Axial velocity variations in high-current free-burning arcs

Abstract

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.

A mathematical model of the cathode region of a high intensity carbon arc

“…Jordan et a1 (1970) cited Maecker's (1959) results to assign a temperature of 9750 K to the core boundaries. Strachan and Barrault (1976) proposed an experimentally based correlation for the optical radii of carbon arcs up to 8 kA, of the following form: R = (0.71 + 0 . 3 5 ) ~" .…”

“…For the high intensity carbon arc, experimental measurements (Bowman et a1 1969, Strom 1946 indicate average electric fields of 9 to 15 V cm-'. Strachan and Barrault (1976) suggest that for graphite cathode arcs the following expression may be valid E = 14.710.22z-0.65 z < 8 .…”

Collisional avalanche exponentiation of runaway electrons in electrified plasmas

“…(1 1) -with to = 2meca(Zeff)(ln A)/eE (12) i.e., with an exponentiation time equal to the time needed for a relativistic runaway to gain a the above mentioned energy of a(Zeff)(10-.…”

Flow velocity measurement in high-current arcs using Doppler-shifted plasma scattering

“…In free-burning, high-current arcs the velocity is mainly directed axially from cathode to anode (Strachan and Barrault 1976). It should be noted however, that the models which lead to the acceptance of this axial velocity as the dominant energy connecting agent do not provide significant information about the high velocity which exists along the axis.…”