Resonant Interactions Between Energetic Electrons And Plasma Waves In The Earth’s Radiation Belts

For scientists, the Earth’s magnetosphere is a fascinating spontaneous plasma laboratory, which can be used to explore the dynamics of energetic charged particles. As the spacecraft and human space activities are executed more frequently, more and more investigations for the magnetospheric energetic particles distribution and dynamics are carried out. The Earth’s radiation belts comprise a very active area for magnetospheric physics research, as is evidenced by the past and onging radiation belt satellite missions, such as SAMPEX, Polar (CEPPAD), GPS (BDD-Ⅱ), CRRES (MEA), LANL (SOPA), GOES, Cluster, and HEO. Based on these satellite observations, various phenomena of the spatial and temporal evolution of energetic particles in the magnetosphere are revealed, promoting the dynamic research of the Earth’s radiation belts energetic particles. In the approach of high solar activity, the space exploration will be of high need and the planned projects will be implemented for the research of dynamic changes of magnetospheric radiation belts. Several upcoming missions, such as, RBSP of the U.S.A., ORBITALS of Canada, and ERG of Japan, have set up scientific focuses for comprehensive understanding of the variability, transport, acceleration and loss of radiation belt particles.The results of this thesis help to understand the Earth’s radiation belt electron acceleration and loss processes, which are significant for practical purposes of space asset protection of low-to-high altitude orbiting spacecraft.Those results also help to explain various physical phenomena in the magnetosphere, to understand the dynamics of radiation belt energetic electron distribution, and further to establish the global distribution of radiation belt electron dynamics model for national defense and human lives under service. Based on above considerations and current research developments, we study the radiation belt energetic electron distribution and resonant interactions between those electrons and plasma wave in the magnetosphere both theoretically and numerically.The main results of this study are as follows:1. Statistical analysis of the radiation belt electron flux distribution and pitch angle distribution using the CRRES data.(1) By utilizing the 15-month energetic electron flux data provided by the MEA instrument onboard CRRES, energetic radiation belt electron fluxes are analyzed statistically for electrons at energies of 148keV,509keV,1090keV, and 1581keV under periods of quiet (0≤Kp< 3), moderate (3≤Kp≤6) and active (6<Kp≤9) geomagnetic activity condition, respectively. A global model of the Earth’s radiation belt electron flux distribution is presented as a function of L-shell, magnetic local time (MLT) and geomagnetic activity condition. The results indicate a strong dependence of radiation belt electron omni-directional flux on the level of geomagnetic activity in the inner magnetosphere within 2< L< 8. Considerable increases in energetic electron omni-directional fluxes are also shown to occur in 12-18 MLT sector.(2) A statistical analysis of energetic radiation belt electron pitch angle distributions (PADs) at the radial distances of 6 RE and 6.6 RE is performed on the basis of the pitch angle resolved flux observations from the Medium Electrons A (MEA) instrument onboard the Combined Release and Radiation Effects Satellite (CRRES). In this study we present a detailed statistical analysis of electron PADs including the dependence on electron kinetic energy, magnetic local time (MLT), and the level of geomagnetic activity. By fitting the measured PADs with a power law function of sine of local pitch angle, the power law index n that relates to the category of radiation belt electron PAD is quantified in detail as a function of electron kinetic energy, MLT interval and geomagnetic index Kp. Statistical averaged n-values vary considerably with respect to MLT, ranging from n～0 within 00-04 MLT to n～1.5 within 12-16 MLT, due to the MLT dependence of wave scattering and the effects associated with drift shell splitting and magnetopause shadowing. Drift shell splitting and magnetopause shadowing result in often observed negative values of n. At lower energies of a few hundred keV the pitch angle distributions are more flat than at MeV energies, which is consistent with faster pitch angle scattering at low energies by chorus waves. These quantitative results of radiation belt electron PAD, consistent with the previous studies by Vampola [1998] and Gannon et al. [2007], provide further insight into the global dynamics of energetic radiation belt electrons near the geostationary orbit and also are useful for inferring electron phase space densities and assimilating their radial profiles using omni-directional electron flux measurements.2. Based on the resonance condition and full dispersion relation, we establish theoretical model of energetic electron interactions with plasma wave with the background of Dungey magnetic field and Sheeley electron density. The minimum resonance energies and resonance regions for electrons interaction with plasma waves including Chorus, Hiss and EMIC (Electromagnetic Ion Cyclotron) are examined in this paper.