Laboratory Astrophysics Studies of Magnetized Collisionless Shock Precursors and the ³He³He Proton Spectrum at the OMEGA Laser Facility

Abstract

Laboratory astrophysics enables the study of astrophysical systems in the lab. There are broadly two types of laboratory astrophysics experiments: macrophysics and microphysics. Macrophysics experiments study a scaled down version of an astrophysical system while microphysics experiments create a small volume of matter with the same conditions as an astrophysical system. This thesis details work related to both macrophysics and microphysics laboratory astrophysics experiments. For the macrophysics contribution, collisionless shocks experiments were conducted at the OMEGA laser facility using the new gas jet platform. Collisionless shocks are shock waves formed through plasma processes when particle collisions are negligible. These shocks can form as bow shocks in the interaction between the solar wind and planetary ionospheres and can accelerate charge particles to high energies. In the experiment, a CH plasma flow collides with a hydrogen gas jet plasma to create a forming magnetized collisionless shock. Different diagnostics show a moving density jump, strong magnetic fields, and the acceleration of electrons. These observations coupled with magnetohydrodynamics and kinetic particle-in-cell simulations paint a complete physical picture of the forming shock in a configuration similar to the bow shock of Venus. Late time proton radiographs show a complicated structure which is studied for magnetic turbulence. Turbulence is important in several astrophysical systems, especially collisionless shocks where it dissipates shock kinetic energy and is essential for accelerating charged particles to cosmic ray energies. Magnetic power spectra extracted from proton radiography data show a break in the spectrum between the ion Larmor radius and the ion skin depth for high plasma β, a sign of kinetic turbulence. Large scale particle-in-cell simulations of high β turbulence also have this feature showing that the experimental data are consistent with high β kinetic turbulence. For the microphysics contribution, a new proton spectrometer is designed for measurements of the ³He³He proton spectrum. The ³He³He fusion reaction is the last step of the proton-proton I chain which produces the majority of the sun’s power. Previous experiments were not able to measure the ³He³He proton spectrum below 6 MeV. A new proton step range filter (SRF) spectrometer with a larger energy range is designed using a Monte Carlo tool. This tool uses Geant4 and is able to self-consistently apply the instrument response function. The new SRF design is validated and a method for analyzing experimental data using the Monte Carlo code is presented.