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ABSTRACTS GEM XVII Conference
5th -8th February 2012
1
SundayWelcome reception and registration at 6 pm. Canapes and open bar (beer, wine and soft drinks for 1 hour)
Monday08.50 to 10.30 Session 1 Chair: Rod Boswell
Lowke 8.50-9.10 Toward a New Theory of Electrical Breakdown in Air?
Buckman 9.10-9.30 Positron Interactions with the Rare-Gas Atoms
Charles 9.30-9.50 Research and development activities of the Space Plasma, Power and Propulsion laboratory
Hole 9.50-10.10 Plasma Theory and Modelling at the ANU
Murphy 10.10-10.30 The Formation and the Effects of Metal Vapour in Welding Arcs
Morning tea
11.10 to 12.30 Session 2 Chair: John Howard
Samuell 11.10-11.30 A hydrogen global model to complement plasma-surface interaction experiments
Dixon 11.30-11.50 Characterisation of a micro discharge array source
Jacob 11.50-12.10 RF Plasma Polymer Thin Films for Emerging Electronics and Biomedical Applications
Hong Young Chang 12.10-12.30 Fast Measurement of Electron Density using Fourier Cutoff Probe
Lunch
14.00 to 15.20 Session 3 Chair: Hong-Young Chang
Corr 14.00-14.20 The Material Diagnostic Facility: A linear plasma device for studying fusion relevant plasma-surface interactions
Caneses 14.20-14.40 Initial wave activity in the “Material Diagnostic Facility” (MDF)
Hae June Lee 14.40-15.00 The effect of magnetic field in diocotron instability of a hollow electron beam
J. W. Shon 15.00-15.20 Industrial Application of Very High Frequency CCP Plasma Source
Afternoon tea
16.00 to 17.40 Session 4 Chair: Ron White
Machacek 16.00-16.20 Threshold Effects in Positron Scattering with Atoms and Molecules
GEM Program
2
M. G. Neira-Velázquez 16.20-16.40 Gas ionization of CO2/H2S using plasma of radiofrequency
Eun Ha Choi 16.40-17.00 Measurement of Hydroxyl Radical, Plasma Density and Electron temperature for atmospheric Bioplasma Jet
Boadle 17.00-17.20 Positronic Helium? - Search for Positron Bound States in the Doubly Excited Region of the Helium Atom
Tran 17.20-17.40 Plasma modification and deposition of polymers for biofuel production
Dinner not provided, please organise your own.
Tuesday
09.00 to 10.20 Session 5 Chair: Christine Charles
Mozetic 9.00-9.20 Improved hemocompatibility of PET vascular grafts by oxygen plasma treatment
Booth 9.20-9.40 Plasma deposition of nanocrystalline silicon for solar cells: RF waveform tailoring to optimize deposition
rate and film morphology
Shahidi 9.40-10.00 Self cleaning and antibacterial effect on Cotton Fabrics Using Dc Magnetron Sputtering
Garcia 10.00-10.20 Electron scattering data to model electron tracks in gases: application to ethylene and sulfur hexafluoride
Morning tea
11.00 to 12.20 Session 6 Chair: Paul Booth
Dedrick 11.00-11.20 Control of diffuse and filamentary discharge modes in a pulsed, radio-frequency surface discharge in
atmospheric-pressure argon
Howard 11.20-11.40 Imaging studies of the ion velocity distribution function in the MDF helicon plasma source
Haskey 11.40-12.00 Initial results from the new Helical Mirnov Array for the H-1NF Heliac
Myoung-Jae Lee 12.00-12.20
Lunch
14.00 to 15.00 Session 7 Chair: Tony Murphy
O’Connell 14.00-14.20 Propagation of ionization fronts in atmospheric pressure plasma jets and their interactions
Lei Chang 14.20-14.40 Wave modelling in cylindrical non-uniform plasmas: electrostatic and electromagnetic waves
Schroeder 14.40-15.00 Expanding structures in magnetized plasmas
Afternoon tea
16.00 to 17.20 Session 8 Chair: J. W. Shon
3
White 16.00-16.20 Kinetic and fluid equation treatments of non-equilibrium electron and positron transport in dense gases and liquids
Tam 16.20-16.40 3D Modelling of dc Atmospheric Arc Discharges
Sang-Hun Seo 16.40-17.00 An experimental study on a large area multi-electrode discharge in the fabrication of microcrystalline thin film solar cell
Kim Chang-Bae 17.00-17.20
19:00 Conference banquet and open bar (wine beer and soft drinks for 2 hours)
Wednesday
09.00 to 10.20 Session 9 Chair: Deborah O’Connell
L.Campbell 9.00-9.20 Electron impact excitation of the higher-energy states of molecular oxygen in the atmosphere of Europa
Couedel 9.20-9.40 Mode coupling due to ion wakes in 2D complex plasma crystals
Dai 9.40-10.00 Enhancing inorganic nanomaterials by plasma functionalization/doping
C. Campbell 10.00-10.20
Morning tea
11.00 to 12.00 Session 10 Chair: Matthew Hole
Limao-Vieira 11.00-11.20 Electron transfer-induced fragmentation by atom-molecule collisions
Boswell 11.20-11.40 Particle-in-cell simulations of hollow cathode enhanced capacitively coupled rf discharges
Gans 11.40-12.00 Manipulating electron dynamics and plasma chemistry in dual radio-frequency driven atmospheric pressure plasmas
Farewell
Extending the Usefulness of an Electron Scattering Setup by the Addition of a Light Polarization Detector and Magnetic Angle
Changer
4
Toward a New Theory of Electrical Breakdown in Air?
John J LowkeCSIRO Materials Science and Engineering, Sydney.
Traditional breakdown criteria are given by the Townsend and streamer theories. The Townsend criterion requires that an initiating electron at the cathode be replaced by a secondary emission process such as photo -emission or electron emission by the impact of positive ions. But measurements of voltages of corona inception for positive and negative polarity, where the cathodes are markedly different, are equal to within a few percent. The streamer theory requires ionisation from space charge effects, in which case charge densities must be high and the value of exp(∫αdx) for the region of ionisation must be of the order of 10 8; α is the net ionisation coefficient and the integral is taken over the length of a path over which ionisation occurs. An analysis has been made of published onset corona voltages for both cylinders and points and it is found that exp (∫αdx) ~ 10 4 fits measured potentials for all published values, with cathode tip radii varying from 0.01 to 20 cm. It is proposed that the new breakdown criterion of exp (∫αdx) ~ 10 4 corresponds to the onset of ionisation from collision processes between the vibrational states of nitrogen, which are all metastable, the fitted effective rate coefficient for such ionisation being 10 - 10 cm 3 s - 1.
5
Positron Interactions with the Rare-Gas Atoms
J.R. Machacek, A. Jones, P. Caradonna, C. Makochekanwa, D. Slaughter, J.P. Sullivan and
S.J. Buckman
ARC Centre for Antimatter-Matter Studies, Research School of Physics and Engineering,
Australian National University, Canberra, 0200 ACT
We have recently completed a comprehensive study of positron interactions with the rare-gas
atom series He, Ne, Ar, Kr, Xe [1-4]. The measurements have been carried out using a high-
resolution, trap-based positron beam and the results consist of absolute cross sections for a
range of interactions, including:
● Total scattering
● Total elastic scattering
● Positronium formation
● Differential elastic scattering
One of the attractions of such studies with the rare gases is that their closed-shell structure
facilitates, in principle, a more accurate theoretical treatment using ab inito quantum
scattering calculations. Such calculations pose significant difficulties for even the simplest
atomic species and, as a result, various approximations are required in their application to
many-electron targets. Thus much of the motivation for these studies is a comparison of
experimental results with the best such scattering calculations.
Details of the experimental techniques, the experimental results, and comparisons with state
of the art theory will be given in the presentation.