(2) The minimum resonance energy in the low-mid latitude is lower compared with in the high latitude. Interactions for electrons with Chorus and Hiss can take place in the low-mid latitude, which impact on the radiation belt electron distribution. EMIC mainly interact with >～MeV electrons and changes those electron distribution. At the same location, the minimum energy with high resonance order is higher than for the Landau resonance. For electron interaction with Chorus and Hiss, the Landau resonance mainly occurs in high latitude.(2) The impact of solar activity on the minimum energy is mainly in the outer radiation belt, because the magnetic configuration and intensity change obviously at the location of higher L-shells during the solar activity. The cold plasma parameter is also variable with the solar activity levels.(3) The resonance regions depend on electron energy, electron pitch angle, wave normal angle, wave frequency, the resonance harmonic, solar activity level and spatial location. High order resonance always occurs in the low-mid latitude and the Landau resonance takes place in the high latitude.(4) Solar activity has obvious effect on the resonance region and the effect is greater with the increasing L-shell. Resonance region for energetic electron with plasma wave relate closely with D value (the solar activity parameter) in the outer radiation belt, but there are seldom resonance interactions in the inner radiation belt.3. Based on quasi-linear theory, the pitch angle, mixed and momentum diffusion rates for electron wave-particle resonance interaction with plasma wave are investigated. Moreover, we carry out bounce-averaging of the diffusion coefficients over an electron bounce-orbit. Diffusion coefficients depend on the resonance condition and dispersion relation and relate with electron energy, electron pitch angle, wave normal angle, wave frequency, the resonance harmonic, solar activity level and spatial location as well as resonance region. The results indicate that lower-energy 100keV electrons can undergo pitch angle diffusion scattering into loss cone at a bigger rate and are subject to rapid precipitation into the atmosphere. However, for higher-energy electrons (>1MeV), pitch angle scattering is reduced and does not extend to the loss cone, because those electron are not in first-order resonance with Chorus at lower pitch angles. Diffusion rate also relate with the solar activity. The lower-energy electrons with lower pitch angle can interact with the Chorus in the outer radiation when the solar is quiet, but the interaction does not occur when the solar is active.4. Based on the previous theory of the motion of charged particles in the Earth’s magnetic field [Stomer,1955], we have firstly derived the spatial region to which energetic particles around the Earth can extend. Using an empirical model for radioactive debris triggered by the high altitude nuclear detonation (HAND), we investigate the primary region where HAND-induced artificial radiation belt can form. Finally, in terms of the fission property of HAND and the characteristic features of energetic electron distributions in the natural belts, the electron flux within the artificial radiation belt is calculated and its dependence on the explosion latitude, altitude, and equivalent is evaluated in a preliminarily quantitative way. The numerical results show that, under certain circumstances, the HAND with 0.1～1Mt TNT explosion equivalent can be expected to produce an artificial radiation belt near the Earth with the flux more than the natural ones by an order of 3 to 4. The central location of the artificial belt largely relies on the magnetic latitude that the detonation is released while the thickness and electron flux of the artificial radiation belt are affected by the explosion altitude and equivalent.5. Based on the quasi-linear theory of gyroresonant wave-particle interaction, we compute diffusion coefficients and loss timescales for radiation belt energetic electrons due to cyclotron resonance with artificial ELF/VLF emissions that are radiated through modulating the currents in the lower ionosphere by ground-based powerful high-frequency (HF) transmitter. We test electron pitch-angle scattering in the outer zone typically at L=4.6 (where the HAARP facility is located) and in the inner zone typically at L=1.5. The results indicate that the electron loss timescales due to artificial injection of ELF/VLF waves in the inner and outer radiation belts depend largely on the value of cold-plasma parameterα* (∝B2/N0, where B is the ambient magnetic field and No the electron number density), the properties of wave frequency spectrum, the wave power, and electron energy in resonance with the waves. Generally, relativistic electrons in the outer zone are much easier to be precipitated into the atmosphere by artificial ELF/VLF whistler waves and lower-energy electrons (≤200 keV) can undergo pitch-angle scattering more efficiently than higher-energy electrons (≥500 keV). Since ELF/VLF waves can experience in situ amplification due to multiple magnetospheric reflections within the magnetospheric cavity, it can be reasonably expected that, under suitable situations, ground-based HF transmitters can release feasible radiation power into the ionosphere to induce the injection of ELF/VLF waves into the inner magnetosphere, and consequently account for potential rapid removal of outer belt relativistic electrons in a timescale of 1 to 3 days and of inner belt relativistic electrons that generally hold a lifetime of 100 days or more in an order of 10 days.