Bulletin of the American Physical Society
67th Annual Gaseous Electronics Conference
Volume 59, Number 16
Sunday–Friday, November 2–7, 2014; Raleigh, North Carolina
Session MW1: Poster Session II (17:30-19:30) |
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Room: Exhibit Hall |
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MW1.00001: The viscosity cross section for electron scattering from the heavy noble gases Allan Stauffer, Robert McEachran The viscosity cross section is defined in terms of the elastic differential cross section $\sigma(\theta)$ as $$ \sigma_v = \int_0^\pi (1-\cos^2\theta) \, \sin\theta \, \sigma(\theta) \, {\rm d}\theta $$ and appears in the Boltzmann equation for the electron distribution function in velocity space. If this distribution function is expanded in Legendre polynomials, the viscosity cross section arises from the third term. Normally, only the first two terms in this expansion are retained in the solution of the Boltzmann equation. We have recently published results for the elastic and momentum transfer cross section for electron scattering from the heavy noble gases (argon, krypton and xenon) using our complex, relativistic optical potential method which includes the effect of excitation and ionization channels on the elastic cross sections. We also provided simple analytic fits to these cross sections to aid in plasma modelling calculations. We will present similar results for the viscosity cross sections for these gases including fits using similar analytic functions. By including the third term in the expansion of the Boltzmann equation which depends on this cross section, an evaluation of the accuracy of the two-term solution can be made. [Preview Abstract] |
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MW1.00002: Single and double photoionization of atoms by n-photon absorption at low intensity laser fields: a Generalized Sturmian approach Juan M. Randazzo, Flavio D. Colavecchia, Gustavo Gasaneo, Dario M. Mitnik, Lorenzo Ugo Ancarani We apply the Generalized Sturmian approach for the study of single and double photoionization of atoms by n-photon absorption at low intensity laser fields. We start with the double photoionization of helium by absorption of a single photon. The three-body wave functions necessary for the calculations (the ground state of the helium atom, and the scattering wave function which contains the post-collisional dynamics after one photon absorption) are both expanded with spherical Generalized Sturmian Functions (GSF) [1]. Very accurate triple differential cross sections for single photon double ionization are obtained helium for 20 and 40 eV. If two or more photons are absorbed, we have to consider the corresponding wave functions which describe the spatial distribution in each stage. We will then consider the scattering solutions for n>1 analyzing the applicability of an iterative scheme with a focus on the computational requirements for each n.\\[4pt] [1] G. Gasaneo et al, Adv. Quantum Chem., 67, 153 (2013) [Preview Abstract] |
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MW1.00003: Molecular Dynamics simulation of Ru flattening by Gas Cluster Ion Beam Masaaki Matsukuma, Kazuyoshi Matsuzaki, Kenji Inaba, Ryuji Miura, Ai Suzuki, Nozomu Hatakeyama, Akira Miyamoto Noble metals such as platinum or ruthenium have been hardly used in the semiconductor devices in spite of their physical and electrical properties, because they were hard to process. High energy monomer ion beams which can cut hard materials may induce structural damages. A gas cluster ion beam (GCIB) consists of a few thousands of atoms or molecules and is accelerated up to several tens keV. GCIB is able to realize localized high energy deposition with low energy per components in the cluster. This means that each component in clusters cannot have enough energy to react with surface. On the other hand, the clusters with tens keV of kinetic energy may make a high reactive field at the hypocenter areas. In consequence it is expected that the GCIB irradiation should achieve the metal processing with low damage. Recently flattening of Ru thin films using GCIB is reported. We conducted molecular dynamics simulation of GCIB incident to Ru surface with the in-house interatomic potential models obtained based on the quantum chemical calculations and found that the internal degree of freedom of a cluster played important roles during the GCIB bombardment. [Preview Abstract] |
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MW1.00004: Comparison of analytical formulae and quantum calculations for differential cross sections in e-Ar J.F.J. Janssen, O. Zatsarinny, K. Bartschat, G.J.M. Hagelaar, L.C. Pitchford We have previously shown [1] that the fully \textit{ab initio}, quantum mechanical $B$-spline $R$-matrix calculations of Zatsarinny and Bartschat for e-Ar cross sections yield accurate values of swarm parameters (transport and rate coefficients vs. reduced electric field strength, for uniform and constant E/N) when used as input in a Boltzmann solver. These comparisons were made by employing the calculated angle-integrated elastic momentum transfer and total inelastic cross sections (usually sufficient for accurate calculations of swarm parameters). The theory, however, also provides fully differential scattering information, which is now available for argon on the open access website LXCat (www.lxcat.net). In this presentation, we compare predictions from several previously proposed analytical formulae for the angular dependence of the cross sections with the quantum predictions.~ Such comparisons are of interest, for example, in PIC-MC simulations where, due to lack of information, some approximations about the angular dependence must be made and thus the use of analytical formulae is common. \\[4pt] [1] L. Pitchford \textit{et al}., J. Phys. D \textbf{46} (2013) 334001. [Preview Abstract] |
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MW1.00005: Electron collisions with cesium atoms -- benchmark calculations and application to modeling an excimer-pumped \hbox{alkali} laser Oleg Zatsarinny, Klaus Bartschat, Natalia Babaeva, Mark Kushner The {\it B}-spline {\it R}-matrix (BSR) with pseudo\-states method~[1] was employed to describe electron collisions with cesium atoms. Over 300 states were kept in the close-coupling expansion, including a large number of pseudostates to model the effect of the Rydberg spectrum and the ionization continuum on the results for transitions between the discrete physical states of interest. Predictions for elastic scattering, excitation, and ionization for incident energies up to 200~eV are presented and compared to previous results~[2,3] and experimental data. Our data were used to model plasma formation in the excimer-pumped alkali laser, XPAL, operating on the Cs$\rm (6^2P_{3/2,1/2} \to (6^2S_{1/2})$ (852$\,$nm and 894$\,$nm) transitions. At sufficiently high operating temperature, pump power, and repetition rate, plasma formation in excess of $\rm 10^{14}-10^{15}\,cm^{-3}$ occurs. This may reduce laser output power by electron collisional mixing of the upper and lower laser levels [4].\\[4pt] [1]~O.~Zatsarinny and K.~Bartschat, J.~Phys.~B~{\bf 46} (2013) 112001.\\[0pt] [2]~K.~Bartschat and Y.~Fang, Phys.~Rev.~A {\bf 62} (2000) 052719.\\[0pt] [3]~O.~Zatsarinny and K.~Bartschat, Phys.~Rev.~A {\bf 77} (2008)\\[0pt] [4]~O.~Zatsarinny, K.~Bartschat, N. Babaeva, and M. J. Kushner, PSST {\bf 23} (2014) 035011. [Preview Abstract] |
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MW1.00006: Electronic excitation of methanol by low-energy electrons Leigh Hargreaves, Ken Varela, Murtadha Khakoo, Carl Winstead, Vince McKoy Differential and integral excitation cross section measurements for the 4 lowest-lying states of states for methanol will be presented, at electron energies between 9 -- 20eV. The data were obtained via electron-energy loss spectroscopy, incorporating a moveable aperture gas source, and applying a least squares data fitting routine to each spectra that separated overlapping contributions from discrete transitions. The results are compared with current theoretical calculations, as well as previously obtained data for water and preliminary results for excitation of ethanol. [Preview Abstract] |
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MW1.00007: A vortex line for K-shell ionization of a carbon atom by electron impact S.J. Ward, J.H. Macek We obtained using the Coulomb-Born approximation [1] a deep minimum in the TDCS for K-shell ionization of a carbon atom by electron impact for the electron ejected in the scattering plane [2]. The minimum is obtained for the kinematics of the energy of incident electron $E_i$ = 1801.2 eV, the scattering angle $\theta_f$ = 4$^\circ$, the energy of the ejected electron $E_{\bf k}$ = 5.5 eV, and the angle for the ejected electron $\theta_k$ = 239$^\circ$. This minimum is due to a vortex in the velocity field. At the position of the vortex, the nodal lines of ${\rm Re}[T]$ and ${\rm Im}[T]$ intersect. We decomposed the CB1 T-matrix into its multipole components [1] for the kinematics of a vortex, taking the $z^\prime$-axis parallel to the direction of the momentum transfer vector. The $m = \pm 1$ dipole components are necessary to obtain a vortex. We also considered the electron to be ejected out of the scattering plane and obtained the positions of the vortex for different values of the y-component of momentum of the ejected electron, $k_y$. We constructed the vortex line for the kinematics of $E_i$ = 1801.2 eV and $\theta_f$ = $4^\circ$.\\[4pt] [1] J. Botero and J. H. Macek, Phys. Rev. A {\bf 45}, 154 (1992).\\[0pt] [2] S. J. Ward and J. H. Macek, submitted to Phys. Rev. A. [Preview Abstract] |
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MW1.00008: Out-of-plane ($e,2e$) measurements with 150eV incident beam energy on He autoionizing levels Nicholas L.S. Martin, B.A. deHarak, K. Bartschat In previous work we reported out-of-scattering-plane $(e,2e)$ measurements and calculations for helium $2\ell2\ell'$ auto\-ionizing levels at 488eV incident electron energy and scattering angle 20.5$^\circ$. The results were presented as $(e,2e)$ angular distributions energy-integrated over each level\footnote{B.A. deHarak, K. Bartschat, and N.L.S. Martin, Phys. Rev. Lett. {\bf 100}, 063201 (2008)} and the detailed energy dependence of the recoil/binary peak ratio\footnote{B. A. deHarak, K. Bartschat, and N. L. S. Martin, Phys. Rev. A {\bf 89}, 012702 (2014)}. We have now begun similar measurements at 150eV electron beam energy and scattering angle 39.2$^\circ$. The geometry is then the same as for the earlier high energy experiments: ejected electrons are detected in a plane that contains the momentum transfer direction and is perpendicular to the scattering plane. The momentum transfer is 2.1~a.u., which is the same as in the earlier experiments. We will present preliminary data and compare the angular distributions with the high energy results. [Preview Abstract] |
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MW1.00009: Experimental and Theoretical Fully differential cross sections for electron impact ionization of phenol molecules Esam Ali, D. Jones, G. Silva, L. Chiari, R. Neves, M. Lopes, M. Brunger, C. Ning, D. Madison Experimental and theoretical Fully Differential Cross Sections (FDCS) are presented for 250 eV electron impact ionization of the highest and next highest occupied molecular orbitals (HOMO and NHOMO). Theoretical results are compared with experiment for in plane scattering with projectile scattering angles of 5$^{\circ}$, 10$^{\circ}$, and 15$^{\circ}$. Different theoretical models are examined - the molecular 3 body distorted wave (M3DW), and the distorted wave Born approximation (DWBA), with the effects of the post collision interaction (PCI) treated either exactly or with the Ward-Macek approximations. These approximations show good agreement with experimental data for binary peaks. However, for the recoil peak region, experiment finds a noticeable peak while theory predicts no peak. No recoil peak suggests no (or very weak) nuclear scattering, so we have investigated the importance of nuclear scattering by moving the nuclei closer to the center of mass. [Preview Abstract] |
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MW1.00010: Single electron impact ionization of the methane molecule Mammar Bouamoud, Mohammed Sahlaoui, Nour El Houda Benmansour Triply differential cross sections (TDCS) results of electron-impact ionization of the inner $2a_{1}$ molecular orbital of CH$_{4}$ are presented in the framework of the Second Born Approximation and compared with the experimental data performed in coplanar asymmetric geometry. The cross sections are averaged on the random orientations of the molecular target for accurate comparison with experiments and are compared also with the theoretical calculations of the Three Coulomb wave (3CW) model. Our results are in good agreement with experiments and 3CW results in the binary peak. In contrast the Second Born Approximation yields a significant higher values compared to the 3CW results for the recoil peak and seems to describe suitably the recoil region where higher order effects can occur with the participation of the recoiling ion in the collision process. [Preview Abstract] |
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MW1.00011: Single photoionization of many electron atoms and molecules: a Sturmian approach. Carlos M. Granados Castro, Lorenzo Ugo Ancarani, Dario M. Mitnik, Gustavo Gasaneo The Sturmian approach, using Generalized Sturmian Functions (GSF), has been applied successfully for the study of several atomic ionization processes [1]. The extension of the method to molecular systems is under development, and is the subject of the present contribution. As a first step, in order to test our methodology, we started with some atomic systems and calculated the photoionization cross section using the one-active electron approximation together with model potentials. We solved the time-independent, first-order perturbative, Schr\"{o}dinger equation; the scattering wave function is expanded in GSF. Having validated our approach and computer codes, we then studied the photoionization of molecules, such as CH$_{4}$, using a similar method. After considering initially an angular-averaged model potential, we then used a non-central one leading to a set of angular-coupled of equations. The scattering wave function is again expanded in a GSF basis set, but this time with many different angular momenta. In order to take into account the random orientation of the molecule, an angular average over all the possible spatial orientation of the molecule is finally performed. The calculated cross sections are compared with theoretical and experimental data (see [2] and references therein). \\[4pt] [1] G. Gasaneo et al, Adv. Quantum Chem. 67, 153 (2013).\\[0pt] [2] C. M. Granados-Castro et al, Few-Body Systems, in press (2014). [Preview Abstract] |
