novel helical shape argon plasma jet using a pulse modulated 13.56 MHz RF power source at atmospheric pressure. This unconventional helical structure is observed for the first time and originates due to the pressure pulsation in the discharge region caused by on-off pulsing of the RF power at a 2 kHz modulation frequency. An appropriate selection of the modulation frequency, applied power, duty cycle, and gas flow rate provide control over the shape of the plasma jet i.e. from a conventional smooth conical shape to the unique helical one. This study will provide valuable insight into the fundamental physics of the origin of the helical shape of plasma which also has an impact in diverse fields which include lasers, communications, solar atmosphere, turbulent flows, biophysics, and other areas. The experimental scheme of helical plasma generation and its dependence on the input parameters will be presented.