Bulletin of the American Physical Society
55th Annual Meeting of the APS Division of Plasma Physics
Volume 58, Number 16
Monday–Friday, November 11–15, 2013; Denver, Colorado
Session CO5: Plasma Sources, Sheaths, and Diagnostic Techniques |
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Chair: Richard Magee, Tri Alpha Energy Room: Governor's Square 10 |
Monday, November 11, 2013 2:00PM - 2:12PM |
CO5.00001: ABSTRACT WITHDRAWN |
Monday, November 11, 2013 2:12PM - 2:24PM |
CO5.00002: ABSTRACT WITHDRAWN |
Monday, November 11, 2013 2:24PM - 2:36PM |
CO5.00003: ABSTRACT WITHDRAWN |
Monday, November 11, 2013 2:36PM - 2:48PM |
CO5.00004: Determination of the EEDF using a Bayesian analysis framework Dominic Poznic, Alex Samarian, Brian James A statistical analysis framework is presented that determines the electron energy distribution function (EEDF) of an argon discharge plasma from optical emission spectra and Langmuir probe data. The analysis framework is based on Bayesian inference, in which data are treated in a rigorously statistical manner, that naturally includes all sources of uncertainty. The framework is designed to allow models describing different data sets from the same system to be combined in a straightforward manner. Spectral line intensities are described using a collisional-radiative model, while Langmuir probe data are described with a simple 1D Langmuir probe model. The models are inverted and combined using Bayesian probability theory in a joint analysis of both data sets. This framework was tested using data simulated by the two models from a known set of plasma conditions. The testing confirmed the ability of the framework to determine non-Maxwellian EEDFs and use multiple data sets to increase the accuracy of results. [Preview Abstract] |
Monday, November 11, 2013 2:48PM - 3:00PM |
CO5.00005: A Charge-Exchange Neutral Particle Analyzer for an Inertial Electrostatic Confinement Fusion Device Gabriel Becerra, Gerald Kulcinski, John Santarius, Gilbert Emmert An electrostatic energy analyzer for outgoing charge-exchange neutral particles has been designed and constructed for application on HELIOS, an inertial electrostatic confinement (IEC) fusion device designed for advanced fuel studies. Ions are extracted from an external helicon plasma source and subsequently accelerated radially into an electrostatic potential well set up by a semi-transparent cathode grid inside the HELIOS spherical chamber. Analysis of fast neutrals produced by charge exchange between energetic ions and background gas yields information on primary ion energy spectra, as well as a quantitative measure of charge exchange as an energy loss mechanism in IEC devices. Preliminary data with helium is used to benchmark the two-charge-state helium formalism of VICTER, a numerical code on spherically convergent ion flow, as it relates to IEC operation with helium-3 fuel. [Preview Abstract] |
Monday, November 11, 2013 3:00PM - 3:12PM |
CO5.00006: Ion flow velocities at the sheath edge in a plasma with two warm ions species Nong Xiang, Jing Ou How to determine the ion flow velocities at the sheath edge in a plasma containing two positive ion species with finite temperatures is still an open question. In additional to the well known Bohm criterion $N_1/u_1^2 + N_2/u_2^2$ = 1 (here $N_1$ and $N_2$ are the ion concentrations, $u_1$ and $u_2$ are the ion flow velocities normalized to the individual sound speed), a second constraint is required to determine the flow velocity for each ion species at the sheath edge. In this work, the flow velocities are determined by numerically solving the time-dependent fluid equations for electrons as well as ions. The second constraint is obtained and it is shown that the constraint depends not only on local plasma parameters at the sheath edge, but weakly on parameters in the plasma region. The ion flow velocities at the sheath edge deviate slightly from each individual sound speed. [Preview Abstract] |
Monday, November 11, 2013 3:12PM - 3:24PM |
