Kang-ok Lee

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.

Single pass acceleration experiment using coaxial cavity

The high power electron accelerator (FANTRON-I) for industrial applications is under development at Physico-technology laboratory, KAPRA (Korea Accelerator and Plasma Research Association). To validate the acceleration scheme, single pass acceleration experimental setup using nonagon shape coaxial cavity has been installed. The experimental setup consists of an electron gun, coaxial cavity, bending magnet, beam diagnostic and dump chamber, RF amplifier, vacuum and cooling system. A Rogowiski type gun with Th-W wire filament was used as an electron gun and produced 20 kV, 0.8 mA electron beam. A 159.41 MHz, 3 kW RF system consists of an oscillator, 100 W solid state amplifier and 3 kW tetrode amplifier. The bending magnet composed of main and supplementary magnet for weak focusing was designed, fabricated and tested. In this paper, the test results of the acceleration system components using nonagon shape coaxial cavity are analyzed and the design status of FANTRON-I are presented.

Design, study on the rf source for KOMAC

A study on the design of 700 MHz, 1 MW CW klystron amplifier for KOMAC (KOrea Multipurpose Accelerator Complex) proton accelerator has been carried out by KAPRA (Korea Accelerator and Plasma Research Association). A triode type electron gun including a modulating anode, six cavities including one second harmonic cavity and electromagnet for electron beam focusing were designed to produce desired output rf power. Thermal analysis at the collector according to the magnetic field profile near the collector side pole face was performed to efficiently cool the heat generated through the kinetic energy loss of the electron beam. In addition to the design study, an operation experiment of the klystron for broadcasting whose output power was 15 kW and frequency range 574 - 698 MHz was performed at 700 MHz. In this paper, the results of the design study and the operation experiment of the klystron for broadcasting at 700 MHz are presented.

RaD Status of the 700 MHz, 1MW Klystron for PEFP

KAPRA (Korea Accelerator and Plasma Research Association) are undertaking the first phase R&D for the 1 MW, CW 700 MHz klystron, which is targeting the future stage of the PEFP (Proton Engineering Frontier Project) accelerator at KAERI (Korea Atomic Energy Research Institute). The objectives of the first phase R&D are 1) setting up infra structures/procedures for the design and fabrication, 2) developing a prototype klystron for proofs of principles, and 3) making a performance test of the prototype at a reduced duty. The second phase R&D is supposed to cover full power, CW operation and reliability issues. In this paper, a summary of the R&D status during the first phase for PEFP 1 MW, 700 MHz klystron is reported.

Suppression of Initial Energy Spreads in Electron Radio Frequency Linacs for Intense Irradiation Applications

RF linacs for high-power beams are operated under the fully beam-loaded condition for power efficiency. Under this condition, initial energy spreads are generated by the transient beam-loading effect. Irradiation sources require a beam energy of less than 10 MeV for radiation safety. In order to maximize the beam power and maintain the beam energy at a safe level, we need to suppress the initial energy spreads. In an L-band traveling-wave linac for irradiation applications, the initial high-energy electrons are suppressed by beam current modulation with RF power modulation. In this study, the temporal profile of beam energy is calculated by a numerical method and verified by measurement. As a result, the average beam energy and the corresponding beam power are improved by nearly 60% compared with the case without any modulations. The effect of beam current modulation on bunching and acceleration is also discussed in this paper.

Cellulose modification study by e-beam irradiation & its applications

Fossil fuel reserves would be exhausted at the current rate of consumption in the near future. So an alternative renewable energy technique for producing alcohol by fermenting an alcohol spawn of grain has been developed in many countries. Cellulose is not easy to hydrolyze and lignin and hemi-cellulose are bad in accessibility, a manufacturing process is lengthy and not efficient. Therefore there is an urgent need for a manufacturing process that mass production is possible. Three kinds of industrial electron accelerators (400keV 12mA Cockcraft Walton type, 2MeV 50mA ELV type, and lOMeV 3mA Linac Type) and its irradiation facilities including shielding blocks have been designed, fabricated and under construction by the KAPRA (Korea Accelerator and Plasma Research Association). In this paper, we report cellulose modification study for producing biofuel using electron beam irradiation and its applications.

Measurement of edge plasma parameters in KT-1 tokamak by single/Mach probes

Summary form only given, as follows. A combined system of a single probe and a Mach probe is used for the simultaneous measurement of electron temperature, plasma density, floating potential and flow velocity from edge plasma in a KT-1 small tokamak (R:27 cm a:5 cm) during Ohmic discharges. Typical values of electron temperature, plasma density, and floating potential by a single probe are 19/spl sim/22 eV, /spl sim/3/spl times/10/sup 11/ cm/sup -3/, and -14/spl sim/-22 volts, respectively, for most discharges. A Mach probe has been used for the measurement of toroidal flow velocity, plasma density, and directional electron temperatures. The big difference of parallel and antiparallel electron temperatures indicates the asymmetry of the electron behavior around the plasma facing components (PFC).