Significant Contribution of Projectile Excited States to the Stopping of Slow Helium Ions in Hydrogen Plasma

TL;DR

This study combines experimental and theoretical methods to show that projectile excited states significantly enhance the stopping power of slow helium ions in hydrogen plasma, resolving discrepancies in energy loss predictions.

Contribution

It introduces a comprehensive model including projectile excited states and radiative decays, improving agreement with experimental data on ion stopping in plasma.

Findings

Experimental data shows higher energy loss than semi-classical predictions.

Including excited states in models aligns calculations with experimental results.

Projectile excited states significantly increase ion stopping in plasma.

Abstract

The energy deposition and the atomic processes, such as the electron-capture, ionization, excitation and radiative-decays for slow heavy ions in plasma remains an unsolved fundamental problem. Here we investigate, both experimentally and theoretically, the stopping of 100 keV=u helium ions in a well-defined hydrogen plasma. Our precise measurements show a much higher energy loss than the predictions of the semi-classical approaches with the commonly used effective charge. By solving the Time Dependent Rate Equation (TDRE) with all the main projectile states and for all relevant atomic processes, our calculations are in remarkable agreement with the experimental data. We also demonstrated that, acting as a bridge for electron-capture and ionization, the projectile excited states and their radiative decays can remarkably influence the equilibrium charge states and consequently lead to a substantial increasing of the stopping of ions in plasma.