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MW1.00012: Cross Sections and Transport Properties of BR$^{-}$ Ions in AR Jasmina Jovanovic, Vladimir Stojanovic, Zoran Raspopovic, Zoran Petrovic We have used a combination of a simple semi-analytic theory - Momentum Transfer Theory (MTT) and exact Monte Carlo (MC) simulations to develop Br$^{-}$ in Ar momentum transfer cross section based on the available data for reduced mobility at the temperature $T=$300 K over the range 10 Td $\le \quad E/N \quad \le $ 300 Td. At very low energies, we have extrapolated obtained cross sections towards Langevin's cross section. Also, we have extrapolated data to somewhat higher energies based on behavior of similar ions in similar gases and by the addition of the total detachment cross section that was used from the threshold around 7.7 eV. Relatively complete set was derived which can be used in modeling of plasmas by both hybrid, particle in cell (PIC) and fluid codes. A good agreement between calculated and measured ion mobilities and longitudinal diffusion coefficients is an independent proof of the validity of the cross sections that were derived for the negative ion mobility data. In addition to transport coefficients we have also calculated the net rate coefficients of elastic scattering and detachment. [Preview Abstract] |
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MW1.00013: Limitation of the local approximation for EDF determination on the periphery of the high pressure plasmas Kirill Kapustin, Mikhail Krasilnikov, Anatoly Kudryavtsev Local approximation is widely used for the calculation of electron distribution function (EDF). In this approximation, terms which correspond to spatial gradients and ambipolar electric fields in a Boltzmann kinetic equation can be omitted, and EDF can be factorized in a product of electron density, which depends on radius and time and on part of EEDF, which depends on kinetic energy. In this case, EEDF is a function of local parameters such as heating (current-carrying) electric field, gas temperature, density of excited particles \textit{etc}. These simplifications of calculations of the kinetic equation make this approximation widely used. In this work, physical formation mechanisms of EEDF in a high pressure positive column glow discharge are discussed. It is shown that criterion of applicability of local approximation depends not only on ratio between energy relaxation length and characteristic plasma dimension but also on ratio between heating and ambipolar electric fields. So that, in the gas periphery where ambipolar electric field becomes larger then axial electric field, the local approximation for EEDF is not valid even at a high pressures. This work was supported by RSCF and SPbSU. [Preview Abstract] |
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MW1.00014: Monte Carlo simulation of electrons in dense gases Wade Tattersall, Greg Boyle, Daniel Cocks, Stephen Buckman, Ron White We implement a Monte-Carlo simulation modelling the transport of electrons and positrons in dense gases and liquids, by using a dynamic structure factor that allows us to construct structure-modified effective cross sections. These account for the coherent effects caused by interactions with the relatively dense medium. The dynamic structure factor also allows us to model thermal gases in the same manner, without needing to directly sample the velocities of the neutral particles. We present the results of a series of Monte Carlo simulations that verify and apply this new technique, and make comparisons with macroscopic predictions and Boltzmann equation solutions. [Preview Abstract] |
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MW1.00015: Electron swarm transport coefficients in mixtures of H2O with He and Ar: Experiment and Boltzmann equation calculations Jaime de Urquijo, E. Basurto, A.M. Juarez, Kevin Ness, Robert Robson, Michael Brunger, Ron White The drift velocity of electrons in mixtures of gaseous water with helium and argon are measured over the range of reduced electric fields from 0-300Td using a pulsed-Townsend technique. Small admixtures of water to both helium and argon are found to produce negative differential conductivity (NDC), despite NDC being absent from the pure gases. Comparison of the measured drift velocities with those calculated from a multi-term solution of Boltzmann's equation provides a further discriminative assessment on the accuracy and completeness of electron water vapour cross-sections. [Preview Abstract] |
(Author Not Attending)
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MW1.00016: Transport properties derived from ion-atom collisions: $^{6}$Li-$^{6}$Li$^{+}$ and $^{6}$Li-$^{7}$Li$^{+}$ Cases Moncef Bouledroua, Fouzia Bouchelaghem This investigation treats quantum-mechanically the ion- atom collisions and computes the transport coefficients, such as the coefficients of mobility and diffusion. For the case of lithium, the calculations start by determining the gerade and ungerade potential curves through which ionic lithium approaches ground lithium. Then, by considering the isotopic effects and nuclear spins, the elastic and charge-transfer cross sections are calculated for the case of $^{6}$Li$^{+}$ and $^{7}$Li$^{+}$ colliding with $^{6}$Li. Finally, the temperature-dependent diffusion and mobility coefficients are analyzed, and the results are contrasted with those obtained from literature. The main results of this work have been recently published in [Phys. Chem. Chem. Phys. Vol. 16, 18751 (2014)]. [Preview Abstract] |
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MW1.00017: Positron cooling by vibrational and rotational excitation of a molecular gas M.R. Natisin, J.R. Danielson, C.M. Surko A better understanding of low energy positron-molecule collisions and thermalization processes will aid in the development of novel experimental techniques and technology. In particular, cryogenic positron plasmas would allow the creation of positron beams with significantly higher energy resolution than currently available, enabling the study of scattering features and annihilation processes not measurable using current techniques.\footnote{A. C. L. Jones et al., {\it Phys. Rev. Lett.} {\bf 108}, 093201 (2010).} Measurements of positron temperature as a function of time are presented when a positron gas, confined in an electromagnetic trap at an elevated temperature ($\geq1200$~K), is cooled by interactions with the 300~K molecular gases CF$_4$, N$_2$ and CO. A simple model describing positron thermalization by coupling to vibrational and rotational modes is also presented and used to make cooling-rate predictions calculated in the Born approximation. Comparisons to the measured positron cooling-rate curves permit estimates of the magnitudes of the relevant cross sections. Positron cooling rates are compared for these gases at 300~K, and estimates of their effectiveness in cooling positrons to cryogenic temperatures is discussed. [Preview Abstract] |
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MW1.00018: Two-Electron Systems in Generalized Exponential Cosine Screened Coulomb Potentials Karina V. Rodriguez, Lorenzo Ugo Ancarani, Dario M. Mitnik We look at the ground state of two-electron systems placed in a dense quantum plasma environment where the three interactions between two particles of charges z$_{i}$ and z$_{j}$ placed at a distance r$_{ij}$ can be described by exponential-cosine-screened Coulomb potential (ECSCP) [1] V(r$_{ij})=$z$_{i}$z$_{j\, }$exp(-$\lambda $r$_{ij})$ cos($\delta $r$_{ij})$/r$_{ij}$ where $\lambda $ and $\delta $ are two positive real screening parameters related to the plasma frequency. The first calculations of the ground and first excited states of H$^{-}$, He and Li$^{+}$ where all three interactions between pairs of particles were represented by the same ECSCP, and with $\lambda = \delta $, were recently reported [2,3]. In the present work we show results for two-electron systems for which the interactions are described by generalized ECSCP with unequal parameters. Our calculations are performed with a rather versatile Configuration Interaction approach (see [3] and references therein), with correlated basis functions which explicitly depend on the three interparticle distances and which respect exactly all three cusp conditions. \\[4pt] [1] P. K. Shukla and B. Eliasson, Phys. Lett. A 372, 2897 (2008).\\[0pt] [2] A. Ghoshal and Y. K. Ho, J. Phys. B 42, \quad 075002 (2009).\\[0pt] [3] L. U. Ancarani and K. V. Rodriguez, Phys. Rev. A 89, 012507 (2014). [Preview Abstract] |
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MW1.00019: A particle-in-cell/Monte Carlo simulation of a dual frequency capacitively coupled chlorine discharge Shuo Huang, Jon Tomas Gudmundsson The effect of the control parameters of both the high and low frequency sources on a dual frequency capacitively coupled chlorine discharge is investigated using a hybrid approach consisting of a particle-in-cell/Monte Carlo simulation and a volume averaged global model. The dependence of the plasma parameters such as particle density, effective electron temperature, electron energy probability function and ion energy and angular distributions for both Cl$^+$ and Cl$_2^+$ ions, on the discharge pressure, driving frequency, driving current density and secondary electron emission, is systematically investigated. As the low-frequency current density is increased the flux of Cl$_2^+$ ions to the surface increases only slightly while the average energy of Cl$_2^+$ ions to the surface increases almost linearly with increasing low-frequency current, which shows possible independent control of the flux and energy of Cl$_2^+$ ions by varying the low-frequency current in a dual frequency capacitively coupled chlorine discharge. Besides, as the high frequency current increases, the electron heating is enhanced in the sheath region and diminished in the bulk region, showing a transition of the electron heating from the drift-ambipolar mode to the $\alpha$ mode. [Preview Abstract] |
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MW1.00020: Generalized Analytical Model for the Radio-Frequency Sheath Uwe Czarnetzki An analytical model for the planar radio frequency (RF) sheath in capacitive discharges is developed based on the applied RF voltage as the boundary condition. The model applies to all kind of waveforms for the applied RF voltage, includes both sheaths in a discharge of arbitrary symmetry, and allows for an arbitrary degree of ion collisionallity in the sheaths (charge-exchange collisions). Further, effects of the finite floating potential during sheath collapse are included. The model can even be extended to electronegative plasmas with low bulk conductivity. The individual sheath voltages, the self-bias, and the RF floating potentials are explicitly calculated by a voltage balance equation using a cubic-charge voltage relation for the sheaths. In particular, the RF-phase as a function of the sheath voltage is determined. This is an input for a single second order non-linear integro-differential equation which is governing the ion flow velocity in the sheath [1]. Fast numerical integration is straight forward and in many cases approximate analytical solutions can be obtained. Based on the solution for the ion flow velocity, densities, electric fields, currents, and charge-voltage relations are calculated. Further, the Child-Langmuir laws for the collisionless as well as the highly collisional case are derived. Very good agreement between model and experiments is obtained. \\[4pt] [1] U.Czarnetzki, Phys. Rev. E \textbf{88}, 063101 (2014). [Preview Abstract] |
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MW1.00021: Experimental Study of Sheath Voltage Scaling Laws in Asymmetric RF Capacitive Discharges Milka Nikolic, Janardan Upadhyay, Lepsha Vuskovic, Svetozar Popovic Asymmetric radio frequency (RF) capacitive discharges have been attracting a continuous interest in ongoing research on complex shaped, three dimensional niobium superconducting radio frequency (SRF) cavities. To increase their performance, the SRF cavities can be etched by capacitively coupled RF discharges, a technology already used in semiconductor industry. Since the SRF performance parameters depend highly on plasma properties, we have studied the effects of different pressure, power and inner and outer electrode area ratio on the sheath voltage scaling laws in the finite length coaxial symmetry RF capacitive discharge, treated originally in [1]. The experimental set up used in this study consists of two finite-length cylindrical coaxial electrodes, the inner RF powered electrode and the outer grounded electrode. We performed the experiment in Ar and in 15{\%} Cl diluted with Ar mixture at pressure range 0.0375 -- 0.45 Torr and applying the powers from 25 -- 200 W. The results are presented in the form of asymmetric sheath voltage scaling law. \\[4pt] [1] M. V. Alves, M. A. Lieberman, V. Vahedi, and C. K. Birdsall, J. Appl. Phys. \textbf{69}, 3823 (1991). [Preview Abstract] |
(Author Not Attending)
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MW1.00022: Ion velocity distribution function measurements in a dual-frequency rf sheath Nathaniel Moore, Walter Gekelman, Patrick Pribyl, Yiting Zhang, Mark Kushner Ion dynamics are investigated in a dual-frequency rf sheath above a 300 mm diameter biased silicon wafer in an industrial inductively coupled (440 kHz, 500 W) plasma etch tool. Ion velocity distribution (IVD) function measurements in the argon plasma are taken using laser induced fluorescence (LIF). Planar sheets of laser light enter the chamber both parallel and perpendicular to the surface of the wafer in order to measure both parallel and perpendicular IVDs at thousands of spatial positions. A fast (30 ns exposure) CCD camera measures the resulting fluorescence with a spatial resolution of 0.4 mm. The dual-frequency bias on the wafer is comprised of a 2 MHz low frequency (LF) bias and an adjustable 10-20 MHz high frequency (HF) bias. The bias voltages may be switched on and off (f$_{rep}$ up to 1 kHz, duty cycle 10-90\%). Several different bias and timing combinations were tested. Ion energy distribution function and ion flux measurements for each case are compared. For the LF case (no HF), the IVD was found to be uniform to within 5\% across the wafer. IVDs as a function of phase of the LF bias were also measured. The LF experimental results are compared with simulations specifically designed for this particular plasma tool. [Preview Abstract] |
