ISSN 0021-3640, JETP Letters, 2009, Vol. 90, No. 6, pp. 444–448. © Pleiades Publishing, Ltd., 2009. Original Russian Text © B.A. Klumov, G.E. Morfill, 2009, published in Pis’ma v Zhurnal Éksperimental’noі i Teoreticheskoі Fiziki, 2009, Vol. 90, No. 6, pp. 489–493. 444 Interest in processes in a plasma containing micro- particles has increased considerably in recent years. Such a plasma is usually called a complex plasma or dusty plasma (see, e.g., [1, 2]). First, complex plasma is of interest due to its great abundance in nature. Interstellar clouds, gas–dust clusters, planetary rings [3], comet atmospheres [4], and the ionospheres and magnetospheres of planets are complex plasmas to a certain extent, where dust particles often decisively affect the state of the system containing them. For example, noctilucent clouds [5] formed in the cold dusty upper Earth’s atmosphere are dusty structures determining the ionization properties of the mesos- phere. Dusty ejecta formed in the high-speed collision between celestial bodies of the solar system provide important information on the chemical composition of the projectile and target [6], etc. Second, modern laboratory experiments make it possible to trace the behavior of a single microparticle providing the most detailed kinetic description of the properties of the ensemble of dust particles. Owing to these circum- stances, dusty plasma is an attractive tool for studying various fundamental physical problems such as phase transitions [7, 8], hydrodynamic instabilities [9], crys- tallization waves [10], etc. One of these important problems is a change in the local order of the dust component of complex plasma in the process of its crystallization and melting, which is discussed in this work. Note that it is technically possible now to deter- mine the x, y, and z coordinates of N ~ 10 5 micropar- ticles in a characteristic time of τ s  1–10 s [11–13], which for the time being is larger than the typical times of the indicated phase transitions in the complex plasma. A decrease in τ s by an order of magnitude will allow for an experimental investigation of the kinetics of the melting and crystallization of the complex plasma; such an advance is expected in the near future. Under laboratory conditions, a complex (dusty) plasma is usually obtained by introducing microparti- cles into a weakly ionized low-temperature gas-dis- charge plasma of low-pressure inert gases. The recom- bination of electrons and ions on the surface of dust particles gives rise to the fast charging of the particles; the charge value depends on the size of a particle and the plasma parameters; for example, a 1-μm particle in a usual microwave discharge in argon acquires a negative charge of Z d ~ 10 3 e, where e is the elementary charge. Such a large charge of the microparticle often results in the strong nonideality of the dust compo- nent, which can be in various phase states, i.e., can be manifested as a gas, liquid, or crystal. The crystal state of the dust component of the complex plasma (plasma crystal) was experimentally discovered in 1994 [14, 15], being theoretically predicted in 1986 [16]. Owing to the fast diffusion of electrons towards the walls of the discharge chamber, the central region of the gas discharge is positively charged and is a poten- tial well (confinement) for negatively charged micro- particles. The profile of the confining potential in the Structural Properties of Complex (Dusty) Plasma upon Crystallization and Melting B. A. Klumov a, b and G. E. Morfill a a Max Planck Institut für Extraterrestrische Physik, D-85740 Gaiching, Germany b Joint Institute for High Temperatures, Russian Academy of Sciences, Izhorskaya ul. 13, Moscow, 125412 Russia Received August 11, 2009 A change in the local order of a bounded complex (dusty) plasma in the process of its crystallization and melt- ing has been examined by molecular dynamics simulations. The dynamics of microparticles is considered in the framework of a Langevin thermostat, the pair interaction between charged particles is described by a screened Coulomb potential (Yukawa potential) with the hard wall potential as a confinement. It has been shown that the beginning of the crystallization of such a system is accompanied by the formation of clusters with the hexagonal close packed (hcp) structure; a noticeable number of these clusters are then transformed to the face centered cubic (fcc) phase. A plasma crystal formed after crystallization consists of the metastable hcp phase, fcc clusters, and a small number of clusters with a body centered cubic (bcc) crystal lattice. Begin- ning with a certain threshold value of the thermostat temperature, the number of fcc/bcc clusters decreases sharply with increasing temperature, which is an important signature of the beginning of the melting of the plasma crystal. PACS numbers: 52.27.Lw, 61.20.Ja, 64.60.Cn DOI: 10.1134/S002136400918009X