Energetic Particle Dynamics Research Articles

The lower exosphere of Titan: Energetic neutral atoms absorption and imaging

The Saturn magnetosphere interacts with the Titan atmosphere through various mechanisms. One of them leads, by charge exchange reactions between the energetic Saturnian ions and the exospheric neutrals of Titan, to the production of energetic neutral atoms (ENAs). The Ion and Neutral Camera (INCA), one of the three sensors that comprise the Magnetosphere Imaging Instrument (MIMI) on the Cassini/Huygens mission to Saturn and Titan, images the ENA emissions in the Saturnian magnetosphere. This study focuses on the ENA imaging of Titan (for 20–50 keV H ENAs), with the example of the Ta Titan flyby (26 October 2004): our objective is to understand the positioning of the ENA halo observed around Titan. Thus we investigate the main ENA loss mechanisms, such as the finite gyroradii effects for the parent ions, or the charge stripping with exospheric neutrals. We show that multiple stripping and charge exchange reactions have to be taken into account to understand the ENA dynamics. The use of an analytical approach, taking into account these reactions, combined with a reprocessing of the INCA data, allows us to reproduce the ENA images of the Ta flyby and indicates a lower limit for ENA emission around the exobase. However, the dynamics of energetic particles through the Titan atmosphere remains complex, with an inconsistency between the ENA imaging at low and high altitudes.

December 2006 solar extreme events and their influence on the near-Earth space environment: “Universitetskiy-Tatiana” satellite observations

The Russian microsatellite “Universitetskiy-Tatiana” was launched on Jan. 20, 2005 and was both a scientific and educational mission. Its two main aims were declared as: (1) monitoring of the energetic particles dynamics in the near-Earth space environment after solar events and during quiet times, (2) educational activities based on experimental data obtained from the spacecraft. In this paper observations acquired during Dec. 5–16, 2006, known as “Solar Extreme Events 2006”, were analyzed. The “Universitetskiy-Tatiana” microsatellite orbit permits one to measure both solar energetic particle dynamics, variations of the boundary of solar particle penetration, as well as relativistic and sub-relativistic electrons of the Earth’s outer radiation belt during and after magnetic storms. Both relativistic electrons of the Earth’s outer radiation and solar energetic particles are an important source of radiation damage in near-Earth space. Therefore, the presented experimental results demonstrate the successful application of a small educational spacecraft both for scientific and educational programs.

Search for the relationship between background VHF radio bursts and energetic particle dynamics based on data from the MKL instrument onboard the CORONAS-F satellite

The solar flare of November 4, 2001, at 16.03–16.57 UT (GOES soft X-ray class X1.0, optical importance 3B, and coordinates N06W180) is used as an example to investigate the relationship between sporadic VHF radio bursts and charged particle fluxes (of both solar and magnetospheric origins) at an altitude of 500 km. The radio background intensity was recorded at frequencies of 280, 300, 151, and 500 MHz by nondirectional ground-based mid-latitude radio antennas spaced ∼700 km apart. The results of our radio measurements are compared with the dynamics of 0.2–12 MeV electron and 1–5 MeV proton fluxes based on data from the MKL instrument onboard the CORONAS-F satellite (the orbit altitude and inclination are 500 km and 82.5°, respectively).

Benchmark Tests of Fusion Plasma Simulation Codes for Studying Microturbulence and Energetic-Particle Dynamics

Benchmark tests of two simulation codes used for studying microturbulence and energetic-particle dynamics in magnetic fusion plasmas are conducted on present-day parallel supercomputer systems. Both the codes achieved high efficiency on the Earth Simulator with vector processors, and showed good performance scaling on massively parallel supercomputers with more than 10,000 commodity processors. The benchmark results obtained indicated high adaptability of fusion plasma simulation codes to state-of-the-art supercomputer systems.

X-ray, γ-emission and energetic particles in near-Earth space as measured by CORONAS-F satellite: From maximum to minimum of the last solar cycle

The Russian solar observatory CORONAS-F was launched into a circular orbit on July 31, 2001 and operated until December 12, 2005. Two main aims of this experiment were: (1) simultaneous study of solar hard X-ray and γ-ray emission and charged solar energetic particles, (2) detailed investigation of how solar energetic particles influence the near-Earth space environment. The CORONAS-F satellite orbit allows one to measure both solar energetic particle dynamics and variations of the solar particle boundary penetration as well as relativistic electrons of the Earth’s outer radiation belt during and after magnetic storms. We have found that significant enhancements of relativistic electron flux in the outer radiation belt were observed not only during strong magnetic storms near solar maximum but also after weak storms caused by high speed solar wind streams. Relativistic electrons of the Earth’s outer radiation belt cause volumetric ionization in the microcircuits of spacecraft causing them to malfunction, and solar energetic particles form an important source of radiation damage in near-Earth space. Therefore, the present results and future research in relativistic electron flux dynamics are very important.