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MW1.00023: Capacitively coupled dc/rf discharges driven by arbitrary linear circuits John Cary, Ming-Chieh Lin, C. Zhou, David Smithe We have developed a method for computing the system of an arbitrary linear circuit coupled to a capacitively coupled plasma discharge. The method relies on the known method of separation of the vacuum and plasma generated fields for the discharge. It is time centered and implicit in the circuit quantities, thus guaranteeing second-order accuracy in time. This method has been implemented in the VSim engine (Vorpal). Numerical verification of the order of accuracy will be shown. [Preview Abstract] |
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MW1.00024: Observation of Transient Electric Fields in Particle-in-Cell Simulation of Capacitively Coupled Discharges Sarveshwar Sharma, Sanjay Kumar Mishra, Predhiman Kaw The analytical prediction of the presence of transient electric field regions between the bulk plasma and sheath edge in \textit{radio frequency capacitively coupled plasma }(\textit{RF-CCP}) \textit{discharges }has been reported by \textit{Kaganovich }(\textit{PRL }89, 265006 \quad 2002). In this paper we have used the semi-infinite particle-in-cell (PIC) simulation technique to verify the theoretical prediction for the existence of transient electric field in the linear regime; it is shown that the \textit{PIC} simulation results are in good agreement with the results predicted by analytical model in this regime. It is also demonstrated that the linear theory overestimates the transient electric field as one moves from linear to weakly nonlinear regime. The effect of applied \textit{RF }current density and electron temperature on evolution of transition field and phase mixing regime has been explored. [Preview Abstract] |
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MW1.00025: Investigation of self-excited plasma series resonance oscillations in multi-frequency capacitive discharges Edmund Schuengel, Julian Schulze, Ihor Korolov, Aranka Derzsi, Zolt\'an Donk\'o The self-excitation of plasma series resonance (PSR) oscillations is a dominant feature in the current of asymmetric capacitively coupled radio-frequency discharges. The asymmetry can be caused by an asymmetry of the chamber geometry and/or that of the applied voltage waveform. We study the self-excitation of the PSR in a geometrically symmetric, electrically asymmetric capacitive argon discharge using PIC/MCC simulations as well as an analytical model. The results show that increasing the number of subsequent harmonics in the driving voltage waveform enhances the asymmetry and, therefore, leads to a significant increase of the current amplitude of higher harmonics, which are generated due to the nonlinearities of the sheaths. These high-frequency resonance oscillations between the capacitive sheaths and the inductive plasma bulk can only be reproduced correctly by the analytical model, if the cubic sheaths charge-voltage relation and the temporal modulation of the bulk length and electron density within the RF period are taken into account. Furthermore, we demonstrate that the nonlinear electron resonance heating (NERH) associated with the presence of PSR oscillations significantly contributes to the total electron heating and causes a spatial asymmetry of the ionization. [Preview Abstract] |
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MW1.00026: Control of ion energy distributions in capacitive RF discharges using customized voltage waveforms Edmund Schuengel, Julian Schulze, Ihor Korolov, Aranka Derzsi, Zolt\'an Donk\'o The flux and energy distribution of ions flowing onto the substrate in capacitive radio-frequency discharges is vitally important for the plasma surface interaction. Therefore, controlling and optimizing the shape of the ion flux-energy distribution (IED) allows for an improvement of various plasma surface processing applications. Recently, separate control of the mean energy and the total flux of ions has been achieved via the Electrical Asymmetry Effect. Here, we study the control of the IED shape in capacitively coupled radio-frequency discharges by applying customized voltage waveforms to the powered electrode. Data obtained from PIC/MCC simulations in helium at low pressures show that the dominant features in the shape of the IED result from the energy gain of ions flowing into the sheath and ions created in the sheath (in ion neutral collisions) in the periodically oscillating sheath electric field. The high-energy component of the IED is determined by ions flowing into the sheath, whereas ions created within the sheath lead to peaks in the IED at lower energies. We demonstrate, how the shape of the high-energy component as well as the position (energy) and height (flux) of the peaks can be controlled by varying the phases and amplitudes of the multiple applied frequencies. [Preview Abstract] |
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MW1.00027: Transition of Plasma Electrons from Anisotropy to Isotropy at Beginning of the Pulsed Discharges Hyo-Chang Lee, Chin-Wook Chung We present experimental studies on the transition of plasma electrons from anisotropy to isotropy at beginning of the pulsed discharges. The electron energy probability functions (EEPFs) are obtained from the first derivate of the measured I-V curve at planar type Langmuir probes. Strong anisotropy is found depending on the probe direction at the first stage of the low pressure pulsed plasma. The anisotropy of the electrons is transited into isotropy on the EEPF. This study may provide fundamental understanding of both the electron acceleration via wave-electron interaction and the electron thermal transport in plasma discharges. [Preview Abstract] |
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MW1.00028: E-H transition and Hysteresis in Radio-Frequency Inductively Coupled Plasmas Hyo-Chang Lee, Chin-Wook Chung We present both experimental and theoretical studies of E-H transition and hysteresis in radio-frequency inductive discharges. It is found that the hysteresis is significantly affected by nonlinearity of the plasma with the modification of electron energy distribution (EED). This kind of hysteresis is also observed in various plasma discharges with powers, pressures, and magnetic field where EEDs are evolved. [Preview Abstract] |
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MW1.00029: Comprehensive Plasma Diagnostics of Oxygen ICP Thomas Wegner, Christian K\"ullig, J\"urgen Meichsner A planar inductively coupled 13.56\,MHz discharge (ICP) in pure oxygen was studied using comprehensive plasma diagnostics. In particular the 160\,GHz Gaussian beam microwave interferometry, the Langmuir probe technique, the phase resolved optical emission and VUV absorption spectroscopy were applied. During the transition from the capacitive (E-) to the inductive (H-) mode all plasma parameter are changed. The E-mode at low electron density and high electron temperature is characterized by high electronegativity. The gas temperature is comparable to room temperature and the molecular oxygen ground state and metastable state ($\mathrm{O}_2\left(\mathrm{a}^1\Delta_{\mathrm{g}}\right)$) density are not significantly changed with increasing RF power in the E-mode. During the transition into the H-mode the electron density increases over two orders of magnitude whereas the electron temperature decreases to about the half of the E-mode. The heating mechachnisms change from the rf sheath heating and electrical field reversal in the E-mode to two excitation rate patterns in the first and second half of the RF cycle. In the H-mode, the electronegativity is strongly reduced, the gas temperature and the metastable density are increased by a factor of about two. [Preview Abstract] |
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MW1.00030: Experimental observation of transit time resonance heating through electron energy distribution function measurement in a low pressure inductively coupled plasma Hyun-Ju Kang, Chin-Wook Chung The maximum electron heating by transit time resonance is related to the driving frequency and the skin depth. In this study, electron energy distribution functions (EEDFs) were measured at various frequencies (8MHz, 10MHz, 13,56MHz) and powers in a low-pressure inductively coupled plasma. It was observed that the heated electron energy on the EEDFs is shifted toward lower energy, as the frequency decreases or the power increases. [Preview Abstract] |
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MW1.00031: Simulation of Plasma Characteristics for Inductively Coupled Argon Plasma Using Dual-Frequency Antennas Xue-chun Li, Xiao-yan Sun, You-nian Wang A large-area wafer size is necessary for plasma processing in the micro-electronics industry. However, it is one of the most important issues to obtain uniform plasma over a large-area substrate in addition to high-density plasmas for the plasma processing. Recently, the experimental study on the dual-frequency inductively coupled plasma (ICP) has been reported as a mean of improving the plasma uniformity over the large-area substrate [1]. In this work, we develop a self-consistent method combined with the electromagnetic theory and fluid model to simulate the plasma characteristics for dual-frequency inductively coupled argon plasma. In the model, the ICP source consists of two planar-spiral coils. We investigate the plasma uniformity problem by adjusting the parameters of the two coils, such as the RF current, the position of the coils and the RF frequency ratio. It was found that the uniformity of the ion density over the wafer is improved with dual-frequency antennas comparing with a single-frequency antenna. The plasma uniformity increases when the coils are located farther from the centre of the ICP source. It is consistent with the experimental study. \\[4PT] [1] A. Mishra, K. N. Kim, T. H. Kim, and G. Y. Yeom. Plasma Sources Sci.Technol. 21 (2012) 035018. [Preview Abstract] |
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MW1.00032: Discharge Characteristic of VHF-DC Superimposed Magnetron Sputtering System Hirotaka Toyoda, Yushi Fukuoka, Takashi Fukui, Noriharu Takada, Kensuke Sasai Magnetron plasmas are one of the most important tools for sputter deposition of thin films. However, energetic particles from the sputtered target such as backscattered rare gas atoms or oxygen negative ions from oxide targets sometimes induce physical and chemical damages as well as surface roughening to the deposited film surface during the sputtering processes. To suppress kinetic energy of such particles, superposition of RF or VHF power to the DC power has been investigated. In this study, influence of the VHF power superposition on the DC target voltage, which is important factor to determine kinetic energy of high energy particles, is investigated. In the study, 40 MHz VHF power was superimposed to an ITO target and decrease in the target DC voltage was measured as well as deposited film deposition properties such as deposition rate or electrical conductivity. From systematic measurement of the target voltage, it was revealed that the target voltage can be determined by a very simple parameter, i.e., a ratio of VHF power to the total input power (DC and VHF powers) in spite of the DC discharge current. [Preview Abstract] |
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MW1.00033: Carbon Multicharged Ion Generation from Laser Plasma Oguzhan Balki, Hani E. Elsayed-Ali Multicharged ions (MCI) have potential uses in different areas such as microelectronics and medical physics. Carbon MCI therapy for cancer treatment is considered due to its localized energy delivery to hard-to-reach tumors at a minimal damage to surrounding tissues. We use a Q-switched Nd:YAG laser with 40 ns pulse width operated at 1064 nm to ablate a graphite target in ultrahigh vacuum. A time-of-flight energy analyzer followed by a Faraday cup is used to characterize the carbon MCI extracted from the laser plasma. The MCI charge state and energy distribution are obtained. With increase in the laser fluence, the ion charge states and ion energy are increased. Carbon MCI up to C$^{+9}$ are observed along with carbon clusters. When an acceleration voltage is applied between the carbon target and a grounded mesh, ion extraction is observed to increase with the applied voltage. [Preview Abstract] |
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MW1.00034: Energy Distribution of Aluminum Multicharged Ions Generated from Laser Plasma Md Haider Shaim, Alexey Bugayev, Hani E. Elsayed-Ali Multicharged ion sources are an emerging tool for nanoprocessing and nanofabrication. The higher charge state of multicharged ions has significant potential energy equal to the sum of ionization energies of stripped electrons. Multicharged ion interaction with solids involves the release of this potential energy that causes electronic exchange interaction along with the electronic excitation. We report on measurement of aluminum multicharged ion energy distribution generated by laser ablation of an aluminum target. A Q-switched Nd:YAG laser is used to ablate the aluminum target in an ultrahigh vacuum while an electrostatic time-of-flight spectrometer is used to detect the laser-generated multicharged ions. An increase in the ions' signal and generation of higher charge state is observed with the increase of laser ablation energy. The energy distribution of ions for increasing laser fluence shows an increase in the ion energy along with narrowing of the distribution. Applying an accelerating voltage to the aluminum target increases the charge extraction and the energy of multicharged ions. Angular distribution of the multicharged ions is dependent on the ion charge state. Multicharged ions up to Al$^{+4}$ are detected. [Preview Abstract] |
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MW1.00035: Optical Studies of Sputtering in Magnetically Enhanced Helium Discharges James E. Lawler, Thomas J. Feigenson, Timothy J. Sommerer, David J. Smith, Jason Trotter, Steven C. Aceto A cold-cathode gas-discharge switch for the electric power grid must operate at the highest possible current density to be competitive. Magnetic enhancement, similar to that of a magnetron sputtering discharge, achieves current densities far above the classic ``normal'' cold-cathode fall current density. One of two physical mechanisms, power dissipation or sputtering, is likely to limit the ultimate current density of a magnetically enhanced device. Using forced cooling a power dissipation density of about 1 kW/cm$^{2}$ should be achievable. This corresponds to a current density of 5 A/cm$^{2}$ assuming a 200 V cathode fall. Sputtering can be much reduced using a light buffer gas such as hydrogen or helium. We are studying the transition to `metal mode' operation in such discharges. Metal mode is often described as a current density at which lines of sputtered metal dominate buffer gas lines in the emission spectrum. Preliminary results in a magnetically enhanced discharge operating in the A/cm$^{2}$ range with helium buffer gas over some cathode materials are presented. [Preview Abstract] |
