skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Wave induced barrier transparency and melting of quasi-crystalline structures in two dimensional plasma turbulence

Abstract

The conservation of energy and enstrophy in two dimensional inviscid hydrodynamics leads to dual cascade behavior. The energy cascades towards long scales and the enstrophy is transferred to shorter scales. The interplay of these dynamical processes leads to self organization and formation of coherent patterns in the two dimensional hydrodynamic turbulence. It was shown by Kukharkin et al. [Phys. Rev. Lett. 25, 2486 (1995)] that this process of self organization occurs in an even more interesting fashion in the Hasegawa Mima (HM) equation [Phys. Fluids 21, 21 (1978)] This equation is a generalization of the two dimensional Navier Stokes hydrodynamics model in which there is a characteristic natural scale in the system (e.g., Larmor radius in the drift wave context). Kukharkin et al. observed that this scale acts as a barrier in the energy cascade, such that the cascade rate at the longer wavelength side of the barrier is smaller. This work has also shown that the accumulation of energy around the intrinsic scale leads to the formation of quasi-crystalline patterns. In the present paper it has been demonstrated that the presence of wave excitations leads to an increased cascade towards longer scales past the natural length scale barrier. Itmore » has also been demonstrated that wave excitations lead to the melting of quasi-crystalline structures. Another intriguing but interesting observation is that even though the faster cascade is induced by waves arising through an anisotropic inhomogeneity in one of the plasma parameters, the spectrum of the fluctuations continues to remain predominantly isotropic. A physical understanding of the observations is provided by illustrating a close connection between the Kelvin-Helmholtz destabilization of shear flows and the phenomenon of inverse cascade in 2D fluid flows.« less

Authors:
 [1]
  1. Institute for Plasma Research, Bhat, Gandhinagar-382428 (India)
Publication Date:
OSTI Identifier:
20974928
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 14; Journal Issue: 4; Other Information: DOI: 10.1063/1.2718927; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ANISOTROPY; EXCITATION; FLUCTUATIONS; FLUID FLOW; LARMOR RADIUS; MAGNETOHYDRODYNAMICS; NAVIER-STOKES EQUATIONS; NONLINEAR PROBLEMS; PLASMA; PLASMA DRIFT; PLASMA INSTABILITY; SHEAR; TURBULENCE; TWO-DIMENSIONAL CALCULATIONS; VORTICES; WASTE HEAT UTILIZATION; WAVE PROPAGATION