[1] P. Caradonna et al. Phys. Rev. A 80 032710 (2009)
[2] A. Jones et al. Phys. Rev. A83 032701 (2011)
[3] C. Makochekanwa et al. Phys. Rev. A83 032721 (2011)
[4] J.R. Machacek et al. New J. Phys. 13 125004 (2011)
6
Research and development activities of the Space Plasma, Power and
Propulsion laboratory
C. Charles and SP3
Space Plasma, Power and Propulsion Laboratory
Research School of Physics and Engineering,
The Australian National University, Canberra ACT 0200, Australia
The Space Plasma, Power and Propulsion laboratory conducts work on both
basic and applied plasma physics. The core research areas involve experimental and
theoretical aspects of low pressure helicon discharges and of high pressure (including
atmospheric pressure) radiofrequency discharges and of their numerous applications.
Interaction of these plasmas with surfaces (etching, sputtering, deposition,
surface functionalization) are applied to microelectronics and optoelectronics
processes, fuel cell manufacturing for the hydrogen economy and design of materials
with biological responses, catalytic activity, optical or mechanical properties. SP3’s
expertise in the control of reactive and non reactive electropositive and
electronegative discharges is extended by national and international collaborations in
the field of polymer deposition for plasma medicine, focused ion beam sources for
materials diagnosis and for neutral beam injection in high temperature plasmas.
SP3 has developed a unique expertise in the application of low pressure
radiofrequency plasmas to electric propulsion with the development of three thrusters:
the DS4G ion thruster and two new plasma thrusters: the Helicon Double Layer
Thruster (HDLT), and the Pocket Rocket thruster. Performance tests and space
qualification are under way in three space simulation facilities.
In parallel with the development of basic global models of plasmas for electric
propulsion and material design, SP3 has a major program to simulate (Particle In Cell
methods) and model (analytical theories) the laboratory double layers which are being
applied to understanding space plasma physics such as the magnetic funnels of the
solar corona and the Earth's aurora. Other research on space plasma physics and
electric propulsion includes studying high-beta plasmas, wave-plasma interactions,
plasma instabilities, cross-field diffusion, momentum imparted from plasma
expansion and plasma detachment from magnetic fields.
7
Plasma Theory and Modelling at the ANU
M. J. Hole, R. L. Dewar, G. von Nessi, M. Fitzgerald, G. Dennis,
L. Chang, A. Gibson, M. McGann, J. Larson
Research School of Physics and Engineering, ANU
In this talk I will give an overview of active research in the plasma theory and modelling group at
the ANU. Research pursuits include:
● Burning plasma physics, in which we use novel fluid models to gain an understanding of
the changes in the magnetic configuration and wave activity produced by beam injected
and fusion alpha particles in fusion plasmas.
● Integrated modelling, in which we use Bayesian statistics to integrate different diagnostics
with advanced physics models to compute probabilistic models of magnetic configuration,
and infer poorly resolved physics in tokamaks.
● Fully 3D-MHD models, in which we develop a rigorous description of fully three
dimensional magnetic fields in toroidal magnetic confinement.
● Interpretation and modelling, in which we provide support for various plasma physics
experiments, including international machines MAST (UK) and KSTAR (Korea), and
Australian experiments H-1 and MDF.
Each of these research pursuits involves at least one international partner.
I will outline future plans, and show how these international research pursuits might contribute to
a possible future Australian engagement with ITER.
8
The Formation and the Effects of Metal Vapour in Welding Arcs
Anthony B. Murphy
*CSIRO Materials Science and Engineering, PO Box 218, Lindfield NSW 2070, Australia
Arc plasmas, such as those used in arc welding, are (a) formed between metal electrodes and (b) very
hot, reaching temperatures up to around 20 000 K. It is therefore not surprising that large quantities of
metal vapour can be formed by evaporation of the electrodes [1]. The importance of the metal vapour
has only recently been fully appreciated, with studies indicating some dramatic effects, including a
decrease in arc temperature by more than 5000 K [2] and a large decrease in the depth of the molten
region of the workpiece (i.e., of the lower electrode). The vapour also leads to the formation of fume
(chains of metal oxide nanoparticles), which is an important health hazard in arc welding [1,3]. In the
first part of the presentation, I will give an overview of the effects of metal vapour, including a
discussion of how it cools the arc plasma (which is a controversial topic) [1,4,5]. Recent results
obtained using a three-dimensional computational model of arc welding will be featured [6]. In the
second part, I will present the predictions of a multi-scale model that nicely illustrates how fume is
formed from metal vapour in welding arc plasmas [3].
[1] A. B. Murphy, J. Phys. D: Appl. Phys. 43 (2010) 434001.
[2] S. Zielińska et al., Plasma Sources Sci. Technol. 16 (2007) 832-838.
[3] S. Tashiro et al., J. Phys. D: Appl. Phys. 43 (2010) 434012.
[4] M. Schnick et al., J. Phys. D: Appl. Phys. 43 (2010) 022001.
[5] J. Haidar, J. Phys. D: Appl. Phys. 43 (2010) 165204.
[6] A. B. Murphy, J. Phys. D: Appl. Phys. 44 (2011) 194009.
9
A hydrogen global model to complement plasma-surface interaction experiments
C. M. SamuellP and C. S. Corr
Plasma Research Laboratory, Research School of Physics and Engineering,
The Australian National University, Canberra 0200, Australia [email protected]
Plasma-surface interactions are important in a variety of processes including fusion plasmas, nanotechnology and biomedical applications. These processes require an in-depth knowledge of the plasma chemistry. To further develop an understanding of experimental observations, global models are becoming an increasingly popular tool for benchmarking plasma systems. The principal purpose of this model is to capture the scaling of various plasma properties with input control parameters including reactor design, applied power and background gas pressure. A global model employs a set of coupled non-linear differential equations that are solved, with the constraints imposed by maintaining energy, charge and particle balance, to give volume averaged plasma quantities such as temperatures and densities. In this work a steady-state hydrogen global model is developed that takes account of positive and negative hydrogen ions and electrons as well as fourteen vibrational states of H2. The model, which builds upon and extends previous work in this area, is applied to investigate plasma dynamics in a low temperature system. These are of relevance to plasma interactions with wall components in the context of an ITER-relevant device.
10
Characterisation of a micro discharge array source
Sam Dixon, Christine Charles, Rod Boswell SP3, PRL/RSPhysSE, ANU
[email protected] An investigation into the characteristics of the plumes of an argon and electronegative SF6 plasma expanding from an array of micro discharges has been performed. A characterisation of the parameters necessary for stable operation was conducted resulting in minimum power and flow relationship for stable operation. The effects of source geometry were also investigated by varying the spacing between active micro discharges, with the result that a more compact array produces a more stable discharge overall. Optical and electrical data was gathered to allow comparison with similar sources and to identify the concentration of atomic fluorine. A two dimensional sweep was performed with a Langmuir probe and coupled with a fluid flow simulation to gather data on plume density and shape. Density data also provides a clue as to whether the system has a resistive impedance or behaves simply as a capacitively coupled discharge.
11
RF Plasma Polymer Thin Films for Emerging Electronics and Biomedical Applications
Mohan V. Jacob*, Kateryna Bazaka and Liam Anderson
Electronic Materials Research Lab, School of Engineering and Physical Sciences, James Cook University, Townsville QLD 4811, Australia
*Email: [email protected]
Radio Frequency (RF) plasma polymerization technique is an effective tool for the fabrication of pinhole free thin films with properties that can be tailored for a given application by controlling the deposition conditions. Plasma-assisted techniques can be used for developing nanostructures and complex nanoassemblies and high-quality polymer thin film materials at defined positions, with large-scale control of location and orientation. The exploitation of plasma-enhanced nanofabrication presents great opportunities especially to understand mechanisms of nanostructure formation. We will present the fabrication process used for the polymerisation of non-synthetic precursors using the RF plasma polymerisation and the characteristics of the fabricated polymer thin films.
12
Fast Measurement of Electron Density using Fourier Cutoff Probe
B. K. Na1, K. H. You
1, D. W. Kim
1, S. J. You
2, and H. Y. Chang
1,
1KAIST, Daejeon, 305-701, Korea
2KRISS, Daejeon, 305-340, Korea
Cutoff probe is a diagnostic tool for absolute electron density measurement. Electron density
(plasma frequency) can be acquired from the transmission spectra analysis. In this presentation, a
fast measurement method using cutoff probe, Fourier cutoff probe (FCP), will be newly
introduced.
