J.K. Rhee

α, γ, and normal, abnormal glow discharge modes in radio-frequency capacitively coupled discharges at atmospheric pressure

Discharge modes, α and γ, of a radio-frequency helium capacitively coupled discharge at atmospheric pressure were investigated with the discharge gap distance between electrodes varied from 1 to 5mm. As similarly observed in other experiments, the α and γ mode and the α–γ mode transition were observed with large drops in the voltage (310–179V) and the phase angle between the voltage and current (54°–18°), and a contraction of the plasma volume (8.5–0.17cm3, at 3mm gap distance). The discharge voltage where the α–γ mode transition occurred versus the gap distance showed a similar behavior with the Paschen curve for a gas breakdown. Depending on the gap distance, normal and abnormal glow regimes were observed in the αmode. At 1 and 2mm, the α mode remained in the abnormal glow discharge until the α–γ mode transition occurred as the discharge current increases. At 3mm, however, the α mode was excited as a normal glow discharge with a constant current density (17mA∕cm2) but it became an abnormal glow discharg...

The driving frequency effects on the atmospheric pressure corona jet plasmas from low frequency to radio frequency

Lately, the atmospheric pressure jet type corona plasma, which has been typically driven by dc to low frequency (LF: several tens of kHz), is often generated by using radio frequency of 13.56 MHz. Yet, the relationship between the plasma and its driving frequency has seldom been investigated. Hence, in this study, dependence of the atmospheric pressure corona plasma characteristics on the driving frequency was explored experimentally from LF to rf (5 kHz–13.56 MHz). The plasmas generated by the driving frequency under 2 MHz were cylindrical shape of several tens of millimeters long while the 13.56 MHz plasma is spherical and a few millimeters long. As the driving frequency was increased, the plasma length became shortened. At the lower driving frequencies (below 2 MHz), the plasmas existed as positive streamer and negative glow for each half period of the applied voltage, but the discharge was more continuous in time for the 13.56 MHz plasma. It was inferred from the measured I–V curves that the higher dr...

Study of RF Plasma Characteristics and Plasma Sterilization at the Atmospheric Pressure

Summary form only given. Plasma characteristics were studied through electrical and optical diagnostics for a volumetric (105 times 40 times 4 mm) RF plasma (MyPL; www.applasma.com) produced at the atmospheric pressure in the ambient air. The main discharge device has a conducting rod as a powered electrode, which is covered with a dielectric material and placed between two ground electrodes. A flow of the main supply gas is provided onto the conducting rod. The plasma length is extendable by having a longer rod. The plasma was produced at the peak to peak voltage of about 90 V with an ignition. The spatial uniformity of the visible emission was obtained through an image processing of the plasma image captured by a CCD camera. Varying the gas flow and the applied power, the uniformity along the length direction was maintained less than 10%. The gas temperature measured by a thermocouple and a fiber probe was between 300 and 400 K for the input power range of 40 and 100 W. The feasibility of plasma sterilization was also studied. An E-coli sample was treated with the plasma by varying treatment time, gas flow rate, treatment position etc. After the plasma treatment, the E-coli sample was cultured for 12 hours to study the plasma effects. So far, 30 s of treatment time is enough to kill every E-coli that there was none survived after the plasma treatment.

Comparative study of atmospheric pressure LF and RF micro jet plasmas produced in a single electrode system

Summary form only given. Non-thermal atmospheric pressure micro jet plasmas were generated in a single electrode system using either LF (several tens of kHz) or RF (13.56 MHz) power sources, and the characteristics of the produced plasmas were compared. A copper electrode with radius of about 360 mum was placed in a glass tube with radius of 3 mm, and the main gas was helium. The plasma characteristics, such as physical appearance, electrical properties, and temperature, were measured by various means. The LF plasma shown to be about 50 mm long on the average, and its temperature, measured using a thermocouple, was about the room temperature. When the helium flow rate was 3 l/min, the breakdown voltage was less than 1000 V. Also, the plasma was maintained with up to 1 % of oxygen gas mixed. On the other hand, the RF plasma was about 5 mm long at the most, but it was thicker in radius than the LF plasma. The measured rotational temperature was between 300 K and 380 K, which was higher than the LF plasma temperature. The emission spectrum was more intense with a larger number of He I lines. Both plasmas exhibited different characteristics, and a further study would define their advantages and disadvantages and thus match appropriate applications for each.

