An experimental arrangement for the production of a quasi-stationary, high-current arc is described. It is stabilized by an axial gas flow in a high-pressure environment (current: 1900 A, pressure: 23 atm, gas: nitrogen). The conditions are described under which part of the arc assumes a cylindrical form. For such an arc the radial temperature distribution was measured. Because of the cylindrical shape a relatively simple evaluation yields quantitative data about the local radiative energy balance and the other energy transport mechanisms. This leads, for the first time, to a quantitative understanding of the different physical processes in this arc, and makes it possible to formulate a simplified arc model which is useful in practical applications.

In a previous paper (Hermann et al 1974) a detailed experimental and theoretical investigation of an arc in a supersonic nozzle flow was initiated by discussing the high-pressure arc section near the stagnation point. This paper is a continuation of this work for the section further downstream, especially within the nozzle. Extensive measurements of temperature, flow velocity, pressure and electric field strength are described. Theoretical results are obtained by a two-zone model. A detailed comparison between theory and experiment allows for the first time a complete quantitative discussion of all effects influencing the arc and the flow. Compared with the arc in the high-pressure section the influence of radiative energy transfer decreases. Instead, flow turbulence becomes the dominating exchange mechanism.

Transport Properties of Nitrogen up to 26,000 ~The E(1)-characteristic and a large number of T(r,/)-distributions measured in a 5 mm ~ N 2 cascade arc at normal pressure are used to evaluate the transport properties of nitrogen up to 26,000 ~ The electrical conductivity a(T) and from this the cross-section for atom-electron collision and the Coulomb-cross-section are determined directly from the E(1)-and several T(r,/)-curves. For the evaluation of the thermal conductivity ~c(T) three temperature regions are discerned: Up to about 10,000 ~ lc(T) is derived directly from the energy equation since here the energy transport by radiation does not play an important role. Between 10,000 and 15,000 ~ the radiative energy flux for different arc currents, the thermal conductivity and from this the charge exchange cross-section are determined in a good approximation utilizing the large number of measured temperature distributions. Above 15,000 ~ the already evaluated collision cross-sections are used to compute K(T).With x(T) known the radial distribution of the balance between emission and absorption of radiative power per unit volume is evaluated for different arc currents. It turns out, that at the highest measured arc current, i.e. 570 A, in the axial region of the arc about 95% of the supplied energy is carried off by radiation.

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