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16Complex Systems of Charged Particles and their Interactions with Electromagnetic Radiation 2016
SELF-CONSISTENT APPROACH FOR DESCRIPTION OF PHASE TRANSITIONS IN
PLASMA
G.E. Norman, I.M. Saitov
Joint Institute for High Temperatures of RAS, Moscow, Russia, e-mail: [email protected]
An approach is developed [1], which provides a self-consistent description of optical and electronic properties of warm dense matter (WDM) and dense plasma. Optical properties include reflectance (normal and polarized), Brewster angle, absorption, transmission. Corrections are considered which allow for the finite width of the transient layer at the plasma border. Electronic properties are conductivity, plasma frequency and electronic density of states. The density functional theory is used for computation of the dielectric function (DF). DF is used as the basic value for the calculation of the plasma properties. The core electrons are considered by means of the projector augmented wave (PAW) method potential, which is non-local. The Kohn-Sham set of equations with the PAW potential is solved for valent electrons. Due to the non-locality of the PAW potentials, the longitudinal expression for the imaginary DF is used. The method is suggested to calculate plasma frequency, which is based on the sum rule. The effective free electron number density is also treated.
For validation of the approach we provide theoretical analysis of the experimental data on reflectances of shocked compressed xenon for normal incidence of laser radiation [2, 3] as well as for the dependence of s- and p- polarized reflectivity on incidence angle [4]. Three wavelengths 1064 nm, 694 nm and 532 nm are considered. For A =1064 nm and 694 nm good agreement with the experiment is obtained for normal incidence of the laser radiation without introduction of the wave front broadening. However, for 532 nm, the calculated reflectances are overestimated in comparison with the experiment. The discrepancy can be related to the nonzero width of the region with a non-uniform profile of density (wave front), which leads to an optical non-uniformity. The width of the wave front is estimated under assumption of the linear dependence of the DF on distance.
A first-order fluid-fluid phase transition is observed experimentally in warm dense hydrogen [5-10]. It is attributed to either pressure metallization, or pressure dissociation, or liquid-liquid, or plasma phase transition. The nature of the transition remains unclear. We present theoretical evidences in this work that it is a plasma phase transition. Dependencies of the plasma frequency, conductivity, pair correlation function and density of electron states on plasma density are investigated for warm dense hydrogen. Plasma frequency jump is calculated to verify the nature of the phase transition. The change of the pair distribution function points to the consistent change of the ionic structure because of the electronic structure change. The relation between jumps in plasma frequency, conductivity, reflectivity and a first-order phase transition is discussed. Brazhkin et al [11] observe the triple point experimentally on the melting line in selenium.
The work is supported by Grant No. 14-19-01295 of the Russian Science Foundation. References
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[3] Reinholz H., Röpke G., Morozov I. et al., J. Phys. A: Math. Gen. 2003, 36, 5991.
[4] Zaporozhets Yu. B., Mintsev V., Gryaznov V. et al., Contrib. Plasma Phys., 2010, 50, 60.
[5] Loubeyre P. et al, High Press. Res. 2004, 24, 25.
[6] Fortov V. et al, Phys. Rev. Lett. 2007, 99, 185001.
[7] Dzyabura V., Zaghoo M., and Silvera I., PNAS USA, 2013, 110, 8040.
[8] Zaghoo M., Salamat A., and Silvera I.F.. arXiv:1504.00259, 2015.
[9] Ohta K. et al., Scientific Reports, 2015, 5, 16560.
[10] Knudson M. D. et al., Science, 2015, 348, 1455.
[11] Brazhkin V., Voloshin R., and Popova S., JETP Lett., 1990, 50, 424.