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MW1.00036: Operation of a high-voltage, high-power gaseous electronics switch for electric grid power conversion Timothy Sommerer, Sergey Zalubovsky A series of approximations and simple models is used to estimate the properties of a cold-cathode plasma in a high-voltage, high-power gas switch for use in grid-scale electric power conversion. The active volume is a plane-parallel gap $\sim$ 1 cm filled with hydrogen at a pressure $\sim$ 0.3 torr. A magnetic field in the region adjacent to the cathode is used to increase the current density to practical levels \textgreater 1 A/cm$^{2}$. The estimated bulk plasma density is mid-10$^{12}$ cm$^{-3}$ and the electron temperature is $\sim$ 3 eV, to offset volume recombination. The magnetic field enhances ionization near the cathode and also impedes electron diffusion away from the region, sometimes resulting in a peak of plasma density in an extended presheath region. The switch is opened by applying a positive potential to a grid between the cathode and anode, leading to the formation of an ion matrix sheath around the grid, and an ion-acoustic wave that sweeps out the conducting plasma between the grid and the anode in about 1 $\mu $s. [Preview Abstract] |
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MW1.00037: Modeling of High-Power Gas Switch for Electric Grid System Alexander V. Khrabrov, Johan Carlsson, Igor D. Kaganovich, Timothy Sommerer, Sergey Zalubovsky There has been recent interest in utilizing gas switches in high-power AC/DC conversion for the purpose of power transmission over long distances. These devices would be based on a glow discharge with magnetically insulated cold cathode [1]. Their operation is similar to sputtering magnetrons [2,3], but at much higher pressures (0.1 to 1 Torr) in order to achieve high current densities. We present results of numerical (the particle-in-cell code EDIPIC 1d3v PIC [4]) and analytical investigation of a gas switch in the conduction phase. The important properties of the high-pressure magnetron discharge are a very narrow cathode sheath and a considerable voltage drop in the magnetized pre-sheath where most of the ionization takes place due to Joule heating. *The information, data, or work presented herein was funded in part by the Advanced Research Projects Agency-Energy (ARPA-E), U.S. Department of Energy, under Award Number DE-AR0000298. \\[4pt] [1] D. M. Goebel, Rev. Sci. Instr. \textbf{67}, 3136 (1996).\\[0pt] [2] A. Rauch, et al, J. App. Phys. \textbf{111}, 083302 (2012).\\[0pt] [3] C. Huo, et al, Plasma Sources Sci. Technol. \textbf{22}, 045005 (2013).\\[0pt] [4] D. Sydorenko, et al, Phys. Rev. Lett. \textbf{103}, 145004 (2009). [Preview Abstract] |
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MW1.00038: Experimental and Numerical Investigation of the Dependency of Reaction Dynamics on the Plasma Gas Temperature in He/N$_{2}$ Cryoplasmas Hitoshi Muneoka, Keiichiro Urabe, Sven Stauss, Kazuo Terashima The plasma gas temperature ($T_{\mathrm{g}})$ is one of the essential parameters in plasma science and technology, but so far, the effect of $T_{\mathrm{g}}$ on low-temperature high-gas-density plasma chemistry has not been investigated in detail yet. Cryoplasmas, which are defined as plasmas whose $T_{\mathrm{g}}$ can be controlled below room temperature (RT), have the potential for various applications. In this study, to investigate the effect of $T_{\mathrm{g}}$ on the reaction dynamics in He/N$_{2}$ cryoplasmas, we developed a new 0D reaction model and also investigated the cryoplasmas by time-resolved laser absorption spectroscopy (LAS) and optical emission spectroscopy (OES). LAS measurements in He cryoplasmas at the same gas density as at RT and 1 atm, showed a longer lifetime (\textgreater 50 times) of metastable helium atom (He$^{\mathrm{m}})$ at cryogenic temperature (CT) compared to those at RT. OES revealed a time delay of the N$_{2}^{+}$ emission peak relative to the He emission peak of a few microseconds, and the delay decreased with increasing $T_{\mathrm{g}}$. The simulation using our reaction model suggested that the long lifetime of He$^{\mathrm{m}}$ at CT are due to the change of the reaction dynamics related to He$^{\mathrm{m}}$ as a function of $T_{\mathrm{g}}$. [Preview Abstract] |
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MW1.00039: Electron avalanche and spark evolution along laser path in resonant laser-induced ignition Steven Adams, Boyd Tolson, Amber Hensley A multi-photon ionization scheme is studied that could provide laser-induced ignition within a high-voltage gap across an aircraft combustion chamber. The multi-photon resonant enhanced ionization (REMPI) technique could potentially be applied as a laser trigger from a compact low power laser source leading to breakdown and ignition of an aircraft air-fuel flow. In this experiment, an ultraviolet laser is passed through an aperture in the anode and into the flow chamber. The REMPI process forms an ionized channel between the electrodes and, with an applied electric field, eventually leads to breakdown precisely along the laser path. A delay time of 200 to 1000 ns between the laser pulse and breakdown event is typical for our range of conditions. High speed imaging and spectroscopic data reveal evidence of space charge regions and local field distortion within the interelectrode space during the delay time and a model is applied to simulate the electron avalanche process. Spatially resolved spectroscopic analysis identifies various regions and degrees of laser photoionization, electron impact ionization, radical species and gas heating during the delay time. [Preview Abstract] |
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MW1.00040: Preliminary investigation of an atmospheric microplasma using Raman and Thomson laser scattering Bradley Sommers, Steven Adams A triple grating spectrometer system has been coupled with an ultraviolet laser at 266 nm for the purpose of investigating Rayleigh, Raman, and Thomson scattering within atmospheric plasma sources. Such laser interactions present a non-invasive diagnostic to investigate small scale atmospheric plasma sources, which have recently garnered interest for applications in remote optical sensing, materials processing, and environmental decontamination. In this work, the laser scatter and temperature relationship were calibrated with a heated nitrogen cell held at atmospheric pressure while subsequent scattering measurements were made in atmospheric discharges composed of nitrogen and air. An adjustable electrode configuration and dc circuit were assembled to produce a microdischarge operating in normal glow mode, thus providing a non-thermal plasma in which the translational, rotational, vibrational and electron temperatures are not in equilibrium. Preliminary results include measurements of these temperatures, which were calculated by fitting simulated scattering spectra to the experimental data obtained using the triple grating spectrometer. Measured temperatures were also compared with those obtained using standard optical emission spectroscopy methods. [Preview Abstract] |
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MW1.00041: Numerical Investigations of Positive Surface Streamer Discharges For High-Pressure Large Gap Arc Breakdown Ashish Sharma, Laxminarayan Raja Streamers are thin conducting channels which are formed by application of fast high-voltage pulses at the electrode surface. Surface streamers are used in a flash-lamp approach to initiate an arc breakdown in a large electrode gap at atmospheric and higher pressures. In this study, high-fidelity simulations are performed to study the propagation of cathode directed surface streamers into high pressure argon medium. The streamer model employed is based on the self-consistent multispecies and continuum description of the plasma. The model predicts transient dynamics of a surface streamer. Of particular interest is the conductivity of the streamer channel as a function of the electron density in the trail of the streamer head. The spatially continuous conductive streamer successfully bridges the gap between two electrodes from which an arc column can develop. The model predicts the conductivity of the streamer column as a function of gas properties, applied voltages on the electrodes and wall losses. The Model results compare favorably with accompanying experimental results for a flash-lamp based approach for large gap arc breakdown. [Preview Abstract] |
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MW1.00042: Atomic oxygen production scaling in a nanosecond-pulsed externally grounded dielectric barrier plasma jet Brian Sands, Jacob Schmidt, Biswa Ganguly, James Scofield Atomic oxygen production is studied in a capillary dielectric barrier plasma jet that is externally grounded and driven with a 20-ns risetime positive unipolar pulsed voltage at pulse repetition rates up to 25 kHz. The power coupled to the discharge can be easily increased by increasing the pulse repetition rate. At a critical turnover frequency, determined by the net energy density coupled to the discharge, the plasma chemistry abruptly changes. This is indicated by increased plasma conductance and a transition in reactive oxygen species production from an ozone-dominated production regime below the turnover frequency to atomic-oxygen-dominated production at higher pulse rates. Here, we characterize atomic oxygen production scaling using spatially- and temporally-resolved two-photon absorption laser-induced-fluorescence (TALIF). Quantitative results are obtained via calibration with xenon using a similar laser excitation and collection system. These results are compared with quantitative ozone and discharge power measurements using a helium gas flow with oxygen admixtures up to 3\%. [Preview Abstract] |
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MW1.00043: Characterization of combined power plasma jet using AC high voltage and nanosecond pulse for reactive species composition control Keisuke Takashima, Hideaki Konishi, Toshiaki Kato, Toshiro Kaneko In the application studies for both bio-medical and agricultural applications, the roles of the reactive oxide and/or nitride species generated in the plasma has been reported as a key to control the effects and ill-effects on the living organism. The correlation between total OH radical exposure from an air atmospheric pressure plasma jet and the sterilization threshold on Botrytis cinerea is presented. With the increase of the OH radical exposure to the Botrytis cinerea, the probability of sterilization is increased. In this study, to resolve the roles of reactive species including OH radicals, a combined power plasma jet using nanosecond pulses and low-frequency sinusoidal AC high voltage (a few kHz) is studied for controlling the composition of the reactive species. The nanosecond pulses are superimposed on the AC voltage which is in synchronization with the AC phase. The undergoing work to characterize the combined power discharge with electric charge and voltage cycle on the plasma jet will also be presented to discuss the discharge characteristics to control the composition of the reactive species. [Preview Abstract] |
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MW1.00044: Modeling of non-equilibrium and non-thermal plasma discharge in air: Three temperature modeling approach Rajib Mahamud, Tanvir Farouk The rapid progress in atmospheric pressure non-thermal plasma discharge has made air to be a preferable choice for feed gas. Despite the ease of operation of such discharges in air, the preference of air provides added complexity to modeling and simulations in terms of kinetics and different temperature modes. The diatomic nature of both N$_{2}$ and O$_{2}$ contributes to this complexity. In this work we report simulation results from a one-dimensional multi-physics model. A dc driven air plasma discharge operating at atmospheric and higher pressure is simulated. The model considers 50 species and 200 elementary reactions. The reaction scheme considers electron introduced and heavy particle reactions for N$_{2}$ and O$_{2}$ as well as interactions between nitrogen and oxygen. In addition to the species conservation equations, poisson's equation three different temperature's are resolved - electron, vibrational and translational. A special focus has been the coupling between the different temperatures to accurately resolve the energy cascade. The predictions from the model are found to be in good qualitative agreement against experimental measurements available in the literature. [Preview Abstract] |
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MW1.00045: Comparison of Fabrication Techniques for Micro-Scale Spark Gap Plasma Switches Matthew Burnette, David Staack Microplasma spark gaps with 2D geometries were fabricated by two techniques on alumina, first using photolithography and metal sputtering with thicknesses of hundreds of nanometers, and second using thermal-spray several microns thick, but with lower feature resolution. Several high temperature metals were tested as electrode material for the microplamsa device, including tungsten and chromium; however the chromium samples were not robust enough, eroding away too quickly for extensive testing. Scanning electron microscope (SEM) images were taken before and after testing to determine the wear on the samples. The sputtered tungsten thin films and thermal-spray deposited nickel films on alumina were compared after testing in 1 atm of helium running for one hour at a current of 1 mA. Slight wear and discoloration were noted on the anodes, yet significant erosion occurred on the cathodes; no wear was noted on the alumina. The thermally-sprayed nickel sample had the least wear, while the thin tungsten sample had the most wear. Discoloration was also seen on the nearby floating-voltage electrodes despite not being a part of the circuit, most likely due to heating. As the electrodes eroded, the plasma attachment point moved unpredictably. [Preview Abstract] |
