Charge state distribution and energy loss for 100 keV protons moving in discharge H plasmas

Abstract

Ab initio theoretical simulations are performed for charge state distribution and energy loss of a 100 keV proton beam propagating in partially ionized discharge H plasmas. In the simulation, all transition processes are calculated accurately among eight main projectile electronic configurations including the most relevant excited states. Projectile configuration evolution is computed by solving rate equations, and the effective charge state Zeff is obtained during all discharge stages. A new way is suggested to get the projectile energy loss with the contributions of all configurations considered separately. Such obtained energy losses are in the best agreement with experimental measurements among all the related models. However, both traditional empirical models with estimated Zeff and the standard stopping model are found invalid in this case, and relevant reasons are explored. Projectile capture and ionization processes in plasmas are found to be especially important in the stopping process. We predict that projectile excited states would make a much larger difference in energy deposition when a higher atomic number projectile is chosen, which has not been deeply recognized in plasmas yet.