Abstract
The emission of microparticles in a vacuum gap under the action of an electric field has been studied. Electrodes were prepared by abrasive polishing and an electrostatic detector located behind a grid constituting the cathode was used. The charges and sizes of microparticles depend on the conditioning state of the electrodes. The ratio F of the electrical charge of an actual microparticle to the charge of a hypothetical metal sphere with the same mass lying on a plane, called 'the over-charge factor', ranges from 0.2 to 10. Usually it decreases when the size of the particles increases.