Hyung Dal Park

Control of magneto-transport characteristics of Co-doped ZnO by electron beam irradiation

Electron beam irradiation can be used to modify the physical properties of materials, but its effects have never been studied in Co-doped ZnO (ZnCoO), a promising magnetic semiconductor material. Here, we demonstrate that electron beam irradiation enables modification of the magneto-transport properties of ZnCoO. The electron beam irradiation cannot affect the electrical and magnetic properties of ZnCoO significantly, due to the insulating nature of pristine ZnCoO showing paramagnetic behavior. However, intentional hydrogen doping increases carrier concentration and induces ferromagnetism in ZnCoO, which allows ZnCoO to be affected by electron beam irradiation. As a consequence of s–d exchange interaction, hydrogen-doped ZnCoO shows positive magnetoresistance and anomalous Hall conductivity. Electron beam irradiation reduced the carrier concentration in hydrogen-doped ZnCoO by removing shallow donor-type hydrogen and consequently increasing s–d exchange interaction, which resulted in an increase in positive magnetoresistance and a decrease in the anomalous Hall conductivity. These findings demonstrate the novel applicability of electron beam irradiation for tailoring the physical properties of ZnO-based materials.

Beam dynamics in 10 MeV S-band LINAC for Container Inspection System

The Beam dynamics of S-band 10 MeV electron LINAC for Container Inspection System (CIS) was carried out with beam dynamics code E-GUN[1] and PARMELA[2]. This S-band LINAC is consists of DC-gun injector, side-coupled accelerating structure, waveguide power coupler, klystron with modulator, vacuum device, water cooling and control system. The DC-gun is produce 20 kV electron beam with 0.5 A beam current and 4.9 mm-mrad emittance. The accelerating structure consists of bunching section and accelerating section. The bunching section consists of one pre-bunching cell with β=0.50.65 and one bunching cell with β=0.7-0.9. The accelerating section consists of 10 accelerating cells with β=1 respectively. In addition to this, the side coupled cavities are also involved, it provides a 3% coupling coefficient from cell to cell coupling. A taped waveguide power coupler is used to provide RF power for exciting π/2 mode of the structure. In order to reduce electron beam size and increase electron capture coefficient, a solenoid is placed ahead the accelerating structure to generate axial magnetic field for beam focus. The 10 MeV beam energy with 1 kW beam average power has a beam size less than 5 mm, 30 πmm-mrad normalized emittance with the energy spread less than 5%. The operation radiofrequency and macro-pulse duration are set to 2856 MHz and 4 us, respectively. The designed beam peak current and average current are 125 mA and 0.1 mA.

Computer simulation of the cavity geometry for a S-band side coupled cavity

In recent year, the computer codes for solving 3-D full-wave electromagnetic field, for example CST (microwave studio) or HFSS (high frequency structure simulation), just have enough accurate to used for the multi-cavities accelerating structure design, such as dispersion relation, cavity geometry, et.al.. Before that, the geometry design was just based on analytical expression, experimental trial test and designers experience. Due to non-linearity and complication, it is very difficult to determine the geometry of cavities or structure without computer simulation code. This paper technically describes the calculation method of the cavity geometry by CST code[1].

Dual-energy driving method for S-band Interlaced Electron LINAC

An interlaced dual-energy electron LINAC was developed for cargo inspection systems. The electron energy is varied based on the RF power level and initial current of the E-gun. This paper describes a dual-energy driving method for an interlaced dual-energy electron LINAC using variable applied levels of the E-gun dual-pulse power supply, a high voltage modulator, and a dual RF power source. The electron energy is controlled using dual RF power based on the voltages of the electron gun and RF power source. Consequently, we can control the variable electron energy from about 5 MeV to 9 MeV in our designed S-band RF LINAC system.

Design of the DC gun for S-band Electron LINAC

A DC gun for the dual-energy S-band electron Linear Accelerator (LINAC) was designed for the Cargo Inspection System (CIS) at the Korea Atomic Energy Research Institute (KAERI). The main design factors affect the accelerating performance, and provide experiences and design references in a further optimization of the structure. This design is a beam energy of 20 keV, beam current of 0.5 A, working distance of 50 mm, beam radius of 0.5 mm at the working distance, current density on the surface of the cathode of less than 2 A/cm2, energy spread of <;2%, and normalized emittance of εn<; 10 π mm mrad.