Collisional and Radiative Processes in Optically Thin Plasmas

TL;DR

This paper reviews key collisional and radiative processes in optically thin plasmas, discussing diagnostics, equilibrium assumptions, and departures from equilibrium to enhance understanding of plasma microphysics.

Contribution

It provides a comprehensive overview of plasma processes and diagnostics, including non-equilibrium effects often overlooked in standard analyses.

Findings

Summarizes main collisional and radiative processes in optically thin plasmas.

Discusses diagnostics for microphysical plasma processes.

Analyzes departures from equilibrium and their diagnostic implications.

Abstract

Most of our knowledge of the physical processes in distant plasmas is obtained through measurement of the radiation they produce. Here we provide an overview of the main collisional and radiative processes and examples of diagnostics relevant to the microphysical processes in the plasma. Many analyses assume a time-steady plasma with ion populations in equilibrium with the local temperature and Maxwellian distributions of particle velocities, but these assumptions are easily violated in many cases. We consider these departures from equilibrium and possible diagnostics in detail.