Bulletin of the American Physical Society
71st Annual Gaseous Electronics Conference
Volume 63, Number 10
Monday–Friday, November 5–9, 2018; Portland, Oregon
Session FT2: Magnetically-enhanced Plasmas |
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Chair: Shahid Rauf, Applied Materials Room: Oregon Convention Center A105 |
Tuesday, November 6, 2018 2:00PM - 2:15PM |
FT2.00001: Whistler modes with angular momentum Reiner Stenzel, Manuel Urrutia In unbounded plasmas whistler waves with angular momentum are ubiquitous. The field rotation is the salient feature of general helicon modes. It gives rise to new wave-particle interactions. These waves are studied experimentally in a large uniform laboratory plasma. Their helical wave topology is demonstrated by three-dimensional probe measurements of the wave magnetic field. The orbital angular momentum has been measured quantitatively. The helicity density $\mathbf J \parallel \mathbf B$ has been determined. Helicons have nearly force-free fields. The field lines are writhed and twisted. In general a loop antenna with a perpendicular rf magnetic field excites a "plane parallel" whistler mode of finite transverse dimension. Its field is circularly polarized and rotates, hence is a generalized helicon mode. For oblique propagation the field rotates around the wave vector. On curved ambient field lines new 3D helicon modes are observed. On circular fields whistler modes propagate near the resonance cone angle. Helicons are reflected by strong magnetic field gradients. Near magnetic null points helicons propagate on the separatrix. Helicons can be trapped in an FRC. The observations are relevant to magnetic reconnection and helicon sources. [Preview Abstract] |
Tuesday, November 6, 2018 2:15PM - 2:30PM |
FT2.00002: Abstract Withdrawn
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Tuesday, November 6, 2018 2:30PM - 2:45PM |
FT2.00003: Anomalous transport in a magnetized plasma column under laboratory conditions Romain Lucken, Antoine Tavant, Anne Bourdon, Mike Lieberman, Pascal Chabert The problem of instability-enhanced plasma transport in low-temperature magnetized discharges is addressed using two-dimensional particle-in-cell (PIC) simulations of a magnetized plasma column for ion Knudsen numbers between 0.3 and 1, and magnetic fields ranging from 0 to 40\,mT. The influence of the type of gas (argon, xenon, and helium) is investigated, with and without accounting for the effect of the magnetic field on the ions. The spectral analysis of the data generated by the various PIC runs when the instability triggers was shown to agree with a dispersion relation coming from linearized fluid equations. An anomalous collision frequency depending only on the electron cyclotron frequency and the electron plasma frequency was found, yielding accurate predictions of the flux of ions at the walls through an anisotropic model of the plasma transport that applies for all magnetization regimes. It is demonstrated that the effect of the magnetic field totally saturates when the instability controls the plasma transport, setting a limit to magnetic confinement in laboratory plasmas. [Preview Abstract] |
Tuesday, November 6, 2018 2:45PM - 3:00PM |
FT2.00004: Kinetic derivation of a gyro-fluid model for magnetized technological plasmas Ralf Peter Brinkmann, Dennis Krüger Plasma processes such as magnetically enhanced reactive ion etching (MERIE), plasma ion assisted deposition (PIAD), and dc and high power impulse magnetron sputtering (dcMS/HiPIMS) employ magnetized high density plasmas at relatively low pressures. This regime is very difficult to analyze. Conventional fluid models do not apply, and numerical kinetic approaches like particle-in-cell (PIC) are rather expensive. This contribution will present an alternative approach based on the framework of gyro-kinetics. This theory - actually more a class of theories – relies on the insight that the fast gyro motion of magnetized particles can be mathematically separated from the slower drift motion and be integrated out, leaving only the dynamics on slower time scales and larger length scales. Starting from a general kinetic description of the electron component, the gyro-kinetic approach allows to systematically reduce the model to a system of two coupled partial differential equations in just two dimensions which may be termed a gyro-fluid model. [Preview Abstract] |
Tuesday, November 6, 2018 3:00PM - 3:15PM |
FT2.00005: Student Excellence Award Finalist: Phase mixing and collisionless dissipation at the plasma boundary sheath of magnetized low temperature plasmas Dennis Krueger, Ralf Peter Brinkmann One important example of magnetized low temperature plasmas is high power impulse magnetron sputtering (HiPIMS). The regime is characterized by $n_{\mathrm{e}}\leq10^{19}\, \mathrm{m}^{-3}$, $p\approx 0.5\, \mathrm{Pa}$ and the occurrence of symmetry breaking phenomena (spokes). Conventional kinetic approaches like particle-in-cell (PIC) methods are too resource consuming to simulate relevant time scales. One possible alternative makes use of the fact that the electron Larmor radius $r_{\mathrm{L}}$ is small compared to the typical length scale $L$ of the system. This ansatz, however, breaks down at the plasma boundary sheath in front of the target. A hard wall model might be an effective boundary condition for the interaction of magnetized electrons with this interface [I,II]. Scattering matrices obtained for different inclination angles of the magnetic field relate the incoming to the outgoing electron velocity distribution function (EVDF). An interesting feature which can be observed in the outgoing EVDF are fractal type structures which disappear due to phase mixing about a distance of some Larmor radii away from the sheath edge.\\ I \,\,D. Kr\"uger et al., Plasma Sources Sci. Technol. 26, 115009 (2017)\\ II D. Kr\"uger et al., Plasma Sources Sci. Technol. 27, 025001 (2018) [Preview Abstract] |
Tuesday, November 6, 2018 3:15PM - 3:30PM |
FT2.00006: Current-dependent microturbulence features in pulsed magnetron operation : experiments and simulations Sedina Tsikata, Tiberiu Minea, Adrien Revel Interest in the pulsed, high-current operation of planar magnetrons has grown over the last decade. Under certain conditions, operation in such regimes may favor the deposition of thin films with properties superior to those generated under direct current operation. However, the physics of the magnetron plasma is notoriously complex: the discharge exhibits transient features and complex phenomena such as plasma turbulence and large-scale self-organization. In addition, realistic modeling of high-current, high-density regimes poses a major challenge. In this work, we present recent progress in our understanding of this discharge. Recent experimental measurements of microturbulence using coherent Thomson scattering are discussed, with a focus on transient features observed within microsecond-duration pulses. These experimental analyses are complemented by information gained from quasi-3D particle-in-cell simulations. [Preview Abstract] |
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