Citation Formats

Das, Amita. Wave induced barrier transparency and melting of quasi-crystalline structures in two dimensional plasma turbulence. United States: N. p., 2007. Web. doi:10.1063/1.2718927.
Das, Amita. Wave induced barrier transparency and melting of quasi-crystalline structures in two dimensional plasma turbulence. United States. doi:10.1063/1.2718927.
Das, Amita. Sun . "Wave induced barrier transparency and melting of quasi-crystalline structures in two dimensional plasma turbulence". United States. doi:10.1063/1.2718927.
@article{osti_20974928,
title = {Wave induced barrier transparency and melting of quasi-crystalline structures in two dimensional plasma turbulence},
author = {Das, Amita},
abstractNote = {The conservation of energy and enstrophy in two dimensional inviscid hydrodynamics leads to dual cascade behavior. The energy cascades towards long scales and the enstrophy is transferred to shorter scales. The interplay of these dynamical processes leads to self organization and formation of coherent patterns in the two dimensional hydrodynamic turbulence. It was shown by Kukharkin et al. [Phys. Rev. Lett. 25, 2486 (1995)] that this process of self organization occurs in an even more interesting fashion in the Hasegawa Mima (HM) equation [Phys. Fluids 21, 21 (1978)] This equation is a generalization of the two dimensional Navier Stokes hydrodynamics model in which there is a characteristic natural scale in the system (e.g., Larmor radius in the drift wave context). Kukharkin et al. observed that this scale acts as a barrier in the energy cascade, such that the cascade rate at the longer wavelength side of the barrier is smaller. This work has also shown that the accumulation of energy around the intrinsic scale leads to the formation of quasi-crystalline patterns. In the present paper it has been demonstrated that the presence of wave excitations leads to an increased cascade towards longer scales past the natural length scale barrier. It has also been demonstrated that wave excitations lead to the melting of quasi-crystalline structures. Another intriguing but interesting observation is that even though the faster cascade is induced by waves arising through an anisotropic inhomogeneity in one of the plasma parameters, the spectrum of the fluctuations continues to remain predominantly isotropic. A physical understanding of the observations is provided by illustrating a close connection between the Kelvin-Helmholtz destabilization of shear flows and the phenomenon of inverse cascade in 2D fluid flows.},
doi = {10.1063/1.2718927},
journal = {Physics of Plasmas},
number = 4,
volume = 14,
place = {United States},
year = {Sun Apr 15 00:00:00 EDT 2007},
month = {Sun Apr 15 00:00:00 EDT 2007}
}
  • We study the evolution of fronts in a nonlinear wave equation with global feedback. This equation generalizes the Klein-Gordon and sine-Gordon equations. Extending previous work, we describe the derivation of an equation governing the front motion, which is strongly nonlinear, and, for the two-dimensional case, generalizes the damped Born-Infeld equation. We study the motion of one- and two-dimensional fronts, finding a much richer dynamics than for the classical case (with no global feedback), leading in most cases to a localized solution; i.e., the stabilization of one phase inside the other. The nature of the localized solution depends on the strengthmore » of the global feedback as well as on other parameters of the model.« less
  • Within the framework of a quasi-optical approach, we develop 2D and 3D self-consistent theory of relativistic surface-wave oscillators. Presenting the radiation field as a sum of two counter-propagating wavebeams coupled on a shallow corrugated surface, we describe formation of an evanescent slow wave. Dispersion characteristics of the evanescent wave following from this method are in good compliance with those found from the direct cst simulations. Considering excitation of the slow wave by a sheet electron beam, we simulate linear and nonlinear stages of interaction, which allows us to determine oscillation threshold conditions, electron efficiency, and output coupling. The transition frommore » the model of surface-wave oscillator operating in the π-mode regime to the canonical model of relativistic backward wave oscillator is considered. We also described a modified scheme of planar relativistic surface-wave oscillators exploiting two-dimensional periodic gratings. Additional transverse propagating waves emerging on these gratings synchronize the emission from a wide sheet rectilinear electron beam allowing realization of a Cherenkov millimeter-wave oscillators with subgigawatt output power level.« less
  • Low-frequency, flute-type electrostatic fluctuations propagating across a strong, homogeneous magnetic field are studied experimentally. The fluctuations are generated by the Kelvin--Helmholtz instability. The presence of relatively long-lived vortexlike structures in a background of wide-band turbulent fluctuations is demonstrated by a conditional sampling technique. Depending on plasma parameters, the dominant structures can appear as monopole or multipole vortices, dipole vortices in particular. The importance of large structures for the turbulent plasma diffusion is discussed. A statistical analysis of the randomly varying plasma flux is presented.
  • Theoretical estimates are presented for the transparency coefficient of the wave barrier to electron plasma waves in a magnetized plasma. Experimental plots of the spatial damping of the wave and of the transparency coefficient of the barrier against the density of the surrounding plasma and the frequency of excited oscillations are obtained for various barrier widths. The experimental plots are compared with the theory. Satisfactory agreement is demonstrated.
  • Nucleating and collapsing wave packets relevant to electromagnetic strong plasma turbulence are studied theoretically in two dimensions. Model collapsing Langmuir and transverse potentials are constructed as superpositions of approximate eigenstates of a spherically symmetric density well. Electrostatic and electromagnetic potentials containing only components with azimuthal quantum numbers m=0, 1, 2 are found to give a good representation of the electric fields of nucleating collapsing wave packets in turbulence simulations. The length scales of these trapped states are related to the electron thermal speed v{sub e} and the length scale of the density well. It is shown analytically that the electromagneticmore » trapped states change with v{sub e} and that for v{sub e} < or approx. 0.17c they are delocalized, in accord with recent simulations. In this case, the Langmuir mode collapses independently, as in electrostatic plasma turbulence. For v{sub e} > or approx. 0.17c, the Langmuir and transverse modes remain coupled during collapse, with autocorrelation lengths in a constant ratio. An investigation of energy transfer to packets localized in density wells shows that the strongest power transfer to the nucleating state occurs for Langmuir waves. Energy transitions between different trapped and free states for collapsing wave packets are studied, and the transition rate from trapped Langmuir to free plane electromagnetic waves is calculated and related to the emission of electromagnetic waves at the plasma frequency.« less