Brownian Motion of Grains and Negative Friction in Dusty Plasmas

Within the approximation of dominant charging collisions the explicit microscopic calculations of the Fokker-Planck kinetic coefficients for highly-charged grains moving in plasma are performed. It is shown that due to ion absorption by grain the friction coefficient can be negative and the appropriate threshold value of the grain charge is found. The stationary solutions of the Fokker-Planck equation with the velocity dependent kinetic coefficient are obtained and the considerable deviation of such solutions from the Maxwellian distribution is established.