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Nanoplasma formation by high intensity hard x-rays
Tetsuya Tachibana, Zoltan Jurek, Hironobu Fukuzawa, Koji Motomura, Kiyonobu Nagaya, Shin-ichi Wada, Per Johnsson, Marco Siano, S. Mondal, Yuta Ito, M. Kimura, T. Sakai, K. Matsunami, H. Hayashita, J. Kajikawa, Xiao-Jing Liu, E. Robert, Catalin Miron, Raimund Feifel, John P. Marangos, Kensuke Tono, Yuichi Inubushi, Makina Yabashi, Sang-Kil Son, Beata Ziaja, Makoto Yao, Robin Santra, and Kiyoshi UedaSci. Rep. 5, 10977 (2015)
Using electron spectroscopy, we have investigated nanoplasma formation from noble gas clusters exposed to high-intensity hard-x-ray pulses at ∼5 keV. Our experiment was carried out at the SPring-8 Angstrom Compact free electron LAser (SACLA) facility in Japan. Dedicated theoretical simulations were performed with the molecular dynamics tool XMDYN. We found that in this unprecedented wavelength regime nanoplasma formation is a highly indirect process. In the argon clusters investigated, nanoplasma is mainly formed through secondary electron cascading initiated by slow Auger electrons. Energy is distributed within the sample entirely through Auger processes and secondary electron cascading following photoabsorption, as in the hard x-ray regime there is no direct energy transfer from the field to the plasma. This plasma formation mechanism is specific to the hard-x-ray regime and may, thus, also be important for XFEL-based molecular imaging studies. In xenon clusters, photo- and Auger electrons contribute more significantly to the nanoplasma formation. Good agreement between experiment and simulations validates our modelling approach. This has wide-ranging implications for our ability to quantitatively predict the behavior of complex molecular systems irradiated by high-intensity hard x-rays.
Tags: Ar, Xe, cluster, molecular dynamics, SACLA, experiment, XFEL, XMDYN, XATOM, CFEL, DESY
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