A Simple Method for Modeling Collision Processes in Plasmas with a Kappa Energy Distribution
Abstract
We demonstrate that a nonthermal distribution of particles described by a kappa distribution can be accurately approximated by a weighted sum of MaxwellBoltzmann distributions. We apply this method to modeling collision processes in kappadistribution plasmas, with a particular focus on atomic processes important for solar physics. The relevant collision process rate coefficients are generated by summing appropriately weighted Maxwellian rate coefficients. This method reproduces the rate coefficients for a kappa distribution to an estimated accuracy of better than 3%. This is equal to or better than the accuracy of rate coefficients generated using “reverseengineering” methods, which attempt to extract the needed cross sections from the published Maxwellian rate coefficient data and then reconvolve the extracted cross sections with the desired kappa distribution. Our approach of summing Maxwellian rate coefficients is easy to implement using existing spectral analysis software. Moreover, the weights in the sum of the MaxwellBoltzmann distribution rate coefficients can be found for any value of the parameter κ, thereby enabling one to model plasmas with a timevarying κ. Tabulated Maxwellian fitting parameters are given for specific values of κ from 1.7 to 100. We also provide polynomial fits to these parameters over this entire range. Several applications of our technique are presented, including the plasma equilibrium charge state distribution (CSD), predicting line ratios, modeling the influence of electron impact multiple ionization on the equilibrium CSD of kappadistribution plasmas, and calculating the timevarying CSD of plasmas during a solar flare.
 Publication:

The Astrophysical Journal
 Pub Date:
 August 2015
 DOI:
 10.1088/0004637X/809/2/178
 arXiv:
 arXiv:1506.07127
 Bibcode:
 2015ApJ...809..178H
 Keywords:

 atomic data;
 atomic processes;
 Sun: flares;
 techniques: spectroscopic;
 Astrophysics  Solar and Stellar Astrophysics;
 Physics  Space Physics
 EPrint:
 Accepted in the Astrophysical Journal