E.H. Choi

Pulsewidth and rising time of relativistic electron beam in gas-filled diode

The pulsewidth and rising time of a mildly relativistic electron beam (300 kV, 1-3 kA) passing through a gas-filled diode region are investigated experimentally under various gas pressures P. The pulsewidth and rising time of a relativistic electron beam (REB) were controlled by adjusting the gas pressures P of the diode region. The pulsewidth and rising time of the relativistic electron beam are experimentally found to scale as P/sup -0.807/spl plusmn/0.054/ and P/sup -0.770/spl plusmn/0.058/, respectively. The REB pulsewidth and rising time are shown to have the same scaling law, within the experimental error range as a function of pressure. In particular, the empirical scaling law of the REB pulsewidth is in remarkably good agreement with the numerical scaling law P/sup -0.809/spl plusmn/0.059/ of the full-space charge neutralization time t/sub n/ at which the ion density n/sub i/ is just equal to the electron beam density n/sub b/ at the diode region under a given gas pressure P. It also is found that ion density n/sub i/ at the full space-charge neutralization time t/sub n/ has quite a similar profile in terms of pressure P to that of the REB peak current detected by a Faraday cup.

A submillimeter Raman free-electron laser in a dense plasma background

Growth characteristics of a Raman free-electron laser in a dense plasma background are investigated. The background plasma is beneficial in the sense that it allows a beam current over the vacuum space-charge limit. It is found, however, that an excessive plasma density reduces the linear growth rate significantly if the radiation mode is not confined well inside the electron beam. The growth rate reduction accompanies a large positive frequency shift of the radiation field. This indicates that the background plasma causes the optical beam to expand outward farther into the plasma.

Influence of auxiliary discharges on a multi-lamps backlight for large area LCD TVs

Summary form only given, as follows. In this study a new model is presented for a direct lighting backlight arrayed with multi-lamps of the cold cathode fluorescent lamps (CCFLs) and the external electrode fluorescent lamps (EEFLs). Avoiding the non-uniformity of luminance and the high voltage operation in a conventional direct lighting backlight driven by a single inverter power system for large area panels of LCD TVs, the auxiliary electrodes are placed under the reflection sheet in the backlight, of new model These electrodes lead to an auxiliary discharge at the center of the tube and also sustain the uniform field strength along the discharge tube inside of the longitudinal direction. These auxiliary discharges provide the luminance uniformity in each lamps and the low driving voltage.

Measurement of electron temperature and plasma density in coplanar AC plasma display panels

The electron temperature and plasma density in coplanar alternating-current plasma display panels (AC-PDPs) have been experimentally investigated by a micro Langmuir probe and the high speed discharge images in this experiment. It is noted in this experiment that the electron temperature obtained from both the micro Langmuir probe and high speed ICCD camera decreases from 2.5 eV to 1.2 eV as the filling Ne+Xe gas pressure increases from 150 Torr to 350 Torr. It is noted that these electron temperatures are in good agreement with each other within 5% error limit. The plasma density at the lateral distance of 125 /spl mu/m away from the center of sustaining electrode gap has been found to be saturated from 0.73/spl middot/10/sup 11/ cm/sup -3/ to 7.54/spl middot/10/sup 11/ cm/sup -3/ at the Ne+Xe filling pressures ranged from 150 Torr to 350 Torr.

Measurement of ion-induced secondary electron emission coefficient for MgO thin film with plasma treatment

The characteristics of MgO protective layers are very important for the development of recent AC-type plasma display panel (AC-PDP). The ion-induced secondary electron emission coefficient /spl gamma/ is one of the characteristics of the MgO protective layer which correlates to the ignition voltage of AC-PDPs. Recently many researchers have been studying to get the highest /spl gamma/. Therefore we selected the method of oxygen (O/sub 2/, Ar, H/sub 2/) plasma treatment for MgO protective layer. In this research, We used two steps of MgO protected layer growing method to get higher quality of it First MgO thin films were prepared by using electron beam evaporation method from sintered materials. And then they were treated by O/sub 2/, Ar and H/sub 2/ plasma by using RF-plasma generation system. And secondary electron emission coefficient obtained for MgO protective layers deposited from sintered material with O/sub 2/ plasma treatment by 5, 10, minutes and without plasma treatment, respectively. The ion-induced secondary electron emission coefficient /spl gamma/ of MgO protective layer was measured by /spl gamma/-FIB (focused ion beam) system throughout this experiment to investigate the influence of these plasma treatments on it. The energy of Ne/sup +/ ions used has been ranged from 100 eV 10 200 eV throughout this experiment.

Electro-optical characteristics in accordance with dielectric thickness of AC-PDP

Summary form only given, as follows. The improvement of luminance and luminous efficiency is the one of the most important part in AC-PDP. To achieve high luminance and luminous efficiency, we make an experiment on electro-optical characteristics in accordance with the dielectric thickness of AC-PDP. The wall voltages play an important role in lowering the sustaining voltage through wall charges accumulated on the dielectric surface in AC-PDP. The wall charges and voltages, as well as capacitances, are experimentally measured in terms of the dielectric thickness, whose thickness is ranged from 20 /spl mu/m to 50 /spl mu/m. We have developed a simple method to measure the wall charges and voltages resulting from the measurements of all capacitances in AC-PDP. These values are based on charge-voltage (Q-V) characteristic curves before and after the discharge, along with the voltage margin relation to the wall voltage and dielectric-gap voltage induced by wall charge. To find out optimal condition of dielectric thickness in AC-PDP, we make an experiment in the variety of dielectric layer thickness.

