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        • SCISCIESCOPUS

          Cold Plasma Jets Made of a Syringe Needle Covered With a Glass Tube

          Guangsup Cho,Hyungyo Lim,Jung-Hyun Kim,Dong Jun Jin,Gi Chung Kwon,Eun-Ha Choi,Han Sup Uhm IEEE 2011 IEEE transactions on plasma science Vol.39 No.5

          <P>A syringe needle assembled with a glass tube has been used as a plasma jet device for biomedical applications. According to the various types of ground electrode installed at the glass tube, argon plasma from an atmospheric pressure discharge has been investigated with a dc-ac inverter of several tens of kilohertz. When the ground electrode is absent or floated, the length of the plasma jet is about 10 mm at an ignition voltage of about 3 kV, and it extends further to a few tens of millimeters as the voltage increases to 5 kV. If the ground electrode is inserted inside the end of the glass tube, all plasma current is sunk directly to the ground electrode so that the plasma plume cannot emit out of the glass tube. For the case of an external ground electrode which is similar to a dielectric barrier discharge, the ignition voltage is as low as 1 kV, and the plume length is easily adjustable to be 1-10 mm in the voltage range of 1-3 kV.</P>

        • SCISCIESCOPUS

          Propagation of Plasma Diffusion Wave According to the Voltage Polarity in the Atmospheric Pressure Plasma Jet Columns

          Guangsup Cho,Yun-Jung Kim,Eun Ha Choi,Han Sup Uhm IEEE 2014 IEEE transactions on plasma science Vol.42 No.11

          <P>Propagation of optical signals measured along the atmospheric plasma-jet column according to the operational voltage polarity is analyzed with the electrostatic plasma-diffusion wave in terms of the characteristic speeds of plasma fluids, such as the plasma drift u<SUB>d</SUB>, the gas flow u<SUB>b</SUB>, and the plasma diffusion u<SUB>n</SUB>. For the positive voltage, the ion wave propagates with the wave-packet velocity of u<SUB>g</SUB> ~ c<SUB>s</SUB><SUP>2</SUP>/u<SUB>n</SUB>, where c<SUB>s</SUB> is the acoustic velocity along the whole column of plasma jet without any restrictions. The electron wave propagates backward with the group velocity of electron drift with u<SUB>g</SUB> ~ -u<SUB>ed</SUB> toward the high voltage electrode right after passing of the frontline of ion wave-packet. For the negative voltage, the ion wave propagates on the high ionization column with the wave-packet velocity of u<SUB>g</SUB> ~ c<SUB>s</SUB><SUP>2</SUP>/u<SUB>n</SUB>. The electron wave propagates forward while its propagation mode varies from the group velocity of u<SUB>g</SUB> ~ c<SUB>s</SUB><SUP>2</SUP>/u<SUB>n</SUB> on a region of high electric field to the velocity of electron drift with ug ~ +u<SUB>ed</SUB> on a low field region.</P>

        • SCISCIESCOPUS

          Plasma Diffusion Along a Fine Tube Positive Column

          Guangsup Cho,Jung-Hyun Kim,Jong-Mun Jeong,Ha-Chung Hwang,Dong-Jun Jin,Je-Huan Koo,Eun-Ha Choi,Verboncoeur, J.P.,Han-Sup Uhm IEEE 2009 IEEE transactions on plasma science Vol.37 No.3

          <P>The propagation velocity of light emission is observed to be u<SUB>p</SUB> ~0.92 times10<SUP>+5</SUP> m/s along a tube of an inner diameter r<SUB>o</SUB> ~1.5 times10<SUP>-3</SUP> m with an external electrode fluorescent lamp filled with 97% Ne and 3% Ar at a total pressure of 30 torr, a mercury-free lamp without phosphor coating the inside glass wall. The origin of this propagation is shown to be ambipolar diffusion with a plasma diffusion speed of u<SUB>p</SUB> ~ (4.8/r<SUB>o</SUB>)D<SUB>a</SUB> for diffusion coefficient D<SUB>a</SUB> along the positive column. When a high voltage magnitude is applied at the external electrode, a high-density plasma is generated inside the hollow electrode, and the plasma diffuses along the positive column toward the ground electrode.</P>

        • KCI우수등재
        • KCI등재

          The Jet-Stream Channels of Gas and Plasma in Atmospheric-Pressure Plasma Jets

          Guangsup Cho,Yunjung Kim,Han Sup Uhm 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.69 No.4

          A solution to the fluid momentum equation for incompressible steady-state flow is obtained for the streams of gas and plasma inside a jet nozzle and in the open-air space. Three pressure forces are considered in the equation. The first is the pressure force of the shear stress resulting from the flow viscosity and is balanced against the second pressure force of the gas stream that is ejected into the air. The third pressure force is due to the radial expansion of the fluid channel, reducing the velocity of the fluid to zero so that we obtain the reaching distance of the fluid after ejection from the nozzle. From the solution for the fluid channel, the regional profile and the density profile of the plasma flow are also determined. The maximum distance of the gas flow with a critical Reynolds number of Rnc 2000 is calculated to be 100 times that of the nozzle diameter for Ar, Ne, and He. Because the radial expansion of the plasma is ten times larger than that of neutral gases, the length of the plasma flume is a few tens of the nozzle diameter, which is significantly shorter than the gas flow distance. In the experiments, the maximum length of the plasma plume increases and then saturates as the operation voltage increases.

