engleski

Self-organization of Coulomb particles in plasmas, from low to high temperatures

Plasmas containing particles, in addition to electrons and icons are called "dusty" or "colloidal plasmas". The charging of initially neutral particles starts by collection of electrons on their surface from surrounding plasma. The particles become negatively charged with respect to the plasma potential and can support a large number of electrons: a 1 mm particle can support ~104 electrons, or more. This leads to "ion dressing", because negative particles start to attract positive ions from the plasma, thus growing in size and mass. This ion shild is Debye shield. The repulsive interaction between particles immersed in the plasma is described by the screened Coulomb potential of the Yukawa type: , where k is the inverse screening length ( ; lD=Debye screening length). Depending on the value of the coupling parameter G (the ratio of the interaction strength and thermal kinetic energy), various kinds of particle selforganization (SO), in the form of Coulomb crystals and liquids, as well as the phase transitions between them, can occur. A well known example of selforganized charged particles (existing at room temperature), are the colloidal suspensions in liquids. Another example of ordered particle systems was observed in DC and RF plasmas from the room temperature up to a few hundreds degrees of Kelvin. Trajectories of particles, their regular and chaotic motion, as well as transition into one-dimensional (chains) two-dimensional (layers), and three-dimensional ordered structures, were clearly observed. The ordered particle systems were also observed at extremely low temperatures, close to the absolute zero (in the mK and mK range), in laser cooling of ions in Paul's and Penning traps. Surprisingly, the SO particle systems were found in the high-temperature, laser-generated plasmas (T ~ 103-104 K), existing for a short period of time. Generated by the high power laser pulses in pressurized gaseous atmospheres, they show the short range order of hcp and the long range order of bcc type, as well as disordered phase. The systems containing charged particles that mutually interact via screened Coulomb potential are known to exist from laboratory to astrophysical scales (galactic dusts). Recently (France, Netherlands), a 2D crystals of nano-particles formed in DC and RF plasmas were deposited (layer by layer) on the substrate to obtain homogeneous nanocrystals, what represents a new simple method for generation of controlled layered structures.

laser-matter interaction; Coulomb particles;plasma

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