Impact of free electron degeneracy on collisional rates in plasmas

Abstract

Degenerate plasmas, in which quantum effects dictate the behavior of free electrons, are ubiquitous on earth and throughout space. Transitions between bound and free electron states determine basic plasma properties, yet the effects of degeneracy on these transitions have only been theorized. Here, we use an x-ray free electron laser to create and characterize a degenerate plasma. We observe a core electron fluorescence spectrum that cannot be reproduced by models that ignore free electron degeneracy. We show that degeneracy acts to restrict the available electron energy states, thereby slowing the rate of transitions to and from the continuum. We couple degeneracy and bound electron dynamics in an existing collisional-radiative code, which agrees well with observations. The impact of the shape of the cross section, and hence the magnitude of the correction due to degeneracy, is also discussed. This study shows that degeneracy in plasmas can significantly influence experimental observables such as the emission spectra, and that these effects can be included parametrically in well-established atomic physics codes. This work narrows the gap in understanding between the condensed-matter and plasma phases, which coexist in myriad scenarios.

Review of the 10th Non-LTE code comparison workshop

“…At higher temperatures, even the models with similar treatments of continuum lowering diverge significantly. Finally, we note that while a partially degenerate electron energy distribution can significantly reduce collisional rates [1,38,39] when temperatures are near the Fermi energy (12 -16 eV for the two cases), the impact is not evident here because degenerate rates still follow the detailed balance relations that enforce LTE populations, and in steady-state without an external radiation field the lower-temperature cases here are firmly in LTE. Detailed charge state distributions and emission spectra are given in Fig.…”

Stability and evolution of electromagnetic solitons in relativistic degenerate laser plasmas

“…Such high-density degenerate plasmas may be directly created via ultraviolet or x-ray free electron lasers (Williams et al. 2019). Also, by varying the laser intensity, partially or fully degenerate plasmas can also be produced in the laboratory (Hayes et al.…”

“…in the interior of white dwarfs, neutron star and magnetars with particle number density ranging from 10 26 cm −3 to 10 34 cm −3 . Such high-density degenerate plasmas may be directly created via ultraviolet or x-ray free electron lasers (Williams et al 2019). Also, by varying the laser intensity, partially or fully degenerate plasmas can also be produced in the laboratory (Hayes et al 2020), which makes laser produced plasmas useful in recreating astrophysical plasmas in the laboratory.…”