Experimental study on the kinetics of granular gases under microgravity

The kinetics of granular gases, including both freely cooling and steadily driven systems, is studied experimentally in quasi-two-dimensional cells. Under microgravity conditions achieved inside an aircraft flying parabolic trajectories, the frictional force is reduced. In both the freely cooling and steadily driven systems, we confirm that the velocity distribution function has the form exp(-alpha vertical bar v vertical bar(beta)). The value of exponent beta is close to 1.5 for the driven system in a highly excited case, which is consistent with theory derived under the assumption of the existence of the white-noise thermostat (van Noije & Ernst, Gran. Mat., vol. 1, 1998, p. 5764). In the freely cooling system, the value of P evolves from 1.5 to I as the cooling proceeds, and the system's energy decays algebraically (T-g = T-0(1 + tau)(-2)), agreeing with Haff's law (Haff, J. Fluid Mech., vol. 134, 1983, p. 401430).