M.H. Cho

Design study on standing-wave linear accelerator

A compact standing-wave linac has been designed using S-band microwaves for medical and industrial applications. It uses a bi-periodic structure with constant impedance. It consists of a buncher section with three-cells and on-axis coupled cavities with nine-cells. The total length is 740.0 mm including the electron gun. Using SUPERFISH, HFSS and PARMELA codes, it is capable to deliver 4.5 MeV electron beams with pulsed microwaves of 4.8 MW at 2,856 MHz. In this paper, we present the detailed design studies on a compact S-band standing-wave linac.

Pulsed plasma process for the flue gas removal from the industrial incinerator using peak 200-kV, 10-kA pulse modulator

The electrical discharge process, especially the pulsed plasma discharge process can be applied to the removal of pollutant gases from industrial plants such as power generation plants and incinerators. Up to now, most of the study has been performed in a laboratory scale with short-term tests due to the lack of a reliable pulse modulator with a high average power. The pulsed corona discharge method shows encouraging results for the removal of NOx and SO2 gases based on smallscale experiments. A 120-kW high average power modulator for industrial applications of the pulsed corona process to remove flue gas has been designed and manufactured. It is one of the largest scale modulator systems in the world for treating NOx and SO2 simultaneously. Its design specifications are as follows: an average power of 120 kW, a peak voltage of 200 kV with a full width at half maximum (FWHM) of 500 nsec, a peak current of 10 kA, and a pulse repetition rate of 300 Hz. It is required to have long lifetime and high reliability for commercial plant application because the downtime for maintenance affects plant availability. A high-power, fast semiconductor switch, a magnetic-pulse-compression (MPC) switch, and a fast-pulse transformer are essential components to meet these requirements. The 120-kW high average power modulator has been installed and tested at an industrial incinerator plant with a gas flow of 50,000 Nm/Hr. This modulator was operated with pulses of up to 150 kV with 500-nsec (FWHM) pulse widths at a 240-Hz repetition rate in a plasma reactor. This paper presents the design details and operational test results. Especially, the dynamic operating characteristics of the MPC modulator combined with the non-thermal plasma reactor were measured, and the SO2 and NOx removal characteristics were analyzed.

Development of 2.45 GHz waveguide-based air torch system

Summary form only given, as follows. We developed a waveguide air torch system using a 2.45 GHz magnetron. This torch system is designed for the decomposition of toxic gases, such as fluoro-carbon or chlorocarbon gases. The microwave torch system is consisted of a magnetron tube, an isolator, a directional coupler, a 3-stub tuner, an E-plane tapered section, and the torch region where a quartz tube and a nozzle are located. The magnetron generates a maximum RF-power of 15 kW. The plasma is initiated by touching the nozzle tip with a grounded metal piece. A plasma flame is formed at the the tip of the nozzle with varying size following the air stream from the tip of the nozzle. Due to the high collision rate with the surrounding air, the plasma flame appears the same as a flame from a gas burning torch.

Investigation of γ-multiplicity spectra and neutron capture cross-sections of 232Th in the energy region 21.5–215 eV

Abstract Applying multiplicity spectrometry and using 238 U as the reference sample, the coincidence multiplicity spectra and the radiative capture cross-sections of 232 Th were measured for the energy range 21.5–215 eV. The gamma rays originating from neutron capture were detected by 16 sections of liquid scintillator, where the coincidence multiplicity ranged from 1 to 16. It seems that the γ-multiplicity spectra of the s resonances of 232 Th in the above energy region are almost identical. The radiative capture cross-sections were determined for each s resonance and for the three energy groups 21.5–46.5, 46.5–100 and 100–215 eV. Our group average cross-sections agree well with the values calculated with the resonance parameters given in the evaluated data libraries ENDF/B-VI, JENDL-3 and BROND-2.

Surface resistivity modification of polyimide film by plasma source ion implantation

Summary form only given. Plasma source ion implantation (PSII) is a very useful technique in modifying characteristics of the material surfaces. We used a modified PSII process in which repetitive high voltage pulses were applied to grids placed far outside of the sheath region. It was formed at the surface of the polyimide immersed in the plasma. The mechanism of the ion acceleration in the modified PSII system was investigated by the simulation using the XOOPIC program. After the surface treatment using the modified PSII process with the inductive coupled plasma, the surface resistivity of polyimide was decreased from 1016 ohm/square to the range of 106 ~ 109 ohm/square. Polyimide was modified to improve the surface electrical conductivity in the energy range of 5 ~ 30 kV. The TEM analysis showed that the MPSII treatment with -30 kV pulse changed the structure of the polyimide to a depth of 90 nm. We present the modified PSII system and the surface resistivity dependency by the pulse shape and treatment time.

