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The synchronization of dust acoustic waves to an external periodic source is studied in the framework of a driven Korteweg-de Vries-Burgers equation that takes into account the appropriate nonlinear and dispersive nature of low frequency waves in a dusty plasma medium. For a spatio-temporally varying source term the system is shown to demonstrate harmonic (1:1) and super-harmonic (1:2) synchronized states. The existence domains of these states are delineated in the form of Arnold tongue diagrams in the parametric space of the forcing amplitude and forcing frequency and their resemblance to some past experimental results is discussed.

Spacecraft data reveals a nonuniform ambipolar electric field transverse to the magnetic field in a thin magnetotail current sheet that leads to intense ExB velocity shear and non-gyrotropic particle distributions. The ExB drift far exceeds the diamagnetic drift and drives lower hybrid waves localized to the magnetic field reversal region, which is ideally suited for the anomalous dissipation necessary for reconnection. It also reveals substructures embedded in the current density, indicating the formation of a non-ideal current sheet., Comment: 6 pages, 4 figures

Plasma in the earth's magnetosphere is subjected to compression during geomagnetically active periods and relaxation in subsequent quiet times. Repeated compression and relaxation is the origin of much of the plasma dynamics and intermittency in the near-earth environment. An observable manifestation of compression is the thinning of the plasma sheet resulting in magnetic reconnection when the solar wind mass, energy, and momentum floods into the magnetosphere culminating in the spectacular auroral display. This phenomenon is rich in physics at all scale sizes, which are causally interconnected. This poses a formidable challenge in accurately modeling the physics. The large-scale processes are fluid-like and are reasonably well captured in the global magnetohydrodynamic (MHD) models, but those in the smaller scales responsible for dissipation and relaxation that feed back to the larger scale dynamics are often in the kinetic regime. The self-consistent generation of the small-scale processes and their feedback to the global plasma dynamics remains to be fully explored. Plasma compression can lead to the generation of electromagnetic fields that distort the particle orbits and introduce new features beyond the purview of the MHD framework, such as ambipolar electric fields, unequal plasma drifts and currents among species, strong spatial and velocity gradients in gyroscale layers separating plasmas of different characteristics, \textit{etc.} These boundary layers are regions of intense activity characterized by emissions that are measurable. We study the behavior of such compressed plasmas and discuss the relaxation mechanisms to understand their measurable signatures as well as their feedback to influence the global scale plasma evolution., Comment: 88 pages, 44 figures

The growth of electromagnetic ion cyclotron waves (EMIC) due to a ring distribution of Hydrogen ions is examined. Though these distributions are more commonly implicated in the generation of equatorial noise, their potential for exciting EMIC waves is considered here. It is shown that since the ring distribution is non-monotonic in perpendicular velocity, the amplification achieved by this instability is greater than bi-Maxwellian distributions for typical anisotropies, because the waves can maintain resonance over a much longer part of its trajectory. For ring speeds V_R close to the Alfven speed V_A, the growth rate is maximum at parallel propagation but is much larger at oblique angles compared with a bi-Maxwellian, and can have a second peak approximately at kperp c/omegaPH V_R/V_A ~2.3 for ring speeds about the parallel thermal speed. Strong wave gain is achieved for moderate ring speeds V_R~V_A . The analysis suggests that EMIC wave activity should be closely associated with equatorial noise.

Using electromagnetic particle-in-cell simulations Winske and Daughton [Phys Plasmas, 19, 072109, 2012] have recently demonstrated that the nonlinear evolution of a wave turbulence initiated by cold ion ring beam is vastly different in three dimensions than in two dimensions. We further analyze the Winske-Daughton three dimensional simulation data and show that the nonlinear induced scattering by thermal plasma particles is crucial for understanding the evolution of lower hybrid/whistler wave turbulence as described in the simulation.