A cutoff probe system consists of two antennas and a network analyzer. The network analyzer
provides the transmission spectrum by frequency sweeping. However, the frequency sweeping
time, the time resolution of the wave-cutoff method, is about 1~10 seconds like any other
diagnostic tools. In FCP method, we used a short impulse signal with a broad band spectrum of a
few GHz instead of a network analyzer to reduce the measurement time. The transmission
spectrum was acquired using Fourier analysis.
The measurement using FCP made a good agreement with the network analyzer cutoff probe
and Langmuir probe. FCP’s measurement was much faster than the network analyzer cutoff
probe. FCP’s time resolution was only 15 nano-seconds. This method is very useful especially in
fast varying plasma such as pulsed plasma and tokamak edge plasma measurement.
13
The Material Diagnostic Facility: A linear plasma device for studying
fusion relevant plasma-surface interactions
C. Corr, C. SamuellP, J. Caneses, B. Blackwell
and UJ. Howard
1Plasma Research Laboratory, Research School of Physics and Engineering,
The Australian National University, Canberra 0200, Australia
Plasma–surface interactions are crucial to determining the success of ITER and the ultimate viability of
generating fusion power under steady state conditions. The first walls of magnetic fusion reactors must
sustain large particle and heat fluxes and present a major challenge to achieving fusion power. To
answer fundamental questions about the science of plasma-surface interactions at the complex fusion
boundary a new purpose-built linear plasma device, the prototype “Materials Diagnostic Facility”
(MDF), has been constructed at The Australian National University (ANU) to test materials under
aggressive plasma conditions. In this work we employ optical emission spectroscopy, electrostatic
probes and fast imaging to characterize the plasma environment and its interaction with various
materials.
14
Initial wave activity in the “Material Diagnostic Facility” (MDF)
Juan Francisco Caneses, Boyd Blackwell, Cormac Corr, Cameron Samuell, John Wach, John Howard.
Plasma Research Laboratory, Research School of Physics and Engineering, The Australian National University, Canberra 0200, Australia
The “Material Diagnostic Facility” (MDF) is a new linear plasma device that has been constructed at the Australian National University to study basic plasma interactions, test materials under extreme conditions and serve as a test bed for developing diagnostics for fusion reactors. The prototype MDF employs a 5kW RF source to launch helicon waves into a non-uniform magnetic field in order to produce high density hydrogen, helium and argon plasmas. It has been shown by other authors ([1], [2], [3]) that converging magnetic field geometries, such as the one on MDF, contribute to the production of high density plasmas (1019 m-3), which are required for the testing of materials relevant to fusion reactors. In this work we explore the propagation of helicon waves into a magnetic mirror in the attempt to characterize the plasma production process. We observe that when enough RF power is supplied an Ar II blue core mode is formed indicating the presence of fast electrons (~30 eV). We employ RF Langmuir probes and RF magnetic probes to measure plasma densities and helicon wavefield structures formed when operating above and below the formation of the Ar II blue core mode.
[1] Y. Mori, H. Nakashima, F. W. Baity, R. H. Goulding, M. D. Carter, and D. O. Sparks, “High density hydrogen helicon plasma in a non-uniform magnetic field,” Plasma Sources Science and Technology, vol. 13, no. 3, pp. 424-435, Aug. 2004.
[2] Y. Mori, H. Nakashima, F. W. Baity, R. H. Goulding, M. D. Carter, and D. O. Sparks, “Focusing magnetic field contribution for helicon plasma on Mini-RFTF,” Thin Solid Films, vol. 506–507, no. 0, pp. 583-587, May 2006.
[3] M. D. Carter et al., “Comparing experiments with modeling for light ion helicon plasma sources,” Physics of Plasmas, vol. 9, no. 12, pp. 5097-5110, Dec. 2002.
15
The effect of magnetic field in diocotron instability of a hollow electron
beam
Seung Il Jung
1, Seung Bo Shim
1, Moses Chung
2, Ho Jun.Lee
1, Hae June Lee
1
1Department of Electrical Engineering, Pusan National University, Pusan, South Korea
2Handong Global University, Pohang, South Korea
Email contact: [email protected]
The diocotron instability for the development of a beam collimator system in high-energy
colliders such as the Tevatron in Fermi Accelerator Lab, US is resurfaced lately. It is based on
the interaction of the circulation beam, magnetically confined, pulsed halo electron beam. The
electrons enclose the circulating beam, kicking halo particles transversely and leaving the
beam core unperturbed. However, the cross section of the hollow electron beam is expected to
distort as it propagates, which has already been observed in many standard non-neutral
plasma experiments with remarkable agreement with theories. When these kicks are under
controlled, it is possible to lessen the uncontrolled beam losses and enhance the collimation of
the proton beam. Relation with the diocotron instability is surely the main cause of dwindle
the collimation. Linear analyses show that the electrostatic perturbations for an annular
electron layer can grow due to the free energy associated with the shear in the flow velocity.
The cross-sectional view of two-dimensional particle-in-cell simulation in a cylindrical
geometry indicates that the electron column is eventually converted into a finite number of
vortices. In this study, we report delay time of a hollow electron column confined in uniform
or helical magnetic fields and the way how to control the propagation of hollow electron
beam.
16
Industrial Application of Very High Frequency CCP Plasma Source
J. W. Shon and A. R. Ellingboe
Lastest applications in semiconductor manufacturing, display industry and solar industry
benefits greatly by using VHF CCP plasma source. This is due to the changes in electron
energy distribution with increasing frequency. We will review the potential industrial
applications on using VHF CCP plasma sources for unique benefits.
17
Threshold Effects in Positron Scattering with Atoms and Molecules
J.R. Machacek, C. Makochekanawa, J.P. Sullivan and S.J. Buckman
ARC Centre for Antimatter-Matter Studies, Research School of Physics and Engineering,
Australian National University, Canberra, 0200 ACT
A cusp feature can occur in partial scattering cross sections at the opening of a new scattering
channel [1]. In general, the magnitude of the cusp is proportional to the strength with which
the new channel opens. For the case of positron scattering from atoms or molecules, it is the
positron formation threshold which provides the new channel which causes a cusp feature in
the elastics scattering cross section.
Our group has recently observed a series of Cusp features in positron scattering with noble
gases [2]. These features were observed in the elastic scattering cross section at the opening of
the positronium formation channel. However, no simple trend has been found relating the size
and width of these cusps to any specific atomic parameter.
Thus, we have expanded the search for cusp features to molecules. Firstly, a homo-nuclear
diatomic target was chosen. Comparison will be made between the isoelectric species helium
and molecular hydrogen. Molecular systems have vibrational and rotational excitation
channels which are open at the positron formation threshold. These channels likely play an
important role in determining the magnitude and shape of a cusp. Therefore, we will discuss
an extension of the search for these features in molecules which are isoelectric with Neon.
[1] E.P. Wigner Phys. Rev. 73 1002 (1948)
[2] A.C.L. Jones Phys. Rev. Lett. 105 073201 (2010)
18
Gas ionization of CO2/H2S using plasma of radiofrequency
M. G. Neira-Velázquez, E. Hernández-Hernández, Y. Perera-Mercado, A. Y. Ruíz-Martínez, C. G.
Hernández-Hernández.
Centro de Investigación en Química Aplicada (CIQA), Boulevard Enrique Reyna Hermosillo No. 140,
Saltillo, Coah., México, CP25253.
Email contact: [email protected]
Abstract
In this study, a mixture of CO2/H2S was ionized using a plasma of radiofrequency (13.56 MHz),
to carry out the mixture decomposition a cylindrical glass reactor was used, the plasma generator
was connected to the plasma reactor inductively, and the gas was ionized at plasma powers of 50,
150, 250 and 350 W, the gas was characterized in situ by Optical Emission spectroscopy, the
reactor temperature was also measured in situ. After the plasma reaction, the gas decomposition
produced solid products that were deposited on the walls of the cylindrical reactor, the products
obtained in form of powders were characterized by infrared spectroscopy (FTIR), scanning
electronic microscopy (SEM), transmission electronic microscopy (TEM) and scanning
differential calorimetry (DSC). The analytical techniques showed that the powder was constituted
mainly by sulphur, and this product has a melting point of 122 C.
