Ion field emission from micrometer-sized spherical glass grains

An experimental investigation of ion field emission from spherical glass gr ains in a 1-10 mum size range is described. A single dust grain is trapped in an electrodynamic quadrupole and charged positively by a monoenergetic i on beam, The energy of these ions (5 keV) results in a high surface potenti al and high electric field intensity. A limitation of the surface potential due to ion field emission was observed for the surface field intensity of 3 x 10(8) V/m, which is a considerably lower value than expected. The densi ty of the discharging current was as high as 10(-5) A/m(2), and increased e xponentially with increasing intensity of the electric held, As there are n o data of the ion field emission from insulators, we have used the zinc gra ins for a comparison. Taking into account the irregular shape of used metal lic grains, we conclude that the ion field emission from the glass grains s tarts at a significantly (two orders of magnitude) lower electric field int ensity than that from metals. This may lead to the limitation of the attain able surface potential of small insulator grains. The possible effect of th e ion Field emission on the charging of dust grains in the interplanetary s pace is discussed.