Spectroscopic characterization of a- and .-mode in a capacitively-coupled plasma in the high pressure range up to atmospheric pressure

Summary form only given. Optical characteristics of different capacitive discharge modes, namely alpha- and gamma-mode, were investigated in the high gas pressure (10 torr) up to the atmospheric pressure. The plasma was produced between parallel copper electrodes using a 13.56 MHz RF source. An alpha-mode was excited as igniting the plasma at a low current region. At a certain discharge voltage and current, however, the alpha-mode was abruptly transformed into a gamma-mode with a voltage drop and a discharge volume contraction. Using optical spectroscopic methods, different discharge parameters were investigated. Because of the helium discharge gas, both discharge modes emitted intense excited atomic helium spectral lines, such as 587.6 nm and 667.8 nm. From the experimental results, the gamma-mode showed more intense emission and higher excitation temperature than that of the alpha-mode. On the other hand, the rotational temperature, corresponding to the gas temperature at the atmospheric pressure, were 350 K and 473 K for alpha-and gamma-mode, respectively

/spl alpha//spl gamma/ and normal, abnormal glow discharge modes in radio-frequency capacitively-coupled discharges at atmospheric pressure

Summary form only given. Discharge modes, alpha and gamma, of a radio-frequency helium capacitively-coupled discharge at atmospheric pressure were investigated with the discharge gap distance between electrodes varied from 1 mm to 5 mm. As similarly observed in other experiments, alpha- and gamma-mode and the alpha-gamma mode transition were observed with large drops in the voltage (310 V to 179 V) and the phase angle between the voltage and current (54deg to 18deg), and a contraction of the plasma volume (8.5 cm3 to 0.17 cm3, at 3 mm gap distance). The discharge voltage at which the alpha-gamma mode transition occurred versus the gap distance showed a similar behavior with the Paschen curve for a gas breakdown. Depending on the gap distance, normal and abnormal glow regimes were observed in the alpha-mode. At 1 and 2 mm, the alpha-mode was remained in the abnormal glow discharge until the alpha-gamma mode transition occurred as the discharge current increases. At 3 mm, however, the alpha mode was excited as a normal glow discharge with a constant current density (17 mA/cm2) but it became an abnormal glow discharge as the current increased. At 4 mm, the alpha-mode was sustained as a normal glow discharge, then the transition to the gamma-mode occurred. The effect of the gap distance was resulted from the different system impedance. Using a simple resistor-capacitor circuit model and the alpha-sheath breakdown model, the discharge modes and the mode transition properties were studied

Characteristics of an atmospheric pressure low temperature discharge produced for 3-d surface treatments

Summary form only given. A volumetric plasma was produced at the atmospheric pressure using a low frequency power supply. Two parallel electrical wires were placed at the inner surface of the cylindrical dielectric tube. The tube diameter and length were 30 mm and 80 mm, respectively. A helium gas was supplied for stable plasma generation. Based on the electrical and optical diagnostics, the plasma properties were studied. The plasma was produced at a peak to peak voltage of about 1000 V and filled the whole surface of the dielectric tube along the wires. The plasma current of 10 mA and the gas temperature of 350 K made the plasma surface treatment of thermally sensitive material possible. Some 3-dimensional shape materials of aluminum, Teflon, paper, and polymers were treated by the plasma. Using the contact angle method, it was shown that the plasma treatment enhanced the surface wettability. Sealing up the active discharge region enhanced the surface treatment effect

Atmospheric pressure micro-plasma in a single pin-electrode configuration

Summary form only given. A micro-plasma of non-transferred jet type was produced in the ambient air using a single pin electrode of radius 360 im and a low frequency power supply. Then, its characteristics, such as size and light emission, were studied. A typical operation condition was the input voltage of about 1000 V at the applied frequency of 50 kHz and the helium flow rate of 4 lpm. The plasma was lengthened towards the helium flowing direction, making a long and thin cylindrical shape. It was as long as about 30 cm at 1500 V. The plasma length and radius could be varied for a quite large range by controlling the experimental parameters such as the input voltage and the gas flow rate. The emission spectra showed helium lines (587 nm, 706 nm etc.) with a few nitrogen and oxygen lines (391 nm and 777 nm) due to the air molecules. The measurement of optical emission intensity was performed as the measurement position, the input voltage, and the helium flow rate were varied. At the electrode tip, the emission was discrete and different for each half period of the input voltage. For instance, during the positive half period of the input voltage, the emission was broader in time. However, at further away from the electrode tip, there was no emission during the negative half period. The emission intensity, integrated over one period of the input voltage showed that it was increased with the input voltage and was maximum at the helium flow rate of 4 lpm