CO5.00007: Ion distribution functions in magnetized rf Argon plasma presheaths M. Umair Siddiqui, Noah Hershkowitz A helicon plasma source was operated in a low power inductive mode to create a magnetized Argon plasma with densities of 10$^{11}$ -- 10$^{12}$ cm$^{-3}$ and electron temperatures from 3 -- 5 eV. A grounded plate oriented perpendicular to the axial magnetic field was placed 2.5 antenna lengths downstream from the near edge of the rf antenna. Using laser-induced fluorescence, the ion velocity distribution functions were investigated along the axis of the chamber in the bulk plasma and in the plate's presheath. Bimodal and non-Maxwellian distribution functions were observed in the presheath, though not in the bulk plasma. In certain situations ion populations traveling in opposite directions were observed. In this work the authors investigate these phenomena as a function of neutral pressure, rf power and axial magnetic field strength. [Preview Abstract] |
Monday, November 11, 2013 3:24PM - 3:36PM |
CO5.00008: Measurement of Time-Dependent Ion Velocity Distribution Function by Laser Induced Fluorescence in a Cylindrical Hall Thruster with Driven Spoke Yuan Shi, Yevgeny Raitses, Ahmed Diallo, Stephane Mazouffre This paper reports, for the first time, effects of spoke on ion velocity distribution function measured by time-resolving laser induced fluorescence. To scan ion speed, the 5d 4 F -6p 4 5/2 D 5/2 transition of Xe+ is excited using tunable diode laser. Photons from 6p 4 D -6s 4 5/2 P 3/2 transition are collected by a photomultiplier tube and counted by a multichannel scaler. To subtract background, a mechanical chopper is used to generate laser pulses whose power is monitored by a photodiode. To achieve phase-locked accumulation of fluorescence photons, spoke is driven using successively phase-shifted square waves on anode segments and the driving signal is used to synchronize photon accumulation to spoke in data post processing. To resolve three ion velocity components, two laser beams are established, with one beam measuring axial velocity and the other beam measuring some linear combination of radial and azimuthal velocities, depending on the position of collection volume with respect to thruster plume. Measurements shows ion distribution function oscillates with spoke. Along the thruster axis, ion density is strongly modulated while axial ion velocities are not affected. Off-axis effects of spoke will also be discussed. [Preview Abstract] |
Monday, November 11, 2013 3:36PM - 3:48PM |
CO5.00009: Simulation of Mach Probes in Non-Uniform Magnetized Plasmas: the Influence of a Background Density Gradient Christian Bernt Haakonsen, Ian H. Hutchinson Mach probes can be used to measure transverse flow in magnetized plasmas, but what they actually measure in strongly non-uniform plasmas has not been definitively established. A fluid treatment in previous work has suggested that the diamagnetic drifts associated with background density and temperature gradients affect transverse flow measurements, but detailed computational study is required to validate and elaborate on those results; it is really a kinetic problem, since the probe deforms and introduces voids in the ion and electron distribution functions. A new code, the Plasma--Object Simulator with Iterated Trajectories (POSIT) has been developed to self-consistently compute the steady-state six-dimensional ion and electron distribution functions in the perturbed plasma. Particle trajectories are integrated backwards in time to the domain boundary, where arbitrary background distribution functions can be specified. This allows POSIT to compute the ion and electron density at each node of its unstructured mesh, update the potential based on those densities, and then iterate until convergence. POSIT is used to study the impact of a background density gradient on transverse Mach probe measurements, and the results compared to the previous fluid theory. [Preview Abstract] |
Monday, November 11, 2013 3:48PM - 4:00PM |
CO5.00010: Experimental Evidence of Multiple Double Layer in a Helicon Antenna Produced Plasma Prabal Kumar Chattopadhyay, Kshitish Barada, J. Ghosh, Devendra Sharma, Y.C. Saxena A strong current free double layer has been observed in an geometrically and magnetically expanding helicon antenna produced plasma. Double layer strength is shown to increase with magnetic field gradient near the geometrical boundary. However, further increases of magnetic field degrade DL strength before finally increases again with the occurrence of multiple double layers. The detail measurement of DL strength, position along with plasma density will be presented. [Preview Abstract] |
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