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MW1.00046: On cathode spot motion in magnetically driven high-pressure arcs Valerian Nemchinsky, Vladimir Kolobov, Robert Arslanbekov High-pressure magnetically driven arcs are used in many industrial applications. In gas heaters, the arc is forced to rotate by axial magnetic fields along tubular electrodes to reduce electrode erosion. Many questions about the nature cathode and anode spot motion and electrode erosion remain unclear. We develop computational tool for simulations of electrode erosion in high pressure moving arcs. We assume that the operation of cathode spot operation in the high-pressure arc has many features of the vacuum arc (so called cold cathode mode) modified by the high pressure gas environment under high current density on the level of 10$^{9}$A/m$^{2}$ and temperature exceeding melting point. The gas-dynamic interaction of the cathode vapor jet with background gas defines the erosion rate. We study the arc column attachment to the cathode. The arc column motion by the Lorentz force produces a tilt near the cathode due to time lag of electrode heating processes. It is suggested that the tilt of the arc column leads to asymmetry of the cathode voltage drop: it is larger at the leading end of the cathode attachment and lower at the opposite (trailing) end. The asymmetry of the cathode voltage drop causes asymmetry of the heat transfer to the cathode: it is shifted ahead of the cathode temperature distribution. As a result, the cathode spot moves catching up running away heat flux. The proposed model allows to connecting the tilt angle of the arc column with the speed of the arc rotation and current density at the cathode. [Preview Abstract] |
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MW1.00047: Optical emission in a sonoplasma production system with the help of a punching metal plate K. Sasaki, Y. Iwata, S. Tomioka, S. Nishiyama, N. Takada Sonoplasmas are liquid-phase plasmas produced by ultrasonic power. We have reported an efficient method for producing standing sonoplasmas (Y.~Iwata, et al., Appl. Phys. Express \textbf{6} (2013), 127301). This method employs a punching metal plate which is inserted just below the water surface with the irradiation of ultrasonic wave. In this work, we examined spatiotemporal variations of optical emission (sonoluminescence) intensities from sonoplasmas. The optical emission images were captured at various phases using an ICCD camera. The region with the strong optical emission intensity coincided with the region with cavitation bubbles. In addition, the optical emission intensity was observed in the shrink phase of the sizes of cavitation bubbles. These experimental observations indicate that the optical emission is caused by sonoplasmas which are produced at the collapses of cavitation bubbles. Optical emissions were also observed at different positions and different phases, but the distributions of these optical emission intensities were broader than that observed at the shrink phase of cavitation bubbles. The distribution of the optical emission intensities can be utilized as a hint for understanding the spatiotemporal distribution of the ultrasonic power. [Preview Abstract] |
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MW1.00048: Oxide nanoparticles synthesis via laser-induced plasma in liquid Taku Goto, Hansel Weihs, Mitsuhiro Honda, Sergei Kulinich, Yoshiki Shimizu, Tsuyohito Ito Laser ablation in fluids has recently attracted a lot of attention as one of synthetic techniques to prepare new attractive nanomaterials, with the ability to control both product chemistry and morphology in many systems. In this study, we generated laser-induced plasma in H$_{\mathrm{2}}$O -- ethanol mixtures, while ablating metal targets to produce oxide nanoparticles and to study the effect of the medium on their properties. The ablated targets used in this study were Zn or Sn plates. A nanosecond Nd:YAG laser with the wavelength of 532 nm (10 Hz, 20-30 mJ/pulse) was applied to irradiate the targets. The liquid media were maintained at 0.1 to 30 MPa to study the effect of pressure. We found that the H$_{\mathrm{2}}$O/ethanol ratio (at atmospheric pressure) can control the properties of the produced ZnO nanoparticles, such as defects and oxidation degree. The properties were examined by photoluminescence (PL) spectroscopy, X-ray diffraction, electron microscopies, and so on. More details will be presented at the symposium. [Preview Abstract] |
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MW1.00049: Comparison of temporal variation in emission intensity of OH(A) in after-glow period of Ar/H$_2$O and He/H$_2$O gas-mixture plasmas in water Tatsuru Shirafuji Previously, we have reported quite long duration (approx. 500 ns) of optical emission intensity of OH(A) in an after glow period of Ar plasma in water.\footnote{T. Shirafuji, Y. Oguda and Y. Himeno: Jpn. J. Appl. Phys. \textbf{53}, 010211 (2014).} Numerical simulation has revealed that this phenomenon can be explained in terms of production of OH(A) through the reaction of H$_3$O$^+$ and low temperature electrons. We can perform similar plasma processing using He plasma in water with almost the same process performance in the case of decomposition of methylene blue molecules in aqueous solution. Thus, we have expected that the long duration of OH(A) optical emission can be observed also in He plasma in water. However, such long duration of OH(A) optical emission has not been observed in the case of He plasma in water. To understand this difference, we have performed numerical simulation of Ar/H$_2$O and He/H$_2$O plasmas, and discuss differences in major reaction pathways to produce OH(A) in Ar/H$_2$O and He/H$_2$O plasmas. [Preview Abstract] |
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MW1.00050: A two-phase multi-physics model for simulating plasma discharge in liquids Ali Charchi, Tanvir Farouk Plasma discharge in liquids has been a topic of interest in recent years both in terms of fundamental science as well as practical applications. Even though there has been a large amount of experimental work reported in the literature, modeling and simulation studies on plasma discharges in liquids is limited. To obtain a more detailed model for plasma discharge in liquid phase a two-phase multiphysics model has been developed. The model resolves both the liquid and gas phase and solves the mass and momentum conservation of the averaged species in both the phases. The fluid motion equation considers surface tension, electric field force as well as gravitational force. To calculate the electric force, the charge conservation equations for positive and negative ions and also for the electrons are solved. The Possion's equation is solved in each time step for obtaining a self consistent electric field. The obtained electric field and charge distribution is used to calculate the electric body force exerted on the fluid. Simulation show that the coupled effect of plasma, surface and gravity results in a time-evolving bubble shape. The influence of different plasma parameters on the bubble dynamics is studied. [Preview Abstract] |
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MW1.00051: Exploration of Underwater Laser Breakdown Using Two Synchronized Gated Cameras Lutz Huwel, Clayton Baumgart, Susannah Betts, Thomas J. Morgan, William G. Graham Using two synchronized intensified CCD cameras, we have studied spatial and temporal characteristics of optical breakdown in water created by a focused 10 ns pulsed Nd:YAG laser operating at 1064 nm. For three water samples with different impurity content (ultrapure, distilled, and tap water), the plasma evolution was monitored up to 1 ms after breakdown. Images taken by the two cameras, systematically delayed relative to each other, reveal that the center of emission intensity does not remain at a fixed location. In single plasma events, the center first moves, on average, toward the incoming laser beam. Then, at about 100 to 200 ns, the apparent direction of motion reverses and the center returns towards the focal point. On the other hand, in repetitive breakdown the time averaged center moves steadily downstream with each subsequent pulse. Details of this behavior depend on repetition frequency. We will also present shadowgraphy results revealing time resolved speeds of both shockwave and bubble expansion. [Preview Abstract] |
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MW1.00052: Modulation frequency dependence of bispectrum of laser light scattering intensity from nanoparticles formed in reactive plasmas Teppei Ito, Daisuke Yamashita, Hyunwoong Seo, Kunihiro Kamataki, Naho Itagaki, Kazunori Koga, Masaharu Shiratani Interactions between plasmas and nano-interface are one of the most important issues in plasma processing. We have studied effects of plasma fluctuation on growth of nanoparticles in reactive dusty plasmas with amplitude modulation (AM) and have clarified that plasma fluctuation leads to generation of a large amount of nanoparticles with small size [1]. Here we report results of bispectrum analysis of time evolution of laser light scattering intensity from nanoparticles in reactive plasmas. Experiments were carried out using a capacitively-coupled discharge reactor. We employed Ar$+$DM-DMOS discharge plasmas to generate nanoparticles. We found higher harmonics and sub-harmonics in spectra of laser light scattering intensity, suggesting nonlinear coupling between plasma parameters and nanoparticle growth rate. We will report modulation frequency dependence of bispectrum of laser light scattering intensity. \\[4pt] [1] M. Shiratani, et al., Jpn. J. Appl. Phys. 53 (2014) 010201. [Preview Abstract] |
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MW1.00053: Iodine as propellant for electric space propulsion Pascaline Grondein, Pascal Chabert, Ane Aanesland In PEGASES (an electric gridded thruster) both positive and negative ions are expelled after extraction from an ion-ion plasma formed downstream a localized magnetic field placed a few centimeters from the ionization region. For this thruster concept, we believe that Iodine is the best candidate. Its advantages are multiple: heavy and therefore good for high thrust, low ionization threshold and high electronegativity (the latter crucial for PEGASES) leading to high ion-ion densities and low RF power, at solid state at STP with a high vapor, and finally inexpensive. Iodine is also di-atomic and therefore energy loss in dissociation processes are reduced compared to SF6. We present here a dedicated experimental set-up intended for iodine experiments. The injection system consists of an evaporation chamber with temperature controlled gas lines and vacuum chamber to control condensation. A global model of the iodine electronegative plasma will be developed to compare and predict the plasma behavior and composition inside the thruster. The main challenge in this model is to reproduce the conditions of a strongly segregated plasma with two regions: one with rather high electron temperature and low electronegativity and the other an ion-ion plasma with low temperature. [Preview Abstract] |
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MW1.00054: Computational modeling of nanoparticle charging mechanism in a hydrocarbon flame Parth Shah, Alexei Saveliev A model that describes the charging mechanism of a 20 nm nanoparticle introduced in a methane-air counterflow laminar diffusion flame was developed and analyzed. The detailed kinetic model considers the production of ions and electrons in a methane-air flame due to chemi-ionization, thermal ionization and charging due to diffusion. The chemi-ionization model considers a one-step reaction that produces ions and electrons in a flame in addition to the detailed neutral reaction mechanism. The model is analyzed to study the effects of temperature, total nanoparticle concentration and chemi-ionization on charge formation in nanoparticles as well as on ions and electrons. The results show that thermal ionization is more dominant at high temperatures whereas diffusion charging is important at low temperatures. High concentration of nanoparticles influences the gas-phase ion and electron concentration to a very significant level whereas low concentration has a negligible effect on the same. [Preview Abstract] |
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MW1.00055: Negative ion surface production on carbon materials in hydrogen plasma: a thermodesorption analysis of carbon surface states Gilles Cartry, Kostiantyn Achkasov, C\'edric Pardanaud, Jean-Marc Layet, Alain Simonin, Alix Gicquel, Othmen Saidi, R\'egis Bisson, Thierry Angot Negative ion surface production in plasmas has been studied in the context of fusion where H- surface production in cesium-seeded plasmas is of a primary interest for neutral beam injection devices. Although surface production is much lower in Cs-free plasmas, it may be non-negligible. Indeed it has been observed that significant numbers of H- ions can be created on a graphite surface upon positive ion bombardment in H2 plasmas. Graphite material has been compared to a large variety of diamond layers, in particular poly-crystalline boron-doped and non-doped diamond thin films. It has been shown an enhancement of the negative-ion yield by a factor 5 for diamond materials at high temperature, while the yield continuously decreases for graphite. The difference is due to the different properties of the pristine materials but also to the modifications bring by the plasma to the materials during exposure. In order to study in detail these modifications, plasma exposed samples have been analyzed by Raman spectroscopy and Temperature Programmed Desorption (TPD). These diagnostics helped to trace the surface state changes of the materials and identify the reasons for the elevated negative ion production at high temperature on diamonds. [Preview Abstract] |
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MW1.00056: Mass- spectrometric Observations of Plasma-assisted Catalysis Dave Seymour, Alan Rees, David Lundie Plasma discharges are known to facilitate the catalysis of reactive gas mixtures. A variety of plasmas, including surface barrier discharges, have been demonstrated to enhance the efficiency of the catalysts such as nickel/alumina or silver/alumina, used in conventional thermally--activated reactors. The observed improvements have included a lowering of the onset temperature at which the catalyst becomes effective, and an increase in the over-all efficiency of the process. A number of diagnostic methods have been employed to study the synergistic behaviour of plasmas and heated catalysts, the technique adopted often being specific to the monitoring of a particular reaction product. The work described here is aimed at demonstrating the versatility of mass-spectrometric methods in following the behaviour of typical plasma-assisted catalytic processes. [Preview Abstract] |
