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The physical phenomena in cold and arc heated double-nozzle gas flows have been investigated for SF6 by interference and shadow methods. The cold-flow phenomena are discussed as a basis for a better understanding of the arc-gas flow interactions, their interference pattern is clearly interpreted: the observed fringes, which also can be calculated theoretically, are lines of constant flow velocity. In the case of arc heated flows a sharp distinction is made for the first time between different types of arc-gas flow interactions. At low peak currents the interference pattern still shows a cold gas flow around the arc. At higher current levels a fringe system, which indicates a density reduction, expands into the volume around the nozzles; however, the flow is still directed towards the gap between the nozzles. In contrast to this case the strongest form of interaction is characterized by the appearance of arc heated gas, which flows turbulently back into the high-pressure volume. The radial temperature distribution for a special arc has been calculated theoretically and is discussed in detail.