On anode spots, double layers and plasma contactors

Abstract

Luminous, sharply defined and nearly spherical objects ('fireballs'), typically several centimetres in diameter, have been observed in Ar, Kr and Xe plasmas. The 'fireballs' are anchored on a disk anode biased at 40-50 V above ground potential. They have been analysed in terms of a spherical double-layer model, in which ionization of the gas atoms by electrons energized at the double layer plays an essential role. The relevance is discussed of the results to the so-called 'plasma contactors' to be used in space, especially in view of applications to electrodynamic tethers.