Spectroscopic analysis of high‐current free‐burning ac arcs between copper contacts in argon and air

A technique has been developed to take short‐time‐exposure photographic spectra of ac arcs between separating electric contacts. In these experiments the arc was formed in both argon and air between copper electrodes which separated a total of 0.96 cm. Side‐on spectra were taken for five axial positions at ±500 μsec around the current maximum (1100 A). In order to obtain a symmetrical arc with less than 0.01% copper vapor impurity, freshly polished electrodes had to be used each time the arc was formed. The spectra were used to calculate the arc temperature and the arc radius. The argon arc had a maximum temperature of 16 000 K and a diameter of 1.6 cm. The air arc had a temperature of 21 000 K and a diameter of 0.7 cm. The assumption of LTE (local thermodynamic equilibrium) which was used in the analysis of these arcs, was shown to be a reasonable assumption for the argon arc. The random introduction of a small percentage of zinc vapor into the argon arc was analyzed and found not to affect the assumptio...