Kinetics of Dusty (Complex) Plasmas: Role of Variable Charges

Summary form only given. Charges of microparticles in complex (dusty) plasmas are not constant, but fluctuate in time around some equilibrium value which, in turn, is some function of spatial coordinates. Generally, ensembles of particles with variable charges are non-Hamiltonian systems where the mutual collisions do not conserve energy. An appropriate way to investigate evolution of such systems is to employ the kinetic approach. We studied (both analytically and numerically) two cases: (a) inhomogeneous charge - it depends on the particle coordinate but does not change in time, and (b) fluctuating charge - it changes in time around the equilibrium value, which is constant in space. For the theoretical analysis we used the Fokker-Planck approach to derive the collision integral which describes the momentum and energy transfer in mutual particle collisions as well as in the collisions with neutrals, for the numerical analysis the molecular dynamics simulations were employed. We obtained that the mean particle energy grows in time when the neutral friction is below a certain threshold. In case (a) the energy changes as prop(t_cr-t)^-2, in case (b) it scales as prop(t_cr-t)^-1, exhibiting the explosion-like growth with t_cr a critical time scale. The obtained solutions can be of significant importance for laboratory dusty plasmas as well as for space plasma environments, where inhomogeneous charge distributions are often present. For instance, the instability can cause dust heating in low-pressure complex plasma experiments, it can be responsible for the melting of plasma crystals, it might operate in protoplanetary disks and affect the kinetics of the planet formation, etc.