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MW1.00057: Structure and Characteristics of a Spherical Plasma Focus: Theory and Simulation Yasar Ay, Mohamed A. Abdal-Halim, Mohamed Bourham Most studies of dense plasma focus devices use cylindrical coaxial shapes, however,~a spherical shape is investigated herein. Snow plow model and shock wave equations are coupled with the circuit equations to model the spherical plasma focus. Of interest in spherical plasma focus is to have both sheath expansion and the magnetic pressure changing rate for the rundown phase instead of the constant sheath only for the cylindrical case. The developed model is compared to published experimental results for validation and good agreement was obtained. Hydrogen and its isotopes were separately used for investigating the effect of the different molecular weights on plasma parameters. The gas pressure and discharge voltage were varied for these gases to study their effect on the plasma parameters. The study predicts a peak discharge current of 1.5MA for tritium with 0.92MA dip discharge current, and less for deuterium and hydrogen. The current drop for tritium indicates focus action. It indicates that the sheath velocity for heavy gases is lower than lighter gases. Predicted maximum temperature variation is about 11.1eV for hydrogen, 14.6eV for deuterium, 15.9eV for DT mixture and 17eV for pure tritium; which indicates higher temperature with heavier gasses. [Preview Abstract] |
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MW1.00058: Feasibility Study of an EEDF Driven Rare Gas Metastable Laser Guy Parsey, Yaman G\"{u}\c{c}l\"{u}, John Verboncoeur, Andrew Christlieb Following advancements in dipole-pumped alkali vapor lasers (DPAL), it has been shown that metastable excited rare gas atoms exhibit similar spectral properties with an inherently less reactive gain medium. Rare gas lasers (RGL) use an electric discharge to maintain the metastable species densities analogous to heating for the alkali vapor, both of which focus on optical pumping to induce lasing with a three-level scheme. We propose using a modified electron energy distribution function (EEDF) to either modify RGL efficiency characteristics or to drive the optical gain process. Using our general-purpose kinetic global modeling framework (KGMf), we present a study on the effect of the EEDF on the RGL reaction kinetics with an emphasis on determining if lasing can be achieved without optical pumping. Considering the classical optically driven RGL as a baseline, we focus on the EEDF as a pumping mechanism. A pure Ar model is used along with models of Ar, Kr, Xe using He to drive collisional relaxation of the upper level. [Preview Abstract] |
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MW1.00059: Characterization of Plasma Generated in a Commercial Grade Plasma Etching system Gabriella Bessinger, Dereth Drake, Svetozar Popovic, Leposava Vuskovic The use of plasma for etching and cleaning of many types of metal surfaces is becoming more prominent in industry. This is primarily due to the fact that plasma etching can reduce the amount of time necessary to clean/etch the surface and does not require large amounts of environmentally hazardous chemicals. Most plasma etching systems are designed and built in academic institutions. These systems provide reasonable etching rates and easy accessibility for monitoring plasma parameters. The downside is that the cost is typically high. Recently a number of commercial grade plasma etchers have been introduced on the market. These etching systems cost near a fraction of the price, making them a more economical choice for researchers in the field. However, very few academicians use these devices because their effectiveness has not yet been adequately verified in the current literature. We will present the results from experiments performed in a commercial grade plasma etching system, including analysis of the pulse characteristics observed by a photo diode and the plasma parameters obtained with optical emission spectroscopy. [Preview Abstract] |
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MW1.00060: Ion densities of CH$_{2}$F$^{+}$ and CHF$_{2}^{+}$ generated by dissociative ionization of charge exchange collisions in Ar or Kr diluted CH$_{2}$F$_{2}$ Plasmas Makoto Sekine, Yusuke Kondo, Yudai Miyawaki, Kenji Ishikawa, Toshio Hayashi, Keigo Takeda, Hiroki Kondo, Masaru Hori Hydro-fluorocarbon gas, CH$_{\mathrm{x}}$F$_{\mathrm{4-x}}$ is used for SiO$_{2}$ and Si$_{3}$N$_{4}$ etching, where the reduction of F in molecule leads high selectively. High selectively were reported as using hydro-fluorocarbon gases having more molecular mass such as C$_{5}$HF$_{7}$ [1]. H reacts to N and removes it from Si$_{3}$N$_{4}$. Therefore H works as an etchant of Si$_{3}$N$_{4}$. By using CH$_{2}$F$_{2}$ gas as an addition of conventional process, high selectively was obtained [2]. In order to understand the etch mechanism for the CH$_{2}$F$_{2}$ containing plasma, we investigate the gas phase species and reaction to produce etchants. In many cases, multiple fragmentation of the parent gas is suppressed by dilution of large amount of rare gas (M). Besides, dissociative ionization of charge exchange collisions, CH$_{2}$F$_{2}+$M$^{+}\to $CH$_{2}$F$^{+}+$F$\cdot+$M* and CHF$_{2}^{+}+$H$\cdot+$M* (M$=$Ar, Kr) has not been clarified yet. Here we show that the CH$_{2}$F$^{+}$ ion was dominant in the Ar-diluted plasma, because the channel of resonant dissociative ionization between Ar$^{+}$ (ca. 15.8 eV) and C-F bonding cleavage (ca. 15.6 eV) became dominant. In contrast, for the Kr-diluted plasma, similar exchange between Kr$^{+}$ (ca. 14.0 eV) and C-H bonding cleavage (ca. 13.9 eV) generated dominantly CHF$_{2}^{+}$ ion. This behavior in the fraction of ion densities in the CH$_{2}$F$_{2}$ plasma affects significantly to the selectivity.\\[4pt] [1] Y. Miyawaki, et al., J. J. Appl. Phys. 52 (2013) 016201.\\[0pt] [2] M. Darnon, et al., J. Vac. Sci. {\&} Tec. B24 (2006) 2262. [Preview Abstract] |
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MW1.00061: Roughness formation on photoresist during etching examined by HBr plasma-beam Makoto Sekine, Yan Zhang, Kenji Ishikawa, Keigo Takeda, Hiroki Kondo, Masaru Hori For highly precise patterning in device fabrication, it is required to suppress roughness formations on photoresist (PR) polymers during plasma etching. HBr plasma treatment called ``plasma cure'' was proposed to reduce the roughness [1]. By using a beam irradiation, we reported the PR roughness formation in fluorocarbon plasma [2], and the effect of HBr cure. We report the roughness formation mechanism by surface analyses and power spectral density (PSD) of the roughness. Average slope and roll-off frequency of PSD are characterized by frequency components, the high-frequency roughness. We treated the data for six samples: a) pristine, b) after Ar plasma irradiation , c) after Ar plasma followed by HBr cure, d) after HBr cure, e) after HBr followed by Ar plasma beam, and f) after HBr followed by H$_{2}$ and Ar plasma beam irradiations. The PSD slopes were changed by each process. Based on the results, we speculated that the Ar-plasma beam formed a crust layer on the PR surface with unrelieved stress and HBr cure may soften the bulk PR to relieve the stress and cause agglomeration of polymers at the size over 10 nm.\\[4pt] [1] A. Ando et al., Thin Solid Films 515, 4928 (2007).\\[0pt] [2] T. Takeuchi et al., J. Phys. D: Appl. Phys. 46, 102001 (2013). [Preview Abstract] |
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MW1.00062: N-doped TiO$_{2}$ Prepared by RF DBD Plasma Zhi-Guang Sun, Jing-Lin Liu, Xiao-Song Li, Zhao-Jun Zhai, Ai-Min Zhu TiO$_{2}$ is the most promising photocatalyst because of its chemical stable, nontoxic, low cost, high photocatalytic activity and other attractive properties. Anatase has the highest photocatalytic activity among the three crystal form of TiO$_{2}$. However, the 3.2 eV bandgap of anatase TiO$_{2}$ makes it can only utilize the ultraviolet part of solar spectrum. Nitrogen doping is an effective method to extend the absorption range of anatase to visible light. N-doped TiO$_{2}$ preparation methods, such as heat treatment under NH$_{3}$ flow, the hydrolytic precipitation and the sol-gel process, have been reported. In this work, preparation of N-doped TiO$_{2}$ was explored by radio-frequency (RF) dielectric barrier discharge (DBD) plasma using Ar as discharge gas. TiCl$_{4}$, O$_{2}$ and N$_{2}$ were used as Ti, O and N precursors, respectively. In addition, H$_{2}$ was added to the plasma. X-ray photoelectron spectra (XPS) showed nitrogen was successfully doped into the as-prepared TiO$_{2}$. Further investigations on structure, composition and optical property of the as-prepared TiO$_{2}$ samples were conducted by X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) and UV-Vis absorption spectra techniques. [Preview Abstract] |
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MW1.00063: Cluster Incorporation Control by Hydrogen Silane Mixture in Multi Hollow Discharge Plasma CVD Susumu Toko, Yoshihiro Torigoe, Yoshinori Kanemitu, Hunwoong Seo, Kazunori Koga, Masaharu Shiratani Light-induced degradation has been one of the most important issues for hydrogenated amorphous silicon (a-Si:H) solar cells. In SiH4 discharges employed for a-Si:H deposition, there coexist SiH3 radicals and clusters. Our previous results show that incorporation of amorphous silicon clusters is responsible for the light-induced degradation. Therefore, it is important to control the incorporation of clusters into films. We have developed multi-hollow discharge plasma CVD method, by which clusters are driven toward the downstream region and high quality a-Si:H films can be deposited in the upstream region. In this study, we report that the generation rate of clusters and the amount of clusters incorporated into films can be controlled by hydrogen silane mixture. The generation rate of clusters correlates with electron temperature, which information was obtained by the optical emission intensity ratio ISi*/ISiH*. The amount of cluster incorporation was measured with quartz crystal microbalances (QCMs) [1]. With decreasing hydrogen gas flow rate the amount of cluster incorporation decreases.\\[4pt] [1] Y. Kim, et. al., Jpn. J. Appl. Phys. 52 (2013) 01AD01. [Preview Abstract] |
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MW1.00064: Effect of oxygen atoms dissociated by non-equilibrium plasma on flame of methane oxygen and argon pre-mixture gas Haruaki Akashi, Tomokazu Yoshinaga, Koichi Sasaki For more efficient way of combustion, plasma-assisted combustion has been investigated by many researchers. But it is very difficult to clarify the effect of plasma even on the flame of methane. Because there are many complex chemical reactions in combustion system. Sasaki et al [1] has reported that the flame length of methane and air premixed burner shortened by irradiating microwave power. They also measured emission from Second Positive Band System of nitrogen during the irradiation. The emission indicates existence of high energy electrons which are accelerated by the microwave. The high energy electrons also dissociate oxygen molecules easily and oxygen atom would have some effects on the flame. But the dissociation ratio of oxygen molecules by the non-equilibrium plasma is significantly low, compared to that in the combustion reaction. To clarify the effect of dissociated oxygen atoms on the flame, dependence of dissociation ratio of oxygen on the flame has been examined using CHEMKIN. It is found that in the case of low dissociation ratio of 10$^{-6}$, the ignition of the flame becomes slightly earlier. It is also found that in the case of high dissociation ratio of 10$^{-3}$, the ignition time becomes significantly earlier by almost half.\\[4pt] [1] K. Sasaki et al, J. Phys. D:Appl. Phys., 45, 455202 (2012). [Preview Abstract] |
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MW1.00065: Multiplex coherent anti-Stokes Raman scattering microspectroscopy for monitoring molecular structural change in biological samples Takayuki Ohta, Hiroshi Hashizume, Keigo Takeda, Kenji Ishikawa, Masafumi Ito, Masaru Hori Biological applications employing non-equilibrium plasma processing has been attracted much attention. It is essential to monitor the changes in an intracellular structure of the cell during the plasma exposure. In this study, we have analyzed the molecular structure of biological samples using multiplex coherent anti-Stokes Raman scattering (CARS) microspectroscopy. Two picosecond pulse lasers with fundamental (1064 nm) or the supercontinuum (460-2200nm) were employed as a pump and Stokes beams of multiplex CARS microspectroscopy, respectively. The pump and the Stokes laser beams were collinearly overlapped and tightly focused into a sample using an objective lens of high numerical aperture. The CARS signal was collected by another microscope objective lens which is placed facing the first one. After passing through a short pass filter, the signal was dispersed by a polychromator, and was detected by a charge-coupled device camera. The sample was sandwiched by a coverslip and a glass bottom dish for the measurements and was placed on a piezo stage. The CARS signals of the quinhydrone crystal at 1655, 1584, 1237 and 1161 cm-1 were assigned to the C-C, C$=$O stretching, O-H and C-O stretching vibrational modes, respectively. [Preview Abstract] |
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MW1.00066: Inactivation of the biofilm by the air plasma containing water Ryota Suganuma, Koichi Yasuoka Biofilms are caused by environmental degradation in food factory and medical facilities. Inactivation of biofilm has the method of making it react to chemicals including chlorine, hydrogen peroxide, and ozone. Although inactivation by chemicals has the problem that hazardous property of a residual substance and hydrogen peroxide have slow reaction velocity. We achieved advanced oxidation process (AOP) with air plasma. Hydrogen peroxide and ozone, which were used for the formation of OH radicals in our experiment, were able to be generated selectively by adjusting the amount of water supplied to the plasma. We inactivated Pseudomonas aeruginosa biofilm in five minutes with OH radicals generated by using hydrogen peroxide and ozone. [Preview Abstract] |
