Bulletin of the American Physical Society
57th Annual Meeting of the APS Division of Plasma Physics
Volume 60, Number 19
Monday–Friday, November 16–20, 2015; Savannah, Georgia
Session BO6: Waves, Oscillations, and Instabilities |
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Chair: Ilya Dodin, Princeton University Room: 201/202 |
Monday, November 16, 2015 9:30AM - 9:42AM |
BO6.00001: Plasma-based laser-pulse amplification via strongly coupled Brillouin scattering Marco Chiaramello, Fran\c{c}ois Amiranoff, Stefan Weber, Livia Lancia, Michael Grech, Tommaso Vinci, Jean-Raphael Marqu\'es, Julien Fuchs, Caterina Riconda The use of plasma as an amplification medium for laser pulses is currently discussed because it can overcome current solid-state technology limitations in terms of maximum achievable intensity. Via parametric scattering off a plasma oscillation the energy from a long pump pulse can be transferred into a short seed pulse. Brillouin scattering has the potential to become a robust amplification process. In this presentation we will show theoretical and numerical (PIC) studies aimed at better understanding the role on the amplification mechanism of each plasma parameter, such as the interaction length, the shape of the density profile, the duration of the long pump signal, the relative delay between the seed and pump signals, the role of the chirp of the long pump laser pulse. Comparisons with recent experiments will be performed. [Preview Abstract] |
Monday, November 16, 2015 9:42AM - 9:54AM |
BO6.00002: Analytical model of Weibel-mediated electron-ion collisionless shock formation C. Ruyer, L. Gremillet, G. Bonnaud, C. Riconda We address the formation of ion-electron collisionless shocks in the non-relativistic regime. The shocks formed by the non-linear evolution of the Weibel-type instabilities, arise during plasma collisions in numerous high-energy astrophysical scenario such as pulsar wind nebulae or supernova remnants [N. Kato et al, Astrophys. J. Lett. 2008, T. Piran, Rev. Mod. Phys. 2004]. For the first time, a predictive fully analytical model of the ion Weibel saturation based on the coalescence of filaments is presented and allows to describe the evolution of the plasma and its characteristics until shock-formation [C. Ruyer et al, Phys. Plasmas 2015]. It is compared successfully to Weibel-mediated shock simulations until quasi-isotropisation of the ions, and close to shock formation. Our model compares well with two different recent experiments [W. Fox et al, Phys. Rev. Lett. 2013, C. M. Huntington et al, Nat. Phys. 2015] and allows us to pinpoint the role of the electron screening on the ion-Weibel dynamics. Our theoretical results, supported by both experiments and simulations, proves for the first time the effect of an artificially low ion to electron mass ratio on the formation of collisionless shocks commonly used in many numerical works. [Preview Abstract] |
Monday, November 16, 2015 9:54AM - 10:06AM |
BO6.00003: Kinetic analysis of electromagnetic wave-plasma interaction at oblique and perpendicular incidence Shabbir A. Khan, Atsushi Fukuyama The electromagnetic wave-plasma interaction near the plasma frequency in an inhomogeneous unmagnetized plasma is studied using an integral form of the dielectric tensor which has been derived by following unperturbed particle orbits. With this kinetic dielectric tensor, integro-differential full wave analysis was carried out numerically. For the case of oblique incidence to the density gradient, the wave excites an electrostatic Langmuir wave which is absorbed by Landau damping. The incident angle dependence of the absorption rate is almost the same as that of collisional fluid model, but the power deposition profiles for finite temperature is quite different from the collisional model. In the case of perpendicular incidence, convensional analyses predict no absorption since there is no longitudinal wave electric field to excite the electrostatic wave. Our new analysis based on the integral formulation, however, indicates the absorption in this case due to strong gradient of wave electric field amplitude. This is a result of stochastic heating caused by the random phase of electron oscillating velocity when the electrons goes through the boundary layer. The integral formulation of dielectric tensor enables us self-consistent analysis of wave structure and kinetic absorption. [Preview Abstract] |
Monday, November 16, 2015 10:06AM - 10:18AM |
