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P Vervisch - One of the best experts on this subject based on the ideXlab platform.
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streamer to spark transition initiated by a nanosecond overvoltage pulsed discharge in air
Plasma Sources Science and Technology, 2017Co-Authors: Armelle Cessou, Corine Lacou, Ertrand Lecordie, P Oube, Christophe O Lau, P VervischAbstract:This study is focused on the streamer-to-spark transition generated by an overvoltage nanosecond pulsed discharge under atmospheric pressure air in order to provide a quantitative insight into plasma-assisted ignition. The discharge is generated in atmospheric pressure air by the application of a positive high voltage pulse of 35 kV to pin-to-pin electrodes and a rise time of 5 ns. The generated discharge consists of a streamer phase with high voltage and high current followed by a spark phase characterized by a low voltage and a decreasing current in several hundreds of nanosecond. During the streamer phase, the Gas temperature measured by optical emission spectroscopy related to the second positive system of nitrogen shows an ultra-fast Gas Heating up to 1200 K at 15 ns after the current rise. This ultra-fast Gas Heating, due to the quenching of electronically excited species by oxygen molecules, is followed by a quick dissociation of molecules and then the discharge transition to a spark. At this transition, the discharge contracts toward the channel axis and evolves into a highly conducting thin column. The spark phase is characterized by a high degree of ionization of nitrogen and oxygen atoms shown by the electron number density and temperature measured from optical emission spectroscopy measurements of N+ lines. Schlieren imaging and optical emission spectroscopy techniques provide the time evolution of the spark radius, from which the initial pressure in the spark is estimated. The expansion of the plasma is adiabatic in the early phase. The electronic temperature and density during this phase allows the determination of the isentropic coefficient. The value around 1.2-1.3 is coherent with the high ionization rate of the plasma in the early phase. The results obtained in this study provide a database and the initial conditions for the validation of numerical simulations of the ignition by plasma discharge. © 2017 IOP Publishing Ltd.
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space and time analysis of the nanosecond scale discharges in atmospheric pressure air ii energy transfers during the post discharge
Journal of Physics D, 2014Co-Authors: Armelle Cessou, P VervischAbstract:The better understanding of nanosecond scale discharges under atmospheric pressure and the validation of plasmachemical models, require an increasing need for reliable data. This paper presents, in the first time to our knowledge, spatiotemporal description of the Gas number densities of major species including O atoms, the hydrodynamic expansion and the relative distribution of the energy deposited in the specific molecular modes of N2(X) and O2(X) following a nanosecond pulsed air discharge at atmospheric pressure. These data are obtained from phase-locked average profiles of the ground states of N2 and O2 probed by spontaneous Raman scattering. The results complete part I of this investigation dedicated to the Gas temperature and the vibrational distribution function of N2 and O2 and show that half of the total energy deposited is loaded on the vibrational mode (48% for N2 and 2% for O2). The energy released into fast Gas Heating represents 19% of the energy deposited. This fast Gas Heating (up to 1000 K) observed in tens of nanoseconds after the current rise leads to a shock wave propagation shown with the pressure measurements. These processes combined with vibration–vibration/translation energy transfers and convective transports induced by the shock wave propagation are spatiotemporally studied. The experimental data of this study provide space and time database for the validation of plasmachemical models of nanosecond pulsed discharges in atmospheric pressure air.
