Lifang Dong

Hexagon and square patterned air discharges

Hexagon and square patterned air discharges are realized by using a dielectric barrier discharge device with two water electrodes. With increasing voltage, the filaments (plasma columns) tend to be dense and regularly arranged, and the current in each half cycle changes from several peaks to one leading peak followed by a broad hump of current peaks. It shows that the spatiotemporal correlation between filaments is enhanced with increasing voltage. A phase diagram of hexagon patterned air discharge with different gas gap widths as a function of air pressure and applied voltage is presented.

Square pattern formation in a gas discharge system

The square pattern is observed in dielectric barrier discharge in argon for the first time. The hexagon pattern and the mixture of hexagon and square structure are also observed. The square pattern can remain stable for several tens of minutes. The spatio-temporal dynamics of square pattern formation is investigated by optical method. The measurement results show that the square pattern is an interleaving of two square patterns, which is the reason of the stability of square pattern.

Characteristics of an atmospheric pressure argon glow discharge in a coaxial electrode geometry

An atmospheric glow discharge controlled by a dielectric barrier is realized in a coaxial electrode geometry in argon. The discharge characteristics are studied by the electrical method and optical emission spectroscopy. The experimental results indicate that there is only one discharge pulse per half cycle when the applied voltage is very low, and the rise time of the discharge pulses at the positive half cycle is much shorter than that at the negative one. With an increase in applied voltage, the width of the discharge pulse increases, while the inception voltage at which breakdown occurs decreases. The rise time at positive half cycle almost equals that at negative half cycle when the applied voltage is high enough. The research results pertaining to gas gap voltage indicate that the critical electric field for breakdown decreases with increasing applied voltage. The electron temperature is estimated from the Einstein relation, and the result indicates that the electron temperature and the electron density are functions of the applied voltage and the gas flow rate. The electron temperature is also studied by emission spectroscopy and a similar result is obtained.

A simple device of generating glow discharge plasma in atmospheric pressure argon

Atmospheric pressure glow discharge is realized in argon by using a plasma needle. With increasing the applied voltage, uniform plasma increases in scale from a small region near the needle tip to a plasma plume with a length of about 20mm. The discharge mechanism is discussed based on the light emission waveforms from the plasma. Optical emission spectroscopy is used to determine excited electron temperature and vibrational temperature, and the results indicate that the excited electron temperature and the molecular vibrational temperature are about 6000 and 2300K, respectively.

Spatio-temporal patterns in dielectric barrier discharge in air/argon at atmospheric pressure

A rich variety of patterns including travelling hexagon, travelling square, quasi-crystal, static hexagon and stripe have been studied in a dielectric barrier discharge system. The phase diagram of pattern types as a function of air concentration and the applied voltage is given. The spatio-temporal correlations between discharge filaments in these patterns are measured in a nanosecond time scale by an optical method. It is found that the travelling pattern is an interleaving of two sub-patterns with a temporal sequence inversion in consecutive half-cycles.

A simple dielectric barrier discharge device for generating slot homogeneous plasma in atmospheric pressure air

We report a simple dielectric barrier discharge device for generating slot homogeneous plasma in atmospheric pressure air. It consists of two parallel water electrodes with a distance adjusting micrometer. With increasing the applied voltage, the discharge becomes homogeneous. The electron temperature, vibrational temperature (TV) of N2, and rotational temperature (TR) of N2+ are estimated by optical emission spectroscopy. Both TV and TR remain unchanged along the slot in the homogeneous discharge regime. The trend of the TV with respect to the applied voltage is opposite from that of TR, while the electron temperature keeps constant with the increasing applied voltage.

Hexagon and stripe patterns in dielectric barrier streamer discharge

We present a specially designed dielectric barrier discharge (DBD) system for the study of pattern formation. Hexagon and stripe patterns have been observed in a streamer discharge in a DBD for the first time. The phase diagram of pattern types as a function of applied voltage is given.

Electron density of an individual microdischarge channel in patterns in a dielectric barrier discharge at atmospheric pressure

The electron density of an individual microdischarge channel in different stable patterns including a square and a hexagon pattern in a dielectric barrier discharge in argon at atmospheric pressure is investigated using a spectral line profile method. The procedure for deconvolution of the asymmetric convolution integral is used to obtain the Stark broadening and shift of Ar I 696.54 nm for the calculation of electron density. The broadening parameters such as electron impact width ωe and ion impact width α can also be obtained from the procedure. By comparing ωe with the theoretical values at different electron temperatures given by Griem, the electron temperature can be reasonably estimated. It is found that the electron density in an individual microdischarge channel increases with increasing voltage.

Dissociation process of CH4/H2 gas mixture during EACVD

The dissociation process of CH4/H2 gas mixture during EACVD has been investigated using Monte Carlo simulation for the first time. The electron velocity distribution and H2 dissociation were obtained over a wide range: 100<E/N<2000 Td. The variation of CH4 dissociation with CH4 concentration in the filling gas has been simulated. The electron velocity profile is asymmetric for the component parallel to the field. Most electrons possess non-zero velocity parallel to the substrate. The number of atomic H is a function of E/N. There are two peaks at E/N=177 Td and 460 Td. The appropriate E/N is suggested to be 500–800 Td for low temperature deposition. The main diamond growth precursor is proposed to be CH3 and CH3+.

The spectra of conical bubble sonoluminescence in 1,2-propanediol and glycol

A conical bubble straight tube apparatus was set up to study sonoluminescence. The spectra of conical bubble sonoluminescence for 1,2- propanediol and glycol were detected. The results show that the luminescence is intense, and the spectra consist of a broad background on which five clear sequences of Swan bands and three sequences of the B-2 Sigma(+) -> X-2 Sigma(+) transition of CN are superimposed. A band assigned to the A(2)Delta -> X-2 Pi transition of CH was also measured and the vibrational and rotational structures of Swan bands could be resolved. The origin of the C-2(*) and C2H* is discussed. Finally, the achieved molecular vibrational temperature is estimated to be about 5400 +/- 350 K.