Plasma Seminar: Role of Linear Mode Conversion on Generation and Propagation of Space Plasma Waves

Eun-Hwa Kim, Princeton Plasma Physics Laboratory, Princeton University

Tuesday, February 26, 2013, 3:30pm

MacLean B01

Although wave modes are distinct in uniform plasmas, in inhomogeneous plasmas the modes can be coupled in frequency-wave vector space. In this case, for some range of frequency and angles of propagation, energy can be converted linearly from one mode to another. Various linear-mode conversion (LMC) processes occur over a broad frequency range from ω << ωci to ω ≥ ωpe, where ωci and ωpe are ion gyro- and electron plasma frequencies. In this talk, we present applications of LMC at Alfven/ion-ion hybrid resonances in a multi-fluid plasma and at the electron plasma frequency. Alfven resonances play an important role on energy transport from the outer to inner regions of magnetospheres. The linear polarization of electromagnetic ion cyclotron (EMIC) waves can be explained by mode conversion at the ion-ion hybrid (IIH) resonance in multi-ion plasma when externally driven compressional waves propagate into an increasing or decreasing heavy ion concentration. Compressional waves also can interact with Mercury's magnetosphere exciting IIH resonances as global eigenmodes. We show how mode converted waves at the IIH resonance develop in magnetospheric geometries and discuss implications for field-line resonances at Mercury. As another example of LMC, we discuss how Langmuir waves convert to electromagnetic waves in density gradients and implications type II and III radio bursts. Through the LMC, both right- and left-hand polarized wave modes are produced providing an explanation of linear/partial polarized type II and III radio bursts without invoking depolarization.