Study of the short-time dynamics of a thick and highly dense vibro-fluidized granular system by using diffusing wave spectroscopy

A thick. highly dense vibro-fluidized granular bed is studied using diffusi ng wave spectroscopy which measures the time correlation of the photons dif fusively scattered photons through the granular medium. The air pressure of the granular medium is reduced down to 10(-2) Torr, so there are only dens ity fluctuations of granular particles without arty macroscopic flow and th ere is no energy dissipation due to air drag. The granular temperature is f ound to be proportional to the square of the maximum oscillation velocity o f the vessel floor. This result agrees with the recent theoretical calculat ion for a dense vibro-fluidized bed. (No theoretical work exists oil highly dense medium.) Also, the density profile deviates completely from that of art ideal gas system. The intensity of the velocity fluctuations of the sys tem decreases exponentially with the depth from the free surface. This work is the first study of the short-time dynamics of a granular system without art ambient gas.