Now showing 1 - 10 of 18
  • Publication
    Restricted
    Teaching physics using an IT tool
    (1998)
    Information technology is a critical element in teaching and learning and is central to our mission of preparing students for the 21St century. This work explores the use and benefit of computer aided techniques in undergraduate physics teaching. It is demonstrated that the computer aided teaching techniques indeed promote students' deep learning and critical thinking skills, especially for undergraduate theoretical and experimental physics courses. The results show that such a non-conventional approach provides a great opportunity to effectively motivate students in understanding some abstractive physical concepts and principles.
      158  11
  • Publication
    Open Access
    Discharge mode transition in a Krypton-fed 1 A-class LaB6 cathode for lowpower Hall thrusters for small satellites
    (2020)
    Potrivitu, George-Cristian
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    Xu, L.
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    Huang, Shih-Hao
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    Mohd Rohaizat Abdul Wahab
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    Thermionic cathodes are essential for the operation of various electrostatic propulsion devices. They strongly influence the performance and lifetime of the propulsion system. In this study, a 1 A-class LaB6 laboratory model hollow cathode has been tested with krypton in diode and triode configurations in order to assess for the cathode discharge mode transition behavior. Measurements have been performed over a range of krypton mass flow rates (0.1, 0.15 and 0.21 mg/s, or 1.6, 2.4 and 3.4 sccm), keeper (0.1, 0.15, 0.2 A) and anode currents (0.1 to 1 A) at a fixed cathode-to- anode distance. Seven criteria were used to distinguish between the spot and plume mode operations. The results show that the mode transition in low-current cathodes may be a non-linear phenomenon and only some of the existing mode transition criteria can be used to accurately predict the spot/plume discharge regions at low emission currents.
    WOS© Citations 17Scopus© Citations 17  57  141
  • Publication
    Metadata only
    Miniaturized rotating magnetic field–driven plasma system: Proof-of-concept experiments
    (2021)
    Sun, Yan
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    Levchenko, Igor
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    Lim, John William Mark
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    Xu, Ling
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    Huang, Sheng
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    Zhang, Zhi
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    Thio, Francis
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    Potrivitu, Gheorghe-Constantin
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    Rohaizat, Muhammad W. A. B.
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    Cherkun, Oleksiy
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    Chan, Chong Soon
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    Baranov, Oleg
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    Bazaka, Konstantinos
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    The development of plasma-based propulsion thrusters for spacecraft has seen a rapid growth over the past few decades, with the number of spacecraft including small satellites and Cubesats increasing exponentially. Although traditional chemical propulsion is still widely employed in space flights, it cannot meet the more challenging requirements for deep space travel due to low specific impulse. Electric propulsion thrusters have already helped humans travel further from Earth and have the potential to be developed for interstellar flights due to their advantages such as high velocity increments, long operational lifetimes, high impulse-to-weight ratios and high impulse-to-power ratios. The electrodynamic thrusters have significant potential for applications in the remote regions of space, and several types of electrodynamic plasma thrusters are currently under investigation. In this paper we present conceptual experiments to study a miniaturized Rotamak-type device initially proposed for the controlled thermonuclear fusion, with a view to assess its potential for the application as a small space thruster. An outline of the physical characteristics of the experiments that has been carried out, and measurements were done to try to elucidate the important mechanisms at work in the Rotamak, which will help design next-generation thruster capabilities. A discussion is also presented about the Rotamak systems and the opportunities they present for space applications.
    WOS© Citations 4Scopus© Citations 6  29
  • Publication
    Metadata only
    Evidence of the ionization instability and ion acoustic turbulence correlation in sub-ampere hollow cathodes
    (2022)
    Potrivitu, George-Cristian
    ;
    Plasma instabilities in the plume of hollow cathodes have been extensively researched in particular for high-current operation. The rise of plume mode ionization-like instability leads to a degradation of cathode’s performance along with the emergence of highly energetic ions that can produce sputtering of various cathode’s surfaces. Numerical simulations using 2D fluid or hybrid codes brought forward an interesting correlation between the evolution of ion acoustic turbulence (IAT) and emergence of plume mode oscillations. Such numerical findings were proven to be true by experimental measurements of wave dispersion and plume mode-IAT correlation in the plume of cathodes emitting currents >10 A. This study brings forward evidence of the correlation between plume mode oscillations and IAT in the plume of low-current cathodes operating with Kr at sub-ampere current levels. It is shown that at <1 A the plume mode instability is highly correlated with the IAT and the anomalous electron collision drives the electron transport in the cathode plume. The fluctuations in IAT wave energy lead to large temperature oscillations which then drive fluctuations in the density via ionization.
