Ki Baek Song

Measurement of hydroxyl radical density generated from the atmospheric pressure bioplasma jet

Atmospheric pressure bioplasmas are being used in a variety of bio-medical and material processing applications, surface modifications of polymers. This plasma can generate the various kinds of radicals when it contacs with the water. Especially, hydroxyl radical species have very important role in the biological and chemical decontamination of media in this situation. It is very important to investigate the hydroxyl radical density in needle-typed plasma jet since it plays a crucial role in interaction between the living body and plasma. We have generated the needle-typed plasma jet bombarding the water surface by using an Ar gas flow and investigated the emission lines by OES (optical emission spectroscopy). It is noted that the electron temperature and plasma density are measured to be about 1.7 eV and 3.4 × 1012 cm−3, respectively, under Ar gas flow ranged from 80 to 300 sccm (standard cubic centimeter per minute) in this experiment. The hydroxyl radical density has also been investigated and measured to be maximum value of 2.6 × 1015 cm−3 for the gas flow rate of 150 sccm in the needle-typed plasma jet by the ultraviolet optical absorption spectroscopy.

Measurement of excited Xe atoms density in alternating current plasma display panel by means of laser absorption spectroscopy

The exited Xe atoms in the 1s/sub 5/ metastable state and the 1s/sub 4/ resonance state across the two sustaining electrode have been monitored in a micro-discharge cell of alternating current plasma display panels (PDPs) by laser absorption spectroscopy. In this study, it is found that the maximum excited xenon density is 5.4/spl times/10/sup 12/ cm/sup -3/ in the 1s/sub 5/ metastable state and 1.2/spl times/10/sup 12/ cm/sup -3/ in the 1s/sub 4/ resonance state for the PDP cell with gap distance of 150/spl mu/m and width of 350/spl mu/m under the fixed gas pressure of 350 torr and a mixture of Xe content ratio of 10% with Ne under driving frequency of 35 kHz. It is also observed that the exited Xe atom density and the plasma ion density are strongly correlated with one another in this experiment. It is noted that the plasma ion density reaches a minimum at the center of electrode gap and a maximum of 9.0/spl times/10/sup 11/ cm/sup -3/ in a region located 200 /spl mu/m away from this center under the filling pressure of 350 torr, which corresponds to the strongest discharge in alternating current plasma display panel (ac-PDP). When increasing PDP driving frequency from 35 kHz, 50 kHz up to 100 kHz, it is found that density of excited Xe atom in the 1s/sub 5/ metastable state increase from 6.5/spl times/10/sup 12/ cm/sup -3/ up to 1.39/spl times/10/sup 13/ cm/sup -3/.

Analytical investigation of electrical breakdown properties in a nitrogen-SF6 mixture gas

The electrical breakdown properties in nitrogen gas mixed with SF6 are analytically investigated in this article by making use of the ionization and attachment coefficients of the mixed gas. The ionization coefficients of nitrogen and SF6 gas are obtained in terms of the electron temperature Te by assuming a Maxwellian distribution of the electron energy. The attachment coefficient of SF6 gas is also obtained in terms of the gas temperature Te. An algebraic equation is obtained, relating explicitly the electron breakdown temperature Tb in terms of the SF6 mole fraction χ. It was found from this equation that the breakdown temperature Tb increases from approximately 2 to 5.3 eV as the mole fraction χ increases from zero to unity. The breakdown temperature Tb of the electrons increases very rapidly from a small value and then approaches 5.3 eV slowly as the SF6 mole fraction increases from zero to unity. This indicates that even a small mole fraction of SF6 in the gas dominates the electron behavior in the ...

A diode design study of the virtual cathode oscillator with a ring-type reflector

A numerical simulation study of the high-power microwave generation from the vircator (virtual cathode oscillator) is carried out for coaxial diode structure by using a three-dimensional particle-in-cell (PIC) code called MAGIC. The coaxial vircator has a centered annular cathode body, cathode ring and cylindrical meshed-anode in order to enlarge the active interaction region in the virtual cathode space. In order to enhance a conversion efficiency of the output microwave power, ring-type reflector was installed to coaxial-type diode structure. The simulation results show that the output microwave frequency has a narrow bandwidth and its output microwave power sensitively depends upon the position and width of ring-type reflector. The maximum output microwave power is obtained by adopting a ring-type reflector 10 mm in width and 40 mm in the distance from the intense relativistic electron beam to the ring-type reflector. The output microwave mode without a ring-type reflector is a mixture of TM and TE mode. However, the TM/sub 01/ mode with its resonance frequency of 2.2 GHz is dominant for the ring-type reflector.

