Change of plasma propagation state due to force balance with collision

The main findings of this study are that the plasma propagation state changes with the force equilibrium relationship between the driving force due to the electromagnetic field and neutral gas flow. The plasma propagation transitions from a continuous state to a discontinuous state when plasma emission light intensity changes. The plasma emission light intensity changes suddenly as the applied voltage frequency varies. The frequency at which plasma emission light changes is inversely proportional to the dynamic pressure with the flow velocity of neutral gas. The plasma with strong light emission at high frequency propagates continuously, while that with weak light emission at low frequency propagates discontinuously. Because the plasma current with strong light emission is larger than that with weak light emission, the plasma charge quantity—the amount of plasma generated—increases. Consequently, when the plasma quantity is enough to exist continuously as a group, the plasma group propagates in space with time variations like a stationary wave. However, when the plasma quantity is inadequate to exist continuously, the plasma group propagates through the space discontinuously like a bullet state.