Emission Characteristics of Vacuum Spark Discharges III Aluminum and Carbon Spectra in the Visible Region

Abstract

The intensity of a number of lines of Al i, Al ii, Al iii, C ii, and C iii, in the visible region, has been measured as a function of the peak current in a vacuum spark discharge at values of self-inductance ranging from 2.4 to 45 μhenries. The spark was energized from a bank of condensers, with a total capacitance of 21.6 μf, charged to five different voltages from 5.3 up to 20.5 kv.The line spectrum is accompanied by a continuum which is most intense during the first oscillation of the spark current and then decays rapidly. At large currents most of the apparent line intensity during the first current cycle comes from the continuous background.At values of inductance above 2.4 μhenries, the intensity of the lines of Al i and C ii increases about linearly with the peak current. However, at 2.4 μhenries the intensity of the Al iii lines is enhanced in the neighborhood of 32 kamp as had been observed in earlier work. At a particular current, the intensity is always larger at the larger inductances, but at constant voltage, the addition of inductance does not in all cases reduce the intensity.The behavior of the C iii lines is very irregular, particularly at the lower inductances, and the enhancement of the intensity at about 32 kamp, and at minimum inductance, is very pronounced. Indeed, the carbon spectrum appears to be considerably more sensitive to the magnitude of the peak current than is the aluminum spectrum.The results for all the lines show a remarkable sensitivity to the direction of the current flow in the spark.