        • Plasma Bullet as a Plasma Diffusion Wave-Packet in Plasma Jets

          Guangsup Cho,Eun-Ha Choi,Han Sup Uhm IEEE 2013 IEEE transactions on plasma science Vol.41 No.6

          <P>The propagation of a plasma bullet in a plasma jet is described under the base of plasma fluid theory in terms of the plasma drift, the gas flow, and the plasma diffusion. The analysis reveals that the plasma bullet originates from the electrostatic diffusion wave in plasma propagating in the plasma column of jets. The plasma diffusion waves, electron waves, and ion waves propagate in the form of a wave-packet modulated by the operation frequency of the voltage pulse. The waves have the dispersion relation of ω ~ <I>ku</I><SUB>αφ</SUB>, and the wavelength has the order of Debye length λ<I>D</I> ~ 10<SUP>-4</SUP> m as <I>k</I><SUP>2</SUP> λ<I>D</I><SUP>2</SUP> ~ 1. The phase velocity is <I>u</I><SUB>αφ</SUB> ~ (<I>u</I><SUB>α</SUB><I>d</I> +<I>ub</I>+<I>un</I>+κ<SUB>α</SUB><I>un</I>) with the mobility ratio of κ<I>e</I>=|μ<I>e</I>/μ<I>i</I>| for electrons (α = <I>e</I>) and κ<I>i</I>=1 for ions (α = <I>i</I>). The terms <I>ued</I>, <I>uid</I>, <I>ub</I>, and <I>un</I> represent the electron drift velocity, the ion drift velocity, the gas blowing velocity, and the plasma diffusion velocity, respectively. The waves are modulated to be the wave-packet of <I>d</I>ω ~ <I>ugdk</I> with the group velocity of <I>ug</I> ~ <I>cs</I><SUP>2</SUP>/<I>un</I> ~ (10<SUP>4</SUP>-10<SUP>5</SUP>)m/s, where the acoustic velocity is <I>cs</I> ~ 10<SUP>3</SUP> m/s and the diffusion velocity is <I>un</I> ~ (10-10<SUP>2</SUP>)m/s estimated in a plasma jet device.</P>

        • KCI우수등재

          Flexible Plasma Sheets

          Cho, Guangsup,Kim, Yunjung The Korean Vacuum Society 2018 Applied Science and Convergence Technology Vol.27 No.2

          With respect to the electrode structure and the discharge characteristics, the atmospheric pressure plasma sheet of a thin polyimide film is introduced in this study; here, the flexible plasma device of a dielectric-barrier discharge with the ground electrode and the high-voltage electrode formulated on each surface of a polyimide film whose thickness is approximately $100{\mu}m$, that is operated with a sinusoidal voltage at a frequency of 25 kHz and a low voltage from 1 kV to 2 kV is used. The streamer discharge is appeared along the cross-sectional boundary line between two electrodes at the ignition stage, and the plasma is diffused on the dielectric-layer surface over the high-voltage electrode. In the development of a plasma sheet with thin dielectric films, the avoidance of the insulation breakdown and the reduction of the leakage current have a direct influence on the low-voltage operation.

        • SCISCIESCOPUSKCI등재

          The jet-stream channels of gas and plasma in atmospheric-pressure plasma jets

          Cho, Guangsup,Kim, Yunjung,Uhm, Han Sup 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol. No.

          <P>A solution to the fluid momentum equation for incompressible steady-state flow is obtained for the streams of gas and plasma inside a jet nozzle and in the open-air space. Three pressure forces are considered in the equation. The first is the pressure force of the shear stress resulting from the flow viscosity and is balanced against the second pressure force of the gas stream that is ejected into the air. The third pressure force is due to the radial expansion of the fluid channel, reducing the velocity of the fluid to zero so that we obtain the reaching distance of the fluid after ejection from the nozzle. From the solution for the fluid channel, the regional profile and the density profile of the plasma flow are also determined. The maximum distance of the gas flow with a critical Reynolds number of R (nc) ae 2000 is calculated to be 100 times that of the nozzle diameter for Ar, Ne, and He. Because the radial expansion of the plasma is ten times larger than that of neutral gases, the length of the plasma flume is a few tens of the nozzle diameter, which is significantly shorter than the gas flow distance. In the experiments, the maximum length of the plasma plume increases and then saturates as the operation voltage increases.</P>

        • KCI우수등재

          Electron-excitation Temperature with the Relative Optical-spectrumIntensity in an Atmospheric-pressure Ar-plasma Jet

          Gookhee Han,Guangsup Cho 한국진공학회(ASCT) 2017 Applied Science and Convergence Technology Vol.26 No.6

          An electron-excited temperature (Tex) is not determined by the Boltzmann plots only with the spectral data of 4p→4s in an Ar-plasma jet operated with a low frequency of several tens of ㎑ and the low voltage of a few ㎸, while Tex can be obtained at least with the presence of a high energy-level transition (5p→4s) in the high-voltage operation of 8 ㎸. The optical intensities of most spectra that are measured according to the voltage and the measuing position of the plasma column increase or decay exponentially at the same rate as that of the intensity variation; therefore, the excitation temperature is estimated by comparing the relative optical-intensity to that of a high voltage. In the low-voltage range of an Ar-jet operation, the electron-excitation temperature is estimated as being from 0.61 eV to 0.67 eV, and the corresponding radical density of the Ar-4p state is in the order of 10<SUP>10</SUP>~10<SUP>11</SUP> ㎝<SUP>−3</SUP>. The variation of the excitation temperature is almost linear in relation to the operation voltage and the position of the plasma plume, meaning that the variation rates of the electron-excitation temperature are 0.03 eV/㎸ for the voltage and 0.075 eV/㎝ along the plasma plume.

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