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Bratanov V.,Max Planck Institute for Plasma Physics (Garching) | Jenko F.,Max Planck Institute for Plasma Physics (Garching) | Jenko F.,Max Planck Princeton Center for Plasma Physics | Hatch D.R.,Max Planck Institute for Plasma Physics (Garching) | And 2 more authors.
Physical Review Letters | Year: 2013

Turbulence is generally associated with universal power-law spectra in scale ranges without significant drive or damping. Although many examples of turbulent systems do not exhibit such an inertial range, power-law spectra may still be observed. As a simple model for such situations, a modified version of the Kuramoto-Sivashinsky equation is studied. By means of semianalytical and numerical studies, one finds power laws with nonuniversal exponents in the spectral range for which the ratio of nonlinear and linear time scales is (roughly) scale independent. © 2013 American Physical Society.

Hatch D.R.,University of Texas at Austin | Hatch D.R.,Max Planck Institute for Plasma Physics (Garching) | Jenko F.,Max Planck Institute for Plasma Physics (Garching) | Jenko F.,Max Planck Princeton Center for Plasma Physics | And 2 more authors.
Physical Review Letters | Year: 2013

A gyrokinetic model of ion temperature gradient driven turbulence in magnetized plasmas is used to study the injection, nonlinear redistribution, and collisional dissipation of free energy in the saturated turbulent state over a broad range of driving gradients and collision frequencies. The dimensionless parameter LT/LC, where LT is the ion temperature gradient scale length and LC is the collisional mean free path, is shown to parametrize a transition between a saturation regime dominated by nonlinear transfer of free energy to small perpendicular (to the magnetic field) scales and a regime dominated by dissipation at large scales in all phase space dimensions. © 2013 American Physical Society.

Pueschel M.J.,University of Wisconsin - Madison | Told D.,Max Planck Institute for Plasma Physics (Garching) | Terry P.W.,University of Wisconsin - Madison | Jenko F.,Max Planck Institute for Plasma Physics (Garching) | And 4 more authors.
Astrophysical Journal, Supplement Series | Year: 2014

A current sheet susceptible to the tearing instability is used to drive reconnection turbulence in the presence of a strong guide field. Through nonlinear gyrokinetic simulations, the dependencies of central quantities such as the heating rate on parameters like collisionality or plasma β are studied, revealing that linear physics tends to predict only some aspects of the quasi-saturated state, with the nonlinear cascade responsible for additional features. For the solar corona, it is demonstrated that the kinetic heating associated with this type of turbulence agrees quantitatively with observational volumetric heating rates. In the context of short particle acceleration events, the self-consistent emergence of plasmoids or flux ropes in the turbulent bath is found to be important: ubiquitously occurring merger events of these objects cause strong bursts in the heating rate, the timescale of which is consistent with nanoflare observations. Furthermore, anisotropy of the temperature fluctuations is seen to emerge, hinting at a new means of generating coronal ion temperature anisotropy in the absence of cyclotron resonances. © 2014. The American Astronomical Society. All rights reserved..

Soto-Chavez A.R.,Princeton University | Wang G.,Princeton University | Wang G.,Max Planck Princeton Center for Plasma Physics | Bhattacharjee A.,Princeton University | And 3 more authors.
Geophysical Research Letters | Year: 2014

Motivated by the fact that geomagnetic field inhomogeneity is weak close to the chorus generation region and the observational evidence that falling-tone chorus tend to have large oblique angles of propagation, we propose that falling-tone chorus start as a marginally unstable mode. The marginally unstable mode requires the presence of a relatively large damping, which has its origins in the Landau damping of oblique waves in this collisionless environment. A marginally unstable mode produces phase-space structures that release energy and produce wave chirping. We show that the present model produces results in reasonable agreement with observations. © 2014. American Geophysical Union. All Rights Reserved.

Kunz M.W.,Princeton University | Kunz M.W.,Max Planck Princeton Center for Plasma Physics | Stone J.M.,Princeton University | Stone J.M.,Max Planck Princeton Center for Plasma Physics | Bai X.-N.,Harvard - Smithsonian Center for Astrophysics
Journal of Computational Physics | Year: 2014

We describe Pegasus, a new hybrid-kinetic particle-in-cell code tailored for the study of astrophysical plasma dynamics. The code incorporates an energy-conserving particle integrator into a stable, second-order-accurate, three-stage predictor-predictor-corrector integration algorithm. The constrained transport method is used to enforce the divergence-free constraint on the magnetic field. A δf scheme is included to facilitate a reduced-noise study of systems in which only small departures from an initial distribution function are anticipated. The effects of rotation and shear are implemented through the shearing-sheet formalism with orbital advection. These algorithms are embedded within an architecture similar to that used in the popular astrophysical magnetohydrodynamics code Athena, one that is modular, well-documented, easy to use, and efficiently parallelized for use on thousands of processors. We present a series of tests in one, two, and three spatial dimensions that demonstrate the fidelity and versatility of the code. © 2013 Elsevier Inc.

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