Determination of the work function of the Co thin films by using /spl gamma/-FIB system

Summary form only given, as follows. Summary form only given. The physical properties of the metal-semiconductor heterointerfaces have received much attention for many years because of a desire to develop fabrication technology for high-speed electron devices. Recently, the growth of magnetic thin films on compound semiconductor substrates has been particularly attractive from both the scientific and the technological points of view in connection with spintronics. Investigations of the secondary electron emission coefficient /spl gamma/ and the work function of Co thin films grown on GaAs substrate are very important for understanding the electronic properties of the Co/GaAs heterostructures. Co thin films on the GaAs(100) substrates were grown at room temperature by using the ion beam-assisted deposition. The secondary electron emission coefficient /spl gamma/ measurements were carried out using a home made /spl gamma/-Focused Ion Beam system, and the He, Ne, Ar, Xe gases used as ion sources. The work function of the Co thin films can be determined from the dependences of the /spl gamma/ values on the type of incident ion and on the acceleration voltage by using Auger neutralization theory. These results provide important information on the electronic properties of Co thin films grown on GaAs(100) substrates at room temperature.

New-shaped electrode for AC-PDP for enhancement of luminous efficiency in AC-PDP

Summary form only given, as follows. AC-plasma display panel (AC-PDP) is using gas discharge display device which has great potential as a flat display with large display area and high brightness. Because of their high picture quality, light weight, and large screen size, these are now attracting considerable attention in digital broadcasting for use in suitable TV monitors. However, the present-day PDP with a luminous efficiency of typically about 1.0 lm/w is low in comparison with a CRT (5 lm/w) and limits the brightness. Improvement of the luminous efficiency is, therefore, a key factor to obtain a better panel performance. In this research, in order to increase the luminous efficiency of PDP, three new types of AC-PDP cells have been proposed and investigated. New-shaped types of electrodes were developed for high luminance coplanar type AC-PDP. The new-shaped type electrodes had been 3 types in one cell, A, B, and conventional type, respectively. The new-shaped type electrodes that have been developed have a lower breakdown voltage than the conventional type electrode at normal pressure. Also, the luminance efficiency is improved by about 20% at the same firing voltage. This result means that the currents are limited by characteristics of the new-type electrode.

Measurement of ion induced secondary electron emission coefficient (/spl gamma/) and work function of vacuum annealed MgO protective layer in AC PDP

MgO films as the protective layer in AC-PDPs has been annealed here under vacuum environment in order to eliminate absorbed material onto the MgO layer. Vacuum annealed can be one of the most important processes for forming long-lived panel. It is of great important to investigate the influence of vacuum annealed on the ion-induced secondary electron emission coefficient(/spl gamma/) from a MgO protective layer. In this research, /spl gamma/ and work-function of the vacuum annealed MgO films has been investigated by /spl gamma/-FIB(focused ion beam) system. Also the characteristics of /spl gamma/ and work-function for as-deposited and vacuum annealed MgO films have been investigated and compared with each other throughout this research. The MgO protective layer is deposited on the dielectric layer by electron beam evaporation at deposition rates of approximately 5/spl sim/10 /spl Aring//s in a vacuum of about 1.1/spl times/10/sup -6/ Torr. The thickness of MgO layer is about 5000 /spl Aring/. The deposited MgO films have been vacuum annealed at 300/spl deg/C for 15 minutes. Also some of the as-deposited MgO films and Vacuum annealed MgO films have been air-hold by 24-hours in this experiment. The /spl gamma/ and work-function characteristics for these two MgO films have been measured by /spl gamma/-FIB system and compared with each other throughout this experiment.

Initial microwave generation from the vircator system with various anode-cathode (A-K) gap distances

Summary form only given, as follows. The microwave output of vircator system has been shown to be dependent especially on diode anode-cathode (A-K) gap distance. The initial microwave generation time is delayed when the A-K gap distance has been increased from 2 to 8 mm in this experiment, and also it is shown that the central microwave frequency f is inversely scaled as the A-K gap distance. When the electron beam is generated from the cathode, the electrode sheath plasma is also generated just after the peak diode voltage on the electrodes, hence the perveance of diode is being varied to change the diode output characteristics at this moment. In our pulsed power system chundoong, the perveance characteristics had been experimentally investigated, from which the sheath plasma expansion speed could be found to be about 3 cm//spl mu/s inside the diode. It could be shown in this experiment that the microwave output power becomes to be maximum when the effective A-K gap distance due to the sheath plasma expansion becomes to be around 3 mm from the initial-set A-K gap distances. It means that there might be threshold effective A-K gap condition, at which the maximum microwave power could be achieved by virtual cathode oscillator formed by the injected electron beam current exceeding the space charge limited current.