Measuring the charge of microparticles in the radiofrequency plasma sheath by coulomb interaction

Dust particles immersed in plasma gather a highly negative charge due to the net collection of free electrons. In most plasmas on earth and with particle sizes in the micrometer range, these particles end up being levitated in the plasma sheath region due to balancing gravitational and electrical forces which are dominant and several other forces which appeared smaller. In this region, the well-known OML theory predicts unrealistic charge values caused by local electron depletion and the large directed drift velocity of ions. We have developed a novel method to measure the charge of microparticles (10 μm in diameter and confined in a potential well above an RF powered electrode) by studying the interaction with a second equally sized particle while the angle of the flat part of the potential well is varied with respect to the earth's horizontal plane. Measured particle charges are consistent with earlier experiments under hyper-gravity conditions, conducted with identical plasma parameters.