Jung-Woo Ok

The Effects of Electrode Structures on the Luminous Efficacy of Micro Dielectric Barrier Discharges

A high-efficacy alternating-current plasma display panel utilizing various electrode structures is simulated using a 3-D fluid code for the investigation of the effects of cell structures on the discharge characteristics of micro dielectric barrier discharges. For the modification of the conventional coplanar electrode structure, three suggested electrode structures were simulated, namely, a patterned bus electrode, a multilayer bus electrode, and a two-electrode facial discharge structure. The time evolutions of infrared radiation images for the three structures compare well with the experimental results of test panels. The ultraviolet and visible-light emission profiles, as well as the time evolution of wall charge profiles, are analyzed in order to explain the role of the electrode structure for the improvement of luminous efficacy.

High efficacy plasma display panel with vertically raised bus electrodes

The authors propose a high efficacy alternating current plasma display panel utilizing vertically raised multilayer bus electrodes. The cell structure was designed to provide an opposite discharge mode and low discharge current in a relatively long gap. The test panels having discharge gaps of 330, 350, and 370μm were fabricated and basic properties of the panel were investigated in terms of current-voltage characteristics, luminance, and luminous efficiency. The cells with proposed structure show higher luminance and lower current simultaneously. The improvement in luminous efficiency is found to be a factor of 2 compared with the conventional coplanar structure having an electrode gap of 60μm. Emission spectra and spatio-temporal distribution of infrared light in discharge were measured. It is shown that high luminous efficiency of proposed cell originates from high excitation efficiency, low surface loss of charged particles, and enlarged discharge volume.

Development of compact linear accelerator in KBSI.

The compact linear accelerator using a 28 GHz ECRIS is under construction in KBSI, South Korea. The main capability of this facility is the production of fast neurons for the neutron radiography. The designing of a superconducting magnet, microwave transmission system, beam extraction, and plasma chamber of ECRIS were finished. The nominal axial design fields of the magnets are 3.6 T at injection and 2.2 T at extraction; the nominal radial design field strength at the plasma chamber wall is 2.1 T. We already installed 10 kW, 28 GHz gyrotron, and tested a microwave power from gyrotron using a dummy load. The current status will be discussed in this paper.

The effects of total gas pressure and Xe partial pressure on the properties of plasma display panels with two-opposite-electrode cells

The effects of total pressure and Xe partial pressure on the characteristics of an alternating-current plasma display panel with a two-opposite-electrode discharge cell configuration and a three-electrode surface-discharge cell configuration were investigated in terms of the following electro-optical properties: breakdown voltage, sustain voltage, wall charge transfer curve, infrared emission characteristics, luminance and luminous efficacy. Despite the longer discharge gap length, the results of the experiment and three-dimensional plasma simulation indicated that the opposite-discharge configuration has a significantly lower breakdown voltage than the surface-discharge configuration. Furthermore, the ratio of the increase in the breakdown voltage for the opposite-discharge configuration to the incremental Xe partial pressure was found to be smaller than that of the surface-discharge configuration. Because of its low driving voltage and possible use of high-Xe partial pressure, the opposite-discharge mode exhibited a higher luminous efficacy compared with the surface-discharge mode. These results indicated that the two-opposite-electrode discharge cell configuration has a cost reduction potential in electronics as well as high efficacy for plasma displays.

21.4: Discharge Characteristics of AC-PDP having Doped MgO Protective Layer in a Variation of Temperature

In order to improve the discharge characteristics such as discharge voltage, luminance, luminous efficacy, temperature dependence of misfiring, a small amount of Si was added to the MgO protective layer of an alternating current plasma display panel (AC-PDP). The effect of Si-doping on a MgO protective layer was reported that it reduces the firing voltage and improved electro-optical characteristics of AC-PDP due to the increase of the secondary electron emission with Si concentration. In this study, it was observed that Si-doping on MgO protective layer reduces the temperature dependence of misfiring compared with a pure MgO film. The effects of Si concentration are reported on the surface-discharge characteristics of an AC-PDP.

