Papers by Author: Thiraphat Vilaithong

Abstract: Hardness and wear resistance of thermal-sprayed coatings of titanium containing 0, 3, 5 and 10 wt% bond coat (Ni5Al5Mo) were improved by 1200 K nitridation in 5, 10 and 15 ml.s-1 ammonia for 5 h. The improvement was due to the formation of TiN and Ti2N and governed by the ammonia flow rates and the percentage of bond coat. In addition, the coatings were analysed using a scanning electron microscope to determine the distribution of phases and cavities.

Abstract: Diamond-like carbon (DLC) films were deposited on stainless steel disc substrates by plasma immersion ion implantation and deposition (PIII&D) technique. Ar, CH4 and C2H2 gas were used as the working gases and discharged by radio frequency at 13.56 MHz. During the implantation and deposition process the plasma discharge was monitored by optical emission spectroscopy in order to analyze the state of the chemical species presented in the plasma. Ion implantation (Vbias = -20 kV and –10 kV) process served to produce a graded interface between the DLC films and the substrate material. Deposition (Vbias = -5 kV) process using a gas mixture of C2H2/Ar with a ratio of 1:1. The structure information of the DLC films was evaluated by Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR). The composition of the DLC films and the thickness was measured by Rutherford backscattering spectrometry (RBS). The tribological properties were analyzed using a pin-on-disk tribometer and a microhardness tester, respectively. It was found that the DLC film was 0.8 μm thick with a hardness of 2.54 GPa and had good friction properties. Raman spectra appeared as G-band and D-band centered at 1550 cm-1 and 1418 cm-1, respectively. FTIR analysis observed the sp3 C=H2 asymmetric and sp2 C=C bond at 2928.73 cm-1 and 1667.10 cm-1 peak.

Abstract: At 150 kV-pulsed neutron generator at the Fast Neutron Researh Facility is being upgraded to produce a 280-kV-pulsed-He beam for Time-of-Flight Rutherford Backscattering Spectrometry (TOF RBS). Modification are being done by replacing the existing beamline elements by a 400-kV accelerating tube, 45o-double focusing dipole magnet and quadrupole lens. The beam transport system has to be redesigned based on the new elements. The important part of a good pulsed beam depends on the pulsing system. The two main parts are the chopper and buncher. Radiofrequency (RF) of 2 MHz is used for the chopper and 4 MHz for the buncher. For the buncher the RF amplitude of 13 kV is applied to two gaps, so that the ion pulse is compressed twice. An optimized geometry for the 280-keV pulsed helium ion beam is presented in this paper,. The PARMELA code has been used to optimize the space-charge effect, resulting in a excitated pulse width of less than 2 ns at a target. The calculated distance from a buncher to the target is 4.6 m. Effects of energy spread and phase angle between the chopper and buncher have been included in the optimization of the bunch lengh.

Abstract: The interaction between ion beam and biological cells has been studied to apply ionbeam- induced mutation to breeding of crops and gene transfer in cells. Formation of micro-craters has been observed after ion bombardment of plant cells and they are suspected to act as pathways for exogenous macromolecule transfer in the cells. A technique of in-situ atomic force microscopy (AFM) in the ion beam line is being developed to observe ion bombardment effects on cell surface morphology during ion bombardment. A commercial AFM is designed to place inside the target chamber of the bioengineering ion beam line at Chiang Mai University. In order to allow the ion beam to properly bombard the sample without the risk of damaging the scanning tip and affecting normal operation of AFM, geometrical factors have been calculated for tilting the AFM with 35 degree from the normal. In order to avoid vibrations from external sources, mechanical designs have been done for a vibration isolation system. Construction and installation of the in-situ AFM facility to the beam line have been completed and are reported in details.

Abstract: A 13.56 MHz radio-frequency (rf) driven multicusp ion source has been constructed [1] to produce a high argon ion current density. Milliampere-range argon ion current can be extracted from the source. An in-waveguide microwave plasma source has been utilized as the ion beam neutralizer [2]. The neutralization source was placed 20 cm downstream from the extraction system. With the former extraction system, comprised of extraction electrodes and an Einzel lens, the electrons from the neutralizer were attracted to the high positive potential of the lens. Consequently, the potential of the lens drops and the beam is diverged. To suppress electrons from being accelerated to the Einzel lens a negatively biased electrode was placed before the last electrode, which is grounded, to produce a retarding electric field for electrons. The hole of the electrode was made small to make sure that the potential at the center is negative enough to suppress electrons. All simulations have been performed with the KOBRA3-INP simulation software. The results of the beam shape from the simulation will be presented.

Abstract: The SURIYA project is designed to generate femtosecond (fs) electron pulses at the Fast Neutron Research Facility (FNRF), Thailand. The fs electron pulses production system consists mainly of a thermionic cathode RF-gun, a magnetic bunch compressor in form of an alpha magnet (α-magnet), a linear accelerator (linac), a beam transport line, and various electron beam diagnostic instruments. This system aims to produce a 20-25 MeV electron beam with micropulses of less than 100 fs in length. Theses pulses can be used either for direct experimentation or to produce fs pulses of intense coherent far infrared radiation (FIR) and/or x-ray. In this paper, an overview of the system and characteristics of its major components will be presented.

Abstract: Femtosecond electron bunches can be generated from a system consisting of an RF gun with a thermionic cathode, an alpha magnet, and a linear accelerator and can be used to produce femtosecond (fs) electromagnetic radiation pulses. At the Fast Neutron Research Facility (FNRF), Thailand, we are especially interested in production in Far-infrared (FIR) and x-radiation. In the far-infrared, radiation is emitted coherently for wavelengths which are longer than the electron bunch length, yielding intense radiation. Although, the x-rays emitted are incoherent, its femtosecond time scale is crucial for development of a femtosecond x-ray source.