REFERENCES
[1] Knutson T. R., Tuleya R.E., Kurihara Y.; Simulated Increase of Hurricane Intensities in a
CO2-Warmed Climate; Science; 279: 1018-1020; 1998.
[2] Ramanathan V., Cicerone R. J., Singh H. B., Kiehl J. T.; Trace Gas Trends and Their
Potential Role in Climate Change; J. Geophys Res.; 90(D3): 5547-5566; 1985.
[3] Zaman J.; Production of Hydrogen and Sulphur from Hydrogen Sulphide; Fuel Process
Technol; 41: 159-198; 1995.
[4] Zhao G., John S., Zhang J., Hamann J. C., Muknahallipatna S. S., Legowski S., Ackerman J.
F., Argyle M. D.; Production of Hydrogen and Sulfur From Hydrogen Sulfide in a Nonthermal-
Plasma Pulsed Corona Discharge Reactor; Chemical Engineering Science; 62(8):2216-2227;
2007;
[5] Hippler R., Kersten H., Schmidt M., Schoenbach K. H.; Low Temperature Plasmas; 2nd
edition; Germany; Ed. Wiley-VCH; p. 2; 2008.
[6] Fridman A.; Plasma Chemistry; First edition; US; Ed. New York: Cambridge University
Press; Cap. 10; 2008.
[7] Gutsol A. F., Fridman A.; Hydrogen Production From Hydrogen Sulfide; US; inventor
Drexel University; US 20110044884; 2011.
[8] Gutsol A., Potter W. R., Gutsol K., Nunally T., Starikovskii A., Fridman A., Rabinovich R.;
Methods for Low Temperature Hydrogen Sulfide Dissociation; US; inventor Chevron U.S.A.
Inc., Drexel University; US 20100300872; 2010.
19
MEASUREMENT OF HYDROXYL RADICAL, PLASMA DENSITY AND
ELECTRON TEMPERATURE FOR ATMOSPHERIC BIOPLASMA JET
Eun Ha Choi*, Yonh Hee Kim, Ki Baik Song, Guangsup Cho, Han Sup Uhm
Plasma Bioscience Research Center / Charged Particle Beam and Plasma Laboratory,
Department of Electrophysics, Kwangwoon University, Seoul 139-701, Korea
* E-mail: [email protected]
Nonthermal bioplasmas are being used in a variety of biomedical and material processing
applications, surface modifications of polymers at atmospheric pressures. These bioplasmas
can generate the various kinds of radicals with their own plasma density and temperatures. It
is very important to investigate the hydroxyl radical and plasma density along with electron
temperature in plasma jet since they are significant plasma parameters in the interaction
between the bioplasma and living body. We have generated the needle-typed plasma jet by
using an Ar gas flow and investigated the Ar metastable emission lines by optical emission
spectroscopy (OES). The electron temperature for the nonthermal plasma jet has been
measured to be ~ 1.5eV in this bioplasma jet by collision radiative (CR) model. Also, the
electron density for this bioplasma jet has been determined to be ~ 3×1011
cm-3
by direct
measurement of electrical current density of plasma jet. The hydroxyl radical density has also
been investigated and measured to be ~ 2.4 ×1015
cm-3
by the optical absorption
spectroscopy.
Keywords: Atmospheric pressure bioplasmas, needle-typed plasma jet, optical emission
spectroscopy (OES), electron temperarture, plasma density, hydroxyl radical density, optical
absorption spectroscopy.
20
Positronic Helium? - Search for Positron Bound States in the Doubly
Excited Region of the Helium Atom
R. Boadle, J.R.Machacek, E. Anderson, J.P. Sullivan and S.J. Buckman
ARC Centre for Antimatter-Matter Studies, Research School of Physics and Engineering,
Australian National University, Canberra, 0200 ACT
The existence of bound positron-atom systems has been the subject of many theoretical
calculations in recent years. Positron binding can occur via two different mechanisms: either
the electronic charge cloud is polarized by the presence of the positron and a weak long range
potential results which can tenuously accommodate the positron, or one of the valence
electrons may attach itself to the positron to form positronium (e-e
+ pair) which can also
become polarised and weakly bound to the atom. There is now theoretical evidence of
numerous positron bound-state systems, including the helium atom.
The helium atom in its ground state cannot bind a positron, but it is expected that some of the
excited metastable states of helium are capable of binding a positron. For example,
calculations [1] have indicated that the singly excited metastable 1s2s(3S) state is capable of
attaching a positron. Other, higher excited states of helium may also be expected to support
such bound states which may manifest themselves as structure in the energy dependence of
cross sections for processes such as total scattering or positronium formation.
We have carried out an experimental search for these states in the energy region of the excited
state thresholds of helium using our high-resolution, trap-based positron beam. The results of
these experiments and their potential ramifications will be discussed.
[1] G. Ryzhikh and J. Mitroy J. Phys. B. 31 3465 (1998)
21
Plasma modification and deposition of polymers for biofuel production
C. Tran, A. Kondyurin, S. Hirsh, N. Nosworthy, M. Bilek and D.R. McKenzie
Applied and Plasma Physics (A28), University of Sydney, Sydney, NSW 2006, Australia
Email: [email protected]
Plasma immersion ion implantation (PIII) creates active free radicals in polymers that can be
used to immobilise bio-molecules. We have demonstrated that whole yeast cells can be
immobilised in this way and that they retain their ability to process glucose to ethanol.
Immobilised yeast cells enable the conventional batch fermentation process for ethanol
production to be converted into a continuous flow process with large potential advantages in
production cost. The mechanism for the yeast cell attachment process has been investigated
using surface analysis techniques of FTIR, XPS and mass spectroscopy. The attachment
mechanism is believed to be via an interaction of radicals on the plasma treated polymer
surface with proteins on the cell walls. The cell attachment on PIII treated surface occurs
quicker and the strength of attachment is stronger than that on untreated surface.
22
Improved hemocompatibility of PET vascular grafts by oxygen plasma treatment
M. Modic, I. Junkar, A. Vesel, M. Mozetic
Jozef Stefan Institute, Jamova cesta 39, 1000 Ljubljana, Slovenia [email protected]
Vascular grafts made from polyethileneterephthalate were treated by mild oxygen plasma in order to improve their hemocompatibility. Plasma was created within an electrode-less radiofrequency discharge powered by a generator operating at the frequency of 27.12 MHz and an output power of about 100 W. The basic plasma parameters were estimated with a double electrical probe and a catalytic probe. At the oxygen pressure of 75 Pa the ion density was about 7x1015 m-3 and the density of neutral oxygen atoms about 5x1021 m-3. Optical emission spectroscopy showed weak etching of grafts during oxygen plasma treatment. AFM characterization of the grafts revealed highly inhomogeneous etching since dense nanocones were observed on plasma treated samples. XPS revealed formation of highly polar oxygen rich functional groups while water drop contact angle measurements proved a superhydrophilic character of plasma treated samples. Samples were incubated with blood plasma rich in platelets and their activation was studied by AFM. The concentration of well-activated platelets on oxygen plasma treated samples was two orders of magnitude lower then on untreated samples indicating a dramatic improvement of the vascular graft hemocompatibility upon oxygen plasma treatment.
23
Plasma deposition of nanocrystalline silicon for solar cells:
RF waveform tailoring to optimize deposition rate and film morphology
J-P Booth1, E. V. Johnson
2, P-A . Delattre
1
1Laboratoire de Physique des Plasmas-CNRS, Ecole Polytechnique, 91128 Palaiseau, France
2 LPICM-CNRS, Ecole Polytechnique, 91128 Palaiseau, France
Email: [email protected]
1. Introduction Deposition of device-quality microcrystalline silicon thin films at an adequate rate is a key
challenge in the fabrication of thin film silicon tandem photovoltaic modules for viable large-
scale power generation. Conventionally films are deposited using sinusoidal RF excitation of
parallel plate reactors containing lean H2-SiH4 mixtures. Higher voltages increase the deposition
rate, but also increase the ion bombardment energy which degrades the film, thus limiting the
deposition rate of high quality films to 1 nm/s for RF excitation at 13.56 MHz. We have
investigated plasma excitation using non-sinusoidal waveforms to decouple the injected RF
power from the ion bombardment.
