Energy loss of a test charge in dusty plasmas: Collective and individual particle contributions

The energy loss of a test charge in dusty plasma with dust charge fluctuati ons has been calculated both analytically (within the frame work of dielect ric theory) as well as numerically. The dust charge relaxation rate is foun d to have a significant effect on the total energy loss of a test charge wh ich is the sum of collective response of the plasma and individual particle interaction. It is shown that the dust charge fluctuation enhances the ene rgy loss due to the collective response of the plasma as well as the indivi dual particle contributions. Further, the charge fluctuation converts the s tatic Coulomb potential to a potential well for slow charge relaxation rate s and a small test charge velocity. The test charge therefore gains energy instead of loosing. On the other hand for the large test charge velocity an d fast charge relaxation rate, a shielded Debye Huckel type potential is fo rmed and consequently the energy loss is enhanced. These results are useful for understanding coagulation of dust grains in space and laboratory plasm as.