S. Y. Moon

Comparative study of atmospheric pressure low and radio frequency microjet plasmas produced in a single electrode configuration

Microsize jet-type plasmas were generated in a single pin electrode structure source for two separate input frequencies of 50kHz and 13.56MHz in the ambient air. The copper pin electrode radius was 360μm, and it was placed in a Pyrex tube with a radius of 3mm for helium gas supply. Due to the input frequency difference, the generated plasmas showed distinct discharge characteristics for their plasma physical appearances, electrical properties, gas temperatures, and optical properties. Strengths and weaknesses of both plasmas were discussed for further applications.

Study of geometrical and operational parameters controlling the low frequency microjet atmospheric pressure plasma characteristics

Controllability of small size atmospheric pressure plasma generated at low frequency in a pin to dielectric plane electrode configuration was studied. It was shown that the plasma characteristics could be controlled by geometrical and operational parameters of the experiment. Under most circumstances, continuous glow discharges were observed, but both the corona and/or the dielectric barrier discharge characteristics were observed depending on the position of the pin electrode. The plasma size and the rotational temperature were also varied by the parameters. The rotational temperature was between 300 and 490K, being low enough to treat thermally sensitive materials.

Study of a dual frequency atmospheric pressure corona plasma

Radio frequency mixing of 2 and 13.56 MHz was investigated by performing experimental measurements on the atmospheric pressure corona plasma. As a result of the dual frequency, length, current density, and electron excitation temperature of the plasma were increased, while the gas temperature was maintained at roughly the same level when compared to the respective single frequency plasmas. Moreover, observation of time-resolved images revealed that the dual frequency plasma has a discharge mode of 2 MHz positive streamer, 2 MHz negative glow, and 13.56 MHz continuous glow.

Feasibility study of atmospheric pressure plasma treatments of HEPG-2 and SK-HEP-1 cancer cells

Summary form only given. A feasibility study of plasma cancer cell treatment was performed using a pin-type plasma jet. A 50 kHz AC power was used to generate the plasma in the ambient air assisted by the helium flow. The plasma gas temperature was maintained at the room temperature of 25degC to eliminate the thermal damages to the cell. The liver cancer cells of HEPG-2 and SK-HEP-1 were used as the treatment samples. The sample cells were prepared on the fibronectin coated slide glass for the sake of convenience of the microscopic observation process. The input voltage and the treatment time were controlled in the range of (750-1000) V and (30-120) s, respectively. After the plasma treatments, the sample cells were stained with the viability assay (ethidium homodimer and calcein AM) to make discrimination between live and dead cells. Then, the microscopy scan was performed from the plasma center up to about 1 cm. The necrotized cells as well as a void or cell free zone appeared starting at the input voltage of 800 V and the treatment time of 60 s, . The necrotized zone and the void were well matched to the plasma profile. Normal liver cell, THLE-2, was then treated for comparison with the liver cancer cells.

Decontamination of chemical warefare agent simulator Dimethyl Methylphosphonate (DMMP) using RF large area non-thermal atmospheric pressure plasma

Experimental results of the treatment of dimethyl methylphosphonate (DMMP), which is a chemical stimulant of the sarin gas, are reported. The plasma used for the experiment was a large area non-thermal RF atmospheric pressure plasma produced in the ambient air, of which size was 15times100 mm2. Previously measured current and gas temperature were low enough for thermally-sensitive material treatments, and actual applications to a pork sample and human skin proved its electrical and thermal safety. 100 muliter of the liquid DMMP was dropped on copper and glass plates then treated by the plasma at the input power of 100 W for several tens of minutes. Fourier transform infrared spectroscopy showed that several minute long treatment was enough to significantly affect the DMMP characteristic infrared spectrum. On the other hand, gas chromatography was used for quantitative measurements. The treated copper and glass plates were placed in methane chloride solvent to collect the remaining DMMP. Then, the DMMP concentration of each solution was measured. After 10 minutes of the treatment, 99.05% of DMMP on the copper plate was gone, and 99.96% DMMP on the glass plate was decontaminated after 16 minutes of the treatment. These decontamination rates are far good compared to other conventional methods such as heat, chemical catalyst etc.

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.

Electron density measurement for microwave-induced atmospheric pressure plasmas using laser deflection method

Summary form only given. A laser beam passing through plasma deflects due to a change in the line-integrated refractive index, which is attributed to an electron density gradient along the chord. By measuring the deflection angle of the laser beam, the electron density was obtained for an atmospheric pressure microwave-induced torch plasma generated in the ambient air. The diagnostic set-up, consisting of a low power He-Ne laser, a four channel segmented position-sensitive photodiode detector, and some relevant optical components, demands modest requirements of laser quality and optics alignments. The measured electron density was compared with that obtained by optical emission spectroscopy based on the measured Stark broadening width of the Balmer H-beta line emitted from the plasma. Both the multi channel deflection method and the optical emission method showed the same order of magnitude (~1015 cm-3) electron density values. Comparison of the detailed results will be presented.

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