      38
  • Publication
    Open Access
    A review of low-power electric propulsion research at the Space Propulsion Centre Singapore
    (2020)
    Potrivitu, George-Cristian
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    Sun, Yufei
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    Muhammad Wisnuh Aggriawan Rohaizat
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    Cherkun, Oleksil
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    Huang, Shiyong
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    The age of space electric propulsion arrived and found the space exploration endeavors at a paradigm shift in the context of new space. Mega-constellations of small satellites on low-Earth orbit (LEO) are proposed by many emerging commercial actors. Naturally, the boom in the small satellite market drives the necessity of propulsion systems that are both power and fuel efficient and accommodate small form-factors. Most of the existing electric propulsion technologies have reached the maturity level and can be the prime choices to enable mission versatility for small satellite platforms in Earth orbit and beyond. At the Plasma Sources and Applications Centre/Space Propulsion Centre (PSAC/SPC) Singapore, a continuous effort was dedicated to the development of low-power electric propulsion systems that can meet the small satellites market requirements. This review presents the recent progress in the field of electric propulsion at PSAC/SPC Singapore, from Hall thrusters and thermionic cathodes research to more ambitious devices such as the rotamak-like plasma thruster. On top of that, a review of the existing vacuum facilities and plasma diagnostics used for electric propulsion testing and characterization is included in the present research.
    WOS© Citations 25  166  333
  • Publication
    Open Access
    Scalable production of silicon nanocone solar cells in integrated plasma photovoltaic nanofabrication cluster
    (2016)
    Huang, Shiyong
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    Lim, Mark Jian Wei
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    Chan, Chia Sern
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    Wei, Deyuan
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    Guo, Yingnan
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    Xu, Luxiang
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    Ostrikov, Kostya (Ken)
    Surface texturing is a method widely adopted by industries to reduce the reflective losses in photovoltaic (PV) cells. In this work, a multi-chambered Integrated Plasma Photovoltaic Nanofabrication Cluster facility was used to produce nanocone surface textured polycrystalline (PX) PV cells. An inductively coupled plasma (ICP) discharge of O2 and SF6 was used to remove damage on PX p-type silicon wafers. Following that, a mixture of H2 and Ar plasma was used to texture an anti-reflecting array of silicon nanocones on the surface, while simultaneously forming a p-n junction. A plasma enhanced chemical vapour deposition (PECVD) process was utilized using SiH4, CO2, N2 and H2 precursors for front and back surface passivation for growth of SiNx:H and SiOxH thin films. Aluminium electrodes were sputtered on using an RF magnetron sputtering facility to provide the contacts for the PV cell. Scanning electron microscopy of textured sample surfaces revealed uniform, well defined, high aspect ratio nanocones. The absorption spectra of the resulting surface show dramatic reductions in the reflectance of the wafers, and external quantum efficiency measurements show improved spectral response for the 300 nm – 1100 nm region. The resulting cells showed promising photovoltaic responses, with short circuit-currents of 36 mA/cm2, open circuit voltages of 560 mV, fill factors reaching 80% and conversion efficiencies of up to 14.8%. The feedstock gases utilized in this entire process were mostly environmentally friendly, and the single plasma based processing cluster eliminated the need for excessive waste generated from chemicals that would be otherwise found in commercial production lines. This work shows exciting potential in the pursuit of fabricating low cost, environmentally friendly and highly efficient PV modules to address the problems posed by the global energy crisis.
      135  78
  • Publication
    Metadata only
    A low-current LaB6 open-end knife-edge emitter hollow cathode for low-power hall thrusters
    (2021)
    Potrivitu, George-Cristian
    ;
    Xu, L.
