W. Gong

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

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.

Propagation of an atmospheric pressure plasma plume

The fundamentals on the propagation of the atmospheric pressure plasma jets are not yet well understood. Teschke et al (2005), Lu et al (2006, 2008), Sands et al (2008), Shi et al (2008), and Ye et al (2008) studied the dynamics of the various plasma jets generated by different devices and sustained by different driving voltages. They all found that the plasma plumes are not a continuous volume of plasma; rather the plumes are more like a bullet formed by a small and well-confined plasma volume that travels from the exit aperture and terminates somewhere in the surrounding air. The speed of the “plasma bullets” varies from ∼ 104 – 105 m/s, which is several orders of magnitude higher than the gas velocities. Further analysis shows that the C-APPJs are electrically driven, which is quite similar to positive streamer discharges. However, there are several significant differences between the bullet-like plasma plumes and the widely studied positive streamers (cathode-directed streamer). For a positive streamer, the streamer head is connected to the power electrode by a highly conducting channel, which acts as a metallic “needle” protruding from the power electrode: the field at the end of the streamer is greatly enhanced. Obviously, this is not the case for the “plasma bullet”, which looks like isolated from the power electrode. Nevertheless, more studies are needed to have a better understanding of the plasma bullet behavior.

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

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...

Effect of Nano- to Millisecond Pulse on Dielectric Barrier Discharges

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.

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

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...

Optical and electrical diagnostics of an atmospheric pressure room-temperature plasma plume

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.

Measurements of the Propagation Velocity of an Atmospheric-Pressure Plasma Plume by Various Methods

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.

Plasma bullets behavior in a tube covered by a conductor

In this work, for better applications of atmospheric pressure plasma jets, the physics of plasma streamers in a glass tube with a part of it covered by a conductor is investigated. To better understand the propagation mechanism of plasma bullets in capillary tubes passing through a curved or narrow passage for some biomedical or material applications, the propagation of plasma streamers in a tube covered by a floating conductor is investigated. For a plasma streamer propagating in a tube covered by a conductor, the plasma streamer is suppressed and becomes shorter, and a secondary streamer is generated in the tube at the downstream end of the conductor. The larger the area covered by the conductor, or the thinner the tube, the stronger the plasma streamer is inhibited. The electric potential of the conductor is measured to be as high as 6 kV. On the other hand, a higher voltage applied on the HV electrode, or a higher gas flow rate will make the secondary plasma streamer longer. It is found that the capac...

Effect of Pulse Rise time on Plasma Plume Propagation Velocity

Atmospheric pressure plasma jets driven by a pulsed dc power supply have several advantages over the traditional jets driven by an ac power supply. However, how the pulse rise time affects the characteristic of the plasma jets is not clearly known. In this paper, the simulation results of a plasma jet driven by pulsed dc voltages with different pulse rise time trise are presented. It shows that, the shorter the pulse rise time trise is, the faster the head of the plasma jet propagates.

Control of radial propagation and polarity in a plasma jet in surrounding Ar

In recent years, the use of shielding gas to prevent the diffusion of the ambient air, particularly oxygen and nitrogen species, into the effluent of the atmospheric pressure plasma jet, and thus control the nature of chemical species used in the plasma treatment has increased. In this paper, the radial propagation of a plasma jet in ambient Ar is examined to find the key determinants of the polarity of plasma jets. The dynamics of the discharge reveal that the radial diffusion discharge is a special phenomenon observed only at the falling edge of the pulses. The radial transport of electrons, which is driven by the radial component of the applied electric field at the falling edge of the pulse, is shown to play an important role in increasing the seed electron density in the surrounding Ar. This result suggests a method to provide seed electrons at atmospheric pressure with a negative discharge. The polarity of the plasma jet is found to be determined by the pulse width rather than the polarity of the ap...