65 / 2020-03-13 21:52:48

Ionization potential depression and line shifts

X-ray spectroscopy, ionization potential depression, line shifts

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In a low-density plasma, where atoms and ions are essentially free, atomic population kinetics has been very successful for various scientific and technical disciplines. As density increases, the free atom model breaks down and the energy levels are perturbed. The perturbation manifests itself essentially in a broadening and a shift. These phenomena can be observed with high-resolution spectroscopy [1] and is of great interest in thermodynamics, ICF and also for the understanding of the various radiative properties.
Numerous corrections to the free-atom picture have been developed among which are the models of Debye-Hückel DH [2], the Ion Sphere IS [3], Ecker & Kröll EK [4], Stewart & Pyatt SP [5], the Arbitrary Perturbation Potential APP theory [6] and the Atomic-Solid-Plasma ASP model [7]. Although these models have contributed to a better understanding of IPD, the current set of experimental data does still not provide a unique understanding. E.g., it was claimed [8] that IPD measurements carried out with an XFEL support the early model of EK whereas the well-accepted model of SP is in disagreement with the data. On the other hand, IP measurements carried out at high-energy density laser experiments [9,10] confirmed the validity of the SP model and demonstrated a worse agreement with the EK model. In the framework ASP it has been shown [7], that both, EK and SP fail to interpret the data: they fail with respect to both, absolute values and Z-scaling relations. Previous statements [8] turned out to be based on a misconception and accidental coincidence in scaling relations.
The present talk provides an overview of the ongoing controversy discussion of IPD, illuminates why current models fail in some experiments while describing well other ones.
Keywords: X-ray spectroscopy, ionization potential depression, line shifts
References
[1] O. Renner, F.B. Rosmej, Matter and Radiation at Extremes, Review, Vol. 4, 024201 (2019).
[2] P. Debye, E. Hückel, Zeitschrift für Physik 24, 185 (1923).
[3] G. Zimmermann, R. Moore, JQSRT 23, 417 (1980).
[4] G. Ecker, W. Kröll, Physics Fluids 6, 62 (1963).
[5] J. Stewart, K. Pyatt, Astrophys. J. 144, 1203 (1996).
[6] F.B. Rosmej, K. Bennadji, V.S. Lisitsa, Physical Review A 84, 032512 (2011).
[7] F.B. Rosmej, Letter J. Phys. B. 51, 09LT01 (2018).
[8] O. Ciricosta et al., Phys. Rev. Lett 109, 065002 (2012).
[9] L.B. Fletcher et al., Phys. Rev. Lett. 112, 145004 (2014).
[10] D.J. Hoarty et al., Phys. Rev. Lett. 110, 265003 (2013).