Donko et al. have shown that when a symmetric parallel plate plasma reactor is excited with a
sinusoidal voltage at frequency f, mixed with the first harmonic, 2f, the division of the time-
averaged between the two sheaths can be modified by changing the relative phase of the two
signals. We have extended this concept, using an arbitrary function generator and wide-band
power amplifier to apply arbitrary voltage waveforms to the reactor. Films were deposited in
SiH4/ H2 (+SiF4) plasmas and were characterised using in-situ and ex-situ spectroscopic
ellipsometry and Raman scattering. A waveform comprising sharp spikes (<5ns rise-time) on a
constant background with high repetition rate (15 MHz) permits optimal control of the ion energy
(at the substrate) independently from the plasma density. Furthermore, the fast rise-time leads to
efficient electron heating giving high plasma densities. The effects of the waveform on the
plasma density and DC self-bias, as well as on the film deposition rate and morphology will be
discussed.
24
Self cleaning and antibacterial effect on Cotton Fabrics Using Dc Magnetron Sputtering
Sheila.Shahidi1, Mahmood.Ghoranneviss2
1 Department of Textile Chemistry, Faculty of Engineering, Islamic Azad University, Arak Branch, Arak, Iran
2 Plasma Physics Research Center, Science and Research Branch, Islamic Azad University, Tehran, Iran
E-mail: [email protected]
In order to utilize the photocatalytic properties of TiO2 such as ultra-hydrophilicity, stain resistance, deodorization, and antimicrobial functions, TiO2 has been coated onto cotton fabric using Dc magnetron sputtering. The film thickness was measured using a surface profiler. The crystal structure of the TiO2 film was evaluated using X-ray diffractometry. The surface morphology of the film was investigated using scanning electron microscopy. Hydrophilicity was evaluated by measuring the changes in the contact angles of pure water using a contact angle measuring system. The organics decomposition characteristics were measured using the change in the methylene blue concentration. In the evaluations, black light of main wave length of 352.0 nm was used as the UV source and the measurement was carried out under the UV irradiation of 1.0 mW cm−2. The amorphous form of titanium dioxide is known to have no photo catalytic activity, while the anatase form of titanium dioxide is active. Rutile form seems to present a weaker photo catalytic activity due to its smaller band gap width, though some results suggest that rutile particles present a larger pore size and a better resistance, and that anatase/rutile interface may be an active site for photocatalytic activity. The results show that, deposition of crystalline anatase titanium dioxide could not be achieved at a deposition time lower than 90 seconds. The results of bacterial counting test shows very good antibacterial efficiency on TiO2 nano layer sputtered cotton, however the time of exposure has very important role.
25
Electron scattering data to model electron tracks in gases: application to
ethylene and sulfur hexafluoride
M. Fuss1, F. Blanco
2, A. Muñoz
3, J. C. Oller
3, D. Almeida
4, P. Limão-Vieira
4, T. P. T. Do
5,
M. J. Brunger5, S. J. Buckman
6 and G García
1
1 Instituto de Física Fundamental, Consejo Superior de Investigaciones Científicas,
Serrano 113-bis, 28006 Madrid, Spain 2 Departamento de Física Atómica, Molecular y Nuclear, Universidad Complutense de
Madrid, Ciudad Universitaria, 28040 Madrid, Spain 3 Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT),
Avenida Complutense 22, 28040 Madrid, Spain 4 Laboratório de Colisões Atómicas e Moleculares, CEFITEC, Departamento de Física,
FCT-Universidade Nova de Lisboa, Campus de Caparica, 2829-516 Caparica, Portugal 5ARC Centre for Antimatter-Matter Studies, School of Chemical and Physical Sciences,
Flinders University, GPO Box 2100, Adelaide, SA 5001, Australia 6ARC Centre for Antimatter-Matter Studies, Research School of Physics and Engineering,
Australian National University, Canberra, ACT 0200, Australia
Modelling electron tracks in gases is relevant for many plasma applications both in
atmospheric and industrial processes [1-2]. Electrons play a key role inducing molecular
fragmentation, producing radicals and excited species which generate additional chemical
processes of relevance for these applications [3]. Such models require accurate information
about electron interactions with the atoms and molecules forming the gaseous media in terms
of electron scattering cross sections and energy loss [4]. As all this information is not
generally found in the available databases we have developed a general electron scattering
calculation procedure which provides cross section data over a broad energy range (typically
from 1 to 10000 eV) for a high variety of atomic and molecular targets [5]. As an example,
we here present a full data set for electron scattering with ethylene and sulfur hexafluoride. To
complete the information required by the model, experimental energy loss spectra are also
provide for these energies. We will finally present single electron tracks in different
configurations of these gases and the relevance of the information provided by the model in
laboratory plasmas and industrial applications will be discussed.
Acknowledgement: This work was conducted with support from the Ministerio de Ciencia e
Innovacion (project # FISI2009-10245). Additional support from the Australian Research
Council, through its Centres of Excellence Program, and the European Science Foundation
(COST Actions CM0601 and MP1012) is acknowledged.
[1] H. Kato,T. Asahina, H. Masui, M. Hoshino, H. Tanaka, H. Cho, O. Ingólfsson, F. Blanco, G. Garcia, S. J. Buckman, and
M. J. Brunger, J. Chem. Phys. 132, 074309 (2010).
[2] H. Kato, M. C. Garcia, T. Asahina, M. Hoshino,C. Makochekanwa, H. Tanaka, F. Blanco and G.García, Phys. Rev. A 79,
062703 (2009).
[3] R. Antunes, D. Almeida,G. Martins, N. J. Mason, G. Garcia, M. J. P. Maneira, Y. Nunes and P. Limao-Vieira, Phys.
Chem. Chem. Phys. N12N, 12513 (2010).
[4] M.C. Fuss, A. Muñoz, J.C. Oller, F. Blanco, M.-J. Hubin-Franskin, D. Almeida, P. Limão-Vieira, and G. García, Chem.
Phys. Lett. 486, 110 (2010)
[5] F. Blanco and G. García, J. Phys. B 42, 145203 (2009).
26
Control of diffuse and filamentary discharge modes in a pulsed, radio-
frequency surface discharge in atmospheric-pressure argon
J. Dedrick1, R. W. Boswell
1, H. Rabat
2, D. Hong
2 and C. Charles
1
1Space Plasma, Power and Propulsion Laboratory, Research School of Physics and
Engineering, The Australian National University, ACT 0200, Australia 2GREMI - UMR6606 CNRS/Universit´e d’Orl´eans, Polytech’Orl´eans, 14, rue d’Issoudun -
BP6744, 45067 ORLEANS Cedex 2, France
Non-thermal discharges operated at atmospheric pressure have a range of potential
applications including medical sterilization, surface treatment of materials, bacteria
inactivation, and more recently aerodynamic flow control.
In the surface dielectric barrier discharges, or DBDs, sinusoidal voltages of tens of kV and a
few kHz are typically applied between the electrodes to activate a series of low-temperature
(~300 K) spatially randomized microdischarges. The asymmetric geometry of the reactor
causes a large surface area of the discharge to be in direct contact with the surrounding
atmosphere which is useful for many applications.
Using radio-frequency excitation at 13.56 MHz, i.e heating the discharge at a significantly
higher frequency than traditional DBDs, the generation of diffuse and filamentary modes has
been observed in atmospheric-pressure argon. The mechanisms behind the formation of these
distinct plasma states are explored using non-invasive optical techniques in the continuous an
pulsed power regimes.
