Effects of Non-Maxwellian Electrons on the Ionization of XFEL-heated Neon Plasmas via the Collisional-Radiative Model

The collisional-radiative model, SCFLY, has been successfully employed on analysis of XFEL-matter interaction with the assumption of the fast electron thermalization. The fact that the electron-electron collisional frequency in dense plasmas is comparable to a few femtoseconds makes this assumption valid. However, it would not be the case in a relatively low-density plasma where the electron-electron collisional time estimated is comparable or larger than the plasma evolution time. In this work, SCFLY has been improved to equip the Boltzmann solver to monitor the evolution of electron energy distribution function (EEDF) in that condition. For benchmark purposes, the calculation of the charge state distribution (CSD) of Ne plasma heated by XFEL [1] has been performed. It reveals that higher electron-ion collisional rate driven by energetic electrons remaining in EEDF makes the CSD more consistent with the experimental results than the previous simulation [2] conducted by SCFLY.

[1] L. Young et al., Nature (London) 466, 56 (2010).

[2] O. Ciricosta, H.-K. Chung, R. W. Lee, and J. S. Wark, High Energy Density Phys. 7, 111 (2011).