Temperature measurement of moving arcs in argon

Experiments are described in which time-resolved spectroscopic measurements have been made on arcs of 250 to 1000 A between 0·5 and 3·1 cm in length, moving due to a transverse magnetic field at speeds up to 80 m s −1 in argon at a pressure of 2 atm. On the assumption that the arc cross section did not depart appreciably from a circle, it has been possible to convert the photomultiplier signals of an atomic argon line to radial temperature distributions. By measuring the ratio of the intensities of two lines, the temperature at the arc axis has been found to be nearly constant over a number of revolutions of the arcs around circular electrodes for the range of arc current and speed in which measurements were made. From the measured peak temperatures, values of average column electric field and the radius beyond which little conduction will occur have been calculated. These have been found to be in good agreement with electric fields estimated from arc voltage measurements, and radii estimated from aerodynamic drag force considerations.