In many areas of plasma physics, the interaction of energetic particles with boundaries and background gas plays a key role in the dynamics. Examples include wakefield accelerators, high power microwave sources, and fusion devices. There are several key phenomena involved in these interactions such as collisions, radiation and photoemission. For this work, we adopt particle-in-cell plasma simulation codes by developing and adding models to existing 1D and 2D. This work comprises three parts: a relativistic collision model, a particle-fluid/particle-particle hybrid collision model, and radiation and photoemission generation by energetic particle interaction with solid surfaces.
Previously, collision models were developed for the particle simulation of plasmas in the classical regime, however, the classical model breaks down as energies approach the relativistic regime. In this work, a relativistic Monte Carlo collision model is developed, adding relativistic collision dynamics and improved relativistic differential cross sections. With this model, we extend our simulation capabilities to predict and analyze the time-dependent performance of wakefield accelerators.
In many practical collisional plasma models, such as in oxygen, nitrogen, or air, both target and projectile species in collisions may be particle species, reacting with many other particle and fluid species. A hybrid collision model is introduced to model the reactions between particle and fluid species as well as those between particle and particle species. A hybrid collision model enables particle-in-cell simulation of air or oxygen dielectric breakdown in high power microwave devices, as well as hydrocarbon collisions in the diverter sheath region in a tokamak magnetic fusion reactor.
A computational model has been developed to describe xray generation for energetic particle impact with surfaces in the particle simulation of plasmas, and photoemission of electrons due to photon impact (e.g. xrays). Xray and photoemission may be one of the sources for generation of a first electron, leading to dielectric multipactor breakdown at the vacuum window in high power microwave devices. We are able to predict the energy and angular spectra of xrays generated by energetic impact of electrons on surfaces in high power microwave devices with the xray generation model.
After building each model, we compared our simulation results with experiments and analytic solutions in order to verify our models and demonstrate the new modeling capabilities. The models developed in this work expand the regime of validity for particle simulation of collisional plasmas to higher energy, and enable study of interaction of energetic charged particles with surfaces, background gas, and reactive plasma constituents.