Tokunari Kishimoto

Yukawa system (dusty plasma) in one-dimensional external fields

Abstract The behavior of the Yukawa system in external one-dimensional force fields is analyzed by molecular dynamics simulation. The formation of layered structures at low temperatures is observed and the relation between the number of layers and characteristic parameters of the system is obtained. Periodic boundary conditions are imposed in two dimensions and deformations of periodic boundaries are allowed in order to reduce the effect of boundaries without placing too much constraint on the symmetry.

Structure of dusty plasma in external fields : Simulation and theory

To investigate various structures experimentally observed in dusty plasmas, a Yukawa system in a one-dimensional external field is simulated by molecular dynamics with deformable periodic boundary conditions and constant volume and temperature. At low temperatures, particles are organized into thin layers (sheets) and the number of layers (sheets) changes with the parameters, the whole system being rearranged from nearly equipartitioned layers to other nearly equipartitioned layers. The shell (sheet) model, which has been successful for confined one-component plasmas, is extended to this system and the results of numerical simulations are reproduced accurately. The effect of the cohesive energy in each layer is of essential importance to reproduce discrete changes in the number of sheets.

Dusty plasmas under microgravity

The structures of Yukawa systems spherically confined under the condition of microgravity are analyzed by molecular dynamics simulations. It is shown that the system is separated into the outer and the inner parts and well-developed shells appear in the outer part at low temperatures. In the case of Yukawa mixtures, there occurs the separation of species according to the magnitude of charges.

Two-component nonequilibrium nonneutral plasma in Penning-Malmberg trap

The behavior of the two-component nonneutral plasma in the Penning-Malmberg trap is analyzed by simulations and theoretical approaches. The parameters expected in experiments of antiproton cooling by electrons are assumed. The relaxation of antiproton energy is followed by the rate equation with proper account taken into account for the slow transfer of energy between parallel and perpendicular components of strongly magnetized electrons. The equilibrium distribution of each species are obtained by molecular dynamics simulations for various values of parameters and the results are reproduced by theoretical calculations to a good accuracy. The condition for the centrifugal separation is obtained.

STRUCTURAL TRANSITIONS IN CONFINED YUKAWA SYSTEM AS A MODEL OF DUSTY PLASMAS AND CHARGE STABILIZED COLLOIDAL SUSPENSIONS

We have analyzed the Yukawa system confined by external fields. The structure in the ground state is obtained as a phase diagram in the parameter domain and we have reproduced the diagram by taking intralayer correlation energy into account. Ordered structure in each layer melts before the structure in z-direction and critical temperatures of intralayer melting is determined including the case of two-dimensional Yukawa system. It is shown that the critical temperature is enhanced when neighboring layers are closer.

Structure and madelung energy of Coulomb clusters

The ground state of the system of charged particles of one species confined by the three-dimensional, isotropic, and parabolic potential is investigated by molecular dynamics simulations. It is shown that, with the increase of the system size or the number of particles in the system N, the ground state changes from the shell-structured system to the finite bcc lattice with reconstructed surface. The critical value of the transition is estimated to be between N=104 and N=2×104. The nucleation of the bcc lattice in the shell-structured cluster of 2×104 ions is observed.

On the Madelung energy of spherical Coulomb clusters

Abstract We perform large-scale molecular dynamics (MD) simulations of Coulomb clusters in a spherical trapping field. The fast multipole method have been employed to simulate clusters of up to 5×10 4 particles while previous investigations are limited to clusters of less than 5000 particles. It is found that the Madelung energy of bcc clusters with reconstructed surfaces is substantially smaller than the extrapolated values based on the previous results for smaller multilayered icosahedral clusters.

Structures and Structural Transitions in Strongly-Coupled Yukawa Dusty Plasmas and Mixtures

Publisher Summary Physics of dusty plasmas, assemblies of macroscopic particles immersed in plasmas, is closely related to important practical problems in plasma processes of semiconductor manufacturing and also to subjects of basic statistical physics. This chapter addresses this question through numerical simulations and theoretical analyses. The contribution of the correlation (cohesive) energy in dusty plasma is of essential importance in these phenomena and they can be reproduced by taking the correlation energy into account properly. The one-dimensional confinement in three dimensions and the radial confinement in two dimensions are described in the chapter. The results of simulations have been reproduced to a good accuracy in both cases. It is shown that the inclusion of the correlation energy or the effect of strong coupling is of essential importance in the theory. A crossover from the surface freezing of Coulomb system to surface melting of systems of short-ranged interactions is observed.

Structures and dynamics of dusty plasmas and dusty plasma mixtures

Dusty plasmas can be regarded as assemblies of Yukawa particles in a one-dimensional potential well. We extend the analyses on dusty plasmas in two directions: the two-dimensional Yukawa system and Yukawa mixtures. (1) Under appropriate conditions at low temperatures, dust particles sit in a plane which is perpendicular to the gravitational field. When they are also confined laterally by an electrode, we have a finite two-dimensional system of Yukawa particles. The low temperature structures are obtained by molecular dynamics simulations and the results are reproduced by theoretical analyses. Through these analyses we show that the correlation energy of the Yukawa system plays an essential role in structure formations. As for dynamics of this system, a crossover from the surface freezing of Coulomb system to surface melting of systems of short-ranged interactions is observed. (2) In the case of mixtures, we have an extra parameter characterizing the difference in the gravity on each species. We obtain the low temperature structures of this system and compare them with theoretical predictions based on the results for the case of one component.