Collisionless Plasma Processes at Magnetospheric Boundaries: Role of Strong Nonlinear Wave Interactions

JETP Letters - The sunward Poynting flux throughout the magnetosheath and foreshock (directly measured by INERBALL-1, CLUSTER-4, and DOUBLE STAR TC1) and its correlation and bi-correlation with the...     

Turbulent boundary layer at the border of geomagnetic trap

A new phenomenon was discovered on the basis of analysis of the Interball project data. A hot plasma flow is thermalized through the formation of “long-operating” vortex streets and local discontinuities and solitons in a distributed region over polar cusps. Plasma percolation through the structured boundary and secondary reconnection of fluctuating magnetic fields in a high-latitude turbulent boundary layer account for the main part of solar wind plasma inflow into the magnetospheric trap. Unlike local shocks, the ion thermalization is accompanied by the generation of coherent Alfvén waves on the scales ranging from ion gyroradius to the radius of curvature of the averaged magnetic field, as well as by the generation of diamagnetic bubbles with a demagnetized heated plasma inside. This “boiling” plasma has a frequency region where the spectrum is different from the Kolmogorov law (with slopes 1.2 and 2.4 instead of 5/3 or 3/2). The fluctuation self-organization in the boundary layer (synchronization of three-wave decays) was observed on certain frequency scales.     

On nonlinear cascades and resonances in the outer magnetosphere

The paper addresses nonlinear phenomena that control the interaction between plasma flow (solar wind) and magnetic barrier (magnetosphere). For the first time we demonstrate that the dominant solar wind kinetic energy: (i) excites boundary resonances and their harmonics which modulate plasma jets under the bow shock; (ii) produces discrete three-wave cascades, which could merge into a turbulent-like one; (iii) jet produced cascades provide the effective anomalous plasma transport inside and out of the magnetosphere; (iv) intermittency and multifractality characteristics for the statistic properties of jets result in a super-ballistic turbulent transport regime. Our results could be considered as suggestive for the space weather predictions, for turbulent cascades in different media and for the laboratory plasma confinement (e.g., for fusion devices).     

High energy jets in the Earth’s magnetosheath: Implications for plasma dynamics and anomalous transport

High energy density jets in the magnetosheath near the Earth magnetopause were observed by Interball-1 [1]. In this paper, we continue the investigation of this important physical phenomenon. New data provided by Cluster show that the magnetosheath kinetic energy density during more than one hour exhibits an average level and a series of peaks far exceeding the kinetic energy density in the undisturbed solar wind. This is a surprising finding because the kinetic energy of the upstream solar wind in equilibrium should be significantly diminished downstream in the magnetosheath due to plasma braking and thermalization at the bow shock. We suggest resolving the energy conservation problem by the fact that the nonequilibrium jets appear to be locally superimposed on the background equilibrium magnetosheath, and, thus, the energy balance should be settled globally on the spatial scales of the entire dayside magnetosheath. We show that both the Cluster and Interball jets are accompanied by plasma superdiffusion and suggest that they are important for the energy dissipation and plasma transport. The character of the jet-related turbulence strongly differs from that of known standard cascade models. We infer that these jets may represent the phenomenon of the general physical occurrence observed in other natural systems, such as heliosphere, astrophysical, and fusion plasmas [2–10]. The text was submitted by the authors in English.     

Formation of the flank LLBL: A case study

A formation of the low-latitude boundary layer (LLBL) on open field lines during intervals of southward oriented interplanetary magnetic field is now understood in terms of dayside reconnection. However, observations of counterstreaming particles suggest that the LLBL can exist on closed field lines over some portion of the magnetopause. The fluctuations of plasma parameters inside a layer are attributed either to a transient nature of the processes forming a layer or to sweeping of deformations of the magnetopause or inner edge of the LLBL surfaces along the spacecraft. The INTERBALL-1 and MAGION-4 crossed the LLBL near the terminator during intervals of disturbed solar wind conditions. Two-point observations allow us to distinguish the temporal and spatial changes, to estimate the LLBL thickness and its variations and to find the sources of observed plasma populations. Observations suggest that the flank LLBL is supplied by high-latitude reconnection near the cusp and that it lies on open field lines.     

Anomalous interaction of a plasma flow with the boundary layers of a geomagnetic trap

Using the data from the Interball-1, GEOTAIL, THEMIS and CLUSTER satellites, we propose a mechanism of anomalous magnetosheath dynamics. This mechanism yields that plasma boundaries can be locally deformed over distances comparable to its thickness. In particular, the magnetospheric boundary, the magnetopause, is deformed over distances up to a few Earth radii (R _E) under the pressure of supermagnetosonic plasma streams (SPSs), instead of reacting to plasma pressure decreases, as it was previously thought. Supermagnetosonic plasma streams having a kinetic pressure a few times larger than the solar wind pressure and the magnetic pressure behind the magnetopause, can crush the magnetopause and even push it outside the mean bow shock position, as determined through the average pressures balance. Anomalous magnetosheath dynamics is initiated by plasma flow anomalies (FAs), triggered by rotational discontinuities, by jumps in the solar wind pressure and by interplanetary shocks, which all interact with the bow shock. We show that the generation mechanism for SPSs, adjacent to the FA, is connected with the compensation of the FA flow reduction by the SPS enhanced flow, which is produced by polarization electric fields at the FA edges. Statistically, SPSs are extreme events, relayed with intermittency and multifractality inside the boundary layers of the geomagnetic trap. In this way, SPSs provide “long-range” interactions between global and microscales. A similar role may be played by fast concentrated flows in the geomagnetic tail, in fusion devices, in astrophysical plasmas and in hydrodynamics.     

Eigenmodes of the Boundary of a Magnetic Barrier Flowed Around by Plasma: the Boundary Membrane Model,Linear and Nonlinear Resonances,and Couplings with Internal Modes

Journal of Experimental and Theoretical Physics - The linear and nonlinear resonances and cascades affecting significantly the interaction of a collisionless plasma flow with a magnetic barrier and...     

The influence of ion bombardment on emission properties of small dust grains

Dust grains that are present in many plasma and vacuum systems and in the space usually carry a non-negligible charge. Their charging significantly depends on surface properties of the grain material. In cold plasma, charging is mainly given by electron attachment, nevertheless, when plasma becomes hot, other processes (secondary electron emission, field emission, etc.) take place. Emission properties of the grain surface could be modified by grain baking or by ion bombardment. Our study is carried out at the dust charging experiment dealing with a single dust grain electro-dynamically levitated in a 3D quadrupole trap. The grain can be exposed to the ion beam in the energy range of 100 eV–5 keV and to the electron beam in the energy range of 100 eV–10 keV. We have chosen He⁺ and Ar⁺ ions for the surface treatment and the observed influence on the surface properties is discussed in terms of secondary emission. A non-negligible shift of the secondary electron emission yield, as well as a change of energy distribution of secondary electrons, were measured after Ar⁺ bombardment. A preliminary study suggests that the effects of He⁺ and Ar⁺ are comparable.