Kinetic modeling of x-ray laser-driven solid Al plasmas via particle-in-cell simulation.

Area of Science:

• Plasma physics
• Atomic physics
• Computational physics

Background:

• Intense X-ray Free Electron Laser (XFEL) radiation drives solid-density plasmas.
• Nonthermal electrons from photoionization and Auger ionization seed these plasmas.
• Current simulation codes often assume instantaneous thermalization of source electrons.

Purpose of the Study:

• Introduce and validate the collisional particle-in-cell code, picls.
• Enable fully kinetic simulation of XFEL-driven plasmas with radiation transport.
• Investigate XFEL-driven solid-density aluminum (Al) plasmas.

Main Methods:

• Extended picls with self-consistent radiation transport and Monte Carlo ionization models.
• Simulated two experiments at the Linac Coherent Light Source (LCLS).
• Compared picls results with Ecker-Kröll and Stewart-Pyatt models, and with collisional-radiative (CR) code scfly.

Main Results:

• picls simulations using the Ecker-Kröll model showed improved agreement with experimental pulse transmissions.
• Quantitative agreement was found between picls and scfly for Kα emissions and pulse transmissions.
• Nonthermal electron effects were found to be negligible under the investigated experimental conditions.

Conclusions:

• The picls code provides a robust tool for simulating XFEL-driven plasmas.
• The Ecker-Kröll model is more suitable than the Stewart-Pyatt model for these simulations.
• Further validation of kinetic plasma simulations in XFEL research is demonstrated.