Date of Award
Doctor of Philosophy (PhD)
Heliosphere (Astrophysics), Ion-atom collisions.
The heliosphere is a cavity carved out of the interstellar medium by the supersonic outflow of solar wind (SW) from the Sun. The local interstellar medium (LISM) is partially ionized with the neutral particles penetrating the heliosphere unimpeded by the electric and magnetic (EM) fields. In order to model the heliosphere, both a magnetohydrodynamic (MHD) and a kinetic Boltzmann (or fluid) approach should be used to represent the plasma and neutral particles, respectively. Even though neutral particles are unaffected by EM fields, certain collisions that exchange charge between ions do occur called charge-exchange. This charge-exchange process, in the form of source terms, is the glue coupling the plasma and neutrals together. The characteristic collision length of charge-exchange is roughly the size of the heliosphere itself, which is the reason for needing both MHD and a kinetic approach. In this work, we have developed analytic solutions to the charge-exchange source terms between a Maxwellian species and other non-Maxwellian distributions, namely the kappa and regularized kappa distributions. With these solutions, we studied various assumptions about the form of the cross-section, which could be either an arbitrary function, a power-law, or a hard-sphere and also developed methods to approximate the characteristic interaction speed. In light of our new findings, we suggested several applications ranging from an energy-dependent cross-section with kappa-distributed protons to kappa-distributed energetic neutral atoms (ENAs). The analytic solutions we derived allows researchers to understand the charge-exchange source terms for a large number of parameter choices without having to solve complicated, high dimensional integrals numerically. In effect, this enables modelers to include higher fidelity source terms in heliospheric simulations that contains information about pickup ions (PUIs) or ENAs directly.
DeStefano, Anthony M., "Ion-atom charge-exchange collisions and their effect on plasma-neutral coupling" (2019). Dissertations. 198.