27
Imaging studies of the ion velocity distribution function in the MDF helicon
plasma source
J. Howard, R. Lester, J. Caneses, B. Blackwell, C. Corr
Plasma Research Laboratory, Australian National University, Australia e-mail address: [email protected]
We have deployed spatial heterodyne Doppler coherence imaging techniques to explore the spatial
variation of the Ar+ ion velocity distribution function in helicon-produced (13.56MHz, 2kW)
argon plasmas in the linear magnetized Materials Diagnostics Facility at ANU. The source
produces a plasma with low ion temperature (~0.2 eV) and hollow profile, but with a high Mach
number flow in the axial direction (towards the magnetic mirror) and near supersonic sheared
rotational flows about the axis. The electron temperature is typically ~4eV and density ~5x1018
m-3
.
We will present details of the passive Doppler optical imaging instrument and will discuss the
results of measurements obtained at different spatial locations and for different plasma discharge
conditions and magnetic field strengths (<~0.1T). Due to collisional effects, rotational flows are
found to decrease at higher fill pressures (6mT) while the axial drifts are largely unaffected. The
ion temperature is also found to increase in the high field region, presumably due to the magnetic
mirror. The data is analyzed in the context of the ion force balance both parallel and perpendicular
to the magnetic field.
We will also describe an advanced instrument in which, using multiple spatial heterodyne carriers
and velocity space tomography, the spatial distribution of the ion distribution function f(r,v) can be
recovered from a single image. This instrument will be deployed for more detailed studies of the
coupling between the ion and neutral fluids for a range of magnetic configurations (mirror ratio)
and plasma conditions (pressure, field strength, heating power, gas species) in MDF.
28
Initial results from the new Helical Mirnov Array for the H-1NF Heliac
S. R. Haskey, B. D. Blackwell, M.J. Hole, D.G. Pretty, J.Howard
Plasma Research Laboratory, Australian National University, Australia e-mail address: [email protected]
Motivated by observations of magnetic fluctuation activity in H-1 plasmas from poloidal Mirnov
arrays [1, 2] we have installed a new toroidal/helical Mirnov array with a higher frequency
response and improved mode resolving power. The array is composed of sixteen three-axis Mirnov
coils which follow the helical winding of the machine through one revolution. This places the
array very close to the plasma as it twists around H-1, in an area of strong mode activity, with
varying degrees of “favourable curvature” in the MHD sense but almost constant magnetic angle
which makes phase variation with coil position near linear. The low shear heliac geometry [2, 3]
provides a unique opportunity for detailed study of Alfvén eigenmodes, which could be a serious
issue for future fusion reactors.
A large dataset from a rotational transform (ι) configuration scan has been analysed using several
techniques including singular value decomposition (SVD), data mining, analytic phase calculation
and an averaged coherence selection process. Initial results are very promising with SVD analysis
showing clear separation into rotating cosine and sine-like components and near linear phase
variation along the array. Several results from extensive rotational transform scans will be
presented including the correlation between the magnetic data and optical emission measurements,
mode frequency dependence on density and details of mode polarisation using all three axes of the
coils. Additionally, plans to use an active excitation antenna will be described. Acknowledgements: This work was supported by AINSE and ANSTO.
[1] D. G. Pretty, PhD Thesis, Australian National University, 2007.
[2] B. D. Blackwell et al., 21st
IAEA Fus. Energy Conf., Chengdu, China (2006).
[3] R. Jiménez-Gómez et al., Nucl. Fusion 51, 033001 (2011).
29
Abstract not available
Myoung-Jae Lee
30
Propagation of ionization fronts in atmospheric pressure plasma jets and their interactions
Q. Th. Algwari1, C. O’Neill1, D. O’Connell1,2
1Centre for Plasma Physics, Queen's University Belfast, BT7 1NN, Belfast, UK
2York Plasma Institute, Department of Physics, University of York, York, YO10 5DD, UK
Cold non-equilibrium plasmas, operated at ambient atmosphere and temperature, are efficient
sources of highly reactive species and are of particular interest for many technological applications e.g. in emerging plasma healthcare technologies [1,2]. Control and manipulation of the plasma and its relevant species are important. The excitation dynamics within the main plasma production region and the resulting plasma jets of a kHz atmospheric pressure dielectric barrier discharge (DBD) jet operated in helium was investigated. The electron dynamics and associated sustainment mechanisms are investigated in the main plasma production region inside the dielectric tube and the resulting jets formed at the powered and grounded electrode. Each individual plasma jet consists of transient plasma pulses sustained through streamer-like mechanisms [3]. Ignition of the jets at the powered and grounded electrode are quite different; the jet emitted from the powered electrode can be compared to the plasma formation inside the dielectric tube, while breakdown of the jet at the grounded electrode is seeded through the primary plasma inside the DBD, and is therefore dependent on energy transport from within the dielectric tube.
The interaction between two counter-streaming dielectric barrier atmospheric pressure plasma jets, driven with a kHz excitation frequency, is investigated. In order to further understand the fundamental propagation mechanisms individual jets are allowed to interact with each other in ambient air and within a controlled environment. Time and space resolved images of the spectrally resolved optical emission shows that the plasma pulses repel each another through an electrical interaction. This interaction environment also offers possibilities for improved plasma control in applications. References:
[1] D. O'Connell, L.J. Cox, W.B. Hyland, S.J. McMahon, S. Reuter, W.G. Graham, T. Gans, F.J. Currell,
Cold atmospheric pressure plasma jet interactions with plasmid DNA , Applied Physics Letters, 98, 043701 (2011) [2] J. S. Sousa, K. Niemi, L. J. Cox, Q. Th. Algwari, T. Gans, and D. O’Connell, Cold atmospheric pressure
plasma jets as sources of singlet delta oxygen for biomedical applications, J. Appl. Phys. 109, 123302 (2011) [3] Q. Th. Algwari and D. O'Connell, Electron dynamics and plasma jet formation in a helium
atmospheric pressure dielectric barrier discharge jet, Appl. Phys. Lett. 99, 121501 (2011)
31
Wave modelling in cylindrical non-uniform plasmas: electrostatic and electromagnetic waves
L. Chang, M. J. Hole, C. S. Corr, B. D. Blackwell, J. F. Caneses, G. Chen, a and A. V. Arefiev b
Plasma Research Laboratory, The Australian National University, Canberra, ACT 0200, Australia a Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
b Institute for Fusion Studies, The University of Texas, Austin, Texas 78712, USA E-mail address: [email protected]
Modelling waves in cylindrical non-uniform magnetically confined plasmas and studying their propagation features are of great importance to the fundamental understanding of these waves, e.g. effects of non-uniformity in plasma profiles and equilibrium magnetic field, and their applications. Waves studied in this work include resistive drift and helicon waves.
First, a two-fluid electrostatic model is applied to describe waves observed in a RF generated linear magnetised plasma [WOMBAT (Waves On Magnetised Beams And Turbulence)]. [1] The density distribution is uniform in the axial direction but near Gaussian in radius, with constant magnetic field B0 parallel to the machine axis. The two-fluid model provides a consistent description of the WOMBAT plasma configuration and yields qualitative agreement between measured and predicted kHz-range wave oscillation frequencies with axial field strength. The predicted radial profile of density perturbation is also consistent with the data, indicating the density and floating potential oscillations are resistive drift mode, driven by the density gradient. A schematic of the WOMBAT device, with a single loop antenna, is shown in Fig. 1. Typical Argon plasmas have experimental conditions: on-axis density ni0=1.4×1019 m-3, electron temperature Te=1.5 eV, and field strength B0=0.0185 T.
Diffusion chamberSource region Fig. 1 Schematic of WOMBAT (Waves On Magnetised Beams And Turbulence). [1]
Fig. 2 Schematic of MDF (Material Diagnostic Facility) and the axial profile of B0.
