Kie-Hyung Chung

Sterilization using a microwave-induced argon plasma system at atmospheric pressure

The use of microwave plasma for sterilization is relatively new. The advantages of this method are the relatively low temperature, time-savings and its nontoxic nature, in contrast to traditional methods such as heat and gas treatment, and radiation. This study investigated the sterilization effects of microwave-induced argon plasma at atmospheric pressure on materials contaminated with various microorganisms, such as bacteria and fungi. A low-cost and reliable 2.45 GHz, waveguide-based applicator was designed to generate microwave plasma at atmospheric pressure. This system consisted of a 1 kW magnetron power supply, a WR-284 copper waveguide, an applicator including a tuning section, and a nozzle section. Six bacterial and fungal strains were used for the sterilization test. The results showed that regardless of the strain, all the bacteria used in this study were fully sterilized within 20 seconds and all the fungi were sterilized within 1 second. These results show that this sterilization method is ea...

The design of the KSTAR tokamak

Abstract The Korea Superconducting Tokamak Advanced Research (KSTAR) Project is the major effort of the Korean National Fusion Program (KNFP) to develop a steady-state-capable advanced superconducting tokamak to establish a scientific and technological basis for an attractive fusion reactor. Major parameters of the tokamak are: major radius 1.8 m, minor radius 0.5 m, toroidal field 3.5 Tesla, and plasma current 2 mA with a strongly shaped plasma cross-section and double-null divertor. The initial pulse length provided by the poloidal magnet system is 20 s, but the pulse length can be increased to 300 s through non-inductive current drive. The plasma heating and current drive system consists of neutral beam, ion cyclotron waves, lower hybrid waves, and electron–cyclotron waves for flexible profile control. A comprehensive set of diagnostics is planned for plasma control and performance evaluation and physics understanding. The project has completed its conceptual design phase and moved to the engineering design phase. The target date of the first plasma is set for year 2002.

Removal and sterilization of biofilms and planktonic bacteria by microwave-induced argon plasma at atmospheric pressure

Microbial biofilms are a functional matrix of microbial cells, enveloped in polysaccharides, enzymes and virulence factors secreted by them that can develop on indwelling medical devices and biomaterials. Plasma sterilization has been widely studied in recent years for biological applications. In this study, we evaluated the possibility of removal and anti-recovery of biofilms by microwave-induced argon plasma at atmospheric pressure. We observed that all bacterial biofilms formatted by Gram-negative and Gram-positive bacteria are removed in less than 20 s, and the growth inhibitions of planktonic bacteria within biofilms are also confirmed by plasma exposure for 5 s. These results suggest that our plasma system can be applied to medical and biological fields where the removal of biofilms and their debris is required.

Enhanced chondrogenic responses of human articular chondrocytes onto silk fibroin/wool keratose scaffolds treated with microwave-induced argon plasma.

Silk fibroin (SF) is a natural, degradable, fibrous protein that is biocompatible, is easily processed, and possesses unique mechanical properties. Another natural material, wool keratose (WK), is a soluble derivative of wool keratin, containing amino acid sequences that induce cell adhesion. Here, we blended SF and WK to improve the poor electrospinability of WK and increase the adhesiveness of SF. We hypothesized that microwave-induced argon plasma treatment would improve chondrogenic cell growth and cartilage-specific extracellular matrix formation on a three-dimensional SF/WK scaffold. After argon plasma treatment, static water contact angle measurement revealed increased hydrophilicity of the SF/WK scaffold, and scanning electron microscopy showed that treated SF/WK scaffolds had deeper and more cylindrical pores than nontreated scaffolds. Attachment and proliferation of neonatal human knee articular chondrocytes on treated SF/WK scaffolds increased significantly, followed by increased glycosaminoglycan synthesis. Our results suggest that microwave-induced, plasma-treated SF/WK scaffolds have potential in cartilage tissue engineering.

The KSTAR tokamak

The KSTAR (Korea Superconducting Tokamak Advanced Research) project is the major effort of the Korean National Fusion Program to design, construct, and operate a steady-state-capable superconducting tokamak. The project is led by Korea Basic Science Institute and shared by national laboratories, universities, and industry along with international collaboration. It is in the conceptual design phase and aims for the first plasma by mid 2002. The key design features of KSTAR are: major radius 1.8 m, minor radius 0.5 m, toroidal field 3.5 T, plasma current 2 MA, and flexible plasma shaping (elongation 2.0; triangularity 0.8; double-null poloidal divertor). Both the toroidal and the poloidal field magnets are superconducting coils. The device is configured to be initially capable of 20 s pulse operation and then to be upgraded for operation up to 300 s with non-inductive current drive. The auxiliary heating and current drive system consists of neutral beam, ICRF, lower hybrid, and ECRF. Deuterium operation is planned with a full radiation shielding.

