Bulletin of the American Physical Society
54th Annual Meeting of the APS Division of Plasma Physics
Volume 57, Number 12
Monday–Friday, October 29–November 2 2012; Providence, Rhode Island
Session JO6: Waves and Nonlinear Phenomena |
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Chair: Martin Goldman, University of Colorado Boulder Room: 555AB |
Tuesday, October 30, 2012 2:00PM - 2:12PM |
JO6.00001: The various manifestations of collisionless dissipation in wave propagation Didier Benisti, Olivier Morice, Laurent Gremillet In this talk, we provide a theoretical description of collisionless dissipation [1], for an electrostatic wave propagating in a three-dimensional plasma, from the linear regime when it simply amounts to Landau damping, to the strongly nonlinear one when it significantly affects the wave group velocity, both, along and across the local wave number. We, moreover, discuss the impact of dissipation on the longitudinal and transverse extent of the wave packet, which allows us to reinterpret previously published kinetic simulations [2-4]. Finally, we illustrate our results on a two-dimensional simulation of stimulated Raman scattering.\\[4pt] [1] D. B\'enisti, O. Morice, and L. Gremillet, Phys. Plasmas 16, 063110 (2012). \newline [2] J. E. Fahlen, B. J. Winjum, T. Grismayer, and W. B. Mori, Phys. Rev. Lett. 102, 245002 (2009). \newline [3] J. W. Banks, R. L. Berger, S. Brunner, B. I. Cohen, and J. A. F. Hittinger, Phys. Plasmas 18, 052102 (2011). \newline[4] J. E. Fahlen, B. J. Winjum, T. Grismayer, and W. B. Mori, Phys. Rev. E 83, 045501(R) (2011). [Preview Abstract] |
Tuesday, October 30, 2012 2:12PM - 2:24PM |
JO6.00002: Thomson-Scattering Measurements of Ion-Acoustic Wave Amplitudes Driven by the Two-Plasmon-Decay Instability R.K. Follett, D.T. Michel, J.F. Myatt, S.X. Hu, B. Yaakobi, D.H. Froula Thomson scattering was used to measure enhanced ion-acoustic waves (IAW's) driven by the two-plasmon-decay (TPD) instability. The IAW amplitude scales with the 3/2\textit{$\omega $} emission (a TPD signature). Up to 20 beams with 860-\textit{$\mu $}m-diam laser spots generated by 2-ns-long pulses of 3\textit{$\omega $} (0.351-\textit{$\mu $}m) light with overlapped intensities up to 4 $\times $ 10$^{14}$ W/cm$^{2}$ were used to produce $\sim $300-\textit{$\mu $}m density-scale lengths. The IAW amplitudes were measured using 4\textit{$\omega $} Thomson scattering near 3\textit{$\omega $} quarter-critical densities. Time-resolved 3/2\textit{$\omega $} spectroscopy was used to compare the amplitude of 3/2\textit{$\omega $} emission to the IAW amplitude. \textit{QZAK}\footnote{ K. Y. Sanbonmatsu\textit{ et al.}, Phys. Rev. Lett. \textbf{82}, 932 (1999).}$^{,}$\footnote{ K. Y. Sanbonmatsu\textit{ et al.}, Phys. Plasmas \textbf{7}, 2824 (2000).} modeling shows a similar onset threshold and wave amplitude as the experiments. The model suggests that the source of the IAW growth is from the beating of electron-plasma waves, which drive density perturbations through the ponderomotive force. This conclusion is supported by the experimental geometry. This process is shown to be a saturation mechanism for TPD from simulations.\footnote{ R. Yan\textit{ et al.}, Phys. Rev. Lett. \textbf{103}, 175002 (2009).} This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC52-08NA28302. [Preview Abstract] |
Tuesday, October 30, 2012 2:24PM - 2:36PM |
JO6.00003: Residual coherent structures after 1-D electron wave breaking in a cold plasma Prabal Singh Verma, Sudip Sengupta, Predhiman Kaw 1-D particle in cell simulation of large amplitude plasma oscillations is carried out to explore the physics beyond wave breaking in a cold homogeneous unmagnetized plasma. It is shown that after wave breaking all energy of the plasma oscillation does not end up as random kinetic energy of particles but some fraction which is decided by Coffey's wave breaking limit in warm plasma, always remains with two oppositely propagating coherent BGK like modes with supporting trapped particle distributions. The randomized energy distribution of untrapped particles is found to be characteristically non-Maxwellian with a preponderance of energetic particles. Furthermore, we study long time evolution of large amplitude traveling waves in the beyond wave breaking regime and find that in this case also some fraction of initial energy remains in the form of a single BGK type wave. We believe that these results may have relevance in particle acceleration experiments. [Preview Abstract] |
Tuesday, October 30, 2012 2:36PM - 2:48PM |