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MW1.00067: VUV-Photoionization CES-Detector of Volatile Bio-Marker Molecules Alexander Mustafaev, Nataliya Luneva, George Panasyuk, Nikolay Timofeev, Alexander Tsyganov Energy spectra of characteristic electrons released via photoionization by vacuum ultraviolet (VUV) radiation of admixture molecules in the atmospheric air, not using traditional evacuated energy analyzers, can be determined by Collisional Electron Spectroscopy (CES) method [1]. Some details of CES-photoionization sensor were described in [2]. Our further developments are devoted to application of CES-detectors for a mobile continuous bio-chemical diagnostics. It is known that ``on breathing'' it is possible to find out volatile bio-marker molecules of a lot of diseases (lung cancer, tuberculosis, COPD, asthma, diabetes, kidney disease, mammary cancer, Crohn's disease, ulcerative colitis, etc). But today's weighty and expensive laboratory equipment (like GC MS) provides observation of these bio-markers only during patients' visits to a doctor. In this way we study pocket-size CES-sensor with micro-plasma krypton resonance radiation source (10.6 eV photons) for the photoionization detection of metabolic ammonia, ethanol, acetone and pentane molecules directly in atmospheric air.\\[4pt] [1] A.A. Kudryavtsev, A.B.Tsyganov. US Patent 7,309,992.\\[0pt] [2] G.Y.Panasyuk, A.B. Tsyganov. Journal of Applied Physics, 2012, v.111, p.114503 [Preview Abstract] |
(Author Not Attending)
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MW1.00068: Single and multiple streamer DBD micro-discharges for testing inactivation of biologically contaminated surfaces Vaclav Prukner, Eva Dolezalova, Milan Simek Highly reactive environment produced by atmospheric-pressure, non-equilibrium plasmas generated by surface dielectric barrier discharges (SDBDs) may be used for inactivation of biologically contaminated surfaces. We investigated decontamination efficiency of reactive environment produced by single/multiple surface streamer micro-discharge driven by amplitude-modulated AC power in coplanar electrode geometry on biologically contaminated surface by \textit{Escherichia coli}. The discharges were fed by synthetic air with water vapor admixtures at atmospheric pressure, time of treatment was set from 10 second to 10 minutes, diameters of used SDBD electrodes (single and multiple streamer) and homogeneously contaminated disc samples were equal (25 mm), the distance between the electrode and contaminated surface was 2 mm. Both a conventional cultivation and fluorescent method LIVE/DEAD Bacterial Viability kit were applied to estimate counts of bacteria after the plasma treatment. Inactivation was effective and bacteria partly lost ability to grow and became injured and viable/active but non-cultivable (VBNC/ABNC). [Preview Abstract] |
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MW1.00069: Diagnostics of AC excited Atmospheric Pressure Plasma Jet with He for Biomedical Applications Masaru Hori, Keigo Takeda, Takumi Kumakura, Kenji Ishikawa, Hiromasa Tanaka, Hiroki Kondo, Makoto Sekine, Yoshihiro Nakai Atmospheric pressure plasma jets (APPJ) are frequently used for biomedical applications. Reactive species generated by the APPJ play important roles for treatments of biomedical samples. Therefore, high density APPJ sources are required to realize the high performance. Our group has developed AC excited Ar APPJ with electron density as high as 10$^{15}$ cm$^{-3}$, and realized the selective killing of cancer cells and the inactivate spores of \textit{Penicillium digitatum}. Recently, a new spot-size AC excited APPJ with He gas have been developed. In this study, the He APPJ was characterized by using spectroscopy. The plasma was discharged at a He flow rate of 5 slm and a discharge voltage of AC 9 kV. Gas temperature and electron density of the APPJ were measured by optical emission spectroscopy. From theoretical fitting of 2nd positive system of N$_{2}$ emission (380.4 nm) and Stark broadening of Balmer $\beta $ line of H atom (486.1 nm), the gas temperature and the electron density was estimated to be 299 K and 3.4. $\times$ 10$^{15}$ cm$^{-3}$. The AC excited He APPJ has a potential to realize high density with room temperature and become a very powerful tool for biomedical applications. [Preview Abstract] |
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MW1.00070: Comparison of plasma generated nitrogen fertilizer to conventional fertilizers ammonium nitrate and sodium nitrate for pre-emergent and seedling growth A. Andhavarapu, W. King, A. Lindsay, B. Byrns, D. Knappe, W. Fonteno, S. Shannon Plasma source generated nitrogen fertilizer is compared to conventional nitrogen fertilizers in water for plant growth. Root, shoot sizes, and weights are used to examine differences between plant treatment groups. With a simple coaxial structure creating a large-volume atmospheric glow discharge, a 162 MHz generator drives the air plasma. The VHF plasma source emits a steady state glow; the high drive frequency is believed to inhibit the glow-to-arc transition for non-thermal discharge generation. To create the plasma activated water (PAW) solutions used for plant treatment, the discharge is held over distilled water until a 100 ppm nitrate aqueous concentration is achieved. The discharge is used to incorporate nitrogen species into aqueous solution, which is used to fertilize radishes, marigolds, and tomatoes. In a four week experiment, these plants are watered with four different solutions: tap water, dissolved ammonium nitrate DI water, dissolved sodium nitrate DI water, and PAW. Ammonium nitrate solution has the same amount of total nitrogen as PAW; sodium nitrate solution has the same amount of nitrate as PAW. T-tests are used to determine statistical significance in plant group growth differences. PAW fertilization chemical mechanisms are presented. [Preview Abstract] |
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MW1.00071: Numerical Simulation of Acceleration and Deceleration of Weakly-Ionized Rarefied Arc-Jet along Diverging Magnetic Field Hiroshi Akatsuka, Satoshi Tsuno, Ampan Laosunthara, Atsushi Nezu, Haruaki Matsuura We are studying supersonic helium plasma jet along a diverging magnetic field with low-ionization degree and low electron density. It had been experimentally found that the ion Mach number had its maximum about 3 at 1 cm downstream after passing the magnetic nozzle, and after that, the ion Mach number turned to decrease, and the plasma potential dropped. We numerically simulated the expanding plasma along the open magnetic field. Considering dimensionless numbers of the plasma flow, we chose hybrid scheme, i.e., Direct Simulation Monte Carlo (DSMC) method for neutral particles and ions, and fluid method for electrons. Residual molecules in the vacuum chamber were also included as particles. Consequently, we find the velocity increase just after passing the open field line, followed by deceleration due to collisions with residual molecules with temperature increase. In this acceleration-deceleration phenomenon, the velocity difference between neutrals and charged species are found, which also affects the space potential. We discuss the mechanisms of potential formation by the pressure difference and the friction force between the charged particles and neutral species. The numerical results are, at least qualitatively, consistent with our previous experimental results. [Preview Abstract] |
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MW1.00072: ABSTRACT WITHDRAWN |
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MW1.00073: Kinetic Modeling of Martian Atmosphere Aerobraking Plasma Dereth Drake, Evan Smithwick During Martian atmospheric aerobraking the plasma that forms around a spacecraft can be considered a high-volume plasma reactor that is sustained by the dissipation of the spacecraft's kinetic energy. At altitudes below 100 km, it has been shown that the plasma parameters vary considerably depending on the spacecraft's trajectory. However, in the range which is applicable to aerobraking, 100 km \textless $h$ \textless 200 km, little of this work has been completed. We have evaluated a simple kinetic model to determine a probable range of plasma parameters for altitudes between 100 and 200 km using existing Martian atmospheric data and available probe trajectories. [Preview Abstract] |
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MW1.00074: Study of Unsteady Flow Actuation Produced by Surface Plasma Actuator on 2-D Airfoil Minh Khang Phan, Jichul Shin Effect of flow actuation driven by low current continuous or pulsed DC surface glow discharge plasma actuator is studied. Schlieren image of induced flow on flat plate taken at a high repetition rate reveals that the actuation is mostly initiated near the cathode. Assuming that the actuation is mostly achieved by ions in the cathode sheath region, numerical model for the source of flow actuation is obtained by analytical estimation of ion pressure force created in DC plasma sheath near the cathode and added in momentum equation as a body force term. Modeled plasma flow actuator is simulated with NACA0012 airfoil oscillating over a certain range of angle of attack (AoA) at specific reduced frequencies of airfoil. By changing actuation authority according to the change in AoA, stabilization of unsteady flow field is improved and hence steady aerodynamic performance can be maintained. Computational result shows that plasma actuation is only effective in modifying aerodynamic characteristics of separated flow. It turns out that plasma pulse frequency should be tuned for optimal performance depending on phase angle and rotating speed. The actuation authority can be parameterized by a ratio between plasma pulse frequency and reduced frequency. [Preview Abstract] |
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MW1.00075: Self-assembled Ag nano-patterns forming in downflow of ammonia-Ar atmospheric pressure microplasmas Naoya Kihara, Ella Blanquet, Osamu Sakai Fractal-like Ag nano-patterns were observed after drying silver nitrate solution in downflow of ammonia-Ar atmospheric pressure microplasmas. These atmospheric-pressure microplasmas generated hydrazine, and this hydrazine density in their downflow region was in the order of 10$^{15}$ cm$^{-3}$ [1]. As hydrazine is a very strong reducing agent, Ag nano-particles were extracted from the silver nitrate solution. The Ag nano-structures were fractal-like patterns, with fractal dimension range of 1.6-1.9. The network structures in these patterns with several mm diameter showed good electric conductivity and extraordinary optical responses, which will be favorable for future low-cost optical metamaterials.\\[4pt] [1] K. Urabe, Y. Hiraoka and O. Sakai, Plasma Sources Sci. Technol. 22, 032003 (2013). [Preview Abstract] |
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MW1.00076: Interactions between plasma-treated carbon nanotubes and electrically neutral materials Daisuke Ogawa, Keiji Nakamura A plasma treatment can create dangling bonds on the surface of carbon nanotubes (CNTs). The dangling bonds are so reactive that the bonds possibly interact with other neutral species even out of the plasma if the lifetime of the bonds is effectively long. In order to have good understandings with the interactions, we placed multi-wall CNTs (MWCNTs) in atmospheric dielectric barrier discharge that was created in a closed environment with the voltage at 5 kV. We set 50 W for the operating power and 15 minutes for the process time for this plasma treatment. Our preliminary results showed that the reaction between dangling bonds and neutrals likely occurred in the situation when CNTs were treated with argon plasma, and then exposed in a nitrogen-rich dry box. We did Fourier transform infrared (FTIR) spectroscopy after the treatments. The measurement showed that the spectrum with plasma-treated CNTs was different from pristine CNTs. This is an indication that the plasma-treated CNTs have reactive cites on the surface even after the discharge ($\sim$ minutes), and then the CNTs likely reacted with the neutral species that causes the different spectrum. In this poster, we will show more details from our results and further progresses from this research. [Preview Abstract] |
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MW1.00077: Optimizing Natural Gas Networks through Dynamic Manifold Theory and a Decentralized Algorithm: Belgium Case Study Caleb Koch, Leigh Winfrey Natural Gas is a major energy source in Europe, yet political instabilities have the potential to disrupt access and supply. Energy resilience is an increasingly essential construct and begins with transmission network design. This study proposes a new way of thinking about modelling natural gas flow. Rather than relying on classical economic models, this problem is cast into a time-dependent Hamiltonian dynamics discussion. Traditional Natural Gas constraints, including inelastic demand and maximum/minimum pipe flows, are portrayed as energy functions and built into the dynamics of each pipe flow. Doing so allows the constraints to be built into the dynamics of each pipeline. As time progresses in the model, natural gas flow rates find the minimum energy, thus the optimal gas flow rates. The most important result of this study is using dynamical principles to ensure the output of natural gas at demand nodes remains constant, which is important for country to country natural gas transmission. Another important step in this study is building the dynamics of each flow in a decentralized algorithm format. Decentralized regulation has solved congestion problems for internet data flow, traffic flow, epidemiology, and as demonstrated in this study can solve the problem of Natural Gas congestion. A mathematical description is provided for how decentralized regulation leads to globally optimized network flow. Furthermore, the dynamical principles and decentralized algorithm are applied to a case study of the Fluxys Belgium Natural Gas Network. [Preview Abstract] |
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MW1.00078: Plasma Modeling of Electrosurgery Scott Jensen, Daniel Friedrichs, James Gilbert, Wounjhang Park, Dragan Maksimovic Electrosurgery is the use of high frequency alternating current (AC) to illicit a clinical response in tissue, such as cutting or cauterization. Power electronics converters have been demonstrated to generate the necessary output voltage and current for electrosurgery. The design goal of the converter is to regulate output power while supplying high frequency AC. The design is complicated by fast current and voltage transients that occur when the current travels through air in the form of an arc. To assist in designing a converter that maintains the desired output power during these transients, we have used the COMSOL Plasma Module to determine the output voltage and current characteristics during an arc. This plasma model, used in conjunction with linear circuit elements, allows the full electrosurgical system to be validated. Two models have been tested with the COMSOL Plasma Module. One is a four-species, four-reaction model based on the local field approximation technique. The second simulates the underlying air chemistry using 30 species, 151 chemical reactions, and a coupled electron energy distribution function. Experimental output voltage and current samples have been collected and compared to both models. [Preview Abstract] |
