Analysis of a Long Living Atmospheric

Ball-like plasmoids were generated from discharging a capacitor bank via a water surface. In the autonomous stage after current zero they have diameters up to 0.2 m and lifetimes of some hundreds milliseconds, thus resembling ball lightning in some way. They were studied by means of spectroscopy, high speed cameras, probes and calorimetric measurements. The plasmoids are found to consist of a true plasma confined by a cold envelope. Decreasing electron densities in the order of 1020 m−3 to 1022 m−3 were measured from Stark broadening in the initial (formation) phase. The central electron temperature is found to be 2000–5000 K during most of the plasmoids lifetime. This is determined from intensity ratios of copper lines, assuming local thermodynamic equilibrium and considering optical thickness, as well as from a collisional radiative model for atomic calcium. Gas temperatures above 1300 K have been measured using thermocouples and it is expected to reach values in the range of 2000 K to 4000 K during formation. The plasmoids store chemical energy by dissociating water at their formation, as is supported by spectroscopic investigations of OH-radical emission and by the outcomes of a thermodynamical model assuming chemical equilibrium. Calcium hydroxide (CaOH) molecular band emission is the major sourc