This project will examine ultra-low frequency (ULF) electromagnetic oscillations that are generated by energetic ions in Earth's magnetosphere. The project will utilize gyrokinetic simulations. There are several tasks involved. The first is to develop a gyro-kinetic-magnetohydrodynamic simulation code. The code will make it possible to study the internal excitations of ULF waves in a realistic plasma configuration. The results from the simulations will then be used to develop analytical theories of the waves and their stability properties. The project will examine the couplings of the energetic ions to the waves that result from the curvature of dipole-like magnetic field lines, the coupling between compressional wave modes and mirror wave modes, and the coupling of the waves to Alfvén balloon modes. The simulation and theory results will be compared with satellite measurements of ULF waves.
The results of the research will have applications beyond enhancing our understanding of Earth's magnetosphere, as they will have impacts on our understanding of laboratory experiments as well. Much of the research will be carried out by a graduate student.
Normal 0 7.8 ? 0 2 false false false EN-US ZH-CN X-NONE I. Intellectual merit and impacts The Earth’s magnetosphere is in an environment of plasmas (fully ionized gas of electrons and ions). These plasmas carry charges and currents; and, hence, produce fluctuating electric and magnetic fields. The electromagnetic fields, in turn, can accelerate/heat charged particles to high energies, as well as transport them over large portion of the magnetosphere and across boundaries separating various domains of charged particle populations. Understanding these highly complex, highly nonlinear plasma dynamics (manifesting as, e.g., aurora, disturbed Earth’s magnetic field) is, thus, not only intellectually challenging but also of significant practical importance to a broad scope of disciplines. II. Outcomes Our project has addressed and obtained significant results in two particular issues dealing with wave and particle dynamics in the Earth’s magnetosphere. The first issue is accelerating and heating of charged particles by low-frequency Alfvén waves. Alfvén waves, excited by either external or internal sources, are prevalent in Earth’s magnetosphere. Nominally, Alfvén wave frequency is much smaller than the characteristic charged-particle dynamic frequency, the cyclotron frequency; and, thus, the wave electromagnetic fields are inefficient in accelerating the particles. Our research, however, has discovered the following novel nonlinear properties; that is, at sufficiently large amplitudes, wave-particle interaction phase exhibits higher harmonics of charged particles motion and, consequently, the interaction phase can be kept over a long while (i.e., resonance); rendering efficient accelerating/heating of charged particles. This novel nonlinear resonance mechanism has direct applications to solar corona heating and charged particle transports in various plasma environments. The other issue deals with stability of current sheets which form the boundary layers separating two plasma domains. We have adopted the novel gyrokinetic theory approach to analyze this system of high degrees of nonuniformities. Initial results of our analyses are very promising in that they agree well with those obtained by direct numerical simulation. This topic also constitutes as a doctoral thesis project which has been advancing smoothly. All together, seven articles pertinent to this project have been published in internationally leading scientific journals.