Nitrogen ion implantation into various materials using 28 GHz electron cyclotron resonance ion source

The installation of the 28 GHz electron cyclotron resonance ion source (ECRIS) ion implantation beamline was recently completed at the Korea Basic Science Institute. The apparatus contains a beam monitoring system and a sample holder for the ion implantation process. The new implantation system can function as a multipurpose tool since it can implant a variety of ions, ranging hydrogen to uranium, into different materials with precise control and with implantation areas as large as 1-10 mm(2). The implantation chamber was designed to measure the beam properties with a diagnostic system as well as to perform ion implantation with an in situ system including a mass spectrometer. This advanced implantation system can be employed in novel applications, including the production of a variety of new materials such as metals, polymers, and ceramics and the irradiation testing and fabrication of structural and functional materials to be used in future nuclear fusion reactors. In this investigation, the first nitrogen ion implantation experiments were conducted using the new system. The 28 GHz ECRIS implanted low-energy, multi-charged nitrogen ions into copper, zinc, and cobalt substrates, and the ion implantation depth profiles were obtained. SRIM 2013 code was used to calculate the profiles under identical conditions, and the experimental and simulation results are presented and compared in this report. The depths and ranges of the ion distributions in the experimental and simulation results agree closely and demonstrate that the new system will enable the treatment of various substrates for advanced materials research.

First results of 28 GHz superconducting electron cyclotron resonance ion source for KBSI accelerator.

The 28 GHz superconducting electron cyclotron resonance (ECR) ion source has been developed to produce a high current heavy ion for the linear accelerator at KBSI (Korea Basic Science Institute). The objective of this study is to generate fast neutrons with a proton target via a p(Li,n)Be reaction. The design and fabrication of the essential components of the ECR ion source, which include a superconducting magnet with a liquid helium re-condensed cryostat and a 10 kW high-power microwave, were completed. The waveguide components were connected with a plasma chamber including a gas supply system. The plasma chamber was inserted into the warm bore of the superconducting magnet. A high voltage system was also installed for the ion beam extraction. After the installation of the ECR ion source, we reported the results for ECR plasma ignition at ECRIS 2014 in Russia. Following plasma ignition, we successfully extracted multi-charged ions and obtained the first results in terms of ion beam spectra from various species. This was verified by a beam diagnostic system for a low energy beam transport system. In this article, we present the first results and report on the current status of the KBSI accelerator project.

Surface Treatment of a Titanium Implant using a low Temperature Atmospheric Pressure Plasma Jet

The surface treatment of a titanium implant is investigated with a non-thermal atmospheric pressure plasma jet. The plasma jet is generated by the injection of He and O2 gas mixture with a sinusoidal driving voltage of 3 kV or more and with a driving frequency of 20 kHz. The generated plasma plume has a length up to 35 mm from the jet outlet. The wettability of 4 different titanium surfaces with plasma treatments was measured by the contact angle analysis. The water contact angles were significantly reduced especially for O2/He mixture plasma, which was explained with the optical emission spectroscopy. Consequently, plasma treatment enhances wettability of the titanium surface significantly within the operation time of tens of seconds, which is practically helpful for tooth implantation.

Recondensation performance of liquid helium cryostat for a 28 GHz electron cyclotron resonance ion sourcea)

Cryostat performance is essential for the stable operation of a superconducting magnet. A closed-cycle liquid helium cryostat was adopted for use for a superconducting electron cyclotron resonance (ECR) ion source by recondensing liquid helium vapor. The goal was to maintain the liquid helium filled reservoir at a constant level without transferring any liquid helium during the normal operation of the ECR ion source. To accomplish this, Gifford-McMahon (GM) refrigerators, which have two cold heads, were installed on the top of the cryostat. The cooling power of the GM cryocooler is 1.5 W at the second stage and 50 W at the first stage. Each stage was connected to the liquid helium reservoir, a radiation shield including high-Tc current lead, and related items. Before commissioning the ECR ion source, a preliminary evaluation of the recondensation performance was carried out with the magnet in partial operation. The design of the cryostat, its fabrication, and the experimental results are reported.

Magnetic lens effect using Gd-Ba-Cu-O bulk superconductor in very high magnetic field

We investigate the performance of a magnetic lens in very high magnetic fields exceeding 24 T. The magnetic lens is composed of Gd-Ba-Cu-O superconducting bulk materials. The unique configuration of the magnetic field amplifier, which consists of slits and electrical insulation in the bulk, allows the magnetic flux density to be further enhanced by a background magnet. In field cooling operation, the external magnetic field was varied ∼4 T from 24.2 to 28.3 T and a total magnetic flux density of 30.35 T was found at the center of the device with a background magnet. The magnetic lens additionally increased the magnetic flux density by 2.05 T due to the lens effect. However, it was also observed that the bulk was partially quenched when the external field was varied. This partial quench and recovery of the bulk magnet is considered to be one factor that limits the performance of the lens effect. Finally, we are able to generate a substantial magnetic flux density of 2 T under very high magnetic field becau...