Y. Xian

An

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.

RC

Rather than using noble gas, room air is used as the working gas for an atmospheric pressure room-temperature plasma. The plasma is driven by submicrosecond pulsed directed current voltages. Several current spikes appear periodically for each voltage pulse. The first current spike has a peak value of more than 1.5 A with a pulse width of about 10 ns. Emission spectra show that besides excited OH, O, N2(C–B), and N2+(B–X) emission, excited NO, N2(B–A), H, and even N emission are also observed in the plasma, which indicates that the plasma may be more reactive than that generated by other plasma jet devices. Utilizing the room-temperature plasma, preliminary inactivation experiments show that Enterococcus faecalis can be killed with a treatment time of only several seconds.

Plasma Device for Sterilization of Root Canal of Teeth

The propagation behavior of cold atmospheric pressure plasma jets has recently attracted lots of attention. In this paper, a cold He plasma jet generated by a single plasma electrode jet device is studied. The spatial-temporal resolved optical emission spectroscopy measurements are presented. It is found that the emission intensity of the He 706.5 nm line of the plasma behaves similarly both inside the syringe and in the surrounding air (plasma plume). It decreases monotonously, which is different from the emission lines, such as N2 337.1 nm line, N2+ 391.4 nm line, and O 777.3 nm line. For the discharge inside the syringe, the emission intensity of the He 706.5 nm line decays more rapidly than that of the other three spectral lines mentioned above. The N2 337.1 nm line behaves a similar time evolution with the discharge current. For the N2+ 391.4 nm line and the atomic O 777.3 nm line, both of them decay slower than that of the He 706.5 nm and the N2 337.1 nm. When the plasma plume propagates further awa...

A simple atmospheric pressure room-temperature air plasma needle device for biomedical applications

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 mus 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.

Temporal and spatial resolved optical emission behaviors of a cold atmospheric pressure plasma jet

The fundamental of the generation and propagation of the atmospheric pressure nonequilibrium plasma jets has recently attracted significant interests. In this paper, investigations on the effects of the parameters of the pulsed dc voltages on the optical emission intensity of the plasma jet and the bullet propagation behavior are carried out based on the temporal-spatial resolved optical emission spectroscopy measurements and the high-speed photography. It is found that, with the increase in the applied voltage, the bullet propagates out from the nozzle earlier and accelerates to higher peak-velocities. The increase in the pulse frequency exerts no significant influences on the optical emission of the plasma jet and the bullet propagation velocity. But it can induce the bullet propagates out from the nozzle earlier. Besides, it is interesting to notice that, with the increase in the pulse width in the beginning, the bullet propagates out from the nozzle with longer delay time. However, when the pulse widt...

Effect of Nano- to Millisecond Pulse on Dielectric Barrier Discharges

To better understand the variation in the “plasma bullet” velocity, the dynamics of an atmospheric pressure plasma plume driven by positive and negative pulses are investigated in detail. It is found that, before the plasma exits the nozzle, the plasma propagates at a speed of about 30 km/s for both positive and negative pulses. As soon as the plasma exits the nozzle, the plasma propagation speed increases dramatically for both cases. The peak velocity for the case of the positive pulse is much higher than that of the negative pulse, it is approximately 150 km/s and 70 km/s, respectively. According to the optical emission spectra, the acceleration behavior of the plasma bullet when it exits the nozzle is due to the increase in the N2+ concentration.

Experimental investigations on the propagation of the plasma jet in the open air

Up to now, all studies on the dynamics behavior of non-equilibrium plasma plumes were focussed on noble gas plasma plumes. It was found out that they are electrically driven rather than gas flow dependent. Our study on the dynamics of a non-equilibrium N2 plasma plume reveals that the propagation velocity of the N2 plasma plume is several orders magnitude lower than those previously reported and further studies show that it is close to the gas flow velocity. The gas flow has a significant effect on the length of the plasma plume, and the results provide some fundamental knowledge about atmospheric pressure plasma jets.

On the velocity variation in atmospheric pressure plasma plumes driven by positive and negative pulses

Plasma plumes with exotically segmented channel structure and plasma bullet propagation are produced in atmospheric plasma jets. This is achieved by tailoring interruptions of a continuous DC power supply over the time scales of lifetimes of residual electrons produced by the preceding discharge phase. These phenomena are explained by studying the plasma dynamics using nanosecond-precision imaging. One of the plumes is produced using 2 – 10 μs interruptions in the 8 kV DC voltage and features a still bright channel from which a propagating bullet detaches. A shorter interruption of 900 ns produces a plume with the additional long conducting dark channel between the jet nozzle and the bright area. The bullet size, formation dynamics, and propagation speed and distance can be effectively controlled. This may lead to micrometer- and nanosecond-precision delivery of quantized plasma bits, warranted for next-generation health, materials, and device technologies.

Are all atmospheric pressure cold plasma jets electrically driven

Cold plasmas have recently received great attention. In this paper, optical and electrical diagnostics are carried out on a reliable and user-friendly plasma plume. A simple electrical model is used to simulate the electrical characteristics of the device. The plasma is represented by a resistor connected in parallel with a capacitor, an inductor, and another resistor, which are connected in series. The simulated current-voltage waveforms have very good agreement with experimental measurements. Besides, the emission spectra of the plasma are also studied. It shows that, when Ar is used as working gas, there is strong OH (hydroxyl radical) emission and the emission intensities of the N2 emission bands are more than three times higher than that of He. On the contrary, when He is used as working gas, the emission intensities of N2+ band are much stronger. Detail analyses on these observations are presented.

From short pulses to short breaks: exotic plasma bullets via residual electron control

Dynamics of atmospheric-pressure plasma plumes have recently attracted significant attentions. However, the nature of the ldquoplasma bulletrdquo 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 streamerlike 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.