Intermittent granular flow in the presence of an electric field

In this letter experimental observations of vertical-pipe granular ow in th e presence of an electric field are reported. Granular nickel particles owi ng down a vertical pipe are found to be retarded by a local horizontal ac e lectric field when the field voltage V is greater than a critical voltage V -c. For V<V-c, the steady-state flow rate is practically unaffected by V. T he ow rate decreases discontinuously at V-c, and then decreases gradually f or V>V-c. Physically, particle clusters are formed above an arch interface, which exists in the electric-field region when V>V-c. The vertical ow cons ists of clusters intermittently dropping off from the interface. A transien t density wave with wavelength lengthened by electric field is also observe d.