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MW1.00079: POSTDEADLINE |
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MW1.00080: Solutions of the low-frequency plasma sheath circuit equations Mirko Vukovic We derive a relation between the time derivatives of the current and voltage of the low-frequency plasma sheath. This relation is used to derive a first order differential equation for the electrical current in a driven series resistor, capacitor, and sheath circuit. Analytic and semi-numeric solutions are obtained for pulse and periodic excitations. We use these solutions to analyze the Langmuir probe response in some common diagnostic applications: the pulse excitation (\v{S}amara et al, 2012)\footnote{\v{S}amara et al. A dc-pulsed capacitively coupled planar Langmuir probe for plasma process diagnostics and monitoring, Plasma Sources Sci. Technol. 21 (2012) 065004} and AC Bias (Van Nieuwenhove \& Van Oost, 1988)\footnote{Van Nieuwenhove \& Van Oost, Novel Langmuir probe technique for the real-time measurement of the electron temperature, Rev.Sci.Instrum. 59(7),July 1988} methods. [Preview Abstract] |
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MW1.00081: Atomic Layer Etching of Silicon to Solve ARDE-Selectivity-Profile-Uniformity Trade-Offs Mingmei Wang, Alok Ranjan, Peter Ventzek, Akira Koshiishi With shrinking critical dimensions, dry etch faces more and more challenges. Minimizing each of aspect ratio dependent etching (ARDE), bowing, undercut, selectivity, and within die uniformly across a wafer are met by trading off one requirement against another. At the root of the problem is that roles radical flux, ion flux and ion energy play may be both good and bad. Increasing one parameter helps meeting one requirement but hinders meeting the other. Self-limiting processes like atomic layer etching (ALE) promise a way to escape the problem of balancing trade-offs. ALE [1] was realized in the mid-1990s but the industrial implementation has been slow. In recent years interest in ALE has revived. We present how ARDE, bowing/selectivity trade-offs may be overcome by varying radical/ion ratio, byproduct re-deposition. We overcome many of the practical implementation issues associated with ALE by precise passivation process control. The Monte Carlo Feature Profile Model (MCFPM) is used to illustrate realistic scenarios built around an Ar/Cl$_{2}$ chemistry driven etch of Si masked by SiO$_{2}$. We demonstrate that ALE can achieve zero ARDE and infinite selectivity. Profile control depends on careful management of the ion energies and angles. For ALE to be realized in production environment, tight control of IAD is a necessary. Experimental results are compared with simulation results to provide context to the work. [1] Athavale et al., J. Vac. Sci. Technol. B, 14, 3702 (1996). [Preview Abstract] |
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MW1.00082: Interfacial instability of wormlike micellar solutions sheared in a Taylor-Couette cell Hadi Mohammadigoushki, Susan J. Muller We report experiments on wormlike micellar solutions sheared in a custom-made Taylor-Couette (TC) cell. The computer controlled TC cell allows us to rotate both cylinders independently. Wormlike micellar solutions containing water, CTAB, and NaNo3 with different compositions are highly elastic and exhibit shear banding within a range of shear rate. We visualized the flow field in the $\theta $-z as well as r-z planes, using multiple cameras. When subject to low shear rates, the flow is stable and azimuthal, but becomes unstable above a certain threshold shear rate. This shear rate coincides with the onset of shear banding. Visualizing the $\theta$-z plane shows that this instability is characterized by stationary bands equally spaced in the z direction. Increasing the shear rate results to larger wave lengths. Above a critical shear rate, experiments reveal a chaotic behavior reminiscent of elastic turbulence. We also studied the effect of ramp speed on the onset of instability and report an acceleration below which the critical Weissenberg number for onset of instability is unaffected. Moreover, visualizations in the r-z direction reveals that the interface between the two bands undulates. The shear band evolves towards the outer cylinder upon increasing the shear rate, regardless of which cylinder is rotating. [Preview Abstract] |
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MW1.00083: Inelastic processes of electron interactions with halouracils -- cancer therapy agents Chetan Limbachiya, Minaxi Vinodkumar, Mohit Swadia We report electron impact total inelastic cross sections for important cancer treatment agents, 5-fluorouracil (5FU), 5-chlorouracil (5ClU) and 5-bromouracil (5BrU) from ionization threshold through 5000 eV. We have employed Spherical Complex Optical Potential [1, 2] method to compute total inelastic cross sections Q$_{inel}$ and Complex Scattering Potential -- ionization contribution (CSP-ic) formalism, to calculate total ionization cross sections Q$_{ion}$. Electron driven ionization cross sections for these important compounds of therapeutic interest are reported for the first time in this work. In absence of any ionization study for these cancer therapy agents, we have compared the data with their parent molecule Uracil. Present cross sections may serve as a reference estimates for experimental work. \\[4pt] [1] Minaxi Vinodkumar \textit{et al..} Int. J. Mass Spectrom., \textbf{339-- 340,} 16 (2013)\\[0pt] [2] Chetan Limbachiya \textit{et al.}, Molecular Physics, \textbf{112(1)}, 101 (2014) [Preview Abstract] |
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MW1.00084: Study of striations in a spherically symmetric hydrogen discharge Lowell Morgan, Monty Childs, Michael Clarage, Paul Anderson We have observed, in experiments similar to those of [1, 2], multiple spherically symmetric striations or double-layers in a hydrogen discharge, sometimes containing a small amount of helium having a total gas pressure in the range 0.7 - 5 Torr. The discharge is a positive corona around a 6mm diameter steel anode driven by a 600V, max 3 Amp DC power supply. Using mass spectrometry we have found that sometimes as much as 10{\%} of the H$_{2}$ is dissociated into atomic hydrogen. The dominant positive ion is H$_{3}^{+}$. We have performed UV, visible, and near-IR spectroscopy of the plasma looking at line ratios and Stark broadening in order to obtain an estimate of electron temperature and density. We have also performed Abel transforms on images of the striations in order to find the true relative broad band emissivity from the optically thin plasma as a function of radius out from the anode finding that, typically, it peaks several anode radii out into the plasma striations. Some modeling and simulation of the plasma chemistry and transport will also be presented. Research supported by the International Science Foundation. \\[4pt] [1] Nerushev, \textit{et al}., Phys. Rev. E \textbf{58}, 4897 (1998).\\[0pt] [2] Belikov {\&} Sakhapov, J. Phys D \textbf{44}, 045202 (2011). [Preview Abstract] |
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MW1.00085: Investigation of the rates of surface and bulk ROS-generating reactions using indigo dye as an indicator Carly Anderson, Douglas Clark, David Graves We present evidence for the existence of two distinct processes that contribute to the generation of reactive oxygen and nitrogen species (RONS) in liquids exposed to cold atmospheric plasma (CAP) in air. At the plasma-liquid interface, there exists a fast surface reaction zone where RONS from the gas phase interact with species in the liquid. RONS can also be produced by ``slow'' chemical reactions in the bulk liquid, even long after plasma exposure. To separate the effects of these processes, we used indigo dye as an indicator of ROS production; specifically generation of hydroxyl radical. The rate of indigo decolorization while in direct contact with CAP is compared with the expected rate of hydroxyl radical generation at the liquid surface. When added to aqueous solutions after CAP exposure, indigo dye reacts on a time scale consistent with the production of peroxynitrous acid, ONOOH, which is known to decompose to hydroxyl radical below a pH of 6.8. In this study, the CAP used was a air corona discharge plasma run in a positive streamer mode. [Preview Abstract] |
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MW1.00086: A Global Enhanced Vibrational Kinetic Model for Investigation of Negative Hydrogen Ion Sources Sergey Averkin, Nikolaos Gatsonis A new Global Enhanced Vibrational Kinetic Model (GEVKM) is developed for modeling negative hydrogen ion production and destruction processes in low (mTorr level) to high pressure (Torr level) ion sources. GEVKM couples steady-state space averaged continuity equations for ground-state neutral $\mbox{H}_{2} $, $\mbox{H}$ species, 14 vibrationally excited molecular hydrogen species $\mbox{H}_{2} (v)$ , positive ions $\mbox{H}^{+}$,$\mbox{H}_{2}^{+} $,$\mbox{H}_{3}^{+} $,negative ions $\mbox{H}^{-}$, electronically excited hydrogen atoms $\mbox{H(}n\mbox{=2-3)}$, and electrons with electron energy and total energy equations. Compared to previous global models GEVKM includes a full vibrational kinetics treatment, a self-consistent evaluation of heavy particle temperature and spatial variation of species densities in estimation of wall fluxes. The input parameters to GEVKM are ion source geometry, inlet hydrogen flow rate and absorbed power and outputs include concentration and temperature of all species.The GEVKM is verified and validated by comparisons with previous experimental and computational results for a low pressure (10-100 mTorr) volume negative ion source and a high pressure (10-100 Torr) microwave generated hydrogen plasma reactor. The GEVKM is also used for a parametric investigation of a new high pressure negative hydrogen ion source that includes the RF discharge chamber and a nozzle. [Preview Abstract] |
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MW1.00087: Electron density and temperature diagnostics for atmospheric pressure plasmas using continuum radiation Sanghoo Park, Se Youn Moon, Wonho Choe Information on electrons is particularly valuable because most of the important plasma reactions are governed by electron kinetics. However, diagnostics of electron density (n$_{\mathrm{e}})$ and temperature (T$_{\mathrm{e}})$ of low temperature atmospheric pressure plasmas is still challenging although there are some advanced diagnostics available such as laser Thomson scattering or optical emission spectroscopy combined with complex plasma equilibrium models. In this work, we report a simple spectroscopic diagnostic method with high temporal and spatial resolution based on continuum radiation in the UV and visible range for n$_{\mathrm{e}}$ and T$_{\mathrm{e}}$. Together with the basic principle for the diagnostics including electron-atom bremsstrahlung (or neutral bremsstrahlung) and hydrogen radiative dissociation continuum, some experimental results in several argon and helium atmospheric pressure plasmas will be presented. In a typical argon 13.56 MHz parallel plate capacitive discharge, the measured values are T$_{\mathrm{e}}=$ 2.5 eV and n$_{\mathrm{e}}=$ 0.7-1.1 $\times$ 10$^{12}$ cm$^{-3}$ at P$_{\mathrm{rf}}=$ 110-200 W. Two-dimensional T$_{\mathrm{e}}$ profile of an Ar pulsed plasma jet using a DSLR camera and this diagnostics will also be shown. [Preview Abstract] |
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MW1.00088: High-energy tail formation in an ion energy distribution function in the cylindrical Hall thruster plasma Youbong Lim, Holak Kim, Jaesun Park, Jongho Seon, Wonho Choe Ion energy distribution functions (IEDFs) of individual ion species having different charge states (i.e. Xe$^{+}$, Xe$^{2+}$, Xe$^{3+}$, etc.) in the Hall thruster plasma are obtained from the measured E $\times$ B probe spectrum by a novel inversion technique using the iterative Tikhonov regularization method. The obtained IEDFs show the existence of a high-energy tail in the cylindrical Hall thruster plasmas that is mainly due to Xe$^{+}$ ions despite the presence of Xe$^{2+}$ and Xe$^{3+}$ ions with a large fraction. Ion dynamics inside the plasma was numerically investigated to demonstrate that the high-energy tail is due to nonlinear ion acceleration in the plasma oscillating at typically 100 to 500 kHz. We found that this oscillation driven by transit-time instability is responsible for the shift of the IEDF of the Xe$^{+}$ ions toward the high-energy side, showing the formation of high-energy tail in the overall IEDF. It was also found that the Xe flow rate raised from 4 to 10 sccm increases the oscillation strength at the same frequency of 360 kHz, which can be applied to control of the shape of the IEDF. [Preview Abstract] |
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MW1.00089: Ion beam and performance characteristics in the presence of multiply charged ions in annular and cylindrical type Hall thruster plasmas Holak Kim, Youbong Lim, Jongho Seon, Wonho Choe Operation performance and ion beam characteristics in the presence of multiply charged ions in cylindrical Hall thruster (CHT) and annular Hall thruster (AHT) plasmas are compared under identical conditions such as channel diameter, channel depth, and propellant flow rate. According to our previous results, the propellant utilization of the 200 W class CHT well exceeds unity [J. Lee et al., Appl. Phys. Lett. 99, 131505 (2011); M. Seo et al., Phys. Plasmas 20, 023507 (2013)] and the papers suggest that this may be related to the presence of multiply charged ions. In this work, we report the large fractions of Xe2$+$ and Xe3$+$ ions measured in the CHT plasma, which are about 16-26{\%} and 6-7{\%}, respectively. The measured values of specific impulse and thrust are higher by 1.4 times in CHT than in AHT at 300 V of the anode voltage, and it is found that the high fraction of multiply charged ions is responsible for the higher values of specific impulse and thrust. The details of the comparison of the overall performance and beam characteristics associated with multiply charged ions in AHT and CHT will be presented. [Preview Abstract] |
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