Bulletin of the American Physical Society
2006 59th Annual Gaseous Electronics Conference
Tuesday–Friday, October 10–13, 2006; Columbus, Ohio
Session ET1: Plasma Sources II |
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Chair: S.G. Walton, Naval Research Laboratory Room: Holiday Inn Salon CD |
Tuesday, October 10, 2006 4:00PM - 4:15PM |
ET1.00001: Multilevel non-empirical approach to calculation of light emission properties of of chemically active non-equilibrium plasma B. Potapkin, S. Adamson, V. Astapenko, I. Chernysheva, M. Deminsky, A. Demura, N. Dyatko, A. Eletskii, A. Knizhnik, I. Kochetov, A. Napartovich, E. Rykova, S. Umanskii, A. Zaitsevskii, G. Cotzas, D. Mikhael, V. Midha, D. Smith, T. Sommerer A multi-level approach for calculation of the properties of non-equilibrium plasmas using first principles and theories of elementary processes is described in the paper. In the framework of this approach, unknown properties of molecules, ions and atoms (structure, energy curves, and transition dipole moments) are calculated using quantum-chemical methods. The calculation results are then used to determine emission probabilities, Frank-Condon factors of electronic-vibration transitions, cross sections for electron impact excitation, dissociation, dissociative recombination and attachment. Ion-molecular reactions are treated in terms of the statistical theory. The energy transfer processes involving electronically species are described through the asymptotic approach. The electron impact excitation cross sections for atoms and molecules are calculated using the modified Born approximation. The resulting kinetic state-to-state scheme is then used to compute the dependencies of the electron energy balance and the radiative emission efficiency as a function of the plasma parameters. As an example of this multilevel approach, the radiative emission properties of an Ar-InI DC glow discharge were calculated using the Chemical Workbench computational environment. [Preview Abstract] |
Tuesday, October 10, 2006 4:15PM - 4:30PM |
ET1.00002: Computational modeling of HC discharges in the presence of an applied magnetic field Seth Veitzer, Peter Stoltz We present work on the numerical modeling of hollow cathode discharges using the multi-dimensional, massively parallel, hybrid PIC simulation code VORPAL. We simulate the formation of a plasma in the hollow cathode by modeling the production of ion- and electron-induced secondary electrons from the cathode walls, and electron impact ionization of background Helium gas. We simulate discharge of built-up current through the application of an external magnetic field, effectively shorting out the production of plasma due to secondary electrons, and we compare our results here to published experimental findings. We also discuss the numerical methods that we use to develop the simulations, including the physical models we implement and simulation parameters needed for accurate modeling. [Preview Abstract] |
Tuesday, October 10, 2006 4:30PM - 4:45PM |
ET1.00003: Radially localized helicon mode in helicon plasma sources. Guangye Chen, Charles Lee, Alexey Arefiev, Boris Breizman, Raja Laxminarayan, Roger Bengtson It has been widely believed that helicon waves are excited in helicon discharges. However, an important but often underappreciated feature of helicon plasma sources is that the plasma density is typically strongly nonuniform across the confining magnetic field with a peak at the axis. This nonuniformity can create a radial potential well for non-axisymmetric helicons, allowing radially localized helicon (RLH) waves [1]. This work presents theoretical and experimental evidence that the RLH waves play a significant role in a helicon plasma source. The measurements of a plasma response to a secondary low-power rf generator with variable frequency indicate the existence of an eigenmode close to the driving frequency of the main generator. The 2D plasma density profile was measured and then used to calculate the rf field structure for the experimental setup. The calculations confirm that an RLH wave is the eigenmode excited in the experiment. The calculations were performed using a 2D field solver for a single resonant azimuthal harmonic (m=1) under the assumption that the density profile is axisymmetric. 1D field calculations for the measured radial density profile were used to identify the RLH wave by its dispersion relation and to distinguish it from the conventional helicon and Trivelepiece-Gould waves. [1]B. N. Breizman and A. V. Arefiev, Phys. Rev. Lett. 84, 3863 (2000). [Preview Abstract] |
Tuesday, October 10, 2006 4:45PM - 5:00PM |
ET1.00004: Ionization processes in the high power impulse magnetron sputtering discharge (HIPIMS) Jon T. Gudmundsson, Johan Bohlmark, Arutiun P. Ehiasarian, Ulf Helmersson High power impulse magnetron sputtering (HIPIMS) is a technique that utilizes ionized physical vapor deposition (IPVD). High density plasma is created by applying a high power pulse to a planar magnetron discharge. The plasma parameters in the HIPIMS discharge will be reviewed and discussed as well as some applications of the HIPIMS technique. Measurements of the temporal and spatial behavior of the plasma parameters indicate peak electron density of the order of $10^{19}$ m$^{-3}$, that expands from the target with a fixed speed that depends on the gas pressure and the gas type. The high electron density results in a high degree of ionization of the deposition material. Furthermore, the ionization processes and the fractional ionization of the sputtered material is explored using a time dependent global (volume averaged) model. The model calculations give integrated ionized flux fraction in the range of 80 - 90\% for Al, Cu and C targets and average power 300 W at 10 mTorr argon pressure. [Preview Abstract] |
Tuesday, October 10, 2006 5:00PM - 5:15PM |
ET1.00005: Transition from weakly to strongly magnetized gas discharge plasma Valery Godyak, Natalia Sternberg A study of the fluid model for cylindrical weakly ionized quasi- neutral plasmas in an axial magnetic field is presented. The model takes into account ionization, ion and electron inertia, as well as frictional forces for ions and electrons. The behavior of the plasma parameters for arbitrary magnitudes of the magnetic field, arbitrary gas pressure and plasma size is presented, making the model applicable for a wide range of discharge conditions. A magnetic field parameter is introduced, which specifies a parameter range for the magnetic field, gas pressure and plasma size where the Boltzmann equilibrium with the ambipolar field for the electron distribution is satisfied. In addition, a parametric relation for the magnetic field, gas pressure and plasma size is obtained, which separates the region of weak magnetic field effects from the region of strong magnetic field effects. For strongly magnetized plasmas, an asymptotic solution with non-zero plasma density at the plasma boundary is presented. Analytical approximations for the ionization frequency and the plasma density at the plasma boundary are found for arbitrary external discharge parameters. The theoretical results are supported by numerical computations. [Preview Abstract] |
Tuesday, October 10, 2006 5:15PM - 5:30PM |
ET1.00006: Ion Source Development at the SNS Robert Welton, Martin Stockli, Syd Murray, Rick Goulding , Jerry Carr, Justine Carmichael The US Spallation Neutron Source* (SNS) has recently begun producing neutrons and is currently on track to becoming a world-leading facility for material science based on neutron scattering. The facility is comprised of an H$^{-}$ ion source, a linear accelerator, an accumulator ring and a liquid-Hg target. Over the next several years the average H$^{-}$ current from the ion source will be increased in order to meet the baseline facility requirement of 1.4 MW of beam-on-target power and the SNS power upgrade power requirement of 2+ MW. Meeting these goals will require H$^{-}$ currents of 40-80 mA with an RMS emittance of 0.25-0.35 $\pi $ mm mrad and a $\sim $7{\%} duty-factor. To date, the RF-driven multicusp SNS ion source has only been able to demonstrate sustained operation at 33 mA of beam current at a $\sim $7{\%} duty-factor. This report details our efforts to develop variations of the current ion source which can meet these requirements: designs and experimental results are presented for source variations featuring helicon plasma generators, high-power external antennas employing Cs, glow-dischage plasma guns supplying supplemental electrons and advanced Cs collars. [Preview Abstract] |
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