Thermodynamic quantities of a two-dimensional Yukawa system, a model for various systems including single-layered dust particles observed in dusty plasmas, are obtained and expressed by simple interpolation formulas. In the domain of weak coupling, the analytical method based on the cluster expansion is applied and, in the domain of intermediate and strong coupling, numerical simulations are performed. Due to reduced dimensionality, the treatment based on the mean field fails at the short range and exact behavior of the binary correlation is to be taken into account even in the case of weak coupling.

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We scrutinize the behaviour of the eigenvalues of a hydrogen atom in a quantum plasma as it interacts with an electric field directed along θ = π and is exposed to linearly polarized intense laser field radiation. We refer to the interaction of the plasma with the laser light as laser-plasma. Using the Kramers-Henneberger (KH) unitary transformation, which is the semiclassical counterpart of the Block-Nordsieck transformation in the quantized field formalism, the squared vector potential that appears in the equation of motion is eliminated and the resultant equation is expressed in the KH frame. Within this frame, the resulting potential and the corresponding wavefunction have been expanded in Fourier series, and using Ehlotzky's approximation we obtain a laser-dressed potential to simulate an intense laser field. By fitting the exponential-cosinescreened Coulomb potential into the laser-dressed potential, and then expanding it in Taylor series up to ( ) α O r , 4 0 9 , we obtain the eigensolution (eigenvalues and wavefunction) of the hydrogen atom in laser-plasma encircled by an electric field, within the framework of perturbation theory formalism. Our numerical results show that for a weak external electric field and a very large Debye screening parameter length, the system is strongly repulsive, in contrast with the case for a strong external electric field and a small Debye screening parameter length, when the system is very attractive. This work has potential applications in the areas of atomic and molecular processes in external fields, including interactions with strong fields and short pulses.

Single-layered two-dimensional crystals of dust particles are often observed in dusty plasma experiments and the data on their structure can be obtained by analyzing the images usually taken by charge-coupled [corrected] device cameras. We give here some formulas for practical purposes of estimating the screening length and the electric charge on a dust particle from the surface density and the radius of such finite two-dimensional dust crystals. The formulas are derived on the basis of our theoretical approach which has been successful in reproducing results of molecular-dynamics simulations on dusty plasmas. An example of application is also shown.

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