New results in studies of electric charging of dust particles

Abstract

An electrodynamic quadrupole inside an ultra-high-vacuum chamber was used to trap particles of micron and submicron sizes, which were charged by electron and ion beams of energies up to 5keV. The Q m - ratios of the particles were derived from measurements of particle oscillation frequencies in the quadrupole. The particle's charging history was studied, and from the temporal dependencies of the particle Q m - ratios , the charging and discharging currents were calculated. We studied the dependence of the currents on the particle's surface voltage and developed a new method for determining the particle's size, surface potential, and electric field strength. The effects of electron and ion beam energies on the particle surface potential were measured. The energy spectrum of emitted secondary electrons was obtained and, when charging by electrons, the yield of the secondary electron emission was estimated from the voltage-dependencies of the charging current. While charging by ions there are two discharging effects: one due to secondary electrons emitted from the back wall of the quadrupole and another which is probably field emission of ions from the particle's surface. We see such emission at much lower field strengths than expected; this may imply that equilibrium surface potentials of very small (or irregularly-shaped) particles in the outer solar system might be lower than theoretical estimates predict.