Correlation between helium mole fraction and plasma bullet propagation in low temperature plasma jets

A helium flow dynamics simulation is performed along the propagation region of the plasma bullet to determine the minimum helium mole fraction value necessary to sustain its propagation. The plasma bullet launches from a plasma jet device called the 'plasma pencil' driven by unipolar square nanosecond high voltage pulses and propagates in the surrounding air. During its propagation, air molecules diffuse into the path/helium channel of the plasma bullet. It is found that if the ratio of air molecules to helium atoms exceeds a certain limit, the plasma bullet propagation is inhibited. In this study, the helium mole fraction limits are estimated for different operating conditions of the plasma pencil.