Second, a RF field solver [2] based on Maxwell’s equations with a cold plasma dielectric tensor is employed to interpret wave phenomena observed in the Material Diagnostic Facility (MDF), a cylindrical, helicon machine with a half-turn helical antenna, and magnetic field pinched in the diffusion chamber. We show some initial calculations of wave fields in MDF, and compare these to preliminary measurements. A schematic of MDF is shown in Fig. 2, together with the axial profile of B0. Typical Argon plasmas have experimental conditions: ni0=1.0×1019 m-3, Te=3.0 eV, and B0=0.05~0.19 T. [1] L. Chang, M. J. Hole, and C. S. Corr, Phys. Plasmas 18 , 042106 (2011) [2] G. Chen, A. V. Arefiev, R. D. Bengtson, B. N. Breizman, C. A. Lee, and L. L. Raja, Phys. Plasmas 13 , 123507 (2006)
32
Expanding structures in magnetized plasmas
Timo Schroeder1, Olaf Grulke1, Thomas Klinger1,2, Rod Boswell3, Christine Charles3
1) Max-Planck-Institute of Plasma Physics, Greifswald, Germany2) Ernst-Moritz-Arndt University, Greifswald, Germany3) Australian National University, Canberra, Australia
Double layers (DL, i.e. localized boundary layers between two plasma regimes of signi�cantlydi�erent plasma potential, ∆Φ > kBTe/e) result in strong electric �elds. One can distinguishbetween current-carrying and current-free DLs. Especially the latter can form under variousconditions. Although they have been observed in both space and laboratory plasmas themechanism of their formation is still under debate. Laboratory experiments have shown thatcurrent-free DLs are usually form due to an expanding magnetic �eld and/or an expandingdevice geometry. Nevertheless, in early experiments Hairapetian and Stenzel (1988) founda similar plasma potential structure. In the ignition phase of a thermionic discharge, theydiscovered an exceeded acceleration of ions due to a propagating DL. The present work uses rfdischarges to investigate the mechanisms of the ion acceleration and the formation of possibleDLs in the expansion process. Thereby, static DLs can already be observed in the expansioncreated by a pulsed rf source. By using a fast valve it is possible to inject the working gasdirectly into the source region. Therefore, the expansion chamber can be kept almost atbase pressure. The combination of a short gas pu� and a short rf pulse �nally result in apropagating DL. This contribution will present some results of these experiments.
133
Kinetic and fluid equation treatments of non-equilibrium electron and positron transport in dense gases and liquids
R. D. White1, R. E. Robson1, G. Boyle1, W. Tattersall1 , S. Dujko2 and Z. Lj. Petrovic2 1ARC Centre for Antimatter-Matter Studies, James Cook University, Townsville 4810,
Australia 2 Institute of Physics, Pregrevica 118, 11080 Belgrade, Serbia
Email contact: [email protected]
New frontiers in science and technology have generated an interest in understanding the fundamental physics of electron and positron transport processes in dense gaseous and soft condensed materials/liquids. This paper focuses on the adaptation of gas phase scattering cross-sections to electron/positron transport in dense systems where material structure becomes important. We focus on non-equilibrium situations where the electrons/positrons are driven out of equilibrium by an electric field, using a generalized Boltzmann’s equation. The explicit effects of the coherent scattering on transport will be quantified, including a fluid model with generalisations of the Wannier energy relation and Einstein relations. A scheme for the direct calculation of transport coefficients in dense gas/liquid systems from those in the dilute gas limit will also be presented.
34
3D Modelling of dc Atmospheric Arc DischargesE. Tam and A. B. Murphy
CSIRO Material Science and Engineering, P.O. Box 208, Lindfield NSW 2070, [email protected]
Discharges in helium between carbon electrodes at atmospheric or sub-atmospheric pres-sure have proved to be excellent sources of carbon nanostructures, such as graphene andcarbon nanotubes. However, the formation mechanisms are poorly understood. We havedeveloped a three-dimensional fluid model of a dc arc discharge in helium that includesthe carbon electrodes and their vaporization self-consistently. This allows us to determinethe concentration of carbon species at all points in the arc. In this talk, I will discuss thepreliminary results of my simulations on the influence of the helium inflow rate, the inter-electrode gap and the arc current in the context of optimizing the arc for the growth ofdifferent carbon nanostructures. The model is not limited to carbon arc can be applied toother dc arc discharges for a number of other applications (such as gas metal arc welding,arc lamps and lightning).
35
An experimental study on a large area multi-electrode discharge in the fabrication of
microcrystalline thin film solar cell
Sang-Hun Seo1, Y. S. Lee, and Hong-Young Chang
1 Department of Physics, Korea Advanced Institute of Science and Technology, Daejeon, South Korea 305-701
E-mail [email protected]
Key words: Multi-electrode, CCP, solar cell, microcrystalline silicon
Abstract
Recently, there have been many research for higher deposition rate (DR) and good
uniformity of μc-Si:H film in large-area discharge. Two factors should be the most important
issues in the fabrication of the thin film solar cell. In order to solve these issues, several dicahrge
conditions, including large area electrode (more than 1.1 m 1.3 m), higher pressure (more
than 1 Torr), and very high-frequency RF power (more than 40 MHz), have attracted. But, in the
case of large-area capacitive discharges (CCP) driven at high frequencies, the effect caused by
the standing wave should be important limitation. Furthermore, the ion damage on the thin film
layer by the high sheath voltage can cause the defects, which degrade the film quality.
Here, we will propose new CCP electrode concept, which consists of a series of
electrodes and grounds arranged by turns, and provide the processing results. The high DR (1
nm/s), the controllable crystallinity (~70%), and the relatively good uniformity can be obtained
at the high frequency of 40 MHz in the large-area discharge (280 mm 540 mm). And, we will
show the TEM images of the μc-Si:H films at the various conditions of μc-Si:H films, and
discuss the crystal formation compared to the case of VHF CCP. Finally, we will discuss the
issues in expanding the multi-electrode to the 8G class large-area plasma processing (2.2 m
2.4 m) and in improving the process efficiency.
36
Abstract not available
Kim Chang-Bae
37
Electron impact excitation of the higher-energy states of molecular oxygen in the atmosphere of Europa
Laurence Campbell, Michael J. Brunger and Sudhaghar Jayaraman
ARC Centre for Antimatter-Matter Studies, Flinders University, Adelaide, Australia Email: [email protected]
Measurements and BEf-scaling predictions of electron impact cross sections for excitation of the Schumann-Runge (SR) continuum, longest band (LB) and second band (SB) of molecular oxygen have recently been published1. Almost all of this excitation results in predissociation, so that emissions by radiative decay are negligible. However, most of the predissociations produce one excited O(1D) atom, which radiatively decays to emit a 630.0-nm photon. Due to the long lifetime of O(1D), it is mainly quenched in collisions in the Earth’s atmosphere at altitudes where the molecular oxygen density is significant. However, as densities are much less in the atmosphere of Europa, electron-driven production of 630.0-nm radiation has the potential to dominate over other sources, such as direct excitation of O atoms. We present results of a statistical-equilibrium model of electron-driven processes involving O and O2 on Europa, showing that the intensity ratio 630.0-nm/557.7-nm is much greater at lower altitudes if the electron impact excitation of the SR continuum and the LB is taken into account. 1 D. Suzuki et al., J. Chem. Phys. 134 064311 (2011)
38
Mode coupling due to ion wakes in 2D complex plasma crystals
L. Couëdel1,2
, V. Nosenko2, S. Zhdanov
2, A. Ivlev
2, H. Thomas
2, and G. Morfill
2
1Aix-Marseille Univ./CNRS, Laboratoire PIIM, 13397 Marseille cedex 20, France.2MPI extraterrestrische Phys., Giessenbachstraße, 85741 Garching, Germany.
Email contact: [email protected]
Non-Hamiltonian behaviour of particle ensembles is often a manifestation of asymmetry or non-reciprocity in the interparticle interactions. Such asymmetry can be considered as a result of the system openness. 2D complex plasma crystals, consisting of negatively charged particles immersed in a weakly ionised gas-discharge plasmas, are often observed in the sheath of laboratory discharges in which there is a flow of the ambient plasma. Consequently, the screening cloud around each charged microparticles becomes highly asymmetric. The clouds, referred as “plasma wakes”, play the role of an “external third body” in the interparticle interaction and hence make it non-reciprocal. The non-reciprocity of pair interaction provides a very efficient mechanism of converting the energy of the flowing ions into the kinetic energy of the dust particles. In particular dust-lattice waves mode can contribute to that. The kinetic energy can gro due to resonant particle-wake interactions when different oscillating modes of the microparticles are properly synchronised. In this paper, direct experimental observations of hybrid modes and mode-coupling induced melting in a 2D complex plasma crystal are reported [1,2]. Results are compared to simulation [3] and theory of wake induced mode coupling [4] and show a good agreement. The fingerprints of mode coupling are discussed in details.
