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Lee, Paul Choon Keat
- PublicationOpen AccessDesign of a pixelated imaging system for fast neutron sources(MDPI, 2019)
;Chatzakis, John ;Rigakis, Iraklis ;Syed Hassan ;Clark , Eugene Laurence; Tatarakis , MichaelImaging detectors that use X-ray radiation and pulsed neutron sources have increased in sophistication in recent years due to the use of solid-state detectors. A key method for neutron detection is the nuclear activation of materials by neutrons. Neutron activation can generate radionuclides whose decay produces secondary particle emission that can be detected without interference from the X-rays and other prompt radiation sources and offers advantages over neutrons detection using scintillators. In this paper, we present the design of an imaging system for fast neutron sources. The imaging system utilizes a microcontroller network that communicates using a modified SPI protocol. This network communicates with an interface unit and passes an image to a personal computer. A computer program has been developed to reconstruct the image.102 125 - PublicationOpen AccessComputing plasma focus pinch current from total current measurement(American Institute of Physics, 2008)
;Lee, Sing ;Saw, Sor Heoh; ; Schmidt, H.The total current Itotal waveform in a plasma focus discharge is the most commonly measured quantity, contrasting with the difficult measurement of Ipinch. However, yield laws should be scaled to focus pinch current Ipinch rather than the peak Itotal. This paper describes how Ipinch may be computed from the Itotal trace by fitting a computed current trace to the measured current trace using the Lee model. The method is applied to an experiment in which both the Itotal trace and the plasma sheath current trace were measured. The result shows good agreement between the values of computed and measured Ipinch.
WOS© Citations 52Scopus© Citations 63 234 348 - PublicationOpen AccessNeutron and high energy deuteron anisotropy investigations in plasma focus device(American Institute of Physics, 2009)
;Roshan, M. V.; ;Talebitaher, A.; The anisotropies of neutron and high energy deuteron emissions from the NX2 plasma focus device [M. V. Roshan et al., Phys. Lett. A 373, 851 (2009)] are studied. The nuclear activation of graphite targets is used to measure the fluences of high energy deuterons in the axial and radial directions. Two bismuth germanate scintillation detectors connected to multichannel analyzer systems are used for the detection of 511 keV gamma rays resulting from positron annihilation in the two targets. In addition, fast neutron activation detectors are employed to measure the axial and radial fluences of fusion neutrons. These detection systems are calibrated using the simulation code MCNPX [L. S. Waters et al., AIP Conf. Proc. 896, 81 (2007)]. Two distinct regimes of neutron and deuteron anisotropies are observed for the NX2 device. For deuterium gas pressures below 10 mbar, the neutronanisotropy increases with increasing pressure, while the overall neutron yield remains low. For gas pressures of 10–14 mbar, the neutronanisotropy is essentially constant, while, with increasing pressure, the neutron yield rises rapidly and the deuteron anisotropy falls.
WOS© Citations 19Scopus© Citations 22 220 463 - PublicationMetadata onlyHigh energy density pulsed argon plasma synthesized nanostructured tungsten for damage mitigation under fusion relevant energetic he ion irradiation(Elsevier, 2021)
;Sharma, Priya ;Vas, Joseph Vimal ;Medwal, Rohit ;Mishra, Mayank ;Chaurasiya, Avinash ;Luai, Meng Tzee ;Zheng, Zhang ;Chaudhary, Varun ;Ramanujan, Raju V.; ;Xiao, ChijinTungsten (W) is considered as one of the promising candidates for plasma facing components in fusion reactors since it has high threshold energy, high melting point, low threshold shock resistance, and resistance against formation of co-deposits with tritium. Despite these commendable features, helium ions produced during fusion reaction are known to alter the microstructure of tungsten. In this work, dense plasma focus (DPF) device is used to study the effect of helium ion flux on double forged tungsten samples delivering a heat load of 6.27×104J/m2 per shot. The irradiation of virgin W samples is carried out at 5, 10, and 15 DPF helium shots. High heat loads resulted in blisters and micro-cracks on the sample surface. With an increase in the number of shots, the density of the blisters increased and craters