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space and time analysis of the nanosecond scale discharges in atmospheric pressure air i Gas temperature and vibrational distribution function of n 2 and o 2
Journal of Physics D, 2014Co-Authors: Armelle Cessou, Pascal Boubert, P VervischAbstract:Reliable experimental data on nanosecond discharge plasmas in air become more and more crucial considering their interest in a wide field of applications. However, the investigations on such nonequilibrium plasmas are made difficult by the spatial non-homogeneities, in particular under atmospheric pressure, the wide range of time scales, and the complexity of multi-physics processes involved therein. In this study, we report spatiotemporal experimental analysis on the Gas temperature and the vibrational excitation of N2 and O2 in their ground electronic state during the post-discharge of an overvoltage nanosecond-pulsed discharge generated in a pin-to-plane gap of air at atmospheric pressure. The Gas temperature during the pulsed discharge is measured by optical emission spectroscopy related to the rotational bands of the 0?0 vibrational transition N2(C?3??u, v?=?0)???N2(B3??g, v?=?0) of nitrogen. The results show a rapid Gas Heating up to 700?K in tens of nanoseconds after the current rise. This fast Gas Heating leads to a high Gas temperature up to 1000?K measured at 150?ns in the first stages of the post-discharge using spontaneous Raman scattering (SRS). The spatiotemporal measurements of the Gas temperature and the vibrational distribution function of N2 and O2, also obtained by SRS, over the post-discharge show the spatial expansion of the high vibrational excitation of N2, and the Gas Heating during the post-discharge. The present measurements, focused on thermal and energetic aspect of the discharge, provide a base for spatiotemporal analysis of Gas number densities of N2, O2 and O atoms and hydrodynamic effects achieved during the post-discharge in part II of this investigation. All these results provide space and time database for the validation of plasma chemical models for nanosecond-pulsed discharges at atmospheric pressure air.
Bridgid Lai Fui Chin - One of the best experts on this subject based on the ideXlab platform.
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hydrogen production from palm kernel shell via integrated catalytic adsorption ica steam Gasification
Energy Conversion and Management, 2014Co-Authors: Zakir Khan, Suzana Yusup, Murni M Ahmad, Bridgid Lai Fui ChinAbstract:Abstract The present study investigates the integrated catalytic adsorption (ICA) steam Gasification of palm kernel shell for hydrogen production in a pilot scale atmospheric fluidized bed Gasifier. The biomass steam Gasification is performed in the presence of an adsorbent and a catalyst in the system. The effect of adsorbent to biomass (A/B) ratio (0.5–1.5 wt/wt), fluidization velocity (0.15–0.26 m/s) and biomass particle size (0.355–2.0 mm) are studied at temperature of 675 °C, steam to biomass (S/B) ratio of 2.0 (wt/wt) and biomass to catalyst ratio of 0.1 (wt/wt). Hydrogen composition and yield, total Gas yield, and lower product Gas Heating values (LHVGas) increases with increasing A/B ratio, while particle size has no significant effect on hydrogen composition and yield, total Gas and char yield, Gasification and carbon conversion efficiency. However, Gas Heating values increased with increasing biomass particle size which is due to presence of high methane content in product Gas. Meanwhile, medium fluidization velocity of 0.21 m/s favoured hydrogen composition and yield. The results showed that the maximum hydrogen composition and yield of 84.62 vol% and 91.11 g H2/kg biomass are observed at A/B ratio of 1.5, S/B ratio of 2.0, catalyst to biomass ratio of 0.1 and temperature of 675 °C. The product Gas Heating values are observed in the range of 10.92–17.02 MJ/N m3. Gasification and carbon conversion efficiency are observed in the range of 25.66–42.95% and 20.61–41.95%, respectively. These lower efficiencies are due to significant CO2 capturing in using adsorbent in pilot the scale fluidized bed Gasification system. Comparative study with literature shows that the combination of adsorbent and catalyst produces better results in terms of hydrogen composition and Gas Heating values compared to that of only using biomass in steam catalytic Gasification and in steam Gasification with in situ CO2 adsorbent.
Robert Cattolica - One of the best experts on this subject based on the ideXlab platform.
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neutral Gas density depletion due to neutral Gas Heating and pressure balance in an inductively coupled plasma
Plasma Sources Science and Technology, 2007Co-Authors: Masashi Shimada, G R Tynan, Robert CattolicaAbstract:The spatial distribution of neutral Gas temperature and total pressure have been measured for pure N2, He/5%N2 and Ar/5%N2 in an inductively coupled plasma (ICP) reactor, and a significant rise in the neutral Gas temperature has been observed. When thermal transpiration is used to correct total pressure measurements, the total pressure remains constant regardless of the plasma condition. Neutral pressure is depleted due to the pressure balance when the plasma pressure (mainly electron pressure) becomes comparable to the neutral pressure in high density plasma. Since the neutral Gas follows the ideal Gas law, the neutral Gas density profile was obtained from the neutral Gas temperature and the corrected neutral pressure measurements. The results show that the neutral Gas density at the centre of the plasma chamber (factor of 2–4 ×) decreases significantly in the presence of a plasma discharge. Significant spatial variation in neutral Gas uniformity occurs in such plasmas due to neutral Gas Heating and pressure balance.
