Plasma Physics in Strong Field Regimes

Abstract

In strong electromagnetic fields, new plasma phenomena and applications emerge, whose modeling requires analytical theories and numerical schemes that I will develop in this thesis. Based on my new results of the classical plasma model, the role of strong magnetic fields during laser-plasma interactions can now be understood. Moreover, based my new quantum electrodynamics (QED) models for plasmas, it is now possible to understand strong-field QED effects in astrophysical environments and test them in laboratory settings.

In the classical regime, starting from megagauss magnetic fields, scattering of optical lasers becomes manifestly anisotropic. For the first time, a convenient formula for three-wave coupling coefficient in arbitrary geometry is obtained and evaluated. By solving the fluid model to the second order, I provide an alternative perspective of parametric instability and unveil how magnetic fields affect collective scattering of plasma waves. As an application, I predict that magnetic resonances can be utilized to mediate laser pulse compression. Using magnetized plasma mediation, it is not only possible to achieve higher output intensity for optical lasers with more engineering flexibility, but also possible to compress UV and soft X-ray pulses that cannot be compressed using existing techniques. Taking advantage of the emerging feasibility of strong magnetic fields, I have thus identified a pathway to next-generation powerful lasers, whose viability is supported by particle-in-cell simulations.

In even stronger magnetic fields or intense laser fields, relativistic quantum effects become important. At that point, plasma models based on QED are necessary. Allowing for nontrivial background fields, I develop a new formalism for QED plasmas by computing the effective action using path integrals. My new formalism enables simple wave dispersion relations in strongly magnetized plasmas to be obtained for the first time, based on which the modified Faraday rotation and the anharmonic cyclotron absorptions near X-ray pulsars can now be correctly interpreted. Beyond the perturbative regime, I extend real-time lattice QED to a unique tool for plasma physics, especially when collective scales overlap with relativistic-quantum scales. Applying this numerical tool to laser-plasma interactions, I demonstrate, for the first time, transition from wakefield acceleration to electron-positron pair production, when the laser fields exceed the Schwinger threshold.