BO6.00004: Ladder Climbing and Autoresonant Acceleration of Plasma Waves Ido Barth, Ilya Dodin, Nathaniel Fisch When the background density in a bounded plasma is modulated in time, discrete modes become coupled. Interestingly, for appropriately chosen modulations, the average plasmon energy might be made to grow in a ladder-like manner, achieving up-conversion or down-conversion of the plasmon energy. This reversible process is identified as a classical analog of the effect known as quantum ladder climbing, so that the efficiency and the rate of this process can be written immediately by analogy to a quantum particle in a box. In the limit of densely spaced spectrum, ladder climbing transforms into continuous autoresonance; plasmons may then be manipulated by chirped background modulations much like electrons are autoresonantly manipulated by chirped fields. By formulating the wave dynamics within a universal Lagrangian framework, similar ladder climbing and autoresonance effects are predicted to be achievable with general linear waves in both plasma and other media. [Preview Abstract] |
Monday, November 16, 2015 10:18AM - 10:30AM |
BO6.00005: Electrostatic Instabilities in Unmagnetized Quantum Plasmas of Arbitrary Composition Shane Rightley, Dmitri Uzdensky We present a fully kinetic numerical solution of the linear dispersion relation for electrostatic waves in quantum plasmas in arbitrarily-degenerate Fermi-Dirac equilibrium. We utilize the solution to study the effects of degeneracy and quantum recoil on instabilities in quantum plasmas. We report a full linear analysis of quantum kinetic effects in one-dimensional streaming instabilities in plasmas with multiple populations of particles. This presentation discusses specifically current-driven instabilities, such as the Buneman and ion-acoustic instabilities. These are important as sources of anomalous resistivity. Cases considered include arbitrarily degenerate electrons streaming through cold ions, and beams of electrons or positrons streaming through degenerate electrons. It is found that in quantum plasmas the current-driven instabilities are diminished. [Preview Abstract] |
Monday, November 16, 2015 10:30AM - 10:42AM |
BO6.00006: Raman amplifiers for powerful femtosecond pulses James Sadler, Luke Ceurvorst, Naren Ratan, Muhammad Kasim, Raoul Trines, Peter Norreys, Dan Haberberger, Dustin Froula, Jake Bromage, Andrew Davies, Jonathan Zuegel, Max Tabak An ongoing experiment at LLE Rochester aims to generate the first Petawatt class laser pulse using Raman beam energy transfer in an underdense plasma. I will demonstrate PIC simulations optimising the setup and show how shaping the seed pulse gives a factor of two efficiency increase. At these experimental parameters, it was found that the optimal seed pulse is much shorter than that predicted by the self-similar Pi-pulse theory. Pending experimental verification of the 10\%+ efficiency, I will show how currently active lasers could be configured in a ``Kirkwood'' two stage Brillouin-Raman amplifier to reach frontier level powers. [Preview Abstract] |
Monday, November 16, 2015 10:42AM - 10:54AM |
BO6.00007: Interactions of electrons with multiple lower hybrid waves Guozhang Jia, Nong Xiang, Yueheng Huang, Xueyi Wang, Yu Lin The interactions between electrons and multiple electrostatic plane waves with different phase velocities. It is well known that as the resonance overlap occurs, the motions of trapped electrons become stochastic which results in electron heating. However, in these studies the evolution of the wave field is not taken into account. In this work, the interactions between electrons and multiple lower hybrid waves are investigated via particle-in-cell (PIC) simulations based on GEFI framework [Yu Lin, Xueyi Wang, Zhihong Lin and Liu Chen, Plasma Phys. Control. Fusion 47, 2005, 657]. It is shown that the orbits of trapped electrons in each wave field are altered in the presence of other lower hybrid waves. As a result, the damping of this wave is significantly enhanced. As the resonances overlap, a corresponding plateau of the electron distribution function can be formed. The results are helpful to understand the interactions of lower hybrid waves and plasmas during lower hybrid current drive in Tokamaks. [Preview Abstract] |
Monday, November 16, 2015 10:54AM - 11:06AM |
