Bulletin of the American Physical Society
56th Annual Meeting of the APS Division of Plasma Physics
Volume 59, Number 15
Monday–Friday, October 27–31, 2014; New Orleans, Louisiana
Session DI2: Waves in Plasmas |
Hide Abstracts |
Chair: Joel Fajans, University of California, Berkeley Room: Bissonet |
Monday, October 27, 2014 3:00PM - 3:30PM |
DI2.00001: Stix Award: The ponderomotive effect beyond the ponderomotive force Invited Speaker: I.Y. Dodin The classical ponderomotive effect (PE) is typically understood as the nonlinear time-average force produced by a rapidly oscillating electromagnetic field on a nonresonant particle. It is instructive to contrast this understanding with the common quantum interpretation of the PE as the ac Stark shift, i.e., phase modulation, or a Kerr effect experienced by the wave function. Then the PE is naturally extended from particles to waves and can be calculated efficiently in general settings [1], including for strongly nonlinear interactions and resonant dynamics. In particular, photons (plasmons, etc.) are hence seen to have polarizability and contribute to the linear dielectric tensor exactly like ``true'' particles such as electrons and ions. The talk will briefly review the underlying variational theory [1-4] and some nonintuitive PE-based techniques of wave and particle manipulation that the theory predicts. It will also be shown that the PE can be understood as \textit{the} cause for the basic properties of both linear and nonlinear waves in plasma, including their dispersion, energy-momentum transport, and various modulational instabilities. Linear collisionless dissipation (both on particles and classical waves, treated on the same footing [2]) also appears merely as a special case of the modulational dynamics.\\[4pt] [1] I. Y. Dodin and N. J. Fisch, Phys. Rev. Lett. {\bf 112}, 205002 (2014).\\[0pt] [2] I. Y. Dodin, Phys. Lett. A {\bf 378}, 1598 (2014).\\[0pt] [3] I. Y. Dodin, Fusion Sci. Tech. {\bf 65}, 54 (2014).\\[0pt] [4] I. Y. Dodin and N. J. Fisch, Phys. Rev. A {\bf 86}, 053834 (2012). [Preview Abstract] |
Monday, October 27, 2014 3:30PM - 4:00PM |
DI2.00002: Laboratory Studies of Nonlinear Interactions Relevant to Alfv\'{e}n Wave Decay Instabilities Invited Speaker: Seth Dorfman Alfv\'{e}n waves, a fundamental mode of magnetized plasmas, are ubiquitous in both laboratory and space plasmas. Many theoretical predictions show that these waves may be unstable to various decay instabilities (e.g. [1,2]). Despite the possible importance of these processes in problems such as the heating of the solar corona and the transfer of energy to small spacial scales in the solar wind, observational evidence is limited. The present work at UCLA's Large Plasma Device (LAPD) represents the first fundamental laboratory study of the non-linear Alfv\'{e}n wave interactions responsible for this class of instabilities; in particular, we present 1) laboratory observation of the Alfv\'{e}n-acoustic mode coupling at the heart of the Parametric Decay Instability [3] and 2) laboratory observations consistent with a decay instability in which a Kinetic Alfv\'{e}n Wave (KAW) decays into two co-propagating KAWs. The first study is conducted by launching counterpropagating Alfv\'{e}n waves from antennas placed at either end of the LAPD. A resonance in the beat wave response produced by the two launched Alfv\'{e}n waves is observed and is identified as a damped ion acoustic mode based on the measured dispersion relation. Results are consistent with theoretical predictions for a three-wave interaction driven by a nonlinear ponderomotive force. In the second experiment, a single high-frequency $\omega/\omega_{ci}\sim0.7$ Alfv\'{e}n wave is launched, resulting in two daughter modes with frequencies and wave numbers that suggest co-propagating KAWs produced by decay of the pump wave. The observed process is parametric in nature, with the frequency of the daughter modes varying as a function of pump amplitude. Efforts are underway to fully characterize the second set of experiments and compare with decay instabilities predicted by theory and simulations. \\[4pt] [1] JV Hollweg, J. Geophys. Res. 99, 23 431 (1994).\\[0pt] [2] YM Voitenko, Journal of plasma physics 60.03 (1998).\\[0pt] [3] S Dorfman and T Carter, Phys. Rev. Lett. 110, 195001 (2013). [Preview Abstract] |
