Using Pressure Sensors To Characterize Avalanche Dynamics On A Conical Bead Pile

A system of pressure sensors is used to characterize the dynamics of avalanches as they occur on a conical bead pile. The bead pile is a slowly driven critical system of roughly 20,000 steel beads, 3 mm in diameter, atop a circular base. We slowly drive the pile by dropping one bead at a time on the pile apex, and we record avalanches (the change in mass as beads leave the pile) occurring over the course of 60,000 bead drops. To complement this statistical information about the avalanche size probability distribution, we recently modified the base of the pile to add a system of eight pressure sensors that are monitored continuously during the data run. The sensors respond to shifting of forces within the pile during the avalanche, providing a way for us to characterize the types of bead motions occurring on the pile at different places on the pile and at different stages of the avalanche. With these sensors, we can characterize surface motion of beads on the pile independently from motion of beads off the pile. We are developing analysis techniques to characterize avalanches not just by the number of beads involved but also by the area of the pile participating in the avalanche; we propose an experimental definition for a system-spanning avalanche.