Axial velocity variations in high-current free-burning arcs

A simple method for estimating mean arc velocities in high-current free-burning arcs is presented. Typical results are presented for arcs burning to copper, graphite and steel cathodes employing experimental values of arc current, electric field, radius and radiation loss. These results are compared with laser-Doppler velocity measurements for the case of copper. The method has also been applied to the studies of Bowman (1972) where a direct comparison with measured velocities has also proved possible and successful. The velocity estimates reveal a number of interesting experimental phenomena. Of particular interest is the implied presence of large velocity gradients in both space and time. The spatial gradients indicate that great care will be necessary in plasma velocimetry techniques based on particle tracking.