Particle beams in the vicinity of magnetic separatrix according to near‐lunar ARTEMIS observations
We study characteristics of ion and electron beams observed during 101 crossings of the near-separatrix region by Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) spacecraft in the magnetotail. We found that accelerated ion beams are observed under any level of geomagnetic activity. A duration of earthward moving ion beams is statistically longer (≤ 10 min) than a duration of tailward ion beams (≤ 4 min), which can be due to the transient character of ion acceleration in the vicinity of the near-Earth neutral line (NENL). Energetic characteristics of earthward and tailward ion beams are similar indicating similar acceleration conditions at ion kinetic scales at both sides of an X line independently of its location. Conversely, electron velocity distributions observed near magnetic separatrix earthward of the distant neutral line (DNL) differ from those observed tailward of the NENL. Earthward of the DNL a scattered and thermalized electron population without energetic field-aligned beams is observed near the separatrix. On the contrary, tailward of the NENL field-aligned electron beams accelerated to a few kiloelectron volts are detected. These observations show that near DNL the electron scattering and thermalization dominate over the direct acceleration, whereas stronger electric fields in the NENL produce substantial population of field-aligned kiloelectron volt electrons.
We have examined conditions and parameters of irradiation of materials perspective for use in the mainstream nuclear fusion facilities for two devices of the Dense Plasma Focus (DPF) type (PF-6 and PF-1000) with a number of diagnostics in comparison with conditions expected in the first-wall materials in Iter and NIF. It is found that a so-called “damage factor” helps in modelling of the fusion reactor conditions. Optical microscopy, SEM, Atomic Emission Spectroscopy, images in secondary electrons and in characteristic X-ray luminescence of different elements, and X-ray elemental analysis, present results for a number of materials including low-activated ferritic and austenitic stainless steels, β-alloy of Ti, as well as the double-forged W (candidate material for divertor in Iter). With an increase of the power flux density of hot plasma and fast ion streams irradiating the surface, its morphology changes from a weak wave-like structure of the surface to the strongly developed one for the same material. It was melted with the appearance of the fracturing pattern – first along the borders of grains and then with the intergranular net of microcracks. At the highest values of power flux densities multiple blisters appeared. Besides, in this last case cracks develop because of microstresses at the solidification of melt. Presence of deuterium within the surface nanolayers of irradiated ferritic steel is explained by capture of deuterons in lattice defects of the types of impurity atoms, pores and oxycarbonitride particles presented in the material.
In this work we present an analysis of the dynamics of suprathermal ions of different masses (H+, He+, O+) during prolonged dipolarizations in the near-Earth magnetotail (X>−17RE) according to Cluster/RAPID observations in 2001–2005. All dipolarizations from our database were associated with fast flow braking and consisted of multiple dipolarization fronts (DFs). We found statistically that fluxes of suprathermal ions started to increase ∼1 min before the dipolarization onset and continued to grow for ∼1 min after the onset. The start of flux growth coincided with the beginning of a decrease in the spectral index γ. The decrease in γ was observed for protons for ∼1 min after the dipolarization onset, and for He+ and O+ ions for ∼3 and ∼5 min after the onset respectively. The negative variations of γ for O+ ions were ∼2.5 times larger than for light ions. This demonstrates more efficient acceleration for heavy ions. The strong negative variations of γ were observed in finite energy ranges for all ion components. This indicates the possibility of nonadiabatic resonant acceleration of ions in the course of their interaction with multiple DFs during dipolarizations. Our analysis showed that some fraction of light ions can be accelerated up to energies ≥600 keV and some fraction of oxygen ions can be accelerated up to ∼1.2 MeV. Such strong energy gains cannot be explained by acceleration at a single propagating DF and suggest the possibility of multistage ion acceleration in the course of their interaction with multiple DFs during the prolonged dipolarizations.
We use Cluster and THEMIS simultaneous observations to study the spatial distributions of a shear BY field in the Plasma Sheet (PS) of the Earth's magnetotail at -31 RE < X < -9 RE. The best correlation between the BY field in the PS (BY_PS) and the Y-component of the Interplanetary Magnetic Field (IMF) (BY_IMF) was observed during the quiet PS periods when high speed plasma flows were not detected. During active PS periods the correlation between the BY_PS and BY_ IMF was poor. The analysis of spatial distribution of the BY field along the direction perpendicular to the Current Sheet (CS) plane showed the presence of one of the following configurations, which can be self-consistently generated in the CS: 1) the "quadrupole" distribution of the BY field usually associated with the Hall current system in the vicinity of X-line and 2) the symmetrical "bell-shaped" distribution formed due to the BY amplification near the neutral plane of the CS. Multipoint observations revealed the transient appearance of the "quadrupole" BY distribution during the periods of X-line formation in the mid-tail. This distribution was observed during a few minutes within, at least, 12 RE from the estimated X-line position. On the contrary, the symmetrical "bell-shaped" distribution is more localized in the radial direction and, generally, has a larger observation time (up to ∼10 min). Thus, the internal CS perturbations caused either by the Hall currents related to reconnection or by the peculiarities of the local quasi-adiabatic ion dynamics sufficiently affect the shear BY field existing in the magnetotail due to the partial IMF penetration.
The dynamics of a two-component Davydov-Scott (DS) soliton with a small mismatch of the initial location or velocity of the high-frequency (HF) component was investigated within the framework of the Zakharov-type system of two coupled equations for the HF and low-frequency (LF) fields. In this system, the HF field is described by the linear Schrödinger equation with the potential generated by the LF component varying in time and space. The LF component in this system is described by the Korteweg-de Vries equation with a term of quadratic influence of the HF field on the LF field. The frequency of the DS soliton`s component oscillation was found analytically using the balance equation. The perturbed DS soliton was shown to be stable. The analytical results were confirmed by numerical simulations.
Radiation conditions are described for various space regions, radiation-induced effects in spacecraft materials and equipment components are considered and information on theoretical, computational, and experimental methods for studying radiation effects are presented. The peculiarities of radiation effects on nanostructures and some problems related to modeling and radiation testing of such structures are considered.