Development of high voltage pulse modulator for plasma source ion implantation

High voltage pulse modulator of hard tube type has been developed for plasma source ion implantation (PSII). In this modulator, the crowbar switch is required for the excellent performance of PSII process which is different from conventional PSII. In order to reduce the falling time of pulse, the crowbar switch is used to PSII system. The arc response time for steady operation was designed with 500 ns. The current capacity is 120 A during the pulse at an output voltage of 60 kV. The total pulse length is varied from 3 to 12 us under a maximum repetition rate is 2 kHz. The maximum pulse duty is 0.012. The average power is 40 kW. In this article, we introduce the various type of modulator for PSII and show the performance of the developed modulator.

Localized elecron cyclotron resonance plasma source for hyperthermal neutral beam

Summary form only given. Hyperthermal neutral beams (HNB) have a great potential for semiconductor processes, especially, for etchings and thin film depositions for semiconductor and display fabrications as well as depositions for various thin film applications. Thermal and plasma-induced damages are serious problems for manufacturing deep submicron semiconductor devices and are also expected to be problems for future nanoscale devices. These problems can be overcome by damage-free and low-temperature processes with hyperthermal neutral beams. The HNB process is especially applicable to various thin film growings: oxidation and nitridation for gate insulators of DRAMs and flash memories, transparent conductive oxide films on organic light emitting diodes (OLEDs) or flexible displays, Si thin films for solar cells and thin film transistors (TFT), and crystal thin film growing for optoelectronic devices such as light emitting diodes (LEDs). The HNB can be produced by neutralization of ion beams extracted from an ion sources. However, the flux of the ion beams at a hyperthermal energy range is much lower than required in industrial applications due to the space charge effect. So, in order to obtain a high flux particle beam at a hyperthermal energy range, the ion beams should be neutralized before extracted from a plasma source. The plasma required for a high flux HNB sources should be operated at a lower pressure than 1 mTorr in order to reduce the HNB loss due to collisions with the background gas. The plasmas should also be so thin that the HNB cannot be lost by reionization during passing through the plasmas. We have developed a localized ECR plasma source with a racetrack magnetic field configuration in order to produce a high flux HNB. The operating pressure is 0.3 mTorr and the plasma thickness is less than 25 mm. The plasma is mainly characterized by the line ratio method of the optical emission spectroscopy (OES).

Cold test of compact C-band standing-wave accelerating structures

We designed and fabricated a C-band standing-wave accelerating structure for a compact industrial electron accelerator. It is capable of producing 4-MeV electron beams with 50-mA pulsed beam current. As an RF source, we use a 5-GHz magnetron with 1.5-MW peak power and 0.08% duty factor. This structure is bi-periodic and operated with the pi/2-mode standing-waves. It is on-axis coupled with magnetic coupling slots on the side wall. Each cavity in the bunching and the normal cells is designed by using the MWS code. The coupler cell is designed by using the Omega3p code for determining the resonant frequency and the external Q2. With the measurement of the aluminum prototype cavities, we determined the final dimensions for actual OFHC-copper cavity. In this paper, we present the low-power measurement results for the actual column: the pi/2-mode resonant frequency, the coupling coefficient, and distribution of the field strength.

Commissioning of L-band intense electron linac for industrial applications

An intense L-band electron linear accelerator is under construction at CESC (Cheorwon Electron-beam Service Center) for industrial applications. It is capable of producing 10-MeV electron beams with 30-kW average beam power. For high-power capability, we adopted 1.3 GHz, and the RF source is a 25-MW pulsed klystron with 60-kW average RF output power. The PFN-type modulator and the matched transformer provide 264-kV beam voltage with 230-A beam current to the klystron. The RF pulse length is 7 mus, and the repetition rate is 350 Hz. The thermionic E-gun generates 80-kV electron beams with pulsed 1.6 A. The pre-buncher, a single standing-wave cavity, is used before the bunching section, which is built-in with the regular accelerating section. The accelerating structure is a disk-loaded waveguide with a constant-impedance operated in the 2pi/3-mode. It is to be operated under the fully beam-loaded condition, where the beam power is maximum. The electron beams are accelerated within 6 mus since the traveling-wave filling time of the accelerating structure is almost 0.8 mus. In this paper, we present details of the accelerator system and commissioning results.

Particle-in-cell simulation on power coupling of grill for KSTAR 5.0-GHz LHCD launcher

Summary form only given, as follows. The 5.0-GHz, 2.0-MW KSTAR Lower-Hybrid Current Drive (LHCD) system is under design for the steady-state operations of the KSTAR tokamak. The launcher structure is designed as a grill-type which provides asymmetric power spectra. The KSTAR tokamak plasma is high-density and high-temperature plasma. The power coupling to the KSTAR plasma edge depends on the impedance matching between the grill assembly and the LH wave in the edge plasma. And it depends on the edge density and the phase difference between guidelets. For the coupling calculation, the Brambilla coupling code uses equations derived from wave equations in the waveguide and the plasma with a linear density gradient. The power coupling efficiencies are also investigated using the Particle-in-Cell code called XOOPIC-2D. This paper describes the preliminary result of the LH power coupling calculation using the Brambilla coupling code and XOOPIC-2D code simulation.