JO6.00004: Drift wave and its stability analysis in ECR produced plasma of MaPLE device at Saha Institute of Nuclear Physics Subir Biswas, Rabindranath Pal, Nikhil Chakrabarti Cross-field transport due to the low frequency drift modes destroys the plasma confinement [W. Horton, Rev. Mod. Phys. 71, 735(1999)] and is one of the main barriers to achieve thermonuclear power in nuclear fusion. In the present experiment with the MaPLE (Magnetized Plasma Linear Experimental) device [R. Pal, S. Biswas et. al., Rev. Sci. Instrum. 81, 73507(2011)] where plasma is produced by Electron Cyclotron Resonance (ECR) method using 2.45 GHz microwave, modulation of density at 300 Hz excites the drift wave in its second harmonic. Measurement of poloidal propagation and density gradient scale length confirms it to be a drift wave with mode number $m=2$. Stability analysis shows that parallel electron flow excites this mode. Growth rate also depends on magnetic field value. At a critical magnetic field value, the growth rate is maximum. Parametric couple of this mode with 300 Hz mode also excites 900 Hz mode. Details results will be presented. [Preview Abstract] |
Tuesday, October 30, 2012 2:48PM - 3:00PM |
JO6.00005: High energy electron behaviors in Langmuir solitons Y. Nishimura, Y.H. Chen, C.Z. Cheng Effects of non-thermal high-energy electrons on Langmuir wave-particle interaction is studied by an initial value approach. A Vlasov-Poisson simulation is employed based on the splitting scheme.\footnote{C.Z.Cheng and G.Knorr, J. Comput. Phys. {\bf 22}, 330 (1976).} The interaction between high frequency Langmuir waves and low frequency ion acoustic waves gives rise to Langmuir soliton.\footnote{V.E.Zhaharov, Sov. Phys. JETP {\bf 35}, 908 (1972).} Formation of high energy electrons by the Langmuir solitons is investigated. [Preview Abstract] |
Tuesday, October 30, 2012 3:00PM - 3:12PM |
JO6.00006: A design for a two vortex merger KH experiment on OMEGA-EP G. Malamud, A. Shimoni, C.A. Di-Stefano, Y. Elbaz, C.C. Kuranz, P.A. Keiter, D. Shvarts, R.P. Drake The Kelvin-Helmholtz (KH) is of high importance in inertial confinement fusion (ICF) and super-nova. The two vortex merger KH evolution had not yet been studied experimentally, and is known only due to theoretical considerations [1]. We propose an experiment on Omega EP, capable of driving targets for several times larger than previous high-energy lasers [2]. The shear velocity upon the perturbed interface will be introduced by a steady shock wave in a target platform recently presented [3] and tested. The use of a steady shock, in oppose to past used blast wave system [2] in single mode experiments, allows a constant shear. The details of the experimental design are meant to provide a direct measurement of the perturbation evolution and vortices merging, validating KH models such as the statistical mechanics model~[1].\\[4pt] [1] Rikanati et al. Phys. Fluids {\bf 15},(2003); [2] Harding et al. PRL {\bf103}(4), (2009); [3] Malamud et al., HEDLA 2012 proceedings. [Preview Abstract] |
Tuesday, October 30, 2012 3:12PM - 3:24PM |
JO6.00007: Simulation of the O-X-B conversion process in dense magnetized plasmas Mohammad Ali Asgarian, John Verboncoeur, Akbar Parvazian Electron Bernstein waves (EBWs) are special electrostatic cyclotron waves which propagate with a short wavelength in hot plasma. EBWs are useful for core plasma heating, current drive and temperature diagnostics in high density plasma devices like stellarators and tokamaks. The resonance of EBWs is close to the cyclotron harmonics, and they do not have a density cut-off. The ordinary-extraordinary-Bernstein(O-X-B) conversion is one of the processes for generating EBWs. The generated EBW propagates in the region with density higher than ordinary wave cut-off and is strongly absorbed at the electron cyclotron harmonics. As such, EBWs may provide local electron heating and current drive. This double conversion process has been simulated using the XOOPIC code. XOOPIC is a 2D PIC code with 3D electrostatic and electromagnetic field solvers for slab and cylindrical geometries. The O-X-B simulation has been done in a slab plasma, using the electromagnetic field solver and a surface impedance wave source to generate the O-wave. The maximum energy transformation in O-X conversion will be ensured with the optimized refractive index, parallel to toroidal magnetic field. Moreover, the dependence of the conversion efficiency on the density gradient scale length will be considered. [Preview Abstract] |
Tuesday, October 30, 2012 3:24PM - 3:36PM |