[1] L. Couëdel et al., Phys. Rev. Lett. 103, 215001 (2009)[2] L. Couëdel et al., Phys. Rev. Lett. 104, 195001 (2010)[3] L. Couëdel et al., Phys. Plasmas. 18, 083707 (2011)[4] S. K. Zhdanov, A.V. Ivlev, and G. E. Morfill, Phys. Plasmas 16, 083706 (2009)
39
Enhancing inorganic nanomaterials by plasma functionalization/doping
Xiujuan J. Dai*, Zhiqiang Chen, Ying Chen , Peter R. Lamb, Xungai Wang
Institute for Technology Research and Innovation, Deakin University, Waurn Ponds 3216, Australia
[email protected], Abstract: We have developed specific plasma facilities and novel methods that enable functionalization and doping of inorganic nanomaterials in a controllable manner. In this talk, results from the first experimental demonstration of surface oxygen doping of boron nitride nanotubes (BNNTs), using an oxygen plasma [1], will be presented. This allows testing of theoretical predictions that oxygen doping will change the optical, electric and magnetic properties of BNNTs. Results demonstrating that selected functional groups can be attached to multiwalled carbon nanotubes (CNTs) using a N2+H2 plasma as well as plasma polymerization of heptylamine monomer, will also be presented. This has allowed much better dispersion and bonding of CNTs in composites giving improved performance. In addition, the plasma facilities at Deakin and their potential for improving nanomaterials in solar cells, batteries/fuel cells, and sensors will be briefly introduced. References: [1] X.J. Dai*, Y. Chen, Z. Chen, P.R. Lamb, L.H. Li, J. du Plessis, D.G. McCulloch and X. Wang: Nanotechnology Vol. 22 (2011), p. 245301
40
Extending the Usefulness of an Electron Scattering Setup by the Addition of
a Light Polarization Detector and Magnetic Angle Changer
C.F. Campbell, L.R. Hargreaves and M.A. Khakoo
Department of Physics, College of Mathematics and Natural Sciences,
California State University at Fullerton, Fullerton, CA
Our lab has focused on the measuring of differential cross-sections for atomic and molecular
gasses. We wish to extend not only the angular range over which we can measure, but also the
properties that can be measured.
To extend the usefulness of our electron scattering setup, we have added a polarized light
detector and will be adding a newly built magnetic angle changer. With the polarized light
detector we are able to measure the stokes parameters of light being emitted from electron
excited atomic targets. The detector is an in vacuum device and of the double mirror type. The
Magnetic Angle Changer, or MAC, consists of a series of concentric solenoid pairs. The
magnetic field generated by the MAC is used to deflect both incident and scattered electrons.
The particular style of MAC being used produces a magnetic field which is not only localized
but goes to zero in the target region.
I will present the current experimental setup as it currently stands with the polarized light
detector and our ongoing neon coincidence measurements, as well as the future addition of the
MAC.
41
Electron transfer-induced fragmentation by atom-molecule collisions
P Limao-Vieira1,*
, D Almeida1, F Ferreira da Silva
1 and G García
2
1 Laboratório de Colisões Atómicas e Moleculares, CEFITEC, Departamento de Física,
FCT-Universidade Nova de Lisboa, Campus de Caparica, 2829-516 Caparica, Portugal 2 Instituto de Física Fundamental, Consejo Superior de Investigaciones Científicas,
Serrano 113-bis, 28006 Madrid, Spain
* European Physical Journal D sponsored
It is now well established that low energy electrons provide an effective method for inducing
chemical processes in many natural and industrial processes [1] including, e.g.: a) the
formation of organic molecules within ice mantles on dusty grains in the interstellar medium;
b) the control of fluorocarbon plasmas used to produce silicon chips; (c) the chemical
modification using electron patterning and scanning tunnel microscopy and d) mutagenic and
other potentially lethal DNA lesions, such as single- and double-strand breaks [2]. Unlike
photon induced dissociation, the energy of the incident electron may be significantly below
the energy required to excite the molecule to a dissociative electronic state. Therefore the
incoming electron is ‘captured’ before decaying, producing a negative fragment accompanied
by one or more associated neutral counterpart(s). These neutrals, often radical products may
subsequently initiate new chemistry within the medium. However many elementary
collisional processes are not direct electron impact but rather depend upon electron transfer.
The electron transfer process is however, in general, endoergic i.e. requires a minimum
collisional energy usually of the order of a few eV, and hence the incident neutral electron
transferring species must have a high kinetic energy. We have commenced an experimental
program concerning electron transfer mechanism yielding ion-pair formation in gas phase
molecules through collisions with hyperthermal neutral potassium atoms in a crossed
molecular-beam technique [3–6]. The negative ions formed in the collision region are TOF
mass analysed.
[1] E Illenberger, J Momigny, Gaseous Molecular Ions, Springer Verlag, New York, 1992.
[2] B Boudaiffa, P Cloutier, D Hunting, M A Huels and L Sanche, Science, 2000, 287, 1658.
[3] R Antunes, D Almeida, G Martins, N J Mason, G Garcia, M J P Maneira, Y Nunes, and P Limão-Vieira, Phys. Chem.
Chem. Phys., 2010, 12, 12513.
[4] D Almeida, R Antunes, G Martins, S Eden, F Ferreira da Silva, Y Nunes, G Garcia and P Limão-Vieira, Phys. Chem.
Chem. Phys., 2011, 13, 15657.
[5] F Ferreira da Silva, D Almeida, R Antunes, G Martins, Y Nunes, S. Eden, G Garcia and P Limão-Vieira, Phys. Chem.
Chem. Phys., 2011, 13, 21621.
[6] F Ferreira da Silva, M Lança D Almeida, G Garcia and P Limão-Vieira, Eur. Phys. J. D, submitted.
42
Particle-in-cell simulations of hollow cathode enhanced
capacitively coupled rf discharges
T. Lafleur_ and R.W. Boswell
Space Plasma, Power and Propulsion Group,
Research School of Physics and Engineering,
The Australian National University, Canberra ACT 0200, Australia
A two-dimensional particle-in-cell simulation has been developed to study density
enhancement of capacitively coupled rf discharges with multi-slit electrodes. The
observed density increase is shown to result from a hollow cathode effect that takes
place within the multi-slit electrode configuration, which forms as a result of
secondary electron emission due to ion bombardment. By investigating the ionization
and power deposition profiles, it is found that rf sheath heating is too weak to sustain
the discharge, and that secondary electron acceleration within the sheath is the
primary heating mechanism. Due to a capacitive voltage divider formed by the rf
sheaths at each electrode, the area ratio of the powered and ground electrodes is
observed to have a strong effect on the resulting discharge, and if the ground electrode
area is too small, the voltage drop at the powered electrode is too low to sustain a
hollow cathode discharge.
43
Manipulating electron dynamics and plasma chemistry in dual radio-frequency driven atmospheric pressure plasmas Colm O'Neill1, Jochen Waskoenig1, Kari Niemi2, Timo Gans2 1Centre for Plasma Physics, Queens University Belfast, Belfast, BT7 1NN, Northern Ireland, UK
2York Plasma Institute, Department of Physics, University of York, Heslington, York, YO10 5DQ, UK
Radio-frequency driven cold atmospheric pressure plasmas have the potential for many new technological applications, in particular in healthcare. Plasma ionisation dynamics and chemistry are complex and increased control is desired. Dual-frequency operation has been shown to provide enhanced control over power coupling and ionisation mechanisms [1]. Here a numerical model based on hydrodynamic equations with a semi-kinetic treatment of the electrons considering 184 reactions amongst 20 species is used to determine the effects of dual-frequency excitation on electron dynamics and plasma chemistry. It is found that variations of the frequencies, voltages and relative phase enable the manipulation of the temporal and spatial structures of plasma ionisation and subsequently the electron energy distribution function (EEDF) which governs plasma chemistry. [1] J. Waskoenig and T. Gans, Appl. Phys. Lett. 96, 181501 (2010)
44
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