Time-resolved characterization of a free plasma jet formed off the surface of a piezoelectric crystal

When a piezoelectric transformer (PT) is actuated by a low input voltage (∼10 V), electromechanical coupling leads to a very high (∼10³ V) surface potential at the distal end that can ionize the surrounding gas and lead to a plasma jet emanating from the surface. PTs are attractive for non-equilibrium plasma generation because of their simple operation, low required input voltage, and low power consumption. In this work, the time-resolved characteristics of the free surface plasma jet generated by a PT operating in open air have been investigated. The temporal evolution of the PT-driven plasma was visualized by using an intensified CCD camera and plasma formation was correlated with the current behavior of the plasma jet. Notably, the plasma formation is a discrete process, appearing at a relatively fixed phase of the sinusoidal input, and the strongest plasma jet appears at the end of the positive half-cycle. Simultaneous measurements of the current show that the discharge current response is consistent with the chaotic mode for a plasma jet and appears statistically about a 1 μs earlier than plasma jet light emission, which indicates that there is a strong afterglow. With a low input voltage required for operation, these types of PT-driven plasma jets could have wide utility in emerging plasma applications beyond the laboratory, such as in healthcare and water treatment. (paper)