Agglomerations of Magnetized Particles in Complex Plasmas Abstract

Agglomerations of Magnetized Particles in Complex Plasmas Abstract Dust-dust interactions in complex plasmas are studied when effects of an external magnetic field become important. It is shown that the forces from particle magnetization may result in mutual repulsion as well as attraction. It was found that magnetized grains can coalesce, forming fieldaligned chains. A model was developed to determine the length of these structures. These finding were then applied to recent complex plasma experiments with paramagnetic particles. Recently, multilayer complex plasma structures field have been observed in an external magnetic field [1]. In these experiments, spherical micrometer sized paramagnetic particles were levitated in the sheath region. The levitation increased with the strength of the magnetic field. Moreover, some particles attracted each other and formed elongated structures—grain chains, oriented vertically, parallel to the field lines of the external magnetic field (Fig. 1). These features cannot be explained on the basis of pure electrostatic forces. Short-range dipole interactions between magnetized grains have to be invoked. Various mutual dust–dust interactions, including the forces due to induced magnetic and electric moments of the grains were considered. It turns out that the electromagnetic forces from particle magnetization and polarization may result in mutual repulsion as well as attraction (in Fig. 2. the interactions between two identical magnetized particles is shown schematically. The domain of angles corresponding to the attractive force is hatched ). The further analysis was mainly focused on particle coagulation. It was found that magnetized grains can coalesce, forming field-aligned chains. Since the “disruptive” electrostatic forces increase with the distance from the centre of a chain, whereas the “cohesion” magnetostatic forces decrease, there is an intrinsic length scale for these particle chains. A model was developed to determine the length of these structures. These finding were then applied to recent complex plasma experiments with paramagnetic particles. The theoretical estimations have revealed good agreement with experimentally observed data. Our results are of direct interest to laboratory studies of magnetized complex plasmas, indicating several new effects. In particular, the model predicts that the chain length will increase when the magnetic field is increased, when the permeability of the particle material is higher and the grain size is larger. In addition, our results could be of importance when studying dust particle agglomeration in astrophysical environments and for aerosol removal, cleaning and purification devices. References: 1. D. Samsonov, S. K. Zhdanov, V. Steinberg and G. Morfill, New J. Phys, 5, 24, (2003) V. V. Yaroshenko, G. E. Morfill, and D. Samsonov,