JO6.00008: Electron rings around magnetized electrodes Reiner Stenzel, J. Manuel Urrutia When a permanent dipole magnet is biased strongly negative (-800~V) in the presence of sufficient neutrals ($>5$~mTorr) a ring of light, i.e. hot electrons, is formed in the equatorial plane of the dipole. The phenomenon has been explained by the physics of a magnetron discharge: Energetic ions impact on the magnet, release secondary electrons, which are confined by the magnetic field, $\mathbf{E\times B}$ drift, efficiently ionize and gradually diffuse toward the anode to close the discharge current. Time-resolved measurements have shown that a weak electron ring forms on a fast time scale compared to ion transit or electron diffusion times. It oscillates coherently near the ion plasma frequency ($f\simeq1~$MHz) and exhibits the characteristics of an ion-rich sheath instability. In contrast, under steady-state conditions the instability becomes broadband and turbulent wave packets propagate in the $\mathbf{E\times B}$ direction. While the focus is on the basic physics sputtering applications will also be addressed. The cold-cathode discharge can be operated in reactive gases. [Preview Abstract] |
Tuesday, October 30, 2012 3:36PM - 3:48PM |
JO6.00009: ABSTRACT WITHDRAWN |
Tuesday, October 30, 2012 3:48PM - 4:00PM |
JO6.00010: Linear Electrostatic Waves in Unmagnetized Arbitrarily Degenerate Quantum Plasmas Shane Rightley, Dmitri Uzdensky Plasmas in which the inter-particle spacing approaches the thermal de Broglie wavelength are subject to quantum statistical effects due to Pauli exclusion, and many familiar plasma phenomena are modified on such length scales because of the Heisenberg uncertainty principle. The question of how to model these quantum plasmas is a naturally interesting one, as it pushes the envelope of our knowledge of plasma physics and applies the well-established principles of quantum mechanics in a novel context. Such models are important for microelectronic systems, dense laser-produced plasmas, and some extreme astrophysical environments. For completely degenerate plasmas, both kinetic and fluid theories have already been developed. In this presentation, unmagnetized Fermi-Dirac equilibrium plasmas with finite temperature and arbitrary degree of degeneracy are considered. Linear dispersion relations for electrostatic waves and oscillations, including Landau damping, are derived and analyzed. The analysis is carried out using a self-consistent mean-field quantum kinetic model (the Wigner-Poisson system). Growth of waves due to kinetic instabilities, such as the Buneman and bump-on-tail instabilities, is also considered. [Preview Abstract] |
Tuesday, October 30, 2012 4:00PM - 4:12PM |
JO6.00011: Three-Dimensional Mode Conversion Associated with Kinetic Alfv\'en Waves Yu Lin, Jay Johnson, Xueyi Wang We report the first three-dimensional (3-D) ion particle simulation of mode conversion from a fast mode compressional wave to kinetic Alfv\'en waves (KAWs) that occurs when a compressional mode propagates across a plasma boundary into a region of increasing Alfv\'en velocity. The magnetic field is oriented in the $\hat{z}$ direction perpendicular to the gradients in the background density and magnetic field ($\hat{x}$). Following a stage dominated by linear physics in which KAWs with large wave numbers $k_x \rho_i\sim 1$ (with $\rho_i$ being the ion Larmor radius) are generated near the Alfv\'en resonance surface, the growth of KAW modes with $k_y \rho_i \sim 1$ is observed in the nonlinear stage when the amplitude of KAWs generated by linear mode conversion becomes large enough to drive a nonlinear parametric decay process, accompanied by a simultaneous excitation of zonal flow modes with similar large $k_y$. The simulation provides a comprehensive picture of mode conversion and the fundamental importance of the 3-D nonlinear physics to transfer energy to large perpendicular $k_y$ modes, which can provide large transport across plasma boundaries in space and laboratory plasmas. [Preview Abstract] |
Tuesday, October 30, 2012 4:12PM - 4:24PM |
JO6.00012: Nonlinear Frequency Chirping of beta-induced Alfven Eigenmode Huasen Zhang, Zhihong Lin, Ihor Holod Energetic particles produced by fusion reactions and auxiliary heating can excite various Alfven eigenmodes in fusion experiments such as ITER. Associated nonlinear wave-particle interactions can generate significantly enhanced levels of energetic particle transport that would degrade overall plasma confinement and damage fusion devices. Increased energetic particle transport by Alfven eigenmodes has been correlated with a fast frequency oscillation (chirping) with a submillisecond period that has been observed in many experiments. Here we report the first dynamic observation of fast and repetitive frequency chirping by massively parallel, first-principles kinetic simulations without sources and sinks in a realistic toroidal geometry. The chirping dynamics provides a conceptual framework for understanding the nonlinear wave-particle interaction underlying transport processes in collisionless plasmas. The interaction of energetic particles such as cosmic rays with Alfven turbulence is also an important issue in space and astrophysical plasmas. [Preview Abstract] |
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