Bulletin of the American Physical Society
69th Annual Gaseous Electronics Conference
Volume 61, Number 9
Monday–Friday, October 10–14, 2016; Bochum, Germany
Session QR4: Basic Plasma Physics IIFocus
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Chair: Tsanko Tsankov, Ruhr University Room: 3 |
Thursday, October 13, 2016 8:30AM - 9:00AM |
QR4.00001: Collective dynamics and transport in extremely magnetized dusty plasmas Invited Speaker: Peter Hartmann We have built an experimental setup to realize and observe rotating dusty plasmas in a co-rotating frame. Based on the Larmor theorem, the ``RotoDust'' setup is able to create effective magnetizations, mimicked by the Coriolis inertial force, in strongly coupled dusty plasmas that are impossible to approach with superconducting magnets. At the highest rotation speed, we have achieved effective magnetic fields of 3200 T [1]. The effective magnetization $\beta \quad = \quad \omega_{\mathrm{c}}$/$\omega _{\mathrm{p}}$ (ratio of cyclotron to plasma frequency) reaches 0.76 which is typical for many strongly magnetized and strongly correlated plasmas in compact astrophysical objects [2]. The analysis of the wave spectra as observed in\textunderscore the rotating frame clearly shows the equivalence of\textunderscore the rotating dust cloud and a magnetized plasma.\textunderscore Further, the analysis of the mean square displacement (MSD) and the velocity autocorrelation function (VAC) revealed the transport parameters diffusion and viscosity, which are in reasonable agreement with numerical predictions for magnetized 2D Yukawa systems. Small degree of super-diffusion is observed. [1] P.Hartmann, Z.Donko\textunderscore , T.Ott, H.Ka\textunderscore hlert, M.Bonitz, Phys.Rev.Lett. 111, 155002 (2013) [2] H. Ka\textunderscore hlert, J. Carstensen, M. Bonitz, H. Lo\textunderscore wen, F. Greiner, and A. Piel, Phys. Rev. Lett. 109, 155003 (2012) [3] T. Ott and M. Bonitz, Phys. Rev. Lett. 107, 135003 (2011) [Preview Abstract] |
Thursday, October 13, 2016 9:00AM - 9:15AM |
QR4.00002: Rotating plasma structures in the cross-field discharge of Hall thrusters Stephane Mazouffre, Lou Grimaud, Sedina Tsikata, Konstantin Matyash Rotating plasma structures, also termed rotating spokes, are observed in various types of low-pressure discharges with crossed electric and magnetic field configurations, such as Penning sources, magnetron discharges, negative ion sources and Hall thrusters. Such structures correspond to large-scale high-density plasma blocks that rotate in the E\texttimes B drift direction with a typical frequency on the order of a few kHz. Although such structures have been extensively studied in many communities, the mechanism at their origin and their role in electron transport across the magnetic field remain unknown. Here, we will present insights into the nature of spokes, gained from a combination of experiments and advanced particle-in-cell numerical simulations that aim at better understanding the physics and the impact of rotating plasma structures in the ExB discharge of the Hall thruster. As rotating spokes appear in the ionization region of such thrusters, and are therefore difficult to probe with diagnostics, experiments have been performed with a wall-less Hall thruster. In this configuration, the entire plasma discharge is pushed outside the dielectric cavity, through which the gas is injected, using the combination of specific magnetic field topology with appropriate anode geometry. [Preview Abstract] |
Thursday, October 13, 2016 9:15AM - 9:30AM |
QR4.00003: Hybrid Simulation of Supersonic Flow of Weakly Ionized Plasma along Open Field Magnetic Line Effect of Background Pressure Ampan Laosunthara, Hiroshi Akatsuka In previous study, we experimentally examined physical properties of supersonic flow of weakly ionized expanding arc-jet plasma through an open magnetic field line ($B_{\mathrm{max}}$\textasciitilde 0.16T). We found supersonic velocity of helium plasma up to Mach \textasciitilde 3 and the space potential drop at the end of the magnets. To understand the plasma in numerical point of view, the flows of ion and neutral are treated by particle-based Direct Simulation Monte Carlo (DSMC) method, electron is treated as a fluid. The previous numerical study, we assumed 2 conditions. Ion and electron temperatures were the same (LTE condition). Ion and electron velocities were the same (current-free condition). We found that ion velocity decreased by collision with residual gas molecules (background pressure). We also found that space potential changing with background pressure. In other words, it was indicated that electric field exists and the current-free assumption is not proper. In this study, we add electron continuity and electron momentum equations to obtain electron velocity and space potential. We find that space potential changing with background pressure slightly. It is indicated that electron is essential to space potential formation than ion. [Preview Abstract] |
Thursday, October 13, 2016 9:30AM - 9:45AM |
QR4.00004: The helical kink “STABILITY” in plasmas. Masaru Irie, Miyoko Kubo-Irie The helical plasma “instability” was known for half a century before and it was one of the key issue in the plasma fusion research. The three dimensional MHD simulation on the low pressure linear plasma has been conducted in National Institute of Fusion Sciences around 80's in the consequence with plasma reconnection and Dynamo-effect closely related to the Reversed Field Pinch Plasma as well as the Spheromak / Compact Torus. Both of these trends aiming for controlling the plasma instability especially with current density over 1MA/m2. On the other hand in arc discharge field, helical plasma instability in the current zero region was one of the main issue and explained especially in “this: Ruhr University Bochum” under Prof. Jurgen Mentel. In this proposed presentation, we would like to concentrate on controlling the plasma profile and demonstrate the existence of the “stable” helical plasma and discuss the application of these techniques by applying massively parallel but bench top GPGPU system. This should give good simulation on the fusion plasma such as the Internal Transport Barriers and Serpens mode. [1] H.G.Hulsman {\&} J.Mnetel, Phys.Fluids, 30, 2275(1987) [2] T.Sato,T.Hayashi {\&} R.Horiuchi , Private Communication. [Preview Abstract] |
Thursday, October 13, 2016 9:45AM - 10:00AM |
QR4.00005: Electron drift across the magnetic field in a micro-ECR neutralizer Yoshinori Takao, Kenta Hiramoto, Yuichi Nakagawa, Hiroyuki Koizumi, Kimiya Komurasaki Although neutralization is required for ion propulsion systems to produce thrust by ion beams in space, a neutralizer itself should be low-power and low-propellant consumption because electrons make no thrust. To design such a micro neutralizer, the mechanisms of electron transport should be elucidated. In the present study, three-dimensional particle-in-cell simulations have been conducted for a 4.2-GHz microwave discharge neutralizer, using an electron cyclotron resonance xenon plasma. The size of the discharge chamber is $20 \times 20 \times 4$ mm$^3$ and a plate with four orifices is placed at the downstream of the chamber. The calculations were performed at the gas pressure of 1 mTorr and the absorbed power of 0.3 W. The simulation results have indicated that the electrostatic field inside the plasma source has a dominant effect on the electron extraction. When the electrons are trapped in the magnetic field passing close to the orifice, such electrons can be extracted from the plasma source to the outside at the orifice edge because of the ${\bf E} \times {\bf B}$ drift. The ${\bf E} \times {\bf B}$ drift also seems to play a significant role in electron transport from the ECR layer to the orifice plate across the magnetic field. [Preview Abstract] |
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