on the W surface burst followed by re-solidification of the melted and sputtered surface. Surface nano-structurization, with nanoparticle formation, of W samples (nano-W) is realized by high-energy argon ion exposure of virgin samples in an argon filled DPF device. The average size of nanoparticles is found to increase with the number of shots and also leads to particle agglomeration. At 10 shots, uniformly distributed highly dense nanoparticles of 20–50 nm size have been synthesized. The nano-W samples are then irradiated by instability-accelerated high-energy helium ions in helium filled DPF device for 5, 10, and 15 shots to simulate fusion relevant conditions. The presence of the trapped helium bubbles in virgin-W and nano-W are examined by BSE imaging and XRD, respectively. The nanostructured tungsten shows improved structure and surface properties against Helium ion irradiation.213 - PublicationMetadata onlyMaking sense of the induced EMF in a coil using sensors and visualisation of the voltage–force parametric plot
We investigated the emf (V) induced with time (t) in a search coil due to an oscillating bar magnet along the axis of the coil using the IOLab device. Experimental data was simultaneously collected with the force sensor which tracked the oscillation of the magnet and the voltage sensor which gave real-time readings of the induced emf in the coil. For small amplitudes of oscillation, where the predominant interaction involved the top end of the magnet cutting through the plane of the coil, the V–t graph appeared sinusoidal. With increasing amplitudes of oscillation, the V–t graph started to lose its symmetry with an initial kink appearing within one half cycle and which eventually became an increasing hump as the amplitude of oscillation increased further due to the influence from the bottom end of the bar magnet which affected the overall rate of change of magnetic flux linkage through the coil. The data collected from the experiment was visualised using a novel parametric series of plots of induced emf (V) with force (F). We discussed various cases of the V–F parametric plot. Using a suitable Φ–h function and taking into consideration the rate of change of magnetic flux linkage with respect to displacement along the coil, we discussed how the emf induced changes with time with increasing amplitudes of oscillation.
54 - PublicationRestrictedPBI @ school: A large scale study on the effect of "physics by inquiry" pedagogy on secondary one students' attitude and aptitude in science(2012)
;Wong, Darren Jon Sien ;Lau, Chor Yam"The main purpose of this project is to develop, implement and evaluate a guided-inquiry curriculum using the Physics by Inquiry (PbI) instructional approach. We wanted to investigate the effect of the inquiry-based curriculum and instruction on students' conceptual development and attitude towards the learning of Science. The research questions guiding the project were: 1) What are the favourable modifications in adapting the PbI instructional approach for improving the learning of lower secondary Science in Singapore? 2) What are the differences in the learning outcomes when students learn Physics through the inquiry approach as compared to the standard classroom practices? 3) What are the perceptions of teachers and students on teaching and learning Physics by inquiry in the classroom?" -- p. 2.460 99 - PublicationOpen AccessA 160 kJ dual plasma focus (DuPF) for fusion-relevant materials testing and nano-materials fabrication(World Scientific, 2014)
;Saw, Sor Heoh ;Damideh, Vahid ;Chong, Perk Lin; ; Lee, SingThis paper summarizes PF-160 Dual Plasma Focus (DuPF) numerical experiments using the Lee Model code and preliminary 3D design drawings using SolidWorks software. This DuPF consists of two interchangeable electrodes enabling it to be optimized for both Slow Pinch Mode (SFM) and Fast Pinch Mode (FFM); the latter using a speed factor (SF) of 90 kA cm-1 Torr-0.5 for FFM in deuterium [S Lee et al, IEEE Trans Plasma Science 24, 1101-1105 (1996)]; and the former with SF of less than half that value for SFM. Starting with available 6 x 450 μF capacitors rated at 11kV (10% reversal), numerical experiments indicate safe operation at 9 kV, 6 Torr deuterium with FFM anode of 5 cm radius; producing intense ion beam and streaming plasma pulses which would be useful for studies of potential fusion reactor wall materials. On the other hand operating at 5 kV, 10 Torr deuterium with SFM anode of 10 cm radius leads to long- duration, uniform large-area flow which could be more suitable for synthesis of nano-materials. The dual plasma focus design is illustrated here with two figures showing FFM and SFM electrodes.559 211 - PublicationOpen AccessBroad-energy oxygen ion implantation controlled magnetization dynamics in CoFeTaZr(Elsevier, 2021)