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measurement of radial and axial neutral Gas temperature in a semi conductor plasma reactor
RAREFIED GAS DYNAMICS: 24th International Symposium on Rarefied Gas#N#Dynamics, 2005Co-Authors: M Shimada, Robert Cattolica, G R TynanAbstract:Plasma‐etching and plasma deposition processes are used in the fabrication of ultra large scale integration (ULSI) semi‐conductor circuits. Plasma based processing systems have evolved from capacitive coupled plasma sources to high density inductively coupled and magnetically enhanced plasma sources. As processing evolves from 200‐mm to 300‐mm wafers and as critical dimensions continue to shrink continued improvement in a number of process variables, including process uniformity, are required. Process uniformity is governed by a number of factors including plasma density uniformity, reactive neutral uniformity, wafer temperature, and incident ion energy uniformity. The mechanisms leading to neutral radical non‐uniformity, including Gas Heating and plasma pumping have been given less attention, therefore plasma diagnostics and modeling of neutral Gas density, temperature, and dissociation in the reactor are needed to improve the understanding of how neutral Gas conditions influence process uniformity. Radial and axial rotational temperature profiles in a large‐area high‐density plasma reactor (inductively coupled plasma discharge) have been obtained using the electron beam fluorescence technique (EBF) and optical emission spectroscopy (OES). These two diagnostics can provide the temperature measurements over the entire range of Gas pressure (1–50mTorr) and input power (0‐3000W). These two diagnostic techniques for temperature measurement are compared with a simple analytic model of Gas Heating and Gas depletion.
K Foyle - One of the best experts on this subject based on the ideXlab platform.
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insights into Gas Heating and cooling in the disc of ngc 891 from herschel far infrared spectroscopy
Astronomy and Astrophysics, 2015Co-Authors: T M Hughes, K Foyle, M R P Schirm, T J Parkin, I De Looze, C D Wilson, G J Bendo, M Baes, J Fritz, A BoselliAbstract:We present Herschel PACS and SPIRE spectroscopy of the most important far-infrared cooling lines in the nearby, edge-on spiral galaxy, NGC 891: [Cii] 158 μm, [Nii] 122, 205 μm, [Oi] 63, 145 μm, and [Oiii] 88 μm. We find that the photoelectric Heating efficiency of the Gas, traced via the ([Cii]+[Oi]63)/FTIR ratio, varies from a mean of 3.5 × 10-3 in the centre up to 8 × 10-3 at increasing radial and vertical distances in the disc. A decrease in ([Cii]+[Oi]63)/FTIR but constant ([Cii]+[Oi]63)/FPAH with increasing FIR colour suggests that polycyclic aromatic hydrocarbons (PAHs) may become important for Gas Heating in the central regions. We compare the observed flux of the FIR cooling lines and total IR emission with the predicted flux from a PDR model to determine the Gas density, surface temperature and the strength of the incident far-ultraviolet (FUV) radiation field, G0. Resolving details on physical scales of ~0.6 kpc, a pixel-by-pixel analysis reveals that the majority of the PDRs in NGC 891’s disc have hydrogen densities of 1 < log (n/ cm-3) < 3.5 experiencing an incident FUV radiation field with strengths of 1.7 < log G0< 3. Although these values we derive for most of the disc are consistent with the Gas properties found in PDRs in the spiral arms and inter-arm regions of M 51, observed radial trends in n and G0 are shown to be sensitive to varying optical thickness in the lines, demonstrating the importance of accurately accounting for optical depth effects when interpreting observations of high inclination systems. Increasing the coverage of our analysis by using an empirical relationship between the MIPS 24 μm and [Nii] 205 μm emission, we estimate an enhancement of the FUV radiation field strength in the far north-eastern side of the disc relative to the rest of the disc that coincides with the above-average star formation rate surface densities and Gas-to-dust ratios. However, an accurate interpretation remains difficult due to optical depth effects, confusion along the line-of-sight and observational uncertainties.
