J. J. Choi

Optical measurements of gas temperatures in atmospheric pressure RF cold plasmas

This work was supported by grant No. R01-2000- n00254 fromthe Korea Science and Engineering nFoundation.

Modeling of multistage depressed collectors using a 3D conformal finite-difference time-domain particle-in-cell code

Summary form only given. The feasibility of modeling a multistage depressed collector using a conformal finite-difference time-domain particle-incell code has been studied. A feedback mechanism is implemented to provide stable time-dependent voltages for each stage of the depressed collector. An arbitrary space-time dependent spent beam distribution can be given in our time domain simulations. We demonstrate the design of a five stage depressed collector recovering a triangular spent beam distribution achieving an energy recovery efficiency of 70%. Detail modeling and code capabilities will be presented.

Stable microwave coaxial cavity plasma system at atmospheric pressure

We present a systematic study of the development of a novel atmospheric microwave plasma system for material processing in the pressure range up to 760 torr and the microwave input power up to 6 kW. Atmospheric microwave plasma was reliably produced and sustained by using a cylindrical resonator with the TM(011) cavity mode. The applicator and the microwave cavity, which is a cylindrical resonator, are carefully designed and optimized with the time dependent finite element Maxwell equation solver. The azimuthal apertures are placed at the maximum magnetic field positions between the cavity and the applicator to maximize the coupling efficiency into the microwave plasma at a resonant frequency of 2.45 GHz. The system consists of a magnetron power supply, a circulator, a directional coupler, a three-stub tuner, a dummy load, a coaxial cavity, and a central cavity. Design and construction of the resonant structures and diagnostics of atmospheric plasma using optical experiments are discussed in various ranges of pressure and microwave input power for different types of gases.

Nonthermal plasma effects on mesenchymal stem cell differentiation

Summary form only given. Stem cells have been known to be differentiated by chemical and physical environmental changes. Non-thermal plasma was applied to the cell culture substrates. Chemical modifications induced on carbaon-based materials or biocompatible polymers had effects on mesenchymal stem cell growth and differentiation. Various gases were fed in nonthermal plasma and the following chemical modifications were screened using Raman spectroscopy. The adsorption of adhesion proteins and the differentiation of mesenchymal stem cells were screened by using fluorescence microscopy, and the molecular works were followed. This result suggests easy and cost-efficient method of platform functionalization for stem cell therapy.

A new class of S-band microwave poewr module for phased antenna array radar applications

Summary form only given. A new class of microwave power module (MPM) is being developed for phased antenna array applications. The MPM consists of a compact S-band 1 kW traveling-wave tube (TWT), a solid-state pre-amplifier, and a power supply. The proposed S-band MPM provides tenfold peak power increase compared to state-of-the art S-band MPMs. The TWT amplifier is driven by a 6 kV, 0.9 A electron beam. A depressed collector which was designed by using a 3-D conformal finite-difference time-domain particle-in-cell code,VORPAL [1], was employed to maximize the efficiency. The compact and lightweight S-band TWT is short in length (circuit length is six inches) and weighs only 700 g. The preliminary hot test result of the TWT showed 900 W peak power in S-band. The design, fabrication, and characterization of each components that consist the MPM will be discussed. The cold and hot test results will be presented.

P2-22: Design of multistage depressed collectors using 3D conformal finite-difference time-domain particle-in-cell simulations

The feasibility of designing a multistage depressed collector using conformal finite-difference time-domain particle-in-cell simulations has been studied. A feedback mechanism is implemented to provide stable time-dependent voltages for each stage of the depressed collector. An arbitrary space-time dependent spent beam distribution can be given in our time-domain simulations. We demonstrate the design of a five-stage depressed collector recovering a triangular spent beam distribution achieving an energy recovery efficiency of 70%.

Microwave atmospheric discharge for materials processing

Summary form only given. Microwave atmospheric plasma system using TM011 mode is successfully designed and built for materials processing applications. The microwave applicator and chamber were specifically designed to maximize microwave coupling into the plasma at resonant frequency. The system consists of a magnetron power supply, a circulator, a directional coupler, a three-stub tuner, a dummy load, a coaxial cavity, and a central cavity. Azimuthal slots were placed between the coaxial and the central cavity for efficient magnetic coupling. The plasma was reliably sustained at atmospheric pressure with good uniformity. Design and construction of the plasma system and diagnostics of atmospheric pressure plasma are presented for various ranges of pressure and gas types.

Microwave assisted plasma generation from a hybrid coaxial TE011 resonator

Summary form only given, as follows. Atmospheric plasma generation from a 3kW, 2.45 GHz magnetron is investigated The system consists of a 2.45 GHz magnetron, circulator, dummy load, a three-stub impedance matching network, and a hybrid coaxial TE011 resonator. The resonator is designed to excite a TE011 at 2.45 GHz through a three coupling on a TE311 coaxial cavity, which is connected to a WR-284 rectangular waveguide. The resonator quality factor is measured to be 200 before it is tuned, which is in good agreement with HFSS simulation results. A large-area argon plasma generation is observed in a TE011 coaxial resonator. The plasma volume is an annular configuration which is consistent with the TE011 electric field shape. Experiments show stable plasma generation up to 1 Torr.

High power microwave experiments of gyroklystron amplifier and backward wave oscillator

Summary form only given, as follows. A Ka-band second-harmonic TE/sub 21/ gyro-TWT amplifier with an axis-encircling beam is being constructed at UCD that is predicted to nearly double the efficiency of our previous 200 kW, 12% efficient magnetron injection gun (MIG) TE/sub 21/ gyro-TWT.

Helium concentration measurements in an atmospheric micro-plasmas using visible emission spectroscopy

Summary form only given, as follows. A simple in-situ gas monitoring system can be developed with micro discharge plasma sources based on optical emission spectroscopy. Helium concentrations are estimated from the visible line emission of atmospheric plasmas generated with various micro plasma discharges. With this technique, volumetric helium concentrations are accurately measured even down to a percent. Since selected emission lines are not affected by moisture, this measuring system can be operated even without sampling and drying processes, which is a crucial element of in-situ monitoring system. The compact in-situ gas monitoring system will be presented, and the system is expected to be applicable to measuring other elements than helium.