Effect of magnetic field structure near cathode on the arc spot stability of filtered vacuum arc source of graphite

Amorphic diamond films deposited by the filtered vacuum arc (FVA) method have attracted much attention due to their superior mechanical and optical properties. However, the instability of the arc limits the continuous operation of the FVA source, resulting in a poor productivity. In the present work, we investigated the effects of the cathode shape and the structure of the magnetic field near the cathode on the erosion behavior by both computer simulations and experimental studies. Arc instability in the configuration of parallel magnetic polarities of the source magnet and the extraction could be suppressed by placing a permanent magnet of opposite polarity behind the cathode. We show further that oscillation of the current of the source magnet was effective in extending the area of the arc spot movement. A tapered cathode exhibited a more stable arc than a cylindrical cathode, as confirmed by the time variation of the beam current. By using the oscillating current of the source magnet and a tapered cathode of diameter 80 mm, a continuous operation for 2000 min with an arc current of 60 A was obtained, at which more than 90% of the cathode volume could be used. A stable beam current of about 350 mA was obtained under the present operating conditions.

A continuous winding scheme for superconducting tokamak coils with cable-in-conduit conductor

Abstract Superconducting magnet coils are essential for steady-state or long-pulse operation of tokamaks. In an advanced tokamak, the central solenoid (CS) coils are usually divided into several pairs of modules to provide for an extra plasma shaping capability in addition to those available from the shaping (poloidal field) coils. In the conventional pancake winding scheme of superconducting coils, each coil consists of separate superconducting ‘double-pancake’ coils connected together in series; however, such joints are not superconducting, which is one of the major disadvantages, especially in pulsed operations. A new type of winding was adopted for the ITER CS coil, which consists of cylindrical shell ‘layers’ joined in series. A disadvantage of this layer winding is its inability to yield modular coils that can provide certain degree of plasma shaping. Joints can be removed in a coil winding pack with the conventional pancake winding scheme, if the conductor is sufficiently long and the winding machine is properly equipped. The compactness, however, cannot be preserved with this scheme. The winding compactness is important since the radial build of the CS coils is one of the major parameters that determine the machine size. In this paper, we present a continuous winding scheme that requires no joints, allows coil fabrication at minimum dimension, and meets the flux swing requirement and other practical aspects.

Investigation of a radio frequency-driven multicusp ion source of the diagnostic neutral beam for the Hanbit device at Korea Basic Science Institute

A radio frequency-driven multicusp ion source has been fabricated and tested as a part of the development of a diagnostic neutral beam for the Hanbit magnetic mirror device [S. M. Hwang et al., Trans. Fusion Technol. 35, 99 (1999)]. Hydrogen plasma produced by a three-and-one-half turn antenna and rf power system with 2.5 kW, continuous wave (cw) 1.874 MHz was extracted through a single-aperture accel-decel system. The first results of the ion beam extraction experiments are described in this article.

Conceptual design of 10 MeV, 100 kW CW electron accelerator for industrial application

The application fields of intense gamma-rays or X-rays for industrial purposes are expanding. An electron beam accelerator which can generate X-rays whose dose rate is equivalent to the effect of a several MCi gamma-ray source is a major candidate as an intense X-ray source. The 10 MeV, 100 kW CW electron accelerator Fantron-I is conceptually designed for an X-ray source to irradiate food, corn, forest products and so on. Electrons are accelerated seventeen times through two coaxial cavities with a TM010 mode by means of a bending magnet located outside the cavity. The resonant frequency of the cavity is about 160 MHz and the phase of one cavity is 180/spl deg/ shifted from that of the other. Higher order modes (HOM) which may cause beam instability are analyzed. The design parameters of beam lines and bending magnets are determined from the results of beam phase analysis, especially magnetic flux density and locations of each bending magnet are carefully adjusted to synchronize the beam with the accelerating field. In this paper, characteristics and the overall conceptual design of the Fantron-I are presented.

Design of radially focused uniform X-ray source

The 10 MeV, 100 kW CW electron accelerator (FANTRON I) is being developed in Department of Nuclear Engineering, Seoul National University (SNU). The X-ray generated by the accelerated electron beam will be used in sterilizing the agricultural, forest and aquatic products. For the effective irradiation and the safety of the irradiated products, uniform irradiation is needed. The designed target is mainly featured by the radially focused uniform X-ray. The diameter of irradiation hole is 0.75 m. And the generated X-ray is emitted toward the center of the irradiation hole with uniform distribution along the circumference. To generate the radially focused uniform X-ray, the accelerated electron beam must be focused radially on the target that is the outer shell of the irradiation hole with high uniformity.