Monday, October 27, 2014 4:00PM - 4:30PM |
DI2.00003: Landau Damping and the Onset of Particle Trapping in Quantum Plasmas Invited Speaker: Jerome Daligault The notion of wave-particle interactions, the couplings between collective and individual particle behaviors, is fundamental to our comprehension of plasma phenomenology. Such is the case when the electrons' thermal energy $k_BT$ is of the order of or smaller than their Fermi energy $E_F\!\!=\!\!\frac{\hbar^2}{2m}(3\pi^2n)^{1/3}$ ($n$ and $m$ are the electron density and mass). The physics of quantum plasmas (e.g., of the warm dense matter regime) is a frontier of high-energy density physics with relevance to many laboratory experiments and to astrophysics. The question arises as to how wave-particle interactions are modified when the quantum nature of the electrons can no longer be ignored. Using analytical theory and simulations, we assess the impact of quantum effects on non-linear wave-particle interactions in quantum plasmas. Two regimes are identified depending on the difference between the time scale of oscillation $t_B(k)\!=\!\sqrt{m/eEk}$ of a trapped electron and the quantum time scale $t_q(k)\!=\!2m/\hbar k^2$ related to recoil effect, where $E$ and $k$ are the wave amplitude and wave vector. In the classical-like regime, $t_B(k)\!<\!t_q(k)$, resonant electrons are trapped in the wave troughs and greatly affect the evolution of the system long before the wave has had time to Landau damp by a large amount according to linear theory. In the quantum regime, $t_B(k)\!>\!t_q(k)$, particle trapping is hampered by the finite recoil imparted to resonant electrons in their interactions with plasmons. \\[4pt] Reference: J. Daligault, Phys. Plasmas 21, 040701 (2014). [Preview Abstract] |
Monday, October 27, 2014 4:30PM - 5:00PM |
DI2.00004: Cyclotron Mode Frequency Shifts in Multi-Species Ion Plasmas Invited Speaker: Matthew Affolter Plasmas exhibit a variety of cyclotron modes, which are used in a broad range of devices to manipulate and diagnose charged particles. Here we discuss cyclotron modes in trapped plasmas with a single sign of charge. Collective effects and electric fields shift these cyclotron mode frequencies away from the ``bare'' cyclotron frequencies $ \Omega_s \equiv qB/m_s c$ for each species $s$. These electric fields may arise from applied trap potentials, from space charge including collective effects, and from image charge in the trap walls. \textbullet We will describe a new laser-thermal cyclotron spectroscopy technique, applied to well-diagnosed pure ion plasmas. This technique enables detailed observations of $\cos (m \theta$) surface cyclotron modes with $m = 0$, 1, and 2 in near rigid-rotor multi-species ion plasmas. For each species $s$, we observe cyclotron mode frequency shifts which are dependent on the plasma density through the $E \times B$ rotation frequency, and on the charge concentration of species $s$, in close agreement with recent theory.\footnote{D.H.E. Dubin, Phys. Plasmas 20, 042120 (2013).} This includes the novel $m = 0$ radial ``breathing'' mode, which generates no external electric field except at the plasma ends. These cyclotron frequencies can be used to determine the plasma $E \times B$ rotation frequency and the species charge concentrations, in close agreement with our laser diagnostics. Here, this plasma characterization permits a determination of the ``bare'' cyclotron frequencies to an accuracy of 2 parts in $10^4$. \textbullet These new results\footnote{M. Affolter et al., Phys. Lett. A 378, 2406 (2014).} give a physical basis for the ``space charge'' and ``amplitude'' calibration equations of cyclotron mass spectroscopy, widely used in molecular chemistry and biology. Also, at high temperatures there is preliminary evidence that radially-standing electrostatic Bernstein waves couple to the surface cyclotron modes, producing new resonant frequencies. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700