Kinetic theory of geomagnetic pulsations: 4. Hybrid gyrokinetic simulation of drift‐bounce resonant excitation of shear Alfvén waves

A one‐dimensional linear hybrid gyrokinetic‐magnetohydrodynamic δf particle in cell simulation code is developed to study the detailed mechanisms of energetic particle drift‐bounce resonant destabilization of Alfvén modes in the ring‐current region of the magnetosphere. The model plasma is composed of a cold (10–100eV) component which provides inertia plus a tenuous energetic (∼10 keV) “ring‐current” component which provides both resonant destabilization and compressional stabilization of MHD modes. Full kinetic effects such as finite Larmor radii and particle magnetic bounce and precessional drift motions are retained nonperturbatively. A simple finite β dipolar equilibrium model is assumed (β is the ratio between plasma and magnetic pressures). Simulations show excellent agreement with earlier perturbative analyses. Results show that when the energetic ion thermal velocity is super‐Alfvénic, the ions destabilize both odd and even parity shear Alfvén MHD modes via the drift‐bounce resonances. The growth rates of the resulting modes scale linearly with plasma β. The most unstable of these modes are found to be drift‐bounce resonance destabilized modes with odd parity, with wave numbers such that k⟂ρ ≈ 0.5 at the equator (ρ is the energetic ion Larmor radius). The destabilization typically occurs at a critical wave number k⟂ρ ≈ 0.3. When the wave number is close to this critical value and the plasma β is close to the ideal MHD critical value, the mode frequency is determined by the energetic particle dynamics, similar to the energetic particle modes (EPMs) observed in laboratory fusion plasma experiments. When the energetic particles have Alfvénic or sub‐Alfvénic thermal velocity, they contribute to damping of the MHD modes via the bounce resonance.

The Results of Studying Nonstationary Processes on the Sun by Radioastronomical Methods

This paper presents the results of studies of solar phenomena performed at the Radiophysical Research Institute (NIRFI) in the last years and based on the data of measuring the solar microwave radiation. We obtained new results concerning fragmentation of the regions of initial energy release during solar flares, their spatial and temporal dynamics, the physical conditions in flaring loops, the dynamics of energetic particles accelerated during flares, and the characteristics of sporadic radio emission during the formation and propagation of coronal mass ejections in the lower layers of the solar atmosphere.

Formation of energetic particle fluxes by electrostatic structures in strongly disturbed auroral magnetosphere

Energetic particle dynamics in strongly turbulent magnetospheric plasma is considered using the model of solitary electrostatic structures. In these structures, the electric field component that is parallel to magnetic field is antisymmetric with respect to the centre of the structure. In addition, the electric field component that is perpendicular to magnetic field is symmetric. The stationary kinetic equation is solved for the typical particle energies. The results obtained show that a strong plasma turbulence can effectively accelerate electrons and ions. The velocities of the suprathermal electrons are directed almost along the magnetic field while the ion distributions are essentially isotropic. The electrostatic turbulent structures can form several particle beams with narrow energetic distributions. The results obtained are of great importance for studying the distributions of energetic particles in the auroral magnetosphere.

The GRIF-2 solar-geophysical experiment on board ALPHA

The main purpose of the GRIF-2 solar-geophysical experiment on board the ALPHA space vehicle is the comprehensive study of the temporal and spectral characteristics of the high-energy neutral radiations (gamma-quanta, neutrons, etc.) generated in solar flares. Another important part of the experiment is the study of the dynamics of energetic charged particles (electrons, protons, etc.) in the circumterrestrial space and its correlation with solar phenomena. The complex of instruments includes a high-sensitivity oriented spectrometer of gamma-quanta and neutrons, an oriented spectrometer of X-rays and electrons with a large geometrical factor, and a spectrometer of electrons and protons with a small geometrical factor. The spectrometer of gamma-quanta and neutrons measures particle fluxes and spectra in the gamma-quantum energy range 0.1– 10 MeV and the spectrometer of neutrons is used for energies over 10 MeV. The spectrometer of X-rays and electrons is intended for both the continuous control of magnetospheric electron precipitations and monitoring the X-ray solar activity in the range 10–100 keV. The spectrometer of charged particles with a small geometrical factor is intended for measurement of high-intensity charged particle fluxes in the trapped radiation zones in the Earth magnetosphere.

Simulation of Alfven-wave-resonant-particle interaction

New numerical simulations are presented on the self-consistent dynamics of energetic particles and a set of unstable discrete shear Alfven modes in a. tokamak. The code developed for these simulations has been previously tested in simulations of the bump-on-tail instability model. The code has a Hamiltonian structure for the mode-particle coupling, with the superimposed wave damping, particle source and classical relaxation processes. In the alpha-particle-Alfven-wave problem, we observe a transition from a single mode saturation to mode overlap and global quasi-linear diffusion, which is qualitatively similar to that observed in the bump-on-tail model. A considerable enhancement in the wave energy due to the resonance overlap is demonstrated. The effect of global diffusion on the energetic particle losses is also demonstrated

