Measurements of plasma velocity distributions in free-burning DC arcs up to 2160 A

An experimental technique is described from which plasma velocity distributions have been determined. The technique consists of dropping a line of ball bearings of 3, 4 or 5 mm through a horizontal arc and recording the horizontal deflection of the balls by allowing them to strike a carbon paper. Multiple drops through repeated arcs enabled a deflection curve to be compiled. This curve was then subjected to an Abel inversion so that the radial variation of aerodynamic drag on the balls could be determined. By iterative techniques it was then possible to calculate a plasma velocity distribution compatible both with the Reynold's number and the radial deflection profile.