Temperature variations in an SF6-N2 mixture arc plasma

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Abstract
We present measurements of the axial temperature To in an arc burning in SF6-N2 mixtures, as a function of current intensity I. The T - I curves with SF6 proportion in the mixture as a parameter intersect for a current value of about 50 A, corresponding to a temperature around 12 000 K. In addition, for currents above 50 A, the values of To in a 20 % SF6 mixture are lower than those obtained with all other SF6 proportions in the range 10 to 100 %. These properties are confirmed by a modeling work assuming thermal equilibrium ; they can be explained in terms of energy balance. At high current the arcs having the highest radiative losses exhibit the highest electric field and the lowest axial temperature : To is lower in nitrogen than in SF6. The behaviour of non radiation dominated arcs is more complex and depends on the variations of electrical and thermal conductivities with temperature. In certain cases this results in that the temperature values in a mixture are not intermediate to those obtained in the pure gases constituting the mixture