UCLA

Shock waves, where supersonic and subsonic plasma flows meet, are primiary sites for charged particle acceleration in various space plasma environments, including astrophysical and planetary bow shocks. Earth's bow shock is the most accessible site for experimental investigations of this acceleration process with in-situ measurements. Relativistic electrons, which are often observed near planetary bow shocks, show energy levels significantly higher than those of solar wind electrons, by at least four orders of magnitude. However, present electron acceleration mechanisms, viewed individually, fail to explain the full energization that electrons undergo in such settings. This thesis presents a compound scenario for such acceleration. Specifically, it investigates the combined role of electromagnetic whistler-mode waves and other plasma wave modes in electron acceleration and scattering in the foreshock region, studied in conjunction with Fermi and betatron acceleration, and applied in a realistic setting, as informed by multi-satellite observations. Whistler-mode waves are known for their role in electron scattering and acceleration in the inner magnetosphere, facilitating our studies of their role under the plasma conditions found in the foreshock. Statistical studies using in-situ observations from the THEMIS and MMS missions are utilized to reveal the properties of whistler-mode waves and their resonant interactions with electrons near Earth’s bow shock and foreshock. Theoretical approaches are then developed to describe the effects of these waves on electron dynamics. Finally, a comprehensive acceleration model is constructed, which successfully replicates the observed near-relativistic electron energy spectra. The model assumes that acceleration to energies up to several hundred keV involves a complex, compound process, including shock acceleration, adiabatic heating, and resonant scattering by multiple plasma wave modes - a phenomenon previously underexplored. The model not only reproduces the observed power-law electron spectrum of ~ E^{-4} but also addresses the longstanding challenge of generating energetic and relativistic electrons at planetary shocks. This extends the theoretical framework of electron-wave interactions from the inner magnetosphere to the foreshock and opens new avenues for numerical simulations of electron acceleration in astrophysical shocks, potentially revolutionizing our understanding of particle acceleration in space plasmas.