;Vas, Joseph Vimal ;Medwal, Rohit ;Chaudhuri, Ushnish ;Mishra, Mayank ;Chaurasiya, Avinash ;Mahendiran, Ramanathan ;Piramanayagam, S. N.; In this paper, a novel pulsed broad energy spectrum ion-implantation technique, using the dense plasma focus device (DPF), for uniform oxygen-ion doping along the thickness of a ~250 nm thick magnetic CoFeTaZr layer is investigated. A new operational regime of the dense plasma focus – the off-focus mode – is explored to avoid the surface damage of the exposed sample by the high energy plasma streams/jets and instability accelerated ions, typically observed in conventional efficient-focus mode operation. The faraday cup measurements shows the increase in ion fluence from 3.83 × 1013 ion/cm2 for efficient-focus mode to 8.76 × 1013 ion/cm2 for off-focused mode operation in the broad-ion-energy range of 1–100 keV. The x-ray photoelectron spectroscopy (XPS) of the unexposed sample shows the presence of Co in Co0, Co2+ and Co3+, Fe in Fe0, Fe2+ and Fe3+, and Ta in Ta0 and Ta2+ oxidation states while Zr was observed with only metallic Zr binding energy peaks indicating the surface oxidation of the unexposed sample. The exposure to oxygen plasma in DPF device led to the increase in the higher oxidation states of Co, Fe and Ta with reduction in metallic binding energy peak and the deconvolution of oxygen XPS spectrum confirmed the bonding of oxygen to Co, Fe and Ta. The magnetization dynamics of unexposed and oxygen-ion doped samples was studied using magnetoimpedance measurements in the 1–2.5 GHz frequency range. Gilbert’s damping factor, in-plane anisotropy and effective magnetization of the magnetic substrate were calculated and it is found that these properties can be modulated with a lighter ion dosage using this novel pulsed broad-energy-ion implantation technique. It is concluded that the off-focus mode DPF operation can provide the ions of required energy and fluence to implant oxygen ions across the thickness of the CoFeTaZr magnetic thin film to modulate its magnetic properties.WOS© Citations 4Scopus© Citations 4 278 107 - PublicationOpen AccessBackward high energy ion beams from plasma focus(American Institute of Physics, 2009)
;Roshan, M. V.; ;Lee, Sing ;Talebitaher, A.; High energy neutrons, more than 2.45 MeV from deuteron-deuteron fusion reaction, have been measured in backward direction of plasma focus devices in many laboratories. However the experimental evidence for high energy deuterons responsible for such neutrons has not been reported so far. In this brief communication, backward high energy deuteron beam from NX2 plasma focus [M. V. Roshan et al., Phys. Lett. A 373, 851 (2009)] is reported, which was measured with a direct and unambiguous technique of nuclear activation. The relevant nuclear reaction for the target activation is 12C (d, n)13N , which has a deuteron threshold energy of 328 keV.
WOS© Citations 14Scopus© Citations 16 402 198 - PublicationOpen AccessEffect of energetic ion irradiation on Cdl2 films(American Institute of Physics, 2004)
; ;Arun, P. ;Vedeshwar, A. G.; Lee, SingThe effect of energetic argon ion irradiation, using a 3.3 kJ pulsed plasma focus device, is studied systematically on a 4H polytype (002)-oriented CdI2 stoichiometric film having compressive residual stress. The CdI2 films were exposed to energetic ions from the plasma focus device at different distances from the top of the central electrode. The irradiation was found to change the orientation of the film to (110) at certain moderate irradiation distances. A linear decrease in grain size and residual stress was observed with decreasing irradiation distance (for increasing ion energy), consistent with both structural and morphological observations. The direct optical energy gap Eg was found to increase linearly at the rate 15 μeV/atm with the compressive stress. The combined data of present compressive stress and from earlier reported tensile stress show a consistent trend of Eg change with stress. The iodine–iodine distance in the unit cell could be responsible for the observed change in Eg with stress.
WOS© Citations 80Scopus© Citations 83 604 378