Collective Grain Interaction I. New Paradigm for Plasma Crystal Formation

The concept of collective grain interaction in complex plasmas is developed for large non‐linearity in grain screening. It is shown that for the case where the characteristic collective radius exceeds the non‐linear screening radius the collective interactions can fully determine the non‐linear collective attraction well. Based on the physics of collective non‐linear grain attraction a new paradigm for plasma crystal formation is formulated according to which the plasma crystal formation is related with localization of grains in non‐linear collective attraction wells. Nonlinearity in screening is an important feature of new paradigm and takes into account that the grain charges are large in accordance with most experiments where the plasma crystals where observed. The physical consequence of large non‐linearity is the presence of relative large potential well at distances only several times larger then the non‐linear screening radius. The calculated location of the potential well is of the order of the observed inter‐grain distances in plasma crystals and the deepness of the potential well is close to observed temperature of phase transition. The new paradigm considers formation of plasma crystal as result of grain trapping in the collective non‐linear potential well. The grain interactions close to the position of the potential well are in this paradigm relatively weak contrary to previous paradigm relating the plasma crystal formation with strong grain interactions. This new approach opens the possibility for direct calculation of the deepness of the attraction collective well, the critical value of the coupling constant. Results of these calculations show a reasonable agreement with both the observations of crystals in low pressure high‐frequency discharges and in large pressure discharges. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)