A Model for the Radio Emission from SNR 1987A

The observations of radio emission from SNR~1987A can be accounted for on the basis of diffusive shock acceleration of electrons by the supernova blast wave. However, with this interpretation the observed spectral index implies that the compression ratio of the gas subshock is roughly $2.7$ rather than the value of $4$ expected of a strong shock front. We propose that in SNR~1987A, ions also undergo diffusive acceleration at the shock, a process that is likely to be rapid. Unlike the electron population, the accelerated ions can have an important effect on the gas dynamics. We calculate this coupled gas and energetic particle dynamics on the basis of the two-fluid model, in which the accelerated ions provide an additional component to the total pressure acting on the fluid. By accelerating and possibly heating the upstream plasma, the initially strong shock is modified and a weaker subshock with an upstream precursor results. The electrons behave as test particles. They are accelerated at the evolving subshock, escape downstream, and emit synchrotron radiation in the swept up magnetic field. Two models are considered for the surroundings of the progenitor: that of a freely expanding wind of number density $n\propto r^{-2}$, and that of a wind confined by a shell of denser material, creating a stagnation zone of roughly constant density beyond the standing shock which terminates the free wind. We model the observed radio light curves and the relatively steep spectrum of SNR~1987A using similar values for the ion acceleration parameters to those used in models of cosmic ray acceleration in older SNRs which can also contain high Mach number shocks, and find a good fit for the case in which the termination shock is located at about $2\times 10^{15}\,$m from the progenitor.

Fast particle resonances in tokamaks

Most of the recent studies on fast particles deal with the stabilization-destabilization of magnetohydrodynamics modes. Here the authors present another aspect of fast particle resonances in tokamaks and review some recent results on the dynamics of energetic electrons and alpha particles. The interaction between the runaway population and the magnetic ripple is analyzed. The occurrence of an induced radiative slowing down is demonstrated and its potential is assessed. Then, the resonant channeling of alpha particle free energy, to either fast electrons or fast ions, by means of lower hybrid waves is investigated, and the efficiency of this process is analyzed.

On the energetic particle dynamics in the distant magnetotail

The large scale structure in the energetic electron and proton distributions associated with the Earth's magnetopause and bow shock were identified in the Prognoz 3,7 and 9 experiments in 1973–1984. These energetic particle patterns were studied in /1–3/ using quantitative magnetospheric models. Besides that the medium energy proton spectra were obtained in practice for the first time in the outer magnetosphere and outside the magnetosphere at high latitudes and at great distances (up to ∼100 R E) from the Earth. This report discusses the space-time variations of the energetic particle fluxes and of the magnetic field in the high-latitude tail with varing the interplanetary medium parameters. Special attention is paid to the rearrangement of the magnetosphere during the 22 Mar 1979 magnetic storm observed on several satellites in different regions.

Dynamics of plasma, energetic particles, and fields near synchronous orbit in the nighttime sector during magnetospheric substorms

We discuss two phases of the substorm‐associated magnetospheric dynamics in terms of the particles and fields at synchronous orbit. The first phase corresponds to the ‘decreases’ of energetic particle flux first identified by Erickson and Winckler (1973) and discussed by Walker et al. (1976) and Erickson et al. (1979). This phase begins one‐half hour to one hour before the substorm onset and is characterized by (1) a distortion of the magnetosphere to a more taillike configuration caused by (2) an intensification and/or motion toward the earth of the cross‐tail current and of its earthward part, the partial ring current, (3) a shift of trapped particle trajectories closer to the earth on the nightside following contours of constant B causing the particle ‘decreases,’ accompanied by a change in the pitch angle distributions from ‘pancake’ to ‘butterfly’ as observed at geostationary orbit, (4) an initiation of a response of the auroral electrojet (AE) index. The decreases of energetic particle flux can correspond to the substorm growth phase as defined initially by McPherron (1970) or the growth or precursor phase of Erickson et al. (1979). Plasma motions and currents during decreases tend to be variable, but the description above nevertheless characterizes the large‐scale trend. It is suggested that the electric field induced by the increasing tail current near the earth acts opposite to the cross‐tail convection field and can temporarily inhibit convection near the geostationary orbit. The second phase is the conventional expansion phase that begins with the ‘onset,’ characterized in our study by (1) a sudden decrease in the tail current and a return of the inflated magnetosphere to a dipolelike configuration, (2) a sudden shift of trapped high‐energy particles toward the tail again following contours of constant B, and at the same time (3) a surge of tail plasma toward the earth as the induced electric field now increases the total convection field. Separate effects thus result in the dramatic increases of both high energy and plasma particles seen at substorm expansion phase onset, (4) an AE index response and the appearance of bays at stations near midnight local time accompanied by very active aurora as well as the precipitation of high‐energy particles. The different appearance of the responses at ATS 1 (on the magnetic equator) and ATS 6 (off the magnetic equator) can be well explained by the above description. True diamagnetic effects of the particle population are clearly evident at the ATS 6 region and must be carefully distinguished from the effects of distant currents. The use of oppositely directed detectors on ATS 6 that permit the evaluation of the guiding center particle density gradients has been of great use in this analysis.