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The propagation behavior of atmospheric-pressure plasma plumes has recently attracted lots of attention. In this paper, five different methods are used to measure the propagation velocity of an atmospheric-pressure plasma plume. The first method, named the "current method," obtains the propagation velocity of the plasma plume by measuring the currents carried by the plasma plume at different positions. The second method, named the "voltage method," obtains the plume propagation velocity by measuring the plasma plume voltage potential at different positions along the plasma jet with a voltage divider. The third method, called the "charge method," which significantly interferes with the plume propagation, estimates the plume propagation velocity by measuring the charges deposited on the surface of a quartz tube. The fourth method, which is the noninterference method, obtains the plume propagation velocity by capturing the dynamics of the plasma plume with an intensified charge-coupled device camera. Finally, the fifth method estimates the plume propagation velocity based on the temporal optical-emission intensity measurement of the selected species by using a spectrometer. The advantage and disadvantage of each method are discussed. The experimental results show that plasma plume velocities obtained from the five methods have reasonable agreement with each other. They are all in the range of 104 m/s. [ABSTRACT FROM AUTHOR]

Dynamics of atmospheric-pressure plasma plumes have recently attracted significant attentions. However, the nature of the "plasma bullet" behavior is still not clearly understood. The plasma bullets have some feature of a cathode-directed streamer. However, there are several notable differences between the streamer-like plasma plumes and the cathode-directed streamers. One of the differences is the repeatability (reproducible in time and space) of the two types of the discharges. All reports on the plasma bullet behavior suggested that the plasma bullets are very repeatable. This feature is different with that of the cathode-directed streamers, which are typically unrepeatable due to the stochastic nature of their initiation. In this paper, a simple plasma jet device is used to study the plasma bullet behavior. It is found that, when the applied voltage is 8 kV or lower, the plasma bullets are not repeatable. On the other hand, when the applied voltage is 9 kV or higher, they are very repeatable. This characteristic is similar with that of the cathode-directed streamer discharge. [ABSTRACT FROM AUTHOR]

The application of cold plasma in sterilization of a root canal of a tooth has recently attracted great attention. In this paper, a reliable and user-friendly plasma-jet device, which can generate plasma inside the root canal, is reported. The plasma can be touched by bare hands and can be directed manually by a user to place it into root canal for disinfection without causing any painful sensation. When He/O2 (20%) is used as working gas, the rotational and vibrational temperatures of the plasma are about 300 K and 2700 K, respectively. The peak discharge current is about 10 mA. Preliminary inactivation experiment results show that it can efficiently kill Enterococcus faecalis, one of the main types of bacterium causing failure of root-canal treatment in several minutes. [ABSTRACT FROM AUTHOR]

It has recently been demonstrated that pulsed direct-current (dc) voltages show better performance in generating diffuse plasmas under various conditions. However, it still remains unclear whether the pulsewidth or the rising and falling times of the voltage pulse play the essential role in the improvement of the performance of the dielectric barrier discharges (DBDs). In this paper, we focus on the effect of pulsewidth. Pulsed dc voltages with pulsewidth varying from 0.2 μs to about 1 ms are used to drive the DBDs. High-speed photographs show that diffuse Ar plasmas can be generated by pulsed dc voltages with pulsewidths covering the entire investigated range. It is found that the pulsewidths of the applied voltages affect the discharge current durations significantly when the pulsewidth is shorter than 600 ns or the break between the two consecutive pulses is shorter than 600 ns. [ABSTRACT FROM AUTHOR]