    ;
    Heated thermionic cathodes based on LaB6 emitters are known to consume a relatively large amount of power during the heating part of the ignition phase. Miniaturized electric propulsion systems, and in particular low-power Hall thrusters, rely on the operation of self-sustained cathodes at low-current emission, typically below 1 A. At PSAC/SPC, an open-end knife-edge LaB6 emitter hollow cathode was developed and tested, denoted herein as the PSAC-KE cathode. Here, a detailed description of the new model's design and comparison to the older version, the PSAC cathode, is included. Electrostatic simulations suggested that the open-end emitter geometry allowed for an enhanced electric field within the emitter region during cathode startup and steady-state operation as compared to the orificed emitter PSAC cathode. The PSAC-KE cathode's thermal management was improved based on iterative thermal simulations driven by different cathode geometries and various combinations of materials. The new cathode was tested with xenon in diode mode with an external anode and triode mode with the external anode and the keeper electrode. Furthermore, results from the coupling tests with a low-power Hall thruster are presented. Cathode performance was monitored over a range of anode current from 0.1 to 1 A, mass flow rates from 0.057 to 0.3 mg s−1 and keeper current of 0.05, 0.1, and 0.15 A. The cathode's thermal design was assessed with thermocouple measurements and compared with thermal simulations and results obtained for the PSAC cathode. The preliminary tests showed that the PSAC-KE cathode achieved ignition at low heating power below 35 W, self-sustained operation at 1 A when in standalone mode, and <1 A when against a low-power Hall thruster.
    WOS© Citations 7Scopus© Citations 8  94
  • Publication
    Metadata only
    Mars colonization: Beyond getting there
    (Scrivener Publishing LLC, 2022)
    Levchenko, Igor
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    Mazouffre, Stephane
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    Keidar, Michael
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    Bazaka, Kateryna
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    Beech, Martin
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    Seckbach, Joseph
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    Gordon, Richard
    Colonization of Mars: As humans gradually overcome technological challenges of deep space missions, the possibility of exploration and colonization of extraterrestrial outposts is being seriously considered by space agencies and commercial entities alike. But should we do it just because we potentially can? Is such an undoubtedly risky adventure justified from the economical, legal, and ethical points of view? And even if it is, do we have a system of instruments to effectively and fairly manage these aspects of colonisation? In this essay, a rich diversity of current opinions on the pros and cons of Mars colonization voiced by space enthusiasts with backgrounds in space technology, economics, and materials science are examined.
    Scopus© Citations 12  248
  • Publication
    Open Access
    Structural, electronic, and optical properties of wurtzite and rocksalt InN under pressure
    (2010)
    Duan, Man-Yi
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    He, Lin
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    Xu, Ming
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    Xu, Ming-Yao
    ;
    ;
    Ostrikov, Kostya (Ken)
    Structural stability, electronic, and optical properties of InN under high pressure are studied using the first-principles calculations. The lattice constants and electronic band structure are found consistent with the available experimental and theoretical values. The pressure of the wurtzite-to-rocksalt structural transition is 13.4 GPa, which is in an excellent agreement with the most recent experimental values. The optical characteristics reproduce the experimental data thus justifying the feasibility of our theoretical predictions of the optical properties of InN at high pressures.
    WOS© Citations 17Scopus© Citations 16  156  154
  • Publication
    Open Access
    Plasma and polymers: Recent progress and trends
    (2021)
    Levchenko, Igor
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    Baranov, Oleg
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    Bazaka, Olha
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    Ivanova, Elena P.
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    Bazaka, Kateryna
    Plasma-enhanced synthesis and modification of polymers is a field that continues to expand and become increasingly more sophisticated. The highly reactive processing environments afforded by the inherently dynamic nature of plasma media are often superior to ambient or thermal environments, offering substantial advantages over other processing methods. The fluxes of energy and matter toward the surface enable rapid and efficient processing, whereas the charged nature of plasma-generated particles provides a means for their control. The range of materials that can be treated by plasmas is incredibly broad, spanning pure polymers, polymer-metal, polymer-wood, polymer-nanocarbon composites, and others. In this review, we briefly outline some of the recent examples of the state-of-the-art in the plasma-based polymer treatment and functionalization techniques.
    WOS© Citations 35Scopus© Citations 46  230  103