Clocking femtosecond collisional dynamics via resonant X-ray spectroscopy

Journal article

Electron-ion collisional dynamics is of fundamental importance in determining plasma transport properties, non-equilibrium plasma evolution and electron damage in diffraction imaging applications using bright x-ray free-electron lasers (FELs). Here we describe the first experimental measurements of ultra-fast electron impact collisional ionization dynamics using resonant core-hole spectroscopy in a solid-density magnesium plasma, created and diagnosed with the Linac Coherent Light Source x-ray FEL. By resonantly pumping the 1s ! 2p transition in highly-charged ions within an optically-thin plasma we have measured how off-resonance charge states are populated via collisional processes on femtosecond times scales. We present a collisional cross section model that matches our results and demonstrates how the cross sections are enhanced by dense-plasma effects including continuum lowering. Non-LTE (local thermodynamic equilibrium) collisional radiative simulations show excellent agreement with the experimental results, and provide new insight on collisional ionization and three-body-recombination processes in the dense plasma regime.

Authors: van den Berg, Q; Fernandez-Tello, E; Burian, T; Chalupský, J; Chung, H

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: American Physical Society
• Journal: Physical Review Letters
• Volume: 120
• Issue: 5
• Article number: 055002
• Publication date: 2018-02-01
• Acceptance date: 2017-11-28
• DOI: 10.1103/PhysRevLett.120.055002
• EISSN: 1079-7114
• ISSN: 0031-9007