It is shown that the dispersion relation for whistler waves is identical for a high or low beta plasma. Furthermore in the high-beta solar wind plasma whistler waves meet the Landau resonance with electrons for velocities less than the thermal speed, and consequently the electric force is small compared to the mirror force. As whistlers propagate through the inhomogeneous solar wind, the perpendicular wave number increases through refraction, increasing the Landau damping rate. However, the whistlers can survive because the background kinetic Alfven wave turbulence creates a plateau by quasilinear diffusion in the solar wind electron distribution at small velocities. It is found that for whistler energy density of only ~10^-3 that of the kinetic Alfven waves, the quasilinear diffusion rate due to whistlers is comparable to KAW. Thus very small amplitude whistler turbulence can have a significant consequence on the evolution of the solar wind electron distribution function.

A concept for forced reentry of small orbital debris with characteristic dimension ~ 10 cm from the highly populated sun synchronous orbit by injecting micron scale dust grains to artificially enhance drag is discussed. The drag enhancement is most effective when dust grains counter rotate with respect to the debris resulting in hypervelocity dust/debris impacts. While the natural drag on small debris with ballistic coefficient ~ 5 kg/m2 in orbits with perigee above 900 km is negligible, it is sufficient to decay the orbit of the injected dust grains at a significant rate. This offers a unique opportunity to synchronize the rates of descent of the dust and debris to create a sweeping (snow-plow-like) effect on the debris by a descending narrow dust layer. The dust density necessary to de-orbit small debris is sufficiently low such that the orbits of active satellites which have larger ballistic coefficients are minimally affected. If deemed necessary, contact of the injected dust with active satellites may be avoided by maneuvering the satellite around the narrow dust layer.

Kinetic Alfven wave turbulence in solar wind is considered and it is shown that non-Maxwellian electron distribution function has a significant effect on the dynamics of the solar wind plasmas. Linear Landau damping leads to the formation of a plateau in the parallel electron distribution function which diminishes the Landau damping rate significantly. Nonlinear scattering of waves by plasma particles is generalized to short wavelengths and it is found that for the solar wind parameters this scattering is the dominant process as compared to three wave decay and coalescence in the wave vector range . Incorporation of these effects lead to the steepening of the wave spectrum between the inertial and the dissipation ranges with a spectral index between 2 and 3. This region can be labeled as the scattering range. Such steepening has been observed in the solar wind plasmas., Comment: The following article has been submitted to Phys. Plasma

Dust grains immersed in plasma discharges acquire a large negative charge and settle into a dust cloud at the edge of the sheath. In this region, the plasma ions stream toward the electrode at a velocity u approx. cs=(T(sub e)/m(sub i))(exp 1/2). Experimentally at sufficiently high gas pressure P, the random kinetic energy of the grains is damped by gas friction, and the grains are strongly coupled and self-organize into a crystalline configuration. For lower pressures despite the dissipation of grain kinetic energy to gas friction, the dust grains reach a steady-state kinetic temperature T(sub d) which is much larger than the temperature of any other component in the plasma. T(sub d) is so large that the dust acts like a fluid. We have used the dynamically shielded dust (DSD) model to simulate these physical processes. We find that the known experimental features are nicely reproduced in the simulations, and that additional features are revealed. In the figure we plot the variation of T(sub d) as P is continuously varied in a DSD code run. A marked difference is evident between the critical pressure P(sub m) for the melting transition as P is decreased, and the critical pressure P(sub c) for the condensation transition as P is increased. For P(sub m) is less than P is less than P(sub c), mixed phase states are seen. This hysteresis occurs because the instability which triggers melting is different from the instability that heats the dust in the fluid phase and inhibits freezing. At low pressure, the dust is subject to a two-stream instability with the ions. This instability is responsible for the high temperature of the dust at low pressure. The basic physics underlying the melting transition has been elucidated in a series of papers. We are developing a first-principles analytic approach to the melting transition, which embodies the same physics that is present in the DSD code.