Charge Fluctuation of Dust Grains and Its Impact on Dusty Wave.propagation

Introduction Plasmas with dust grains are of interest both for the cosmic space as well as for the laboratory plasmas. Examples include cometary environments, planetary rings, the interstellar medium, the Earth’s and other planets magnetospheres [1]. Dust has been found to be a determinant component of rarefied plasmas used in the microelectronic processing industry [2], and it may also be present in the limiter regions of fusion plasmas due to sputtering of the carbon by energetic particles. It is interesting to note the recent flurry of activity in the dusty plasma research. It has been driven largely by discoveries of the role of dust in quite different settings: the ring of Saturn [1] and the plasma processing device [2]. Dusty plasmas contain, beside positive ions and electrons, large particles usually negatively charged. They are conglomerations of the ions, electrons and neutral particles. These large particles, to be called grains, have atomic numbers Zd in the range of 10 4 − 10 and their mass md can be equal to 10 6 of the proton mass or even much more. In the considered dusty plasmas, the size of grains is small compared with average distance between the grains.The ratio of charge to mass for a given component of plasma determines its dynamics. We note that for dusty plasmas, ratio of electrical charges of grains to their masses is usually much smaller than in the case of multispecies plasmas with negative ions and hence, here comes the first of the crucial differences between multispecies plasmas with negative ions and dusty plasmas. Because dynamics of the dusty plasma components, electrons, positive ions and dust grains is quite different in the time and length scales considered here, then the equations for these components of the dusty plasma may be different. If it is assumed that all grains have equal masses and charges steady in time, therefore the dust-ionacoustic and dust-acoustic dispersion relations are obtained on the basis of fluid [3], [4] or kinetic [5] models. In this case we have assumed, for simplicity, that all grains have equal masses and charges, but charges are not constant in time they may fluctuate in time. The dust charges are not really independent of the variations in the plasma potentials. Here, even in the fluid theory, appear the crucial differences between the ordinary multispecies plasmas and the dusty plasmas. All modes will influence the charging mechanism, and feedback will lead to several new interesting and unexpected phenomena. The charging of the grains depends on local plasma characteristics. If the waves disturb these characteristic, then charging of the grains is affected and the grain charge is modified, with a resulting feedback on the wave mode.