Output Characteristics of the Axially Extracted Virtual Cathode Oscillator With a Cathode-Wing

Having the merits of conceptual simplicity, high-output-power capacity, and wide tuning characteristics, the vircator (virtual cathode oscillator) has been investigated as a high-power microwave (HPM) generator. In axial vircator, the power, frequency, and pulsewidth are all sensitive to the cathode shape, and the frequency depends strongly on the anode-cathode gap distance. The efficiency of the vircator is reported to only a few percent. Therefore, we devised the new type cathode to enhance the output power. The new type cathode is adding the ring to the cathode with velvet, so-called cathode-wing. The electron beam is only emitted from cathode with velvet, while a cathode-wing forms the electric fields to prevent the backstream electrons due to virtual cathode from leaking to the diode chamber wall. We investigated the axial vircator with the cathode-wing by the HPM generator ldquoChundoongrdquo (max 600 kV, 88 kA, 60 ns). It is found that the cathode-wing contributes to enhancement of the output microwave power efficiency to 7% in comparison with 3% for a conventional axial vircator without cathode-wing.

Simulation study of high power microwave generation by virtual cathode oscillation in coaxial vircator

Summary form only given, as follows. We have numerically simulated the high power microwave generation by virtual cathode oscillation in a coaxial vircator with 3 dimensional PIC code Magic. It is noted that the coaxial vircator has the advantage of an enhancement of power efficiency and gaining of narrow bandwidth frequency. The study is focused on the design of a diode structure for a coaxial vircator suitable for Chundoong IREB pulser (Max. 600 kV, 85 kA, 60 ns). It consists of a center annular cathode, a cylindrical meshed-anode and a reflector. The simulation results showed that the coaxial vircator can indeed be operated at the selected frequency with the narrow bandwidth and the microwave output power strongly depends on the position and geometry of the reflector. From this simulation results we expect that the maximum microwave output power will be obtained by the reflector of 4 cm in width and also 4 cm in distance away from the IREB, where the resonant frequency of microwave from coaxial vircator is simulated to be 6.577 GHz.

A diode design study of the virtual cathode oscillator with ring-type reflector

Summary form only given, as follows. A numerical simulation study of the high power microwave generation from the virtual cathode oscillator (vircator) is carried out for various diode configurations by a 3 dimensional particle-in-cell (PIC) code called MAGIC. The coaxial vircator has a cylindrical cathode, cylindrical anode-mesh, and reflector, in order to enlarge the active interaction region in the virtual cathode space. The simulation results show that the output microwave frequency has a narrow bandwidth and its output microwave power depends sensitively on the position and width of ring-type reflector. The maximum microwave output power is obtained with a reflector 10mm in width and 40mm in distance from the intense relativistic electron beam. Output microwave mode without the ring-type reflector was mixture of the TM mode, however, it is found to be dominantly TM/sub 01/ mode with a resonance frequency of 22 GHz with the ring-type reflector.

Computer simulation of the cavity geometry for a S-band side coupled cavity

In recent year, the computer codes for solving 3-D full-wave electromagnetic field, for example CST (microwave studio) or HFSS (high frequency structure simulation), just have enough accurate to used for the multi-cavities accelerating structure design, such as dispersion relation, cavity geometry, et.al.. Before that, the geometry design was just based on analytical expression, experimental trial test and designers experience. Due to non-linearity and complication, it is very difficult to determine the geometry of cavities or structure without computer simulation code. This paper technically describes the calculation method of the cavity geometry by CST code[1].

Dual-energy driving method for S-band Interlaced Electron LINAC

An interlaced dual-energy electron LINAC was developed for cargo inspection systems. The electron energy is varied based on the RF power level and initial current of the E-gun. This paper describes a dual-energy driving method for an interlaced dual-energy electron LINAC using variable applied levels of the E-gun dual-pulse power supply, a high voltage modulator, and a dual RF power source. The electron energy is controlled using dual RF power based on the voltages of the electron gun and RF power source. Consequently, we can control the variable electron energy from about 5 MeV to 9 MeV in our designed S-band RF LINAC system.

Design of the DC gun for S-band Electron LINAC

A DC gun for the dual-energy S-band electron Linear Accelerator (LINAC) was designed for the Cargo Inspection System (CIS) at the Korea Atomic Energy Research Institute (KAERI). The main design factors affect the accelerating performance, and provide experiences and design references in a further optimization of the structure. This design is a beam energy of 20 keV, beam current of 0.5 A, working distance of 50 mm, beam radius of 0.5 mm at the working distance, current density on the surface of the cathode of less than 2 A/cm2, energy spread of <;2%, and normalized emittance of εn<; 10 π mm mrad.