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insights into Gas Heating and cooling in the disc of ngc 891 from herschel far infrared spectroscopy
arXiv: Astrophysics of Galaxies, 2014Co-Authors: T M Hughes, K Foyle, M R P Schirm, T J Parkin, I De Looze, C D Wilson, G J Bendo, M Baes, J Fritz, A BoselliAbstract:We present Herschel PACS and SPIRE spectroscopy of the most important far-infrared cooling lines in the nearby edge-on spiral galaxy, NGC 891: [CII] 158 $\mu$m, [NII] 122, 205 $\mu$m, [OI] 63, 145 $\mu$m, and [OIII] 88 $\mu$m. We find that the photoelectric Heating efficiency of the Gas, traced via the ([CII]+[OII]63)/$F_{\mathrm{TIR}}$ ratio, varies from a mean of 3.5$\times$10$^{-3}$ in the centre up to 8$\times$10$^{-3}$ at increasing radial and vertical distances in the disc. A decrease in ([CII]+[OII]63)/$F_{\mathrm{TIR}}$ but constant ([CII]+[OI]63)/$F_{\mathrm{PAH}}$ with increasing FIR colour suggests that polycyclic aromatic hydrocarbons (PAHs) may become important for Gas Heating in the central regions. We compare the observed flux of the FIR cooling lines and total IR emission with the predicted flux from a PDR model to determine the Gas density, surface temperature and the strength of the incident far-ultraviolet (FUV) radiation field, $G_{0}$. Resolving details on physical scales of ~0.6 kpc, a pixel-by-pixel analysis reveals that the majority of the PDRs in NGC 891's disc have hydrogen densities of 1 < log ($n$/cm$^{-3}$) < 3.5 experiencing an incident FUV radiation field with strengths of 1.7 < log $G_0$ < 3. Although these values we derive for most of the disc are consistent with the Gas properties found in PDRs in the spiral arms and inter-arm regions of M51, observed radial trends in $n$ and $G_0$ are shown to be sensitive to varying optical thickness in the lines, demonstrating the importance of accurately accounting for optical depth effects when interpreting observations of high inclination systems. With an empirical relationship between the MIPS 24 $\mu$m and [NII] 205 $\mu$m emission, we estimate an enhancement of the FUV radiation field strength in the far north-eastern side of the disc.
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regional variations in the dense Gas Heating and cooling in m51 from herschel far infrared spectroscopy
The Astrophysical Journal, 2013Co-Authors: T J Parkin, M R P Schirm, C D Wilson, M Baes, A Boselli, M Boquien, A Cooray, D Cormier, K FoyleAbstract:We present Herschel PACS and SPIRE spectroscopy of the most important far-infrared cooling lines in M51, [C II](158 mu m), [N II](122 and 205 mu m), [OI](63 and 145 mu m), and [O III](88 mu m). We compare the observed flux of these lines with the predicted flux from a photon-dominated region model to determine characteristics of the cold Gas such as density, temperature, and the far-ultraviolet (FUV) radiation field, G(0), resolving details on physical scales of roughly 600 pc. We find an average [C II]/F-TIR of 4 x 10(-3), in agreement with previous studies of other galaxies. A pixel-by-pixel analysis of four distinct regions of M51 shows a radially decreasing trend in both the FUV radiation field, G(0), and the hydrogen density, n, peaking in the nucleus of the galaxy, and then falling off out to the arm and interarm regions. We see for the first time that the FUV flux and Gas density are similar in the differing environments of the arm and interarm regions, suggesting that the inherent physical properties of the molecular clouds in both regions are essentially the same.
