Physical properties of dense, low-temperature plasmas

Abstract

Plasmas occur in a wide range of the density-temperature plane. The physical quantities can be expressed by Green's functions which are evaluated by means of standard quantum statistical methods. The influences of many-particle effects such as dynamic screening and self-energy, structure factor and local-field corrections, formation and decay of bound states, degeneracy and Pauli exclusion principle are studied. As a basic concept for partially ionized plasmas, a cluster decomposition is performed for the self-energy as well as for the polarization function. The general model of a partially ionized plasma interpolates between low-density, nonmetallic systems such as atomic vapors and high-density, conducting systems such as metals or fully ionized plasmas. The equations of state, including the location of the critical point and the shape of the coexistence curve, are determined for expanded alkali-atom and mercury fluids. The occurrence of a metal-nonmetal transition near the critical point of the liquid-vapor phase transition leads in these materials to characteristic deviations from the behavior of nonconducting fluids such as the inert gases. Therefore, a unified approach is needed to describe the drastic changes of the electronic properties as well as the variation of the physical properties with the density. Similar results are obtained for the hypothetical plasma phase transition in hydrogen plasma. The transport coefficients (electrical and thermal conductivity, thermopower) are studied within linear response theory given here in the formulation of Zubarev which is valid for arbitrary degeneracy and yields the transport coefficients for the limiting cases of nondegenerate, weakly coupled plasmas (Spitzer theory) as well as degenerate, strongly coupled plasmas (Ziman theory). This linear response method is applied to partially ionized systems such as dense, low-temperature plasmas. Here, the conductivity changes from nonmetallic values up to those typical for plasmas in a narrow density range above 10 20 cm −3 for alkali-atom plasmas and 10 22 cm −3 for hydrogen plasma, respectively. Furthermore, the thermopower can change its sign in the same region which indicates that a nonmetal-to-metal transition occurs also in dense, low-temperature plasmas. The magnetic susceptibility and the Korringa relation are calculated for expanded fluid metals along the coexistence line within the partially ionized plasma model. The various contributions to the total susceptibility are derived from an extended RPA which takes into account local-field corrections as well as the influence of localized electron states. The metal-nonmetal transition indicated by an enhancement of the electronic paramagnetic volume susceptibility is strongly connected with the occurrence of charged clusters. Static structure factors are determined for expanded cesium and mercury within the MHNC scheme via effective ion-ion potentials which are derived from the polarization function within an extended RPA. The optical properties of dense plasmas, the shift and broadening of spectral lines, can also be derived within the Green's function technique. Some new results for the spectral line shape are discussed.