BO6.00008: Transient Growth in a Magnetized Vlasov Plasma Valeria Ratushnaya, Ravi Samtaney Collisionless plasmas, such as those encountered in tokamaks, exhibit a rich variety of instabilities. The physical origin, triggering mechanisms and fundamental understanding of many tokamak instabilities, however, is still an open problem. Aiming to gain a better insight into this question, we investigate the stability properties of a collisionless Vlasov plasma for the case of: (a) stationary homogeneous magnetic field, and (b) weakly non-stationary and non-homogeneous magnetic field. We narrow the scope of our investigation to the case of a Maxwellian plasma and examine its evolution with an electrostatic approximation. We show that the linearized Vlasov operator is non-normal, which leads to an algebraic growth of perturbations in a magnetized plasma followed by exponential decay, i.e., classical Landau damping behaviour. This is a so-called transient growth phenomenon, developed in the framework of non-modal stability theory in the context of hydrodynamics. In a homogeneous magnetic field the typical time scales of the transient growth are of the order of several plasma periods. The first-order distribution function and the corresponding electric field are calculated and the dependence on the initial conditions is studied. [Preview Abstract] |
Monday, November 16, 2015 11:06AM - 11:18AM |
BO6.00009: Spin-electron acoustic waves: Linear and nonlinear regimes, and applications Pavel Andreev Considering the spin-up and spin-down electrons as two different fluids we find corresponding hydrodynamic and kinetic equations from the Pauli equation. We find different pressure the spin-up and spin-down electrons due to different concentrations of electrons in the magnetized electron gas. This difference leads to existence of new branches of linear longitudinal waves propagating with small damping. These waves are called the spin-electron acoustic waves (SEAWs) due to linear dispersion dependence at small wave vectors. We obtain two waves at oblique propagation and one wave at propagation parallel or perpendicular to the external magnetic field. Dispersion dependences of these waves are calculated. Contribution of the Coulomb exchange interaction is included in the model and spectrums. Area of existence of nonlinear SEAWs appearing as a spin-electron acoustic soliton is found for the regime of wave propagation parallel to the external magnetic field. It is obtained that the SEAWs lead to formation of the Cooper pairs. This application of our results to the superconductivity phenomenon reveals in a model of the high-temperature superconductivity with the transition temperatures up to 300 K. [Preview Abstract] |
Monday, November 16, 2015 11:18AM - 11:30AM |
BO6.00010: Kinetic instabilities in a mirror-confined ECR discharge plasma Dmitry Mansfeld, Mikhail Viktorov, Alexander Vodopyanov, Sergey Golubev Kinetic instabilities of nonequilibrium plasma heated by powerful radiation of gyrotron in electron cyclotron resonance conditions and confined in a mirror magnetic trap are reported. Instabilities are manifested as the generation of short pulses of electromagnetic radiation accompanied by precipitation of hot electrons from magnetic trap. Measuring electromagnetic field with high temporal resolution allowed to observe various dynamic spectra of electromagnetic radiation related to at least five types of kinetic instabilities. The opportunity to recreate different conditions for excitation and amplification of waves in plasma in a single ECR discharge pulse has been demonstrated. This report may be of interest in the context of a laboratory modeling of nonstationary wave-particle interaction processes in nonequilibrium space plasma since the observed phenomena have much in common with similar processes occurring in the magnetosphere of the Earth, planets, and in solar coronal loops. [Preview Abstract] |
Monday, November 16, 2015 11:30AM - 11:42AM |
BO6.00011: Feedback effect on flute dynamics in a mirror machine Ilan Be'ery, Omri Seemann Active feedback techniques may stabilize the flute instability in mirror traps and make them viable candidates for fusion machines. A fast feedback with optical sensors and electrical actuators was implemented in a table-top mirror machine and used to study several aspects of feedback stabilization. For a cold, dense plasma the feedback reduces dramatically the flute amplitude of the first two mode. For higher temperature plasma, a significant increase of plasma density due to feedback stabilization is also demonstrated. The effect of changing feedback gain and phase has some interesting feature such as asymmetry with respect to positive and negative phase shifts and non-monotonic dependence of flute amplitude on feedback gain. These effects are explained using simplified analytic model of the flute and feedback. [Preview Abstract] |
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