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regional variations in the dense Gas Heating and cooling in m51 from herschel far infrared spectroscopy
arXiv: Cosmology and Nongalactic Astrophysics, 2013Co-Authors: T J Parkin, M R P Schirm, C D Wilson, M Baes, A Boselli, M Boquien, A Cooray, D Cormier, K FoyleAbstract:We present Herschel PACS and SPIRE spectroscopy of the most important far-infrared cooling lines in M51, [CII](158 \mu m), [NII](122 & 205 \mu m), [OI](63 and 145 \mu m) and [OIII](88 \mu m). We compare the observed flux of these lines with the predicted flux from a photon dominated region model to determine characteristics of the cold Gas such as density, temperature and the far-ultraviolet radiation field, G_0, resolving details on physical scales of roughly 600 pc. We find an average [CII]/F_TIR of 4 x 10^{-3}, in agreement with previous studies of other galaxies. A pixel-by-pixel analysis of four distinct regions of M51 shows a radially decreasing trend in both the far-ultraviolet (FUV) radiation field, G_0 and the hydrogen density, n, peaking in the nucleus of the galaxy, then falling off out to the arm and interarm regions. We see for the first time that the FUV flux and Gas density are similar in the differing environments of the arm and interarm regions, suggesting that the inherent physical properties of the molecular clouds in both regions are essentially the same.
B T Draine - One of the best experts on this subject based on the ideXlab platform.
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photoelectric emission from dust grains exposed to extreme ultraviolet and x ray radiation
arXiv: Astrophysics, 2006Co-Authors: Joseph C Weingartner, B T Draine, David K. BarrAbstract:Photoelectric emission from dust plays an important role in grain charging and Gas Heating. To date, detailed models of these processes have focused primarily on grains exposed to soft radiation fields. We provide new estimates of the photoelectric yield for neutral and charged carbonaceous and silicate grains, for photon energies exceeding 20 eV. We include the ejection of electrons from both the band structure of the material and the inner shells of the constituent atoms, as well as Auger and secondary electron emission. We apply the model to estimate Gas Heating rates in planetary nebulae and grain charges in the outflows of broad absorption line quasars. For these applications, secondary emission can be neglected; the combined effect of inner shell and Auger emission is small, though not always negligible. Finally, we investigate the survivability of dust entrained in quasar outflows. The lack of nuclear reddening in broad absorption line quasars may be explained by sputtering of grains in the outflows.
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photoelectric emission from interstellar dust grain charging and Gas Heating
Astrophysical Journal Supplement Series, 2001Co-Authors: Joseph C Weingartner, B T DraineAbstract:We model the photoelectric emission from and charging of interstellar dust and obtain photoelectric Gas Heating efficiencies as a function of grain size and the relevant ambient conditions. We employ improved estimates for photoelectric thresholds, yields, and electron capture rates. Using realistic grain size distributions, we evaluate the net Gas Heating rate for various interstellar environments and find less Heating for dense regions characterized by RV = 5.5 than for diffuse regions with RV = 3.1. We provide fitting functions that reproduce our numerical results for photoelectric Heating and recombination cooling for a wide range of interstellar conditions. Finally, we investigate the potential importance of photoelectric Heating in H II regions, including the warm ionized medium. We find that photoelectric Heating could be comparable to or exceed Heating due to photoionization of H for high ratios of the radiation intensity to the Gas density. We also find that photoelectric Heating by dust can account for the observed variation of temperature with distance from the Galactic midplane in the warm ionized medium.
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photoelectric emission from interstellar dust grain charging and Gas Heating
arXiv: Astrophysics, 1999Co-Authors: Joseph C Weingartner, B T DraineAbstract:We model the photoelectric emission from and charging of interstellar dust and obtain photoelectric Gas Heating efficiencies as a function of grain size and the relevant ambient conditions. Using realistic grain size distributions, we evaluate the net Gas Heating rate for various interstellar environments, and find less Heating for dense regions characterized by R_V=5.5 than for diffuse regions with R_V=3.1. We provide fitting functions which reproduce our numerical results for photoelectric Heating and recombination cooling for a wide range of interstellar conditions. In a separate paper we will examine the implications of these results for the thermal structure of the interstellar medium. Finally, we investigate the potential importance of photoelectric Heating in H II regions, including the warm ionized medium. We find that photoelectric Heating could be comparable to or exceed Heating due to photoionization of H for high ratios of the radiation intensity to the Gas density. We also find that photoelectric Heating by dust can account for the observed variation of temperature with distance from the galactic midplane in the warm ionized medium.
