Experimental methodology for measuring in-vacuum granular tribocharging.

We have developed an experimental methodology for measuring the charge distribution in granular mixtures due solely to particle-to-particle triboelectric charge exchange. Our experiment isolates the charging process from common influencing factors such as particle-to-container contact and atmospheric effects, creating conditions ideal for studying charge exchange on airless, dusty extraterrestrial bodies like the Moon and Mars. Charged grains are observed using high-speed videography as they fall through a uniform electric field, and their charge and size are characterized from their trajectories. This no-contact measurement method does not influence the charge and allows for the characterization of the overall distribution of charge by grain size in an arbitrary mixture. Our preliminary results indicate that charging measured with this test stand agrees well with computational charging models.